i<

US Army Corps

of Engineers«

Engineer Research and

Development Center

Study of Navigation Channel Feasibility,

Willapa Bay, Washington

Nicholas C. Kraus, editor

With contributions by

(in alphabetical order)

Charles E. Abbott, Hiram T. Arden, Hugo Bermudez,

Steven M. Bratos, Mitchell E. Brown, Bruce A. Ebersole,

Scott Fenical, Ken FitzGerald, Suzanne Giles,

Edward B. Hands, Nicholas C. Kraus, Keith Kurrus,

Adele Militello, Shane Phillips, Norman W. Scheffner,

William C. Seabergh, Vladimir Shepsis,

Jane McKee Smith, and Carol Titus

April 2000

20000619 022

Approved for public release; distribution is unlimited.

PTIC QUALITY INSPECTED 4
The contents ofthis report are not to be used for advertising,

publication, or promotional purposes. Citation oftrade names

does not constitute an official endorsement or approval ofthe use

ofsuch commercial products.

The findings of this report are not to be construed as an

official Department of the Army position, unless so designated by other authorized documents.

®PRINTED ON RECYCLED PAPER
U.S. Army Engineer Research and Development Center Cataloging-in-Publication Data

Study of navigation channel feasibility, Willapa Bay, Washington / Nicholas C. Kraus, editor

with contributions by authors Charles E. Abbott... [et al.]; prepared for U.S. Army

Engineer District, Seattle.

440 p. : ill.; 28 cm. —(ERDC/CHL ; TR-00-6)

Includes bibliographic references.

1. Sediment transport — Washington (State) — Mathematical models. 2. Channels

(Hydraulic engineering) — Washington (State) — Mathematical models. 4. Willapa Bay

(Wash.) I. Abbott, Charles E. II. Kraus, Nicholas C. III. United States. Army. Corps of

Engineers. Seattle District. IV. Engineer Research and Development Center (U.S.)

V. Coastal and Hydraulics Laboratory (U.S.) VI. Series: ERDC/CHL TR ; 00-6.

TA7 E8 no.ERDC/CHL TR-00-6
Contents

Preface xvii

Conversion Factors, Non-SI to SI Units of Measurement xix

1—Introduction 1-1

Background 1-1

Purpose of Study 1-5

Related Studies 1-5

Study Procedure 1-6

Scope ofReport 1-7

Units of Measurement 1-8

References 1-8

2—Entrance Engineering 2-1

Project 2-1

Vessels 2-3

Design Vessel 2-4

Design Criteria 2-5

Grays Harbor Experience 2-7

Existing Navigation Conditions and Navigation Safety 2-8

Willapa Bay Design Conditions 2-9

Inlet Channel Stability 2-9

Development of Design Alternatives 2-11

Initial Dredging Requirements 2-16

Navigation Channel Alternatives and Disposal Sites 2-18

References 2-20

3—Geomorphology 3-1

Introduction 3-1

Setting 3-1

Bathymetric Data Used in Analysis 3-3

Comparison of Channel Alternatives by Fairways 3-5

Location of historical channels relative to present alternatives 3-5

Tabulated channel parameters 3-6

Differences in channel longevity 3-6

Differences in channel depths and orientations 3-9
Geomorphic Cycles 3-14

Cycle identification 3-14

Climate and geomorphic controls 3-17

Geomorphic Estimates of Shoaling Rates 3-22

Approaches 3-22

Approach I: Estimates based on spit-growth 3-22

Approach II: Estimates using annual bathymetry changes 3-24

Approach III: Lifetime dredging requirements 3-36

Discussion of Geomorphic Findings 3-41

References 3-44

4—Field Data Collection and Analysis 4-1

Wave Measurements 4-2

Data reduction and quality control procedures for wave

measurements 4-5

Current Measurements 4-11

Moored current measurements 4-11

Data reduction and quality control procedures for moored

current meters 4-15

General properties ofthe moored current meter data 4-16

ADCP transect cruises 4-17

Data reduction for ADCP transect cruises 4-20

General properties ofthe ADCP transect data 4-22

Water Level and In Situ Conductivity and Temperature Measurements... 4-25

Instruments and field procedures 4-25

Data reduction 4-26

Tide gauge water level 4-26

Survey to Toke Point datum .4-26

Gauge water level to Toke Point datum 4-26

Data trends 4-27

Profiling CTD Survey 4-27

Purpose of data collection 4-27

Instruments and field procedures 4-27

Data reduction 4-30

Data properties 4-30

Meteorology 4-30

Instruments and field procedures 4-30

Data trends 4-38

North Channel Borrow Site Monitoring 4-38

Survey methodology 4-45

Survey data processing and analysis 4-45

5—Modeling and Analysis of Short Waves 5-1

Wave Climate 5-1

Wave Transformation Model 5-4

Wave Model Inputs 5-6

Bathymetry grid 5-6

Input wave spectra 5-7

Current fields 5-8

Tide and wind 5-11

IV
Evaluation of Model with Field Data 5-11

Simulation of Design Alternatives 5-12

Waves to evaluate navigation 5-13

Waves to evaluate sediment transport 5-21

Summary 5-21

References 5-23

6—Circulation and Transport Modeling 6-1

Introduction 6-1

Physical Setting ofWillapa Bay 6-2

Tide 6-2

Freshwater inflows 6-4

Local wind 6-4

Salinity 6-4

Previous Modeling Studies 6-6

Circulation Model 6-7

Wave-driven currents 6-8

Verification of Wave Stress Forcing 6-9

Sediment Transport Model 6-15

Verification of Sediment Transport Method 6-17

Salinity Model 6-20

Computational Grid 6-21

Circulation Model Calibration 6-26

Circulation Model Verification 6-28

Comparison of water-surface elevation 6-28

Comparison of velocity 6-31

Circulation patterns 6-32

Evaluation of Design Alternatives by Analysis of Hydrodynamics

and Sediment Movement 6-39

Velocities through alternative channels 6-41

Deposition and erosion 6-46

Salinity Change in Willapa Bay 6-48

Summary of Circulation and Transport Modeling 6-50

References 6-52

7—Evaluation ofNavigation Channel Alternatives 7-1

Alternatives 7-1

Criteria for Evaluation ofNavigation Channel Alternatives 7-2

The Evaluation 7-4

Appendix A—Historical Charts A-l

Appendix B—Template Layouts and Recent Volume Changes B-l

Appendix C—Winter-Wave Time Histories C-l

Appendix D—Representative Wave Plots D-l

Appendix E—Wave Climate Intercomparisons E-l

Appendix F—Comparison of Buoy and Pressure Gauge Measurements F-l

Appendix G—Bathymetry, Current Patterns, and Bathymetry Change in

Design Alternatives G-l

Appendix H—Willapa Bay Dredged Material Disposal Sites Evaluation H-l
List of Figures

Figure 1-1. Regional location map for WillapaBay, Washington 1-2

Figure 1-2. Willipa Bay and adjacent communities 1-4

Figure 1-3. General locations and orientations of natural entrance

channels to Willipa Bay 1-6

Figure 2-1. Willipa River and Harbor navigation channels 2-2

Figure 2-2. Channel depth allowances and wave steepness defined as

wave height divided by wavelength 2-5

Figure 2-3. Response amplitude operator versus wave period for

0-, 45-, and 90-deg wave angles approaching an 824-ft-long,

106-ft-beam, 42-ft-draft bulk carrier 2-7

Figure 2-4. Escoffier diagram for Willapa Bay 2-10

Figure 2-5. Channel and structure location for alternatives 2-16

Figure 2-6. Potential dredged-material disposal sites and means of

disposal 2-20

Figure 3-1. Regional location map 3-2

Figure 3-2. Soundings taken through Willapa Bay from July to

October 1998 3-4

Figure 3-3. Definitions of channel reach and tabulated geomorphic

parameters 3-7

Figure 3-4. One ofthe 64 historical charts forming the basis for the

geomorphic evaluation 3-8

Figure 3-5. Frequency offully-opened channels 3-9

Figure 3-6. Channel depths by fairways 3-10

Figure 3-7. Channel orientation by fairways 3-11

Figure 3-8. Temporal variations in bar depth 3-12

Figure 3-9. Temporal changes in bar channel orientation 3-13

Figure 3-10. Second half of one channel cycle 3-16

Figure 3-11. Twenty-year sequence illustrating two channel-spit cycles 3-18

Figure 3-12. Rates ofNorth Cove shore recession and episodes of Cape

Shoalwater spit dissection or breaching 3-19

Figure 3-13. Timing of channel cycle with El Nino 3-19

Figure 3-14. Positions of north channel bar 3-23

VI
Figure 3-15. Area ofspit above -20-ft-mllw elevation for three episodes for

which the spit growth rate was calculated 3-25

Figure 3-16. Long-term channel shoaling rate estimated from spit

growth rates 3-26

Figure 3-17. Differences between the 1998 and 1999 surveys 3-27

Figure 3-18. Two channel cross-sectional designs 3-30

Figure 3-19. Seven channel alternatives for which geomorphic-based

estimates were made ofshoaling rates 3-31

Figure 3-20. Shoaling and deepening in the shallower alternatives,

1998-1999 3-32

Figure 3-21. Shoaling in the deeper alternatives, 1998-1999 3-33

Figure 3-22. Additional areas in which shoaling statistics were calculated 3-35

Figure 3-23. Relative shoaling rates for the two template cross sections 3-38

Figure 3-24. Alternative 3B avoids tight curve and long north-south run

typical of natural channels 3-40

Figure 4-1. Location of current meters and wave gauges, water-level

gauges, and meteorological station in WillapaBay 4-3

Figure 4-2. Tripod mount as deployed in Willapa Bay 4-5

Figure 4-3. Energy density plots for Station 1 4-9

Figure 4-4. Energy density plots for Station 2 4-10

Figure 4-5. Significant wave height time series for Stations 1, 2, 3, 4, 5,

and Grays Harbor buoy 4-12

Figure 4-6. Comparison of Stations 1 and 2 wave heights and

peak periods 4-13

Figure 4-7. Station 2 wave height, water depth, and current speed

for 3 October 1998 4-14

Figure 4-8. ADCP transects in Willapa Bay, 17-18 November 1998 4-19

Figure 4-9. ADCP transects in southern Willapa Bay, 17 November 1998 ...4-20

Figure 4-10. ADCP transects near Center Channel, Willapa Bay,

7 November 1998 4-21

Figure 4-11. ADCP transects at entrance of Willapa Bay,

18 November 1998 4-22

Figure 4-12. Predicted tide for 3 weeks in November 1998 4-23

Figure 4-13. Water level for ADCP transect collection days 4-23

Figure 4-14. Example oftide gauge data, Station 9, Deployment 4 4-28

Figure 4-15. Temperature, density, and salinity profiles for stations in

Willapa River during low- and high-slack tides (sta 1 -3) 4-31

Figure 4-16. Temperature, density, and salinity profiles for stations in

Willapa River during low- and high-slack tides (sta 4 and 5) 4-32

VII
Figure 4-17. Temperature, density, and salinity profiles for stations in

central Willapa Bay during low- and high-slack tides 4-33

Figure 4-18. Temperature, density, and salinity profiles for stations in

Naselle River Channel during low- and high-slack tides 4-34

Figure 4-19. Temperature, density, and salinity profiles for stations in

Nahcotta Channel during low- and high-slack tides 4-35

Figure 4-20. Temperature, density, and salinity profiles for stations in northern

Willapa Bay during low- and high-slack tides (Stations 6-8) 4-36

Figure 4-21. Temperature, density, and salinity profiles for stations in northern

Willapa Bay during low- and high-slack tides (Stations 9-11)... 4-37

Figure 4-22. Meteorological data from central Willapa Bay, August 1998 4-39

Figure 4-23. Meteorological data from central Willapa Bay, September

1998 4-40

Figure 4-24. Meteorological data from central Willapa Bay,

October 1998 4-41

Figure 4-25. Meteorological data from central Willapa Bay,

November 1998 4-42

Figure 4-26. Meteorological data from central Willapa Bay, December

1998 4-43

Figure 4-27. North Channel Borrow Site, Willapa Bay 4-44

Figure 4-28. Contour maps ofNorth Channel Borrow Site (August and

September 1998) 4-47

Figure 4-29. Contour maps ofNorth Channel Borrow Site (October and

November 1998) 4-48

Figure 4-30. Contour maps ofNorth Channel Borrow Site elevation

changes 4-49

Figure 4-31. Cross sections 1, 2, 3, and 4 ofNorth Channel Borrow Site 4-50

Figure 4-32. Cross sections 5, 6, 7, and 8 ofNorth Channel Borrow Site 4-51

Figure 4-33. Cross sections 9 and 10 ofNorth Channel Borrow Site 4-52

Figure 5-1. Grays Harbor buoy wave rose 5-3

Figure 5-2. STWAVE existing condition bathymetry grid 5-7

Figure 5-3. Wave height with ebb current minus wave height with

no current 5-10

Figure 5-4. Wave height with flood current minus wave height with

no current 5-10

Figure 5-5. Wave height verification for 1-4 September 1998 5-14

Figure 5-6. Wave direction verification for 1-4 September 1998 5-14

Figure 5-7. Wave height verification for 15-20 October 1998 5-15

VIII
Figure 5-8. Wave direction verification for 15-20 October 1998 5-15

Figure 5-9. Wave height verification for 11-16 November 1998 5-16

Figure 5-10. Wave direction verification for 11-16 November 1998 5-16

Figure 5-11. Wave height comparison for most frequent wave 5-18

Figure 5-12. Wave direction comparison for most frequent wave 5-18

Figure 5-13. Grays Harbor measurements for January 1998 5-21

Figure 6-1. Naselle River discharge for May through December 1998 6-5

Figure 6-2. Willapa River discharge for May through December 1998 6-5

Figure 6-3. Wave parameters calculated by STWAVE with input

parameters ofHs = 2.0 m, T= 11.5 sec, and 9 = -30-deg

for a planar beach (1V:30H) 6-10

Figure 6-4. Comparison of STWAVE- and NMLONG-calculated wave

parameters 6-11

Figure 6-5. Comparison of measured and calculated rms wave height for

Leadbetter Beach, California, 4 February 1980 6-13

Figure 6-6. ADCIRC grid and bathymetry for Leadbetter Beach 6-13

Figure 6-7. Calculated and measured longshore current at Leadbetter Beach,

California, 4 February 1980 6-14

Figure 6-8. Calculated water-surface elevation verses time for Leadbetter

Beach, California 6-15

Figure 6-9. Flowchart of hydrodynamic and sediment transport

calculations with wave parameter input 6-16

Figure 6-10. Cross-shore variation ofsignificant wave height calculated

by STWAVE 6-18

Figure 6-11. Cross-shore variation of longshore current calculated by

ADCIRC 6-18

Figure 6-12. Cross-shore variation ofsediment transport and total transport

compared to the CERC formula for three wave cases 6-19

Figure 6-13. Willapa Bay bathymetry 6-22

Figure 6-14. Willapa Bay entrance bathymetry 6-22

Figure 6-15. Regional view of grid for coast of Washington and Oregon 6-23

Figure 6-16. Grid detail for Willapa Bay 6-23

Figure 6-17. Grid detail in Willapa Bay entrance 6-24

Figure 6-18. Nodes in Willapa Bay entrance 6-25

Figure 6-19. Grid detail for Willapa Bay entrance with resolution for

Alternatives 3H-a and 3H-b 6-25

Figure 6-20. Nodes in Willapa Bay entrance with resolution for

Alternatives 3H-a and 3H-b 6-26

IX
Figure 6-21. Nodes at SR-105 dike and groin 6-27

Figure 6-22. Locations ofstations for comparisons of water-surface

elevation and current 6-27

Figure 6-23. Time series of calculated and measured water level at

Station 1 6-29

Figure 6-24. Time series of calculated and measured water level at

Station 2 6-29

Figure 6-25. Time series of calculated and measured water level at

Station 3 6-30

Figure 6-26. Time series of calculated and measured water level at

Station 4 6-30

Figure 6-27. Time series of calculated and measured current at Station 1 6-33

Figure 6-28. Time series of calculated and measured velocity at Station 2 6-33

Figure 6-29. Time series of calculated and measured velocity at Station 3 6-34

Figure 6-30. Time series of calculated and measured velocity at Station 4 6-34

Figure 6-31. Willapa Bay circulation pattern on flood tide 6-36

Figure 6-32. Willapa Bay circulation pattern on ebb tide 6-36

Figure 6-33. Entrance of Willapa Bay circulation pattern on flood tide 6-37

Figure 6-34. Entrance ofWillapa Bay circulation pattern on ebb tide 6-37

Figure 6-35. Entrance of Willapa Bay circulation pattern on flood tide

during January 1998 storm 6-38

Figure 6-36. Entrance of Willapa Bay circulation pattern on ebb tide during

January 1998 storm 6-38

Figure 6-37. Region of SR-105 structure circulation pattern on flood tide 6-40

Figure 6-38. Region of SR-105 structure circulation pattern on ebb tide 6-40

Figure 6-39. Regions of entrance defined for evaluation of current velocities

in channels 6-41

Figure 6-40. Stations for salinity change analysis 6-49

Figure 7-1. Alternatives for evaluation 7-3

Figure 7-2. Yearly shoaling estimates based on geomorphic analysis and

numerical modeling 7-6

Figure E-l. March 1995 wave heights for Long Beach slope array and

Grays Harbor buoy E-3

Figure E-2. March 1995 wave directions for Long Beach slope array and

Grays Harbor buoy E-4

Figure E-3. Scatter plot of Grays Harbor and Long Beach wave directions

for March 1995 E-5
Figure E-4. Monthly average wave directions for Grays Harbor buoy E-6

Figure E-5. Monthly average wave directions for Long Beach slope array E-6

Figure E-6. Monthly average wave directions for coincident Grays Harbor

buoy and Columbia River bar buoy measurements E-7

Figure F-l. Buoy and pressure gauge spectra for 8 June 1999

at 0:30 GMT F-3

Figure F-2. Buoy and pressure gauge spectra for 7 June 1999

at 12:30 GMT F-3

Figure F-3. Buoy and pressure gauge spectra for 7 June 1999

at 4:30 GMT F-4

Figure F-4. Correlation between buoy and pressure gauge F-5

Figure F-5. Comparison of buoy and pressure gauge wave heights F-7

Figure F-6. Comparison of buoy and pressure gauge wave periods F-7

Figure G-l. Bathymetry for Alternative 1 G-7

Figure G-2. Bathymetry for Alternative 3A G-7

Figure G-3. Bathymetry for Alternative 3B G-7

Figure G-4. Bathymetry for Alternative 3F G-8

Figure G-5. Bathymetry for Alternative 3G G-8

Figure G-6. Bathymetry for Alternative 3H G-8

Figure G-7. Bathymetry for Alternative 4A G-9

Figure G-8. Bathymetry for Alternative 4E G-9

Figure G-9. Current patterns in Alternative 1 channel,

January 1998 storm G-10

Figure G-10. Current patterns in Alternative 3A channel,

January 1998 storm G-13

Figure G-l 1. Current patterns in Alternative 3B channel,

January 1998 storm G-l 6

Figure G-l2. Current patterns in Alternative 3F channel,

January 1998 storm G-l 8

Figure G-13. Current patterns in Alternative 3G channel,

January 1998 storm G-21

Figure G-l 4. Current patterns in Alternative 3H-a channel,

January 1998 storm G-23

Figure G-l5. Current patterns in Alternative 3H-b channel,

January 1998 storm G-25

Figure G-l6. Current patterns in Alternative 4A channel,

January 1998 storm G-27

XI
Figure G-l 7. Current patterns in Alternative 4E channel,

January 1998 storm G-29

Figure G-l 8. Current patterns in Alternative 1 channel,

September 1998 fair weather G-31

Figure G-l9. Current patterns in Alternative 3A channel,

September 1998 fair weather G-33

Figure G-20. Current patterns in Alternative 3B channel,

September 1998 fair weather G-36

Figure G-21. Current patterns in Alternative 3F channel,

September 1998 fair weather G-38

Figure G-22. Current patterns in Alternative 3G channel,

September 1998 fair weather G-41

Figure G-23. Current patterns in Alternative 3H-a channel,

September 1998 fair weather G-43

Figure G-24. Current patterns in Alternative 3H-b channel,

September 1998 fair weather G-45

Figure G-25. Current patterns in Alternative 4A channel,

September 1998 fair weather G-47

Figure G-26. Current patterns in Alternative 4E channel,

September 1998 fair weather G-49

Figure G-27. Calculated deposition and erosion in Alternative 1 channel,

January 1998 storm G-51

Figure G-28. Calculated deposition and erosion in Alternative 3A channel,

January 1998 storm G-52

Figure G-29. Calculated deposition and erosion in Alternative 3B channel,

January 1998 storm G-53

Figure G-30. Calculated deposition and erosion in Alternative 3F channel,

January 1998 storm G-54

Figure G-31. Calculated deposition and erosion in Alternative 3G channel,

January 1998 storm G-55

Figure G-32. Calculated deposition and erosion in Alternative 3H-a channel,

January 1998 storm G-56

Figure G-33. Calculated deposition and erosion in Alternative 3H-b channel,

January 1998 storm G-57

Figure G-34. Calculated deposition and erosion in Alternative 4A channel,

January 1998 storm G-58

Figure G-35. Calculated deposition and erosion in Alternative 4E channel,

January 1998 storm G-59

Figure G-36. Calculated deposition and erosion in Alternative 1 channel,

September 1998 fair weather G-60

XII
Figure G-37. Calculated deposition and erosion in Alternative 3A channel,

September 1998 fair weather G-61

Figure G-38. Calculated deposition and erosion in Alternative 3B channel,

September 1998 fair weather G-62

Figure G-39. Calculated deposition and erosion in Alternative 3F channel,

September 1998 fair weather G-63

Figure G-40. Calculated deposition and erosion in Alternative 3G channel,

September 1998 fair weather G-64

Figure G-41. Calculated deposition and erosion in Alternative 3H-a channel,

September 1998 fair weather G-65

Figure G-42. Calculated deposition and erosion in Alternative 3H-b channel,

September 1998 fair weather G-66

Figure G-43. Calculated deposition and erosion in Alternative 4A channel,

September 1998 fair weather G-67

Figure G-44. Calculated deposition and erosion in Alternative 4E channel,

September 1998 fair weather G-68

Figure H-l. Historical bar channel dredging assignments H-7

Figure H-2. Willapa Bay navigation project, historical Cape Shoalwater

disposal sites near USCG Buoy 10 and Buoy 13 H-25

Figure H-3. Willapa Bay navigation project, environmentally sensitive

areas H-26

Figure H-4. Willapa Bay navigation project disposal site alternatives H-27

List of Tables

Table 2-1. Willapa Harbor-Bar Channel O&M Hopper Dredging 2-3

Table 2-2. Definition Of Design Alternatives, Willapa Bay Navigation

Channel Reliability Study 2-13

Table 2-3. Initial Dredging Volumes Assuming a Static 1998 Bathymetry ...2-15

Table 2-4. Dredging Site/Disposal Site Combination Alternatives 2-19

Table 3-1. Geomorphic Parameters Measured in Each Outlet and Each

Channel Reach ofEach Fairway on Each Chart ofthe Willapa

Bay Entrance 3-6

Table 3-2. Timing of Post-1922 El Niiios and Restoration ofNew

North Channel Outlets 3-20

XIII
Table 3-3. 1998 to 1999 Bathymetric Changes Within Templates 3-29

Table 3-4. Historical Volume Differences Within Templates in

Data-Dense Areas 3-36

Table 3-5. Summary ofInitial Dredging and Volume Changes in Templates,

1998-1999 3-38

Table 3-6. Basis for Mixture of Low- and High-Volume Dredging

Requirements for Templates 3B and 3G 3-41

Table 3-7. Lifetime Dredging Estimates 3-42

Table 4-1. Willapa Bay Data-Collection Schedule 4-4

Table 4-2. Tripod Deployment and Retrieval Locations 4-6

Table 4-3. Willapa Bay Equipment Log 4-7

Table 4-4. ADV Data Averages 10-9-98 to 11 -18-98 4-11

Table 4-5. Statistics for Current Records 4-17

Table 4-6. ADCP Configuration Parameters 4-18

Table 4-7. Discharge Values for South Willapa Bay 4-24

Table 4-8. Discharge Values for North Willapa Bay 4-24

Table 4-9. Water Level Station Locations and Measured Parameters 4-25

Table 4-10. Profiling Conductivity Temperature Depth Survey Information.. 4-29

Table 4-11. Meteorological Data Summary 4-38

Table 4-12. Average Change in Depth Along Cross Sections, ft 4-53

Table 4-13. Total Volume Changes (cu yd) 4-53

Table 5-1. Grays Harbor Wave Distribution by Height, Period, and

Direction 5-3

Table 5-2. Mean and Maximum Wave Parameters Measured at Grays

Harbor Buoy 5-4

Table 5-3. Values of nn Defining Direction Distribution in Verification

Spectra 5-8

Table 5-4. Values of y and nn Defining Representative Spectra 5-8

Table 5-5. Sensitivity Analysis of Wave Transformation to Current 5-9

Table 5-6. Verification Statistics 5-13

Table 5-7. Representative Waves for Navigation Evaluation Simulations.... 5-17

Table 5-8. Comparison of Wave Height and Direction for Channel

Alternatives 5-19

Table 6-1. Tidal Constituent Amplitudes, m, at Toke Point, South Bend, and

Nahcotta 6-3

Table 6-2. Tidal Datums, m, for Willapa Tide Gauges 6-4

XIV
Table 6-3. Radiation Stress Values Calculated Analytically from STWAVECalculated Wave Parameters, andbyNMLONG 6-12

Table 6-4. Wave Parameters for Idealized Sediment Transport Cases 6-17

Table 6-5. Ratio of Sediment Transport Rates Calculated by ADTRANS and

the CERC Formula 6-20

Table 6-6. Error in Calculated Water Level 6-31

Table 6-7. Error in Calculated Velocity Components 6-35

Table 6-8. Maximum and Minimum Velocity in Alternative Channels

for Storm 6-42

Table 6-9. Maximum and Minimum Along-Channel Velocity in

Alternative Channels for Fair Weather at Peak Ebb and

Flood Tidal Current 6-42

Table 6-10. Maximum and Minimum Across-Channel Velocity in

Alternative Channels for Fair Weather at Peak Ebb and

Flood Tidal Current 6-43

Table 6-11. Number of Regions in Alternative Channels with Crosscurrents

in Fair Weather at Peak Ebb and Flood Tide 6-45

Table 6-12. Deposition Volume Calculated for Alternative Channels 6-46

Table 6-13. Shoaling in Alternative Channels for January 1998 Storm 6-47

Table 6-14. Grouping of Alternatives Based on Navigation and

Shoaling Factors 6-51

Table 6-15. Properties of Most Favorable Alternative Channels Based on

Crosscurrent and Shoaling Calculations 6-52

Table 7-1. Design Alternative Evaluation, Willapa Bay Navigation Channel

Reliability Study, Operation and Maintenance Factors 7-7

Table 7-2. Design Alternative Evaluation, Willapa Bay Navigation Channel

Reliability Study, Navigability Safety Factors 7-8

Table 7-3. Design Alternative Evaluation, Willapa Bay Navigation Channel

Reliability Study, Beneficial Use of Dredged Material and

Erosion Potential 7-9

Table E-l. Wave Direction Distributions E-2

Table E-2. Percent Data Coverage by Month E-2

Table F-l. Gauge Deployment Times and Locations F-2

Table F-2. Error Statistics for Buoy and Pressure Gauge Comparisons F-8

Table G-l. Maximum and Minimum Velocity in Regions of Alternative 1

for Fair Weather at Peak Ebb and Flood Tidal Current G-2

Table G-2. Maximum and Minimum Velocity in Regions of Alternative 3 A

for Fair Weather at Peak Ebb and Flood Tidal Current G-3

Table G-3. Maximum and Minimum Velocity in Regions of Alternative 3B

for Fair Weather at Peak Ebb and Flood Tidal Current G-3

XV
Table G-4. Maximum and Minimum Velocity in Regions of Alternative 3F

for Fair Weather at Peak Ebb and Flood Tidal Current G-4

Table G-5. Maximum and Minimum Velocity in Regions of Alternative 3G

for Fair Weather at Peak Ebb and Flood Tidal Current G-4

Table G-6. Maximum and Minimum Velocity in Regions of Alternative 3H-a

for Fair Weather at Peak Ebb and Flood Tidal Current G-5

Table G-7. Maximum and Minimum Velocity in Regions of Alternative 3H-b

for Fair Weather at Peak Ebb and Flood Tidal Current G-5

Table G-8. Maximum and Minimum Velocity in Regions of Alternative 4A

for Fair Weather at Peak Ebb and Flood Tidal Current G-6

Table G-9. Maximum and Minimum Velocity in Regions of Alternative 4E

for Fair Weather at Peak Ebb and Flood Tidal Current G-6

Table H-l. Chronology of Federal Dredging, Willapa Harbor, Washington....H-2

Table H-2. Development of Alternatives H-l 8

Table H-3. Dredging Site/Disposal Site Combination Alternatives H-23

XVI
Preface

This report describes a navigation channel reliability monitoring and

evaluation study conducted at Willapa Bay, Washington, by the U.S. Army

Engineer Research and Development Center (ERDC), Coastal and Hydraulics

Laboratory (CHL), Vicksburg, MS, for the U.S. Army Engineer District, Seattle

(NWS). The study was established under a Partnering Agreement between the

NWS and the Willapa Port Commission to investigate the feasibility of

maintaining a reliable navigation channel through the entrance to Willapa Bay.

Funding authority was provided by NWS to CHL on 6 April 1998, and a review

draft ofthis report was submitted to NWS on 21 December 1998. Mr. Hiram T.

Arden was the NWS point of contact for this study, with technical assistance and

review ofthis report provided by Messrs. Arden, Eric E. Nelson, and Robert M.

Parry, NWS.

The ERDC study team was under the technical direction of Dr. Nicholas C.

Kraus, Coastal Sediments and Engineering Division (CSED), CHL, and task-area

leaders were Dr. Adele Militello, Navigation and Harbors Division (NHD), CHL,

for Long Waves, Sedimentation and Salinity; Dr. Jane M. Smith, Coastal

Processes Branch (CPB), CSED, for Short Waves; Mr. William C. Seabergh,

Harbors and Entrances Branch (HEB), NHD, for Engineering; Mr. Edward B.

Hands, Coastal Evaluation and Design Branch (CEDB), CSED, for Morphology,

Mr. Michael W. Tubman, Prototype Measurement and Analysis Branch (PMAB),

CSED, for Field Data Collection Contract Management and Data Management;

and Mr. Larry E. Parson, CEDB, CSED, for SHOALS Surveying.

Significant technical assistance in conducting the study was provided by

Dr. S. Rao Vemulakonda, Estuaries, Bays and Lagoons Group, Tidal Hydraulics

Branch (THB), Estuaries and Hydroscience Division (EHD), CHL, and

Dr. Joon P. Rhee, PMAB, CSED. Additional technical support at CHL was

provided by Ms. Mary Claire Allison, Dr. Andrew Morang, and Mr. Michael

Martinez, CEDB, CSED, Mr. Fulton Carson, CPB, CSED, and Ms. Leonette J.

Thomas, HEB, NHD. Secretarial and clerical support was provided by

Ms. Janie G. Daughtry and Ms. J. Holley Messing, CEDB, CSED, and

Ms. Myra E. Willis, HEB.

Assistance at NWS was provided by Mses. Elizabeth W. Bachtel and

Joyce E. Rolstad at the NWS archive; Messrs. Denny S. Mahar and Lonnie M.

Reid in surveying and cartographic control; and Mr. Thomas G. Landreth,

captain ofthe survey vessel Shoalhunter. Field studies were conducted under

contract with Evans-Hamilton, Inc. (EHI), led by Mr. Keith Kurrus, EHI.

Portions ofthe field study analysis were subcontracted by EHI to Pacific

XVII
International EngineeringPLLC (PIE). Mr. Harry Hosey and Dr. Vladimir Shepsis

were the study leaders for PIE.

This study was conducted during the period April 1999 through June 1999

under the general supervision of Dr. James R. Houston, Director of CHL,

respectively: Mr. Thomas W. Richardson, Chief of CSED; Mr. William H.

McAnally, Chief ofEHD; Mr. Bruce A. Ebersole, Chief of CPB; Ms. Joan Pope,

Chief ofCEDB; Mr. Robert T. McAdory, Chief ofTHB; Mr. Willam L. Preslan,

Chief of PMAB; and Mr. Dennis G. Markle, Chief of HEB.

This study benefited from discussions and coordination meetings involving

representatives from or staff members ofthe following organizations:

Messrs. Gerald J. Heintz and James Neva, Port of Willapa; Mr. Randy Lewis,

City of West Port; Mr. Jeff Cox, EHI; and Messrs. Hosey, Hugo Bermudez, Scott

Fenical, David Simpson, and Nels Sultan, and Dr. Shepsis, PIE.

Contributors to this report are identified on the first page of each chapter.

Dr. Kraus was the report technical editor. Mr. Markle was also assistant to

Dr. Kraus and served as administrative point of contact for this study.

At the time of publication ofthis report, Dr. Lewis E. Link was Acting

Director ofERDC, and COL Robin R. Cababa, EN, was Commander.

XVIII
Conversion Factors

Non-SI to SI Units of

Measurement

Non-SI units of measurement used in this report can be converted to SI units

as follows:

Multiply By To Obtain

acres 4,046.873 square meters

cubic feet 0.028317 cubic meters

cubic yards 0.7645549 cubic meters

feet 0.3048 meters

miles (U.S. nautical) 1.852 kilometers

miles (U.S. statute) 1.609347 kilometers

tons (long, 2,240 lb mass) 1,016.047 kilograms

XIX
1 Introduction1

This chapter presents the background of a study performed for the U.S. Army

Engineer District, Seattle, to determine the technical feasibility of maintaining a

reliable bar navigation channel into Willapa Bay, Washington. The study was

authorized by the Seattle District in cooperation with the Port of Willapa Harbor

under a Partnering Agreement. The study was conducted primarily by staff of

the U.S. Army Engineer Research and Development Center (ERDC), Coastal and

Hydraulics Laboratory. Field data were collected by Evans-Hamilton, Inc.

(EHI), and its subcontractor, Pacific International EngineeringPLLC (PIE), which

is conducting independent field and analytical studies for the State Route 105

(SR-105) project at Willapa Bay (PIE 1997). Included in this chapter are

overviews of the study site and discussions of related studies at Willapa Bay,

study procedure, and scope of this report.

Background

Willapa Bay is a large estuarine system located on the southwest Washington

coast, as shown in Figure 1-1. Its spring or diurnal range tidal prism, compiled

from other sources by Jarrett (1976) at more than 1010 cu ft,2is one of the largest

of all inlets on the coast of the continental United States. The magnitude of the

tidal prism is produced by the broad bay area and relatively large tidal range at

the site. The tidal range at the entrance to Willapa Bay, as measured by the

National Ocean Service (NOS) of the National Oceanic and Atmospheric

Administration, is approximately 7 ft. Daily wind speed is moderate, and river

inflows do not contribute significantly to the flow through the entrance. Bay

hydrodynamic processes are discussed further in Chapters 2 and 6.

1 Written by Dr. Nicholas C. Kraus, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS, and by Mr. Hiram T. Arden, U.S. Army

Engineer District, Seattle, Seattle, WA.

2 A table for converting non-SI units to SI units of measure is given on page xix.

Chapter 1 Introduction 1-1
V/WCOUVtR

ISLAND

BRITISH COLUMBIA

CANADA +

Figure 1-1. Regional location map for Willapa Bay, Washington

1-2 Chapter 1 Introduction
A wave hindcast covering 20 years (Jensen, Hubertz, and Payne 1990)

predicted a mean significant wave height of 7.7 ft and a mean spectral period of

11 sec at hindcast Station 18 located in water depth of 33 ft in the vicinity of

Willapa Bay. The largest wave in the hindcast had a height of 23.8 ft. Ruggierio

et al. (1997) discusses the extreme waves and water levels along this coast during

the 1997-1998 El Nino. Measurements made during the past 3 years at a

nearshore wave buoy located south of Grays Harbor, as well as limited

measurements of the waves at the entrance to Willapa Bay made in this study,

confirm the magnitudes given by the hindcast. Properties of waves incident to

the Willapa Bay entrance are discussed in Chapter 5, where numerical

simulations of waves propagating into the bay are described. Wave

measurements made in this study are described in Chapter 4.

The large tidal prism and energetic waves at Willapa Bay collectively act to

transport millions of cubic yards of sediment on this predominantly sandy coast.

The massive changes in shoals at the Willapa Bay entrance are discussed in

Chapter 4. Neighboring bar entrances, such as Grays Harbor, the mouth of the

Columbia River, and entrances along the coasts of Oregon and northern

California are protected by jetties that are miles long. Construction ofjetties

improves navigation by stabilizing the position of the channel, focusing the tidal

flow to clear sediment from the channel, and protecting vessels from waves as

they transit through the surf zone.

The conception of a navigable channel at a wide and energetic inlet may

seem improbable at first. However, information compiled in Chapter 3 shows

that a natural but mobile channel some 25 ft deep typically penetrates the outer

and middle entrance bars. The tidal prism at Willapa Bay maintains a

dynamically stable channel cross section that usually contains a channel

approaching design requirements. Inlet stability and bulk characteristics of the

entrance, as well as details of the Federal navigation channel at the entrance, are

discussed in Chapter 2.

Authorizations for a Federal navigation channel through the entrance to

Willapa Bay are summarized in U.S. Army Engineer District, Seattle (1971), and

in Chapter 2. The existing project was first adopted in 1916 and last modified

through authorization in 1954. The authorization provides for a channel over the

bar of the mouth of Willapa Bay to be 26 ft deep, measured to mean lower low

water (mllw), and at least 500 ft wide. A bar channel of this dimension is

required for existing shallow-draft commerce. Dredging of the deep-draft river

channel of Willapa Harbor was discontinued by the Seattle District in 1976

because of inadequate benefits. Dredging for shallow draft continues at Willapa

Harbor for facilities at such locations as Toke Point, Bay Center, and Nahcotta,

shown in Figure 1-2. Since 1976, no maintenance dredging has been required

along the Federal river channel leading up from Willapa Bay to port facilities

located at Raymond, Washington.

The Washington Department of Transportation (WDOT) has recently

constructed a groin and dike in the North (ebb) Channel at the entrance to

Willapa Bay to protect SR-105. The adjacent shoreline (Cape Shoalwater) had

been eroding at a rate of approximately 130 ft/year (Terich and Levenseller 1986;

Komar 1998), and the erosion had endangered the State highway. The dike and

groin are expected to significantly alter the flow and, possibly, the location and

Chapter 1 Introduction 1-3
Grays Harbor f ~T

Washington

Scale, Kilometers

I I I I I

0 12 3 4 5 10

Columbia River

Figure 1-2. Willapa Bay and adjacent communities

1-4 Chapter 1 Introduction
stability of the North Channel. Action of the WDOT Cape Shoalwater shore

protection project was considered in the channel stability analysis phase of the

study.

Purpose of Study

The shifting channels at the entrance to Willapa Bay make bar navigation

unreliable (U.S. Army Engineer District, Seattle 1971,1995), and the local port

cannot maintain or attract commercial users. Local interests have obtained

Congressional support to determine if an economical channel can be established

through the entrance bar. An economical channel implies a route that can be

traversed safely under typical waves and tidal currents.

The Seattle District requested the U.S. Army Engineer Research and

Development Center (ERDC) to conduct a study to determine the technical

feasibility of maintaining a reliable channel (28-ft depth including advance

dredging and overdredging allowance) over the entrance bar and into Willapa

Bay. "Channel reliability" refers to stability of location and depth of the channel

for an acceptable construction and maintenance cost, as well as hydrodynamic

conditions for safe passage.

Ebb currents exiting the southern arm of Willapa Bay (the arm extending

toward Oceanside) are directed toward the landmass of Cape Shoalwater, where

they turn and run west in a relatively deep North Channel. Water exiting the tidal

flats along the Willapa River also tends to flow out of the North Channel. Other

channels through the bar exist ephemerally, including a Middle Channel and a

South Channel, sometimes called the Leadbetter Channel in the literature. The

typical locations of these channels are shown schematically in Figure 1-3.

Multiple bar channels through the entrance sometimes exist, but typically one

channel dominates. Properties of the natural channels, including location,

persistence, and depth, are discussed in Chapter 3, based on an extensive record

of bathymetry surveys spanning more than a century. The presence of these

channels and their possible exploitation as a navigation channel form the basis

for developing channel design alternatives, as described in Chapter 2.

Related Studies

The State of Washington is conducting two studies of coastal and inlet

processes of interest to the present proposed effort. The Washington Department

of Ecology (WDOE), in a joint study with the U.S. Geological Survey, is making

a regional coastal assessment that includes analysis of all available historic and

present data on shoreline position and bathymetry (Gelfenbaum et al. 1997;

Kaminsky et al. 1999).

The WDOT, through its lead contractor, PIE, and PIE subcontractor, EHI, is

collecting data on waves and currents at the entrance and is monitoring coastal

and inlet processes for the SR-105 Cape Shoalwater shore protection project (PIE

1997). PIE has also conducted a morphological analysis of bar channel

migration, based on earlier work by the Seattle District and others. The NOS

maintains a long-term water-level station in Willapa Bay at Toke Point. As much

as possible within study constraints, all relevant data were considered and joint

Chapter 1 Introduction ' "5
Figure 1-3. General locations and orientations of natural entrance channels to

Willapa Bay

and coordinated efforts made with these agencies and organizations, including

the University of Washington, for efficient and cost-effective conduct of this

study.

Study Procedure

The study required focused efforts of several specialists who participated as a

team in developing approaches and procedures and in conducting the required

work. Meetings and briefings were held at the study site and at the Seattle

District, as well as at ERDC, with participation from the Port of Willapa, WDOE,

PIE (representing local interests), EHI, Seattle District, and ERDC. ERDC

investigators also toured the study site, made reconnaissance trips for locating

instruments in and around Willapa Bay, and participated in data collection.

The study was developed as a simultaneous effort in two major tasks. One

task involved analytical and numerical studies covering the following:

a. Engineering activities in consideration of entrance channel alternatives

and their relation to maintenance and operation of a navigable channel.

b. Formulation of alternative designs for a reliable bar navigation channel.

c. Analysis and interpretation of inlet morphology change.

1-6 Chapter 1 Introduction
d. Numerical modeling and associated analyses of wave transformation at

the entrance, circulation and water level throughout the bay, transport of

sediment at the entrance, and salinity distribution in the bay.

The other task involved sustained data collection and analysis in support of

the analytical and numerical efforts, as well as documentation of the background

condition of waves, wind, current, and morphology at the entrance, and water

level and salinity around the perimeter of the bay. A survey of the discharge and

salinity within the bay was made by two boats. Bathymetry data, the most basic

information upon which most of the study components depend, were collected by

the Corps' airborne laser system and by a considerable dedicated effort of the

Seattle District's main survey boat, the Shoalhunter.

The Seattle District requested preliminary study results by 1 February 1999,

which required rapid planning and mobilization to deploy instruments in the

severe environment of the entrance to Willapa Bay and along the substantial

perimeter of the bay. Authorization to proceed was received in April 1998, and a

data collection plan was developed and instruments procured and leased for

gradual deployment commencing in July 1998. Data were downloaded in a

series of instrument servicing trips and subsequently quality checked and reduced

expediently for distribution to the analytical and numerical components of the

study. The difficult but successful field data collection program is described in

Chapter 4.

An interim copy of this report was transmitted to the Seattle District on

21 December 1998 for review and discussion by the District and local interests.

Further study was then conducted, leading to this final report.

Scope of Report

This report documents the procedures, results, and conclusions of the subject

study. Study team members described their work in individual chapters. The

chapters were planned to form a coherent approach in meeting the study

objective of determining the feasibility of a reliable bar navigation channel into

Willapa Bay. The approach and content of all chapters were coordinated, and an

attempt was made to provide sufficient background information and crossreferencing to allow each chapter to stand alone with regard to its particular

subject matter.

Chapter 2 documents the Federal navigation project at Willapa Bay and

describes approaches to investigating channel reliability in a natural inlet.

Chapter 3 presents results of a morphology analysis based primarily on surveys

of the bathymetry spanning more than a century. Chapter 4 summarizes the field

data collection program and general properties of the data sets. Chapter 5

presents results of short wave numerical simulations. Chapter 6 presents analysis

of tidal circulation, sediment transport, and salinity change. Chapter 7 discusses

the channel alternative designs considered through the report. Appendices A-H

contain supplementary and background information.

Chapter 1 Introduction 1-7
Units of Measurement

Dimensions and quantities originally reported in American Customary (nonSi) units on engineering documents and in the literature are retained. A table of

conversion factors from non-SI to SI units is given on page xix. Oceanographic

and meteorologic measurements and calculations, such as of waves, water

current, and wind speed are given in SI units.

References

Gelfenbaum, G., Kaminsky, G. M., Sherwood, C. R., and Peterson, C. D. (1997).

"Southwest Washington coastal erosion," Workshop Report, Open-File

Report 97-471, U.S. Geological Survey, St. Petersburg, FL.

Jarrett, J. T. (1976). "Tidal prism-inlet area relationships," GITI Report 3, U.S.

Army Engineer Waterways Experiment Station, Vicksburg, MS.

Jensen, R. E., Hubertz, J. M., and Payne, J. B. (1990). "Pacific Coast hindcast,

Phase III, north wave information," WIS Report 17, U.S. Army Engineer

Waterways Experiment Station, Vicksburg, MS.

Kaminsky, G. M., Daniels, R. C, Huxford, R., McCandless, D., and Ruggiero, P.

(1999). "Mapping erosion hazard areas in Pacific County, Washington" (in

preparation), Journal ofCoastalResearch, Special Issue 28,158-170.

Komar, P. D. (1998). The Pacific Northwest Coast: Living with the shores of

Oregon and Washington. Duke University Press, Durham, NC.

Pacific International Engineering and Pharos Corporation. (1997). "Results of

two-dimensional hydrodynamic modeling of Willapa Bay," Summary Report

SR-105 Emergency Stabilization Project, Seattle, WA.

Ruggiero, P., Kaminsky, G. M., Komar, P. D., and McDougal, W.G (1997).

"Extreme waves and coastal erosion in the Pacific Northwest," Proceedings

Waves 97, ASCE Press, New York, 947-961.

Terich, T., and Levenseller, T. (1986). "The severe erosion of Cape Shoalwater,

Washington," Journal ofCoastalResearch 2(4), 465-477.

U.S. Army Engineer District, Seattle. (1971). "Feasibility report, navigation and

beach erosion, Willapa River and Harbor and Naselle River, Washington,"

Seattle, WA.

. (1995). "Willapa Bay, Washington, FY 95 bar maintenance

dredging evaluation," Unpublished memorandum, 26 April 1995, U.S. Army

Engineer District, Seattle, Seattle, WA.

1 -8 Chapter 1 Introduction
2 Entrance Engineering1

This chapter describes the existing navigation project and reviews

maintenance dredging that was conducted in the past. Vessels transiting the

navigation channel at Willapa Bay are discussed, and a project design vessel for

this study is defined. The limits of environmental operating conditions for

vessels are reviewed. An examination of channel stability is made, and

significant tidal inlet parameters are presented to aid in considering a safe and

reliable Willapa Bar navigation channel. Placement or disposal sites of dredged

material are also discussed, together with estimates of the associated costs.

Further information on disposal sites is given in Appendix H.

Project

This section summarizes the navigation project at the entrance to Willapa

Bay. Depths are referenced to mean lower low water (mllw). Figure 2-1 shows

the project layout. The seaward channel over the bar does not appear in this

figure because it varies in position in time and is marked by the U.S. Coast Guard

(USCG) based on U.S. Army Engineer District, Seattle, surveys. The existing

project, adopted 27 July 1916, and last modified 3 September 1954 (U.S.

Congress 1916,1954), provides the following:

a. A channel over the bar at the mouth of Willapa Bay, 26 ft deep and at

least 500 ft wide. Overdepth of 2 ft is allowable.

b. A channel 24 ft deep and 200 ft wide from deep water in Willapa Bay to

the foot of Ferry Street in South Bend, then 300 ft wide to the westerly

end of the narrows, then 250 ft wide to the forks of the river at Raymond,

including a cutoff channel 3,100 ft long at the Narrows.

c. A channel 24 ft deep and 150 ft wide up the South Fork to the deep basin

above Cram Lumber Mill, and up to the North Fork to 12th Street, with a

turning basin 250 ft wide, 350 ft long, and 24 ft deep.

d. A channel 10 ft deep and 60 ft wide from deep water in Palix River to

Bay Center Dock.

1 Written by Mr. William C. Seabergh, Dr. Nicholas C. Kraus, and Mr. Edward B. Hands, U.S.

Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, Vicksburg,

MS; Dr. Vladimir Shepsis, Pacific International EngineeringPLLC; and Mr. Hiram T. Arden, U.S.

Army Engineer District, Seattle, Seattle, WA.

Chapter 2 Entrance Engineering 2-1
2-2 Chapter 2 Entrance Engineering
e. An entrance channel 15 ft deep and 100 ft wide and a mooring basin

15 ft deep, 340 ft wide, and 540 ft long adjacent to port wharf at

Tokeland.

/. An entrance channel at Nahcotta 10 ft deep and 200 ft wide and a

mooring basin 10 ft deep, 500 ft wide and 1,150 ft long, protected by a

rubble-mound breakwater approximately 1,600 ft long.

The entrance channel and Willapa River channels were completed in 1936,

with additional widening completed by 1958. Annual maintenance costs for

1964-1970 averaged $468,400, but did not provide full project depth year-round.

At the 1998 time of study initiation, the controlling depth over the curved north

channel ebb shoal was about 20 ft, and the controlling depth in the river channel

reach was about 17 ft. (Note: By October 1999, the controlling depth over a

straight-out north channel improved to about 24 ft.) As can be noted from the

authorized widths and depths of the river channel reach, a variation existed in the

size of vessels capable of traversing certain parts of the project.

Recent dredging amounts taken from the bar channel are shown in Table 2-1.

Over a 23-year period, the annual volume removed averaged 288,000 cu yd, with

a maximum of 610,000 cu yd dredged in 1969, an indication of the cyclic

movement of large masses of sediment. One should also note that typically the

authorized depths were maintained for only a few months before depths again

became less than 26 ft, indicating substantial sediment infiltration along the

channels. Dredged volumes were determined in part by the schedule of

availability of Government hopper dredge equipment. A complete chronology of

Willapa Harbor dredging is presented in Table H-l of Appendix H.

Table 2-1

Willapa Harbor-Bar Channel O&M Hopper Dredging

Year

Volume

1,000 cu yd Year

Volume

1,000 cu yd

1951 308 1965 955

1953 30 1966 303

1956 187 1967 341

1957 256 1968 459

1958 253 1969 610

1959 237 1970 324

1960 222 1971 340

1961 282 1972 274

1962 453 1973 189

1963 282 1974 42

1964 278 1997

Test Dredging 80

Note: dredged volumes reflect schedule of availability of government hopper dredge, i.e., dredging

may not have returned the channel to design dimensions.

Vessels

Historic log and lumber ships planning to enter Willapa Harbor typically

would have fully-loaded drafts of 28 to 33 ft. Because of the inadequate channel

depths and shifting outer bar channel, the Twin Harbor Pilots Association has

Chapter 2 Entrance Engineering 2-3
restricted loadings to 20-ft drafts, or one-third capacity, which require the vessel

to top off at another port. Also, the pilots have restricted sailings to daylight

hours. A table in the Feasibility Report (U.S. Army Engineer District, Seattle,

1971) for years 1964-70 indicated that 1964 had the highest number of log

exports and lumber shipments, with 88 shipments. The number decreased yearly

to 45 shipments in 1970. This industry has migrated to Grays Harbor, so it is

questionable if the entrance should be designed for this size vessel. In addition,

the newer lumber ships have 37-ft drafts, which would require a deeper

authorized channel. Most likely though, if Willapa Bay is to be made a viable

port again, some type of cargo vessel should be considered in the design process.

Commercial fishing vessels, charter boats, towboats, and recreational and

other small craft presently would have little difficulty with the previously

maintained bar channel depths (U.S. Army Engineer District, Seattle, 1971).

Drafts of these vessels are on the order of 12 to 16 ft. Potential harbor tenants

originate from the tuna boat fleet, and these vessels have 17-ft drafts. Channel

shifting, strong currents, and turbulence created by storm waves breaking over

shoals make passage hazardous for this size vessel. No criterion was found to

determine the level at which the wave breaking turbulence becomes critical to

this size vessel.

Tugs (draft, 13 ft) and their barges (draft, 11-12 ft, 236-ft-long by 60-ft-wide)

require straight channels for accommodating the length of the towline.

Grounding incidents point to channel curvature as a main cause of navigation

difficulty. The tugs require waves less than 9 ft for safe navigation. Barges

experience 15 to 20 ft of vertical motion around still-water level in the presence

of such waves, based on 30-deg roll with 60-ft beam and 10-deg pitch with a

236-ft length.1 The vertical motion contributes to produce an effective draft of

27 to 32 ft mllw. If vessels enter and exit at the +6-ft tide level, a channel depth

of 21 to 26 ft is required. Pitching dominates at the outer bar and, at the inner

bar, rolling is likely to dominate from reforming waves.

Design Vessel

The design vessel is "usually .. .the largest vessel of the major commodity

movers" (Headquarters, U.S. Army Corps of Engineers 1996). Another

approach, taken in the Grays Harbor project, is to select a vessel that carries the

majority of product tonnage, then check for adequacy of movement of the largest

vessels. The design ship draft for Grays Harbor was 37 ft (for a 46-ft-deep by

1,000-ft-wide authorized project). Presently, the decision for Willapa Bay would

have to be based on tug and barge traffic to satisfy the criterion of the largest

vessel of the major commodity mover. (This decision follows because the deeper

draft lumber ships are not calling at Willapa Bay. However, tugs and barges are

also not calling there at present, but they are the most recent commodity hauler

other than commercial fishing vessels.) For the given project authorization of

26 ft, the tug-barge combination or a commercial fishing vessel apparently

should be the design vessel. To design for the draft of the most recent lumber

ships would require a significant increase in authorized depth.

1 Letter to U.S. Army Engineer District, Seattle, from Brix Maritime Company, 12 May 1992.

2-4 Chapter 2 Entrance Engineering
Design Criteria

Criteria for determining entrance channel depth, width, and alignment (with

respect to wave approach) depend upon the specific vessel. Figure 2-2 shows the

factors involved in determining channel depth. Taking Figure 2-2 as a guide and

assuming a 13-ft draft for a tug, combined squat and trim is less than 2 ft for this

vessel traveling at 10 knots in a wide fairway such as the ocean bar region

(Headquarters, U.S Army Corps of Engineers, in preparation). Advance

maintenance dredging and dredging tolerance (neither is included as part of the

design (authorized) depth) will be assumed combined as 2 ft. Safety clearance is

normally taken as 2 ft.

WAVELENGTH

DESIGN

STILL-WATER J ^ DATUM . . *

>

>

TIDE RANGE ^^_]

-r ^r\ t —„ - "

PITCH R OLL & HEAVE

j < s.

rr^jV^3'

>

>

>

« DRAFT \ .

' WITH TRW ' "

T

WAVE HEIGHT

AUTHORIZED , SQUAT

PROJEC T DEPTH \^ rSAFETY CLEARANCE

>

KADVANCE MAINTENANCE DREDGING

CHANNEL BOTTOM -^ ) DREDGING TOLERANCE

' *"

Figure 2-2. Channel depth allowances and wave steepness defined as wave

height divided by wavelength

At a high-wave location such as Willapa Bay, a large part of the channel

design depth is associated with the vessel movement because of vertical

components of pitch, roll, and heave resulting from wave motion. Waveaccompanying effects tend to increase as wave height increases and decrease

with greater ship length. A typical ship motion response amplitude operator

(RAO) is 1.2. The RAO is a dimensionless factor with which to multiply wave

amplitude (amplitude being one-half the wave height) for determining the

distance below the still-water level to which the ship will move in waves of given

height.

Values of RAO measured in the mouth of the Columbia River ranged from

0.9 to 2.2 for bulk carriers, 1.0 to 2.1 for tankers, and from 0.4 to 1.2 for

container ships (Headquarters, U.S. Army Corps of Engineers, in preparation). If

an operational wave height of relatively high energy is taken as 9 ft, then the

additional channel depth required would be 1.2 x 4.5 ft = 5.4 ft.

Combining wave amplification response and draft, squat, and safety

clearance determined previously yields a value of 22.4 ft. This depth contains

tolerance and leaves room for navigating in higher wave conditions, up to 15-ft

Chapter 2 Entrance Engineering 2-5
wave heights in the channel. The value for a fishing vessel with a 17-ft draft

would be 26.6 ft for the 9-ft wave condition, probably an acceptable value

because of inclusion of a safety clearance. In other words, wave conditions of

9 ft or less in the channel would be necessary for relatively safe operations for

the design vessels.

Required channel width can be determined by evaluating factors as outlined

in Permanent International Association of Navigational Congresses (1997). The

basic maneuvering lane for a vessel of low maneuverability (such as a tug/barge

system) is 1.85, with 5 the beam of the design vessel. For strong crosswinds of a

slow-moving vessel, a factor of 1.05 is added. If strong crosscurrents are

present, 1.35 is added. For strong channel currents and slow vessel speed, 0.45

is added. For significant wave heights greater than 10 ft, 1.55 is added. If

visibility is frequently poor, one should add 0.55. For shallow, hard bottoms,

one should add 0.35. The total is 6.85. For a 60-ft beam, a width of 408 ft

would be required. The 500-ft authorized width meets that requirement. A

possible reason and benefit for increasing channel width is to add storage

capacity for sediment moving into the side of the channel from spits and shoals.

The storage capacity would extend the time interval between dredging operations

required to maintain the authorized channel depth and width, but would require a

dredge to remain on site longer during maintenance.

At times an S-curve is present as a spit emerging from the north beach

pushes the North Channel to the south before it can again turn to the west and

exit to deeper water. Chapter 3 discusses this channel pattern in its historical

context. In this study, 1,500 ft of channel width was estimated to be required for

tows entering an S-curve, allowing for as much as a 45-deg angle off the center

line of the tug. Towlines are typically 300 to 500 ft long, with a minimum of

100 ft. Tugs are typically in the 65- to 100-ft-length range, and barges are 150 to

400 ft long. The 1,500-ft width is based on the maximum dimensions of the

towline, tug, and barge.

The orientation of channel alignment with respect to wave approach (and

thus vessel alignment to some degree; however, the vessel may change its

orientation with respect to waves if the channel is wide enough) enters into

consideration of navigability. In examination of wave conditions for various

alternatives, a value of ±45 deg was selected based on limited output of a ship

motion model called HYDRO.1Figure 2-3 shows the effect of wave angle on a

bulk carrier in terms of wave period versus the RAO. The three wave angles

examined were 0 deg (the vessel is moving directly into the wave crest), 45 deg

to the vessel center line, and 90 deg, with the wave hitting the vessel broadside.

Important to note is that the 0- and 45-deg curves are in about the same range

RAO over the various wave periods. For the 90-deg wave, the RAO peaks up to

a much higher value, as the vessel is near resonance with the 12-sec wave in the

roll mode. Based on this example, the + 45-deg window was selected for

evaluating alternatives.

1 Personal Communication, 1998, Mr. Frank Sargent, U.S. Army Engineer Research and

Development Center, Coastal and Hydraulics Laboratory, Vicksburg, MS.

2-6 Chapter 2 Entrance Engineering
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Figure 2-3. Response amplitude operator versus wave period for 0-, 45-, and

90-deg wave angles approaching an 824-ft-long, 106-ft-beam,

42-ft-draft bulk carrier

Kraus (1997) proposed a wave steepness criterion for establishing navigation

safety in a channel. Wave steepness is defined as the wave height divided by the

wavelength. A critical value of 0.05 was recommended as preliminary guidance,

above which there was concern for the safety of vessels with lengths on the order

of that of the incident waves. The incident wave steepness increases if waves

meet an opposing (ebb) current. The steepening of individual waves in a wave

train creates a "washboard" or chop that can be difficult to navigate.

Grays Harbor Experience

Grays Harbor, Washington, lies to the north of the Willapa entrance and is a

Federal navigation project. Information from the Grays Harbor General Design

Memorandum (U.S. Army Engineer District, Seattle 1989) indicates that recent

log vessels are 25,000 to 30,000 dwt, with 570-ft lengths, 87-ft beam, and design

drafts of 34 to 37 ft, departing at higher tide levels. At Grays Harbor, the outer

bar channel is aligned along a southwest azimuth based on pilot preference.

Grays Harbor pilots indicate they are concerned about being set by currents, and

by the wind and vessel pitch, rather than by roll of the vessel. The channel

dimensions for the Grays Harbor project are 30-ft depth by 600-ft width over the

bar and through the entrance.

Operationally, transits from docks begin 3 hr or more after low tide to move

against the flood current for better steerage, to obtain additional keel clearance,

and to avoid hazardous ebb-flow conditions. The 30- to 37-ft draft vessels transit

the entrance channel only in optimum conditions. Depth allowances for vessel

pitch, roll, and heave in waves moving over the ebb bar are 14 ft. Channel width

Chapter 2 Entrance Engineering 2-7
for strong currents and waves is 600 ft in the entrance and 1,000 ft at the seaward

end of the entrance channel and across the bar.

The maximum significant wave height allowable for outbound transits is

about 8 ft for flood tide conditions. Studies by Wang et al. (1980) showed

maximum excursion of the bow will be less than 14 ft for 95 percent of the time

under these conditions. Maintenance dredging at Grays Harbor occurs mostly in

the interior. The twin jetties at Grays Harbor function to maintain depths in the

entrance channel and over the ebb shoal so that no significant maintenance

dredging is required for a 30-ft-depth channel (U.S. Army Engineer District,

Seattle, 1989). The presently-maintained project (46-ft-deep channel 1,000 ft

wide at the entrance bar) is estimated to require dredging of 100,000 to

200,000 cu yd/year in the entrance channel and less than 100,000 cu yd/year at

the entrance bar.

Existing Navigation Conditions and Navigation

Safety1

Vessels avoid exiting Willapa Bay on the ebb because of longer transit time

when waves are present. When a vessel exits on the ebb, with some waves

breaking in the channel, reading the waves and estimating which ones will break

is a difficult procedure for the navigator. The navigator needs to slow down as

the ebb current pushes the vessel ahead while he or she evaluates if a wave will

break. The vessel is attempting to avoid the chaotic wave action of the breaking

wave that would then wash over it. For example, every 5 min, two or three

waves may break. This lower exit speed increases time of exposure in the

entrance channel. In the case of tug-barges, the decrease in speed reduces the

control of the barge, permitting crosscurrents and wind to push the barges out of

line with the tug.

In the region from Cape Shoalwater into the bay, strong chop exists that can

be difficult to navigate and, in the case of tows, again makes the barge wander

behind the tug. Also, while in this region, no deck work can be performed, but

the vessel is not in danger similar to that when on the bar channel.

When a vessel is traveling in the S-curve of the North Channel, extreme

breaking conditions may exist for waves from the northwest and the west and

wave angle with respect to the vessel travel may be large. The washboard

conditions are difficult for navigation. Within the seaward east-west part of the

S-curve, 400 ft of migration of the channel thalweg can occur within one month.

Conditions are usually acceptable if swell height is less than 3 ft and the vessel

travels in late ebb, flood, and early ebb. Vessels will avoid moderate and greater

ebb-flow conditions when moderate to large waves are present. No

knowledgeable local boat captain wants to navigate the bar channel at night with

ebb conditions. Navigation at slack or early flood is acceptable if there is not

much swell; otherwise, boat captains will wait for stronger flood flows before

exiting during conditions with larger waves.

1

Information in this section was obtained during a 30 October 1998 telephone conversation with

Mr. Randy Lewis, formerly Warrant Officer USCG (retired) stationed at Willapa Bay.

2-8 Chapter 2 Entrance Engineering
Willapa Bay Design Conditions

Based on available information, two design vessels were selected: a tuna

fishing vessel with a draft of 17 ft and a tug/barge vessel combination (13-ft draft

tug and barge with a 12-ft draft, 236 ft long by 60 ft wide). The best alternative

should be selected in part considering the highest percentage of time with waves

less than 9 ft in height on a flood tide. Wave angle with respect to channel

alignment should be less than 45 deg to avoid significant roll of the vessel.

Head-on waves do not always present the best wave angle for tug-barge

combinations because this can produce extra tension in the towlines if the tugbarge systems are in phase with one another. Channel depth must be greater than

26 ft at all times. The barge-tug vessel will require a relatively straight channel

alignment and a minimum width of 1,500 ft if an S-curve exists.

Inlet Channel Stability

Willapa Bay has existed as a relatively stable inlet for more than a century by

maintaining a strong tidal exchange of water entering and exiting the inlet. A

Coast and Geodetic Survey nautical chart, Number 6185, for the period of 1887-

1897, indicated that the mean tide range was 7.4 ft at Sealand (Nahcotta) and

7.5 ft at South Bend (with a mean ocean tide range of 6.2 ft). Present National

Ocean and Atmospheric Administration Tide Tables indicate that the mean range

is 7.9 ft at Nahcotta and 7.8 ft at South Bend. These numbers may not be directly

comparable because of improvements in measurement technology, but in each

case, one can note the recent bay range was only slightly greater than the earlier

tide range. Consequently, the overall tidal hydraulic condition of the inlet system

has been relatively constant over the past one hundred years.

If the slight increase in bay tidal range has actually occurred, this would

follow from a trend seen in the measurement of minimum cross-sectional areas of

the inlet entrance. The minimum area (determined by measurement of the inlet

cross section at the minimum width, considered to be a reasonable assumption)

increased from 450,000 sq ft in 1877, to 480,000 sq ft in 1937, to 520,000 sq ft in

1967, to 530,000 sq ft in 1996. There is some amount of uncertainty in these

area calculations because of lack of data in very shallow regions together with

the usual possibility of measurement error related to many other factors. Errors

in tidal datums could lead to large errors because of the large width of the inlet.

For example, a variation of ±0.5 ft over the approximate 20,000-ft width leads to

a cross-sectional variation of ±10,000 sq ft. Therefore, a variation of 20,000 sq ft

should be assigned.

The minimum cross-sectional area is considered as a measure of the tidal

prism (defined as the volume of water entering (or leaving) the bay during a

flood (or ebb) portion of the tidal cycle). The minimum cross-sectional area Ac

(measured at mean tide level) is related to the spring or diurnal tidal prism P as

P = 5 x 104AC (2-1)

This equation is from O'Brien (1931) based primarily on data from Pacific Ocean

inlets of the United States. Jarrett (1976) determined similar relationships for

Chapter 2 Entrance Engineering 2-9
east coast, west coast, and Gulf coast inlets. Using Equation 2-1 and the 1996

area, an estimate for P would be 2.65 1010 cu ft, a value near the maximum for

United States inlets. Escoffier (1940,1977) developed an analytical or graphical

method to examine the stability of coastal inlets. This technique (Seabergh and

Kraus 1997) is applied to Willapa Bay in Figure 2-4.

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Figure 2-4. Escoffier diagram for Willapa Bay. Plot shows average maximum

velocity versus minimum inlet area (solid line) and the equilibrium

velocity curve (dashed line). Intersection of curves on right side

indicates stable equilibrium area for Willapa Bay, 447,000 sq ft,

based on assumptions discussed in text

The intersection ofthe curves on the right side in Figure 2-4 is a stable

equilibrium area (447,000 sq ft). The inlet area would vary about this value

through sediment flux into and out ofthe channels and changing tidal conditions

(e.g., spring to neap tide range variation). The left-hand intersection is an

unstable equilibrium area (200,000 sq ft). Ifthe minimum area became smaller

than this minimum value because of a large influx ofsand, the inlet would close.

The historical values are on the high side ofstable equilibrium. These higher

values ofinlet area are in qualitative agreement with the long-term scouring of

the north shore. This analysis shows that overall the inlet is stable at the

minimum cross-sectional area location and, by flow continuity, the larger

offshore cross sections maintain relatively constant flow areas even as the

distribution offlow and number of channels change (Chapter 3). However,

channel migration caused by movement ofsand in the more seaward region

creates local instability of channel location and hazards to navigation because of

2-10 Chapter 2 Entrance Engineering
movement and curvature. These patterns of shoaling and channel movement are

governed by the influx of sediment discussed in Chapter 3.

The result of a reduction in channel flow area can be determined by

consulting Figure 2-4. For example, building the State Route (SR)105

Emergency Project on the north shore reduced the flow area in the channel

30,000 sq ft. Assuming the reduction is near the location of the minimum crosssection area, the flow area (530,000 - 30,000 sq ft) would still be above the

stable equilibrium area (447,000 sq ft). Even if the inlet were at its stable area of

447,000 sq ft, a reduction of 30,000 sq ft in inlet area to 417,000 sq ft would still

be in the range where the inlet area would be returned to its stable equilibrium

area by cutting a deeper or wider channel. Bathymetric data from recent surveys

support this conclusion.

An increase in flow area, as produced by excavation of a larger channel,

would move along the solid curve to the right showing an increase in area, but a

reduction in velocity. The result would be an infilling of the channel and a return

to the equilibrium area. This evaluation describes the system as a whole and

does not link changes in one region to changes in another; e.g., if the South

Channel would shoal, one would expect an increase in area in the Middle or

North Channel to maintain the equilibrium of the whole system, but this analysis

cannot predict which channel would deepen.

Development of Design Alternatives

The development of alternatives is based on selection of channel alignments

and channel size that meet certain criteria. First, a reliable channel is desired. A

reliable channel is one that can be maintained to provide safe navigation based on

present and design vessel usage. It must also meet a certain benefit cost ratio and

be environmentally acceptable (not discussed in this report). Therefore, the three

engineering points to consider in evaluating alternatives are as follows:

a. Estimated project scope (initial dredged volume).

b. Estimated average annual maintenance volume.

c. Navigation safety.

Based on examination of historical maps of the inlet as discussed in

Chapter 3, three main locations of potential egress to the ocean from Willapa Bay

exist, not all of which are usually present at the same time (Figure 3-1). A North

Channel is identifiable on all maps of the inlet; however, because of spit growth

from the north, sometimes the North Channel has exited into the ocean through a

wide range of angles, from toward the northwest to the southwest. The present

Middle Channel typically does not connect directly to the ocean bar, but is

incised centrally in the middle of the inlet. Its present geographic location was

once the main exit to the sea, probably because of its alignment with the Willapa

River. During the past 100 years with the movement of the channel northward

and erosion of Cape Shoalwater, the Middle Channel has not been the dominant

flow channel. The South Channel is ephemeral, and it is incised in the shallow

shoal similar to the Middle Channel. The analysis in Chapter 3 characterizes the

longevity, location, depths, and orientation of the channels in a historical

perspective.

Chapter 2 Entrance Engineering 2-11
Possible alternatives are summarized in Table 2-2, and the initial dredging

volumes required (based on 1998 bathymetry) are presented in Table 2-3.

During the 18-month period of Phase I studies, the volume of sediments

associated with the bar channel improvement from a 20-ft deep curved

(Alternative 3B) alignment to a 24-ft deep (approximating Alternative 3A)

alignment exceeds 20 million cu yd without dredging. Volumes vary between

0.2 and 9.9 million cu yd for the depths and widths described in Table 2-2. The

list of 19 alternatives was developed without preconception of a preferred

alternative, and moderate to extreme (expensive) alternatives were considered.

The alternatives were screened in the course of the study, with some initially

deleted based on reasoning described in the next paragraphs, and some

alternatives deleted after reconnaissance numerical simulations as described in

Chapter 6, to arrive at a subset for detailed examination. An additional aspect in

evaluation of alternatives is potential beneficial uses of dredged material, such as

for protection of the North Beach shore and creation of bird islands, oyster habitat, and wetlands (Appendix H). Further refinement of the described alternatives

and possible addition of new alternatives are expected during the future course of

this study.

Table 2-2 shows that the existing procedure (numbered as Alternative 1) is

considered an alternative as it is the least costly approach, and it also defines the

existing condition against which other alternatives may be compared.

Alternative 2 is considered in terms of a future existing condition where

opportunistic dredging may provide a reliable channel. This alternative is

defined by future conditions and thus is not examined in the modeling. All

Alternative 3 variations focus on using the North Channel. Alternative 3A

proposes a straight channel at its present northernmost location (Figure 2-5).

Alternatives 3B and 3C are based on improving the width of the S-curve, which

evolves if the spit from the north is permitted to grow southward. Initially, two

cases of S-curve channels were proposed for investigation.

The 3B Alternative (Figure 2-5) is based on the present (1998-1999)

bathymetry, and the 3C Alternative is based on historical analysis (Chapter 3)

where the channel, extending southward, parallels the ocean bar for up to

2.5 miles. Dredging could be minimized for this configuration, as the channel

markers could be moved to follow the southward migration. The major

drawbacks would be exposure of vessels to turbulent broken waves broadside

and requirement by the USCG for the Seattle District to survey the channel prior

to relocation of navigation aids. Based on the dangerous wave condition of 3C,

only 3B was selected for study. Alternative 3D raised the new SR-105 dike to

-2.0 mllw elevation. Alternative 3E consisted of construction of a jetty on the

north side of the entrance (Figure 2-5), primarily as a terminal groin or holding

structure for sediment, which might enable trapped sediment to move back up the

coast with winter storm waves. Alternatives 3F and 3G are similar in orientation

to 3A and 3B, with the difference in increased channel width and depth providing

increased sediment storage, thus increasing the time between project maintenance

operations.

2-12 Chapter 2 Entrance Engineering
Table 2-2

Definition of Design Alternatives, Willapa Bay Navigation Channel Reliability

Study1

Alternative Description

Potential Benefits and

Beneficial Uses Estimated Feasibility

1. Existing

Procedure

USCG directed to move channel

markers according to natural

shift in channel detected in

Corps surveys. An S-curved

channel could remain.

Least costly O&M

alternative

Low - cannot maintain a

navigable channel. Would

require frequent surveys

2. Modified

Existing

Procedure

Same as 1, but with dredging

performed opportunistically

anywhere according to need

and to improve (widen) any

curved channel condition

May be least costly

because of probable low

frequency of dredging

Fewer and random beneficial

uses. Requires frequent

surveys and subject to

availability of funds and

dredging equipment suited to

Willapa Bar

3. Maintain North

Channel

Maintain north channel at

reasonable cost

Opportunity to place

dredged material on North

Beach

3A Dredge primarily on entrance

bar, straight out and fixed in

position

Safe navigation route.

Possible opportunity for

beach nourishment

Most feasible relative to

navigation alignment

3B Modified S-curve (moderate

curve)

Possible opportunity for

beach nourishment

Feasible if 1,500-ft width

available

3C Modified S-curve (extreme

allowable curve)

Possible opportunity for

beach nourishment

Not desirable due to difficult

navigation

3D Raise the SR-105 dike (-2 ft

mllw) and dredge on entrance.

May reduce erosion on

North Beach

Expensive first cost

3E Construct jetty from tip of Cape

Shoalwater and dredge as

required

Reduce persistent infilling

of channel from the north

Expensive first cost

3F Same as 3A, except dredge to

total depth of 38 ft mllw and with

width 1,000 ft

Reduced frequency of

maintenance and potential

shoaling from the north.

Easier navigation

Subject to availability of highproduction dredge equipment

3G Same as 3B, except dredge to

total depth of 38 ft mllw and with

width 1,000 ft

Reduced frequency of

maintenance and potential

shoaling from the north.

Easier navigation

Relatively expensive due to

initial dredging cost

3H-a Existing SR-105 dike and

deepening on potential new

channel south of North Channel

If new channel continues to

break through, would be

beneficial for north

shoreline

If new channel breaks through,

will be the present channel

3H-b SR-105 dike raised to -2 ft mllw

(3H-b) and deepening on

potential new channel south of

North Channel

More sheltering for North

Cove shoreline; some

deflection of flow away

from North Channel

Expensive first cost. If new

channel breaks through, will be

the present channel.

4. Maintain

Middle

Channel

Maintain Middle Channel at

reasonable cost

Shortest route from Bay

Center

Enhanced flow to help

maintain Bay Center channel

4A Dredge primarily on entrance

bar

Shortest route If dredged entrance bar,

beneficial uses doubtful

(Continued)

1 All channel depths are 26 ft mllw + 2 ft overdredging (500-ft width at bottom) unless otherwise specified.

Chapter 2 Entrance Engineering 2-13
Table 2-2 (Concluded)

Alternative Description

Benefits and Beneficial

Uses Feasibility

4B Construct training structure

northwest of Bay Center to

direct flow away from the North

Channel and into the Middle

Channel. Dredge on entrance

bar only

Create bird islands, oyster

grounds; would reduce

current along the North

Beach

Need to investigate possible

changes to navigation at Bay

Center and Toke Point;

expensive

4C Construct training structure

northwest of Bay Center to

direct flow away from the North

Channel and into the Middle

Channel; dredge primarily on

bay (funnel the ebb flow) and

dredge on entrance bar.

Create strong Middle

Channel; reduce flow in

North Channel and erosion

on North Beach

Expensive

4D Construct training structure

north of Willapa River entrance

to direct flow from North

Channel and into Middle

Channel. Dredge on entrance

bar only

Create strong middle

channel; cut off flow in

north channel and reduce

erosion on North Beach

Need to investigate possible

changes to navigation at Bay

Center and Toke Point;

expensive

4E Same as 4A, except dredge to

total depth of 38 ft mllw and with

width 1,000 ft

Reduced frequency of

maintenance. Easier

navigation

Need to investigate possible

impacts on navigation at Bay

Center and Toke Point;

expensive first cost

5. Maintain

South Channel

Maintain South Channel at

reasonable cost

— Doubtful because of lack of

data on channel longevity and

longer transit for most users

5A Dredge primarily on entrance

bar

Potentially shorter length of

dredging to deeper water.

Similarity to Grays Harbor

Doubtful because of lack of

data on channel longevity and

longer transit for most users

5B Dredge primarily on bay (funnel

the ebb flow)

Same as 5A Considered infeasible because

curvature would be too great to

capture flow out of the South

Bay on ebb

6. Follow Natural

Channel

Implement either 3A or 4A

according to opportunity

May result in least

dredging and safest

navigation if careful

surveying is done

May be difficult to know when

the deepest channel has

switched location with stability

2-14 Chapter 2 Entrance Engineering
Table 2-3

Initial Dredging Volumes Assuming a Static 1998 Bathymetry

Alternative Short Description Volume (1,000,000 cu yd)

3A Straight North Channel 0.8

3B Curved North Channel, 500- to 2,500-ft width 0.2

3C Extreme curved North Channel Somewhat greater than 0.2

3D Raise SR-105 dike with straight North Channel 0.8

3E North Channel with jetty 0.8

3F 3A orientation, 38- x 1,000-ft channel dimensions 5.0

3G 3B orientation, 38- x 1,000 ft channel dimensions 4.2

3H Arm off south side of North Channel at dike 2.1

4A Middle Channel (bar dredging) 3.0

4B Bay Center training structure with 4A 2.6

4C Dredging across whole entrance with 4B 9.9

4D Willapa River training structure with 4A 2.6

4E 4A orientation with 38- x 1,000-ft channel dimensions 12.0

Note: Unless noted otherwise, channels are 500 ft wide at the bottom and have 1 V:3H.

Alternatives 3H-a and 3H-b were selected for evaluation after new

bathymetric measurements made during the course of the study indicated some

deepening of the southside of the North Channel just seaward of the SR-105

project. The two alternatives were added to determine if any advantages could be

found in placing a navigation channel in this vicinity. Alternative 3H-b included

raising the elevation of the SR-105 dike from -18 ft mllw to -2 ft mllw, to deflect

additional flow through the potential channel location.

Alternative 4 variations were all located at the Middle Channel region

(Figure 2-5). The Middle Channel would provide the shortest route for vessel

traffic. The alternatives were developed based on evidence that major ebb flow

exits the North Channel. Therefore, Alternative 4 variations were designed in an

effort to divert flow through the Middle Channel to enhance its persistence at that

location. Alternative 4A involved dredging on the bar, which would provide a

baseline for the more diversionary alternatives. Alternative 4B provided a

training structure just northwest of Bay Center. Alternative 4C added a channel

extending seaward from the training structure of 4B to determine if additional

dredging might enhance capture of the diverted ebb flow. Alternative 4D

consisted of a training dike north of the Willapa River entrance to guide flow

directly into the existing bay entrance of the Middle Channel. Alternative 4E

was similar to 4A except for the additional sediment storage provided by a

deeper and wider channel as was done for Alternatives 3F and 3G.

Chapter 2 Entrance Engineering 2-15
«4

Figure 2-5. Channel and structure location for alternatives

Alternative 5 variations were located at the South Channel. Alternative 5A

proposed dredging on the bar side and 5B included bayside dredging. These

alternatives were not investigated further because their curvature was considered

too great to capture ebb flow out of South Bay and because of the high influx of

sediment likely to occur over the entire channel length with winter storm waves.

Alternative 6 would consider implementing Alternative 3A or 4A according

to which one would require least dredging. This was not an option to be model

studied.

In summary, Alternatives 1, 3A, 3B, 3D, 3E, 3F, 3G, 4A, 4B, 4C, 4D, and 4E

were designated for the calculation-intensive tidal hydrodynamics and sedimenttransport simulations. A subset of these that showed potential was then

examined in the short-wave model. Chapters 5 and 6 describe the short-wave

and long-wave simulations, respectively.

Initial Dredging Requirements

A major consideration in the evaluation of channel alternatives by cost is the

considerable difference that exists in initial dredging requirements. These

differences are examined quantitatively by mathematically cutting design

channels into a terrain model based on recent soundings throughout the entrance

(the 1998 bathymetry is discussed in Chapter 3).

2-16 Chapter 2 Entrance Engineering
An estimate of maximum likely uncertainty in the calculated cut volumes is

100,000 cu yd/mile (equivalent to about a 2-ft uncertainty in the 500-ft-wide

design). In addition, actual volumes that will be required to create the selected

alternatives may differ from those calculated here because the bay entrance is

continually being remolded. Errors arising from imprecise knowledge of the

1998 bathymetry are probably small compared to changes that could occur prior

to actual dredging. The temporal changes do not, however, overshadow the wide

range of cut volume requirements among design alternatives. Calculated

volumes are rounded to the nearest 100,000 cu yd in Table 2-3 and still reveal

major differences between the alternatives. The initial dredging calculations thus

represent reasonable criteria for evaluating initial costs.

Certain calculated differences (e.g., between straight and curved alternatives

in the North Channel) also indicate the magnitude of changes in dredging

requirements that could occur over a few years. Differences among the

calculated values also indicate the magnitude of change in dredging requirements

depending on whether the new channel is maintained in a fixed location or

allowed to shift with the natural channel (natural migration patterns are discussed

in Chapter 3). Following the natural migration would be feasible only within

prescribed bounds. When the natural channel approaches unsafe conditions, it

would be advisable to establish a completely new outlet farther north where

nature began erosion of new outlets in 1941. The cost of maintaining such a

moving channel depends on how well natural migration cycles can be

anticipated, how soon unsafe conditions recur, and how much extra dredging

would be required to force a new outlet ahead of nature's schedule. That extra

effort might be similar to the increase in cut volumes going from Alternatives 3G

to 3F. Historical channel migration patterns are analyzed in Chapter 3.

Channel designs were based on two cross-sectional dimensions. One

provides 26-ft depth plus 2-ft over dredging across a 500-ft width. The other

provides 38-ft depths over a minimum 1,000-ft width. Alternative 3B provides

500-ft widths along the straight reaches, but a 1,500-ft minimum width through

the curved reaches. An informative illustration of 1,000-ft versus 500-ft widths

in Figure 2-5 can be seen along the outer reaches of Alternatives 3A versus 3F

and the outer reach of Alternatives 4A and 4E. All designs include lV-on-3H

slopes between the base of the channel and the 1998 sediment surface. Table 2-3

gives the volume calculations for alternatives shown in Figure 2-5. Navigability

and alteration of hydrodynamics by dredging were considered in placing these

design channels. Minimizing initial dredging was a secondary consideration.

The initial dredging requirements for the 28-ft channel through the middle of

the entrance (Alternative 4A) could have been reduced by reorienting the design

to the shortest path over the bar rather than to the navigationally preferred

alignment shown in Figure 2-5. This less desirable southwest alignment would

have reduced the dredging by only about 13 percent and thus is not shown in

Figure 2-5, or Table 2-3, or considered further in this report.

For the curved North Channel alternatives (3B and 3G), safe passage of

barges on a tow requires a minimum width of 1,500 ft on the curved reaches.

Because the naturally curved channel exceeded 28-ft depths over a width that

was greater than 1,500 ft in 1998, volume changes were also calculated with a

design width that ranged between 500 and 2,500 ft as shown in Figure 2-5. The

total cut volume for Alternative 3B was only 200,000 cu yd. By this approach,

Chapter 2 Entrance Engineering 2-17
Alternative 3B required less dredging than any other alternative and gave

considerable extra width in the curves.

For safe passage by barge traffic, the design width of Alternative 3G (the

curved 38-ft alternative) was also expanded beyond the 1,000- to 1,500-ft

minimum for the straight and curved reaches. A 2,500-ft width was adopted

along the entire ocean extension of 3G. The resulting cut volume was only

slightly larger (8 percent) than the volume obtained for the 1,000-ft-wide straight

alternative (3F).

In summary, Table 2-2 describes the design dimensions for each identified

alternative. In calculating initial dredging requirements, these widths were

implemented except in the case of the two curved alternatives (3G and 3B). A

uniform 2,500-ft width was assigned for Alternative 3G, and a variable width

(500 to 2,500 ft) was assigned in calculating the smallest of all the cut volumes

(Alternative 3B). These widths illustrate how much wider the 28- and 38-ft

clearances could be with little additional dredging beyond that needed for the

minimum safe width. The resulting small inflation of calculated volumes also

better represents the amount of initial dredging that might be incurred when

conditions are not so favorable as obtained with the chosen design channel

placements on the 1998 bathymetry. Further such analyses could be performed

as new alternatives are identified and existing alternatives are defined.

Navigation Channel Alternatives and Disposal

Sites

The location and method of disposal are central factors for evaluating the

economic feasibility of potential dredged-material disposal sites. The dredged

material is expected to consist primarily of sand. Disposal sites were evaluated

relative to proximity to environmental permitting and coordination requirements,

environmentally sensitive areas, biological resources, and resource agency

requirements. Appendix H describes previously and currently permitted disposal

sites, potential new rehandling disposal sites for beneficial reuse, cost of disposal,

possible environmental concerns, site capacity, and disposal equipment

requirements.

The study determined that more than one disposal site is feasible for the

various dredging alternatives. A preliminary attempt was made to assign the

disposal site alternatives to the navigation channel dredging alternatives. The

matching of channel dredging and disposal site alternatives was a logistical and

iterative process that accounted for cost of disposal, schedule of construction, site

capacity and volume of dredging, and dredging and disposal equipment

compatibility. These preliminary dredging site and disposal site combinations

are presented in Table 2-4. Figure 2-6 shows approximate location.

The identified disposal sites, as well as the combination of disposal sites and

navigation channel alternatives, are preliminary and would be specified during

permitting and design. These dredging site and disposal site combinations may

be modified upon possible additional numerical modeling and if new information

about channel sedimentation and volume of future maintenance dredging

becomes available.

2-18 Chapter 2 Entrance Engineering
Table 2-4

Dredging Site/Disposal Site Combination Alternatives

Channel

Alternative

Dredging

Volume,

cu yd Description Disposal Site1

Estimated

Dredging and

Disposal Cost23

per cu yd

3A 800,000 Dredge primarily on

entrance bar, straight

out and fixed in

position.

A - Beach Nourishment

B - Beach Nourishment

D - Nearshore Berm

E - North Channel Disposal

$8.70

$8.70

$6.60

$4.30

3B 200,000 Modified S-curve

(moderate curve).

A - Beach Nourishment

B - Beach Nourishment

D - Nearshore Berm

E - North Channel Disposal

$8.70

$8.70

$6.60

$4.30

3H-a, 3H-b 1,600,000 Added after 1999

survey to coincide

with the straight path

seaward from near

SR-105 project that

had minimal change

since 1998 survey.

Two variations include

existing

SR-105(3H-a)and

SR-105 dike raised to

-2ft(3H-b).

A - Beach Nourishment

B - Beach Nourishment

D - Nearshore Berm

E - North Channel Disposal

$8.70

$8.70

$6.60

$4.30

4A 2,300,000 Dredge primarily on

entrance bar.

F - Goose Point

1 - Side Casting

$6.80

$3.80

4E 12,600,00

0

Same as 4A, except

dredge to total depth

of 38 ft and with width

1,000 ft.

F - Goose Point

1 - Side Casting

$5.90

$3.50

1 Figure 2-6 and Appendix H give locations of disposal sites.

2 Each cost estimate is based on disposal of amount shows in second column, although in some cases, it may be

advantageous to dispose of different portions of this amount at more than one site in a given year.

3 Cost estimate does not include mobilization and demobilization.

Chapter 2 Entrance Engineering 2-19
Figure 2-6. Potential dredged-material disposal sites and means of disposal

References

Escoffier, F. F. (1940). "The stability of tidal inlets," Shore andBeach 8(4),

114-115.

(1977). "Hydraulics and stability of tidal inlets," GITI Report

13, U.S Army Engineer Waterways Experiment Station, Vicksburg, MS.

Headquarters, U.S. Army Corps of Engineers. "Hydraulic design guidance for

deep-draft navigation projects (in preparation)," Engineer Manual EM 1110-

2-1613, Washington, DC.

_. (1996). "Hydraulic design of deep-draft navigation projects,"

Engineer Regulation ER 1110-2-1404, Washington, DC.

Jarrett, J. T. (1976). "Tidal prism-inlet area relationships," GITI Report 3, U.S.

Army Engineer Waterways Experiment Station, Vicksburg, MS.

Kraus, N. C. (1997). "Willapa harbor project channel: Wave transformation on

an ebb current," Memorandum for Commander, U.S. Army Engineer District,

Seattle, U.S. Army Engineer Waterways Experiment Station, Coastal and

Hydraulics Laboratory, Vicksburg, MS.

O'Brien, M. P. (1931). "Estuary tidal prisms related to entrance areas," Civil

Engineering, 738-739.

2-20 Chapter 2 Entrance Engineering
Pacific International Engineering. (1998). "SR-105 Emergency Stabilization

Project, Monitoring Program," Report No. 10, Pharos Corporation, Edmonds,

WA 98020.

Permanent International Association of Navigation Congresses. (1977).

"Approach channels, a guide for design," Supplement to Bulletin No. 95,

Brussels, Belgium.

Seabergh, W. C. and Kraus, N. C. (1997). "PC program for coastal inlet stability

analysis using Escoffier method," Coastal Engineering Technical Note

CETN rV-11, U.S. Army Engineer Waterways Experiment Station,

Vicksburg, MS.

U.S. Army Engineer District, Seattle. (1971). "Feasibility report, navigation and

beach erosion, Willapa River and harbor and Naselle River Washington,"

Seattle, WA.

(1989). "General Design Memorandum, Grays Harbor,

Washington, Navigation Improvement Project," Seattle, WA.

U.S. Congress. (1916). House Document 706. 63rd Congress, 2d Sess (Act

July 27,1916), Improvement of Willapa Harbor and River-Raymond to sea.

. (1954). House Document 425. 83rd Congress, 2d Sess (Act

Sept 3,1954), Mooring Basins at Tokeland and Nahcotta-Widen Willapa

River.

Wang, S., Butcher, C, Kimble, M., and Cox, G. D. (1980). "Columbia River

entrance channel deep draft vessel motion study," Tetra Tech Report No.

TC-3925, U.S. Army Engineer District, Portland, OR.

Chapter 2 Entrance Engineering 2-21
3 Geomorphology1

Introduction

Geomorphology is a science that systematically examines, classifies, and

interprets landforms. This chapter presents results from a geomorphic

investigation of the entrance to Willapa Bay that included recent and historical

bathymetric changes. It also investigates the implications of large-scale,

relatively longer term changes (on the order of 1 to 100 years) on channel

feasibility and design. The basic sources of information are charts and aerial

photographs, which are numerous and cover more than a century of dynamic

change.

The study area extends eastward from the outer edge of the ebb shoal to the

inner bay region where channels are oriented north-south, roughly at the meridian

of Toke Point (Figure 2-1). Cape Shoalwater and Leadbetter Point bound the

entrance on the north and south, respectively. Channels and shoals in the

entrance are subject to rapid changes induced by large waves and strong currents.

Larger scale changes nevertheless include trends and cycles that are well

documented by the charts and photographs discussed in this chapter.

Setting

The coast of Washington extends from Cape Disappointment at the entrance

of the Columbia River northward to Cape Flattery at the entrance of the Straits to

Juan de Fuca (Figure 3-1). The southern half of this 150-mile-long reach follows

a relatively linear north-south line reflecting the marine-fluvial origin of

sediments that have smoothed the coastline between two rock outcrops, Cape

Disappointment north of the Columbia River and Point Grenville at the opposite

end. The broadly north-south shoreline can be segmented into three slightly

concave westward segments by ebb shoals at Grays Harbor, Willapa Bay, and the

Columbia River.

This reach of coast lies south of the extent of Pleistocene glaciation. The

60-ft-depth contour runs north-south about 2.7 miles from shore giving a

nearshore slope of 0.004 except where the contours bulge seaward around deltaic

deposits off the Columbia River, Willapa Bay, and Grays Harbor. The heads of

submarine canyons farther offshore (Astoria, Willapa, Guide, and Grays) are at

1 Written by Mr. Edward B. Hands, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS.

Chapter 3 Geomorphology 3-1
CAPE

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WASHINGTON

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Figure 3-1. Regional location map

3-2 Chapter 3 Geomorphology
depths of about 600 ft. These canyons are too deep to interact significantly with

waves or sediment transport on the scale of interest here. Beach sand samples

taken between the Columbia River and Grays Harbor range from about 0.15- to

0.25-mm in median diameter.1Samples taken from the Willapa Bay entrance bar

by the U.S. Army Engineer District, Seattle, in the 1960s, 1970s and for this

study reveal consistent textural characteristics: well-sorted, fine-grained, angular

sand (0.18-mm median diameter and 0.3-0.5 sorting).

Bathymetric Data Used in Analysis

The Seattle District has conducted hundreds of hydrographic surveys of

portions of Willapa Bay. Almost annually between 1927 and 1978, the Seattle

District prepared charts covering the entire entrance with soundings taken each

year (primarily in July and August). At less frequent and irregular intervals

similar charts were prepared between 1852 and 1922. After 1967, when Federal

maintenance dredging for the Willapa River channel ceased, Seattle District

surveys were curtailed to the portion ofthe entrance near the navigation channel.

Though regular dredging at the entrance ceased in 1974, a small (80,000 cu yd)

experimental channel was dredged in the middle ofthe entrance in 1997. Fiftysix full-entrance charts, compiled between 1852 and 1978, were obtained from

District archives to support this study together with restricted-area channel

surveys for the years 1981, 1982, 1983, and 1984 and District digital

hydrographic data taken between 1993 and 1997. No surveys were obtained for

the period between 1985 and 1992. Less detailed information from this period

was obtained from aerial photographs.

As part ofthe field data collection effort for the present study (Chapter 4),

the most dense and extensive hydrographic survey to date was conducted ofthe

whole bay by combining synoptic soundings taken by Seattle District mediumand shallow-draft survey boats, contractor vessels, and the Scanning

Hydrographic Operational Airborne Lidar Survey (SHOALS) ofthe U.S. Army

Corps of Engineers (Lillycrop, Irish, and Parson 1997). With the SHOALS

system, elevations were surveyed over extensive shallow to slightly emergent

shoals that cover much ofthe central portion ofthe bay entrance. Being the site

of almost continual wave breaking even in the summer, the outer portions of

these shoals had never before been surveyed. Even landward ofthe breakers,

precise elevations over broad areas were unknown because the areas were too

shallow for survey boats.

Because ofthe turbidity in the bay, the extent of SHOALS coverage was

limited primarily to depths less than about 10 ft. Elevations were obtained,

however, in previously unsurveyed areas, which significantly improves the basis

for sediment volume and cross-sectional area calculations for analysis of

sediment volumes and tidal discharge. By combining data from various surveys

as described, nearly 500,000 accurate survey points were obtained over the

40,400 acres ofthe bay entrance. Another 100,000 less dense points were also

sounded in 1998 to determine bathymetry in the lower bay and the lower Willapa

River (Figure 3-2).

1 Personal Communication, July 1998, Mr, M. Buijsman, Washington Department of Ecology.

Chapter 3 Geomorphology 3-3
Symbol Soundings Platform

299,749

130,402

102,925

37,463

28,597

451

SHOALS

Shoal hunter

Shoalhunter

CE Small Boat

PIE Boat

Cpt. Landreth

21,26, 27 Jul 1998

6-20Aug 1998

29 Jul-1 Sep 1998

17, 22, 29 Sep1998; 16 Oct 1998

21,26,27 Jul 1998

21, 26, 27 Jul 1998

Figure 3-2. Soundings taken through Willapa Bay from July to October 1998

3-4 Chapter 3 Geomorphology
Based on evaluations at other sites, the accuracy of the SHOALS data is

reported to be ±3 m horizontally and ±0.15 m vertically.1 Boat survey accuracy

is expected to be ±1 m horizontally and ±0.67 m vertically.2

As part of the data collection for this study, the bottom was surveyed again in

the spring of 1999. The 1999 survey covered only the entrance area where

channels are proposed and was conducted by the Seattle District survey boat

Shoalhunter. In the interval between these two major surveys, Pacific

International EngineersPLLC and Evans-Hamilton, Inc., took additional soundings

in selected areas near instrument stations, in areas of active scour and deposition

(near the State Route (SR) 105 dike, in the borrow area), and in more rapidly

changing areas along the north channel.

The 1998 and 1999 surveys and the sequence of historical bathymetry

covering (at uneven intervals) 147 years reveal processes, trends, and cycles that

provide information on long-term, wide-area changes in sediment and fluid

dynamics. All full-entrance charts consulted in this study are reproduced at

reduced scale in Appendix A except for those years for which there are multiple

charts, in which case only the most informative chart for the year is shown.

Comparison of Channel Alternatives by Fairways

Location of historical channels relative to present alternatives

The alternatives considered in the search for a more reliable channel can be

divided into three subsets with every Alternative Channel (Table 2-2) near one of

three locations: the North Fairway, Middle Fairway, and South Fairway as

depicted in Figure 1-3. Channels tend to occur in or near these fairways

historically. Each channel alternative has a specific design cross section; the

fairways are much broader zones and can contain several channel alternatives.

Many features of the proposed channels will be evaluated in terms of geomorphic

conditions that can be documented for these three fairways. The conceptual

fairways and Alternative Channels are denoted by mixed-case lettering to

distinguish them from evolving natural channels in the north, middle, or south

parts of the bay denoted by lowercase lettering.

Channel alternatives will be compared in terms of relative values of several

channel parameters that have been tabulated from the bathymetric record. The

frequency of occurrence of natural channel parameters in favorable ranges for

each fairway can be compared with those of the Alternative Channel design

parameters to obtain a relative ranking of the engineering effort that would be

required to establish and maintain each proposed Alternative Channel.

1 Personal Communication, September 1998, J. Lillycrop, SHOALS Center of Expertise, Mobile,

Alabama, also see Guenther, Thomas, and LaRocque (1996).

2

Personal Communication, December 1998, H. Arden, U.S. Army Engineer District, Seattle,

Seattle, WA. These error estimates refer to uncertainties in individual points. Biases have not been

investigated.

Chapter 3 Geomorphology g_c
Tabulated channel parameters

The parameters tabulated for this comparative analysis of alternatives are

listed in Table 3-1. The datum for elevations is mean lower low water (mllw).

Except for the historical charts, which were created with Corps-surveyed

shorelines, all figures show the high-water line (hwl) and the low-water line (lwl)

determined from 1996 aerial photography and U.S. Geologic Survey (USGS)

quadrangle sheets. Figure 3-3 shows a typical location where the geomorphic

parameters were evaluated in a particular representative year for three reaches

along the North Channel. Reach 1 always refers to channel outlets over an ocean

bar Four such outlets are shown under Reach 1 in Figure 3-3. Additional

reaches are defined to accommodate major changes in channel orientation or size

moving inland from the bar to Reach 2 and then to Reach 3 farther upstream.

Similar measurements were made for each channel and identified by date,

fairway, and reach for each survey and for each of one to four outlets if the

channel split before reaching the ocean as the north channel does in Figure 3-3.

These parameters were also tabulated from the individual channel charts of the

1980s (Appendix A). To more appropriately contrast the proposed Alternative

Channels however, the database for the following comparative analysis is

restricted to data tabulated from the full-entrance surveys that charted all clear

channels through the entrance between 1852 and 1978. Geomorphic parameters

showing the strongest contrasts among channel alternatives are discussed next.

Table 3-1

Geomorphic Parameters Measured in Each Outlet and Each

Channel Reach of Each Fairway on Each Chart of the Willapa Bay

Entrance -

Measurement

Depth, ft

Orientation, deg

Width, ft

Coordinates, lat, long

Longevity

Description

Limiting depth over the bar and representative depth for upstream

reaches . —

With respect to grid north

Between 24 ft mllw depth contours

Of the bar or of the centroid of the upstream reaches

A count of the number of times a particular channel, reach, or outlet

appeared on one of the annual summary charts regardless of channel

depth or width.

Differences in channel longevity

A clear channel is taken here to be one charted from the ocean bar eastward

entirely across the entrance shoals into the back bay regardless of specific

channel depth or width. Depth and other channel parameters are examined after

first considering channel longevity. By this approach, the number of historical

categories is initially restricted to three fairways, and the results are not biased

toward any one of the channel alternatives (e.g., one with a large versus small

cross section). After considering longevity, the next sections examine questions

of how often and closely the historical channels matched the proposed design

alternatives.

3-6

Chapter 3 Geomorphology
NORTH

HANNEL

FAIRWAY

^ 24-ft ^^65 j^+_^295 deg Channel depth (ft), width (ft), and

Contours Tl,x^2250 ft*^ orientation (deg)

25 ft —•— 220 deg Channel orientation (deg) and

controlling depth over the bar (ft)

Figure 3-3. Definitions of channel reach and tabulated geomorphic parameters

If the Seattle District identified a channel worthy of charting across the bay

mouth, it is considered to have been clear at that time. If no channel was charted

in a particular region, it is assumed none existed. This assumption is considered

reasonable because the charts selected for the comparative analysis portray

conditions over the entire entrance. Journals of some early explorers (quoted in

Swan 1857) and a chart of shipwrecks in the bay entrance (Kranz 1986), suggest

that sailing vessels often attempted to enter Willapa Bay through the southern

half of the bay. Later in the 1980s and early 1990s, when surveys were restricted

to navigationally important reaches, channels in the middle or south fairway may

have escaped inclusion on charts and be underrepresented in the longer period

channel database. Therefore, comparison of channel parameters among the

fairways will be restricted to the 1852-1978 period during which surveys covered

the full entrance area.

Even when the full north-south extent of the entrance was surveyed, wide

areas within it were not sounded because they were too shallow for the survey

boat or were surrounded by breakers. The absence of elevations for these areas

would hinder calculation of precise entrance cross-sectional areas and sediment

Chapter 3 Geomorphology 3-7
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3-8 Chapter

3 Geomorphology
volumes for those periods, but does not mask any navigationally significant

channel. Figure 3-4 is an example of the historical charts of the full entrance

area. One such chart for each year being considered appears at a reduced scale in

Appendix A along with restricted area surveys of the 1980s and 90s and the

detailed surveys taken to support this study.

Considering the more restrictive database (the 56 full-entrance charts, 1857

to 1978, selected for a balanced fairway comparison), the Middle and South

Fairways had clear channels on less than 20 percent of the charts (Figure 3-5),

whereas the North Fairway was not only always clear, but was larger than any of

the channels in the other fairways (Figure 3-6). Therefore, it is concluded that

any navigable channel in the Middle or South Fairways would require substantially greater long-term maintenance than one in the North Fairway unless the

natural tidal patterns were significantly altered.

The extra effort of maintaining a channel in the Middle or South Fairway

may be justified if these fairways offer superior benefits. Geomorphic criteria

that might suggest such benefits are examined in the next sections.

Differences in channel depths and orientations

As can be seen from Figure 3-6, the North Fairway has depths closest to and

sometimes exceeding the design depth of 28 ft mllw (26 ft plus 2 ft of advance

dredging and overdredging). As discussed in Chapter 2, the orientation of

vessels with respect to the waves is a critical risk factor for crossing the bar.

Based on wave climatology to be presented in Chapter 5, the 45-deg sector

centered on 270 deg is considered most desirable for all three fairways.

Figure 3-7 shows that this condition has occurred most frequently in the North

Fairway with the South Fairway coming in second ahead of the Middle Fairway,

which was often too far counterclockwise or south of the favored westward

orientation.

Figures 3-8 and 3-9 show the temporal changes in depth and orientation

addressing each fairway separately. Weak interactions between depth and

orientation are evident. Persistence, trends, and cycles in past values can be

examined in these figures and will be interpreted in a later section as indicative of

likely future conditions.

100

80

40

20

Middle

Channel

South

Figure 3-5. Frequency of fully-opened channels

Chapter 3 Geomorphology 3-9
Primary Outlet, North Channel, 65 Occurrences

I

D

rimary Outlet ,M ddl e Channel 11 Occurreni:es

30-

25-

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Undesirable X

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Desirable

Controlling Depth, ft (mllw)

Figure 3-6. Channel depths by fairways

3-10 Chapter 3 Geomorphology
15

10

Primary Outlet, North Channel, 65 Occurrences

o

O

m imni a

15-

Primary Outlet, Middle Channel, 11 Occurrences

10-

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Primary Outlet, South Channel, 12 Occurrences

10-

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180 200 220 240 260 280 300

^ Undesirable ^ Desirable

320 340 360

^Undesirable^

Grid Azimuth, deg

Figure 3-7. Channel orientation by fairways

Chapter 3 Geomorphology 3-11
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Primary Outlet, South Fairway, 12 Occurrences

1860 1880 1900 1920

Year

1940 1960 1980 2000

Figure 3-8. Temporal variations in bar depth

3-12 Chapter 3 Geomorphology
360

315

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E

3 225

360

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No dredging this year oBefore dredging AAfter dredging Alnterirr

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CO 315~

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1840 1860 1880 1900 1920 1940 1960 1980 2000

Year

Figure 3-9. Temporal changes in bar channel orientation

Chapter 3 Geomorphology 3-13
Though depths were significantly different among the fairways (Figure 3-6),

depths within fairways were relatively stable in time (Figure 3-8). The north

channel bar was dredged from 1931 to 1941, again from 1949 to 1974. As

presented in Chapter 2, the dredging volumes were not large, typically less than

350,000 cu yd. The bar depths shown in Figures 3-7 and 3-8 for these years

might be deeper because of dredging. One should note in the time series

(Figure 3-8), however, that the primary bar in the North Fairway was at times

deeper than 25 ft before, between, and after these two periods of dredging. Also

note that depth symbols are coded to indicate if that year's chart was prepared

before or after dredging; there is no significant increase in depth that can be

related to dredging. So, the dredging contribution to charted channel depth is

small and cannot invalidate the observation that the North Fairway has depths

naturally deeper than the other fairways.

At different times, the North Channel split into multiple outlets (Figure 3-3).

Some years, there was only one outlet, whereas during other years, there were as

many as four. The primary bar is the outlet providing the greatest controlling

depth. Only the primary bar is shown in Figure 3-6. Middle and bottom panels

of Figure 3-6 show the same parameters evaluated similarly for the other two

fairways. Again, note the relative stability of depth with time.

Only a single instance of simultaneous channels in different fairways

occurred prior to 1928, but multiple fairway channels became common after the

1930s. As can be seen in Figure 3-8, the entrance was charted less frequently

prior to 1926 than afterwards. The lack of any Middle and South Channels

during this earlier period suggests that Middle and South Channels were at least

less common during the pre-1928, poorer-sampled period. The entrance to

Willapa Bay has persistently widened from about 4.5 miles (7.2 km) in 1926 to

6.5 miles (10.5 km) along the same transect in 1980. Possibly, the Middle and

South Channels were less common earlier because of the narrowness of the

entrance. The relationship between the entrance width and number of channels

suggests, however, that the change from single to multiple channels occurred

abruptly around 1928, rather than multiple channels gradually becoming more

common and as the width increased.

Geomorphic Cycles

Cycle identification

A compilation of approximately l:60,000-scale charts submitted to the

District Engineer in 1949 (U.S. Army Engineer District, Seattle 1949) indicates

long-standing awareness that the Willapa entrance channel migrated from year to

year for long periods. This observation did not appear in the published literature

prior to 1965. Andrews (1965), Terich and Levenseller (1986), and Shepsis,

Hosey, and Phillips (1996) published accounts of the channel movements relating

them to shoal growth that deflected the main channel southward, but

documentation and analysis of the number and duration of channel cycles were

still lacking. Recent inspection of the longer bathymetry record allows full

documentation (at approximately yearly intervals) of seven cycles of spit

elongation and channel migration between 1933 and 1998. Three additional

cycles will also be identified from earlier charts. The earlier events are, however,

3_14 Chapter 3 Geomorphology
less fully recorded because, prior to 1920, surveys were conducted much less

frequently. Additional cycles between 1887 and 1920 may have been missed

between the infrequent early surveys.

Along more than a mile of bay shore, where the North Channel skirts past

Cape Shoalwater before entering the Pacific Ocean, waves and currents have

eroded the shoreline for at least the recorded 147 years at rates in excess of

100 ft/year (Richey et al. 1966, Komar 1998, Terich and Levenseller 1986).

Between 1852 and about 1940, this bay shore recession completely eroded two

peninsulas (with three former lighthouses). From the charts, these peninsulas

appear to have been low-elevation sand spits that were built back into the

entrance by southbound longshore transport entering the bay from ocean beaches

to the north. Around the turn ofthe century, northward migration ofthe main

channel began to rapidly erode these spits. Inspection ofthe historical charts

indicates that the long-term rate ofshore recession increases westward from the

North Cove lagoon to the ocean shore (Appendix A).

The outer receding bay shore has thus rotated clockwise around a pivot point

near the cove. Lowell (1997) reports that receding outer bay shoreline is

encountering increasingly older, higher, and more consolidated sediments. The

more resistant sediments may be similar to those present in the adjacent,

relatively stable area behind the North Cove lagoon. Throughout most ofthis

century, however, the bay shore recessed rapidly at a fairly constant rate. Only

recently does this rate appear to decline.

In contrast to northward recession ofthe bay shore, the outer portion ofthe

North Channel typically migrates southward across the ebb shoal, deflected by

the shore-tied submerged spit growing from Cape Shoalwater. Periodically,

channel migration is interrupted by spit dissection, which allows ebb currents to

flow directly seaward out ofthe North Channel. Dissection always starts with

erosion of a notch on the landward side ofthe submerged spit. At such times,

multiple incipient outlets often form. Typically, the notch or notches will widen

and extend oceanward for several years until depth across the entire spit reaches

18 ft, at which point the distal end ofthe spit (which is now an isolated shoal)

begins to migrate to the southeast. The shoal migration rate is relatively rapid

compared to extension ofthe spit. The new outlet captures the majority ofthe

North Channel discharge and the other outlets gradually fill. The shoal

eventually merges with others in the middle portion ofthe bay entrance.

Figure 3-10 illustrates the second halfof a cycle that began several years

earlier when the dominant discharge flowed directly seaward through a channel

that over the years rotated clockwise to the north-south position shown in the top

panel. Note that a vessel could avoid depths less than 18 ft by following this

north-south channel except for a short passage over a saddle near the center of

the entrance. In the next phase in 1941, top panel, several new outlets appeared.

By 1945 (middle panel), the distal end ofthe spit had been isolated by a breach

entirely across the spit. By 1949 (lowest panel), the spit-derived shoal had

migrated southwest and merged with inner entrance shoals. All the while, the

submerged ebb-edge spit continued building southward from Cape Shoalwater.

Chapter 3 Geomorphology 3-15
A. Extreme deflection of North

Channel creates unsafe, nearly

north-south heading over primary

bar

LEGEND

^M deeper -36

H -3610-30

|-30to-24

IB -24(0-18

1 -IStoMLLWL

1 |MLU.VLtoHWL

1 | hi^ia-mVL

1941

B. Spit dissection establishes

isolated shoal and new primary

outlet

1945

C. Renewed southward channel

migration, uninterrupted spit

growth, and merging of dissected

portion of spit with entrance

shoals

1948

Figure 3-10. Second half of one channel cycle

3-16 Chapter 3 Geomorphology
Figure 3-11 shows a 20-year series of changes that includes two cycles of

spit elongation and channel deflection. Cycles have been continuous throughout

the 147-year period that the entrance has been charted. Eleven such cycles can

be documented between 1887 and 1997.

Repeated cycles ofspit growth influence not only the position ofthe bar

channel, but its depth and alignment, the size and location of entrance shoals, and

the erosion rates along the North Cove shoreline. Figure 3-12 shows changes in

the rate ofshoreline retreat along the North Cove relative to the cutting oftwo

new north channel outlets.

Climate and geomorphic controls

Peruvian fishermen use the term El Nino to refer to warming oftheir ocean

fishing grounds around December during certain years. Climatologists

independently coined the term Southern Oscillation to refer to an atmospheric

condition in the Southern Hemisphere that explained occasional failures ofthe

Indian monsoon. The term El Nino-Southern Oscillation (ENSO) refers to the

more recent recognition that both phenomena are expressions ofthe same

coupled ocean-atmosphere, global phenomenon. Prediction and identification of

the full impacts ofthe ENSO are the subject ofintense research.

Spit dissections at Willapa Bay follow ENSOs, but dissection occurs much

less frequently than ENSOs. When spit elongation deflected the channel and

possibly other unrecognized conditions were met, ENSO-related processes

seemed to have triggered cutting ofnew north channel outlets directly seaward

across the ebb-edge spit. Table 3-2 lists 13 El Nino events identified and

categorized by strength according to Quinn et al. (1978). All ofthe cycles

(identified from the bathymetric charts, Appendix A) started within 12 months of

the onset of an El Nino.

All but two ofthe ten El Nino-initiated channel reorientations between 1852

and 1998 were followed by a complete growth-rotation-dissection cycle. One of

the two exceptions was in 1954 when a new outlet began during an El Nino,

developed for 5 years, but then filled in, reconnecting the temporarily isolated

distal shoal to the Cape Shoalwater spit. In 1959, when the 1954-iniated outlet

closed, the next outlet was initiated by the next El Nino.

A strong correlation between timing ofspit dissection and El Nino

(Figure 3-13) suggests that a physical connection exists. Understanding this

connection would make new channel alignments predictable. One cost-reducing

opportunity provided by this predictability would be the scheduling of any

channel relocation dredging (discussed further in the next section, Geomorphic

Estimates of Shoaling Rates) to coincide with a predicted El Nino. A second and

more active approach would be to investigate the practicality of engineering

interventions mimicing the El Nino-related processes that restart channel cycles

thereby creating new outlets needed for navigation ahead ofthe natural cycle.

Chapter 3 Geomorphology 3-17
'S^Mwf

1925» 19MP

S~* i

to

.'?*$. /äiNi-Sfi^ ;-Äs35%^ -w;Cl^

1941

ft!

WE H*46

l^/fe*^ m,;

1948

Figure 3-11. Twenty-year sequence illustrating two channel-spit cycles

3-18 Chapter 3 Geomorphology
Figure 3-12. Rates of North Cove shore recession (data from Pacific

International EngineeringPLLC, 1999) and episodes of Cape

Shoalwater spit dissection or breaching (Table 3-6)

Channel Reorientations

Quinn's

El Nino

Intensity

Index

surveys

J2-month moving

average of ssloi

Figure 3-13. Timing of channel cycle with El Nino

Chapter 3 Geomorphology 3-19
Table 3-2

Timing of Post-1922 El Ninos (from Quinn et al. 1978) and Restoration of

New North Channel Outlets

Date Event

1932-33 Weak El Nino

1933 Initiation of spit dissection leading to reorientation of primary North Channel outlet

1939-40 Moderate El Nino

1941-42 Strong El Nino

1941 Initiation of spit dissection leadinq to reorientation of primary North Channel outlet

1943-44 Weak El Nino

1951-52 Weak El Nino

1953-54 Moderate El Nino

1954 Initiation of spit dissection leadinq to reorientation of primary North Channel outlet

1957-58 Strong El Nino

1959 Shoaling seals outlet that was initiated in 1954

1960

Full spit dissection and reorientation of primary North Channel outlet after a temporary

interruption in 1959

1965-66 Moderate El Nino

1969-70 Weak El Nino

1970 Initiation of spit dissection leadinq to reorientation of primary North Channel outlet

1972-73 Stronq El Nino

1976-77 Moderate El Nino

1982-83 Stronq El Nino

1997-98 Stronq El Nino

| 1998 Iniation of spit dissection and reorientation of primary North Channel outlet

This study found evidence ofrepeated increases in monthly mean sea level

on the order of 0.7 to 1 ft that last for about a month at nearby gages during the

El Ninos that coincided with new channel initiations. Because the bay tidal flats

are so large, these higher water levels can significantly increase the tidal prism

and the ebb discharge velocities. It can be speculated that increased momentum

and higher velocity oftidal discharges over an elongate spit that is temporarily

submerged an additional foot might promote cutting of a new outlet. The

position ofsuch a cut would be at the inflection point ofthe channel where

momentum ofthe ebb flow would still be in the direction forced by orientation of

the north bay shore. The alignment ofthe new cut would tend to parallel this

shore-directed flow. These suppositions fit the characteristics of all ten new

outlet initiations identified in Figure 3-13. There would also be, however, a

tendency for the spatially averaged discharge velocity to decrease when higher

water levels increased the flow cross-sectional area. Channelization offlow

could also change and affect the location ofpeak discharge velocities.

Evaluating which ofthese competing factors would dominate is beyond the

present scope of work.

3-20 Chapter 3 Geomorphology
Monthly anomalies in sea surface temperature optimum interpolation indices

(sstoi) were obtained from http://nic.fb4.noaa.gov/data/cddb/cddv/-ssoti.indices.

The buoy measurements of sea surface temperature selected for this study

represent a region from 0 to 10 deg S and 80 to 90 deg W. This region was

selected in a compromise between proximity to the North American Continent

and longevity of the records, but data from other portions of the monitored

equatorial area would probably show similar results. The anomalies are

departures of the optimum interpolated temperature measurements from their

base values for the period 1951-1979. A running average of these values is

shown in Figure 3-13.

The timing of earlier El Ninos was developed by Quinn et al. (1978).

Quinn's index combines many factors and sources of information on global

pressure systems and coastal South American rainfall, fisheries, sea surface

temperatures, and sea bird reports dating back to the 1700s. Quinn's index is

widely cited by climatologists and has been used in coastal investigations (e.g.,

Seymour 1998). It is adopted here to investigate the timing between El Ninos

and earlier episodes of channel reorientation.

Quinn did not attempt to specify the month of initiation or the duration of

El Ninos. A modification that uses bars to represent the time and intensity of

Quinn's index is adapted in Figure 3-13. The bars are centered on 31 December

because the typical El Nino causes warmest water temperatures in the tropical

east Pacific around the end of the calendar year. Bar widths were arbitrarily set

to span the six months from 1 October to 31 March. The actual onset and

duration of El Ninos vary as indicated by changes in peaks of the smoothed sstoi

curve. Heights of the bars reflect Quinn's intensity categories. Pre-1980gaps

between the bars indicate low intensity El Nino-, neutral-, or La Nina-years.

Note that where they overlap, all of Quinn's bars align with a peak in the sstoi

index. All channel reorientations began during an El Nino.

This study also found evidence of repeated increases in month mean sea level

on the order of 0.7 to 1 ft for several months during El Nino events that coincided

with new channel initiation. Because tidal flats are so large, these higher water

levels significantly increase the tidal prism and the ebb discharge velocities. It

can be speculated that the increased momentum and higher velocity of tidal

discharges over an elongate spit temporarily submerged an additional foot would

promote cutting of a new outlet. The position of such a cut would be at the

inflection point of the channel where momentum of the ebb flow would still be in

the direction forced by orientation of the north bay shore. The alignment of the

new cut would tend to parallel this shore-directed flow. These suppositions fit

the characteristics of all ten new outlet initiations identified in Figure 3-13.

Storm paths across the north Pacific shift southward during El Ninos.

Seymour (1998); Inman, Jenkins, and Elwany (1996); and Komar (1986,1997,

and 1998) attribute dramatic increases in shore damage along the California and

Oregon coasts to significantly higher waves coincident with the 1982 and 1998

El Ninos. Changes in storm paths and frequency as well as increased wave

heights and altered wave directions during El Nino are other potential factors that

could alter erosion patterns at Willapa Bay and trigger new channel cycles.

Relationships between these local processes and channel cycles have not been

examined because of time constraints and specific objectives of the present study.

Chapter 3 Geomorphology 3-21
Geomorphic Estimates of Shoaling Rates

Approaches

In the northern half of the Willapa entrance, the general rate of long-term

sediment transport from the north can be inferred from the gradual, but

historically persistent southward growth of the Cape Shoalwater submerged spit

(Figure 3-11 and Appendix A). For a coastal site in Alaska, Moore and Cole

(1960) estimated sediment transport rates from the rates of spit growth. By

adopting a similar approach, the rate of sediment influx to the Cape Shoalwater

spit can be calculated from historical changes in bathymetry. This rate is used to

infer a channel shoaling rate. In a second approach, shoaling rates for the

Willapa Alternatives are estimated from historical shoaling rates in areas related

to the channel templates. Templates are geometric forms that match the channel

design cross section (width, depth, and side slopes). One or more template is

associated with each channel Alternative. Volumes between templates and the

entrance bathymetry were calculated for a number of years. By positioning

templates in various locations, shoaling requirements were estimated for each

alternative. Finally, annual bathymetric changes are combined with the

calculated initial dredging requirements, the conclusions from spit growth

measurements, the impacts of cycles, and differences in shoaling of migrating

versus stationary channels to derive a 50-year dredging estimate.

These methods are approximate and depend on assumptions that greatly

simplify the process of sediment transport, channel trapping, and variations in

channel flushing potential. Other reasonable assumptions are possible.

However, the degree of consistency among these geomorphically based

estimates, comparison of their results with those from numeric simulations, and

engineering experience all combine to support the methodology and to identify

further work that would improve cost predictions for channel alternative.

Approach I: Estimates based on spit growth

Spit elongation. As shown in Figure 3-10 and 3-11, the channel and,

therefore, the ocean bar migrate southward as the Cape Shoalwater spit

progrades. Bar movement tracks with the southern terminus of the submerged

spit. Superposing historical positions of the bar on a modern chart shows that the

bar has moved across the whole entrance area at different times and therefore

crosses all the channel alternatives (Figure 3-14). Not shown in Figure 3-14 is

the continued southward migration of the distal portion of the spit, which carries

the dissected shoal south of the entrance bar. Shoal migration was shown in

Figures 3-10 and 3-11. Calculating the average growth rate of the spit gives an

estimate of the volume of sand that must move over the area of any entrance

channel (either as part of the growing spit or the dissected shoal).

3_22 Chapter 3 Geomorphology
:

igure 3-14. Positions of north channel bar (1911-1985). For general

reference, shorelines and 28-ft depth contours are taken from

1996 aerials and the 1998 survey, respectively. The circles

show that the terminus of the Cape Shoalwater spit reached

positions that historically spread across the whole bay entrance.

Circles indicate historical positions of the bar

Assumptions. Measuring spit growth and inferring transport rates depend on

several assumptions that, although not strictly valid, are considered to be

approximately correct. These assumptions are partially confirmed in this report

through comparison of independent shoaling estimates from other approaches:

spit growth, natural channel shoaling, and numerically simulated shoaling.

For sake of argument, begin by assuming spit elongation is fed by sand

transported out of the north. Sand seems to move predominantly southward

along the spit and accumulates in the deeper water off the south end of the spit.

There are situations, in high-velocity steady flow, in which bed forms migrate in

a direction opposite to sediment transport such as when sand moves downstream

and settles on the upstream flank of the next antidune moving upstream in

supercritical flow. At the Willapa entrance, flow across the channel is not

supercritical, and the spit is large and slow moving. Therefore, the volume of

sand that might be accreting near the southern tip of the spit from a source south

of the proposed channels can be assumed to be volumetrically negligible. This

assumption is not crucial, but simplifies application of the results because spit

growth and/or migration would be driven by processes (including wave and tidal

Chapter 3 Geomorphology 3-23
current transport) that would carry the sand across any proposed channel location

south of the dissection zone.

The last and most uncertain assumption in the spit growth approach is the

percentage of the cross-channel transport that would accumulate in the channel

from one year to the next. Some of the sand carried southward over the spit

probably would not accumulate in the channel because it would be carried over,

through, or seaward of the channel and continue downcoast. Such bypassing, if

not accounted for, would contribute to an overestimation of shoaling by the spit

growth estimates. On the other hand, a portion of the southward transport

probably moves over the submerged spit without enlarging it, i.e., without

settling on the south tip and contributing to its annual growth rate. This portion

of the transport could still become trapped in a channel and therefore would

contribute to an underestimation of channel shoaling by the spit growth approach.

The volume bypassing the channel here tentatively assumed to be only negligibly

larger than that bypassing the spit, i.e., transiting over the spit without

contributing to its annual growth. Under these assumptions, overestimates

approximately balance underestimates, and the growth rate of the spit

approximates a background shoaling rate for any fixed channel across the

Willapa Bay ebb shoal.

Resulting rates. Figure 3-15 shows three mature spits for which progressive

southward growth is well documented by the charts. The volumes contained

under the spit surfaces, above the plane of 20 ft (mllw) depth, and south of the

line of dissection (approximately the proposed location for North Channel

Alternative 3A) are shown in Figure 3-16. These volumes must equal the

product of the average growth rate (on the vertical axis) times the duration of spit

growth (segment on the horizontal axis). On this 1- to 2-decade scale, the

average annual net rate of transport onto the spit varied between 1.5 and

3.1 million cu yd/year.

These derived rates are at the upper limit of reported longshore transport

rates, but they are for an area where wave-driven longshore transport is

supplemented by strong tidal transport in the bay entrance. The magnitudes seem

appropriately large and are not inconsistent with the magnitude of maintenance

dredging from the Columbia River and coastal estuaries in Oregon (U.S. Army

Engineer District, Portland 1988). The large volumes of annual spit growth and

their variations from one episode to the next are the first observations consistent

with accepting the assumptions inherent in the spit growth approach to estimate

shoaling rates. Another approach based upon annual bafhymetric changes is

discussed in the next section.

Approach II: Estimates using annual bathymetry changes

Presentation of 1998-99 changes across the entrance. The most detailed

and accurate surveys to date of the Willapa Bay entrance are those of 1998 and

1999. Therefore, the best-known volume changes in the areas of the proposed

channels are those for this recent period. The period 1998-99 also coincides with

the most intense hydrodynamic measurements (Chapter 4), modeling of wind

waves (Chapter 5), and modeling of circulation, and sediment transport

(Chapter 6) conducted as part of this study. For these reasons, it will be valuable

to examine the 1998-99 bathymetric changes in detail.

3-24 Chapter 3 Geomorphology
Seattle District aerial photographs

from 10 September 1996 and

USGS quadrangle maps

Oft 6000 ft

f

fi

Figure 3-15. Area of spit above -20-ft-mllw elevation for three episodes for

which the spit growth rate was calculated

Chapter 3 Geomorphology 3-25
_>>

>>

O

0)

TO

a:

c

g

**^

<D

Ü

Ü

<

a>

CO 1

3

20.0 M cuyd 37.5 M cu yd

1933 1941 1960 1971

Spit Dissection, Year

Figure 3-16. Long-term channel shoaling rate estimated from spit growth rates

The 1999 survey covered a much smaller area than the baywide survey of

1998. Interim results obtained in the winter of 1998 had focused attention on

North and Middle Fairways. So, in the spring of 1999, instruments were moved

to the northern half of the entrance and the hydrographic survey confined to this

area. Over the 8.5-month period between these two surveys extensive and

substantial erosion (>10 ft) occurred along inner and outer reaches of the North

Channel. Substantial deposition (thicker than 10 ft) marked both banks of the

inner North Channel and its outer S-curve. Enlargement of the outlet initiated

during the 1997-98 El Nino had continued. Ocean waters moved more directly in

and out of the north channel as the older outlet to the south shoaled. Shoaling

was especially rapid in the north-to-south reach of this older outlet (Figure 3-17).

There appears to have been widespread, but thinner erosion over most of the

offshore area beyond the channels. There also appears to have been substantial

erosion along the north bank of the inner middle channel. These changes are

probably more apparent than real. Although the offshore changes are

widespread, vertical differences there are small; therefore, any datum error could

have contributed to a relatively large part of this apparent erosion. The more

substantial drop in elevations along the inside of the middle channel could be

largely an artifact due to the high resolution of depths around Sand Island by the

SHOALS system in 1998 and the confinement of 1999 soundings to the nearby

deeper channel. Both of these uncertainties are avoided by the methodology

adopted here to estimate channel shoaling.

3-26 Chapter 3 Geomorphology
D

e

P

0

- i>30ft

t

" 10-28

i

0

n

wipr*i,i^2 - 8

F

r 2-8

r

n

:-' MO- 16

0

n wHHB> 18ft

^ow-wnlci- hne

Figure 3-17. Differences between the 1998 and 1999 surveys

The 1998-99 period, as any other year, is only a snapshot in the evolution of

a navigation channel. Rates of erosion (like the winds, waves, and currents that

drive sediment transport) are extremely variable. Long-term trends seen in the

channel cycle further compound the danger of extrapolating from changes

measured in any single year. Integration of 1998-99 changes presented in this

section into a longer term picture are dealt with later in this chapter.

Presentation of 1998-99 in channel templates. Soundings were conducted

over an 87-day period in the summer of 1998. The areas of the Alternative

Channels (used in the approach ofthis section to shoaling estimates) were

surveyed over a shorter period in August ofthat year (Figure 3-2). The area of

Alternatives was resurveyed on 28 and 29 April 1999 except for five

supplemental lines added on 27 May. Differences between the 1998 and 1999

surveys capture the net change over an 8.5-month period.

A template is a geometric form having the dimensions ofthe design

channels. There is a channel template for each Alternative. Alternatives that

differ only in regard to design oftraining structures share the same template.

Volume changes were quantified by calculating volume differences within each

ofseven distinct channel templates associated with the Alternatives that passed

screening (columns 2-4 in Table 3-3), i.e., changes outside the sloping sides of

the templates or beneath their base were not included in this analysis.

In the right-hand portion of Table 3-3, volumes are reexpressed as annual

change rates (obtained by dividing 8.5/12 into the volume measurement). The

volumes are also reexpressed as annual changes in elevations averaged over the

areas ofthe templates. Changes in elevation are easily visualized but should be

Chapter 3 Geomorphology 3-27
considered cautiously, bearing in mind the large area covered by the templates.

Templates are close to 6 miles in length and include sizable areas of negligible or

no change that reduce the impact ofthe large changes in elevation that were

confined to more restricted areas.

In some areas, the templates crossed regions where the natural depths were

uniformly below the template. Over these areas, by the adopted methodology,

cuts and fill are zeroed because they would not affect navigation. It could be

argued that sedimentation below the design depth might eventually raise the

bottom above the channel design depth and, therefore, indicate greater shoaling

potential for that particular channel alternative. This argument is speculative and

disregards the observation that the bottom had not reached the design elevation in

1999. Therefore, it is appropriate to exclude changes below the design depth just

as it is to exclude changes laterally outside the templates.

Ifthe bar channel had been maintained in 1999, the volumes that would have

needed dredging can be judged from either the net volume differences or the

volume offill that accumulated within each template. Net and fill volumes are

given in Table 3-3. To compare modeled bathymetric changes to measured

changes, it may be more informative to look at cut and fill separately.

As indicated by the predominance of erosion (negative changes) in

Table 3-3 none ofthe alternatives would have required much dredging in 1999.

The only net accumulations were in templates 3B and 3G. These accumulations

should not be mistaken as indicating any requirement to dredge Alternatives 3B

or 3G Templates 3B and 3G would not be maintained by dredging. These

templates represent only the most extreme acceptable position of migration for

the North Channel. Before dredging in 1999, it would have been apparent that

dredging operations needed to be relocated to expand newly formed northern

outlets. In considering relative dredging requirements for each alternative, the

implications for Alternative 3A and 3B would be identical for 1999, as would be

the implications for 3F and 3G. None ofthe alternatives would have had

unacceptable dredging requirements in 1999. What, however, do the long-term

statistics imply?

Historical changes over templates. The magnitude of annual sedimentation

can be estimated by averaging year-to-year differences over a long period^ Two

weaknesses are acknowledged. First, the design channels, being deeper than

natural depths, will act as sediment traps and accumulate more sediment than

they would without dredging. There would be no significant increase in tidal

flushing following the increase in channel cross section because the bay already

completely fills during normal tidal cycles as shown in Chapter 5 Therefore no

reduction is expected in sediment trapping. The second neglected aspect m the

annual bathymetry approach is that historical data are probably insufficient to

resolve differences by comparing changes under one design template with those

under another. Soundings were often sparse over the 500-ft-wide templates. The

Seattle District had little need historically to survey details away from the natural

channels. Large areas over the templates were dry land during many ofthe

earlier surveys. The annual bathymetry approach will therefore establish

differences among the alternatives by assigning them to certain classes rather

than examining historical changes within each Alternative template.

3-28

Chapter 3 Geomorphology
Table 3-3

1998 to 1999 Bathymetric Changes Within Templates

Design Depth is 8-Month Change 8-98 to 4-99 Annualized Change Rate

-28 ft mllw

Fill

cu yd

Cut

cuyd

Net

Change

cu yd

Fill Net Change

cuyd cf/sq ft cu yd cf/sq ft

Channel Template 3A

Template Area, sq ft 17,168,038

Above Desiqn Depth 3.7E+04 -8.0E+05 -7.6E+05 5.2E+04 0.1 -1.1E+06 -1.7

Below Desiqn Depth 1.4E+05 -3.8E+06 -3.7E+06

Total 1.7E+05 -4.6E+06 -4.5E+06 2.5E+05 0.4 -6.3E+06 -9.9

Channel Template 3B

Template Area, sq ft 33,155,116

Above Desiqn Depth 1.0E+06 -3.4E+03 1.0E+06 1.4E+06 1.2 1.4E+06 1.2

Below Desiqn Depth 2.4E+06 -2.0E+06 4.3E+05

Total 3.4E+06 -2.0E+06 1.4E+06 4.9E+06 1.1 2.0E+06 1.6

Channel Template 3H

Template Area, sq ft 17,061,317

Above Desiqn Depth 5.7E+05 -1.0E+06 -4.5E+05 8.0E+05 1.3 -6.3E+05 -1.0

Below Desiqn Depth 1.1E+05 -1.7E+06 -1.5E+06

Total 6.8E+05 -2.7E+06 -2.0E+06 9.6E+05 1.5 -2.8E+06 -4.4

Channel Template 4A

Template Area, sq ft 11,923,267

Above Desiqn Depth 2.9E+05 -2.4E+05 5.1E+04 4.1E+05 0.9 7.2E+04 0.2

Below Desiqn Depth 4.0E+05 -4.5E+05 -5.3E+04

Total 6.9E+05 -6.9E+05 -1.7E+03 9.7E+05 2.2 -2.4E+03 0.0

Channel Template 3F

Template Area, sq ft 24,499,897

Above Desiqn Depth 3.1E+05 -3.2E+06 -2.9E+06 4.3E+05 0.5 -4.1E+06 -4.6

Below Desiqn Depth 1.3E+05 -2.3E+06 -2.2E+06

Total 4.3E+05 -5.5E+06 -5.1E+06 6.1E+05 0.7 -7.2E+06 -8.0

Channel Template 3G

Template Area, sq ft 43,596,918

Above Desiqn Depth 3.5E+06 -7.5E+05 2.7E+06 4.9E+06 3.0 3.9E+06 2.4

Below Desiqn Depth 3.7E+05 -3.3E+06 -2.9E+06

Total 3.8E+06 -4.0E+06 -1.6E+05 5.4E+06 3.4 -2.3E+05 -0.1

Channel Template 4E

Template Area, sq ft 39,797,130

Above Desiqn Depth 1.6E+06 -1.7E+06 -9.0E+04 2.2E+06 1.5 -1.3E+05 -0.1

Below Desiqn Depth 4.1E+05 -1.1E+06 -6.8E+05

Total 2.0E+06 -2.8E+06 -7.7E+05 2.8E+06 1.9 -1.1E+06 -0.7

Values "Above Design [

Values "Below Design [

Depth" are related to maintenance dredging.

)epth" are for model corroboration.

Chapter 3 Geomorphology 3-29
Size class. Larger channels have greater capacity for shoaling. All Willapa

Channel Alternatives fall into one of two size classes depending on the cross

section (Figure 3-18). Although not of identical lengths, all the North Channel

templates extend from their respective design depths on the ocean ends to a

common area near the region of the SR-105 project so that the areas are roughly

compatible in terms of comparative shoaling volumes and locations

(Figure 3-19). Little shoaling occurred toward the landward end of the North

Channel templates because the North Channel is naturally wide and deep in this

region. Middle Channel Alternatives were extended over sufficient lengths to

encompass all bathymetric changes that occurred above design depths. Bottom

changes beyond the 1V:3H side slopes of the templates or below their 28- and

38-ft design depths will be zeroed for reasons discussed previously.

The total fill volume within each channel template was obtained as the sum

of the volume differences in all the areas where the terrain model for 1999 was

above that for 1998 (Column 2 of Table 3-3). The calculated cut volume

reported in Column 3 is the negative of the sum of the volumes from all the areas

where the 1999 model was below that of 1998. The net change (Column 3) is the

algebraic sum of cut and fill. Results are summarized in Table 3-3 and given

more fully in Appendix B. Erosion prevailed, but Figures 3-20 and 3-21 show

the spatial isolated areas of significant shoaling inside the templates.

d

\ '

Channel Templates, ft (mllw)

1

Small Large

d 28 38

3

w 500 1000

' tr

^ w. ' w '

Figure 3-18. Two channel cross-sectional designs

3-30 Chapter 3 Geomorphology
low-water line

high water line

miles

low-water line

high-water line

miles

Figure 3-19. Seven channel alternatives for which geomorphic-based estimates

were made of shoaling rates. Top panel shows 500-ft-wide, 28-ftdeep (mllw) alternatives and bottom panel shows 1,000-ft-wide,

38-ft-deep alternatives

Chapter 3 Geomorphology 3-31
538000 3A

534000

530000

7260Ü0 730000 734000 738000 740000 744000

3F

536000-

532000- ^^! •&7*4^^^

528000-

726000 730000 734000 738000 742000 744000

533C0O

•^32^-

3H

* 531000

ZT

JZ ^"""^^^-Sls?

| 523000 ^SSgteQj

723B00 727000 731000 735000

Easting, ft

733000 743000 747000

10

-10-

15

•201

1

20

10

10

-20-

I

10

10

•15-

20-

•25"

Figure 3-20. Shoaling and deepening in the shallower alternatives, 1998-1999.

Note: shoaling was confined to a small area of the outer bar in

Alternative 3A

3-32 Chapter 3 Geomorphology
533000 3B

531000 /fl SJS*--"~"i

-^-.—-^T%>>.

529000 N5P ' ' /

N^

723000 7270D0 731000 735000 739000 743000

526000

722000 725000 730000 734000 738000 742000 746000

522000 4A

"" "^^S^^

520000-

"rN-

518000- Is^**^^

724000 728000 732000 736000 740000

522000 4E

d> 520000 fejäj^~-

1

o 518000 2

^Eifete^ fljgffira? ^T£>^

724000 728000 732000 736000 740000

Easting, ft

744000 748000 752000

15-

10-

-10-

15-

-20-

251

15-

10-

o10-

15-

-20-1

20-

15-

10"

30-

20-

10-

•10-

20-

Figure 3-21. Shoaling in the deeper alternatives, 1998-1999

Chapter 3 Geomorphology 3-33
Dredging requirements are less ifthe maintained channel is allowed to

migrate from year to year in a manner that takes advantage ofnatural channel

migration. The Willapa Channel Alternatives fall into one oftwo classes based

on position: stationary or migrating. Alternative 3B is in the migrating class.

Positions of 3B migrate between positions represented by the 3A and 3B

templates in Figure 3-20. Alternative 3F allows the channel to migrate between

positions represented by Templates 3F and 3G. The other Alternatives are in the

stationary class, i.e., dredging would maintain a fixed channel location from year

to year as the entrance bathymetry and natural channels evolved around the

navigation channel.

Table 3-3 indicates the savings obtainable from the migrating channel design.

During the interval 1998-99, no material shoaled in the 3A template. By the

assumptions ofApproach II, it is inferred that no maintenance would have been

required in 1999 if 3A had been the maintained channel in 1998. For the same

period, 1 million cu yd shoaled in Template 3B. Alternative 3B is a migrating

design, so maintenance is not inferred from this 1-million-cu-yd shoaling in a

fixed geodetic template, but from shoaling that would have occurred along the

migrating thaiweg as long as the channel met navigation requirements. For 1999,

Alternative 3B would have required moving the authorized channel (and buoy

markers) to the newly opened northwest outlet in the position ofthe 3A template.

So, from the measurements (Table 3-3) zero maintenance is inferred for both the

stationary 3A and the migrating 3B. Likewise, zero maintenance is inferred from

the 1998-99 changes in the wider migrating Alternative 3G even though nearly

3 million cu yd accumulated in the S-curve that 3G occupied in 1998 (compare

net changes, Table 3-3).

Similar comparisons with the historical data would not be particularly useful.

Earlier soundings were too sparse or did not cover template areas, and the

variations in historical shoaling from year to year are noisy compared with spatial

differences between alternatives. Therefore, historical volume changes have

been calculated where the data are more suitable and used to estimate shoaling by

channel classes.

Historical changes over data-dense areas not congruent with

Alternatives. The data are suitably dense in time for the dates shown in

Table 3-4 and dense spatially for the areas shown in Figure 3-22. The templates

shown in Figure 3-22 are not the templates for the Channel Alternatives, but are

thought to provide better historical data that are used to evaluate classes of

Alternatives. Concentrating on fill that accumulated between surveys as most

important for maintenance dredging estimates, the historical fill rates usually are

in the range of 1-3 million cu yd/year. Assuming that the 16 cases in Table 3-4

are equally relevant to any ofthe Channel Alternatives, the average annual

shoaling of 2.5 million cu yd/year can be adopted as an approximate background

level ofshoaling for any fixed channel across the northern part ofthe bay

entrance.

3-34 Chapter 3 Geomorphology
low-water line

high-water line

mi les

km

CHNL TMPLT 67-72. |j|rFlv~-w^

1998 Bathymetry

Dike &

Groin

i

-28 ft

Figure 3-22. Additional areas in which shoaling statistics were calculated (contour

elevation is with respect to mllw)

Size of template. The data from Tables 3-3 and 3-4 also verify the concept

that the potential for shoaling goes up with increased cross section. Prior

navigation studies have proposed methods for estimating shoaling that depend

only on examination of historical bathymetric surveys of existing channels. For

constant channel widths, Vincente and Uva (1984) proposed that the shoaling

rates remain proportional to the difference between the actual channel depth and

an equilibrium depth. The equilibrium depth could be determined by curve

fitting to historical depth changes. Trawle and Herbich (1980) proposed a

simpler relationship in which the percent increase in shoaling is equal to the

percent increase in channel volume. Rather than adopt one of these empirical

methods, the Willapa bathymetry provides a direct relationship that is expected to

produce more accurate estimates. Note that in Figure 3-23 a nearly linear

relationship exists between bathymetric changes in the large and small templates

at Willapa. This relationship will be used in estimating shoaling for various

classes of Alternative Channels

Stationary versus migrating Alternatives. Position is one of the classes

used to estimate shoaling by the bathymetric change approach. A much smaller

background shoaling rate is appropriate for migrating channels. The approximate

background level for Alternatives 3B and 3G will be based on the rates measured

in 1999 and on the observation that bar depth and width have always remained

fairly steady in the North Fairway except during years when outlets are either

growing or being sealed off in response to initiation of a new outlet to the

northwest across the spit.

Chapter 3 Geomorphology 3-35
Resulting rates. Table 3-5 summarizes 1998-99 volume changes in ways

that will be input to a lifetime shoaling rate. Net differences between these two

particular surveys indicate widespread erosion. These "negative shoaling" rates

are not considered typical, but several relationships based on the historical

volume changes still apply to this atypical year. The magnitude of fills is similar.

The linear relationship between volumes trapped in 28- and 38-ft-deep templates

also agrees with that obtained using historic data.

Table 3-4 provides the statistics for estimating a background shoaling that

would apply to any channel over the long term. This background shoaling rate

exceeds the historical dredging rates (Table 2-1). Geomorphic methods are

inexact, but the difference between past dredging volumes and estimated future

requirements seems reasonable because past practice did not maintain the

presently proposed channel dimensions.

Approach III: Lifetime dredging requirements

Lifetime dredging estimates are helpful for developing relative costs of the

different Alternatives. For the stationary Alternatives, the lifetime requirements

are simply the initial dredging costs plus the sum of annual maintenance costs

over the lifetime of the project. Both components can be approximated well

enough so that at least the relative ranking of stationary Channel Alternatives is

robust. The migrating Alternatives require more consideration.

Table 3-4

Historical Volume Differences Within Templates in Data-Dense Areas

Changes Under Various Channel Footprints Annualized Change Rate

Design Depths

Referenced to mllw

Area

sqft

Fill

cu yd

Cut

cuyd

Net

Change

cu yd

Fill Net Change

cu yd cf/sq ft cuyd cf/sq ft

ChIN TMPLT (50-66

July 1961 - October 1960 Elapsed Time, years = 0.75

Above Desiqn Depth (28 ft) 1.6E+07 4.0E+05 -1.7E+06 -1.3E+06 5.3E+05 0.9 -1.7E+06 -3.0

Above Design Depth (38 ft) 2.9E+07 3.8E+06 -3.2E+06 5.9E+05 5.1E+06 4.6 7.8E+05 0.7

July 1962-July 1961 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.6E+07 3.9E+05 -1 .OE+06 -6.3E+05 3.9E+05 0.7 -6.3E+05 -1.1

Above Desiqn Depth (38 ft) 2.9E+07 9.4E+05 -3.1E+06 -2.2E+06 9.4E+05 0.9 -2.2E+06 -2.0

July 1963-July 1962 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.6E+07 4.5E+05 -4.3E+05 2.5E+04 4.5E+05 0.8 2.5E+04 0.0

Above Desiqn Depth (38 ft) 2.9E+07 1.8E+06 -1.5E+06 2.7E+05 1.8E+06 1.7 2.7E+05 0.3

July 1964 -July 1963 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.6E+07 5.1E+05 -2.5E+05 2.6E+05 5.1E+05 0.9 2.6E+05 0.4

Above Desiqn Depth (38 ft) 2.9E+07 2.0E+06 -6.8E+05 1.3E+06 2.0E+06 1.8 1.3E+06 1.2

August 1965 - July 1964 Elapse Time, years = 1.08

Above Desiqn Depth (28 ft) 1.6E+07 8.3E+05 -4.1E+05 4.2E+05 7.6E+05 1.3 3.9E+05 0.7

Above Desiqn Depth (38 ft) 2.9E+07 2.2E+06 -2.0E+06 1.8E+05 2.0E+06 1.8 1.6E+05 0.1

(Continued)

3-36 Chapter 3 Geomorphology
Table 3-4 (Concluded)

Changes Under Various Channel Footprints Annualized Change Rate

Design Depths

Referenced to mllw

Area

sqft

Fill

cu yd

Cut

cu yd

Net

Change

cuyd

Fill Net Change

cu yd cf/sq ft cu yd cf/sq ft

CHN TMPLT 60-66

July 1966-August 1965 Elapse Time, years = 0.92

Above Desiqn Depth (28 ft) 1.6E+07 2.4E+06 -3.0E+05 2.1E+06 2.7E+06 4.6 2.3E+06 4.0

Above Desiqn Depth (38 ft) 2.9E+07 6.4E+06 -7.1E+05 5.7E+06 7.0E+06 6.4 6.2E+06 5.7

CHN TMPLT 67-72

August 1967-July 1966 Elapse Time, years = 1.08

Above Desiqn Depth (28 ft) 1.5E+07 6.5E+05 -3.8E+05 2.7E+05 6.0E+05 1.1 2.5E+05 0.5

Above Desiqn Depth (38 ft) 2.7E+07 1.9E406 -1.1E+06 7.8E+05 1.7E+06 1.7 7.2E+05 0.7

July 1968-August 1967 Elapse Time, years = 0.92

Above Desiqn Depth (28 ft) 1.5E+07 7.8E+05 -1.8E+05 5.9E+05 8.5E+05 1.6 6.5E+05 1.2

Above Desiqn Depth (38 ft) 2.7E+07 2.9E+06 -3.7E+05 2.5E+06 3.1E+06 3.1 2.7E+06 2.7

July 1969 -July 1968 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.5E+07 1.6E+06 -1.1E+05 1.4E+06 1.6E+06 2.9 1.4E+06 2.7

Above Desiqn Depth (38 ft) 2.7E+07 3.0E+06 -6.8E+05 2.4E+06 3.0E+06 3.0 2.4E+06 2.3

July 1970-July 1969 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.5E+07 7.6E+05 -7.5E+05 1.6E+04 7.6E+05 1.4 1.6E+04 0.0

Above Desiqn Depth (38 ft) 2.7E+07 1.9E+06 -1.7E+06 2.1E+05 1.9E+06 1.9 2.1E+05 0.2

July 1971-July 1970 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.5E+07 7.7E+05 -6.5E+05 1.2E+05 7.7E+05 1.4 1.2E+05 0.2

Above Desiqn Depth (38 ft) 2.7E+07 1.8E+06 -1.6E+06 2.0E+05 1.8E+06 1.7 2.0E+05 0.2

July 1972-July 1971 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.5E+07 9.0E+05 -3.5E+06 -2.6E+06 9.0E+05 1.7 -2.6E+06 -4.8

Above Desiqn Depth (38 ft) 2.7E+07 2.3E+06 -7.2E+06 -4.9E+06 2.3E+06 2.2 -4.9E+06 -4.9

August 1973-July1972 Elapse Time, years = 1.08

Above Desiqn Depth (28 ft) |l .5E+07 5.7E+05 -1.8E+06 -1.2E+06 5.3E+05 1.0 -1.1E+06 -2.0

Above Desiqn Depth (38 ft) |2.7E+07 2.0E+06 -4.0E+06 -1.9E+06 1.9E+06 1.9 -1.8E+06 -1.8

CHN TMPLT 80s

July 1981 - April & May 1981 Elapse Time, years = 0.21

Above Desiqn Depth (28 ft) 1.4E+07 1.6E+05 -7.4E+05 -5.8E+05 7.8E+05 1.5 -2.8E+06 -5.5

Above Desiqn Depth (38 ft) 2.6E+07 1.2E+06 -2.6E+06 -1.4E+06 5.8E+06 6.0 -6.7E+06 -7.0

August 1982 - July 1981 Elapse Time, years = 1.08

Above Desiqn Depth (28 ft) 1.4E+07 3.0E+05 -5.2E+05 -2.2E+05 2.8E+05 0.5 -2.1E+05 -0.4

Above Desiqn Depth (38 ft) 2.6E+07 8.6E+05 -2.5E+06 -1.7E+06 8.0E+05 0.8 -1.5E+06 -1.6

July & August 1983 - August 1982 Elapse Time, years = 1.00

Above Desiqn Depth (28 ft) 1.4E+07 4.6E+04 -5.6E+05 -5.2E+05 4.6E+04 0.1 -5.2E+05 -1.0

Above Desiqn Depth (38 ft) 2.6E+07 3.5E+05 -1.7E+06 -1.4E+06 3.5E+05 0.4 -1.4E+06 -1.4

Chapter 3 Geomorphology 3-37
T!

(1) >^

^5

(J

_i ^_^

£ CO

<1) ro

c

CO

r

3

o

o

O ^ ,

<i> <1)

E C3

3 Qo

>

Fill DNel

9.E+06

~ 7.E+06

5.E+06

3.E+06

1.E+06

-1.E+06

£ -3.E+06

§ -5.E+06

-7.E+06

y = 2.025x +599511

-3.0E+06 -2.0E+06 -1.0E+06 0.0E+00 1.0E+06 2.0E+06 3.0E+06

Volume Change in Small Template (500x28ft), cu yd

Figure 3-23. Relative shoaling rates for the two template cross sections

Table 3-5

Summary Of Initial Dredging and Volume Changes in Templates, 1998-1999

Template Description

Initial Cut

cuyd

1998-1999 Survey Changes, cu yd

Cut Fit! Net

3A* North Channel Straight 7.60E+05 -8.00E+05 3.70E+04 -7.60E+05

3B* North Channel 1,500 ft on curves 4.30E+04 -4.20E+03 1.00E+06 1.00E+06

3D Raise SR-105 Dike

3E North Channel with Jetty

3F*

3A, but 38- x 1,000-ft channel

dimensions 5.70E+06 -4.20E+06 3.40E+05 -3.80E+06

3G*

3B, but 38- x 1,000-ft channel

dimensions 4.20E+06 -1.20E+06 3.60E+06 2.40E+06

3H* Straiqht seaward from off SR-105 dike 2.10E+06 -1.40E+06 5.70E+05 -7.90E+05

4A* Middle Channel bar dredging 2.20E+06 -3.80E+05 5.30E+05 1.40E+05

4B Bay Center training structure with 4A

4C Dredging across whole entrance with 4B 9.40E+06 -3.90E+05 5.70E+05 1.80E+05

4D Willapa River training structure with 4A

4E*

4A, but 38- x 1,000-ft channel

dimensions 1.20E+07 -1.60E+06 2.80E+06 1.20E+06

Grand Averaqe 4.60E+06 -1.20E+06 1.20E+06 -5.90E+04

Averaqe for 1,000- x 38-ft cross section 2.20E+06

Averaqe for 500 -x 28-ft cross section 5.20E+05

Averaqe for Template 3B 4.00E+04

*Altematives 1 hat passed screening.

3-38 Chapter 3 Geomorphology
The concept of a migrating Channel Alternative is to allow the authorized

and buoyed channel to be moved slightly from year to year within prescribed

bounds to take advantage ofthe fairly constant channel cross section historically

maintained by nature even as the channel migrated. Because ofthe strong

channel migration cycle at Willapa, this means that the maintained channel

would shift systematically southward, rotating counterclockwise, and usually

increasing in curvature over a series ofyears. When the natural channel no

longer supports safe navigation, a new channel will be dredged through the spit

in a position to provide favorable navigation for a number ofsubsequent years.

The number ofsuch channel relocations can be estimated from the geomorphic

history of natural channel migration.

Avoidance of extreme curves and south heading. The Port of Willapa

Harbor identified the 1999 channel as the maximum safe southward channel

deflection. In the past, deflection created unsafe conditions for years in

succession (Appendix A). Examples of extreme unsafe deflection are shown in

Figure 3-24 along with the worse-case acceptable condition under

Alternative 3B. If Alternatives 3B or 3G were adopted, dredging would be

necessary at intervals to force establishment of a new northwest outlet along the

line of Alternative 3A or 3F, respectively. The number of years nature has taken

to complete channel cycles and establish a new northwest outlet are tabulated in

Table 3-6. Also shown are the number of years before these new outlets captured

the main flow, before unacceptable channel deflection reoccurred, and finally

before the next outlet was initiated.

Timing of the natural cycle with navigational requirements. Table 3-6

shows five episodes during which new outlets formed an average of 1.6 years

after the channel developed an undesirable deflection (DUD). An average of

4.5 years elapsed after DUD before the new outlet completely dissected the Cape

Shoalwater spit to a depth of 18 ft mllw and the severed shoal began migrating

away from the spit. An average of 6 years after DUD, the new outlet captured

the main flow ofthe north channel. Historically, the Coast Guard moved marker

buoys to the new outlet at about this time (6 years after DUD). So, Alternative

3B and 3G would have to shorten the natural 12-year channel cycle by 6 years on

the average to avoid undesirable deflection. This analysis highlights the

distinction between the Seattle District's past dredging practice (which followed

the migrating channel until the new outlet dominated, Table 3-6) and Alternatives

3B and 3G which would relocate the channel as needed. Again, 1998-99 was not

a typical year. The naturally occurring new outlet gained dominance in time so

that no relocation would have been required to switch the authorized channel

back to the northwest in time to avoid an unsafe curved channel.

The lifetime dredging requirement for a migrating Alternative is the sum of

initial dredging, annual maintenance, and occasional relocation dredging. A

modest volume would be dredged annually to eliminate isolated shoals and

facilitate continuous marking ofthe channel. Larger volumes will be dredged

less frequently to avoid unsafe navigation by relocating the entire approach

channel. To apply this concept, the project lifetime is set to 50 years, the

duration oflow-maintenance dredging is set to 6 years, and typical shoaling rates

are inferred from rates ofspit growth and shoaling within the templates

(Tables 3-3 and 3-4).

Chapter 3 Geomorphology 3-39
deeper-36 H"3610

"

30 H"30 t0

~

24 H"24to-18 [ |-18 to MLLWL

| | MLLWL to HWL Qhigher HWL

Figure 3-24. Alternative 3B avoids tight curve and long north-south run typical of

natural channels

The resulting dredging estimates are thus based on simplifying assumptions,

past natural bathymetric changes, and an average channel cycle description

assuming the past can serve as an indication ofthe future. Furthermore it is

assumed the new dredging project will not significantly alter the long-term rates

or cycles. The only known mechanism that would change past rates is not

quantifiable, but will be discussed in the last section ofthis chapter.

Combining components into a lifetime estimate. For Alternatives 3G and

4E a typical volume change rate of 2.5 million cu yd/year is taken as

representative ofthe measurements combined from different approaches

(Figure 3-16, Table 3-3 and 3-4). This background shoaling rate is multiplied by

50 years to estimate the lifetime estimate for these two Alternatives. For

migrating Channel Alternative 3B, it is assumed that a new outlet will have to be

dredged across the Cape Shoalwater spit at intervals of every 6 years. After

calculating the volume that Template 3B would cut into bathymetry from

different years, a typical value of 1 million cu yd was adopted to represent the

3-40 Chapter 3 Geomorphology
Table 3-6

Basis for Mixture of Low- and High-Volume Dredging Requirements for

Templates 3B and 3G

Events in the Willapa Channel Cycle

Years Between Undesirable Navigation and

New Outlet

Initiation

of New

Outlet

Dissection

of Shoal

New Outlet

Dominates

Navigation

Switches

Undesirable

Curve for

Navigation Initiation Dissection Dominance

Navigation

Switched

1886

1918 1922 1924 1924 1932

1933 1934 1936 1935 1939 0 2 4 3

1940 1942 1945 1945 1953 1 3 6 6

1954

Outlet initiated in 1954 grows and migrates south for 5 years, but fails to capture the main flow and

shoals over in 1959.

1959 1960 1961 1961 1967 6 7 8 8

1970 1973 1973 1973 1999 3 6 6

1997 200? 200?+ 1999 -2

Average Life 1.6 4.5 6 5.75

Column 1 gives the year of the chart first showing evidence of a new outlet starting to erode into the Cape

Shoalwater Spit.

Column 2 shows the years that new outlets extended entirely across the ebb shoal with depths >18 ft.

Column 3 shows the years that new outlets became larger in cross section than the older outlet.

Column 4 indicates the first year when District records indicate navigation switched to the newer outlet.

Column 5 indicates the first year when the navigation channel developed an S-shape and the North-to-South

passage that appears similar to the 1998 condition was identified by the Port of Willapa Harbor as barely acceptable

for navigation.

larger dredging amount that would relocate the channel every 6 years. The

amount of dredging that would have been required for the initial cut of

Alternative 3B into 1998 was similar to the amount that shoaled into 3B during

the 1998-99 period (Table 3-3). This average was adopted as the lower

maintenance estimate for the years between major channel relocations. Estimates

for the other four Alternatives were derived using the relationship between large

and small template trapping shown in Figure 3-18. Assumptions and final

estimates are summarized in Table 3-7.

This concludes a description and application of a methodology that should be

reapplied with revised input (especially for the initial dredging requirements) if

the project is not adopted until some later phase of the channel cycle.

Discussion of Geomorphic Findings

A prominent channel occupied the North Fairway on all of the examined

historical charts (1952-1984) and all of the recent surveys. Channels first

appeared in the Middle Fairway on the 1928 chart and in the South Fairway in

1936. Middle and South fairways had clear channels on less than 20 percent of

the full-entrance charts produced between 1852 and 1978. This stark difference

in frequencies of channels in the three fairways suggests that conditions only

infrequently favored a short-lived Middle or South Fairway channel. There is no

indication that this tendency changed in recent years.

Chapter 3 Geomorphology 3-41
Table 3-7

Lifetime Dredging Estimates

Components from Geomorphic Analysis

2.27 to 3.70 Background shoaling rate (million cu yd/year) measured in large cross-section at fixed

locations which agrees with independent results from the spit-growth approach

(Fiqure3-16)

0.45 to 0.81 Background shoalinq rate (M cu yd/vear) for Alternative 3B

1.00 to 1.67 Estimated dredqinq required to relocate 3B (M cu yd)

Y = 2.21X+.44 Relationship between larqe (Y) and small (X) cross-section trapping (M cu yd/year)

1.72 Standard deviation of estimated annual shoalinq rate within channel templates (ft)

6 Interval between required relocate of Alternatives 3G and 3B (years)

50 Project life (years)

Estimated 50-year Dredging Requirement, million cu yd/year

Template

Excluding Initial Dredging

Total With Initial Dredging Based on

Conditions Like Those of 1998 (Table 3-5)

Lower Estimate Upper Estimate Lower Estimate Upper Estimate

3A 42 74 43 75

3B 27 48 27 48

3F 114 185 120 191

3G 58 102 62 106

3H-a 42 74 44 76

3H-b 42 74 44 76

4A 42 74 44 76

4E 114 185 126 197

There is no significant trend to bar depths with time for any fairway. Bar

depth and orientation of the channel over the bar follow patterns consistent with a

cycle of approximately 12-year average duration for the North Fairway.

Undesirable alignment of the bar channel with respect to the waves has been a

major obstacle to safe passage in and out of Willapa Bay (Chapter 2, Chapter 3).

Changes in orientation of smaller channels in the South and Middle are linked to

the same 12-year cycle that dominates the North Fairway. South and Middle

fairway channel size is, however, more closely related to a much longer term

trend. A minor channel began off Leadbetter Point in 1945, grew gradually, and

migrated slowly north to finally become the prominent channel in the middle of

the entrance on the 1993 63rd edition National Oceanic and Atmospheric

Administration chart of Willapa Bay. This channel represented the culmination

of a 50-year growth-migration trend that ended around 1992. As evidenced in

the 1998 and 1999 surveys, the middle channel continues diminishing as the

ocean end fills.

The initial dredging quantities that would have been required in 1998 were

largest for Middle Channel Alternative 4A and smallest for North Channel

Alternative 3B. Rapid changes occurred between the 1998 and 1999 surveys, so

that Alternative 3A and 3B share the designation as the alternatives requiring

least initial dredging for 1999.

3-42 Chapter 3 Geomorphology
Two independent approaches for estimating maintenance requirements

indicated shoaling rates of at least several million cubic yards/year for any

fixed-position channel located in the northern two-thirds of the entrance (North

or Middle Fairways). This estimate pertains to typical years with potentially

many more millions of cubic yards fill during severe years. Although the

geomorphically based shoaling rates depend on assumptions considered as only

approximately valid, internal consistency suggests these large inferred rates are

reasonable, but probably low. The assumption used to derive these rates, that the

volume of sand bypassing channel templates during surveyed years is the same as

would bypass the channel Alternatives, underestimates shoaling by an amount

that can not be quantified from geomorphology. Two observations suggest

underestimation. First, without increased flushing, bigger channels will tend to

trap more sediment per unit channel area than natural channels. Second, depth

and width parameters tabulated from the historical charts were not significantly

greater for years when charts were based on postdredging soundings than they

were based on either predredging charts or charts depicting conditions when no

dredging had occurred for a year or more. This lack of identifiable increases in

channel size attributable to dredging suggests that rapid shoaling can quickly fill

dredged (artificially deepened) areas returning the total cross-sectional area to

equilibrium. Historical conditions never included deeply dredged channels that

correspond to the proposed Alternatives. So, past bathymetric changes do not

include direct evidence of the increased shoaling expected with the larger

proposed Alternatives. A portion of this increased shoaling rate related to

channel size was inferred empirically (Figure 3-18), but results in this chapter do

not include any increase corresponding to increased specific trapping efficiency.

Combining initial and maintenance estimates from the geomorphic analyses

indicates the migrating Alternatives, 3B and 3G, would minimize lifetime

dredging requirements. In contrast, Alternatives 3F and 4E would require the

most dredging. Dredging estimates are intermediate for the other Alternatives.

Further distinction among Alternatives on the basis of lifetime of dredging

requirements inferred strictly from historic changes does not appear warranted.

The infrequent occurrence of any middle channel does, however, compound

concern that Alternatives 4A and 4E would shoal rapidly.

The long-term steadiness of natural channel dimensions (tabulated over the

bar), the small difference between the shallower design depth and the apparent

equilibrium bar depth in the North Fairway, and the low rate of bathymetric

change calculated by repositioning channel templates from year to year (to

follow the natural channel) show that considerable savings are possible if the

authorized channel were allowed to migrate. The maintained channel did migrate

during earlier dredging episodes. Future plans would avoid past unsafe

north-to-south deflection of the channel by relocating the channel to the north

about 6 years earlier than nature normally moves the main flow. Artificially

advancing the natural timetable of channel relocation was not part of the earlier

dredging programs.

Allowing the channel to follow nature within safe limits is the

geomorphically based key for reducing dredging requirements. Other channel

design criteria must, however, be considered in the final evaluation (Chapter 8).

In conclusion on geomorphology, two migrating Channel Alternatives were

postulated at the onset of the study. The other Alternatives were stationary by

Chapter 3 Geomorphology 3-43
definition. Some of the cost savings achievable with migrating channels could be

incorporated into the other North Channel Alternatives by modification of

definitions given for this study.

References

Andrews, R. S. (1965). "Modern sediments of Willapa Bay, Washington: A

coastal plain estuary," University of Washington Oceanography Technical

Report 118, University of Washington, Seattle, WA.

Guenther, G. C, Thomas, R. W., and LaRocque, P. E. (1996). "Design

considerations for achieving high accuracy with the SHOALS bathymetnc

lidar system." Laser remote sensing ofnatural waters: From theory to

practice, selectedpapers. The International Society of Optical Engineering,

54-71.

Inman, D. L., Jenkins, S. A., and Elwany, M. H. S. (1996). "Wave climate

cycles and coastal engineering practice," Proceedings, 25th International

Conference on Coastal Engineering. B. L. Edge, ed., American Society of

Civil Engineers, New York, 314-327.

Komar, P. D. (1986). "The 1982-83 El Nino and erosion on the coast of

Oregon," Shore and Beach 54(2), 3-12.

. (1997) The Pacific Northwest Coast: Living with the shores of

Oregon and Washington. Duke University Press, Durham, NC.

. (1998). "The 1997-98 El Nino and erosion on the Oregon coast,"

Shore andBeach 66(3), 33-41.

Kranz. (1986). "Appendix D: Historic sunken vessels in the vicinity of Grays

Harbor, Washington," Willapa Bay Interim Ocean Dredged Material

Disposal Site Designation Study, prepared for the U.S. Army Engineer

District, Seattle, by Shapiro and Associates, Inc., Seattle, WA.

Lillycrop, W. J., Irish, J. L., and Parson, L. E. (1997). "SHOALS system - Three

years of operation with lidar bathymetry experience; capability and

technology advancements," Sea Technology 38(6), 17-25.

Lowell, S. M. (1997). "Geological study of the North Channel of Willapa Bay -

Vicinity of North Cove, Washington," Contract Report, Washington State

Department of Transportation, Olympia, WA.

Moore, G. W., and Cole, J. Y. (1960). "Coastal processes in the vicinity of Cape

Thompson, Alaska," Trace Elements Investigations Report 753, U.S.

Geological Survey, Ruston, VA, 41-55.

Quinn, W. H., Zopf, D. O., Short, K. S., Yang, R. T. W. K. (1978). "Historical

trends and statistics of the Southern Oscillation, El Nino, and Indonesian

droughts," Fishery Bulletin 76, 663-378.

Richey, E. P., Dean, R. G, Ekse, M. I., and Kent, J. C. (1996). "Considerations

for the temporary arresting of the erosion at Cape Shoalwater, Washington,"

State of Washington, Department of Conservation, Olympia, WA.

o_44 Chapter 3 Geomorphology
Shepsis, V., Hosey, H., and Phillips, S. (1996). "The use of dredged material for

erosion control at North Cove, Washington," Proceedings, 15th World

Dredging Congress 2, Western Dredging Association, Center for Dredging

Studies, College Station, TX, 811-819.

Seymour, R. J. (1998). "Monitoring coastal change in Southwest Washington

and Northwest Oregon during the 1997-98 El Nino," Shore and Beach 66(3),

3-6.

Swan, J.G. (1857). "The northwest coast, or three years' residence in

Washington Territory," University of Washington Press, Seattle, WA.

Terich, T., and Levenseller, T. (1986). "The severe erosion of Cape Shoalwater,

Washington," Journal ofCoastal Research 2(4), 465-477.

Trawle, M. J. and Herbich, J. B. (1980). "Prediction of shoaling rates in

offshore navigation channels," Department of Civil Engineering, Texas

A&M University, College Station, TX.

U.S. Army Engineer District, Portland. (1998). "Portland District Dredging

Records," AVG93-97/TS CENWP-OP-NWC, Portland, OR.

U.S. Army Engineer District, Seattle. (1949) "Willapa Harbor Washington,

surveys of bar channels from 1852 to 1931," File E/4/2/49, Seattle, WA.

Vincente, C. M., and Uva, L. P. (1984). "Sedimentation in dredged channels

and basins - prediction of shoaling rates." Proceedings, 19th International

Conference on Coastal Engineering. American Society of Civil Engineers,

NY, 1863-1878.

Chapter 3 Geomorphology 3-45
4 Field Data Collection and

Analysis1

The Willapa Bay field data collection program was executed by EvansHamilton, Inc. (EHI) under task-order contract with the U.S. Army Engineer

Research and Development Center (ERDC), Vicksburg, MS. The program

incorporated measurements of waves, currents (point measurements and profiles

through the water column), water level, salinity (conductivity and temperature),

wind velocity, air temperature, and air pressure. Each of three field deployments

included five wave and current stations, four combined water-level and salinity

recording stations, and one weather station. Wave and current instruments were

arranged on the same bottom mounts, and stations were divided geographically

into two groups as the entrance gauges and as the inner, or back-bay, gauges.

Water-level recording stations were distributed around the periphery of the bay

and in the river channels. The weather (meteorological) station was deployed

near the center of Willapa Bay, approximately 10 m above the water surface.

The instruments stored data internally, with measurement times referenced to

Greenwich Mean Time (GMT). Two cruises were conducted to measure

baywide variations in the current structure and to define the vertical density

(salinity) structure of the water column.

Data collection was conducted both for project-specific objectives and for

documenting the existing physical processes as a baseline for monitoring

changes, should channel dredging take place. Project-specific objectives

concerned primarily acquisition of data to verify numerical simulation models of

the bay hydrodynamics (Chapter 6) and the waves at the entrance to Willapa Bay

(Chapter 5). The data also served to characterize the hydrodynamic environment

at the Willapa Bay entrance for assessing navigation reliability of the various

project design alternatives discussed in Chapter 2.

The data collection program was initially developed at the ERDC Coastal

and Hydraulics Laboratory (CHL), to meet the project objectives, including

selection of instruments, rates and duration of sampling, and length of

deployments. EHI subsequently reviewed and offered recommendations for the

program. The instrument types and suites were based on experience of CHL in

data collection at the mouth of the Columbia River and in other projects. EHI

1 Written by Mr. Keith Kurrus, Ms. Carol Titus, Mr. Ken FitzGerald, and Ms. Suzanne Giles of

Evans-Hamilton, Inc., and Dr. Vladimir Shepsis and Mr. Hugo Bermudez of Pacific International

EngineeringPLLC.

Chapter 4 Field Data Collection and Analysis 4-1
constructed mounts to house the instruments based upon cumulative experience

in data collection at Willapa Bay and similar ocean-estuary environments.

Wave Measurements

A combination of directional and standard wave measurements (wave height

and period) was made during the Willapa Bay field effort. Two types of systems

were deployed, and station locations are shown in Figure 4-1. For the entrance

gauges (Stations 1, 2, 3 and 10,11,12), directional wave measurements were

made with SonTek, Inc., Hydra instruments incorporating a SonTek AcousticDoppler Velocimeter (ADVOcean) probe coupled with a Paroscientific, Inc.,

digi-quartz pressure sensor. Current and pressure readings were collected once

an hour, starting at the top of the hour, and instruments were set to collect

4,096 data points at 2 Hz. For the back-bay gauges (Stations 4,5, and 13),

pressure readings were collected with a digi-quartz pressure sensor connected

externally to a SonTek Acoustic Doppler Profiler (ADP). Pressure readings

were collected once an hour, starting 1.5 min before the hour, recording

1,024 data points at 1 Hz.

The ADPs coupled with a Paroscientific pressure sensor operated with two

sampling schemes, one for measuring currents and one for measuring waves.

Because the current data were averaged over 3-min intervals and centered at the

top of the hour, the pressure data had to be synchronized with the current

readings, causing the awkward start time. All pressure sensors had a measuring

range of 0-45 psia. Field service dates and the parameters measured at each

station are summarized in Table 4-1.

Instruments were deployed on the seabed on two types of mounts, either on a

tripod or on a trawl-resistant frame. Mounts were selected based on the

anticipated sediment type, predicted waves and currents, and site-specific

characteristics that would have bearing upon the success of the data collection

effort. Tripods provide the flexibility of mounting multiple instruments on one

deployment package while maintaining a stable platform. They also provide

some protection from instrument burial by shifting sand. Figure 4-2 shows a

tripod with an ADP current meter and a Hydra system mounted on the tripod.

The trawl-resistant frames were originally designed to provide protection for

the instruments mounted in the frame and to incorporate a low profile to avoid

damage by local vessel activity. Trawl-resistant frames also possess a wider

footprint to hinder settling in softer sediments.

Before deployment, one or two cross-channel bathymetry transects were

obtained to aid the placement of each instrument package. Deployment and

recovery positions were recorded during both deployment and retrieval cruises.

The survey vessel was equipped with differential Global Positioning System

(GPS) (Trimble DSM-Pro), which provides ±l-m accuracy. Water depths were

measured with an echosounder on the survey vessel. Bar checks were conducted

to calibrate the echosounder. Deployment and recovery information is

summarized in Tables 4-2 and 4-3.

4_2 Chapter 4 Field Data Collection and Analysis
Figure 4-1. Location of current meters and wave gauges (triangles), waterlevel gauges (circles), and meteorological station (squares)

in Willapa Bay

Chapter 4 Field Data Collection and Analysis 4-3
Table 4-1

Willapa Bav Data-Collection Schedule

Station No.

Parameters

Measured

1998

Deployment 1 Deployment 2 Deployment 3

August September |October

Deployment 4

November | December

Waves

1

1 Current speed, current

direction, temperature,

pressure, pitch, roll,

and heading

26th -10th 10th -9th 9th -18th

2

1 25th -9th 11th -7th 14th -17th

3

1 25th -9th 11th -7th 14th -11th

10'

111

12'

Wave Height & Period

3 Pressure 17th- 16th

4 26th -9th 10th -13th 14th -11th

5 25th -10th 10th -12th 14th -12th

13 17th- 17th

Currents

1 Current speed, current

direction, temperature,

pitch, roll, and heading

26th -10th 10th -9th 9th -18th

2 25th -9th 11th -7th 14th -17th

3 25th -9th 11th -7th 14th -11th 17th- 16th

4 26th -9th 10th -13th 14th -11th

5 25th -10th 10th -12th 14th -12th

13 17th- 17th

MicroCAT

1 Conductivity and

temperature

26th -10th 10th -9th 9th -18th

Water- Level Gauges

4 J Conductivity,

temperature, and

pressure

26th -9th 10th -13th 14th -11th

6 (South Bend) 13th -16th 16th -21st 21st -17th 17th- 17th

7 (Nahcotta) 12th -15th 15th -22nd 22nd -17th 17th- 18th

8 (Naselle River) 12th -15th 15th -22nd 22nd -18th 18th- 18th

9 (Bay Center) 11th -16th 16th -21st 21st -17th 17th- 17th

13 17th- 17th

Meteorological Station

Bay Center

Channel Light,

Number 2

Wind speed, wind

direction, air

temperature, and

barometric pressure

12th -11th 11th -7th 7th -17th 17th- 17th

Field Service Dates

Waves/Currents 24th - 26th 9th-11th 7th-9th &

11th-14,h

11th-13th&

16th-18th

16th-17th

Water-Level

Gauges

(Stations 6-9)

11th-13th 15th-16th 21st-22na 17th -18th 17th-18th

Meteorological

Station

12th 4th & 11th 7"' 17th 17th

ADCP Transects"* 17th -18th

Profiling CTD

Survey

16th -18th

directional.

2ADCP = Accoustic

3CTD = Conductivity

function of depth.

Doppler Current Profiler

(, temperature, and depth (pressure) sensor - primarily deployed to measure water salinity as a

4-4 Chapter 4 Field Data Collection and Analysis
Figure 4-2. Tripod mount as deployed in Willapa Bay

Data reduction and quality control procedures for wave

measurements

Processing and analysis of the Willapa Bay wave data were performed by

Pacific International Engineering (PIE) under the direction of ERDC. The work

included quality assurance checks of the recorded data and spectral analysis.

Five stations were occupied; the three located at the entrance measured

directional waves, and the two in the bay measured non-directional waves.

Wave data from each deployment were first checked for inconsistencies by

developing time-series plots of heading, pitch, and roll recorded by each

ADVOcean or ADP instrument. Pressure time-series were generated and

analyzed to identify discrepancies in the record. Deployment and recovery

information is summarized in Table 4-2.

Chapter 4 Field Data Collection and Analysis 4-5
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Chapter4 Field Data Collection and Analysis 4-7
Equipment locations, sampling configurations, and mounting parameters are

summarized in Table 4-3. As noted in Table 4-2, one ADVOcean flooded during

two separate deployments, shorting out the compass card. The compass card

measures pitch, roll, and heading, which are used to convert the three measured

beam velocities to velocities referenced to earth coordinates. Current speeds

from the flooded ADVOcean looked reasonable, but the directions were

obviously wrong. Data were corrected by using the compass values from the

ADP mounted on the tripod above the ADVOcean, and incorporating the ADP

compass values to calculate velocities referenced to earth coordinates. Quality

checks for all deployments determined that the data were good.

Wave energy spectral analysis was performed to determine adequate

high-frequency cutoff values. Energy distributions by frequency and direction

were plotted for each data burst collected at each station. Typical spectra for the

offshore station showed a single or double peak arriving at periods between 8

and 16 sec, indicating swell arriving from offshore (Figure 4-3).

Energy spectra for stations located east of the outer bar (inside the mouth of

the bay) did not usually exhibit a distinct energy peak, with energy spread across

frequency (periods between 4 and 10 sec). Figure 4-4 shows typical spectra at

Station 2 (inside bay) throughout a tidal cycle. The plots show a decrease in

energy density as ebb current speed increases and an increase in energy density

as the flood current speed increases.

The differences in spectral shape between the offshore station and those

inside the bay (specifically changes in wave energy distribution by frequency)

are most likely caused by a combination of depth-limited wave breaking over the

outer bar and the neglect, in the analysis, of changes in wavelength induced by

currents. These changes in wave energy distribution by frequency made the task

of choosing a high-frequency cutoff for the inner bay stations difficult. The

following high-frequency cutoff recommendations by CHL were applied in the

processing:

a. Station 1: 0.25 Hz.

b. Station 2: 0.21 Hz.

c. Station 3: 0.21 Hz.

d. Station 4: 0.25 Hz.

e. Station 5: 0.25 Hz.

Wave data for all stations were analyzed with the wave data analysis

standard, spectral analysis program developed by ERDC and the Field Wave

Gaging Work Unit at ERDC, Vicksburg, MS.1 Routine processing of the wave

data did not include changes in wavelength produced by wave-current

interaction.

1 Earl, M. D., McGehee, D. D., and Tubman, M. W. (1995). "Field Wave Gaging Program wave

data analysis standard," Instruction Report CERC-95-1, U.S. Army Engineer Waterways

Experiment Station, Vicksburg, MS.

4_3 Chapter 4 Field Data Collection and Analysis
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Chapter 4 Field Data Collection and Analysis 4-9
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Water Depth- 13.7 m

Current Speed - 35.5 cm/s

Current Direction -107 deg

0.1 0.15

Frequency (Hz)

Figure 4-4. Energy density plots for Station 2

4-10 Chapter 4 Field Data Collection and Analysis
Wave height time series were generated and comparisons were made

between Stations 1 through 5 and records from the buoy deployed at Grays

Harbor, Washington. Figure 4-5 shows the wave height time-history for

Deployment 2. Wave heights from Station 1 were similar to the wave heights

collected from the Grays Harbor buoy. However, inside the bay, daily changes

in wave height and peak period corresponded primarily to changes in

water-surface elevation.

Figure 4-6 shows a comparison of Station 1 (west of the outer bar) and

Station 2 (east ofthe bar) wave height and peak period during a typical tidal

cycle. Figure 4-7 also shows water depth, current speed, and significant wave

height on 3 October 1998.

ADVOcean averages of current speed and direction are shown in Table 4-4

for Deployment 3.

Table 4-4

ADV Data Averages 10-9-98 to 11-18-98

Station No.

Mean Current Speeds cm/sec

Mean Current Direction deg Relative to

True North

Ebb Flood Ebb Flood

1 16.5 10.9 287.7 76.6

2 41.1 27.3 312.0 111.0

3 44.6 40.5 263.5 99.1

Current Measurements

To define the current regime within the Willapa Bay study area, two

measurement strategies were incorporated into the field plan. First, current

meters were moored to obtain time series at specific locations (Figure 4-1).

Second, to define regional variations in the structure ofthe current, and to better

define the net movement ofwater in particular channels, the current was

measured along transects. Transect data were recorded with a profiling Doppler

current meter (RD Instruments (RDF), Acoustic Doppler Current Profiler

(ADCP)) mounted over the side of a moving vessel. The instrument is capable

ofbottom tracking, which removes the velocity ofthe moving vessel from the

recorded current data to retrieve the current velocity profile. Field service dates

and the parameters measured at each station are summarized in Table 4-1.

Moored current measurements

Moored current measurements were made with ADPs. Current and wave

instruments were deployed on the same bottom mounts as discussed in the wave

measurement section (Figure 4-2).

Chapter 4 Field Data Collection and Analysis 4-11
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4-12 Chapter 4 Field Data Collection and Analysis
Figure 4-6. Comparison of Stations 1 and 2 wave heights and peak periods

Chapter 4 Field Data Collection and Analysis 4-13
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Chapter 4 Field Data Collection and Analysis
Five ADPs were deployed. Three of the five ADPs were configured with

optional external sensors. One ADP was configured with a Sea-Bird Electronics,

Inc., MicroCAT, and two ADPs were configured with Paroscientific, Inc., digiquartz pressure sensors. Equipment locations, sampling configurations, and

mounting parameters are summarized in Table 4-3. Current stations that

included directional wave measurements (entrance gauges - Stations 1,2, and 3)

were set to record 10-min averages, once every 20 min, and averages were

centered on the top of the hour. ADPs configured with a digi-quartz pressure

sensor (back-bay gauges - Stations 4, 5, and 13) were set to record 3-min

averages, once every 6 min, and averages were centered at the top of the hour.

Currents were also incorporated in the directional wave measurements

discussed in the wave measurement section. Three ADVOcean gauges were

deployed at Stations 1, 2, and 3, and the sampling volume was located

approximately 1 m above the seafloor.

Data reduction and quality control procedures for moored current

meters

The current meter data were processed with a combination of manufacturer

and in-house programs. Both ADPs and ADVOceans recorded in binary format.

Following instrument retrieval, data files were downloaded and converted from

binary to text (ASCII) file format. Subsequent data processing for the two

instrument types involved different procedures as described in the following

paragraphs.

Initial quality assurance/quality control (QA/QC) procedures for the ADP

current meters were to generate amplitude data files for all beams and to inspect

those files to verify that all current meters worked correctly. Pitch, roll, and

heading data were then plotted to verify that the mooring remained upright and in

place throughout the deployment. Each data file generated by SonTek software

was then combined into one file to display the data as profiles. The ADPs were

set to profile beyond the anticipated water depth to ensure that tidal fluctuations

were included in the data. Profiles were edited to remove the erroneous data

beyond the water depth by reference to both the pressure readings from the ADP

or ADVOcean (if no pressure sensor was available on the ADP) and the recorded

ADP beam amplitude data. The beginning and end of each file were removed for

any data collected while the moorings were not deployed. Direction values were

converted from degrees magnetic to degrees true north, decimal Julian dates

calculated, and profiles vertically averaged. The vertically averaged profiles

were then sent to the CHL FTP site.

The ADVOcean current meters were set to sample in burst mode for

4,096 data points at 2 Hz, once an hour. Bursts were averaged to obtain one

reading per hour, and directions were converted from degrees magnetic to

degrees true north. The beginning and end of each file were removed if data

were collected while the instruments were not in the water. Averaged data were

merged with the header files to add a time stamp to the record, and decimal

Julian days were calculated prior to sending the data to the CHL FTP site.

Chapter 4 Field Data Collection and Analysis 4-15
For a final check of the data, vector time series plots were generated for each

station location. Each plot contained vectors for the averaged ADP profile, the

bottom ADP bin, and the averaged ADVOcean data where applicable (Stations 1,

2, and 3).

In addition to current measurements, the ADP at Station 1 had a MicroCAT

installed, which measured conductivity and temperature. Temperature and

conductivity values were recorded at the beginning of each sample interval and

stored in the header file. Salinity values were calculated, the measurements were

time stamped, and the data files transferred to the CHL FTP site.

General properties of the moored current meter data

Table 4-5 shows 28-day statistics for Deployments 1, 2, and 3 for both the

ADP and ADVOcean current meters. One should note, for Deployment 1, the

statistics calculated were for 15 days because of the short deployment length, and

caution is warranted when comparing these values with the 28-day averages for

Deployments 2 and 3. Data quality was good with two exceptions:

(a) Mooring 5 during Deployment 1 tipped over after day 3, and the current data

are unusable following this event, and (b) the ADVOceans at Station 3

Deployment 1 and Station 1 Deployment 2 flooded, rendering the compass

unusable. Data were corrected by using the compass values from the ADP

mounted on the tripod above the ADVOcean, and incorporating the ADP

compass values to calculate velocities referenced to earth coordinates.

Measurements of the current at the five stations within Willapa Bay show

both site-specific and seasonal trends. Beginning with the seasonal trends, there

was generally a small increase in the velocity with each successive deployment at

all stations over the months of August through November.

As will be further discussed in the section, "Meteorology," measured wind

speed increased over the months of August through November (Figures 4-22

through 4-25). Periods of stronger wind are evident in the current records. Three

events of note occurred during 16-19 September, 1-4 October, and

12-17 November. All winds were from the south, producing northerly flowing

currents. The exception to this was Station 5, which showed little or no visible

influence of wind, but this station is well protected in the south end of the bay.

Direction of the current was site specific. The current at Station 1 had a

north-south flow, exhibiting an alongshore flow pattern. Station 1 was also

influenced by the prevailing wind. As the wind direction changed during the

deployment months from northerly to southerly, the current flowed

predominantly to the north in October and November. Directions of the current

for Stations 2 and 3 were roughly mirror images of each other. Station 2 had a

northwest to southeast flow pattern, and Station 3 had a southwest to northeast

flow pattern. The measurements for both stations were strongly influenced by

their location within the Middle Channel and their proximity to the surrounding

shoals. Station 4, located near the entrance to Willapa River, had an east-west

flowing current, which would be expected because of the orientation of the river.

The current at Station 5 in Nahcotta Channel was directed southwest and

northeast, which was consistent with the orientation of the channel.

4-16 Chapter 4 Field Data Collection and Analysis
Table 4-5

Statistics for Current Records

Deployment

No.

Site

No.

Start

Date End Date

Mean

Temp

deg C

Residual

E-W

Current

cm/sec

Residual

N-S

Current

cm/sec

Mean

Speed

cm/sec

Maximum

Speed

cm/sec

Residual

Speed

cm/sec

Net

Direction

deg True

North

Total

Variance

cm2/sec2

1 (15 day) ADP1 08/26/98 09/10/98 8.8 3.7 0.4 12.4 46.5 3.7 84 182

ADV1 08/26/98 09/10/98 8.7 2.4 -0.6 8.3 33.0 2.5 103 94

ADP2 08/26/98 09/09/98 11.3 -14.1 6.1 47.1 153.5 15.4 293 3,091

ADV2 08/26/98 09/09/98 11.1 -12.4 4.1 42.9 152.1 13.1 288 2,565

ADP3 08/26/98 09/09/98 11.6 6.7 -1.4 47.7 126.0 6.9 101 2,991

ADV3 08/26/98 09/09/98 11.7 1.4 -2.2 41.1 109.0 2.6 147 2,181

ADP4 08/26/98 09/09/98 15.1 3.7 1.6 37.8 93.4 4.0 67 1,897

ADP5 08/26/98 09/09/98 Mooring turned over near beginning of deployment - no available data

2 (28 day) ADP1 09/11/98 10/08/98 10.9 -1.2 3.7 14.4 80.1 3.8 342 304

ADV1 09/11/98 10/08/98 10.7 -1.0 0.3 9.6 69.4 1.0 285 180

ADP2 09/11/98 10/07/98 12.3 -8.0 5.3 44.9 167.8 9.6 303 2,716

ADV2 09/11/98 10/07/98 12.2 -6.0 4.7 29.2 137.1 7.7 308 1,317

ADP3 09/11/98 10/07/98 12.6 8.7 -1.1 46.8 115.4 8.8 96 2,789

ADV3 09/11/98 10/07/98 12.4 4.5 -2.3 36.3 88.1 5.0 117 1,673

ADP4 09/10/98 10/05/98 14.4 -3.0 1.2 37.1 103.1 3.3 292 1,842

ADP5 09/11/98 10/08/98 16.4 -0.2 -0.3 36.9 86.4 0.4 216 1,644

3 (28 day) ADP1 10/10/98 11/06/98 12.8 0.3 4.8 16.2 65.4 4.8 4 331

ADV1 10/10/98 11/06/98 12.7 -0.8 4.2 11.2 53.8 4.3 349 183

ADP2 10/15/98 11/11/98 12.8 -8.5 9.8 51.5 196.1 13.0 319 3,478

ADV2 10/15/98 11/11/98 12.6 -3.9 11.2 39.4 154.3 11.8 341 2,181

ADP3 10/14/98 11/10/98 12.8 -2.9 -5.5 54.0 165.9 6.2 208 3,699

ADV3 10/14/98 11/10/98 12.6 -4.3 -4.5 43.1 133.5 6.3 224 2,346

ADP4 10/14/98 11/10/98 13.0 -5.3 0.9 38.4 122.4 5.4 280 2,008

ADP5 10/15/98 11/11/98 12.6 -0.6 -1.4 34.9 87.2 1.5 202 1,483

ADCP transect cruises

Over-the-side Doppler current measurements were collected in midNovember 1998 during a spring-tide condition. Measurements of the current

were made in conjunction with the profiling CTD cruise. The purpose of the

over-the-side current measurements was to obtain discharges across the various

channels at the mouth and head of the bay during both ebbing and flooding tides.

The discharges indicate the net movement of water into and out of the bay. In

addition, the transect measurements provide information on the regional variation

of the current structure across the channels.

An RDI Broadband 600-kHz ADCP was mounted on the port side of a vessel

during transects across the bay. Navigation information was obtained with a

Trimble GPS station with differential capabilities. Configuration of the ADCP

for the cruise is detailed in Table 4-6. Setup of the instrumentation occurred on

16 November. Communication with all systems was verified, and configuration

files were created.

Chapter 4 Field Data Collection and Analysis 4-17
Table 4-6

ADCP Configuration Parameters

Parameter

Cell (bin) size

Blank after transmit cell size

Pings per ensemble

Time between pings

Average (ensemble) interval

Magnetic offset

Maximum bottom tracking depth

Value

0.5 m

0.5 m

Osec

4 sec

19deg

30 m

Transect cruises were conducted on 17-18 November 1998. Current data

were collected in three geographic regions displayed in Figure 4-8. Transects in

the south bay across Nahcotta and Stanley Channels were obtained on

17 November. Fifteen transects were measured across the south bay

(Figure 4-9). Visibility was low during the first 2 hr of data collection because of

fog. Difficulties were also encountered during the first day when navigation data

were not collected by the data acquisition software. Bottom tracking was

functional, so ship speeds were still subtracted from the recorded current

measurements. As a backup for the lost navigation data, time and ship position

displayed on the GPS were handwritten in a field log at approximately 5-min

intervals. Positions were recorded by hand along all transects during the

remainder of the cruise. Total discharge as reported on the display monitor was

noted in the field log for each transect.

Transects 1 through 12 were traversed during the flood tide, and Transects 13

through 16 were traversed on the ebb tide (note: there is no Transect 2). Transits

across the south bay on the ebb tide were frequently split into two transect files

because of the presence of a shoal between the two channels. The depths over

the shoal were generally too shallow for the ADCP to collect data. Transects on

the flood tide were located further north than the ebb-tide transects because the

water at the original transit area was too shallow for the boat to safely operate

without grounding. Because of the northern location of the flood tide transects,

measurements were possible across the complete channel without having to split

the transect into two separate files.

4-18 Chapter 4 Field Data Collection and Analysis
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Figure 4-8. ADCP transects in Willapa Bay, 17-18 November 1998

Chapter 4 Field Data Collection and Analysis 4-19
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Figure 4-9. ADCP transects in southern Willapa Bay, 17 November 1998

The final two transects on 17 November (17 and 18) were made outside the

entrance to Bay Center (Figure 4-10).

Transects near the mouth of the bay were obtained on 18 November. Nine

transects were made on this date, five on the morning flood tide and four on the

afternoon ebb (Figure 4-11). Because of the wave action and exposed shoals

during the early part of the flood tide, transects were completed across the mouth

of the Willapa River (Transects 23, 25, and 26) and across the entrance to the

southern channels (Transects 21 and 22). On the ebb tide, with higher water

levels and calmer seas, a box pattern of transect measurements was obtained at

the mouth of the bay (Transects 29 through 32). Problems were encountered

occasionally with bottom tracking during times of stronger current. When

bottom tracking was lost, navigation was recorded; thus, ship motion was

continually subtracted from the measured currents.

Data reduction for ADCP transect cruises

Data were collected and partially processed with RDI Transect software that

accompanies the ADCP. ASCII profiles created in Transect were further

manipulated with EHI software to produce depth-averaged vectors with location

fixes for each profile.

4-20 Chapter 4 Field Data Collection and Analysis
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RDI Transect calculates values for discharge along a channel section while

the ship is underway. These values were recorded in the log at the conclusion of

each channel-crossing transect. Two methods were used to fix the profile

locations. Transects 1 through 23 use bottom track information to find location.

Transects 25 through 32 use GPS coordinates to record location.

For Transects 1 through 23, current speed was obtained by removing the

bottom-track velocity, but no coordinate stamps were recorded in the profiles.

Transect software records bottom-track displacement north (AN) and

displacement east (AE) with each profile. Consulting logged coordinates for the

beginning of each transect made correcting possible by the AN and the AE values

recorded for a profile to arrive at a location for that profile.

Transects 25 through 32 had GPS coordinate stamps in the ADCP profiles.

These coordinates were read for each profile and reissued with the depthaveraged values in the final output. Speed and direction were plotted for each

transect to verify that software output conformed to expected values. Attention

was focused on transects with reciprocal tracks to verify that ADCP headalignment corrections were accurate, giving similar current profiles on all

courses.

Chapter 4 Field Data Collection and Analysis 4-21
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General properties of the ADCP transect data

As noted in the "ADCP transect cruises" section, the ADCP transects were

collected during a spring tide the week of 16 November (Figure 4-12).

Figure 4-13 provides an expanded view of the water-level variation for the data

collection days, with markers indicating at what tidal stage each transect was

measured. For both days, approximately the same number of transects were

traversed on the flood tide as for the ebb tide. Transport and regional current

structures for each measurement day are reviewed in the following paragraphs.

Discharge is defined as the total volume of water flowing through a cross

section. The ADCP measures discharge in cubic meters per second for each

ensemble and yields a sum of the discharge for each transect. Table 4-7 lists the

summed discharge values for each transect measured at the southern end of the

bay. Negative discharge indicates southward or flooding flows, and positive

discharge indicates northward or ebbing flows. For the location of each transect,

refer to Figure 4-9. The tidal height referenced to meters mllw at the beginning

of each transect is also listed in Table 4-7.

4-22 Chapter 4 Field Data Collection and Analysis
Figure 4-12. Predicted tide for 3 weeks in November 1998

£ 8

17 November 1998

£ 8

S 4

23 25 26

18 November 1998

Figure 4-13. Water level for ADCP transect collection days (circles denote tidal

stage each transect was collected, and numbers refer to transect

number)

Chapter 4 Field Data Collection and Analysis 4-23
Table 4-7

Discharge Values for South Willapa Bay

Transect Number

1

10

11

12

13

14

15

16

Location Description

South Channel

Nahcotta Channel

Stanley Channel

Stanley Channel

Shoal Area

Nahcotta Channel

Nahcotta Channel

Shoal Area

Stanley Channel

Stanley Channel

Nahcotta Channel

South Channel

South Channel

South Channel

South Channel

Discharge, cu m

-9,407

-7,585

-3,781

-3,340

-990

-3,472

-2,320

870

-61

664

6,404

8,718

5,802

5,873

9,801

Tidal Height, m (mllw)

2.07

2.59

2.71

2.93

3.05

3.11

3.26

3.26

3.23

3.20

3.02

2.65

2.47

2.32

2.19

Discharges summed across all channels on the mid-ebb and flood tides were

approximately equal. For example, Transects 1 and 16 were collected near the

same location at roughly the same stage on the flooding and ebbing tides,

respectively. The sums of other transects indicate this same result. The total for

Transects 5, 6, and 7 on the flooding tide equals -7,802 cu m/sec, and the total

for Transects 11 and 12 on the ebbing tide was +7,068 cu m/sec.

The shoal area between Nahcotta and Stanley Channels showed smaller

discharges than expected. It also exhibited the first ebbing discharge values

(Transect 9) while the two channels were still flooding (Transects 8 and 10).

Depth-averaged current speed across Stanley Channel ranged between 10 and

60 cm/sec, with peak speed reaching about 70 cm/sec. The current range had less

variability for the Nahcotta Channel at 30-50 cm/sec with peaks reaching about

75 cm/sec. Current speed to the north of both channels ranged from 40 to

80 cm/sec with peaks reaching 100 cm/sec.

Table 4-8 lists the summed discharge values for the transects measured at the

north end of the bay. Transect locations are displayed in Figure 4-11.

Table 4-8

Discharge Values for North Willapa Bay

Transect Number

21

22

23

25

26

29

30

31

32

Location Description

Southern Mouth

Southern Mouth

Willapa River

Willapa River

Willapa River

Outer Mouth

Outer Mouth

Southern Mouth

Willapa River

Discharge, cu m

-27,042

-28,079

-8,872

-6,308

1,033

14,472

11,520

23,008

10,530

Tidal Height, m (mllw)

2.23

2.56

2.80

2.90

2.80

2.41

2.01

1.55

1.46

Discharge at the mouth of the bay shows the same directions as that for the

southern bay, outbound on the ebb tide and inbound on the flood. One major

difference was the magnitude, which showed a factor of 10 increase.

Comparisons between the ebb- and flood-tide discharges were more difficult to

4-24 Chapter 4 Field Data Collection and Analysis
make for this area because of the inability to occupy all transect areas during the

same phase of the tide. However, some general comparisons can be made. For

example, discharges for Transects 21 and 22 compared reasonably well with

discharge for Transect 31. Similar comparisons can be made between

Transects 23 and 26 at the mouth of the Willapa River.

Increases in the current at the bay entrance as compared with the southern

transects of the previous day were also evident. Current speed on transects across

the southern mouth ranged between 50 and 120 cm/sec. Current speeds across

the mouth of the Willapa River were in the range of 20 to 100 cm/sec, averaging

around 50 cm/sec. The least variable current speeds across transects were seen at

the outer mouth area. Current speed for Transects 29 and 30 ranged between

approximately 60 and 80 cm/sec.

Water Level and In Situ Conductivity and

Temperature Measurements

Much of the water exchange between Willapa Bay and the Pacific Ocean is

tidally driven, and any quantification of the flow in the bay will depend upon the

predicted tide level throughout the bay.

Instruments and field procedures

Conductivity, temperature, and pressure data were collected using Sea-Bird

Electronics, Inc., SBE 26-03 tide gauges. Tide gauges were installed at

Stations 6, 7, 8, and 9 (Figure 4-1 and Table 4-9).

Gauges were set to record 3-min averages every 3 min. Three-minute

averages were synchronized to logging times of the four gauges to begin at

01:30 min before the hour so that the first average each hour centered at the top

of the hour.

Table 4-9

Water Level Station Locations and Measured Parameters

Station

Number

Location

Description

Latitude

deg N

Longitude

degW

Elevations Relative to

Toke Point, m (mllw)

Sensors Bay Floor

6 South Bend 46 40.110 123 48.771 -1.276 -1.65

7 Nahcotta 46 30.098 124 01.430 -0.632 -1.15

8 Naselle River 46 25.794 123 54.374 -1.674 -2.13

9 Bay Center 46 37.404 123 56.844 -1.762 -3.13

Gauges were mounted on pilings in swinging pipe brackets that allowed

servicing without diving. Work on the gauges was done in small boats by

swinging the pipe up and away from the base of the piling. After data download

and battery change-out, the pipe was returned to vertical with the gauge

reoccupying the elevation prior to servicing. All tide gauge mounts performed

well over the duration of the project with no slippage relative to the pilings.

Chapter 4 Field Data Collection and Analysis 4-25
Data reduction

Water levels at Stations 6, 7, 8, and 9 were derived from subsurface pressure

records. This derivation was made using the United Nations Educational,

Scientific and Cultural Organization (UNESCO) 19831equation of the state for

seawater density. Water level was then referenced to Toke Point mllw datum

using offsets measured during a leveling survey of the gauge locations relative to

National Geodetic Survey benchmarks.

Tide gauge water level

Total pressure (barometric pressure plus water pressure) was recorded at

each water-level station, and barometric pressure was logged hourly at the EHI

meteorological station in the Bay Center Channel. During data processing,

atmospheric pressure values were subtracted from the recorded water-level data.

The equation of state of seawater was used to calculate local seawater density

in the area of the gauge based upon measured gauge pressure, salinity, and

temperature. Depth of the gauge was calculated from density, pressure, and

gravitational acceleration for the 40°N latitude.

Survey to Toke Point datum

The leveling survey accessed in this study was performed by the Washington

Department of Ecology (WDOE).2In summary, water level at marked times was

surveyed to the North American Vertical Datum of 1988 (NAVD 88) vertical

datum by means of Real-Time Static GPS. Observations were taken to National

Geodetic Survey (NGS) 2-cm standards using two control stations for each site.

Each site was occupied twice over consecutive days.

An offset from NAVD 88 to Toke Point mllw was established by consulting

published National Ocean Service (NOS) and NGS data sheets. The end product

of this survey was water-level height to Toke Point mllw established at each site

for a known time.

Gauge water level to Toke Point datum

By taking the water-level record from a tide gauge for the time of the

elevation water-level survey to Toke Point mllw, it was possible to create an

individual offset for each tide gauge, correcting the gauge-derived water level to

a Toke Point mllw reference. This correction based on observed conditions at a

known time was unique to each gauge installation and provided consistent

reference regardless of hydraulic conditions within the individual pressure cell.

1 Fofonoff, N. P., and Millard, Jr., R. C. (1983). "Algorithms for computation of fundamental

properties of seawater," UNESCO technical papers in Marine Science 44.

Daniels, R. (1998). Letter report to Evans-Hamilton, Inc. on the Washington Coastal Gauge

Control Project as part of a U.S. Army Corps of Engineers study on Willapa Bay, p. 14.

4-26 Chapter 4 Field Data Collection and Analysis
With this process, it was possible to reference all four tide measuring gauges

to an existing mllw datum at Toke Point with the assumptions that water density

above the gauge was homogenous and that barometric pressure was stable over a

60-min period.

Data trends

Data from all water-level gauges were plotted after processing to observe

trends and check quality. Figure 4-14 shows a sample plot of Deployment 4 at

Station 9.

Processed data showed strong tidal signals in salinity and temperature at river

Stations 6, 8, and 9. Station 7 in Nahcotta Harbor showed less variance in

salinity and temperature.

Unknown factors periodically dampened tidal fluctuations in salinity at

Station 6 in South Bend. Salinity became stable over several days and then

returned to a tidally varying signal. Sensor malfunction is not the most likely

source of unusual stability followed by a strong variance in amplitude. Other

sources of this variance may be saline discharge from an adjacent oysterprocessing industry or biological activity interfering with the flow of water

through the conductivity cell. Little bio-fouling was noted on the water-level

gauges at all stations.

Profiling CTD Survey

Purpose of data collection

Profiling Conductivity Temperature Depth (PCTD) data were collected to

determine the vertical structure of the water column within Willapa Bay. PCTD

casts were taken on high- and low-slack tides during a spring tidal sequence.

Instruments and field procedures

Salinity data were collected with a Sea-Bird Electronics, Inc., SBE-19

Profiler. The conductivity cell, the temperature sensor, and pressure gauge had

been calibrated within the preceding year. This instrument derived salinity from

conductivity measurements; likewise, density was calculated from temperature

and salinity.

All stations were sampled on both a high-slack and low-slack tide with the

exception of Station 11, which was not sampled on a low-slack tide because of

weather constraints. Pertinent station information is listed in Table 4-10. Station

position was determined by means of differential GPS. In addition to stations

within the bay channels, PCTD measurements were taken at the tide gauges.

Once on station, the instrument was soaked at the water surface for roughly

3 min to allow the sensors to equilibrate. The instrument was then lowered

through the water column at a rate of approximately 20 cm/sec, allowed to gently

touch bottom, and then raised back to the surface. Data were downloaded at each

station and checked in the field for data quality.

Chapter 4 Field Data Collection and Analysis 4-27
22

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Site 9: Bay Center Deployment 04, S/N 213

10/25

10/25 11/01 11/08 11/15

1

11/08

1

11/15

1

Figure 4-14. Example of tide gauge data, Station 9, Deployment 4

11/22

11/22

11/22

11/22

11/22

11/22

4-28 Chapter 4 Field Data Collection and Analysis
Table 4-10

Profiling Conductivity Temperature Depth (PCTD) Survey Information

Date

Time

(downcast)

GMT

Julian Day

(downcast)

GMT

Station

No. Tide

Latitude

deg N

Longitude

degW

Maximum

CTD

Depth, m

Echosounder

reading, m

11/17/98 15:28:37 321.6448669 1 Low 46 40.133 123 48.710 6.5 7.0

11/17/98 18:46:24 321.7822164 1 High 46 40.133 123 48.710 9.0 9.1

11/17/98 15:11:07 321.6327141 2 Low 46 41.178 123 49.066 10.0 10.1

11/17/98 18:57:10 321.7896991 2 High 46 41.169 123 49.059 10.5 11.6

11/17/98 14:59:01 321.6243229 3 Low 46 42.447 123.50.884 8.5 8.5

11/17/98 19:10:13 321.7987616 3 High 46 42.454 123 50.891 10.5 10.4

11/17/98 14:35:04 321.6076852 4 Low 46 42.160 123 53.356 7.5 7.9

11/17/98 19:23:26 321.8079398 4 High 46 42.167 123 53.333 9.5 9.8

11/17/98 14:03:30 321.5857639 5 Low 46 41.606 123 55.678 6.0 13.5

11/17/98 19:37:48 321.8179109 5 High 46 41.617 123 55.655 9.0 9.1

11/16/98 20:45:51 320.8651736 6 High 46 41.895 123 58.128 13.5 14.0

11/16/98 23:06:53 321.0464468 6 Low 46 41.916 123 58.097 11.0 11.4

11/16/98 19:30:25 320.8127836 7 High 46 42.285 124 01.636 14.0 13.4

11/17/98 00:49:20 321.0342593 7 Low 46 42.270 124 01.609 11.0 11.6

11/16/98 19:55:25 320.8301447 8 High 46 43.436 124 03.718 25.0 27.4

11/17/98 00:34:06 321.0236806 8 Low 46 43.368 124 03.621 20.5 21.9

11/16/98 19:10:36 320.4656887 9 High 46 41.879 124 03.012 12.5 14.0

11/17/98 00:14:51 321.0103067 9 Low 46 41.843 124 03.121 10.0 10.1

11/16/98 18:30:26 320.7711285 10 High 46 40.382 124 00.775 9.5 9.8

11/16/98 23:50:18 320.9932581 10 Low 46 40.400 124 00.814 8.0 7.9

11/16/98 17:45:26 320.7398843 11 High 46 37.680 123 59.783 11.5 12.5

11/18/98 15:31:01 322.6465451 12 Low 46 35.065 123 58.068 16.5 16.5

11/18/98 19:56:09 322.8306597 12 High 46 35.052 123 58.060 18.0 18.1

11/18/98 15:51:02 322.660434 13 Low 46 33.546 123 56.756 10.0 10.4

11/18/98 20:11:56 322.8416204 13 High 46 33.531 123 56.758 12.0 11.6

11/18/98 15:14:15 322.63489 14 Low 46 32.067 123 59.025 14.0 14.3

11/18/98 20:36:25 322.8593171 14 High 46 32.072 123 59.060 16.0 16.5

11/18/98 16:19:24 322.6801331 15 Low 46 30.739 123 58.319 9.5 9.8

11/18/98 19:28:07 322.8111921 15 High 46 30.745 123 58.325 11.0 11.6

11/18/98 13:53:55 322.5791088 16 Low 46 30.096 124 01.431 3.0 3.0

11/18/98 21:37:09 322.9007986 16 High 46 30.103 124 01.430 5.0 4.0

11/18/98 14:31:20 322.6050926 17 Low 46 29.150 124 00.830 14.0 14.3

11/18/98 20:56:41 322.8726968 17 High 46 29.165 124 00.852 15.5 16.2

11/18/98 16:31:42 322.6886748 18 Low 46 29.192 123 57.797 11.5 11.6

11/18/98 19:14:41 322.8018634 18 High 46 29.172 123 57.795 7.5 13.1

11/18/98 16:44:24 322.6975 19 Low 46 27.978 123 56.486 17.0 17.4

11/18/98 19:00:12 322.7918056 19 High 46 27.935 123 56.453 19.5 13.1

11/18/98 14:48:49 322.617228 20 Low 46 26.723 124 00.300 15.0 14.9

11/18/98 21:11:48 322.8831887 20 High 46 26.738 124 00.301 17.0 17.7

Chapter 4 Field Data Collection and Analysis 4-29
Data reduction

All data were processed with Sea-Bird software. Upcast data and data

recorded while soaking were discarded, leaving the downcast data. Temperature,

salinity, and density data were then averaged into 0.5-m bins to produce a profile

corresponding to saltwater depth. These data were then averaged over the water

column to produce a single datum. The profiles were graphed in Figure 4-15

through 4-21 to illustrate the water column structure and to verify data quality.

In these figures, the plotted variable "PSS" represents practical salinity scale

units, parts per thousand. The density is presented in a, values where o, = (water

density -1 x 103g/cm3).

Data properties

The salinity and density structure for the Willapa River (Stations 1 through

5) greatly differed between high and low tide (Figures 4-15 and 4-16). The

freshwater lens was much larger throughout the river during the low slack than

on the high slack. This lens persisted somewhat at Station 1 (South Bend) on the

high slack, but was less than 2 m thick for the remaining stations. Temperature

throughout the water column did not change.

Unlike the Willapa River stations, the vertical structure for sites within the

central portion of the bay (Stations 12 through 14) remained largely unchanged

between high- and low-slack tides. Although the profile shape did not change,

the salinity during low slack was generally lower than on high slack

(Figure 4-17). Salinity levels at stations in the Naselle River channel

(Stations 15,18,19) varied between the tidal stages; much like the Willapa River

stations, salinity was lower throughout the water column on the low tides

(Figure 4-18). High-slack measurements showed little stratification within the

water column. Nahcotta channel stations (Stations 16,17, 20) showed little

variation between high- and low-slack tides (Figure 4-19). Water temperature

remained constant at all stations.

Vertical profiles for stations located in the northern portion of the bay

(Stations 6 through 11) changed relative to their proximity to the Willapa River

(Figures 4-20 and 4-21). Salinity and density values at Stations 6, 7, and 8

showed a lens on the low slack that was greatly diminished (Station 6) or gone

(Stations 7 and 8) on the high slack. Stations farther removed from the mouth of

the Willapa River showed little or no change between the two tidal stages. As

with all other stations, temperature did not vary.

Meteorology

Instruments and field procedures

A Campbell Scientific, Inc., MetData 1 weather station was installed

12 August 1998 on the Bay Center Channel Light, Number 2 platform near the

center of the study area (Figure 4-1). The MetData 1 weather station measured

wind speed, wind direction, air temperature, and barometric pressure

approximately 10 m above the water surface. All data were stored in a CR10

data-logger and retrieved approximately once a month (Table 4-1) using a

portable computer.

4-30 Chapter 4 Field Data Collection and Analysis
Station 1, Low Slack

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Figure 4-15. Temperature, density, and salinity profiles for stations in Willapa River during

low- and high-slack tides (Stations 1-3)

Chapter 4 Field Data Collection and Analysis 4-31
S

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Figure 4-16. Temperature, density, and salinity profiles for stations in Willapa River

during low- and high-slack tides (Stations 4 and 5)

4-32 Chapter 4 Field Data Collection and Analysis
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Figure 4-17. Temperature, density, and salinity profiles for stations in central Willapa

Bay during low- and high-slack tides (Stations 12-14)

Chapter 4 Field Data Collection and Analysis 4-33
Station 18, High Slack

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Figure 4-18. Temperature, density, and salinity profiles for stations in Naselle River

Channel during low- and high-slack tides (Stations 15, 18, and 19)

4-34 Chapter 4 Field Data Collection and Analysis
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during low- and high-slack tides (Stations 16,17, and 20)

Chapter 4 Field Data Collection and Analysis 4-35
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Bay during low- and high-slack tides (Stations 6-8)

4-36 Chapter 4 Field Data Collection and Analysis
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Bay during low- and high slack-tides (Stations 9-11)

Chapter 4 Field Data Collection and Analysis 4-37
Data trends

Wind speed averages remained steady until November, when a series of

storms caused the average of that month to increase greatly over previous months

(Table 4-11, Figures 4-22 to 4-26). Similarly, wind gusts did not vary greatly

from August through November, but reached a maximum of 23.5 m/sec during

the storms. Net wind direction was from the northwest during August and

September (308 and 307 deg true north, respectively), then shifted to the

southeast during October and November (158 and 160 deg true, respectively).

Air temperature decreased steadily throughout the study period with the

maximum occurring in October (Table 4-11, Figure 4-24).

Average barometric pressure did not vary significantly between August and

November. The lowest reading in November corresponded with a storm and its

associated strong winds.

Table 4-11

Meteorological Data Summary

Parameter Month Average Minimum Maximum

Wind speed, m/sec Auqust 4.2 0.00 12.1

September 3.9 0.01 11.3

October 4.6 0.03 14.2

November 6.6 0.60 17.0

Wind gusts, m/sec Auqust 5.4 0.0 14.7

September 5.1 1.1 14.7

October 6.0 1.1 17.9

November 8.6 1.9 23.5

Air temperature, deg C Auqust 15.4 11.8 18.9

September 13.8 10.1 20.4

October 12.5 5.9 24.3

November 10.3 6.7 13.3

Barometric pressure, mb Auqust 1,019.4 1,014.4 1,026.7

September 1,015.1 1,008.7 1,022.4

October 1,018.0 1,005.6 1,030.0

November 1,014.2 1,000.6 1,021.9

North Channel Borrow Site Monitoring

PIE has been monitoring changes in the North Channel Dredged Borrow Site

that was used for placing material on the shore near SR-105. Monitoring has

included monthly hydrographic surveys starting after completion of the dredging

work. Analysis of the data was performed through bathymetric data contouring,

plotting cross sections of the survey area, and calculating sedimentation rates and

volumes. Survey methodology, survey data processing, and analysis are

presented in this report. The North Channel Borrow Site is shown in

Figure 4-27. This area is referred to as the Borrow Site.

4-38 Chapter 4 Field Data Collection and Analysis
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Figure 4-22. Meteorological data from central Willapa Bay, August 1998

Chapter 4 Field Data Collection and Analysis 4-39
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Figure 4-23. Meteorological data from central Willapa Bay, September 1998

4-40 Chapter 4 Field Data Collection and Analysis
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Chapter 4 Field Data Collection and Analysis 4-41
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Figure 4-25. Meteorological data from central Willapa Bay, November 1998

4-42 Chapter 4 Field Data Collection and Analysis
Mean Wind Speed and Maximum Wind Gust

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Figure 4-26. Meteorological data from central Willapa Bay, December 1998

Chapter 4 Field Data Collection and Analysis 4-43
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4-44 Chapter

4 Field Data Collection and Analysis
Survey methodology

Bathymetric data were acquired with an Innerspace-448 precision survey

echosounder (3-deg narrow-beam transducer) fixed to a 26-ft survey vessel. The

echosounder and positioning equipment were interfaced to a computer-based data

acquisition system running HYPACK (Coastal Oceanographies). A Trimble

DSM-Pro DGPS receiver linked to the U.S. Coast Guard differential correction

signal at Fort Stevens, Oregon, continuously provided position information. This

positioning system provided continuous submeter horizontal position accuracy

for all data collection. Soundings were corrected for vessel heave by an onboard

heave/pitch/roll sensor (Seatex MRU-5).

Horizontal positions were logged as x- and y-coordinates in feet using the

North American Datum of 1983 (NAD 83) and the Washington State Plane Zone

#4602 (south). Depth values were logged in feet referenced to mllw and were

corrected to the National Oceanic and Atmospheric Administration (NOAA) tide

station at Toke Point using the integrated navigation software program

HYPACK. Digitized depth soundings were checked against the analog record

produced by the echosounder for additional quality control.

The WDOT Borrow Site survey area was established as a series of 65

parallel lines, oriented at 128 deg relative to true north, with 25-ft spacing

between lines. This survey line configuration was established to be consistent

with the predredging and postdredgjng surveys performed by David Evans and

Associates, Inc., in June and July 1998. Surveys performed for the monthly

monitoring of the Borrow Site were determined to require only a 100-ft line

spacing. Therefore, every fourth line of the David Evans survey was run during

each monthly monitoring survey. The horizontal extents of the survey are as

follows:

a. North Corner: 751588 E, 524629 N.

b. West Corner: 752842 E, 523642 N.

c. South Corner: 751837 E, 522365 N.

d. East Corner: 750583 E, 523352 N.

Data quality was also verified by running survey lines oriented perpendicular

to the primary survey lines ("tie lines"). All of the data acquisition systems,

including the echosounder, heave/pitch/roll sensor, and the onboard computer

systems, were calibrated before and after each hydrographic survey.

Hydrographie surveys of the Beach Nourishment Borrow Site (as of

December 1998) were performed on 5 August, 4 September, 10 October, and

18 November 1998.

Survey data processing and analysis

Data obtained in XYZ format from each survey were used to generate a grid

with 5-ft spacing between nodes. The grid was rotated clockwise 52 deg about

point (0, 0) of the Washington State Plane NAD 83 horizontal datum. The

rotation was performed consistently for every survey to create regularly shaped

rectangular grids (software limitations). This manipulation was required because

the North Channel Borrow Site is aligned with the North Channel bottom

Chapter 4 Field Data Collection and Analysis 4-45
contours. This rotation changed the northings and eastings of each bathymetric

data point.

After grid generation, color contour maps were generated. Figure 4-28

shows the contoured survey data grids for surveys performed in June

(predredging), July (postdredging), August, and September 1998. Figure 4-29

shows the contour maps for surveys performed in October and November 1998.

The color bar scales in these figures give the corresponding elevations in the area

surveyed relative to mllw. A comparison of the predredging and postdredging

contour maps shows where dredging occurred. The Borrow Site is

approximately 24 acres in size and was dredged to depths as large as 70 ft (mllw)

in some areas. Figure 4-30 shows the depth changes that occurred between the

postdredging survey in July and the PIE survey on 18 November 1998.

Sedimentation of up to 20 ft was noticed in some areas of the Borrow Site.

Ten cross sections were taken through the surveyed area at 150-ft spacing.

Figure 4-27 shows the location of each cross-section. Figure 4-31 shows cross

sections 1, 2, 3 and 4. Each cross-section plot shows bottom surface variation

obtained for the predredging and postdredging during the August, September,

October, and November 1998 surveys. The dredge cut and subsequent

deposition are clear on most of the cross sections. Figure 4-32 shows cross

sections 5, 6, 7 and 8, Figure 4-33 shows cross sections 9 and 10.

Table 4-12 shows calculated changes in depth along each cross section. The

average change in depth was calculated only within the identified dredged area

and not along the whole cross section. Further averaging was performed to

determine the average change in depth over the entire dredged area. For

example, the Borrow Site was dredged about 7.7 ft on average over the entire

site. Approximately 1 ft of accretion occurred between the postdredging survey

taken in July and the 5 August 1998 survey. During the following month,

erosion of 0.7 ft was noticed between 5 August and 4 September, followed by

accretion of 1.8 ft between 4 September and 10 October. The most recent

monitoring period showed accretion of 0.3 ft (between 10 October and

18 November 1998). It should be noted that erosion took place over the entire

survey area between 5 August and 4 September.

Table 4-13 presents the volume changes calculated in the dredged hole

between consecutive surveys. These volume changes were calculated using cross

sections 1-10. Approximately 350,000 cu yd were dredged from the borrow site

for beach nourishment. However, the volume change between predredging and

postdredging surveys is about 315,000 cu yd in the dredged hole. This

discrepancy may be attributable to filling of the dredged hole during the monthlong dredging process. The dredged hole experienced accretion of approximately

42,000 cu yd from July to 5 August. Between 5 August and 4 September,

approximately 24,000 cu yd of material was eroded from the dredge hole.

Between 4 September and 10 October and between 10 October and

18 November, accretion of approximately 70,000 and 9,500 cu yd occurred,

respectively.

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4-52 Chapter

4 Field Data Collection and Analysis
Table 4-12

Average Change in Dep th Along Cross Sections, ft

Line Number Pre to Post Post to 8/5 8/5 to 9/4 9/4 to 10/10 10/10 to 11/18

1 -1.0 -0.5 -2.6 1.0 0.8

2 -5.6 0.7 -1.1 1.8 0.3

3 -9.0 2.1 -0.3 2.1 0.3

4 -8.0 0.9 -0.2 2.0 0.4

5 -8.7 0.5 -0.1 1.8 0.1

6 -9.7 1.7 -0.3 1.4 0.4

7 -9.3 1.6 -0.7 1.9 0.5

8 -10.2 1.5 -0.2 2.0 0.3

g -9.0 1.4 -0.5 2.2 -0.2

10 -6.6 0.3 -1.0 1.5 -0.1

Average Over

Dredged Area

-7.7 1.0 -0.7 1.8 0.3

Note:

Negative = Increase in depth (dredging or erosion).

Positive = Reduction in depth (accretion).

Table 4-13

Total Volume Changes (cu yd)

Pre to Post Post to 8/5 8/5 to 9/4 9/4 to 10/10 10/10 to 11/18

Area of Borrow

Site, sq ft

-312,482 41,969 -23,382 69,860 9,346 1116,667

Chapter 4 Field Data Collection and Analysis 4-53
5 Modeling and Analysis of

Short Waves1

Wind waves and swell that are generated by local or distant storms are

defined as short waves. These surface gravity waves have periods less than about

25 sec. Quantitative information about short waves at the Willapa Bay entrance

is required in this study for determining navigability and estimating sediment

transport for evaluating navigation channel alternatives. Wave height, period,

and direction (relative to the channel orientation) in part determine navigability.

Sediment transport, which determines the frequency and cost of channel

maintenance, is driven by a combination of short waves and currents as discussed

in Chapter 6.

The purpose of this chapter is to describe modeling of the transformation of

short waves across the Willapa bar and into the bay. First, the wave climate

offshore of Willapa Bay is described. The offshore climate provides boundary

conditions to initialize the wave model. Next, the STeady-state spectral WAVE

transformation model STWAVE is described. STWAVE is based on the

conservation of wave action, and it includes depth- and current-induced

refraction, shoaling, and wave breaking. The bathymetry grid used in the model

is presented next. Accurate bathymetry information is required, as discussed in

Chapter 2, because waves refract and shoal according to the configuration of the

sea bottom. The wave model is then evaluated with field measurements obtained

in Chapter 4. Finally, simulations of the nearshore waves for evaluating channel

design alternatives are presented.

Wave Climate

The first step in evaluating alternatives for the Willapa navigation channel is

to define the wave climate seaward of the inlet, in relatively deep water. The

offshore wave climate provides representative wave boundary conditions that

initiate the wave transformation model. The model can then estimate the

variation in wave height and direction along the channel. For highest accuracy,

the source of wave information used to develop the offshore wave climate should

be a site near Willapa Bay. Also, the water depth should be sufficient to avoid

depth-limited breaking and refraction and shoaling induced by local nearshore

contours or shoals. The source of wave data must have a long record (for

1 Written by Dr. Jane McKee Smith and Mr. Bruce A. Ebersole, U.S. Army Engineer Research and

Development Center, Coastal and Hydraulics Laboratory, Vicksburg, MS.

Chapter 5 Modeling and Analysis of Short Waves 5-1
accurate climate statistics) and be presently operating (to facilitate verification

with 1998 data collected at Willapa).

Offshore wave information near Willapa Bay is available from four sources:

a. Directional wave buoy offshore of Grays Harbor, Washington. This is a

Datawell buoy located at 46°51.4'N, 124°14.7'W, in a depth of 40.2 m

(Station 03601). The buoy is supported by U.S. Army Engineer District,

Seattle, through the Corps of Engineers Field Wave Gauging Program

and operated by the Scripps Institute of Oceanography (SIO), Coastal

Data Information Program (CDIP). The buoy was installed in 1993 and

is still operating.

b. Bottom-mounted slope array offshore of Long Beach, Washington. The

slope array was located at 46°23.2'N, 124°4.7'W, in a depth of 10 m

(Station 05401). The gauge was supported by the Corps of Engineers

Field Wave Gauging Program and operated by the SIO CDIP. The

gauge was installed in 1983 and operated until mid-1995.

c. Directional wave buoy offshore of the Columbia River Bar, Oregon.

This is a 3-m discus buoy located at 46 7'N, 124°30'W, in a depth of

128 m (Station 46029). The buoy is supported and operated by the

National Data Buoy Center. The buoy was installed in 1984 and is still

operating.

d. The U.S. Army Corps of Engineers' Wave Information Study (WIS)

wave hindcast. The closest WIS Phase II station is located at 46°16.2'N,

124°46.2'W, in deep water (Station 46) (Corson et al. 1987). The WIS

hindcast covers the period 1956-1975.

The Grays Harbor buoy and the Long Beach gauge are located closest to Willapa

Bay. The Grays Harbor buoy is approximately 20 km northwest of the Willapa

entrance, and the Long Beach gauge was about 30 km south of the entrance.

Because the Long Beach gauge was in relatively shallow water, wave direction

was strongly influenced by the local bathymetry, and the higher waves would

break at the site, biasing the distribution of the highest wave heights. Also, the

Long Beach gauge is no longer operational, so evaluation of the wave model with

wave data collected at the inlet in 1998 cannot use the Long Beach gauge for

incident wave conditions. The Columbia River Bar buoy and the WIS

information provide longer periods of records than the Grays Harbor buoy, but

are also much further away from Willapa Bay. Also, the WIS information does

not overlap with the 1998 Willapa Bay measurements for evaluation of the

model. For these reasons, the Grays Harbor buoy was selected to determine the

wave climate for Willapa Bay. Appendix E contains comparisons of wave

climate statistics from the Grays Harbor buoy, the Long Beach slope array, and

the Columbia River buoy.

A wave climate was developed using Grays Harbor data from September

1996 through August 1998. In September 1996, the reporting of wave angles

changed from an arithmetic weighted average to a peak wave direction (wave

direction band with the maximum energy). Thus, for consistency, only the newer

data were used. Although a 2-year data record is short for describing extreme

wave statistics, it is sufficient to characterize waves for navigation and typical

storms to assess channel shoaling. To construct the wave climate, percent

5-2 Chapter 5 Modeling and Analysis of Short Waves
occurrence tables (broken down by height, period, and direction) were calculated

for each month of data and then the monthly tables were combined, giving equal

weight to each month. The equal monthly weighting takes into account gaps in

the data and changes in sampling frequency. The Grays Harbor wave climate is

illustrated in Figure 5-1 as a wave rose with directional resolution of 22.5 deg.

Table 5-1 shows overall distributions by height, period, and direction.

Frequency of Occurrence, %

270

Wave Height (m)

I 0.00-2.00

2.01-3.00

3.01-4.00

4.01-5.00

5.01-7.00

IGT 7.00

Grays Harbor Buoy

Figure 5-1. Grays Harbor buoy wave rose

Table 5-1

Grays Harbor Wave Distribution by Height, Period, and Direction

Height

m

Occurrence

percent

Period

sec

Occurrence

percent

Direction

deg

Occurrence

percent

0.00-2.0 57.5 0.00- 6.0 2.8 180.0 0.4

2.01-3.0 24.7 6.01-10.0 52.2 202.5 2.7

3.01-4.0 11.1 10.01-14.0 28.1 225.0 8.7

4.01-5.0 4.4 14.01-18.0 13.8 247.5 11.2

5.01-7.0 2.2 >18.01 3.1 270.0 38.5

>7.01 0.1 292.5 34.6

315.0 3.7

337.5 0.1

Chapter 5 Modeling and Analysis of Short Waves 5-3
The average conditions over the period August 1993 through July 1999 were

wave height of 6.9 ft, peak period of 10.6 sec, and peak direction of 273 deg

(based on wave data revised by CDIP in the spring of 1999). A monthly

distribution ofthe mean and maximum wave heights, periods, and directions and

occurrence of heights less than 9 ft are given in Table 5-2 (maximum period and

direction given in the table are the values associated with the maximum wave

height). The maximum wave height in the record is 29.6 ft, with a period of

13.3 sec and direction of 234 deg (24 November 1998 at 0719 Greenwich mean

time (GMT)). Large winter storms impede navigation at the Willapa entrance

channel. Based on the Grays Harbor buoy, wave height exceeds 9.8 ft 42 percent

ofthe time and exceeds 4.9 ft 92 percent ofthe time during winter months

(December-February). Time-histories of winter wave heights and directions

from the Grays Harbor buoy are given in Appendix C.

Table 5-2

Mean and Maximum Wav

(August 1993-July 1999

e Parameters Measured at Grays Harbor Buoy

Month

Mean

Height

ft

Mean

Period

sec

Mean

Direction

deg

Occurrence

of H ^ 9 ft

percent

Maximum

Height

ft

Maximum

Period1

sec

Maximum

Direction1

deg

January 8.83 11.6 257 57 27.8 13.3 258

February 9.84 13.0 261 48 24.3 13.3 269

March 8.14 12.0 264 63 23.1 12.5 238

April 6.92 11.0 274 79 18.2 11.1 290

May 5.54 9.4 278 95 13.3 11.8 278

June 5.15 9.4 283 95 11.6 15.4 261

July 4.27 8.1 287 99 11.3 10.0 300

August 3.84 8.5 283 100 9.8 9.1 283

September 5.28 9.6 282 95 12.2 11.8 281

October 6.92 10.9 275 78 21.3 12.5 269

November 9.12 11.1 264 58 29.6 13.3 234

December 10.50 12.4 264 36 25.7 14.3 272

Value associated with the maximum wave height.

Wave Transformation Model

The numerical model STWAVE (Resio 1987, 1988; Smith, Resio, and

Zundel 1999) was used to transform waves across the Willapa bar for evaluation

of channel alternatives. STWAVE numerically solves the steady-state

conservation ofspectral action balance along backward-traced wave rays:

<c„),

d CaCgacos(iu-a)E(f,a)

dx CO,

+ (C„) ga'y

d CaCgacos(ß-a)E(f,a)

Öy cor

= 1—

CO.

(5-1)

5-4 Chapter 5 Modeling and Analysis of Short Waves
where

Cga = absolute wave group celerity

x,y = spatial coordinates; subscripts indicate x-and y-components

Ca = absolute wave celerity

fi - current direction

a = propagation direction of spectral component

E = spectral energy density

F = frequency of spectral component

(Or = relative angular frequency (frequency relative to the current)

5 = energy source/sink terms

The source terms include wind input, nonlinear wave-wave interactions,

dissipation within the wave field, and surf-zone breaking. The terms on the lefthand side of Equation 5-1 represent wave propagation (refraction and shoaling),

and the source terms on the right-hand side of the equation represent energy

growth or decay in the spectrum.

The assumptions made in STWAVE are as follows:

a. Mild bottom slope and negligible wave reflection.

b. Spatially homogeneous offshore wave conditions.

c. Steady waves, currents, and winds.

d. Linear refraction and shoaling.

e. Depth-uniform current.

/. Negligible bottom friction.

STWAVE is a half-plane model, meaning that only waves propagating

toward the coast are represented. Waves reflected from the coast or waves

generated by winds blowing offshore are neglected. Wave breaking in the surf

zone limits the maximum wave height based on the local water depth and wave

steepness:

Hmn =O.LLtanh£rf (5-2)

max

where

Hm0 = zero-moment wave height

L = wavelength

k = wave number

d = water depth

STWAVE is a finite-difference model and calculates wave spectra on a

rectangular grid with square grid cells. The model outputs zero-moment wave

Chapter 5 Modeling and Analysis of Short Waves 5-5
height, peak wave period Tp, and mean wave direction am at all grid points and

two-dimensional spectra at selected grid points.

Wave Model Inputs

The inputs required to execute STWAVE are as follows:

a. Bathymetry grid (including shoreline position and grid size and

resolution).

b. Incident frequency-direction wave spectrum on the offshore grid

boundary.

c. Current field (optional).

d. Tide elevation, wind speed, and wind direction (optional).

Bathymetry grid

Both the wave and circulation models (Chapter 6) require bathymetry data to

construct computational grids over which the waves propagate and transform.

Accurate bathymetry is required for modeling waves at Willapa Bay because the

complex shoals control transformation and breaking. Bathymetry data collected

in this study include high-resolution Lidar surveys with Scanning Hydrographie

Operational Airborne Lidar Survey (SHOALS) (Lillycrop, Parson, and Irish

1996) and broad-coverage surveys collected by the Seattle District survey boat,

the Shoalhunter. These data were combined with existing National Ocean

Service (NOS) data to provide coverage of the nearshore, bar, and bay

(Chapter 3).

Very shallow areas across the Willapa bar could not be surveyed because of

continuous wave breaking. Bathymetry in these areas was estimated from local

knowledge.1'

2 A bathymetry grid for the circulation model was generated from

the combined SHOALS, Shoalhunter, and NOS data to represent the existing

conditions at Willapa (see Chapter 6). For wave modeling, the unstructured

circulation model grid was linearly interpolated onto a rectilinear STWAVE grid.

The STWAVE grid has a resolution of 100 m, with 301 grid cells across the

shore and 511 cells along the shore. The area of coverage is 30 km (west to east)

by 51 km (south to north). The grid origin (southwest corner of the grid) is

located at the Universal Transverse Mercator (UTM) Northing 5,136,069 m

(lat. 46.3719°N) and Easting 407,546 m (long. 124.2021°W). The existing

condition bathymetry and STWAVE grid coverage are shown in Figure 5-2.

Depths are given in meters relative to the mean tide level (mtl). Note that other

chapters typically reference depths to mean lower low water (mllw) datum, and a

value of 1.52 m mllw was used to convert depths to mtl based on the tidal datum

at Toke Point. In addition to the grid generated for existing bathymetry, grids

were developed in the same manner for Alternatives 3A, 3B, 4A, and 3H. Each

of these grids incorporates modifications to the existing bathymetry that

correspond to the particular alternative.

1 Personal Communication, October 1998, Mr. Thomas Landreth, Shoalhunter Captain, U.S. Army

Engineer District Seattle, Seattle, WA.

2

Personal Communication, October 1998, Mr. Randy D. Lewis, City Administrator, Westport,

WA.

5-6 Chapter 5 Modeling and Analysis of Short Waves
Figure 5-2. STWAVE existing condition bathymetry grid

Input wave spectra

Input wave spectra are the forcing for the wave model and provide the

distribution of wave energy as a function of frequency and direction. For this

project, the input spectra were generated in two ways:

a. Verification spectra. For evaluation ofthe wave model with field

measurements (1-4 September 1998, 15-20 October 1998, and

11-16 November 1998), one-dimensional frequency spectra from the

Grays Harbor buoy were used. The directional distributions measured at

the buoy lack sufficient resolution to drive the model, so a theoretical

distribution ofthe form cos"" (a - am) was applied, where nn is the

spreading coefficient, and am is the mean wave direction. The values

used for nn are given in Table 5-3 (Thompson et al. 1996). Large values

of nn indicate a narrow directional distribution (swell waves), and small

values represent a wide distribution (sea waves). The value of nn for the

peak ofthe spectrum (Table 5-3) was applied for the peak and lower

frequencies. For frequencies higher than the peak, the values in

Table 5-3 were applied.

Chapter 5 Modeling and Analysis of Short Waves 5-7
Table 5-3

Values of nn Defining Direction Distribution in Verification

Spectra

f.Hz <0.04 0.045 0.05 0.055 0.06 0.08 >0.1

nn 38 36 30 26 22 10 4

b. Representative spectra. For model runs made to evaluate channel

alternatives and sediment-transport potential, representative wave spectra

were generated. These spectra are representative ofthe height, period,

and direction ranges shown in Table 5-1. The spectra were generated

with a TMA1frequency distribution (Bouws et al. 1985) and a cos""(a -

am) directional distribution. The TMA shape is defined by the wave

height, peak period, and spectral peakedness parameter y. Large values

of /indicate a narrow frequency distribution (swell waves), and small

values represent a wide distribution (sea waves). Combinations of y and

nn used to generate the representative spectra are given as a function of

peak period in Table 5-4.

Table 5-4

Values of and nn Defining Representative Spectra

TD (sec) 5 8 12 16 20

Y 3.3 3.3 4 6 8

nn 4 4 10 20 30

Current fields

For applications where wave-current interaction significantly alters the wave

height or blocks the waves, current fields are needed as an input to the model.

Wave height increases on strong ebb currents and decreases on strong flood

currents. Currents also alter wave direction. The current modifies waves with

higher frequencies (shorter periods) more than it does waves with lower

frequencies. In addition to shoaling and refraction by currents, wave breaking is

also changed by an opposing or following current (L and k change in

Equation 5-2). Wave breaking is enhanced on an opposing current (ebb) and

reduced on a following current (flood). Ifthe ebb current is strong, waves with

short periods cannot propagate against it, and wave energy is blocked and

dissipated.

For Willapa, model runs with and without a current were made to assess the

sensitivity ofthe wave transformation at the study site to wave-current

interaction. For the sensitivity analysis, relatively commonly occurring shortand long-period waves at Willapa Bay were selected: Hmo = 1.5 m, Tp = 8 sec,

and am = 292.5 deg (probability of occurrence of21.6 percent) and//mo = 2.5 m,

1 Named for the three data sets used to develop the spectrum: TEXEL storm, MARSEN, and

ARSLOE.

5-8 Chapter 5 Modeling and Analysis of Short Waves
Tp = 16 sec, and am = 270 deg (probability of occurrence of 2.9 percent). The

waves were run for a typical peak ebb and flood, and the first wave was also run

for a maximum spring tide ebb and flood.

Figures 5-3 and 5-4 are plots ofthe difference in wave height with and

without current for the first wave and typical ebb and flood conditions,

respectively (Cases 1 and 2 in Table 5-5). The increase in wave height on the

outer bar for a typical ebb is about 2 ft (0.6 m), which is equal to the value

estimated based on local knowledge.1 Table 5-5 summarizes the maximum

differences in wave height (height modified by the current minus height

neglecting current) for ebb and flood currents. The percent differences are

calculated as the difference in wave height calculated with and without currents

divided by the height calculated without currents.

Table 5-5

Sensitivity Analysis of Wave Transformation to Current

Case

Incident Wave Conditions Max North

Channel Current

m/sec

Max Wave Height

Difference

m

Max Wave Height

Difference

percent

"mo

m sec deg

1 1.5 8 292.5 1.6 ebb 0.6 67

2 1.5 8 292.5 1.4 flood -0.2 -15

3 2.5 16 270 1.6 ebb 0.4 17

4 2.5 16 270 1.4 flood -0.4 -9

5 1.5 8 292.5 2.0 ebb 0.8 79

6 1.5 8 292.5 1.6 flood -0.2 -16

1 Personal Communication, October 1998, Mr. Randy D. Lewis, City Administrator, Westport,

Washington. Mr. Lewis has served in the U.S. Coast Guard and is familiar with the channels and

sea state at the Willapa entrance.

Chapter 5 Modeling and Analysis of Short Waves 5-9
Wave he gh: Merer=e(~;

C"0

CSD

!'::3

00

i::>o -*,

C.20

a ÄL

CÜ 4

yL K.-'

ij. 3C i^^.fct.

[- ' -0.1 C

>3SM ^m^

n

'"SW"«M^IKr^ !? "« * ^m 1 1 v&#" s

Figure 5-3. Wave height with ebb current minus wave height with no current

Hcnjl't CiFefence ( )

3 :>0i:

Figure 5-4. Wave height with flood current minus wave height with no current

5-10 Chapter 5 Modeling and Analysis of Short Waves
The maximum differences in wave height with and without current are

significant (0.4 to 0.8 m on ebb and 0.2 to 0.4 m on flood). The largest

differences occur in the North Channel through the bar, so by the present

sensitivity analysis, wave-current interaction should be included in evaluation of

navigability. However, the model shows that the regions where wave-current

interaction is significant are fairly small. Regions of wave-height differences

greater than 30 percent (peak ebb) were seven grid cells wide (700 m) or less

(which is less than 9 percent of the inlet width). Thus, wave-current interaction

need not be considered in estimating channel shoaling, which is determined more

by wave breaking, wave-driven currents, and sediment transport on the ebb

shoals than by wave height in the navigation channel. Wave-current interaction

was included for wave model runs to assess navigability, but this intensive,

iterative calculation was neglected for runs performed to provide sediment

transport forcing.

Tide and wind

Tide elevation is applied in STWAVE as constant water depth change over

the entire grid. Within the Willapa grid domain, the tide elevation does vary

spatially, but the influence of this variation on wave transformation is relatively

small (and is on the order of wind and wave setup, which are neglected). Tide

elevation for wave runs is specified from either tide measurements at the NOS

Toke Point station or, for typical conditions, set to mtl (0 m), mean low water

(mlw) (-1 m), or mean high water (mhw) (+1 m). Because the grid depths are

specified relative to mtl, tide fluctuations are specified relative to mtl.

Wind input in STWAVE creates wave growth across the grid domain. Wave

measurements at the Grays Harbor buoy contain most of the local wavegeneration processes. Fetch lengths from the buoy depth (40 m) to the Willapa

entrance are short, so additional growth would be small. Thus, local generation

is neglected in the STWAVE calculations, including locally generated waves

within Willapa Bay.

Evaluation of Model with Field Data

Willapa is a challenging environment in which to apply a wave

transformation model. The inlet is subjected to high waves, strong currents, and

large variations in water elevation; and the bathymetry at the Willapa entrance is

complex and continually changing. Before STWAVE was applied to simulate

project alternatives, the model was evaluated with field data to assess the

accuracy for such demanding conditions. The initial emphasis of the project was

the Middle Channel; thus, wave gauges were deployed at Middle Channel

Stations 1, 2, and 3 (see Chapter 4 for discussion of field measurements) to

provide verification data. Three verification periods were selected for modeling:

1-4 September 1998,15-20 October 1998, and 11-16 November 1998. These

periods include wave heights of 1.0 to 5.5 m, periods of 4 to 18 sec, offshore

wave directions of 205 to 306 deg, peak tidal amplitudes of 1 to 1.5 m, and peak

near-bottom currents of 0.5 to 1.2 m/sec. These wave conditions are

representative of waves in which vessels navigate through the entrance, as well

as the most commonly occurring waves. Measurement accuracy is estimated as

Chapter 5 Modeling and Analysis of Short Waves 5-11
about ±10 percent for wave height and ±10 deg for direction. An evaluation of

the pressure gauge record used for the wave measurements is given in

Appendix F. The root-mean-square (rms) error in wave height for the pressure

gauge, compared with that of a wave buoy, is approximately 0.1 m. The pressure

gauge generally underestimates small wave heights (at low tide) and is unbiased

at other tide elevations.

Wave transformation at Willapa is sensitive to the minimum water depth

across the Willapa bar. The initial attempt to verify STWAVE for the existing

Willapa bathymetry produced poor agreement with the measurements.

STWAVE gave little wave attenuation between Station 1 and Stations 2 and 3.

The lack of agreement called into question the bathymetry data across the

Willapa bar. The bar was not surveyed because of the presence of breaking

waves, so surveyed depths on either side of the bar were averaged across the bar

to give minimum depths of 6 m mtl. Persons knowledgeable about the entrance

provided estimates of 1- to 2-m mtl depths in the breaking regions. After

modifying the depths across the bar, reasonable agreement was found between

STWAVE calculations and the field measurements. STWAVE was initialized

with data from the Grays Harbor wave gauge, and the tide was represented with

water elevations measured at Station 1.

Comparisons of the calculated and measured wave heights and directions are

plotted in Figures 5-5 through 5-10. Statistics are presented in Table 5-6. The

calculations tend to overestimate the wave height at low tide at Station 2,

although the variation in wave height with the tide is reproduced. The wave

directions are modeled well for Station 1, but the calculated directions at

Stations 2 and 3 are less variable than measured. The wave directions at

Station 2 are more out of the northwest at low tide, when energy from the west is

dissipated over the bar and energy reaches Station 2 through the North Channel

entrance. At Station 3, wave directions are more from the west at low tide

because the energy reaching Station 3 is conveyed through the Middle Channel.

The larger errors in wave direction at Station 2 for 12-14 November coincide

with strong winds from the south and southeast (as great as 17 m/sec), which

generate short-period waves from the south bay. These locally generated waves

are not represented in the model. The large uncertainty in the bathymetry over

the shoals that front Stations 2 and 3 (because of lack of direct measurements in

the breaking regions and sand movement during the interval between the

bathymetry surveys and wave measurements) contributes to the model error.

Overall, the verification is considered to show reasonable agreement between the

calculations and measurements for this energetic and complex environment.

Simulation of Design Alternatives

To evaluate Willapa channel alternatives, two types of wave model

simulations were performed. Fifteen representative wave spectra were

transformed for ebb, slack, and flood currents to evaluate navigation conditions

in the channels. Then, a time-history of waves for a winter month was

transformed to provide input for sediment transport estimates.

5-12 Chapter 5 Modeling and Analysis of Short Waves
... ■■'— - ' 1 I — 1 .111.1 ■■■' s^^^=...

Table 5-6

Verification Statistics

Date Sta

Wave Height Wave Direction

Mean Error

percent

Mean Error

m

rms Error

percent

rms Error

m

Mean Error

deg

rms Error

deg

9/1/98-

9/4/98

1 6.6 0.10 11.0 0.22 -0.2 2.2

2 35.1 0.20 45.1 0.23 8.1 14.7

3 17.1 0.06 31.8 0.09 3.4 12.5

10/15/98-

10/20/98

1 -2.4 -0.05 11.5 0.22 -6.7 7.7

2 25.8 0.13 43.0 0.21 3.8 15.2

3 17.4 0.07 32.2 0.12 13.3 19.8

11/11/98-

11/16/98

1 -3.9 -0.13 11.0 0.37 -7.7 11.3

2 22.5 0.18 35.3 0.27 15.4 74.3

3 -22.1 -0.08 26.7 0.10 6.4 8.5

Waves to evaluate navigation

To evaluate the channel alternatives from the perspective of navigability, 15

representative waves were selected. These waves are the most commonly

occurring in the wave climate with heights less than 3 m (occurrence greater than

1.5 percent), and account for 70 percent of all wave conditions (85 percent of all

waves under 3 m). Only waves less than 3-m cutoff were considered because it

is about the limiting wave height to navigate the entrance (see Chapter 2). The

15 waves include incident directions of 225 to 315 deg and periods of 8 to 16 sec.

The waves are listed in Table 5-7 with their probability of occurrence.

The navigation evaluation considered five alternatives: Alternative 1

(existing condition), Alternative 3A (existing condition with dredging on the

bar), Alternative 3B (North S-Channel), Alternative 4A (Middle Channel), and

Alternative 3H (North Channel displaced to the south). Because the navigation

evaluation focuses only on the bar channel, these five alternatives cover the range

of all North and Middle Channel alternatives. Alterations of the interior channels

(except Alternative 4D) resulted in only minor changes to currents in the bar

channel (Chapter 6); thus, results for Alternative 4A are representative of 4B, 4C,

and 4E. Simulation of the five alternatives included the following steps:

a. The bathymetry grid was modified for each channel alternative as

discussed in Chapter 6.

b. Fifteen representative spectra were generated with heights, periods, and

directions selected from the wave climate and spectral parameters given

in Table 5-4.

c. Typical peak ebb and flood current fields were saved from ADCIRC

simulations of each alternative.

Chapter 5 Modeling and Analysis of Short Waves 5-13
9/1/98 0:00 9/2/98 0:00 9/3/98 0:00

Date

9/4/98 0:00 9/5/98 0:00

Figure 5-5. Wave height verification for 1-4 September 1998

360

340

320-

D 300

280-

260-

n 240-

220

200-

1-4Sep98

*-~s .

Meas Sta1

Meas Sta2

* Meas Sta3

STWStal

---STWSta2

STWSta3

180-

9/1/98 0:00 9/2/98 0:00 9/3/98 0:00

Date

9/4/98 0:00 9/5/98 0:00

Figure 5-6. Wave direction verification for 1-4 September 1998

5-14 Chapter 5 Modeling and Analysis of Short Waves
3.5

3"

2.5-

£

0)

O

X

o

> 1.5 1

re

0.5-

. 15-20Oct98

\ *_ / m,

,* *

i/ *"

10/15/98 0:00 10/16/98 0:00 10/17/98 0:00 10/18/98 0:00 10/19/98 0:00 10/20/98 0:00 10/21/98 0:00

Date

Figure 5-7. Wave height verification for 15-20 October 1998

360

0>

V

w

a

300

c

o

u

0)

C 240

ra

0)

E

180

15-20 Oct 98

. > " v-/ ' ' ^ \ '

■■■ m\: * »I V. "- "\

Meas Sta1

" Meas Sta2

* Meas Sta3

STWStal

-•- STWSta2

STW Sta3

10/15/98 0:00 10/16/98 0:00 10/17/98 0:00 10/18/98 0:00 10/19/98 0:00 10/20/98 0:00 10/21/98 0:00

Date

Figure 5-8. Wave direction verification for 15-20 October 1998

Chapter 5 Modeling and Analysis of Short Waves 5-15
.c

01

ö

X

a

>

a

11/11/98 0:00 11/12/98 0:00 11/13/98 0:00 11/14/98 0:00 11/15/98 0:00 11/16/98 0:00 11/17/98 0:00

Date

Figure 5-9. Wave height verification for 11-16 November 1998

360

300-

»

— 240

c

o

Q 180

>

0)

S

60

11-16 Nov 98

Meas Sta 1

Meas Sta 2

& Meas Sta 3

STWStal

— STWSta2

STW Sta 3

11/11/980:00 11/12/980:00 11/13/980:00 11/14/980:00 11/15/980:00 11/16/980:00 11/17/980:00

Date

Figure 5-10. Wave direction verification for 11-16 November 1998

5-16 Chapter 5 Modeling and Analysis of Short Waves
d. STWAVE was run to transform the 15 representative waves across each

of the bathymetry grids for the five alternatives. Runs were made at mtl

with no current, mlw (-1 m) with a typical peak ebb current, and mhw

(1 m) with a typical peak flood current. The total number of model runs

was 225 (15 waves times three tide/current combinations times five

alternatives).

The purpose of the STWAVE navigation-evaluation runs is to compare wave

heights and directions in the channels for the five alternatives to identify a

preferred alternative. To compare the results, three regions were selected in the

entrance channel as the outer channel, midchannel, and inner channel. The outer

channel location is the seaward end of each channel, where the channel

"daylights" (channel depth equals the longshore depth contour). The midchannel

location is the most restricted channel cross section (narrowest width through the

shallowest bar section). The inner channel location is bayward of the bar. The

locations are separated by distances of 1-2 km. Examples of the wave heights

and wave directions (relative to the channel orientation) for the most frequently

occurring wave condition (Wave 4 in Table 5-7) are given in Figures 5-11 and

5-12, respectively. Wave heights and directions for ebb, slack, and flood are

averaged (heights are generally higher for ebb and lower for flood). In the outer

channel and midchannel, the wave heights are similar for the five alternatives. In

the inner channel, Alternatives 3B and 3H have significantly higher wave height.

The wave directions relative to the local channel orientation are within about

±20 deg in the outer channel and midchannel, but increase to over 60 deg for

Alternative 3B and 30 deg for Alternative 4A in the inner channel. The 60-deg

obliqueness relative to the channel orientation exceeds the 45-deg window for

safe navigation discussed in Chapter 2.

Table 5-7

Representative Waves for Navigation Evaluation S mulations

Wave

"mo

m sec

am

deg

Probability

Percent

1 1.5 8 225.0 1.5

2 1.5 8 247.5 3.1

3 1.5 8 270.0 10.0

4 1.5 8 292.5 21.6

5 1.5 8 315.0 2.7

6 1.5 12 270.0 5.0

7 1.5 12 292.5 3.3

8 1.5 16 270.0 2.6

9 2.5 8 225.0 1.6

10 2.5 8 270.0 2.6

11 2.5 8 292.5 3.0

12 2.5 12 247.5 1.9

13 2.5 12 270.0 4.8

14 2.5 12 292.5 3.2

15 2.5 16 270.0 2.9

Chapter 5 Modeling and Analysis of Short Waves 5-17
1.8

Hmo = 1.5 m, Tp = 8 sec, direction = 292.5 deg (22%)

Outer Channel Midchannel

Location

Inner Channel

Figure 5-11. Wave height comparison for most frequent wave

70

01>

a

60

_ 50

0)

c

I 40

O

0

u 30

>

& 20

c

o

'= 10

u

-10

-20

-30

Hmo = 1.5 m, Tp = 8 sec, direction = 292.5 deg (22%)

V\\NV

V\\NV

Outer Channel Midchannel

Location

existing

H3A

03B

4A

H3H

Inner Channel

Figure 5-12. Wave direction comparison for most frequent wave

5-18 Chapter 5 Modeling and Analysis of Short Waves
The obliqueness of waves in the inner channel for Alternative 3B is

especially problematic because of the higher waves, thus greater wave steepness

and potential for wave breaking. Results of averages from the 15 representative

waves (weighted by their percent occurrence) are given in Table 5-8.

Navigability for any alternative is dictated by the worst conditions that are

encountered along the channel. Although Alternative 1 (existing conditions)

provides the smallest wave heights, the channel depth is less than the 26-ft design

depth (Chapter 2). Alternatives 3A and 4A are similar from the standpoint of

waves for navigability. Alternative 3H has significantly higher wave heights in

the inner channel than Alternatives 3A and 4A (wave height is approximately

double), but has similar characteristics in the outerchannel and midchannel

positions. Alternative 3B has poor wave height and direction characteristics in

the inner channel.

Alternatives 1 and 3A. The statistics in Table 5-8 show that wave height

and direction are fairly consistent between Alternatives 1 and 3A. This is

reasonable because these alternatives have the same channel alignment, with a

slightly deeper and wider channel in Alternative 3A. The wave height increases

10 to 15 percent for Alternative 3A relative to Alternative 1, because the

deepening and widening of the entrance channel increase wave penetration.

Wave angles relative to the channel exceed 45 deg in the outer channel or

midchannel for about 10 percent of wave conditions less than 3 m (based on the

15 representative waves). Typically, incident wave directions of 247.5 deg and

less result in angles greater than 45 deg relative to the outer channel and

midchannel.

Alternative 3B. Alternative 3B (S-channel) has the poor characteristics in

the inner channel of high wave heights (122 percent of Alternative 1) and wave

angles oblique to the channel (51 deg, on average). Wave energy is focused on

the inner channel by the entrance bar. Also in the inner channel, the channel

orientation is toward the northeast/southwest (230 deg), so dominant incident

waves from the west and west-northwest are oblique to the channel. A channel

configuration similar to Alternative 3B was the marked channel until recently

(October 1998). The difficulties in navigating this channel are the primary

motivation of this study. Wave angles relative to the channel exceed 45 deg for

about 60 percent of wave conditions less than 3 m. Typically, incident wave

directions of 225 deg and less for the outer channel or 292.5 deg and greater for

the inner channel result in angles greater than 45 deg relative to the channel.

Table 5-8

Comparison of Wave Height and Direction for Channel Alternatives

Alternative

Average Hmo

M

Increase in Hmo Relative to

Alternative 1

percent

Average • m Relative to

Channel Orientation

deq

Outer Mid Inner Outer Mid Inner Outer Mid Inner

1 existinq 1.5 1.5 0.8 0 0 0 19 30 9

3A 1.6 1.7 0.9 9 15 9 20 23 10

3B 1.8 1.5 1.9 24 4 122 15 15 51

4A 1.7 1.4 1.1 17 -8 44 12 8 26

3H 1.7 1.8 1.9 14 10 158 14 10 11

Chapter 5 Modeling and Analysis of Short Waves 5-19
Alternative 4A. Alternative 4A (Middle Channel) generally has higher

wave heights in the outer and inner channels and lower heights in the midchannel

compared with Alternatives 1 and 3A. The wave angles are generally less

oblique in the midchannel, but more oblique in the inner channel. The reason for

increased wave height and more oblique wave directions in the inner channel for

Alternative 4A is that wave energy enters the region of the North Channel and is

refracted and diffracted into the inner reach of the Middle Channel. For

Alternatives 1 and 3A, wave energy is sheltered in the inner channel by Cape

Shoalwater. Wave directions do not exceed 45 deg for the representative wave

conditions.

Alternative 3H. Alternative 3H generally has similar wave heights and

directions in the outer channel and midchannel to those of Alternatives 1 and 3A.

But, the wave height is approximately double that of Alternatives 1 and 3A in the

inner channel. The wave angles are generally slightly less oblique in the outer

channel and midchannel. The reason for increased wave height in the inner

channel for Alternative 3H is that wave energy is focused by the ebb shoal and

interior shoals and there is less sheltering from Cape Shoalwater to the north

(compared with Alternatives 1 and 3A). Wave directions do not exceed 45 deg

for the representative wave conditions.

Navigability is a function not only of wave height and direction, but also of

wave steepness (ratio of wave height to wavelength) and wave breaking. Steeper

waves increase potential for a vessel to be overturned or swamped. Waves

steepen in shallow water because wavelength decreases and height increases

through refraction and shoaling. Similarly, waves steepen on ebb currents. For

each of the alternatives, ebb and flood current magnitudes and channel depths are

similar, so wave steepnesses are also similar (except the inner channel of 3B and

3H, where wave height and thus steepness can double). Wave breaking is also a

function of wave height, wave steepness, and water depth. Thus, the wavebreaking characteristics of Alternatives 1, 3A, and 4A are expected to be similar.

Alternatives 3B and 3H would experience increased breaking in the inner

channel, where wave heights are higher than with the other alternatives.

STWAVE can estimate regions of increased steepness or wave breaking, but not

the timing or location of individual steep or breaking waves that might cause

difficulty for navigation.

This study focused on waves in the bar channel, but results show that there

are differences in wave height between the bay portions of the North and Middle

Channels, also. At high tide (flood), waves are smaller in the bay portion of the

North Channel than in the Middle Channel because of sheltering from Cape

Shoalwater. At low tide (ebb), waves are slightly smaller in the bay portion of

the Middle Channel because most of the wave energy is dissipated on the bar.

Because vessels generally navigate through the outer bar on flood, near high tide,

the North Channel alternatives offer decreased wave action in the interior bay

channel, compared with that of the Middle Channel.

Detailed plots of the wave height and direction for the outer channel,

midchannel, and inner channel for each alternative are given in Appendix D.

Ebb, slack, and flood simulations for each wave are displayed separately.

5-20 Chapter 5 Modeling and Analysis of Short Waves
Waves to evaluate sediment transport

To support sediment transport modeling, nearshore wave fields for one

typical winter month were required. The month of January 1998 was selected

because the Grays Harbor buoy record was continuous, and the mean wave

height was near the mean winter wave height at the buoy (3.2 m for January 1998

versus 3.0 m for all winter months). A time-history of Grays Harbor

measurements for January 1998 is given in Figure 5-13 (other winter months are

plotted in Appendix C). STWAVE simulations were made with input every 3 hr

from the Grays Harbor buoy, for a total of 248 model runs. Tide elevations were

taken from the NOS Toke Point gauge. Tidal currents were neglected in the

wave simulations because sensitivity tests showed that wave height and direction

variation produced by the wave-current interaction were localized and would

have minor influence on sediment transport calculations. The wave- and currentdriven sediment transport calculations are discussed in Chapter 6.

Summary

The wave transformation model STWAVE was applied to calculate wave

heights and directions at the entrance to Willapa Bay. The model resolution was

100 m and covered a domain of 30 by 51 km. The model was driven with input

wave information from the Grays Harbor wave buoy. Field measurements taken

at three stations in the mouth of Willapa Bay were used to evaluate the model for

application to the complex environment of Willapa entrance. Verification results

showed reasonable agreement between calculations and measurements at three

locations where measurements were available. The model was applied to

compare relative differences in wave height and direction for different channel

alternatives.

Wave Height

Wave Direction

1/1/98 0:00 1/6/98 0:00 1/11/98 0:00 1/16/98 0:00 1/21/98 0:00 1/26/98 0:00 1/31/98 0:00

Date

Figure 5-13. Grays Harbor measurements for January 1998

Chapter 5 Modeling and Analysis of Short Waves 5-21
Following verification, five channel alternatives for Willapa Bay,

Alternatives 1, 3A, 3B, 4A, and 3H, were evaluated. For each alternative, the

model was run for 15 representative waves at ebb (mlw), slack (mtl), and flood

(mhw). From the perspective of navigation, the following conclusions are made

based on the short-wave modeling:

a. Alternatives 1 and 3A give equivalent results within the accuracy of the

model. Wave heights for Alternative 3A are slightly higher

(9-15 percent) because more wave energy can penetrate the deeper and

wider entrance channel. Wave directions (relative to the channel axis) in

the outer channel and midchannel exceed 45 deg for waves incident from

the southwest and west-southwest. These North Channel alternatives

have lower wave heights in the bay channel during high-tide conditions

because wave energy is sheltered by Cape Shoalwater.

b. Alternative 3B gives consistently higher wave heights and more oblique

wave directions (relative to the channel orientation) than Alternatives 1

and 3A. The higher waves also imply larger wave steepnesses and more

frequent wave breaking. In the inner channel, wave directions would

often exceed 45 deg, and typical wave heights would be near 2 m

(compared with less than 1 m for Alternatives 1 and 3A), making

Alternative 3B less preferable for navigation.

c. Alternative 4A gives results similar to those of Alternatives 1 and 3A,

but the wave height is slightly higher in the outer and inner parts of the

channel (17 and 44 percent, respectively, compared with Alternative 1),

but lower in the midchannel (8 percent compared with Alternative 1).

Wave angles tend to be less oblique than Alternative 1 in the

midchannel, but more oblique in the inner channel. Waves at the inner

channel for Alternative 4A are higher and more oblique because the

Middle Channel is not naturally sheltered by Cape Shoalwater, and wave

energy entering through the North Channel is refracted and diffracted

around the Willapa bar to the inner channel region. Wave directions for

the 15 representative waves do not exceed 45 deg in the Middle Channel.

d. Alternative 3H gives consistently higher wave heights in the inner

channel compared with Alternatives 1 and 3A. The higher waves also

imply larger wave steepnesses and more frequent wave breaking. The

wave directions for Alternative 3H are generally less oblique to the outer

channel and midchannel, than with Alternative 1 and 3A. Although the

wave characteristics of Alternative 3H do not violate the navigation

criteria, the larger interior wave heights would result in more difficult

navigation over a longer distance in the entrance channel.

The STWAVE simulations do not show a clear preference for Alternative 1,

3A, or 4A based on navigation criteria of wave height and wave direction relative

to the channel, within the accuracy of the model. Alternatives 3B and 3H are

relatively less preferable because of the high waves (and oblique wave directions

for Alternative 3B) in the inner channel.

Wave fields were also calculated for a typical winter month. STWAVE was

run every 3 hr with input from the Grays Harbor buoy for January 1998. These

STWAVE results are applied in Chapter 6 for sediment transport calculations.

5-22 Chapter 5 Modeling and Analysis of Short Waves
References

Bouws, E., Günther, H., Rosenthal, W., and Vincent, C. L. (1985). "Similarity

of the wind wave spectrum in finite depth waves; 1. Spectral form," Journal

ofGeophsyical Research 90(C1), 975-986.

Corson, W. D., Abel, C. E., Brooks, R. M., Farrar, P. D., Groves, B. J., Payne,

J. B., McAneny, D. S., and Tracy, B. A. (1987). "Pacific coast phase II wave

information." WIS Report 16, U.S. Army Engineer Waterways Experiment

Station, Vicksburg, MS.

Lillycrop, W. J., Parson, L. E., and Irish, J. L. (1996). "Development and

operation of the SHOALS Airborne Lidar Hydrographie Survey System,"

SPIE: Laser remote sensing ofnatural waters -from theory to practice

2964, Proceedings, International Society for Optical Engineering. V. I.

Feigels and Y. I. Kopilevich, eds., 26-37.

Resio, D. T. (1987). "Shallow-water waves. I: Theory," Journal of'Waterway,

Port, Coastal, and Ocean Engineering 113(3), ASCE, 264-281.

(1988). "Shallow-water waves. II: Data comparisons," Journal of

Waterway, Port, Coastal, and Ocean Engineering 114(1), ASCE, 50-65.

Smith, J. M., Resio, D. T., and Zundel, A. K. (1999). "STWAVE: Steady-state

spectral wave model; Report 1: User's manual for STWAVE version 2.0,"

Instructional Report CHL-99-1, U.S. Army Engineer Waterways Experiment

Station, Vicksburg, MS.

Thompson, E. F., Hadley, L. L., Brandon, W. A, McGehee, D. D., and Hubertz,

J. M. (1996). "Wave response of Kahului Harbor, Maui, Hawaii," Technical

Report CERC-96-11, U.S. Army Engineer Waterways Experiment Station,

Vicksburg, MS.

Chapter 5 Modeling and Analysis of Short Waves 5-23
6 Circulation and Transport

Modeling1

Numerical simulations of tidal circulation, sediment transport, and salinity at

Willapa Bay were conducted to evaluate and compare engineering Alternatives

for a safe and reliable entrance channel to Willapa Bay. This approach provides

an objective means for comparing the performance of Alternatives. Details of

the circulation, sediment transport, and salinity modeling conducted in this study

are presented in this chapter.

Introduction

This chapter primarily describes implementation of the ADvanced

CIRCulation (ADCIRC) and ADvanced TRANSport (ADTRANS) models.

ADCIRC is a long-wave hydrodynamic model applied for simulating watersurface elevation and circulation over the entire bay as a function of tidal forcing,

freshwater inflow, wave stress forcing, and wind forcing. Sediment transport for

Willapa Bay was calculated within ADCIRC with a formulation for the total

sediment load. ADTRANS is a model that calculates the concentration of

specified parameters, in this case salinity, by application of the convectiondiffusion equation.

Chapter details include a general description of the bay, circulation modeling

approach, transport modeling approach, development of the computational grid,

and results of the modeling efforts, as follows:

a. Physical properties of Willapa Bay are documented to provide a

background for understanding the processes that force and define the

system. The primary forcing for the bay is the tide, but wind and

freshwater influx also contribute to motion in the bay.

b. Previous modeling studies of Willapa Bay are described.

c. Circulation modeling is presented. An overview of the ADCIRC model,

information on boundary condition specifications, and bottom- and windstress formulations are presented.

1 Written by Dr. Adele Militello, Dr. Norman W. Scheffner, and Mr. Steven M. Bratos, U.S. Army

Engineer Research and Development Center, Coastal and Hydraulics Laboratory, Vicksburg, MS;

Mr. Mitchell E. Brown, Mevatec Corporation, Vicksburg, MS; and Mr. Scott Fenical, Pacific

PLLC International Engineering , Seattle, WA.

Chapter 6 Circulation and Transport Modeling 6"1
d. Wave-driven current calculations are described and verified for a planar

beach.

e. Sediment transport calculations are described and examined for

reasonability. Formulations for the transport rate and related parameters

set in the algorithm are given.

/. The salinity transport method is presented, as well as an overview of the

ADTRANS model and information on boundary condition specifications.

g. Local and global features of the computational grid are described. Grid

details presented are the computational domain, bathymetry, and

resolution. The Alternatives and the State Highway Route (SR) 105 dike

and groin structure are presented in detail.

h. Model calculations are compared with measurements of water level and

current velocity.

i. Alternatives are evaluated based on current speed and sediment

deposition within the channels.

Physical Setting of Wiliapa Bay

Physical properties of Willapa Bay are presented here to provide background

information. Circulation and salinity transport in Willapa Bay are driven by the

tide, freshwater inflows, and wind. Sediment transport is a function of these

processes as modified by short (wind-generated) waves, especially at the

entrance. Continental shelf processes outside the bay, such as the Columbia

River freshwater plume and upwelling (Sternberg 1986; Landry et al. 1989;

Hickey 1989), play a role in flow and transport inside the bay. Additionally,

episodic events such as winter storms and processes related to El Nino can

modify the circulation, thereby changing sediment and salinity transport.

Tide

Diurnal and semidiurnal constituents are the dominant contributors to tidal

motion in Willapa Bay. The primary constituents forcing the bay are M2, Ki, S2,

Oi, and Pi, in order of largest to smallest amplitude. The M2 tidal constituent is

dominant, being 2.3 times greater than the Ki constituent at Toke Point.

Table 6-1 gives tidal constituent amplitudes for water level at Toke Point, South

Bend, and Nahcotta as calculated by the National Ocean Service (NOS), National

Oceanic and Atmospheric Administration (NOAA). Tidal amplitudes increase

from the entrance into the interior of the bay. The M2 amplitude is 14 percent

and 20 percent greater at South Bend and Nahcotta, respectively, than at Toke

Point, according to NOS-calculated constituents based on measurements of water

level.

6-2 Chapter 6 Circulation and Transport Modeling
Table 6-1

Tidal Constituent Amplitudes, m, at Toke Point, South Bend, and

Nahcotta (NOS 1991 http://www.opsd.nos.noaa.gov)

Constituent Toke Point South Bend Nahcotta

M2 0.98 1.12 1.18

s2 0.26 0.30 0.29

N2 0.20 0.23 0.23

K, 0.43 0.43 0.44

M4

0.02 0.06 0.07

0, 0.26 0.26 0.26

M6

0.01 0.03 0.03

NU2 0.04 0.05 0.04

MU2 0.01 - --

2N2 0.02 0.03 0.03

00, 0.01 0.01 0.01

LDA2 0.01 0.01 0.01

s. 0.01 — -

M, 0.01 0.02 0.02

Ji 0.02 0.02 0.02

MM 0.02 -- -

MSF 0.03 -- --

MF 0.04 - --

RHOi 0.01 0.01 0.01

Qi 0.04 0.05 0.05

T2 0.02 0.02 0.02

R2

0.00 0.00 0.00

2Qi 0.01 0.01 0.023

Pi 0.13 0.14 0.14

L2 0.02 0.03 0.03

K, 0.06 0.08 0.08

S4 __ 0.01 0.01

Me - 0.00 0.01

Tidal range is defined as the difference in height between consecutive higher

high and lower low water levels. At Toke Point the tide range has a mean value

of 2.7 m, but varies considerably during the year and can reach almost 4 m

during a strong spring tide. The tide range increases from the entrance to the

upper reaches of the bay because of the amplification of the tidal wave as it

propagates into the bay. Tidal datums computed at gauges located in Willapa

Bay are given in Table 6-2. Values are referenced to mean lower low water

(mllw).

Chapter 6 Circulation and Transport Modeling 6-3
Table 6-2

Tidal Datums, m, for Willapa Tide Gauges (NOS 1998)

Datum Toke Point South Bend Nahcotta Naselle River

Highest observed

water level 4.4 3.4 3.5 3.8

Mhhw 2.7 3.0 3.1 3.3

Mhw 2.5 2.8 2.8 3.0

Mtl 1.4 1.6 1.6 1.7

Mlw 0.4 0.4 0.4 0.5

Mllw 0.0 0.0 0.0 0.0

Lowest observed

water level -1.2 -1.2 -1.0 -1.3

Note: mhhw = mean higher high water, mhw = mean high water, mtl = mean tide level, mlw = mean

low water, mllw = mean lower low water.

Freshwater inflows

Stream tributaries to Willapa Bay include the Willapa, Naselle, North, Bear,

Nemah, Palix, and Cedar Rivers, and Smith Creek. Discharge data for May

through December 1998 were obtained from the U. S. Geological Survey

(USGS) for the Naselle and Willapa Rivers and are plotted in Figures 6-1 and 6-

2, respectively. Both rivers had low discharges from May through October.

Discharges increased significantly in November and December, following

seasonal trends in precipitation. Peak discharges were approximately 120 m /sec

greater for the Willapa than for the Naselle.

Local wind

Meteorological data for the Washington coast near Willapa Bay were

compiled by Sternberg (1986). Winds are typically directed toward the north to

northeast during October through April, and toward the south to southeast during

May through September. The strongest winds occur during November through

February, with wind speeds on the order of 5 m/sec for fair weather. Because of

the large tidal range of Willapa Bay, local fair-weather wind forcing does not

contribute significantly to water-level change in the bay.

Salinity

Coastal ocean salinity near Willapa Bay varies during the year as a function

of wind forcing and northward movement of the Columbia River plume.

According to Landry et al. (1989), from May to August, nearshore salinity

typically ranges from 30 to 32 parts per thousand (ppt), with a maximum

occurring in June. During the remainder of the year, nearshore salinity is in the

range of 29 to 30 ppt. Because of strong Columbia River discharges during the

summer coupled with seasonal winds typically directed toward the south, the

6-4 Chapter 6 Circulation and Transport Modeling
ü

0

co

a>

03

200

150

cÖ 100

sz

o

CO

50

Naselle River

I i I ,-i, „^ fvj|

125 150 175 200 225 250 275 300 325 350

Year Day 1998

Figure 6-1. Naselle River discharge for May through December 1998

300

Willapa River

250

o

CD

CO

E

200 -

CD

O)

co

.c

o

CO

b

150

100

:

j

50 —

v—I , U i | , i I..JN—i—A- i

0

1225 150 175 200 225 250 275 300 325 350

Year Day 1998

Figure 6-2. Willapa River discharge for May through December 1998

Chapter 6 Circulation and Transport Modeling 6-5
Columbia River plume manifests itself as a low-salinity surface feature that lies

offshore and south of the river discharge at the Oregon-Washington border.

During the remainder of the year, northward-directed winds force the plume

north and against the shoreline (Landry et al. 1989). Low-salinity water from the

Columbia River can enter Willapa Bay, decreasing bay salinity.

Inside the bay, variability in the distribution of salinity occurs because of

freshwater discharge from rivers. For example, in 1965 salinity at Nahcotta

varied from 15 to 30 ppt, whereas at the Naselle River, the variation was from

5 to 29.5 ppt (U.S. Army Engineer District, Seattle, 1971). Long-term (1961-

1987) monitoring data collected by the Washington State Department of Fish and

Wildlife in the southern part of the bay indicate that the average monthly surfacelayer salinity varies from 15 ppt in February to 29 ppt during August and

September.2 Monthly mean salinity values in the Willapa River near Toke Point

calculated from measurements taken from 1990 through 1997 show a seasonal

trend, with lowest salinity in December, increasing through July, and peak values

occurring during July through November (Newton et al. 1998). In general, the

bay is vertically well mixed during low tributary flows (May to October) and

alternates between vertically well mixed and partly mixed during strong tributary

flows (November through April) (U.S. Army Engineer District, Seattle 1971).

The total freshwater contribution into the bay, even during high tributary

flows, represents less than 5 percent of the tidal prism, estimated to be on the

order of 3.74 x 108 m

3

for a mean tidal range (Johnson 1973). During times of

low discharge, salinity is nearly uniform over the water column, but decreases

from the entrance to the interior along the major channels. This behavior is

observed in vertical profiles of salinity measured along transects in the Willapa

River and Nahcotta Channel taken during May-June 1995.3 Vertical stratification

was observed near and within tributaries, even during weak discharge. Salinity

profiles conducted for this study during November 1998 (Chapter 4) showed

similar behavior. Strong vertical stratification occurred in the Willapa and

Naselle Rivers, and weak or no vertical stratification occurred in the central bay.

In general, stratification was stronger during low slack tide and weaker during

high slack.

Because of the presence of a major oyster industry in Willapa Bay, there is

concern about long-term salinity change in the bay. Both Pacific and native adult

oysters thrive in salinity greater than about 20 ppt.4Therefore, salinity changes

that may arise from proposed Alternatives are of interest.

Previous Modeling Studies

Pacific International EngineeringPLLC (PIE) and PHAROS Corporation

performed a two-dimensional (2-D) hydrodynamic modeling study of

Willapa Bay for the Washington Department of Transportation (WDOT) to

evaluate a proposed project to stabilize the SR-105 near North Cove of Willapa

2 Data provided by Mr. Bruce Kauffman, Willapa Field Station, Washington State Department of

Fish and Wildlife, Ocean Park, WA, 19 November 1998.

3

Plots furnished by Dr. Barbara Hickey, University of Washington, Seattle, WA, 1998.

4

Personal Communication, Mr. Brett Dumbauld, Willapa Field Station, Washington State

Department of Fish and Wildlife, Ocean Park, WA, 4 December 1998.

6-6 Chapter 6 Circulation and Transport Modeling
Bay (PIE and PHAROS Corporation 1997). The study applied the FESWMS2DH model together with a finite-element grid of the bay. The grid had 3,732

nodes and 1,180 elements and primarily covered the interior of the bay. The

model was calibrated with velocity measurements. Flow modifications from

construction of a North Channel plug together with dredging of the Middle

Channel were studied by comparing resultant calculations for preproject and

postproject velocity values. The study concluded that the proposed project

changed the depth-averaged maximum currents in the North and Middle

channels, but had no significant flow modifications elsewhere in the bay.

Circulation Model

Water-surface elevation and current for Willapa Bay were calculated by the

2-D depth-integrated, hydrodynamic model ADCIRC (Luettich, Westerink, and

Scheffner 1992). The ADCIRC model is a finite element hydrodynamic model

developed under the U.S. Army Corps of Engineers Dredging Research Program.

The finite element formulation has the advantage of great flexibility in resolution

over the calculation domain. Coarse resolution can be specified in areas distant

from the local region of interest, and fine resolution can be specified locally to

meet project requirements. For instance, channels and structures can be defined

for accurate calculation of flow through and around them.

Specifications for ADCIRC simulations of hydrodynamics in Willapa Bay

include forcing with tidal constituents, forcing with wind, wetting and drying,

calculation of nonlinear continuity and advection, quadratic bottom stress, and

quadratic wind stress. Open-ocean boundaries were forced by tidal constituents

obtained from the Le Provost et al. (1994) database. Wind data obtained from

the National Center for Environmental Prediction (NCEP) were applied as

meteorological forcing for simulations. ADCIRC has robust wetting and drying

algorithms that were applied to simulate the inundation and exposure of

expansive tidal flats in Willapa Bay. Bottom friction was specified for the

Willapa Bay simulations as a quadratic bottom-stress formulation given by

cf(u

2+v2

)

1

n

>- (6-1)

D

where

Cf = friction coefficient specified as 0.0025 for the Willapa Bay

simulations

U - current velocity along the x-axis

V = current velocity along the y-axis

D = total water depth

Within ADCIRC, flow toward the east is taken as positive along the x-axis

and flow toward the north is taken as positive along the y-axis. Wind stress given

in terms of direction components xx and xy is

^=CmPa\W\Wx (6-2)

Chapter 6 Circulation and Transport Modeling 6-7
xy=Cw9a\W\Wy

where

Cm = wind-drag coefficient for wind at 10 m above the water surface

pa = density of air

W = wind velocity

Wx = x component of the wind velocity

Wy = y component of the wind velocity

Wind velocities are at 10 m above the water surface. The wind-drag

coefficient is calculated as (Garrett 1977)

(6-3)

Cio = (0.75 + 0.067 x 102 W) xl0": (6-4)

where wind speed is specified in centimeters per second.

Wave-driven currents

To meet the objectives of this study, the ADCIRC model was upgraded to

include wave-driven currents by implementation of wave stresses in the

momentum equations. Spatial gradients of radiation stresses were calculated

from wave parameters computed by STWAVE (see Chapter 5). These wave

stresses were added into the momentum equations in a form analogous to the

wind stress.

Wave stresses Rx and Ry, corresponding to the x- and y-directions,

respectively, are given by

R =

P

dS„ dS:

-+- *y

dx dy

(6-5)

and

*,= P

'

dS

^.+

8SlL

dx dy

(6-6)

where p is the density of water, and S^, S^, and Syy are radiation stresses. By

applying linear wave theory, the radiation stresses are represented as

$xx ~ E

-1

«(cos2e + i) —

•SJT, =—nsin29 xy 2

Syy=E

i

«(sin20 + l)

(6-7)

(6-8)

(6-9)

6-8 Chapter 6 Circulation and Transport Modeling
where

E = wave energy

n = ratio of group velocity to wave celerity

9 = wave angle

For more information on linear wave theory, see Dean and Dalrymple (1992).

Verification of Wave Stress Forcing

Wave-stress forcing was verified by comparing radiation-stress values

calculated from STWAVE wave output to those calculated by the longshore

current model Numerical Model of LONGshore current (NMLONG) (Larson and

Kraus 1991) and with an analytical solution. A planar beach was specified to

provide an idealized situation for model comparison. Wave-stress forcing within

ADCIRC was validated by comparison of the calculated wave-driven current

with measurements made on Leadbetter Beach, California (Thornton and Guza

1986).

Radiation-stress gradients computed from STWAVE-calculated wave

parameters were evaluated by simulating wave propagation over a planar beach

with a IV on 30H slope. The input wave conditions were significant height of

2.0 m, period of 11.5 sec, and direction with respect to normal of-30 deg.

Figure 6-3 shows plots of the wave-stress vector field, wave-stress magnitude,

wave height, depth, and wave direction for the nearshore portion of the profile.

The wave refracts to an angle of-10 deg and breaks at x = 2,400 m at depth of

3.8 m. After the wave breaks, the wave height decays as the wave propagates

across shore. After breaking there is also a significant increase in wave stress

from near zero to 0.06 m

3

/sec2at x = 2,420 m followed by a more gradual

decrease to zero as the wave propagates to the shore. The wave-stress field

shows that the wave stresses in the surf zone are directed primarily toward shore,

but contain a small alongshore component.

Radiation stresses computed from STWAVE-calculated wave parameters

were compared with those calculated by NMLONG. Figure 6-4 shows the rootmean-square (rms) wave height Hrms, radiation-stress magnitude S, and the

radiation stress components S^ and S^ for each model along the profile.

Radiation-stress values shown in the figure have been normalized by the density

of seawater. STWAVE and NMLONG apply different methods for calculating

wave propagation and breaking; therefore, wave heights calculated along the

profile by the two models are not quite equal. Because the radiation-stress

components are proportional to the square of the wave height, radiation stresses

calculated by each model differ by a corresponding amount. Peak rms wave

height calculated by NMLONG is 1.5 m, a value that is comparable to 1.4 m

Chapter 6 Circulation and Transport Modeling 6-9
~55

o

c

o50

45

230 235 240 245 250

CMb 0.05

CDW

0^

230 235 240 245 250

E 2

£0

Q.2

-4

— Hs

De| 3th

230 235 240 245 250:

u

CD

"D -10

<x>

230 235 240

X (10m inc)

245 250

Figure 6-3. Wave parameters calculated by STWAVE with input parameters of

Hs = 2.0 m, 7=11.5 sec, and 9 = -30 deg for a planar beach

(IV:30H). Panels from top to bottom are wave stress vector

field, wave stress magnitude R, significant wave height and water

depth, and wave angle

calculated by STWAVE. The peak NMLONG-calculated rms wave height

occurs further offshore, at x = 2,350 m, than that calculated by STWAVE, which

is located at x = 2,400 m. The NMLONG-calculated rms wave height has a

broader distribution across the surf zone than that calculated by STWAVE. The

rms wave height calculated by STWAVE is greater than that calculated by

NMLONG in the area where the STWAVE-calculated rms wave height is

decaying. Differences in radiation-stress magnitude and components between the

two models correspond to those in rms wave height. Despite the difference in

wave propagation and breaking methods, the models produce similar results for

rms wave height and radiation stress.

Further evaluation of radiation stress calculated by STWAVE output was

conducted by comparison to analytical solution of radiation stress at locations

along the profile. Local wave conditions for the analytic solution were calculated

6-10 Chapter 6 Circulation and Transport Modeling
E

"i

x'

.

—- STW

NML

1

2000 2100 2200 2300 2400 2500

-Sr'

CO

2000 2100 2200 2300 2400 2500

CO ^

E

^2

co

g

Al%

\ V

2000

0

2100 2200 2300 2400 2500

co

E

d-0.5

CO

-1

2000 2100 2200 2300

X, m

2400 2500

Figure 6-4. Comparison of STWAVE- and NMLONG-calculated wave

parameters. Panels from top to bottom are rms wave height,

radiation stress magnitude S/p, and the magnitude of radiation

stress components, S„/p and Syp

with linear wave theory. The objective was to produce local wave conditions

similar to those calculated from STWAVE-calculated wave parameters. This

objective was accomplished by adjusting the incident deepwater wave height in

the linear calculations until the resulting local wave conditions were similar to

those of the model for a particular depth. Table 6-3 shows that the radiation

stress values calculated from STWAVE output (referred to herein as STWAVE

radiation stress) in the cross-shore direction due to the cross-shore momentum S*

are within 4 percent of the analytical values when the local wave conditions are

similar.

Radiation-stress gradients for Willapa Bay were calculated from values of

Hs, T, and G as given by STWAVE. Radiation-stress components were

calculated with Equations 6-7 through 6-9 substituting the rms wave height,

tirms - 0.707 Hs, for the energy-based calculation. The wave-stress components

were then calculated with Equations 6-1 and 6-2. Wave-induced currents were

Chapter 6 Circulation and Transport Modeling 6-11
Table 6-3

Radiation Stress Values Calculated Analytically from STWAVEt>iniilaterf Wave Parameters, and bv NMLONG1

Linear Theory

Radiation Stress

S«/b, m

3

/sec2 —

H, e

M deg Ca/C

Local

Depth

m Analytical STWAVE NMLONG

2.09 8.80 0.968 3.21 3.78 - 3.80

2.09 9.43 0.963 3.67 3.75 3.61 -

2.23 10.59 0.954 4.67 4.18 - 4.20

1 Significant figures do not imply accuracy, but are given for comparison of calculation method.

simulated by including the STWAVE wave-stress components in the ADCIRC

momentum equations. The wave-stress components were interpolated from the

STWAVE finite-difference grid to the ADCIRC finite-element grid by means of

a bilinear interpolation algorithm.

The wave stresses implemented in ADCIRC were evaluated by comparison

to field measurements from the National Sediment Transport Study made at

Leadbetter Beach, California (Thornton and Guza 1986). This evaluation was

conducted by calculating wave stresses in STWAVE for Leadbetter Beach and

applying those stresses within ADCIRC. Currents calculated by ADCIRC were

then compared to measurements. Input spectra for STWAVE were derived from

a significant wave height of 0.78 m, peak period of 14 sec, peak wave direction

of 9 deg, spectral peakedness factor of 3.3, and directional spreading coefficient

nn = 8. The spectral peakedness factor controls the width of the frequency

spectrum where smaller values correspond to broader peaks. The energy in the

frequency spectrum is spread in direction proportional to cos"" (9 - 9m), where 9

is the direction of the spectral component and 9m is the mean wave direction.

Bathymetry in the STWAVE grid was represented as a plane sloping beach of IV

on 26H with a constant depth of 3.84 m offshore and a grid spacing of 5 m alongand across-shore. Figure 6-5 shows a comparison of the measured and

STWAVE-calculated rms wave height.

An ADCIRC grid developed for Leadbetter Beach is shown in Figure 6-6.

Node spacing varied between 10 and 2.5 m from the offshore boundary to the

shoreline. The grid extended 185 m offshore and 200 m alongshore. Water level

at the offshore boundary was held constant. The shore and lateral boundaries

were closed and given a no-slip condition. This simulation was run for 12 hr,

with a ramp of approximately 2.5 hr. The friction coefficient was set at 0.004,

and the mixing coefficient was set at 0.3. The parameter x0, which controls the

weighting of the generalized wave continuity equation between the pure wave

equation (x0 = 0) and the primitive continuity equation (x0 = 1) (Luettich,

Westerink, and Scheffner 1992), was set to 1.0 to give full weight to the

primitive continuity equation for this very shallow-water calculation.

6-12 Chapter 6 Circulation and Transport Modeling
0.7

0.6 —

0.5 + /

_l_ / rms wave height

E

0.4 + / Leadbetter Beach

E ++ / 4Feb1980

X

0.3

0.2

/ Hs = 0.79 m, Hms= 0.56 m, T = 14 sec 9 = 9 deg

RTWAVF

0.1

0.0

(

/ i

+ OBSERVED

i i I i i i I i i i J i i i 1 i i .i

) 20 40 60 80 100

Distance from Shore, m

Figure 6-5. Comparison of measured and calculated rms wave height for

Leadbetter Beach, California, 4 February 1980

Figure 6-6. ADCIRC grid and bathymetry for Leadbetter Beach

Chapter 6 Circulation and Transport Modeling 6-13
A comparison between the calculated and measured longshore current v is

shown in Figure 6-7. The model values are in good agreement with the

measurements except for an overprediction in the area just outside the surf zone.

The calculated peak longshore current is 5 percent above that ofthe

measurement. From the breaking point at x = 40 m to where the longshore

current peaks, the model overestimates the measurements by about 15 percent.

Just offshore ofthe breaking point the model overestimates the longshore current

by 70 percent compared to the measured value (in a region ofsmall current

magnitude).

0.6

0.5

0.4

0.3

0.2

0.1

0.0

—

/

+ \

Longshore Current

4Feb1980

ADCIRC

— +\ + OBSERVED

— /

/+ +\

—

+ N.

-

I i I i i i i , 7*-—r-—r"

20 40 60 80

Distance from Shore, m

100 120

Figure 6-7. Calculated and measured longshore current at Leadbetter Beach,

California, 4 February 1980

A second ADCIRC simulation was run for 60 hr with the same wave

condition, but for a wave direction of 0 deg. Normal wave incidence is expected

to produce an equilibrium condition with a time-invariant water level (setupsetdown), and no current. Figure 6-8 shows the water-surface elevation for four

cross-shore locations. Equilibrium was reached in approximately 3 hr of

simulation time and transient oscillations were present for another 15 to 20 hr.

The water-surface elevation located 125 m from the shoreline in the constant

depth area is zero. Outside the surf zone at a distance of 45 m, the setdown is

approximately 0.01 m. Across the surf zone, the setup increases to

approximately 0.075 m at the 5-m cross-shore location.

6-14 Chapter 6 Circulation and Transport Modeling
0.10

0.05

c

o

'§

-0.05 -

-0.10

Water-Surface Elevation

/

-rI

.'

\

Cross-Shore Location

125 m

45 m

I , I . I

25 m

5m

I

50000 100000 150000 200000 250000

Time, sec

Figure 6-8. Calculated water-surface elevation versus time for Leadbetter

Beach, California

Sediment Transport Model

To calculate sand transport and bottom change, a total-load sediment

transport model was applied. The sediment transport model was embedded

within ADCIRC for dynamic exchange of information between the two models.

The sediment-transport algorithm applies the Ackers and White (1973)

formulation for coarse material modified for the presence of waves (Bijker 1967).

Bottom elevation change is given by

dD

dt

Sqx ,

d

4 +-

where

D

t =

dx dy

total depth relative to a datum

sediment transport directed along the x-axis

sediment transport directed along the y-axis

time

(6-10)

For detailed information on the methodology applied in the sediment transport

calculations, see Scheffner (1996).

Coupling of the sediment-transport calculations with the hydrodynamics was

conducted by calculating the change in bottom elevation over the grid. Sediment

transport was calculated every 100th hydrodynamic time-step. After each set of

sediment transport calculations over the grid, the bottom elevation was adjusted

by the amount of material that entered or exited at each node. In this manner,

time evolution of the bottom change was calculated. Figure 6-9 illustrates the

coupling between the sediment transport and hydrodynamics.

Chapter 6 Circulation and Transport Modeling 6-15
ADCIRC hydrodynamic calculations At = 3 hr Wave

stresses %

N = 100

Update bottom

elevation

Sediment transport

calculations

At = 3 hr Wave height

and period

Figure 6-9. Flowchart of hydrodynamic and sediment transport calculations with

wave parameter input

Because waves are a significant force for movement of sediment into the

water column, all sediment-transport calculations were conducted with wave

stress forcing included in the hydrodynamic (ADCIRC) simulations. Wave

modeling was conducted prior to the sediment transport simulations and

descriptions of the runs are given in Chapter 5. Wave fields (wave stress, height,

and period) were updated every 3 hr in the hydrodynamic and sediment-transport

calculations and held constant over each 3-hr interval. Wave calculations were

conducted outside of the sediment-transport calculations, and wave stress, height,

and period were not updated for changes in bottom elevation calculated by the

sediment-transport model.

The ADCIRC grid domain for the Willapa Bay simulations is larger than the

domain of the STWAVE grid. Wave parameters were calculated on the

STWAVE grid and interpolated onto the ADCIRC grid. In areas where the two

grids did not overlap, wave parameters were set to zero for sediment transport

and wave stress forcing calculations. Thus, outside of the STWAVE grid

domain, it was assumed that waves did not contribute significantly to sediment

transport and wave-induced currents at Willapa Bay.

During initial testing of the combined hydrodynamic and sediment-transport

modeling, stability was not maintained in the vicinity of the SR-105 structure

because of strong advection. To enhance stability, advective terms in the

momentum equations were turned off in all simulations in which sediment

transport was coupled to hydrodynamics. Elimination of the advective terms did

not significantly change the current patterns in the entrance, with the exception of

areas adjacent to the SR-105 structure. Eddies that normally form next to the

structure were not present in simulations without the advective terms. Sediment

transport calculated without the advective terms in the velocity calculation (in the

circulation model) is not expected to significantly alter the sediment transport

values within the Alternative channels.

6-16 Chapter 6 Circulation and Transport Modeling
Verification of Sediment Transport Method

This section describes the performance of the coupled ADCIRC, STWAVE,

and total-load sediment-transport calculations for idealized physical situations.

The objective is to demonstrate reliability of the modeling system for an

idealized situation prior to application at Willapa Bay.

The modified Ackers and White (1973) total-load formula as modified by

Scheffner (1996) and implemented in ADCIRC was evaluated with bathymetry

from the Leadbetter Beach, California, example described in the previous

section. A sediment grain size of 0.3 mm was specified. Radiation-stress

gradients were computed from STWAVE-calculated wave parameters for the

three wave conditions shown in Table 6-4 for evaluating sediment transport rate

predictions.

Table 6-4

Wave Parameters for Idealized Sediment Transport Cases

Case Hm m T, sec e,deg

1 2 14 -10

2 1 12 -10

3 2 12 -15

The purpose of the exercise was to demonstrate that the total-load transport

formula was properly implemented in ADCIRC and that the Ackers and White

(1973) methodology was appropriate for surf zone conditions as occur on the

entrance to Willapa Bay. Figure 6-10 shows the cross-shore variation of

significant wave height for the three wave cases. In Cases 1 and 3, waves began

breaking about 75 m from shore and decayed in approximately linear proportion

to the decreasing depth across shore. In Case 2, waves shoaled slightly above

1.0 m then began to break about 45 m from the shore and decayed toward the

shore.

Wave-driven currents were calculated by ADCIRC with wave-stress forcing.

Three simulations were conducted that correspond to the wave parameters given

in Table 6-4. Each ADCIRC simulation was conducted over a 12-hr interval in

which the wave-stress field was held constant. Total-load calculations were

computed at approximately Hour 4 of each simulation. Figure 6-11 shows the

longshore current calculated for the three cases. Case 2 has significantly weaker

current than Cases 1 and 3. This situation is expected because of the smaller

wave height in Case 2. Figure 6-12 shows the corresponding longshore

sediment-transport rate per unit width qy, expressed in cubic meters per linear

meter across shore per second. The variation in longshore transport rate

corresponds to the cross-shore distribution of longshore current. The smallest

longshore transport rate, with a peak value of 0.0005 m

3

/m/sec, corresponds to

Case 2 (1-m wave height). Even though Cases 1 and 3 have the same incident

wave height of 2.0 m, the corresponding peak longshore transport rate for Case 1

(qy = 0.0046 m

3

/m/sec) is about half of that for Case 3 (qy = 0.01 m

3

/m/sec). The

greater rate for Case 3 owes to the larger incident wave angle and shorter wave

period.

Chapter 6 Circulation and Transport Modeling 6-17
E

(0

X

2.b

Significant Wave Height

2.0

^

1.5 - /

1.0

y/— .._

Hs(m) T(sec) 6 (deg)

2.0 14 -10

0.5 1.0 12 -10

: 1,1,1,

2.0 12 -15

1,1,1,

20 40 60 80 100

Distance from Shore, m

120 140

Figure 6-10. Cross-shore variation of significant wave height calculated by

STWAVE

1.5

1.0

o

CD

CO

E

>

0.5

0.0

(

/' A

//

/ /v \

Longshore Current

i / \ >

Hs(m) T(sec)

?0 14

9(deg)

-10

-10

-15

1.0 12

2.0 12

\ \

\ \

\ \

*. - — i I i

) 50 100 150

Distance from Shore, m

2C)0

Figure 6-11. Cross-shore variation of longshore current calculated by ADCIRC

6-18 Chapter 6 Circulation and Transport Modeling
Figure 6-12 compares the Ackers and White total load calculation to the

Coastal Engineering Research Center (CERC) formula (Shore Protection Manual

1984). The total longshore transport rate Q was calculated by integrating the

transport rate per unit width qy across the surf zone. The CERC formula, as a

standard, has an expected accuracy of about ±50 percent (SPM 1984). The surf

zone is defined as the area from the onset of breaking, calculated by STWAVE,

to the beach. Two methods for calculating the total transport rate with the CERC

formula are shown. The first method, labeled CERC/LIN, applies linear wave

theory to calculate the wave parameters at the break point. The second method,

0.010

0.008

0.006

E 0.004

0.002

0.000

Longshore Sediment Transport

TOTAL Q (10° cum/year)

ADCIRC CERC/LIN CERC/STW

5.11 12.6 5.39

100

Distance from Shore, m

200

Figure 6-12. Cross-shore variation of sediment transport and total transport

compared to the CERC formula for three wave cases

labeled CERC/STW, applies breaking wave parameters calculated by STWAVE.

Both methods include the standard CERC formula for longshore transport rate

given by:

(6-11)

where

K

P5

a'

g

nondimensional empirical sand transport coefficient (K = 0.77)

density of sediment (2.65 kg/m )

volume of solids/total volume (accounts for sand porosity, a' = 0.6)

acceleration due to gravity

Chapter 6 Circulation and Transport Modeling 6-19
y = wave breaking index (Hs = y db, db = breaking depth, y = 0.78)

Hb = breaking wave height, • b - breaking wave angle.

Comparison of total longshore sediment-transport rates calculated by the

Ackers and White formulation within ADCIRC and the CERC formula is given

in terms of the ratio

R =

*JAckWht

QcERC

(6-12)

where QAckwht denotes the total longshore sediment-transport rate calculated by

the Ackers and White formulation within ADCIRC, and QCERC denotes the total

longshore sediment transport rate calculated by the CERC formula. For

reference, ifR = 1, then the transport rates computed within ADCIRC and the

CERC formula are equal; ifR = 0.5, then the transport rate calculated within

ADCIRC is half that (50 percent below) calculated by the CERC formula.

Table 6-5 gives R values comparing sediment-transport rates calculated

within ADCIRC and by the CERC formula. Sediment-transport rates calculated

within ADCIRC compare well with those calculated by the CERC formula

applying the CERC/STW method for the larger wave cases examined.

Table 6-5

Ratio of Sediment Transport Rates Calculated by

ADTRANS and the CERC Formula

Case ADCIRC and CERC/LIN

Ft,

ADCIRC and CERC/STW

1 0.5 1.05

2 0.2 0.5

3 0.7 1.2

Salinity Model

Transport ofsalinity was calculated by the ADTRANS model, which applies

the convection-diffusion equation to compute concentration of a material or

substance. ADTRANS is linked to ADCIRC to provide coupled hydrodynamics

and transport. The ADTRANS model can be applied to calculate concentration

of conservative or nonconservative substances and requires specification of

coefficients and boundary conditions appropriate for a given constituent. For

example, calculation ofsalinity requires specification of representative salinity

values at the ocean boundaries and at freshwater tributaries.

Concentration of a constituent is described within the ADTRANS model by

the depth-averaged convection-diffusion equation written in nonconservative

form as

6-20 Chapter 6 Circulation and Transport Modeling
D—+D

dt dx dy

= -D

dx

K

dC

dx

} a f.. 8cW

+— K— J fy l '%)}

+E-F (6-13)

where

C

Kx

Ky =

E =

F =

depth-averaged concentration of a constituent

horizontal diffusion coefficient applied for the x-directed

concentration gradient

horizontal diffusion coefficient for the ^-directed concentration

gradient

source term

sink term

Source and sink terms are required for applications where modeled constituents

can be produced or can decay within the system. Calculation of salinity does not

require source or sink terms because salts are conservative substances.

Computational Grid

The computational grid developed for Willapa Bay encompasses a regional

area extending from 40.8 to 51.2 deg North and from -130.5 to -122.7 deg West.

Shoreline data were obtained from the NOAA Medium Resolution Shoreline

Database, which is composed of shoreline position information digitized from

NOAA navigation charts. Bathymetry data were obtained from several sources.

National Ocean Service bathymetry data were applied in the Pacific Ocean.

Within Willapa Bay, high-density bathymetry data were obtained from the

Seattle District. These data were collected in 1998 as decribed in Chapter 3.

Regions of Willapa Bay not covered by the 1998 surveys have bathymetry

applied from NOS charts. Figure 6-13 shows bathymetry contours of Willapa

Bay calculated from the composite data, and Figure 6-14 shows detail of

bathymetry in the entrance. Tidal-flat elevations were estimated from NOS

charts. Typical tidal-flat elevation specified in the grid is 1.5 m below mtl.

The computational grid contains 24,170 nodes and 46,250 elements. Lowest

resolution was specified in the Pacific Ocean, and highest resolution was

specified in the entrance to Willapa Bay. Figure 6-15 shows a regional view of

the grid that illustrates the variation in resolution over a portion of the domain.

Figure 6-16 shows the grid for the entire Willapa Bay, and Figure 6-17 shows

grid detail in the entrance. Resolution for the Alternative channels can be seen in

Figure 6-17. Alternatives represented in this grid are 1, 3A, 3B, 3F, 3G, 4A, and

4E. High resolution was specified so that direct comparisons of velocity and

flow rate can be made among Alternatives. Figure 6-17 shows the base grid for

the existing condition based on 1998 bathymetry (Figure 6-13), and bathymetry

has not been modified for representation of action Alternatives. Alternative 1 (no

action) is shown with a dashed line to separate it from action Alternatives.

Chapter 6 Circulation and Transport Modeling 6-21
Figure 6-13. Willapa Bay bathymetry. Contours at 2.5-m intervals relative to mtl

Figure 6-14. Willapa Bay entrance bathymetry

6-22 Chapter 6 Circulation and Transport Modeling
Grays Harbor

Willapa Bay

Columbia River

Figure 6-15. Regional view of grid for coast of Washington and Oregon

Raymond

Figure 6-16. Grid detail for Willapa Bay

Chapter 6 Circulation and Transport Modeling 6-23
Figure 6-17. Grid detail in Willapa Bay entrance (existing bathymetry with

resolution for Alternatives with the exception of Alternatives 3H-a

and 3H-b)

For each Alternative requiring dredging, a separate grid was developed from the

base grid where modifications (dredged channel and/or structures) were

implemented. Changes in the grid for action Alternatives (those requiring dredging)

involved only modification to bathymetry; resolution remained consistent with the

base grid, with the exception of Alternatives 3H-a and 3H-b (described in the

following paragraph). Figure 6-18 shows nodes (calculation points) at the entrance

to Willapa Bay. In locations where Alternative channels were proposed, node

density in the base grid was increased above that in surrounding areas. In general,

channels for Alternatives were specified as 500 ft and 1,000 ft in width.

Representation of these channels was accomplished by placing three nodes across

500-ft channels and five nodes across 1,000-ft-wide channels. Nodes for the

500-ft-wide channels overlap those in the l,000-ft-wide channels. Because of the

high resolution in the entrance, the model was run with a 1.5-sec time-step to

maintain numerical stability. Contour plots of bathymetry for each Alternative are

shown in Appendix G.

Modifications to the base grid for Alternatives 3H-a and 3H-b were required

because these Alternatives were defined after the base grid was developed.

Alternative 3H-a consists of a 28-ft channel dredged along a line extending from

the end of the SR-105 groin and dike seaward across the bar at a direction of

approximately 285 deg relative to True North. Alternative 3H-b has the same

configuration as Alternative 3H-a except for an increase in the dike crest

elevation from -18 to -2 ft mllw. Changes implemented for Alternatives 3H-a

and 3H-b included increased resolution along the channel alignment as specified

previously for the other Alternatives, as shown in Figures 6-19 and 6-20. The

revised grid contains 46,970 elements and 24,530 nodes. Alternatives 3H-a and

3H-b were the only channel configurations simulated with the revised grid.

6-24 Chapter 6 Circulation and Transport Modeling
Figure 6-18. Nodes in Willapa Bay entrance (existing bathymetry with resolution

for Alternatives with the exception of Alternatives 3H-a and 3H-b)

lÄsil?

'8Ä$jSs8§5ä

ISllp^

3

3

H-ag

H-b I

Figure 6-19. Grid detail in Willapa Bay entrance with resolution for

Alternatives 3H-a and 3H-b

Chapter 6 Circulation and Transport Modeling 6-25
To enhance numerical stability, the crest elevation of the dike was raised to

+9.8 ft msl. Because the dike elevation in the Alternative 3H-b grid is higher

than that specified for this Alternative, changes in calculated velocity for

Alternative 3H-b over those of Alternative 3H-a are expected to be greater than

what would occur if the dike were raised to the design elevation of -2 ft mllw.

However, velocity changes caused by this structural modification are assumed to

be qualitatively correct.

The dike-and-groin structure located in the North Channel was included in

the grids. Pacific International Engineering provided information on the

structure including its position, dimensions, and crest elevations. Representation

of the structure in the base grid is shown in Figure 6-21 in terms of nodes. An

image overlay of the structure is shown for reference. Nodes were specified

along the crest and foot of the structure. Grid resolution at the SR-105 groin and

dike was increased for Alternatives 3H-a and 3H-b to better resolve local velocity

changes.

Circulation Model Calibration

Calibration of the circulation model (ADCIRC) was conducted for tidal

conditions. Initial calculations by the circulation model overpredicted water

level and current speed at four measurement stations, shown in Figure 6-22, at

Willapa Bay. Examination of the overpredictions revealed that the M2 tidalconstituent forcing amplitude was too large. This amplitude was reduced by

20 cm at all ocean forcing boundary nodes, which led to good agreement between

the measurements and model. The tidal constituent database (Le Provost et al.

1994) from which the tidal parameters were obtained was not verified for much

of the Pacific Ocean region where the Willapa Bay model was forced. Because

the tidal constituents were calculated from a numerical model, errors are present

6-26 Chapter 6 Circulation and Transport Modeling
• .* • •: *v

Figure 6-21. Nodes at SR-105 dike and groin

Cape Shoalwater

D

Station 1

D

Station 2

Station 3

Toke Point

D

Station 4

Ledbetter Point Bay Center

Figure 6-22. Locations of stations for comparisons of water-surface elevation

and current

Chapter 6 Circulation and Transport Modeling 6-27
in the database. Therefore, amplitudes and phases may be adjusted for increased

accuracy in simulations. For this project, the M2 amplitude reduction ranged

from a 14 to 19 percent change from values extracted from the database.

The friction factor was set to 0.0025 throughout the model domain and was

not adjusted in the calibration process.

Circulation Model Verification

Comparisons between calculated and measured water level and current

velocities are presented for a 1-month tidal simulation for the 1998 bathymetry.

Water level and velocity were compared for the four stations shown in

Figure 6-22. Model forcing was specified with tidal constituents only; wind and

freshwater influx were not applied. The time interval selected for comparison

commenced on 5 September 1998 (Day 248) and ended on 6 October 1998

(Day 279). This time interval was selected for initial comparison because data

indicate that there was little influence of the wind or other nontidal processes.

Comparison of water-surface elevation

Calculated water-surface elevation at the four measurement stations is

compared with measurements and described. Water-level measurements were

de-meaned (mean subtracted) for comparison with calculated values. Because

the calculations were conducted with only diurnal and semidiurnal tidal forcing

(no wind or river discharge), the measurements were high-pass filtered with a

cutoff frequency of 0.6667 cycles per day (cpd) to remove motion with duration

longer than 1.5 days. The calculated water levels at the four stations were in

good agreement with measurements. Peaks and troughs of the calculated tidal

wave were in phase with those of the measurements. Figures 6-23 through 6-26

plot calculated and measured water level at Stations 1 through 4, respectively.

Calculated water levels exhibit increased tidal range with distance into the bay,

which is a property of the Willapa Bay system.

Error in calculation of water level was quantified by computing rms error

and percent error between measured and calculated water level at Stations 1

through 4. The rms error Erms of a variable % is

j £j\/£meas,i /tcalc,i)

E^=\\^ (6-14) rms

where

•th lmeas,i =

i measured value of %

%caic,i = *'hcalculated value of x

N = is the number of points.

6-28 Chapter 6 Circulation and Transport Modeling
-2.0

Sept5-Oct6, 1998 Station 1

l I I I I I I I I I I I I I I I I L

248 253 258 263 268

Day, 1998

273 278

Figure 6-23. Time series of calculated and measured water level at Station 1

248 253 258 263 268

Day, 1998

273 278

Figure 6-24. Time series of calculated and measured water level at Station 2

Chapter 6 Circulation and Transport Modeling 6-29
263 268

Day, 1998

Figure 6-25. Time series of calculated and measured water level at Station 3

Sept5-Oct6, 1998 Station 4

248 253 258 263 268

Day, 1998

273 278

Figure 6-26. Time series of calculated and measured water level at Station 4

6-30 Chapter 6 Circulation and Transport Modeling
Percent error EPCT in water level was calculated by

F rms

UPCT R

(6-15)

where Rtis the tide range at Toke Point, taken to be the difference between the

mhhw and mllw datums given in Table 6-2. Toke Point was selected as the

reference point for the comparisons because it was the closest location to the

measurement stations at which tidal datums were available. Table 6-6 gives the

rms error and percent error for Stations 1 through 4 for the 30-day verification of

the base grid. Because of gaps in measurements at Stations 3 and 4, the time

series applied for error calculations was shorter than for Stations 1 and 2. Data

gaps during the verification period are listed in Table 6-6. Calculated water

levels were in good agreement with measurements. Minimum and maximum

percent errors were 6 and 9 percent at Stations 1 and 3, respectively, for the base

grid. Error calculations were also conducted for the grid that was modified for

resolution of the Alternative 3H-a and 3H-b channels. The percent errors for the

modified grid were within 1 percent of those for the base grid, except at Station 2

where it was within 2 percent. Thus, the increased resolution of the modified

grid did not significantly alter the calculated values.

Table 6-6

Error in 1Calculated Water Level

Station rms Error, m Percent Error Day Range, 1998

Data Gap,

Days 1998

1 0.15 6 247.75 - 253.67 253.71 - 278.96

2 0.19 7 247.75 - 278.96 252.71 -- 254.75

3 0.25 9 247.75 - 278.96 252.71 - 254.78

4 0.18 7 247.75 - 278.96 247.79 - 253.68

Comparison of velocity

Measured and calculated velocities were compared at the four stations shown

in Figure 6-22 for the 1-month verification simulation. Velocities were

decomposed into north-south and east-west components. Decomposition of

velocity provides information on dominant flow direction and agreement

between measured and calculated values along specific directions. Measured

velocities were depth averaged and band-pass filtered for the comparisons.

Band-pass filtering was performed to remove nontidal motion from the velocity

measurements because the verification simulation was conducted for tidal forcing

only. The low- and high-frequency cutoffs for the filter were 0.6667 cpd and

8.0 cpd, respectively. All time-series plots of measured and calculated currents

show the band-pass filtered measurements.

Velocity comparison for Station 1 is shown in Figure 6-27. Direction of flow

is denoted in the plot. Overall, the model reproduces the measurements for the

east-west velocity component, although it tends to underpredict the peak velocity

during Days 248 through 254 and 275 through 278 and overpredicts during

Days 261 through 268. For the north-south flow component, the model agrees

Chapter 6 Circulation and Transport Modeling 6-31
overall with the south-directed flow peaks, but underpredicts the northwarddirected flow peaks during the same intervals as when the east-west velocity is

underpredicted.

Comparison of velocities at Station 2 is shown in Figure 6-28. The

magnitude and direction of the calculated velocity are in good agreement with

measurements. The dominant east-west flow at Station 2 is reproduced in the

calculations. Peak east velocity is underpredicted by a typical value of

0.25 m/sec. The north-south current component is weak at Stations 2,3, and 4

compared with the east-west component. Scales on the y-axes of the velocity

plots should be noted for comparison of the east-west and north-south currents.

Currents at Station 3 are plotted in Figure 6-29. As at Station 2, calculations

agree well with measurements, both in magnitude and phase. The dominant eastwest flow is reproduced in the calculations. Typical calculated eastward current

is underpredicted by approximately 0.2 m/sec.

Currents at Station 4 are shown in Figure 6-30. The east-west current

component shows overall good agreement throughout the simulation, although

the calculated current consistently overpredicts the measured current by

approximately 0.4 m/sec on the east-directed flow. The north-south component

is weak, with the calculations apparently out of phase with measurements. This

phase difference is attributed to relatively small-scale bathymetric features that

are not resolved in the model. In addition, the range of the north-south velocity

component is smaller after Day 253 than it is before Day 253. This change in

range occurred when the instrument was serviced and the mount redeployed.

The location of the mount was different before and after servicing, which

explains the difference in the north-south current component.

Table 6-7 lists error statistics between measured and calculated velocity

components at the measurement stations. Error was calculated with the bandpass-filtered measurements. Because datum-like values are not available for

velocity, percent error was calculated with the range of values (maximum -

minimum) contained in the measurements as R, in Equation 6-15. Percent error

for the east-west velocity component was less than 10 percent for Stations 1,2,

and 3 and was 12 percent for Station 4. These low errors indicate good

agreement between calculated and measured velocity. The percent error for the

north-south component of velocity is greater, with values of 14 and 13 percent

for Stations 1, 2, and 3, and a value of 29 percent for Station 4. Stations 2,3, and

4 have relatively weak north-south velocity components, and a small-magnitude

error can give a large percent error. For Station 4, the large percent error owes

primarily to the phase difference between the measured and calculated velocity.

Circulation patterns

Representative circulation patterns for the flood and ebb portions of the tidal

cycle are presented in the form of vector plots. The vectors have been plotted

with uniform distance between them rather than at each calculation point. This

distribution of vectors increases readability of the plots, particularly in regions

dense with calculation points.

5-32 Chapter 6 Circulation and Transport Modeling
in

E

o

o

0)

>

East Sept5-Oct6, 1998 Station 1

248 253 258 263 268 273 278

0.4 North ;

248 253 258 263 268

Day 1998

273 278

. Calculated

. Measured

Figure 6-27. Time series of calculated and measured (band-pass filtered)

current at Station 1

1.5

</> 1.0

F

.& O.b

o

o

0.0

> -0.5

-1.0

-1.5

East Sept 5 - Oct 6, 1998 Station 2

i i i i I i i i i I i i i i I i i i i I i i i i I I I I I I i

248 253 258 263 268 273 278

(O

E

o

o

2

North

i !

248 253 258 263 268

Day 1998

273 278

Calculated

Measured

Figure 6-28. Time series of calculated and measured (band-pass filtered)

velocity at Station 2

Chapter 6 Circulation and Transport Modeling 6-33
East Sept5-Oct6, 1998 Station 3

) ! }

248 253 258 263 268 273

248 253 258 263 268

Day 1998

273 278

Calculated

Measured

Figure 6-29. Time series of calculated and measured (band-pass filtered)

velocity at Station 3

Station 4

248 253

" South

i i I I I I I I I I I 1—I L

248 253 258 263 268 273 278

Day 1998 Calculated

Measured

Figure 6-30. Time series of calculated and measured (band-pass filtered)

velocity at Station 4

6-34 Chapter 6 Circulation and Transport Modeling
Table 6-7

Error in Calculated Velocity Components

Station

East - West North - South

Day Range, 1998

Data Gap,

Days 1998

rms

Error,

m/sec

Percent

Error

rms

Error,

m/sec

Percent

Error

1 0.07 8 0.09 14 248.01 - 278.98 Numerous1

2 0.23 9 0.11 14 248.01 - 278.98

Numerous,

limited range2

252.70 - 254.77

3 0.27 9 0.11 13 248.01 - 278.98 252.73 - 254.82

4 0.27 12 0.12 29 248.00 - 278.67 252.77 - 253.70

1 Brief gaps are present throughout data set; gaps range from 1 to 4 points.

2 Brief gaps are present through time interval 248.16 to 252.60; gaps range from 1 to 4 points.

Figures 6-31 and 6-32 show circulation patterns for Willapa Bay on flood

and ebb tide, respectively, where no wave or wind forcing has been imposed.

During the flood cycle, strong flows are seen in the entrance and main bay

channel. Channelized flow is evident in the southern portion of the bay and into

the Willapa River. During ebb, strong flow occurs in the major channels similar

to the flood tide, but in the opposite direction. Strong flows are present in the

entrance, particularly in the North Channel. Over the bar, the northern portion of

the flow (toward the northwest) has stronger velocities further from the entrance

than do the central and southern portions of the flow (directed toward the west

and southwest). This stronger northern flow appears to be forced primarily by

the current in the North Channel, with some contribution from flow moving over

the central region of the bar.

Calculated tidal-circulation patterns in the entrance to Willapa Bay on flood

and ebb tide are shown in Figures 6-33 and 6-34, respectively. Flow in the

entrance can be roughly divided into two portions, that through the North

Channel and that over the shallower bar region south of the channel. In both

figures, strong channelized flow is present in the North Channel. The bar creates

a region of converging flow on flood tide and diverging flow on the ebb cycle.

Current patterns are well organized during both ebb and flood tide.

During storms, waves can significantly modify the current patterns from

those of the tide alone. Figures 6-35 and 6-36 show calculated currents in the

entrance to Willapa Bay during the January 1998 storm at flood and ebb tide,

respectively. Wave and wind forcing were applied in the storm calculations.

During the storm, currents at the entrance exhibit complex patterns as a result of

wave transformation and breaking.

Chapter 6 Circulation and Transport Modeling 6-35
Uli

Figure 6-31. Willapa Bay circulation pattern on flood tide

S^^^^^^W"«!'^^^^^

N\N.\\\ 1 \ ft sxvv\l r

Figure 6-32. Willapa Bay circulation pattern on ebb tide

6-36 Chapter 6 Circulation and Transport Modeling
Figure 6-33. Entrance of Willapa Bay circulation pattern on flood tide

Figure 6-34. Entrance of Willapa Bay circulation pattern on ebb tide

Chapter 6 Circulation and Transport Modeling 6-37
FT.' V,<.vvv\ AvsW.K

' r\' \VVVVn ///^Asl

/". VV..... ill I

/ /.-/I I ~.\\ It t\

./)^l ^

'<<<-\UV"—- '\^\(!''/l {<>l~<~5>**

L \r/i I //s*-~*> /^- sff.sst ,W/M\UI,.W/I /> /•/// \ I f/l\ \\\s\\ \N.VS\ \ / //J\ ////;11111 11,

\111 t

1 VNSW w I • •> jvvvwi

Figure 6-35. Entrance of Willapa Bay circulation pattern on flood tide during

January 1998 storm

-j^r^w. i\v v J i_\\C:vYI f < SN>>3JMi tflfl?

^s\\ ifi U /7t 1 /' \\v t. ''s^J)il%}/,'C/X

! I I I I 1.1.

^\U.-,, 1 t I I I I t 1 1 H\.xw\\«\\\\\ i tit ,,t lit , -,n\\\\^ ■■

\\AS>1> J\\S\\\\\\\\

U\VX }\\vv\v\\\\\ Wsvvvvww K\\\\\\\\\ JWNNWWW KsWWWW lw>»\\\\\\\ \v \\\\\\\

\v—.\\\\\\\

svwwww wvvwww

a mm

Figure 6-36. Entrance of Willapa Bay circulation pattern on ebb tide during

January 1998 storm

6-38 Chapter 6 Circulation and Transport Modeling
Flow around the SR-105 dike and groin structure during flood and ebb tide is

shown in Figures 6-37 and 6-38, respectively, for the situation of only tidal

forcing. The above-water portion of the structure is shown in the figures where

no vectors are present in the flow. On the flood cycle (Figure 6-37) an eddy

forms upstream of the structure. The eddy circulation results in a northwestdirected current in a limited region located east of the structure. During the ebb

cycle (Figure 6-38), an eddy is formed on the west side of the structure creating

an eastward flow north of the eddy. On both flood and ebb cycles, velocities east

and west of the structure are weaker than those in the North Channel. Note that

on both cycles, flow is directed east on the west side of the structure, whereas it

is directed toward the west on the eastern side of the structure.

Evaluation of Design Alternatives by Analysis of

Hydrodynamics and Sediment Movement

Calculated current velocity and sediment transport are evaluated for

Alternative channels. The model results provide guidance as to where areas of

channel infilling can be expected and identify reaches of channels where

navigation would be difficult or hazardous. By this means, Alternatives can be

compared on an objective basis. Two simulations were conducted for evaluation

of the Alternatives:

a. January 1998 storm, starting on 13 January. This storm is considered

severe with high wave energy for sediment transport. Forcing for the

circulation and sediment transport models were tides, wave stress, waves,

and wind. Wind fields, obtained from the NCEP, were at 0.25-deg

spacing and at time interval of 6 hr. Waves were calculated by STWAVE

as discussed in Chapter 5.

b. Fair-weather simulations, starting on 4 September and ending on

6 October 1998, represent typical conditions in which vessels pass

through the Willapa Bay entrance. Forcing for the models were tides and

representative waves and wave stress. Representative waves for this

simulation are given in Table 5-7.

For comparison of velocity and sediment transport, a channel was defined for

Alternative 1 based on the route that vessels took during 19985and on the

bathymetry that year. To facilitate comparison of physical quantities with other

Alternatives, the channel was specified as generally following the 28-ft mllw

contour along the vessel route. The Alternative 1 channel as defined here is

shown as a dashed line in Figure 6-39. The dashed line indicates that

Alternative 1 is not a design channel.

Personal communication, Mr. Terry Larson, local crabber, August 1999

Chapter 6 Circulation and Transport Modeling 6-39
SR105 Structure

^^^^^^^^^^^ss^cs:

Figure 6-37. Region of SR-105 structure circulation pattern on flood tide

SR105 Structure

Figure 6-38. Region of SR-105 structure circulation pattern on ebb tide

6-40 Chapter 6 Circulation and Transport Modeling
3A I

3F^- I

36^

3B 3H-a

3H-b

4E

^

V

4A

1 2 3 4 5

Figure 6-39. Regions of entrance defined for evaluation of current velocities in

channels. Regions are defined as the east-west limits of the boxes

denoted as 1, 2, 3, 4, and 5

Velocities through alternative channels

Maximum and minimum calculated speeds within the Alternative channels

are given for the January 1998 storm and for September 1998 fair weather.

Along- and across-channel current components are discussed. Strong alongchannel currents enhance self-scouring of channels, but may pose difficulties for

navigation. Strong across-channel currents can make navigation hazardous and

can carry material into channels.

Locations of the reported velocities are given in five Regions shown in

Figure 6-39. These Regions are as follows (reference Figure 6-14 for bottom

topography):

a. Far outer entrance: outer bar, most seaward extent of channels.

b. Outer entrance: interior portion of outer bar, region of curvature of

S-channel.

c. Midentrance: transition area from outer to inner bar.

d. Interior midentrance: inner bar.

e. Inner entrance: interior inner bar.

In addition to storm and fair weather conditions, current velocity was

documented with respect to the direction of the current relative to the channel

axis and for maximum and minimum speed. Along- and across-channel currents

are specified in Tables 6-8, 6-9, and 6-10. Currents are assigned "along" or

"across" designations by their dominant velocity component relative to the

channel axis. Thus, the range of direction for velocity specified as "along

channel" can range from parallel to the channel to an angle of 45 deg from

parallel. The range of direction for "across-channel" velocity can range from

Chapter 6 Circulation and Transport Modeling 6-41
Table 6-8

Maximum and Minimum Velocity in Alternative Channels for Storm1

Alternative

Maximum

Speed,

m/sec

Direction2

of

Maximum

Region3of

Maximum

Minimum

Speed,

m/sec

Direction

of

Minimum

Region of

Minimum

1 3.7 Along 3 <0.1 Mixed 3,4

3A 3.7 Along 3 <0.1 Mixed 4,5

3B

3.7

3.1

Along

Across

3

2

<0.1

<0.1

Mixed

Across

1

3,4

3F 3.7 Along 3

<0.1

<0.1

Along

Across

2

4,5

3G

3.3

3.0

Along

Across

3

2

<0.1 Mixed 5

3H-a 3.4 Along 2 <0.1 Across 1,2,4

3H-D 3.4 Along 2

<0.1

<0.1

Mixed

Across

1

3,4

4A 3.2 Along 2 <0.1 Across 2

4E 3.2 Along 3 <0.1 Along 1,5

1 January 1998 storm simulation, duration = 15 days.

2 Along or across channel at corresponding Region. Along-channei is defined as current directed at

angles ranging from 0 to 45 deg relative to channel axis. Across-channel is defined as current

directed at angles ranging from 45 to 90 deg relative to channel axis. Mixed indicates both alongand across-channel velocity.

3 Regions defined in Figure 6-39.

Table 6-9

Maximum and Minimum Along-Channel1 Velocity in Alternative

Channels for Fair Weather2at Peak Ebb and Flood Tidal Current

Alternative

Max Ebb Min Ebb Max Flood Min Flood

Speed,

m/sec Region

Speed,

m/sec Region

Speed,

m/sec Region

Speed,

m/sec Region

1 2.6 4 0.5 2 1.6 3,4 0.3 2

3A 2.6 3 0.6 1 1.3 3,4,5 0.3 1

3B 2.6 3,4 0.4 2 1.4 3,4 0.2 2

3F 2.6 3 0.7 1 1.4 3 0.3 1

3G 2.4 4 0.4 2 1.3 3,5 0.2 2

3H-a 2.0 4,5 0.5 2 1.5 5 0.5 1,2

3H-b 1.9 3,4 0.6 2 1.3 3,5 0.5 1,2

4A 2.8 3 0.3 1 1.8 4 0.3 1

4E 1.9 4 0.3 1,2 1.8 4 0.4 1,2

1 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

2 September 1998 fair weather simulation, duration = 31 days.

6-42 Chapter 6 Circulation and Transport Modeling
Table 6-10

Maximum and Minimum Across-Channel1 Velocity in Alternative

Channels for Fair Weather2at Peak Ebb and Flood Tidal Current

Alternative

Max Ebb Min Ebb Max Flood Min Flood

Speed,

m/sec Region

Speed,

m/sec Region

Speed,

m/sec Region

Speed,

m/sec Region

1 1.6 2,3 1.1 3 1.0 3 0.5 2

3A 3-- -- -- 0.7 2,3 0.7 2,3

3B 1.6 2 0.4 2 1.0 2 0.5 2

3F -- -- -- -- -- - -- -

3G 1.5 2 0.4 2 1.0 2 0.2 1,2

3H-a 0.8 1,2 0.7 1,2 0.8 3 0.4 2

3H-b 2.3 5 0.6 2 1.7 5 0.4 2

4A -- -- -- -- - -- -- --

4E 1.8 2 0.4 2 1.4 5 0.6 2

1 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

2 September 1998 fair weather simulation, duration = 31 days.

3

"-" indicates negligible current.

perpendicular to the channel to 45 deg from perpendicular. In many instances,

currents were angled at approximately 30 deg from channel-parallel. Although

these currents contain cross-channel components of flow, they were considered

as predominantly along-channel currents.

Maximum and minimum velocities within Alternatives for the January 1998

storm are listed in Table 6-8. During this storm, currents at the Willapa Bay

entrance were strongly modified by waves. Velocities were selected from hourly

snapshots during 12 hr of peak wave conditions. Current fields during this 12-hr

time interval for each Alternative are shown in Appendix G. For all Alternatives,

the maximum currents occurred in Regions 2 and 3 (Figure 6-39) and direction

was along channel. Alternatives 1, 3A, 3B, and 3F had the greatest alongchannel current speed, peaking at 3.7 m/sec. Weakest maximum current was in

Alternatives 4A and 4E, with speed of 3.2 m/sec. Alternatives 3B and 3G had

persistent cross currents in Region B that reached at least 3.0 m/sec, and these are

also listed in Table 6-8.

Minimum current speed for the January 1998 storm was less than 0.1 m/sec

for all Alternatives. Locations of minimum currents covered all Regions.

Minimum current directions did not favor a particular along- or across-channel

direction overall.

Maximum and minimum calculated along- and across-channel currents for

fair weather are listed in Tables 6-9 and 6-10, respectively. Current speeds are

given for peak ebb and flood current in the entrance. Appendix G provides tables

of maximum and minimum current speed in each Region of each Alternative for

both along- and across-channel water movement. In some cases, the maximum

Chapter 6 Circulation and Transport Modeling 6-43
and minimum current for ebb or flood within an Alternative will occur in the

same Region and owes to velocity variation along the channel.

Maximum along-channel ebb currents for Alternatives were typically

contained in Regions 3 and 4. For Alternatives 1,3A, 3B, 3F, and 3G, these

maxima were within the North Channel. Alternative 4A was found to have the

strongest calculated maximum along-channel ebb current at 2.8 m/sec, although

Alternatives 1, 3A, 3B, 3F, and 3G also had strong currents at 2.6 m/sec.

Weakest maximum along-channel ebb speeds were found for Alternatives 3H-b

and 4E at 1.9 m/sec. Minimum along-channel speeds were located in Regions 1

and 2, on the outer bar. Alternative 3F had the strongest minimum along-channel

current at 0.7 m/sec, and Alternatives 4A and 4E had the weakest at 0.3 m/sec.

Maximum along-channel currents during flood tide were weaker than those

of ebb tide for all Alternatives, indicating that the channels identified for the

Alternatives would be ebb dominated. The Alternative 1 channel was ebb

dominated during 1998. Maximum along-channel flood speed was located in

Regions 3,4, and 5. This maximum was in the North Channel for Alternatives 1,

3A 3B, 3F, 3G, and 3H-a. Alternatives 4A and 4E had the greatest maximum

along-channel speed at 1.8 m/sec, and Alternatives 3A, 3G, and 3H-b had the

weakest at 1.3 m/sec.

Minimum along-channel flood speeds were located in Regions 1 and 2 on the

outer bar. Of these currents, the greatest were in Alternatives 3H-a and 3H-b at

0.5 m/sec, and the weakest were in Alternatives 3B and 3G at 0.2 m/sec.

Maximum and minimum across-channel current speeds for each Alternative

are listed in Table 6-10. The presence and location of cross currents are more

variable than those of along-channel currents. Across-channel currents can occur

in channel locations other than those provided in Table 6-10. Appendix G

contains tables listing information on across-channel currents for all Regions of

each Alternative.

Maximum ebb across-channel current, where it exists, was located in

Region 2 with the exception of Alternative 3H-b. Alternatives 3F and 4A did not

experience crosscurrents at peak ebb and peak flood tide. Because Region 2 is in

an area of breaking waves, complex current patterns are formed and cross

currents can occur at channels. Alternatives 1, 3B, and 3G were calculated to

have persistent and strong crosscurrents within the S-curve, which may pose

difficulties for vessels traversing that area. Alternative 3H-b has strongest

maximum crosscurrent in Region 5 where this channel overlaps with the North

Channel. Strongest maximum across-channel current was located in

Alternative 3H-b with a speed of 2.3 m/sec. This strong crosscurrent is located at

the position where vessels would enter or exit this Alternative on the bay side and

may present difficulties in navigating to and from it and the North Channel.

Weakest ebb crosscurrent speeds were calculated for Alternative 3H-a in

Regions 1 and 2 at 0.8 m/sec. Maximum ebb crosscurrents in Alternatives 1, 3B,

and 3G are stronger in Region 2 than those of Alternative 3H-a indicating that

Alternative 3H-a may be easier to navigate in this Region during ebb tide.

Alternative 3A did not have crosscurrents during ebb tide.

Minimum ebb across-channel current occurs primarily in Region 2, with the

exception being Alternative 1 in which the minimum occurs in Region 3. The

6-44 Chapter 6 Circulation and Transport Modeling
greatest minimum occurs in Alternative 1 with a speed of 1.1 m/sec, and the

weakest occurs in Alternatives 3B, 3G, and 4E with speeds of 0.4 m/sec.

Maximum flood across-channel currents are distributed within Regions 2,3,

and 5. Alternatives 3B and 3G have maximum crosscurrents within the S-curve.

Alternative 3H-b has maximum crosscurrents in Region 5, at its intersection with

the North Channel. The strongest maximum flood across-channel current is in

Alternative 3H-b with speed of 1.7 m/sec, and the weakest occurs in

Alternative 3A at 0.7 m/sec.

Minimum flood across-channel currents occur in Regions 1,2, and 3. The

strongest is in Alternative 3A with a speed of 0.7 m/sec, and the weakest is in

Alternative 3G with a speed of 0.2 m/sec.

The number of Regions in which crosscurrents were calculated to occur at

peak ebb and flood during fair weather are listed in Table 6-11. Vessels traveling

through Alternatives could encounter crosscurrents within the number of Regions

listed in the table (a full listing of along- and across-channel currents for fair

weather is presented in Appendix G). The type of vessel combined with the

strength of the crosscurrent would determine whether or not a potential hazard

might exist. For evaluation purposes, smaller numbers of Regions with crosscurrents are favorable.

Table 6-11

Number of Regions in Alternative Channels with Crosscurrents1in

Fair Weather2at Peak Ebb and Flood Tide3

Alternative

Number of Regions,

Ebb

Number of Regions,

Flood

1 2 2

3A 0 2

3B 2 2

3F 0 0

3G 1 3

3H-a 2 3

3H-b 3 4

4A 0 0

4E 3 2

1 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

2 September 1998 fair weather simulation; duration = 31 days.

3 Number of Regions computed from Tables G-1 through G-9 in Appendix G.

Chapter 6 Circulation and Transport Modeling 6-45
Alternatives 1, 3B, and 3G exhibit reversals of crosscurrent in Region 2

(Figures G-18, G-20, and G-22). The S-curve has an area in which the current

flows to the northwest then rotates around forcing flow toward the southeast.

The northwest and southeast crosscurrents are adjacent to one another within the

Alternative channels. The oppositely-directed crosscurrents commence when the

tidal current switches from ebb to flood and endures for approximately 5 hr. A

vessel traversing this Region during this interval in the tidal cycle may

experience crosscurrents in one direction followed by crosscurrents from the

opposite direction.

To illustrate the velocity patterns within each of the design channels, vector

plots are presented in Appendix G at hourly intervals over two 12-hr time

intervals. The first time interval occurs during peak wave conditions in the

January 1998 storm. The second time interval is during fair weather conditions

from the September 1998 simulation. Both sets of plots show tide- and wavegenerated currents. These plots illustrate the time-varying currents including

intensification of currents by waves, formation and dissipation of eddies, and

overall circulation within and near each Alternative.

Deposition and erosion

Bathymetry change was calculated by the sediment transport model for two

situations: a 15-day storm simulation during January 1998 and a 31-day fair

weather condition from 4 September through 6 October 1998. These two

conditions were simulated to give estimates of maximum and minimum

bathymetry change expected to occur over the time scale of weeks. Volumechange calculations were conducted to determine the amount of material that was

deposited into the proposed Alternative channels. Estimates of shoaling volume

for each Alternative were made by calculating the volume difference between the

bottom elevation at the end of the simulation and the initial bottom elevation.

Shoaling volumes were calculated within the Alternative channels. Table 6-12

lists the volume deposited into the channel for each Alternative and each

condition.

Table 6-12

Deposition Volume Calculated for Alternat ve Channels

Alternative

Storm1

Volume Deposited, yd3

Fair Weather2

Volume Deposited, yd3

1 1,500,000 420,000

3A 280,000 95,000

3B 870,000 260,000

3F 600,000 190,000

3G 1,630,000 450,000

3H-a 300,000 66,000

3H-b 340,000 78,000

4A 270,000 87,000

4E 320,000 144,000

1 January 1998 storm simulation, duration = 15 days.

2 September 1998 fair weather simulation, duration = 31 days.

6-46 Chapter 6 Circulation and Transport Modeling
The greatest shoaling volume was calculated for Alternative 3G for both

storm and fair weather conditions (1,630,000 and 450,000 yd3, respectively).

The calculated volumes deposited into Alternatives 1, and 3G channel during the

January 1998 storm were almost double that of Alternative 3B, which had the

third greatest shoaling volume. Smallest shoaling volumes were calculated for

Alternatives 4A and 3A for the storm and for Alternatives 3H-a and 3H-b during

fair weather. Volumes calculated are consistent with dredging volumes for the

Pacific Ocean coast of the United States. Calculated shoaling volumes are

appropriate for this engineering study, but may not be applicable for other

studies.

Contour plots of depth change for Alternatives are given in Appendix G for

the January 1998 storm and for fair weather. Patterns of deposition and erosion

are shown and shoaling hot spots can be discerned.

Distribution and location of deposited material are central factors in

maintenance dredging. Table 6-13 lists the calculated sediment shoaling

(reduction in depth) in each Region of the Alternatives for the January 1998

storm. The storm was selected for comparison of shoaling between Alternatives

because the high-energy waves during storms induce more material transport

than during fair weather. Deposition on the outer bar in Region 1 was minimal,

with Alternatives 3A and 3F having small deposits of material. In Region 2,

deposition was variable between Alternatives. Alternatives 1 and 3G had

significant shoaling, greater than 8 ft, which occurred within the S-curve in an

area of strong crosscurrents. Alternative 3B also had significant shoaling, 5 ft,

within the S-curve area. Moderate shoaling, 3 ft, was calculated for

Alternatives 3H-a, 3H-b, and 4E. Alternative 4A had minor shoaling at 1 ft.

Dredging in Region 2 may be difficult because of the presence of breaking

waves.

Table 6-13

Shoaling in Alternative Channels for January 1998 Storm1

Alternative

Maximum Shoaling in Region, ft

1 2 3 4 5

1 — >8 >82 >8 4

3A 1 — 4 - >8

3B — 5 4 1 >8

3F 2 - 4 - >8

3G — >8 4 1 >8

3H-a — 3 >8 2 4

3H-b — 3 >8 2 5

4A — 1 >8 - -

4E — 3 3 1 -

1 January 1998 storm simulation, duration = 15 days.

2 Deposition in localized mounds.

Chapter 6 Circulation and Transport Modeling 6-47
In Region 3, sediment shoaling varied between a large amount in

Alternatives 1,3H-a, 3H-b, and 4A at more than 8 ft, and moderate in the

remaining Alternatives (3 to 4 ft). Within Alternative 1, shoaling in Region 3

was limited to relatively small mounds that did not extend across the channel (see

Figure G-27). Dredging in Region 3 may be difficult because of the frequent

presence of breaking waves.

In Region 4, there was little to no sediment shoaling in all Alternative

channels with the exception of Alternative 1. Shoaling of more than 8 ft was

calculated in Region 5 for Alternatives 3A, 3B, 3F, and 3G, and moderate

shoaling (4 to 5 ft) was calculated for Alternatives 1, 3H-a and 3H-b. The area of

shoaling was common to Alternatives within Region 5 and was located in the

North Channel seaward of the dike-and-groin structure. The presence of the

structure may have contributed to calculation of deposition near it.

Alternatives 4A and 4E had no shoaling in Region 5 (Alternative 4A does not

extend into Region 5).

Elevation change greater than 8 ft was calculated to occur in Regions 1

through 4 for Alternatives 1, 3G, 3H-a, 3H-b, and 4A during the storm.

Deposition in Alternative 4A did not extend fully across the channel, as it did for

the four other Alternatives. The deposition calculated for Alternatives 3A, 3B,

3F, and 3G in Region 5 does not present a navigation hazard because the North

Channel is deep and self-maintaining in this area.

Salinity Change in Willapa Bay

Modeling of salinity was conducted to evaluate changes in salinity within

Willapa Bay that would arise from construction of a navigation channel.

Comparisons of salinity at points in Willapa Bay were made between the existing

condition and each Alternative from a 5-day simulation of salinity transport.

Tides were the only forcing applied in the salinity simulations. Salinity modeling

was conducted by running the existing condition for 14 days so that the model

was equilibrated from the initial condition. The salinity distribution at the 14'

day served as the initial condition for the 5-day simulations. Simulations were

conducted from 15 through 20 August 1997, during spring tide. Salinity

boundary conditions at the Willapa River and Nahcotta River were set to 22 ppt

and 27 ppt. These salinity values are representative of monthly mean salinity

values for the month of August 1997, when the bay was vertically well mixed

(Newton et al. 1998). Selection of a time when the bay was vertically well mixed

is an appropriate condition for simulating salinity transport with depth-integrated

hydrodynamic and transport models.

Because salinity is a significant factor for oysters, stations for analysis of

salinity change were selected at tidal flats at 11 locations in Willapa Bay.

Salinity change was also calculated at eight stations in Willapa Bay channels.

Figure 6-40 shows the 19 stations where salinity change was calculated. Stations

were widely distributed over the bay to identify any area where significant

salinity change would occur.

6-48 Chapter 6 Circulation and Transport Modeling
Figure 6-40. Stations for salinity change analysis

Salinity change was determined by calculating the difference appearing

between the individual Alternatives and the existing condition over the 5-day

simulation. Positive values of salinity difference indicate that salinity is greater

for the Alternative than for the existing condition. At all Alternatives, the mean

salinity change over the 5-day simulation interval was calculated to be <0.1 ppt.

Greatest salinity change was calculated for Alternatives 3H-a and 3H-b in which

the average salinity was decreased by 0.2 ppt at Station 3. The remaining

Stations had calculated mean salinity changes of <0.1 ppt. These small

differences are well within variability of the system and much less than the

variation in vertical profile of salinity as measured, for example, in this study

(Chapter 4).

Chapter 6 Circulation and Transport Modeling 6-49
Summary of Circulation and Transport Modeling

Circulation and transport modeling were conducted with the goal of

evaluating Alternatives for a safe and reliable entrance channel at Willapa Bay.

Currents and water level were calculated with the finite-element model ADCIRC.

The model grid was developed from 1998 bathymetry at Willapa Bay, and high

resolution was specified in the entrance. Resolution for each Alternative was

specified so that calculation points were placed every 250 ft within the channels.

Wave-induced currents were calculated by including wave stresses,

computed from STWAVE-calculated wave parameters, in the momentum

equations within ADCIRC. Wave-induced currents caused a substantial change

in the circulation patterns compared with tidal flow only. In particular, waveinduced currents typically cause cross-channel flows and sediment deposition in

channels. Sediment transport was implemented in the ADCIRC model using the

Ackers and White total-load formulation. Both wave-induced currents and

sediment transport calculation were verified for the situation of a planar beach.

Modeling was conducted to calculate change in salinity within Willapa Bay

for each Alternative. Tides were the only forcing applied in the salinity

simulations. Calculated salinity for each Alternative showed no significant

change from the existing condition. The greatest mean salinity change, -0.2 ppt

occurred at one tidal flat location on the Willapa River for Alternatives 3H-a and

3H-b.

To evaluate proposed channel Alternatives for Willapa Bay, factors related to

navigation and maintenance dredging were calculated. With respect to

circulation, the most significant factor for navigation is the presence of crosscurrents. For maintenance dredging, the most significant factor is volume of

material deposited into the channel. As a summary of work presented in this

chapter, Table 6-14 lists Alternatives based on calculated crosscurrents during

fair weather and deposition during the January 1998 storm. Alternatives are

grouped into categories for maximum crosscurrent speed and shoaling volumes.

Alternatives within these groups are listed in order of increasing speed or

volume, as calculated by the model.

Alternatives were also listed with regard to crosscurrent speed and number of

Regions in which crosscurrents could be encountered. Alternatives 3A, 3F, 4A,

and 3H-a had weakest crosscurrent speeds, whereas Alternatives 3A, 3F, and 4A

had the fewest number of Regions in which crosscurrents might be experienced

by vessels. Thus, with respect to navigation, Alternatives 3A, 3F, and 4A would

be the preferable Alternatives because of least influence of crosscurrents on

vessels.

Table 6-14 lists three groups of Alternative channels by calculated volume of

material deposited into them during the January 1998 storm. The storm was

selected for this comparison because high waves during storms initiate

suspension of material into the water column and increase the current velocity for

material transport. Alternatives with ranks of 1 are 4A, 3A, 3H-a, 4E, and 3H-b,

as the least amount of material was deposited into their channels during the

storm.

6-50 Chapter 6 Circulation and Transport Modeling
Table 6-14

Groupinq of Alternatives Based ori Navigation and Shoaling Factors

Navigation: Crosscurrents in Alternative channels during fair weather

Max Speed during

Ebb, m/sec

Alternatives

Ebb Tide

Max Speed during

Flood, m/sec

Alternatives

Flood Tide

0.0-<1.0 3A, 3F, 4A, 3H-a 0.0-<1.0 3F, 4A, 3A, 3H-a

1.0 - <2.0 3G, 1,3B, 4E 1.0-< 2.0 1,3G, 3B,4E,3H-b

>2.0 3H-b -- --

Number of Regions

with Cross currents

on Ebb Tide

Alternatives

Ebb Tide

Number of Regions

with Crosscurrents

on Flood Tide

Alternatives

Flood Tide

0 3A, 3F, 4A 0 3F, 4A

1 3G 1 -

2 1, 3B, 3H-a 2 1, 3A, 3B, 4E

3 3H-b, 4E 3 3G, 3H-a

4 - 4 3H-b

Shoaling volume for January 1998 storm

Volume, cu yd Alternative

270,000 - 340,000 4A, 3A, 3H-a, 4E, 3H-b

600,000 - 870,000 3F.3B

1,500,000 - 1,630,000 1.3G

The four most favorable Alternatives are Alternatives 3A, 3F, 3H-a, and 4A,

if both navigation and shoaling considerations are combined. Although crosscurrents in Alternative 3F were negligible, the volume of material deposited into

it during the storm was more than twice that of the other three most favorable

Alternatives. Thus, Alternative 3F can be eliminated from evaluation based on

the present analysis.

The three most favorable Alternatives determined from this analysis are 3A,

4A, and 3H-a. Table 6-15 summarizes the properties of these three Alternatives.

Chapter 6 Circulation and Transport Modeling 6-51
Table 6-15

Properties of Most Favorable Alternative Channels Based on

Crosscurrent and Shoaling Calculations

Alternative Crosscurrents1 Shoaling2,3

3A 3 Regions on flood tide No Regions of great shoaling

4A None Great shoaling in Region 3

3H-a

3 Regions on ebb tide

4 Regions on flood tide Great shoaling in Region 3

1 All three Alternatives had crosscurrents of 1.0 m/s or less.

2 Shoaling in Region 5 in North Channel is not considered as a maintenance dredging problem.

3 Great shoaling indicated calculated depth reduction of at least 8 ft within the Alternative channel

during the January 1998 storm.

References

Ackers, P., and White, W. R. (1973). "Sediment transport: new approach and

analysis," Journal ofthe Hydraulics Division 99(11), ASCE, 2,041-2,060.

Bijker, E. W. (1967). "Some considerations about scales for coastal models with

movable bed," Publication No. 50, Delft Hydraulics Laboratory, Delft, The

Netherlands.

Dean, R. G., and Dalrymple, R. A. (1992). Water wave mechanicsfor engineers

and scientists. World Scientific, Singapore.

Garrett, J. R. (1977). "Review of drag coefficients over oceans and continents,"

Monthly Weather Review 7(105), 925-929.

Hickey, B. M. (1989). "Patterns and processes of circulation over the

Washington continental shelf and slope," Coastal Oceanography of

Washington and Oregon, M. R. Landry and B. M. Hickey, ed., Elsevier

Oceanography Series, Amsterdam, Chapter 2.

Johnson, J. W. (1973). "Characteristics and behavior of Pacific Coast tidal

inlets," Journal ofthe Waterways, Harbors and CoastalEngineering Division

99(WW3), ASCE, 325-339.

Landry, M. R., Postel, J. R., Peterson, W. K., and Newman, J. (1989). "Broadscale distributional patterns of hydrographic variables on the

Washington/Oregon shelf," Coastal Oceanography of Washington and

Oregon, M. R. Landry and B. M. Hickey, ed., Elsevier Oceanography Series,

Amsterdam, Chapter 1.

Larson, M., and Kraus, N. C. (1991). "Numerical model of longshore current

over bar and trough beaches," Journal of Waterways, Port, Coastal and

Ocean Engineering 117(4), ASCE, 326-347.

Le Provost, C, Genco, M. L., Lyard, F., Vincent, P., and Canceill, P. (1994).

"Spectroscopy of the world ocean tides from a hydrodynamic finite element

model," Journal of Geophysical Research 99(C12), 24,777-24,797.

6-52 Chapter 6 Circulation and Transport Modeling
Luettich, R. A., Westerink, J. J., and Scheffner, N. W. (1992). "ADCIRC: An

advanced three-dimensional circulation model for shelves, coasts, and

estuaries; Report 1, Theory and methodology of ADCIRC-2DDI and

ADCIRC-3DL," Technical Report DRP-92-6, U.S. Army Engineer

Waterways Experiment Station, Vicksburg, MS.

Newton, J. A., Albertson, S. L., Nakata, K., and Clishe, C. (1998). "Washington

State marine water quality in 1996 and 1997," Publication No. 98-338,

Washington State Department of Ecology, Olympia, WA.

Pacific International Engineering and PHAROS Corporation. (1997). "SR-105

emergency stabilization project; Summary report, Results of two-dimensional

hydrodynamic modeling of Willapa Bay," Seattle, WA.

Thornton, E. B., and Guza, R. T. (1986). "Surf zone longshore currents and

random waves: Field data and models," Journal ofGeophysical Research 16,

1,165-1,178.

Scheffner, N. W. (1996). "Systematic analysis of long-term fate of disposed

dredged material," Journal of Waterway, Port, Coastal, and Ocean

Engineering 122(3), ASCE, 127-133.

Shore Protection Manual. (1984). 4

th ed., 2 vol., U.S. Army Engineer

Waterways Experiment Station, U.S. Government Printing Office,

Washington, DC.

Sternberg, R. W. (1986). "Transport and accumulation of river-derived

sediment on the Washington continental shelf, USA," Journal ofthe

Geological Society, London 143,945-956.

U.S. Army Engineer District, Seattle. (1971). "Feasibility report, navigation and

beach erosion, Willapa River and Harbor and Naselle River, Washington;

Exhibit D, fish and wildlife in relation to the ecological and biological aspects

of Willapa Bay - Estuary, Washington," Seattle, WA.

Chapter 6 Circulation and Transport Modeling 6-53
7 Evaluation of Navigation

Channel Alternatives1

The objective of this study is to determine the engineering feasibility of

maintaining a reliable navigation channel through the entrance to Willapa Bay.

This chapter discusses the factors or criteria relevant for judging navigation

reliability. In addition to navigation safety, selection of feasible alternatives also

involves the cost of dredging, both through possible beneficial uses of the

dredged material and through the stability of the adjacent beach as part of the

overall inlet system.

The preceding chapters and associated appendices describe technical details

and results of the individual study tasks that generated information for evaluating

alternative channel designs. This chapter summarizes those results and adds

integrating interpretations. Material is presented in tabular and graphical form

concerning the following general categories:

a. Project operation and maintenance.

b. Navigation safety.

c. Environment and beneficial uses.

Project operation and maintenance is listed first because if the project is too

costly, it cannot go to construction, so that navigability is not an issue. Such

reasoning was applied in the screening process that reduced the original 19

alternatives to a smaller number for detailed evaluation.

Alternatives

The alternatives are described in Chapter 2. The screening process presented

in Chapters 5 and 6 and elsewhere in the report produced three basic alternative

groups, as shown in Figure 7-1. Depths are referenced to mean lower low water

(mllw).

(1) North Fairway:

Alternative 3A: 28 ft-deep by 500 ft-wide channel, fixed location.

1 Written by Mr. William C. Seabergh and Dr. Nicholas C. Kraus, U.S. Army Engineer

Research and Development Center, Coastal and Hydraulics Laboratory, Vicksburg, MS,

and by Mr. Hiram T. Arden, U.S. Army Engineer District, Seattle, Seattle, WA.

Chapter 7 Evaluation of Navigation Channel Alternatives 7-1
Alternative 3B: 28-ft-deep by 500 ft-wide migrating channel, with

minimum 1,500-ft width in S-curve.

Alternative 3F: 38-ft deep by 1,000-ft wide channel, fixed location.

Alternative 3G: 38-ft deep by 1,000 ft wide migrating channel, with

minimum 1,500-ft width in S-curve.

(2) State Route (SR)-105 alternatives:

Alternative 3H-a: 28-ft deep by 500 ft-wide channel.

Alternative 3H-b: 28 ft-deep by 500 ft-wide channel, with the SR-105

dike raised from 18 ft mllw depth to 2 ft mllw depth.

(3) Middle Fairway:

Alternative 4A: 28 ft-deep by 500 ft-wide channel.

Alternative 4E: 38 ft-deep by 1,000 ft-wide channel.

Alternatives 3H-a and 3H-b were included for evaluation after new

bathymetric measurements made during the course of this study indicated some

deepening of the south side of the north channel just seaward of the SR 105

project. These two alternatives were added to determine if any advantages could

be found in placing a navigation channel in this vicinity. Figure 7-1 shows the

alternatives.

Criteria for Evaluation of Navigation Channel

Alternatives

The criteria for evaluating the various channel alternatives were separated

into three groups, as listed in Tables 7-1, 7-2, and 7-3. Table 7-1, dealing with

operation and maintenance, comprises factors indicating estimated and calculated

sediment volumes requiring removal from the navigation channel. In Willapa

Bay, the high-energy waves, large tidal range, and strong tidal current, coupled

with environmental considerations, combine to give relatively small windows of

opportunity for dredging during the year. Evaluation of alternatives must

consider the amount of maintenance dredging required both for the cost involved

and the limited time dredging can be performed.

Two approaches were taken for evaluating the magnitude of sediment that

would need to be dredged to maintain a safe and navigable channel for the

subject alternative. A geomorphic approach examined long-term or life-cycle

project dredging requirements. This life-cycle dredging was based on a 50-year

project lifetime, and estimates were developed from results of Chapter 3. The

second factor for the operation and maintenance evaluation came from the results

of the numerical modeling discussed in Chapter 6. Volumes deposited in the

channel during a representative severe winter storm and volumes deposited

during a 31-day period of "typical" oceanic conditions defined the conditions for

this evaluation.

7-2 Chapter 7 Evaluation of Navigation Channel Alternatives
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Chapter 7 Evaluation of Navigation Channel Alternatives 7-3
Another factor of operation and maintenance relates to the estimated cost for

surveying the inlet channel. The U.S. Army Corps ofEngineers must provide

guidance to the U.S. Coast Guard (USCG) for marking channels to identify safe

access through the inlet. Before moving any channel markers, the USCG must

receive a channel survey. An Alternative which has a less stable location or

requires surveying under relatively more severe wave conditions will cost more

to survey. The variations in these costs were not significant enough with respect

to the costs associated with dredging, and were not included in Table 7-1.

Table 7-2 lists navigation safety factors. The first criterion is derived from

results ofthe modeling ofsurface waves (Chapter 5) and the discussion of wave

direction with respect to channel orientation in Chapter 2. Wave heights

averaged along the channel are included in the table for 9-ft incident ocean

waves. This wave height was considered a typical operational maximum for tugand-barge traffic. Wave angles greater than 45 deg with respect to the channel

axis are considered problematic for vessels. The Certainty ofDepth factor

evolved from the historic analysis of channel location discussed in Chapter 3 and

channel capacity to maintain a 28-ft depth. Information contributing to the

Channel Curvature and Variation in Location factor was developed from the

historical analysis ofChapter 3. Information for the Alignment ofCurrent With

Channel factor was determined by examining visual results of numerical

simulations of combined tidal circulation and surface waves model (Chapter 6).

Information contained in Table 7-3 concerns beneficial-use factors of

dredged material and erosion potential at North Cove. Potential dredged-material

placement sites are discussed in Appendix H. These results led to an overall

examination ofthe sites for each alternative, based on availability, cost, capacity,

and beneficial use. Numerical modeling oftidal currents provided information to

compare with existing conditions for North Cove Erosion Potential.

The Evaluation

Table 7-1 summarizes the evaluation ofthe operation and maintenance

factors considered. The "1998 Initial Dredging Volume" is the first item

following the "Description" column. Presently, the S-curve channel of

Alternative 3B requires minimal dredging, because it is the existing

configuration. It is now in a filling mode, however, because as the "Annual Net

Shoaling in Location of Potential Channel" column indicates, 1.0 million cu yd

offill occurred between 1998 and 1999. Alternative 3A requires 800,000 cu yd

of dredging and is in a scour mode, as this potential location had 1.1 million

cu yd ofscour in the 1998-1999 time period. The deeper versions of Alternatives

3A and 3B, 3F and 3G, because ofthe greater initial depth, require 5.7 and

4.2 million cu yd of dredging, respectively. Alternatives 3H-a and 3H-b both

require 2.1 million cu yd of dredging. The middle channel locations of

Alternatives 4A and 4B need 2.2 and 12.0 million cu yd ofinitial dredging,

respectively.

Following the aforementioned columns is the "50-Year Lifetime

Maintenance Dredging Estimate," showing the projected amounts of dredging

over a 50-year project lifetime, based on the geomorphic analysis ofChapter 3.

The volumes are presented as an estimated range of values which could occur for

a specific Alternative. The migrating channel Alternative 3B has the smallest

7-4 Chapter 7 Evaluation of Navigation Channel Alternatives
amount, a 27-48 million cu yd range over 50 years, but would probably have the

greatest likelihood of providing unsatisfactory navigation conditions, as is

discussed below. Alternative 3G, also a migrating channel that is deeper and

wider than 3B, has an estimated range of 58-102 million cu yd over 50 years.

Alternatives 3A, 3H-a, 3H-b, and 4A all have lifetime estimated shoaling volume

range of 42-74 million cu yd. The deeper and wider channel of Alternative 3F

has a lifetime shoaling estimate in the range of 114-185 million cu yd. These

shoaling volumes are converted to annual rates and compared to numerical model

results in the next paragraph.

The numerical model results of channel shoaling in Chapter 6 are listed in the

sixth and seventh columns of Table 7-1. The typical condition, 31-day

simulations of channel shoaling, and the 15-day storm results are shown.

Alternatives 3H-a, 3A, 4A, and 3H-b were reasonably close to one another in

channel shoaling. Alternative 4E had slightly greater shoaling than the

previously mentioned Alternatives, and Alternatives 3F, 3B, and 3G had

progressively increasing amounts of channel shoaling. To compare the

geomorphic and numerical modeling results, a yearly estimate of shoaling was

determined from the geomorphic 50-year estimates and, using the following

procedure, the numerical results provided an annual channel shoaling estimate:

the 15-day storm period was multiplied by a factor of 4 to represent a 60-day

period, and the 31-day typical values were multiplied by 10 to represent a

310-day period. Adding the two shoaling results produced a yearly estimate

plotted in Figure 7-2. Shoaling rates of the two approaches were in reasonable

agreement except for the migrating channel Alternatives 3B and 3G, where the

geomorphic approach allows channel movement until channel curvature

approaches 1998 conditions. Therefore, dredging is minimal until strong channel

curvature is present and the channel must be realigned.

Capacity of a channel is another central aspect in the evaluation of channel

shoaling. In the past, typical dredging did not produce a channel that would

maintain depth or alignment for the time span between dredging. This is the

reason the wider and deeper plans of Alternatives 3F and 3G were included in the

evaluation. The wider footprints of these channels capture more sediment

(shoaling), but the increased capacity will produce longer time periods of

navigable depth and alignment.

Table 7-2 presents navigability safety factors. The entries in this table derive

from the wave tests of Chapter 5 (third and fourth columns, "Wave Height and

Angle"), the historic analysis of Chapter 3 (fifth and sixth columns, "Likelihood

of Maintaining Depth Over Bar," and "Channel Curvature and Variation in

Location," respectively), and the tidal and wave-generated current modeling of

Chapter 6 ("Alignment of Current With Channel"). In the wave height and angle

columns, the large wave angles with respect to channel orientation of

Alternatives 3B and 3G are highly undesirable. Alternatives 3H-a and 3H-b had

small wave angles but slightly greater wave heights than Alternatives 3A, 3F,

4A, and 4E.

As shown in the "Likelihood in Maintaining Depth Over Bar" column of

Table 7-2, the historic analysis favors deeper dredged and migrating northern

channel Alternatives 3B, 3F, 3G, and 3H, for certainty of depth, and the middle

Chapter 7 Evaluation of Navigation Channel Alternatives 7-5
3A 3B 3F 3G 3H-a 3H-b 4A

Alternative

Typical Month

Yearly Total

- Low Geomorphic Yearly Average

15-day storm

High Geomorphic Yearly Average

Note 1: Yearly total calculated as 4 times the storm volume plus 10 times the typical monthly volume

Note 2: Geomorphic volumes for Alternatives 3B and 3G assumes the channel moves and dredging

only occurs during periodic readjustment of channel to north. The channel is relocated when

S-curve becomes difficult for navigation.

Figure 7-2. Yearly shoaling estimates based on geomorphic analysis and

numerical modeling

channels less favorably. As far as "Channel Curvature and Variation in

Location" ratings, Alternative 4E is highest because of its large width and depth,

and its distance from the migrating northern spit. Alternatives 3A, 3F, 3H, and

4A are considered to have reasonable success at maintaining alignment and

location through dredging activity.

The fourth factor of "Alignment of Current With Channel," evaluated in

Table 7-2, was determined from results in Chapter 6. Good alignment of the

currents with the channel is critical for tugs towing non-powered barges.

Alternatives 3A, 3F, and 4A have good flow alignment with the channel. The

other alternatives have reasonable alignment except for Alternative 3B, which

has the strongest crosscurrents.

Table 7-3 compares alternatives for "Beneficial Use of Dredged Material and

Erosion Potential." The evaluation of dredged-material disposal sites presented

in Appendix H and summarized in Chapter 2 were consulted for this table. The

straight northerly channel routes of Alternatives 3A, 3F, 3H-a, and 3H-b tend to

rate higher overall with regard to proximity to available disposal sites and

beneficial usage for the dredged material. Alternatives 3B and 3G are at a

slightly greater distance from the optimal disposal sites. Alternatives 4A and 4E

require sidecast dredging or use of the Goose Point disposal site.

7-6 Chapter 7 Evaluation of Navigation Channel Alternatives
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Chapter 7 Evaluation of Navigation Channel Alternatives 7-9
Appendix A

Historical Charts1

This appendix contains reduced-size copies of the 1-in.- to 2,000-ft- and

1-in.- to 5,000-ft-scale drawings compiled and analyzed in Chapter 3 of the main

text.

The original drawings are stored in the archives of the U.S. Army Engineer

District, Seattle. Digital data from the Seattle District surveys conducted in the

1990s were plotted in a similar style to complete the presentation here of one

chart for each of the years analyzed in this study. Inquiries concerning archive

holdings can be addressed to Ms. Joyce E. Rolstad, Engineering Records and

Information Section, CENWS-ED-TB-RI, U.S. Army Engineer District, Seattle.

P.O. Box 3755, Seattle, WA 98124-3755, (206) 764-6704.

1 Organized by Mr. Edward B. Hands, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS. Messrs. Fulton C. Carson and Michael

Martinez scanned full-size copies of the archived D- and C-size charts at 150 dots per inch for use

by Mses. Mary C. Allison and Leonette J. Thomas in preparation of this appendix. Selected charts

were digitized for volume calculations.

Appendix A Historical Charts A-1
A-2 Appendix A Historical Charts
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Appendix A Historical Charts A-3
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SURVEY OF NOV. 1890.

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Appendix A Historical Charts. A-65
A-66 Appendix A Historical Charts
Appendix B

1

Template Layouts and Recent

Volume Changes

Figures in this appendix show positions within the bay entrance ofseven

templates corresponding to the three categories of channel alternatives that

passed screening as described in Chapters 2 and 7 ofthe main text. A template is

a geometric form that matches the channel design cross section (width, depth,

and side slopes). The volumes of erosion (cut) and deposition (fill) within the

templates between the 1998 and 1999 surveys are tabulated. Average, maximum,

and minimum thicknesses and the spatial distribution of changes are shown in

tables and graphs.

This appendix summarizes 1998-99 channel changes within templates

covered by dense soundings that were collected concurrently with extensive

process measurements. The numerical simulations presented in Chapter 6 are

also for this year. Because changes from one year to the next can vary widely,

Chapter 3 combined 1998-to-1999 changes with statistics from other years

(Table 3-4 and 3-5) and other templates (Figure 3-22) to derive the likely longterm cumulative dredging requirement for each channel alternative (Table 3-7).

Depths are referenced to mean lower low water (mllw).

1 Written by Mr. Edward B. Hands, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory (CHL), Vicksburg, MS. Ms. Mary C. Allison (CHL) prepared

the digital images.

Appendix B Template Layouts B-1
North Channel Option

Template 3A

124 ft

20

15

10

,

5~

0

•5

•10 '

15 !

•20

I

si

ä

!

I

22 ft

low water line

,— high water line

1998 Bathymetry

Above or Below

Design Depth

(28 ft mllw)

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

Cu yd

Cut

cu yd

Net

Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cu yd cu ft/sq ft

Above Design Depth 3.7E+04 8.0E+05 -7.6E+05 5.2E+04 0.1 -1.1E+06 -1.7

Below Design Depth 1.4E+05 -3.8E+06 -3.7E+06

Total 1.7E+05 -4.6E+06 -4.5E+06 2.5E+05 0.4 -6.3E+06 -9.9

NOTE: Template area = 17,168,038 sq ft.

B-2 Appendix B Template Layouts
North Channel Option

Template 3B

N^ Aw 4Li M110 (TI^&^LJ

^^llj"äjfeäV.

|l7ft

15

10 1

5

0

-5 "i

•10 1

-15 1

-20 1

•25 1

|-26 ft

i— high water line

*ftL ^

^ 28 ft

depth

\ y. mllw

0 miles 2

s^\0\

j \ 28 ft

p km 3

1998 Bathymetry 28 ft /^\J) \

Though natural channels were smaller than design alternatives, the calculated

changes shown for the other pages in this appendix are indicative ofthe shoaling

potential during 1998-1999. For the migrating Alternative 3B, however, the changes

within Template 3B do not represent either long-term changes or more importantly any

specific dredging requirement because, ifAlternative 3B had been present, unacceptably

large-volume dredging would probably have been scheduled in 1998 to relocate the

authorized channel to a more northerly position close to Alternative 3A. The changes

shown here do represent what would have occurred during 1998-1999 within

Template 3B. These measured changes compare well with modeled current and

deposition patterns for the same area based on simulated conditions for shorter periods

during this same year (Chapter 6 and Appendix G).

Above or Below

Design Depth

(28 ft mllw)

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

cu yd

Cut

cu yd

Net Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cu yd cu ft/sq ft

Above Design Depth 1.0E+06 -3.4E+03 1.0E+06 1.4E+06 1.2 1.4E+06 1.2

Below Design Depth 2.4E-5-06 -2.0E+06 4.3E+05

Total 3.4E+06 -2.0E+06 1.4E+06 4.9E+06 1.1 2.0E+06 1.6

NOTE: Template area = 33,155,116 sq ft.

Appendix B Template Layouts B3
North Channel Option

Template 3F

1998 Bathymetry

Above or Below

Design Depth

(38 ft mllw)

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

cu yd

Cut

cu yd

Net Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cu yd cu ft/sq ft

Above Design Depth 3.1E+05 -3.2E+06 -2.9E+06 4.3E+05 12.7 ^.1E+06 -121.3

Below Design Depth 1.3E+05 -2.3E+06 -2.2E+06

Total 4.3E+05 -5.5E+06 -5.1E+06 6.1E+05 17.9 -7.2E+06 -212.0

NOTE: Template area = 24,499,897 sq ft.

B-4 Appendix B Template Layouts
North Channel Option

Template 3G

ÄMl

^JlKlK /fjfcl'lJj*!j?rflB Mfrri

.--^ur

JwSr

Id»

^^rojloS»^.

4K^pr

|l7ft

15

10 1

5

0

-5

i

1

-10 1

-15 1

-20

-20 ft

■■■■ low water lire

,— high water line

3G / ..

^\\<

^- 28 ft

depth

\ y% mllw

0 miles 2

s^icd

\ 28 ft

p km 3

1998 Bathymetry 28 ft AJF \

Though natural channels were smaller than design alternatives, the calculated

changes shown for the other pages in this appendix are indicative ofthe shoaling

potential for those Alternatives during 1998-1999. For the migrating Alternative 3G, the

changes within Template 3G do not represent either long-term changes or more

importantly any specific dredging requirement because, if Alternative 3G had been in

effect, relocation dredging would probably have been scheduled in 1998 to move the

authorized channel to a more northerly position close to Template 3F. The changes

shown here do represent what would have occurred during 1998-1999 within Template

3G. These changes compare well with modeled current and deposition patterns for the

same area, based on simulated conditions for shorter periods during the same year

(Appendix 3G).

Above or Below

Design Depth

(38 ft mllw)

Above Desiqn Depth

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

cu yd

Cut

cu yd

Net Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cu yd cu ft/sq ft

3.5E+06 -7.5E+05 2.7E+06 4.9E+06 3.0 3.9E+06 2.4

Below Design Depth 3.7E+05 -3.3E+06 -2.9E+06

Total 3.8E+06 -4.0E+06 -1.6E+05 5.4E+06 3.4 -2.3E+05 -0.1

NOTE: Template area = 43,596,918 sq ft.

Appendix B Template Layouts B5
SR-105 Channel Options 3Ha and 3Hb

Template 3H

|13ft

10- 1

5

0'

5

10- I

-15 1

-20' 1

-25 1

{-27 ft

low water line

.— high water line

3Hs4&-^"

.{pv.

^- 28 ft

depth

V y. mllw

0 miles 2

| \ 28 ft

1 p km 3

•^-fct

1998 Bathymetry 28 ft /U7 \

Above or Below

Design Depth

(28 ft mllw)

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

cu yd

Cut

cu yd

Net Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cuyd cu ft/sq ft

Above Design Depth 5.7E+05 -1.0E+06 -4.5E+05 8.0E+05 1.3 -6.3E+05 -1.0

Below Design Depth 1.1E+05 -1.7E+06 -1.5E+06

Total 6.8E+05 -2.7E+06 -2.0E+06 9.6E+05 1.5 -2.8E+06 -4.4

NOTE: Template area = 17,061,317 sq ft.

B-6 Appendix B Template Layouts
Middle Channel Option

Template 4A

[22 ft

20

15 |

10:

5

0 3

-5 I

-10; 1

•15 I

•20 1

-24 ft

low water line

high water line

1998 Bathymetry

Above or Below

Design Depth

(28 ft mllw)

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

cu yd

Cut

cu yd

Net Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cu yd cu ft/sq ft

Above Design Depth 2.9E+05 -2.4E+05 5.1E+04 4.1E+05 0.9 7.2E+04 0.2

Below Desiqn Depth 4.0E+05 -4.5E+05 -5.3E+04

Total 6.9E+05 -6.9E+05 -1.7E+03 9.7E+05 2.2 -2.4E+03 0.0

NOTE: Template area = 11,923,267 sq ft.

Appendix B Template Layouts B7
Middle Channel Option

Template 4E

( 38 ft

30- 1

20;

10 1

0 I

10

-20-

-24 ft 1998 Bathymetry

Above or Below

Design Depth

(38 ft mllw)

8-Month Change 8/98 to 4/99 Annualized Change Rate

Fill

cuyd

Cut

cu yd

Net Change

cu yd

Fill Net Change

cu yd cu ft/sq ft cu yd cu ft/sq ft

Above Desiqn Depth 1.6E+06 -1.7E+06 9.0E+04 2.2E+06 1.5 -1.3E+05 -0.1

Below Desiqn Depth 4.1E+05 -1.1E+06 -6.8E+05

Total 2.0E+06 -2.8E+06 -7.7E+05 2.8E+06 1.9 -1.1E+06 -0.7

NOTE: Template area == 39,797,130 sq ft.

B-8 Appendix B Template Layouts
Appendix C

Winter-Wave Time Histories1

This appendix includes plots of 5 months of winter waves measured at the

Grays Harbor, WA, buoy (December 1996 - February 1998). The average winter

wave height is 3 m, and the wave height exceeds 3 m for 42 percent of the

winter. A wave height of 3 m is approximately the upper limit for navigating the

Willapa Bay entrance.

>

n

5

December 1996

—Wave Height

Wave Direction

12/1/96 0:00 12/6/96 0:00 12/11/96 0:00 12/16/96 0:00 12/21/96 0:00 12/26/96 0:00 12/31/96 0:00

Date

1 Written by Dr. Jane McKee Smith, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS.

Appendix C Winter-Wave Time Histories C-1
01

«

X

0) >

a

?

January 1997

A^«<***t

«? ♦♦♦♦

-•300

IT*

- A

Wave Height

Wave Direction

, , 1 1 1 1

L

0

1/1/97 0:00 1/6/97 0:00 1/11/97 0:00 1/16/97 0:00 1/21/97 0:00 1/26/97 0:00 1/31/97 0:00

Date

February 1997

«*» * ^f -U»

—Wave Height

Wave Direction

240 _

2/1/97 0:00 2/6/97 0:00 2/11/97 0:00 2/16/97 0:00 2/21/97 0:00 2/26/97 0:00

Date

C-2 Appendix C Winter-Wave Time Histories
January 1998

0>

I

Wave Height

Wave Direction

1/1/98 0:00 1/6/98 0:00 1/11/98 0:00 1/16/98 0:00 1/21/98 0:00 1/26/98 0:00 1/31/98 0:00

Date

February 1998

"Wave Height

Wave Direction

2/1/98 0:00 2/6/98 0:00 2/11/96 0:00 2/16/98 0:00 2/21/98 0:00 2/26/98 0:00

Date

Appendix C Winter-Wave Time Histories C-3
Appendix D

Representative Wave Plots1

This appendix includes plots ofthe transformation ofrepresentative waves

calculated by the STWAVE model as described in Chapter 5. Fifteen waves

were transformed for channel Alternatives 1 (existing condition), 3A, 3B, 4A,

and 3H. The plots for each alternative appear on a single page with wave heights

in the top plot and wave directions in the bottom plot. For each plot, the 15

incident wave conditions are listed across the bottom. Across the top ofthe plot

are bars giving the probability of occurrence (reference to the right-hand scale).

For each wave condition, nine bars represent three locations in the channel

(outer, middle, and inner) and three typical tides/currents (mean low water

(mlw)/ebb, mean sea level (msl)/slack, and mean high water (mhw)/flood). The

channel alignments are plotted as horizontal lines for reference.

For Alternatives 1 and 3A, the outer channel and midchannel alignment is

approximately 305 deg and the inner channel alignment is 270 deg. For

Alternative 4A, the channel is straight with an alignment of 270 deg throughout

the channel. The channel alignment for Alternative 3B is sinuous. The

alignment is approximately 300 deg in the outer channel, 270 deg in the

midchannel, and 230 deg in the inner channel. The channel alignment for

Alternative 3H is 281 deg.

1 Written by Dr. Jane McKee Smith, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS.

Appendix D Representative Wave Plots D-1
0 i~«,,r

,l~K»n,~wi,v,~wu^uw^w^~ww,—m^~w^~w^^aw,~um^ ww,~u.<wl*tiM^ 100

225 247.5 270 297.5 315 270 297.5 270 225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2,5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8, sec 8 sec 8 sec 12 sec12 sec16sec 8 sec 8 sec 8sec 12 sec12 sec12 sec16 sec

Wave

mlw/ebb outer msl/slack outer mhw/flood

mlw/ebb mid jgmsl/släck mid Hmhw/flood

amlw/ebb inner Hmsl/slack inner Omhw/flood

Probability

mid

inner

225 247.5 270 297.5 315 270 297.5 270 225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5m, 1.5m, 1.5m 1.5m, 1.5m, 1.5m, 1.5m, 1.5m, 2.5m, 2.5m, 2.5m, 2.5m, 2.5m, 2.5m, 2.5m,

8 sec 8sec 8, sec 8 sec 8 sec 12 sec 12 sec 16 sec 8 sec 8 sec 8 sec 12 sec 12 sec 12 sec 16 sec

Wave

100

D-2 Appendix D Representative Wave Plots
Alternative 3A

mlw/ebb outer

mhw/flood

Hmsl/slack mid

BJmlw/ebb inner

Qmhw/flood inner

msl/slack outer

^mlw/ebb mid

mhw/flood mid

tJmsl/slack inner

Probability

ja

n

a

o

0 l»'l»l!Ml»l[»aLL!»^-il,nn-riini». " "' » ' .-f—^-^"-""'— 100

225 247.5 270 297.5 315 270 297.5 270 225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8sec 8 sec 8 sec 12 sec12 sec 16 sec 8 sec 8 sec 8 sec 12 sec 12 sec 12 sec 16 sec

Wave

Alternative 3A

mlw/ebb outer

^mlw/ebb mid

Qmlw/ebb inner

Probability

msl/slack outer

0 msl/slack mid

Hmsl/slack inner

mhw/flood

mhw/flood mid

mhw/flood inner

225 247.5 270 297.5 315 270 297.5 270 225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8 sec 8sec 8 sec 8 sec 8 sec 12 sec 12 sec 16 sec 8 sec 8 sec 8 sec 12 sec12 sec12 sec16 sec

Wave

Appendix D Representative Wave Plots D-3
Alternative 3B

mlw/ebb outer msl/slack outer mhw/fiood

Elmlw/ebbmid Eä msl/slack mid Emhw/flood mid

Smlw/ebb inner S msl/slack inner mhw/flood inner

DProbability

225 247.5 270 297.5 315

deg, deg, deg, deg, deg,

270 297.5 270 225

deg, deg, deg, deg,

270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8 sec 8 sec 8sec 12 sec 12 sec16 sec 8sec 8 sec 8 sec 12 sec 12 sec 12 sec 16sec

Wave

Alternative 3B

mlw/ebb outer msl/slack outer mhw/flood

Elmlw/ebb mid 0 msl/slack mid mhw/flood mid

Qmlw/ebb inner Qmsl/slack inner Qmhw/flood inner

Probability

230

225 247.5 270 297.5 315

deg, deg, deg, deg, deg,

270 297.5 270

deg, deg, deg,

225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8sec 8sec 8sec 12 sec12 sec16 sec 8sec 8sec 8 sec 12 sec 12 sec 12 sec 16 sec

Wave

n

n

A

o

100

D-4 Appendix D Representative Wave Plots
Alternative 4A

mlw/ebb outer

^mlw/ebb mid

Smlw/ebb inner

Probability

msl/slack outer

Eimsl/slack mid

H msl/slack inner

mhw/flood

mhw/flood mid

mhw/flood inner

.0

IS

a

o

100

225 247.5 270 297.5 315 270 297.5 270 225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m. 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8 sec 8 sec 8 sec 12 sec12 sec16 sec 8 sec 8sec 8sec 12 sec12 sec12 sec16 sec

Wave

Alternative 4A

mlw/ebb outer msl/slack outer mhw/flood

^mlw/ebbmid ESmsl/slack mid mhw/flood

mlw/ebb inner Hmsl/slack inner Emhw/flood

Probability

mid

inner

230

225 247.5 270 297.5 315 270 297.5 270 225 270 297.5 247.5 270 297.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8 sec 8 sec 8 sec 12 sec 12 sec 16 sec 8 sec 8 sec 8 sec 12 sec12 sec12 sec16 sec

Wave

Appendix D Representative Wave Plots D-5
Alternative 3H

mlw/ebb outer

mhw/flood

Emsl/slackmid

[^mlw/ebb inner

mhw/flood inner

msl/slack outer

gmlw/ebb mid

Ejmhw/flood mid

Hmsl/slack inner

Probability

225

deg,

1.5 m,

8 sec

247.5 270

deg, deg,

1.5 m, 1.5 m,

8sec 8 sec

292.5

deg,

1.5 m,

8 sec

315 270 292.5

deg,

270

deg,

292.5 270 225 270 292.5 247.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, ~~a, —3,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8 sec 12 sec 12 sec 16 sec 8 sec 8 sec 8 sec 12 sec 12 sec 12 sec 16 sec

Wave

Alternative 3H

mlw/ebb outer Bmsl/slack outer mhwflood outer

^mlw/ebb mid ^msl/slack mid Smhw/flood mid

^mlw/ebb inner Bmsl/slack inner Dmhw/flood inner

Probability

230

225 247.5

deg, deg,

1.5 m, 1.5 m,

8 sec 8sec

270 292.5 315 270 292.5 270 225 270 292.5 247.5 270 292.5 270

deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg, deg,

1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 1.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m, 2.5 m,

8sec 8sec 8sec 12 sec12 sec16sec 8sec 8sec 8 sec 12 sec12 sec 12 sec 16 sec

Wave

a

n

o

100

D-6 Appendix D Representative Wave Plots
Appendix E

Wave Climate

Intercomparisons1

Wave-climate statistics from the Grays Harbor buoy are accessed in this

report to describe the wave climate incident at Willapa Bay (Chapter 5). Wave

data from the Long Beach slope array and the Columbia River bar buoy were

also analyzed to collaborate climate information obtained from the Grays Harbor

buoy. Differences were found between the Grays Harbor and Long Beach wave

directional distributions. The purpose of this appendix is to discuss these

differences and document why the Grays Harbor data were selected to provide

offshore boundary conditions for wave modeling conducted in this project.

The Grays Harbor, Long Beach, and Columbia River bar gauges are

described in Chapter 5. For review, the Grays Harbor buoy is located northwest

of Willapa Bay (closest gauge to the entrance) in a water depth of 40 m. The

Long Beach slope array was southwest of the entrance in a water depth of 10 m.

The Columbia River bar buoy is still further southwest in a water depth of 128 m.

Table E-l shows the percent occurrence of wave directions for the Grays Harbor

buoy, Long Beach slope array, and the Columbia River bar buoy. In this table,

each month is given the appropriate weight (based on the number of days in the

month), so large gaps in the data sets do not bias the statistics toward a particular

month or season. Also, Grays Harbor data with sampling intervals of 1 hr or less

were decimated to 3-hr intervals for consistency. The percent coverage of data

for each month is given in Table E-2. The Grays Harbor and Columbia River

buoys have similar directional distributions, with the Columbia River buoy

recording slightly more waves from the northwest and fewer from the southwest.

The Long Beach array gives a much different distribution with more waves

from the west (270-deg band), more from the southwest (247.5-deg band), and

fewer from the northwest (292.5-deg band) (Table E-l). These directional

differences between the gauges could reverse the direction of estimated

longshore sediment transport and change the magnitude of transport. Thus, some

explanation of the differences is required to select the most appropriate climate

for furnishing offshore boundary conditions to the wave transformation model.

1 Written by Dr. Jane McKee Smith, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS.

Appendix E Wave Climate Intercomparisons E-1
Table E-1

Wave Direction Distributions

Direction

Deg

Grays Harbor Buoy

% occurrence

Long Beach Array

% occurrence

Columbia River Bar Buoy

% occurrence

180.0 0.6 1.8 1.0

202.5 3.8 2.7 4.6

225.0 9.4 8.9 7.6

247.5 12.1 31.4 8.2

270.0 37.8 45.7 33.0

292.5 30.5 8.3 32.0

315.0 5.3 0.4 12.0

337.5 0.1 0.0 1.1

360.0 0.0 0.0 0.4

Table E-2

Percent Data Coverage by Month

Month

Grays Harbor Buoy

% coverage

Long Beach Slope Array

% coverage

Columbia River Bar Buoy

% coverage

Jan 8.7 8.3 9.8

Feb 8.4 7.7 3.1

Mar 8.6 8.4 3.4

Apr 5.9 8.1 3.3

May 7.4 8.0 9.6

Jun 7.7 7.0 10.0

Jul 9.4 5.7 10.9

Aug 8.9 8.3 11.0

Sep 9.7 10.0 10.3

Oct 10.1 10.8 10.4

Nov 7.3 9.0 10.0

Dec 7.9 8.6 8.2

Figure E-1 compares a time-history of zero-moment wave height measured at

the Grays Harbor and Long Beach gauges for March 1995 (one of the few

coincident months of data). The heights agree well for this month. For some

events, the Long Beach heights are higher, probably produced by local wave

shoaling in the shallower water. For the largest wave height in the month, the

Grays Harbor buoy wave height is higher, probably because of depth-limited

breaking at the Long Beach gauge. Figure E-2 compares significant wave

direction for the same month. The directions for the two gauges show similar

trends, but there are significant differences. First, the Grays Harbor directions

E-2 Appendix E Wave Climate Intercomparisons
— Long Beach

~*~ Grays Harbor

3/1/95 3/6/95 3/11/95 3/16/95 3/21/95 3/26/95 3/31/95

Date

Figure E-1. March 1995 wave heights for Long Beach slope array and Grays Harbor

buoy

are generally more oblique (further from 270 deg). Reduced obliqueness at the

Long Beach gauge is caused by more refraction (wave aligning with the normal

to shore, 270 deg). Second, the Long Beach directions oscillate 5 to 25 deg with

the tide (most obvious in the last third of the record), caused by refraction over

the tide-varying water depth. The tidal variation in direction is strongest at Long

Beach because the tide range is a large fraction of the water depth (on the order

of one-third the depth).

Figure E-3 shows a scatter plot of measured directions for March 1995 for

the Grays Harbor and Long Beach gauges. This shows again the reduced spread

in direction at the Long Beach gauge caused by refraction. The mean wave

direction for March 1995 was 256.8 deg at the Grays Harbor gauge and

253.2 deg at the Long Beach gauge. Figures E-2 and E-3 support the increased

occurrence of waves in the 270-deg band at Long Beach (45.3 percent at Long

Beach versus 37.8 at Grays Harbor), but they do not explain why the Long Beach

array distribution is skewed to the south and that of the buoy is skewed to the

north. The local bottom contour and shoreline orientation at both Grays Harbor

and Long Beach are approximately north-south. Thus, local refraction does not

explain the difference in distribution skewness. To better understand the

difference in directional distribution, the monthly variation in direction is

investigated in the next paragraph.

Appendix E Wave Climate Intercomparisons E-3
360

330

180

"Long Beach

• Grays Harbor

03/01/95 03/06/95 03/11/95 03/16/95 03/21/95 03/26/95 03/31/95

Date

Figure E-2. March 1995 wave directions for Long Beach slope array and Grays

Harbor buoy

The monthly-averaged wave directions for Grays Harbor and Long Beach are

given in Figures E-4 and E-5, respectively. Each year is plotted separately to

show year-to-year variability and anomalies in the data. The Grays Harbor buoy

data exhibit a strong trend of southwesterly mean direction from November to

April and northwesterly direction from May to October, with a total range of 240

to 300 deg. The Long Beach gauge data show much less seasonal variation in

mean direction (range of 240 to 280 deg). In May through July, the monthly

mean wave directions at Long Beach are 10 to 20 deg less than at Grays Harbor.

During the other months, the mean directions are similar at the two gauges.

Figure E-6 shows coincident months of mean wave directions for Grays Harbor

and Columbia River (the Long Beach gauge stopped operating by the time the

Columbia River buoy became directional). This figure indicates good seasonal

agreement in wave direction between Grays Harbor and Columbia River. This

agreement supports the accuracy of the Grays Harbor measurements and brings

into question the measured directions by the Long Beach gauge.

Because of the good direction agreement between Grays Harbor and

Columbia River buoys, which bracket the Willapa entrance and the Long Beach

gauge position, it is concluded that the Grays Harbor gauge is most

representative of the wave climate at Willapa Bay. The difference in summer

wave angles at the Long Beach gauge may be related to limitations of the

bottom-mounted pressure gauge in resolving wave direction for the shorterperiod summer waves in 10-m water depth. In addition to the apparent problems

in resolving the direction of summer (shorter period) waves at Long Beach, the

gauge has a compressed directional variation because of refraction, increased

variance in direction introduced by the tide, and depth limitations for maximum

E-4 Appendix E Wave Climate Intercomparisons
wave height. These factors make the Grays Harbor buoy the appropriate source

of wave climate information for the Willapa entrance.

People with local experience navigating the Willapa entrance have stated that

waves from the southwest are significant and suggested that they may be

underrepresented in the Grays Harbor climate. This perception of underrepresentation may owe to the fact that although the waves south of west

comprise only 26 percent of the distribution, these waves include the large winter

storm waves that can limit navigation and are the most visible.

c

0

O

P

0)

>

(0

L.

0

n

X

in

>.

ra

320.

~. 300-

O

o

280-

260-

240-

220-

Ü 200-

Line of Perfect

Agreement

180 200 220 240 260 280 300

Long Beach Wave Direction (deg)

320

Figure E-3. Scatter plot of Grays Harbor and Long Beach wave directions for

March 1995

Appendix E Wave Climate Intercomparisons E-5
OS

> 250

240

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Figure E-4. Monthly average wave directions for Grays Harbor buoy

300

240 -i r~

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Figure E-5. Monthly average wave directions for Long Beach slope array

E-6 Appendix E Wave Climate Intercomparisons
300

g> 290

c

i 280

» 270

n

0)

< 260

£

C

| 250

240

- -GH98

•- CR98

-»-GH97

-- -CR97

- -®- GH96

•€> CR96

-*-GH95

- *■■ CR95

.

•

• /A"'.

/*'/\*/7 v •

•-_..../*/

/ / .-*V.;4

.

, .._

•—~/*\

/'"" •

..-*

\

\X V' '

'S* ""* K*>ZlL

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Figure E-6. Monthly average wave directions for coincident Grays Harbor buoy and

Columbia River bar buoy measurements

Appendix E Wave Climate Intercomparisons E-7
Appendix F

Comparison of Buoy and

Pressure Gauge

Measurements1

Wave measurements in Willapa Bay at Stations 2 and 3 were made with

bottom-mounted pressure gauges in water depths of approximately 10 m

(Chapter 4). The maximum current magnitudes at Stations 2 and 3 were

approximately 1.5 m/sec on ebb and 1.0 m/sec on flood. The bottom-mounted

pressure gauges were used to estimate the wave height on the surface by

correcting for the attenuation of the wave pressure between the surface and the

bottom. This correction factor is a function of water depth and tidal current.

Examination of the surface-corrected pressure measurements showed spectral

energy densities that increased exponentially at frequencies greater than about

0.2 to 0.3 Hz. This divergence of the spectrum occurred at lower frequencies

during flood currents (0.2 to 0.25 Hz) and at higher frequencies during ebb

currents (0.25 to 0.3 Hz). Wave heights calculated from the surface-corrected

pressure spectra are dependent on the choice of the spectral cutoff (the higher the

cutoff, the larger the wave height).

To quantify the appropriate cutoff to be specified in the wave analysis, a

wave buoy and pressure gauge were installed at Station 2 for two short-term

deployments. The wave buoy follows the water surface and thus does not require

application of a correction factor as does the pressure gauge. In this appendix,

the spectra from the surface-following buoy and the bottom-mounted pressure

gauge are compared to select the most appropriate spectral cutoff. The purpose

of this appendix is to describe the comparison of the buoy and pressure gauge

data and document the cutoff used in analysis of the pressure data for Stations 2

and 3.

1 Written by Dr. Jane McKee Smith, U.S. Army Engineer Research and Development Center,

Coastal and Hydraulics Laboratory, Vicksburg, MS, Messrs. Keith Kurrus and Charles E. Abbott,

Evans-Hamilton, Inc., and Mr. Scott Fenical, Pacific International EngineeringPLLC.

Appendix F Wave Gauge Analysis F-1
Gauge Deployment

The wave buoy deployed was a 0.9-m diameter, nondirectional Waverider

manufactured by Datawell B.V. The pressure gauge was a Paroscientific, Inc.,

pressure sensor, which was deployed on a tripod (approximately 1 m off the

bottom) with a SonTek ADVOcean current meter to give directional

characteristics and current magnitude and direction. The gauges were deployed

on 14 May 1999. The tripod was recovered on 28 May 1999. Data quality

checks in the field revealed the tripod fell on its side after approximately two

days for unknown reasons. After the tripod fell, output from the ADVOcean

pitch, roll, and compass sensors was invalid, producing corrupted current data.

Therefore, the tripod was redeployed on 28 May to acquire additional

measurements. Both the buoy and tripod were recovered on 9 June 1999, and

data quality checks confirmed the tripod remained upright throughout the second

deployment. These two deployments are denoted as Deployments 7 and 8,

respectively (the previous deployments are documented in Chapter 4). The

locations and depths of the gauges are given in Table F-l.

Table F-1

Gauge Deployment Times and Locations

Deployment Waverider Buoy Tripod Deployment 7 Tripod Deployment 8

Deployment date1 14 May 1999 13:55 GMT 14 May 1999 14:12 GMT 28 May 1999 21:21 GMT

Recovery date1 9 June 1999 23:00 GMT 28 May 1999 13:45 GMT 9 June 1999 22:45 GMT

Latitude 46° 41'46.88547" 46° 41'47.77641" 46° 41'47.98735"

Longitude 124° 05'57.94298" 124° 05' 55.3766" 124° 05'55.70806"

Depth 9.3 m mllw2 9.1 m mllw 9.1 m mllw

1Times given in Greenwich Mean Time (GMT).

2Mean lower low water.

Spectral Comparisons

Figures F-l through F-3 show sample spectra from the buoy and pressure

gauge. Figure F-l shows a typical case where the pressure gauge spectrum

diverges at around 0.3 Hz. This type of divergence is expected if a bottommeasured pressure signal is corrected to estimate the water-surface displacement.

The pressure correction increases exponentially with frequency; at some illdefined "high" frequency, the noise of the measurement system, multiplied by

the pressure correction, far exceeds the wave signal. The spectrum should be

truncated at a frequency below this point. The pressure correction is calculated

as

1 coshjkd) |

R

2

p ~\cosh[k(z + d)]\

(F-l)

F-2 Appendix F Wave Gauge Analysis
1

0.9-

0.8-

"N 0.7- I

J.0.6-

£

8 0.5-

a

O

»0.4-

k.

a

UJ 0.3-

0.2-

0.1 -

0

C

I"

—•— Press

Press+tail

Buoy

I

A J

ju, A /

iV\fbj\n um f v Y^w\^

*^r "" •--"^v—^_

) 0.1 0.2 0.3 0.4 0.5

Frequency (Hz)

0.6 0.7

Figure F-1. Buoy and pressure gauge spectra for 8 June 1999 at 0:30 GMT

1

0.9

0.8

NÜ.7-

X

£ 0.6

>

lo.5

41

Q

is 0-4 u

0)

LU 0.3

0.2-

0.1

Press

" Press+tail

'Buoy

0.1 0.2 0.3 0.4

Frequency (Hz)

0.5 0.6 0.7

Figure F-2. Buoy and pressure gauge spectra for 7 June 1999 at 12:30 GMT

Appendix F Wave Gauge Analysis F-3
1 -

0.9

0.8-

-N 0.7-

X

£o.6-

8 0.5 -

0

Q

0)0.4-

Cl

W 0.3-

0.2-

0.1 -

ot

* Pieas

Press+tail

Buoy

I

I

Akt ^

V

\ /

y/v W\/ ^ ^\ J

*V-

"--- ^-—^-

) 0.1 0.2 0.3 0.4

Frequency (Hz)

0.5 0.6 0.7

Figure F-3. Buoy and pressure gauge spectra for 7 June 1999 at 4:30 GMT

where

Rp = pressure-response function

k = wave number

d = water depth

z = elevation of the pressure gauge measured relative to the mean

water surface

A typically applied cutoff is V(Rpf = 100. For the water depths at Station 2, this

cutoff is 0.24 to 0.29 Hz (depending on tide elevation). Other environmental

factors, such as the vertical variation in tidal currents, wave non-linearities, or

wave breaking, may also affect the pressure signal, accelerating the divergence of

the spectrum.

In Figure F-l, the agreement with the buoy spectrum is good up to 0.28 Hz.

Figure F-2 shows a case where the pressure spectrum diverges at a lower

frequency of 0.23 Hz. For this case, the wave height calculated from the pressure

spectrum increases 35 percent if the cutoff is increased from 0.2 to 0.3 Hz.

However, a cutoff of 0.2 Hz neglects higher frequency wave energy as measured

by the buoy. Figure F-3 shows a midtide case where approximately three-fourths

of the wave energy at Station 2 has been dissipated over the bar. This case is

interesting because the buoy shows two peaks in the spectrum, one at 0.1 Hz

(10-sec period) and one at 0.25 Hz (4-sec period). The higher peak is not

represented in the pressure spectrum. The following conclusions can be drawn

from the Deployment 8 buoy and pressure spectra:

F-4 Appendix F Wave Gauge Analysis
a. The pressure spectra at Station 2 diverge in the frequency range of 0.2 to

0.3 Hz. The lower frequency divergences (0.2 to 0.25 Hz) occur while

the current is flooding.

b. Even in cases where the spectrum does not diverge below 0.3 Hz, the

pressure gauge is not capturing wave energy above about 0.2 Hz.

c. Applying a frequency cutoff of 0.2 Hz neglects significant wave energy

as measured by the buoy.

Another way to examine the appropriate cutoff for the pressure gauge is to

calculate the correlation between the buoy and pressure gauge spectra. Regions

of high correlation indicate good agreement, and low correlation indicate poor

agreement between the gauges. Figure F-4 shows the correlation for pressure

gauge Deployment 8. The correlation coefficient (solid line) drops off rapidly

above 0.22 Hz. Thus, a reasonable cutoff frequency is 0.22 Hz.

0.7

0.6

~ °-5

c

o

Ü

£

o 0.4

o

o

c

,0

'I 0.3

ÖS

0.2

0.1

Deployment 8

• Deployment 8 with tail

0.00E+00 5.00E-02 1.00E-01 1.50E-01 2.00E-01 2.50E-01 3.00E-01 3.50E-01 4.00E-01

Frequency (Hz)

Figure F-4. Correlation between buoy and pressure gauge (Deployment 8)

Theoretical Spectral Tail

The previous section showed that the cutoff frequency should be approximately 0.22 Hz, but the spectral comparisons also show that significant energy

(as measured by the buoy) may be neglected if the spectrum is truncated at

0.22 Hz. One method of estimating the truncated energy is to add a theoretical

tail to the spectrum in the form given by Miller and Vincent (1990)

E(f) =

/%**

0.5,-2.5

(F-2)

Appendix F Wave Gauge Analysis F-5
where

E(f) = spectral density at frequency/

ß = constant (with units of m/sec)

g = gravitational acceleration

Cg = wave group celerity

A similar technique is employed by Wolf (1997). The value of /?is estimated

from the spectral density at the cutoff frequency. Examples of adding the

spectral tail are shown as dashed lines in Figures F1-F3. The tail also improves

the correlation coefficient at higher frequencies, as shown with the dashed line in

Figure F-4. Adding the theoretical tail will not significantly improve the

agreement for cases with peak periods shorter than 5 sec (frequency greater than

0.2 Hz), as seen in Figure F-3.

These shorter period waves may originate from three processes. First, these

may be waves generated in Willapa Bay that are propagating out of the bay.

Second, they may be harmonics generated as the waves shoal and are freed in the

breaking process over the bar (Battjes and Beji 1992). Third, they may be wave

components that shoal on the strong ebb currents. Whatever their origin, they are

not reproduced in the pressure record analysis. Use of the near-bottom current

measurement in the analysis, variation of the current over depth, and use of linear

wave theory may contribute to the underestimate of shorter waves in the pressure

gauge analysis. Although high-frequency wave energy is underestimated in

some wave records, the following section shows that reasonable estimates of

wave height and period are produced by applying a 0.22-Hz frequency cutoff

with a theoretical tail.

Wave Height and Period Statistics

The choice of the spectral cutoff can also be evaluated based on wave height

Hmo and peak period Tp comparisons between the buoy and pressure gauge.

Figure F-5 compares the pressure gauge with a cutoff of 0.3 Hz, 0.22 Hz, and

0.22 Hz plus the theoretical tail with the buoy wave heights. The wave height

with the 0.3-Hz cutoff generally overestimates the large wave heights at high

tide. This is because the greater water depth at high tide causes the divergence

region of the spectrum to shift down into the range below 0.3 Hz. At low tide,

the 0.3-Hz cutoff underestimates the wave height because the pressure gauge is

not capturing the higher frequency waves (e.g., Figure F-3). The wave height

with the 0.22-Hz cutoff consistently underestimates the buoy wave heights by

0.05-0.15 m because it neglects any wave energy at frequencies above 0.22 Hz.

The 0.22-Hz cutoff with the theoretical tail provides the best fit to the buoy wave

heights, although it still underestimates the low-tide wave heights, similar to the

other cutoff options.

Figure F-6 compares the pressure gauge with cutoffs of 0.3 Hz and 0.22 Hz

with the buoy wave periods (adding the theoretical tail to the spectra produces

the same peak periods as the 0.22-Hz cutoff). Both pressure gauge cutoffs give

good results for wave periods greater than 5 sec. The 0.22-Hz cutoff cannot

produce peak periods shorter than 4.5 sec. The 0.3-Hz cutoff can produce

F-6 Appendix F Wave Gauge Analysis
1.6

1.4

buoy

• press (0.3 Hz cutoff)

press (0.22 Hz cutoff)

- press (0.22 Hz cutoff+tail)

5/31/99 0:00 6/1/99 0:00 6/2/99 0:00 6/3/99 0:00 6/4/99 0:00 6/5/99 0:00 6/6/99 0:00 6/7/99 0:00 6/8/99 0:00

Date

Figure F-5. Comparison of buoy and pressure gauge wave heights (Deployment 8)

20

18

16

14

8-^

buoy

press (0.3 Hz cutoff)

press (0.22 Hz cutoff)

5/31/99 0:00 6/1/99 0:00 6/2/99 0:00 6/3/99 0:00 6/4/99 0:00 6/5/99 0:00 6/6/99 0:00 6/7/99 0:00 6/8/99 0:00

Date

Figure F-6. Comparison of buoy and pressure gauge wave periods (Deployment 8)

Appendix F Wave Gauge Analysis F-7
periods as short as 3.3 sec, but these short-period estimates do not consistently

match the buoy. Table F-2 lists root-mean-square (rms) errors in wave height

and period for comparisons of the buoy and pressure gauge for Deployments 7

and 8. The lowest errors for wave height and period are for the 0.22-Hz cutoff

and the theoretical tail.

Table F-2

Error Statistics for Buoy and Pressure Gauge Comparisons

Cutoff

Deployment 7 Deployment 8

rms error in Hmo

m

rms error in Tp

sec

rms error in Hm,

m

rms error in Tp

sec

0.3-Hz cuttoff 0.12 3.4 0.12 2.4

0.22-Hz cutoff 0.14 2.7 0.18 2.1

0.22-Hz cutoff+tail 0.09 2.7 0.11 2.1

Analysis Procedure Selected

Based on comparison of the buoy and pressure gauge spectra, wave heights, and

periods, the procedure selected for analysis of the pressure data at Stations 2 and 3 is

to apply a spectral cutoff at 0.22 Hz and add a theoretical tail to the spectrum

(Equation F2). This procedure minimizes error in the pressure gauge analysis, as

evaluated with the buoy measurements. The rms error in wave height using this

procedure is 0.09 to 0.11 m, and the rms error in period is 2.1 to 2.7 sec. The wave

heights at low tide (when heights are the smallest) tend to be underpredicted, but the

results are generally unbiased at other tide levels. The shortest wave period

calculated from this procedure is 5 sec. The 0.22-Hz cutoff and theoretical tail were

applied for the verification data reported in Chapter 5.

References

Battjes, J. A., and Beji, S. (1992). "Breaking waves propagating over a shoal."

Proceedings 23rd Coastal Engineering Conference, ASCE, Reston, VA,

42-50.

Miller, H. C, and Vincent, C. L. (1990). "FRF spectrum: TMA with

Kitaigordskii's/^ scaling," Journal ofWaterway, Port, Coastal, and Ocean

Engineering 116(1), 57-78.

Wolf, J. (1997). 'The analysis of bottom pressure and current data for waves."

Proceedings 7

th International Conference on Electronic Engineering in

Oceanography, Southampton, Conference Publication 439, IEE, 165-169.

F-8 Appendix F Wave Gauge Analysis
Appendix G

Bathymetry, Current Patterns,

and Bathymetry Change in

Design Alternatives1

This appendix supplements Chapter 5 of the main text. It provides contour

plots of bathymetry, tables of maximum and minimum current speed, vector

plots of calculated currents, and contour plots of calculated deposition and

erosion within the channels of design alternatives for Willapa Bay. Two sets of

vector and bathymetry-change contour plots are provided for each Alternative,

one set representing the January 1998 storm and a second set representing fairweather conditions simulated from 4 September through 6 October 1998.

Contoured bathymetry plots for each Alternative are given in Figures G-l

through G-8. These plots show 1998 bottom topography with alternative

channels dug through it. The contour interval is 2 m.

Tables G-l through G-9 give maximum and minimum current speed

calculated within each Region (defined in Figure 6-39) for peak ebb and flood

tide. Peak ebb and flood tide were selected for the entire Willapa Bay entrance

and all speeds were from the same time.

Figures G-9 through G-26 show sets of vector plots of current patterns. Each

set contains 12 snapshots of the current pattern at 1-hr intervals. Vector plots for

the January 1998 storm are given during the time interval of peak wave

conditions (starting 17 January 1998 0000 GMT) to provide fields of wavegenerated currents combined with tide- and wind-generated currents for large

waves. Vector plots for fair weather were selected to show current fields for low

wave conditions over a tidal cycle so that the ebb and flood currents are depicted

in the images. The date of the fair weather plots is 8 September 1998 and time

stamps are Greenwich mean time (GMT).

The primary factors controlling currents in an inlet are bottom topography,

phase of the tide, and presence and magnitude of waves. These factors interact

to form time-varying current patterns and modify the bottom by initiating

1 Written by Dr. Adele Militello, U.S. Army Engineer Research and Development Center, Coastal

and Hydraulics Laboratory, Vicksburg, MS, and by Mr. Mitchell E. Brown, Mevatec Corporation,

Vicksburg, MS.

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-1
sediment into the water column and depositing it in another location. Waves

modify the current by adding momentum and by changing the slope of the water

surface. Changes in current patterns by waves and tidal phase are shown in the

plots of currents fields for each Alternative (Figures G-9 through G-26). As an

example, Figures G-9 and G-18 show sequences of currents during storm and

fair weather conditions, respectively, for Alternative 1. During the storm, waves

drive a well-developed rotational current in and near the western portion of the

alternative. This current moves water toward the northwest over the channel,

then redirects toward the southeast bringing water back across the channel in the

curved part of the channel. In addition, ebb flow is enhanced by the waves in the

channel east of and adjacent to the S-curve. South of the North Channel, eddies

form and disintegrate by wave action on the bar. In contrast, in fair weather,

currents vary more smoothly with reduced eddies and curvature (Figure G-18).

A gyre over the S-curve is present during fair weather, but its size and strength

are reduced from that during the storm. For both storm and fair weather,

channelized flow occurs in the North Channel, demonstrating control by bottom

topography.

Contour plots of bottom elevation change calculated by the sediment

transport model described in Chapter 6 are provided in Figures G-27 through

G-44. These plots show cumulative deposition and erosion over the simulation

interval for the January 1998 storm (15 days) and the fair weather (32 days)

calculations. Plots are divided into two panels. Upper panels show deposition

(shoaling) in the channel and lower panels show erosion (scour). All contour

plots use the same scale for filled contours, which allows for direct comparison

between plots.

Table G-1

Maximum and Minimum Velocity in Regions of Alternative 1 for Fair

Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Maxl

Speed

=lood

m/sec

Mini

Speed

:

lood

m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.0 - 0.7 - 0.7 -- 0.5 -

2 1.3 1.6 0.5 0.3 0.8 0.9 0.3 0.5

3 2.5 1.6 1.5 1.1 1.6 1.0 1.1 0.7

4 2.6 -- 1.5 -- 1.6 -- 1.2 -

5 2.0 -- 1.4 -- 1.5 -- 1.1 -

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

G-2 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Table G-2

Maximum and Minimum Velocity in Regions of Alternative 3Afor

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Min Flood

Speed m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.0 -- 0.6 -- 0.5 - 0.3 --

2 1.1 - 0.8 -- 0.7 0.7 0.5 0.7

3 2.6 - 1.1 - 1.3 0.7 0.8 0.7

4 2.4 - 1.8 - 1.3 -- 1.1 --

5 2.0 -- 1.7 - 1.3 - 1.2 --

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

Table G-3

Maximum and Minimum Velocity in Regions of Alternative 3B for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Mini

Speed

:

lood

m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.0 - 0.7 - 0.7 - 0.5 -

2 1.1 1.6 0.4 0.4 0.7 1.0 0.2 0.5

3 2.6 1.3 1.6 1.1 1.4 0.9 1.0 0.6

4 2.6 - 1.8 - 1.4 - 1.1 -

5 2.0 - 1.7 - 1.3 - 1.2 -

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-3
Table G-4

Maximum and Minimum Velocity in Regions of Alternative 3F for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Min Flood

Speed m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.1 - 0.7 -- 0.5 -- 0.3 -

2 1.2 - 0.9 -- 0.7 -- 0.4 -

3 2.6 -- 1.2 -- 1.4 - 0.7 --

4 2.5 - 1.8 - 1.3 -- 1.1 --

5 2.0 -- 1.6 - 1.3 - 1.2 --

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

Table G-5

Maximum and Minimum Velocity in Regions of Alternative 3G for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Maxl

Speed

=lood

m/sec

Mini

Speed

:

lood

m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.1 - 0.3 - 0.7 0.3 0.3 0.2

2 1.2 1.5 0.4 0.4 0.7 1.0 0.2 0.2

3 2.3 - 1.1 - 1.3 0.9 0.6 0.5

4 2.4 - 1.6 - 0.9 - 1.3 -

5 2.1 - 1.5 - 1.3 - 1.0 -

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

G-4 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Table G-6

Maximum and Minimum Velocity in Regions of Alternative 3H-a for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Min Flood

Speed m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.0 0.8 0.9 0.7 0.7 0.6 0.5 0.5

2 1.2 0.8 0.5 0.7 0.9 0.4 0.5 0.4

3 2.1 -- 1.2 -- 1.3 0.8 0.8 0.8

4 2.0 -- 1.5 -- 1.3 -- 1.1 --

5 2.0 -- 1.6 - 1.5 - 1.3 --

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

Table G-7

Maximum and Minimum Velocity in Regions of Alternative 3H-b for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Min Flood

Speed m/sec

Along2 Across3 Along Across Along Across Along Across

1 1.0 0.9 0.9 0.7 0.7 0.7 0.5 0.6

2 1.1 0.9 0.6 0.6 1.2 0.4 0.5 0.4

3 1.9 - 1.1 - 1.3 0.7 0.7 0.7

4 1.9 - 1.5 - 1.2 - 0.8 -

5 1.7 2.3 1.6 1.7 1.3 1.7 1.1 1.3

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-5
Table G-8

Maximum and Minimum Velocity in Regions of Alternative 4A for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Min Flood

Speed m/sec

Along2 Across3 Along Across Along Across Along Across

1 0.4 -- 0.3 - 0.5 -- 0.3 -

2 2.7 -- 0.4 -- 1.1 -- 0.5 -

3 2.8 -- 1.1 - 1.1 - 0.8 --

4 2.0 -- 1.2 - 1.8 - 1.0 --

5 NA4 NA NA NA NA NA NA NA

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

4 Alternative 4A does not extend into Region 5.

Table G-9

Maximum and Minimum Velocity in Regions of Alternative 4E for

Fair Weather1 at Peak Ebb and Flood Tidal Current

Region

Max Ebb

Speed, m/sec

Min Ebb

Speed, m/sec

Max Flood

Speed, m/sec

Mini

Speed

:

lood

m/sec

Along2 Across3 Along Across Along Across Along Across

1 0.4 - 0.3 - 0.4 - 0.4 -

2 1.6 1.8 0.3 0.4 1.0 0.6 0.4 0.6

3 1.3 1.6 0.8 0.8 1.2 - 0.8 -

4 1.9 - 1.0 - 1.8 - 0.9 -

5 1.3 1.5 0.9 1.2 1.4 1.4 1.0 1.2

1 September 1998 fair weather simulation, duration = 31 days.

2 Along-channel is defined as current directed at angles ranging from 0 to 45 deg relative to channel

axis.

3 Across-channel is defined as current directed at angles ranging from 45 to 90 deg relative to

channel axis.

G-6 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-1. Bathymetry for Alternative 1

Figure G-2. Bathymetry for Alternative 3A

Figure G-3. Bathymetry for Alternative 3B

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-7
Figure G-4. Bathymetry for Alternative 3F

Figure G-5. Bathymetry for Alternative 3G

Figure G-6. Bathymetry for Alternative 3H (3H-a and 3H-b)

G-8 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-7. Bathymetry for Alternative 4A

Figure G-8. Bathymetry for Alternative 4E

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-9
TNNNäVS

'/SSS/Ss-*-

s y j i i i i \ v \ \

Figure G-9. Current patterns in Alternative 1 channel, January 1998 storm

(Sheet 1 of 3)

G-10 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-9. (Sheet 2 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-11
Figure G-9. (Sheet 3 of 3)

G-12 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-10. Current patterns in Alternative 3A channel, January 1998 storm

(Sheet 1 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-13
Figure G-10. (Sheet 2 of 3)

G-14 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-10. (Sheet 3 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-15
0000 GMT

.vv} ill)\-^S$$Sj^^

Figure G-11. Current patterns in Alternative 3B channel, January 1998 storm

(Continued)

G-16 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-11. (Concluded)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-17
- • .- s * / s * S-"

' s / /s / s •VV' --. ^ V \

^X.yN^'. I «~~. AN^^S^

Figure G-12. Current patterns in Alternative 3F channel, January 1998 storm

(Sheet 1 of 3)

G-18 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-12. (Sheet 2 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-19
08001

Figure G-12. (Sheet 3 of 3)

G-20 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
AW,/.

Figure G-13. Current patterns in Alternative 3G channel, January 1998 storm

(Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-21
Sj^Mn55^Hi/.'«-'JHKi

^^öäS^SSäs

Figure G-13. (Concluded)

G-22 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-14. Current patterns in Alternative 3H-a channel, January 1998 storm

(Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-23
Figure G-14. (Concluded)

G-24 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
0000 GMT

Figure G-15. Current patterns in Alternative 3H-b channel, January 1998 storm

(Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-25
Figure G-15. (Concluded)

G-26 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
-//

Figure G-16. Current patterns in Alternative 4A channel, January 1998 storm

(Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-27
/ / / / / —«_..- v v \ "W<

rtt//•-

Figure G-16. (Concluded)

G-28 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
" ~-* •

0000 GMT

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tWSS.VVW

. , i I i l' SÜSw-^r^' f I > \ ^ I I W--X V \ \ \ V V X I I I 0600 061 GMT

Figure G-17. Current patterns in Alternative 4E channel, January 1998 storm

(Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-29
;

*?I^~77~~7Ü *\ \ \ \ \ \ \ \

. / / t t .>

/ ^ » y* - N^s^tgj^^^V^T^^/'t^:»^^?^^0700 GMT

7-r

• ^

j

----- —-* g ^ -^ -—-~^

tul Hi / w h \ s-s'sssr ^///t,r < i//s+ ts/ss-, 0800 w GMT ^ *

0900 GMT v,

Figure G-17. (Concluded)

G-30 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
1200 GMT

' ' ' ' ' /S-"- >.->.\\V\\XK...-- I * \\V^ __

Figure G-18. Current patterns in Alternative 1 channel, September 1998 fair

weather (Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-31
Figure G-18. (Concluded)

G-32 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
. ..^N \S<NNV\V\S\SN\\<\\\\\\\\\\\\ \ I \ \ ' I

ssv\s\\\\\\\\\\\\\\\\\\\\\\\\\t|

^vwvvS^^VV^^v V S V V V \ V \ V \ \ \ \ \ \ \ \ \ \ ,\ .\ ,\ ,.|

>VWSV\\SV>*^5--»^v vv vv VVSNV. \.\N.\ \ > ,\,\.\»\»>1

rVWVVWWN \\V«^v^ic. vv V

NNWVVWWNN^-N^- ^-- -^- - xX

1200 GMT

,\\\\\w\\\\\\\\\ \ v s \ \ \ A n j |

> \\ \ \ \ \\ \ \ \ \ \ \ \ \ \ .\ .\ .\ A .\ .\ \ ,\ \ 11

>fVA \ \ \ \ \ \ \ \ \ \ \ \ \ \ X >\ ,\ »\ ,\ ,\ ,\ A," A

,\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ S N S S N N S N A A A M !

A\W

1300 GMT

, -<S^s\\ \ \ \ \ \ \ \ \ \\ \ J j) 5} J li 1J J ,\ J i J J}}

1400 GMT

- |*-J*-g-* -.^■■J.J*-?

Figure G-19. Current patterns in Alternative 3A channel, September 1998 fair

weather (Sheet 1 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-33
1 \ \ \ \ \ 1 I I U|M)U\lini|

^ SNV^vV-*«^ .vvNSS

1 i i i i i i i i i t i

\ \ t i i i

\ \ \ \ \ \ \ . . -

t \ \ \ \ \ \ \\NW-»«.WWVV

1, \ \ \ \ VVW^^-~—--~.V.^-^^WV

v \ \ \ vv v~ — ^.._--V-v.^

^ \ V \ v ^ ^ -^ .. * -/ V.VWN

.. K V S N -. -\Vv^v «.\\«»->.«»

< X \ V

\ \ \ \ \ \ \ \ \ \ 1 I

\ \ \ \ \ \ \ \ \ \ t I

\ \ \ \ \ \ \ \ \ \ \ I

\ \ \ \ \ \ \ \ \ \ \ \\

1700 GMT

XNS

1800 GMT

t t t

\ t I

. . \ \ \

\ \ \ \ \ \ W./ .

I I I ; i >

t \ t I t l I i t

\\\1\\\NV

I V \ \ V \

,:::::::::::N\\V\:^

.. s\\v;'' , % \ \ \ K — si—^.

..-.v \SLs.

.:l-l~-l—<^~--—' v\\<

. V V *. '

, \ N >* ^ v v V \V

Figure G-19. (Sheet 2 of 3)

G-34 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-19. (Sheet 3 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-35
... ..v v wWWWW-^' Sg^VrxT

^-- »-V^Vv^-'^*-'''-- - - --

v

«

^^-^--~. ^v^ .V\\\\\\\NSSVNS -. , Li-Li -

Figure G-20. Current patterns in Alternative 3B channel, September 1998 fair

weather (Continued)

G-36 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
TTTTTTTTTTTTTTTT

Figure G-20. (Concluded)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-37
1 ^ ^ ^ S I ISS.

^SSK\^->^V^^^r,,'.'.'rrr.-^^

Figure G-21. Current patterns in Alternative 3F channel, September 1998 fair

weather (Sheet 1 of 3)

G-38 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
TTTTTTTTTTTTTTTTTTTTTTTTTTT

' ' ' ' SSS-*'— >->.—.—a---».-.^ ^ .VVV . » - - I 1 I \ \ \ '

OsW

I I t I t t t I t \ \ \ \ \ \ \ \ 1 t ( ( I I

' '- N \\S- .vvWVWWW-

- * * * •—t i

i^~ , S V N N

. N \ \ N

Figure G-21. (Sheet 2 of 3)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-39
Figure G-21. (Sheet 3 of 3)

G-40 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
^*-^

1700 GMT

« V ^ V

Figure G-22. Current patterns in Alternative 3G channel, September 1998 fair

weather (Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-41
1" I i i r r - , *—£ r t - — — — ^ —-

VVVVVVV V ^ O, /-,

Figure G-22. (Concluded)

G-42 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
.•^s'^^J^J^^NNV.>

Figure G-23. Current patterns in Alternative 3H-a channel, September 1998 fair

weather (Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-43
*

<XVN

- -

V \ \ \ \ \ \

.»•>\\\\\\\\v ~T"-!Ü

Figure G-23. (Concluded)

G-44 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Figure G-24. Current patterns in Alternative 3H-b channel, September 1998 fair

weather (Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-45
*. . .\\ \ .V«C-^ —' - - --^-^v*^S=-»~-=.^2^^'*Ä^A \

.* . . -.^-SN-'V % )f\>»\" «.-»».• /-^ 1

•— :: >";Op ''';7/Ärr*^~-^~^^^

2000 GMT

' i i i > 11 Ovr/ I i * •

• ' i /11/ *VvvC / ' ' '

_LiL "i\S"

Figure G-24. (Concluded)

G-46 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
~.WW\\ (./ '~ 1300 GMT

^Ifiä$$fc^IÜä

\ i W-T*" ^ \ \ \ w _

,\\\v \\\\\\\\\1)t

WwwWWJ ,1

/til WWW

- - -

\ \ \ \ \ \ Ww ,

v->W\\

.\\w\\

.WWW

..,.,///// ^^//J

' < /1 cAh K fill I I \\~-

w\WW \ \ \ \ \ H \ t IM/

v^\\\\\v\\\\ \ I I M M / WW \ \ \ I II I \ WWW \ \\\\

't IWWWV WWW \ \\\\\

^M ; I I \ \ \ \ \ vwvvssv

_• / / / t \ \ \ W www ' * - r rrrrmr^c-'11 >) 1111 n > ww W-WN^.

tt./tii

•Sl / / / M|M t 1 j t \ S ^ \sV\WSv

Figure G-25. Current patterns in Alternative 4A channel, September 1998 fair

weather (Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-47
T*S5s=rrrn^.' '

A

^^^f^:~^r:

*S///f***Sff*i • *.^**s-^-~. .. t -»->•

iN.-»>»NWS^>

"•" ; '\ U—NV — N I N

Figure G-25. (Concluded)

G-48 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
//_-/ ,\\NNv /(WNVVNSNS

-l f7üJJHyS\\ -NW^VVWN

, Av-VN^

v

-

vV

- '-_LU

---— 1400 GMT ^

" \\\\

- - - » * y * v ^

A\U\\A\\ ?*/////I\\\ t I /

* *

-////.-// IrM^., i.i 11 \ \\\\\\\w\

1700 GMT ^

Figure G-26. Current patterns in Alternative 4E channel, September 1998 fair

weather (Continued)

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-49
^/s/^/ts. f / / r t \\\\\\\\\

*******

/ ****>/*sss» — -.—'

t t * * - ^^X^^X>----—.

* t / / ****'**•*•**+" —».

* t / / / // ********* ^^m

r * * / / * / //*/'**-** -—.

, * * t r / // / ****** ** /.

***** / / / / * t *///***•***. 1800 GMT

v; \s 2300 GMT ; ;

- * ' * *

Figure G-26. (Concluded)

G-50 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 1 Depth

Change, ft I

P7

ti6

5

4

3

•2

1

0

Figure G-27. Calculated deposition and erosion in Alternative 1 channel,

January 1998 storm

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-51
Alternative 3A

January 1998 Storm

Bottom Elevation

Change, ft

15

12

10

9

h-7

6

5

4

3

2

1

0

1

2

-3

4

5

-6

-7

-9

10

-12

15

Figure G-28. Calculated deposition and erosion in Alternative 3A channel,

January 1998 storm

G-52 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 3B

January 1998 Storm

Bottom Elevation

Change, ft

Figure G-29. Calculated deposition and erosion in Alternative 3B channel,

January 1998 storm

0

-1

-2

-3

-4

-5

-6

I-7

-9

-10

-12

-15

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-53
Alternative 3F

January 1998 Storm

Bottom Elevation

Change, ft

Figure G-30. Calculated deposition and erosion in Alternative 3F channel,

January 1998 storm

0

-1

H-2

3

-4

-5

-10

-12

-15

G-54 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 3G

January 1998 Storm

Bottom Elevation

Change, ft

k °^ v. Erosion

^\c? ^

~^r\/

^^^UyJSv^

1

2

3

-1-4

fy ~0

-6

-7

-9

-10

1-12

1-15

Figure G-31. Calculated deposition and erosion in Alternative 3G channel,

January 1998 storm

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-55
Alternative 3H-a

January 1998 Storm

Bottom Elevation

Change, ft 15

12

10

9

8

7

6

5

4

3

2

1

0

Figure G-32. Calculated deposition and erosion in Alternative 3H-a channel,

January 1998 storm

G-56 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 3H-b

January 1998 Storm

Bottom Elevation

Change, ft 15

12

10

9

8

7

5

4

3

2

1

0

Figure G-33. Calculated deposition and erosion in Alternative 3H-b channel,

January 1998 storm

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-57
Alternative 4A

January 1998 Storm

Bottom Elevation

Change, ft |15

12

10

9

8

7

6

H5

4

H3

2

1

0

-1

-2

-3

-4

-5

-6

-7

-9

-10

12

15

Figure G-34. Calculated deposition and erosion in Alternative 4A channel,

January 1998 storm

G-58 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 4E

January 1998 Storm

Bottom Elevation

Change, ft

-1

-2

-H-3

-j.4

-5

-6

-7

-9

-10

-12

'-15

Figure G-35. Calculated deposition and erosion in Alternative 4E channel,

January 1998 storm

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-59
Alternative 1 Depth

Change, ft

Figure G-36. Calculated deposition and erosion in Alternative 1 channel,

September 1998 fair weather

o

-1

-2

-3

-4

-5

-6

-7

-9

-10

-12

-15

G-60 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 3A

September 1998 Fair Weather Bottom Elevation

Change, ft

—

15

12

10

9

8

— 7

— 6

— 5

— 4

— 1

•1

H-2

-3

-4

-5

-6

-7

-9

-10

-12

'-15

Figure G-37. Calculated deposition and erosion in Alternative 3A channel,

September 1998 fair weather

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-61
Alternative 3B

September 1998 Fair Weather

Bottom Elevation

Change, ft

15

12

10

9

8

7

6

5

4

3

2

1

'—' 0

0

-1

W-2

-3

-4

-5

-6

-7

-9

-10

-12

-15

Figure G-38. Calculated deposition and erosion in Alternative 3B channel,

September 1998 fair weather

G-62 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 3F

September 1998 Fair Weather

Bottom Elevation

Change, ft

0

-1

-2

-3

-4

-5

-6

-7

-9

1-10

12

-15

Figure G-39. Calculated deposition and erosion in Alternative 3F channel,

September 1998 fair weather

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-63
Alternative 3G

September 1998 Fair Weather

Bottom Elevation

Change, ft

u u\/" -->

1 mi

Figure G-40. Calculated deposition and erosion in Alternative 3G channel,

September 1998 fair weather

1

2

3

4

5

•6

7

•9

•10

-12

-15

G-64 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 3H-a

September 1998 Fair Weather

Bottom Elevation

Change, ft

0

-1

-2

-3

-4

-5

-6I

'-15

Figure G-41. Calculated deposition and erosion in Alternative 3H-a channel,

September 1998 fair weather

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-65
Alternative 3H-b

September 1998 Fair Weather

Bottom Elevation

Change, ft 15

12

10

9

8

7

5

4

3

2

1

0

0

-1

-2

-3

-4

-5

-6

-7

-9

-10

-12

-15

Figure G-42. Calculated deposition and erosion in Alternative 3H-b channel,

September 1998 fair weather

G-66 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Alternative 4A

September 1998 Fair Weather

Bottom Elevation

Change, ft 15

H12

10

9

E

8

7

6

5

4

3

2

1

0

-1

-2

-3

-4

-5

-6

-7

-9

-10

-12

-15

Figure G-43. Calculated deposition and erosion in Alternative 4A channel,

September 1998 fair weather

Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives G-67
Alternative 4E

September 1998 Fair Weather

Bottom Elevation

Change, ft

15

12

10

9

8

7

6

5

4

3

2

1

0

Figure G-44. Calculated deposition and erosion in Alternative 4E channel,

September 1998 fair weather

0

-1

-2

-H-3

_|-4

5

-6

-7

9

10

12

15

G-68 Appendix G Bathymetry, Current Patterns, and Bathymetry Change in Design Alternatives
Appendix H

Willapa Bay Dredged Material

Disposal Sites Evaluation1

Introduction

This appendix identifies and evaluates potential dredged material disposal

sites for each of the screened Bar Navigation Channel dredging alternatives at the

entrance of Willapa Bay. The dredging alternatives, as identified in Chapter 2,

are located in areas primarily consisting of clean sand. Currently designated sites

for disposal of dredged material, as well as previously permitted disposal site

locations, are identified. Potential new rehandling disposal sites for beneficial

use of the dredged material are investigated. The cost of disposal, possible

environmental impacts, site capacity, and disposal equipment requirements are

also estimated for each of the disposal site alternatives. This appendix develops

information for use in applying disposal site criteria in the selection process only,

and is not intended as a substitute for a thorough evaluation in appropriate

environmental documentation.

Willapa Bay Dredged Material Historical

Disposal Sites

Historically, maintenance dredging in the Willapa Bay area was conducted

for deep-draft commercial navigation (Outer Bar and Willapa River navigation

channels) and for shallow-draft commercial fishing and pleasure vessels (Bay

Center channel, Tokeland Marina and channel, Nahcotta Marina). Clean, sandy

shoal materials are encountered on the Willapa Bar and at the bay center entrance

channel. A chronology of known Federal dredging activities is listed in

Table H-l and displayed in Figure H-l.

Dredging for deep-draft commercial navigation first occurred in 1928. Deepdraft channel-maintenance dredging of the Outer Bar and Willapa River channels

was conducted regularly for log ship navigation until 1974 on the bar and until

1976 on the Willapa River. Bar channel dredging was performed by Government

1 Written by Dr. Vladimir Shepsis and Mr. R. Shane Phillips, Pacific International EngineeringPLLC

,

and Mr. Hiram T. Arden, U.S. Army Engineer District, Seattle, Seattle, WA.

Appendix H Willapa Bay Dredged Material H-1
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H-2 Appendix H Willapa Bay Dredged Material
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H-6 Appendix

H Willapa Bay Dredged Material
Appendix H Willapa Bay Dredged Material H-7
hopper dredge equipment with bottom dump disposal at open-water sites within

Willapa Bay or at the ocean. The early hopper dredges were small and underpowered compared to present hopper dredge equipment. Hopper agitation

dredging was used in the mud sediments of the Willapa River, but agitation

dredging was not feasible for heavier bar channel sands.1 Willapa River dredging

was performed using large pipeline dredge equipment with disposal at portfurnished disposal sites. The volume of annual maintenance dredging on the

Outer Bar channel varied significantly. Estimated averages of annual

maintenance dredging for two periods between 1930-1940 and 1957-1974 are

815,000 cu yd and 220,000 cu yd, respectively.

Dredging for shallow-draft commercial fishing vessels has continued to the

present time at Bay Center, Tokeland, and Nahcotta. Dredging volumes for the

Tokeland and Bay Center sites have been approximately 25,000 to 60,000 cu yd

every 3 to 4 years. The Nahcotta Marina required maintenance dredging only

once since initial construction of the project in 1958. Maintenance dredging of

the shallow draft projects is restricted to small-business dredge equipment

because only the smaller equipment can access these projects with reasonable

tide delays relative to channel dimensions.

Disposal of dredged material historically had occurred at various open-water

disposal sites both inside and outside the Willapa Bay area and at upland sites.

Five disposal sites have been identified (not including disposal sites along the

Willapa River) that were designated for the open-water and upland disposal of

dredged material from various navigation projects in Willapa Bay. In addition to

disposal associated with the navigation project, the Washington State Department

of Transportation (WDOT) dredged and disposed 350,000 cu yd of sand along

the North Cove shoreline (beach nourishment) in 1998. This disposal was part of

a shoreline protection measure for State Route 105 (SR-105). Of the abovementioned five disposal sites, only the North Cove shoreline is presently

authorized for the disposal of dredged material within Willapa Bay. This site is

located near "Washaway Beach" along the North Cove shoreline. Both historical

and presently authorized Willapa Bay disposal sites are described below.

Cape Shoalwater open water disposal site

Location. The Cape Shoalwater disposal site was located within the North

Channel of Willapa Bay, approximately 1 n.m. east of the Willapa Bay entrance.

Historically, this disposal site location was referenced to the U.S. Coast Guard

(USCG) Entrance Buoy No. 10, which was discontinued. The designated site

was defined by the Washington Department of Natural Resources (WDNR) as an

1,800-ft diameter disposal zone with a center located in the north channel

thalweg, immediately northeast of USCG Buoy No. 10 (Environmental

Protection Agency 1995). The buoy has served as a navigation aid for the North

Channel along the North Cove (Washaway Beach). Because of channel

migration and changes in available depth near the buoy, the USCG relocated

Buoy 10 constantly. As a result, the physical location of the disposal site has

moved, consistent with the buoy movement (Figure H-2). Construction of the

1 Mr. Ted C. Hunt, U.S. Army Engineer District, Portland, Master, hopper dredge Yaquina,

October 1999.

|—1_3 Appendix H Willapa Bay Dredged Material
SR-105 Emergency Stabilization Project caused the USCG to discontinue their

Buoy No. 10 and required the installation of a yellow "D" obstruction marker

buoy to be installed near the underwater rock structure.

Authorization. This disposal site is presently not authorized for disposal of

dredged sediments. Permits authorizing the disposal of dredged sediments at this

Buoy No. 10 location expired on 7 July 1999. Prior to the expiration of the Buoy

No. 13 site in 1978, disposal of sediments within this disposal site was allowed

only during flood tide, (Figure H-2). Since 1978, tidal stage restrictions have

been removed as a condition for use of the Cape Shoalwater site. The WDNR is

finalizing permit applications to Pacific County and the State of Washington for

the continued availability of an open-water site in the vicinity of Cape

Shoalwater. The proposed Cape Shoalwater open-water site location is northeast

of USCG Buoy No. 13. The location of Buoy No. 13 changes and was last

charted by the USCG in 45 ft of water at mean low lower water (mllw) in

September 1999. All references to depth and elevation in Appendix H are

referenced to the plane of mllw, and the annotation mllw will be omitted.

Source of dredged material. This site has been used for disposal of

dredged material primarily from the Tokeland Federal entrance channel and the

Port's Marina maintenance dredging.

Goose Point open-water disposal site

Location. The Goose Point Disposal Site is located 3.6 n.m. east of

Leadbetter Point within the Nahcotta channel of Willapa Bay (Figure H-2). The

coordinates of the site are latitude 46°38'51"N and longitude 123°59'54"W. This

circular-shaped disposal site has a 1,800-ft diameter.

Authorization. Prior to 7 July 1999, this site was authorized for disposal of

suitable dredged sediments from Bay Center, Nahcotta, and Toke Point Marina.

Permits for the disposal of dredged material have expired and are presently under

reapplication for authorization.

Source of dredged material. This site has been used for disposal of

dredged material primarily from the Bay Center channel; however, in 1998

dredged material from the Toke Point Marina was allowed to be disposed at the

Goose Point open-water site to avoid potential conflicts with the WDOT

underwater rock dike construction project at Cape Shoalwater. Maintenance

dredging of the Nahcotta Marina has also considered the Goose Point site as an

alternative, but rather, utilized an upland site owned by the Port of Peninsula.

Interim ocean disposal site

Location. This site was located approximately 3.5 n.m. west of the entrance

to Willapa Bay. The dumping line site was approximately 5 n.m. in length along

a line between latitude 46°44'N, longitude 124° 10'W and latitude 46°39'N,

longitude 124°09'W. The location of the dumping line was based on the

approximate locations of historic hopper dredge ocean disposal relative to the

natural migrations of the bar channel.

Appendix H Willapa Bay Dredged Material H-9
Authorization. The U.S. Environmental Protection Agency (EPA)

designated the site as an interim open-water disposal site in 1977. This site is

not authorized for disposal of dredged sediments. The interim site did not

receive final designation or approval from the EPA.

Source of dredged material. This site had been available for disposal of

dredged material from Outer Bar Channel dredging if the need were to arise for

safe shallow-draft navigation. No hopper maintenance dredging was performed

after 1974 or after the proposed interim site designation in 1977.

Buoy No. 13 disposal site

Location. This site was located where the Willapa River enters the bay

southwest of Toke Point (Figure H-2). Historically, the location of this disposal

site was referenced to the USCG Entrance Buoy No.13. As described for the

Cape Shoalwater disposal site, this site was subject to the regular relocation of

the navigation buoy resulting from the North Channel migration.

Authorization. Prior to being discontinued in 1978, use of this site was

restricted to ebb tide only and is not presently authorized as a disposal site. An

area northeast of USCG Buoy No. 13 is proposed to be the new location for a

Cape Shoalwater open-water disposal site because the USCG Buoy No. 10 has

been discontinued. Relocation of the Cape Shoalwater site is necessary for barge

and hopper dredge equipment safety to avoid the vicinity of the WDOT

submerged rock structure. Water depths in the area of Buoy No. 13 were

measured at 45 ft by the USCG. Estimated depths in the proposed disposal site

are between 15 and 50 ft. The shallower water is based on an estimated

minimum feasible depth that dredged material disposal equipment can access in

conjunction with beach nourishment and beneficial uses of dredged material.

Source of dredged material. This site was used from 1968 to 1978 as an

ebb tide alternative disposal area to the Cape Shoalwater Buoy No. 10 site, which

was restricted to flood tide use. This site served primarily for the disposal of

material dredged from the Tokeland Marina. Sandy materials to be dredged in

the maintenance of the Bay Center entrance channel are being considered for

beneficial uses in conjunction with beach nourishment.

SR-105 Emergency Stabilization Project (ESP) beach

nourishment site

Location. The site is located at the shoreline starting at the east side of the

SR-105 groin structure and extending westward about 3,200 ft and is

approximately 3.5 n.m. east of the Willapa Bay entrance (Figure H-2).

Authorization. This site was authorized for placement of dredged material

under WDOT SR-105 ESP that was constructed during 1998. The existing

permits authorizing placement of dredged material along the SR-105 ESP

shoreline will expire in March 2001.

1 Personal communication with Mr. John Malek, EPA Region 10 office, describing status of interim

open ocean disposal site, September 1999.

H-10 Appendix H Willapa Bay Dredged Material
Source of dredged material. A permitted 350,000 cu yd dredged material

borrow site is located within the North Channel 0.5 n.m. east of the underwater

rock dike.

Comments. Dredging and placement of dredged material were restricted to

hydraulic dredging with direct disposal only above elevation 3.0 ft.

Approximately 350,000 cu yd of sandy material was placed along the shoreline

between SR-105 milepost 20.4 and 21.0 as a temporary feature of the

construction project.

Environmental Issues

Disposal site location and method of disposal are central factors for

evaluating the economic feasibility of potential disposal sites. Disposal sites

were evaluated relative to environmental permitting and coordination

requirements and known resource agency requirements, and environmentally

sensitive areas and biological resources.

Environmental permitting and coordination requirements

The overlapping authorities of Federal, State, and local jurisdiction entities

regulate environmental permitting of dredging and disposal of dredged materials.

The permitting process for any of the dredged material disposal sites listed in this

study will require the interagency coordination among the following agencies:

a. U.S. Army Corps of Engineers (Corps).

b. U.S. Environmental Protection Agency (EPA).

c. Washington Department of Ecology (WDOE).

d. Washington Department of Natural Resources (WDNR).

e. Washington Department of Fish & Wildlife (WDFW).

f. Local Jurisdictions such as Pacific County and the Shoalwater Bay Tribe.

The EPA and other Federal and State agencies become involved through the

Corps' permitting process. The permitting authorities for dredging and dredged

material are described in the following paragraphs.

U.S. Army Corps of Engineers. Under Section 404 of the Clean Water Act

(CWA), the Corps is required to regulate the disposal of dredged or fill material

in the waters of the United States. The purpose of the CWA is to restore and

maintain the chemical, physical, and biological integrity of the waters of the

United States. The CWA prohibits the discharge of dredged or fill material

except in compliance with Section 404.

Under Section 10 of the Rivers and Harbors Act of 1899, the Corps is

required to regulate the dredging, disposal, and performance of most work in the

navigable waters of the United States.

Corps Projects. Corps projects, which involve discharge into navigable

waters, are subject to the same evaluation procedures as non-Corps projects: the

Corps issues a Public Notice and may schedule a public hearing(s). Generally, a

Appendix H Willapa Bay Dredged Material H-11
Corps project has a local sponsor (Port of Willapa Harbor in the present

situation) who, by Congressional authorization, is required to furnish dredged

material disposal areas. Sediment sampling is performed in proposed dredging

areas to characterize dredged materials to determine suitability for open-water

disposal. The local sponsor frequently performs ancillary maintenance dredging

work that is combined into the Corps' Public Notice. If a WDNR open-water

disposal is used (Cape Shoalwater or Goose Point), the local sponsor obtains the

appropriate site use permission from WDNR.

Environmental Protection Agency. The EPA has several roles under

Section 404 of the CWA. First, EPA has the responsibility for developing the

Section 404(b)(1) Guidelines in conjunction with the Corps. Second, EPA

reviews the Corps' Public Notice and gives comments to the Corps. Third, the

EPA Administrator, via Section 404(c), may prohibit the specification of a

discharge site, or restrict its use if it is determined that discharge would have an

unacceptable adverse effect on fish and shellfish areas, municipal water supplies,

wildlife, or recreational areas. In addition, under 40 CFR 230.80, EPA and the

Corps may jointly provide advance identification of suitable or unsuitable

disposal sites.

Section 102 of the Marine Protection, Research, and Sanctuaries Act requires

EPA, in consultation with the Corps, to develop environmental criteria for the

evaluation of proposed ocean disposal activities.

Washington Department of Ecology. The WDOE has the responsibility for

certifying compliance with Section 401 of the CWA. This certification is

required from any applicant for a Federal permit to conduct an activity that may

result in discharge into State waters.

The WDOE's Public Notice for the CWA and the Coastal Zone Management

Act (CZMA) certification are mailed together with the Corps' Public Notice. If a

project involves disposal in water, data on the sediments are required. After the

review of the available data, the application for Water Quality Certification and

CZMA consistency determination is approved or denied. The project applicant is

responsible for providing a copy of the Water Quality Certification and CZMA

decision to the WDNR and the Corps before these agencies, respectively, can

issue a disposal site use permit and Section 10 and 404 permits.

The WDOE coordinates the final overall State of Washington response to the

Corps' Public Notice. To fulfill this responsibility, WDOE sends a "State

Response Letter" to the Corps after receiving comments from interested State

agencies. This letter describes the State's concern, and recommends approval or

denial of the Corps permit.

All dredging projects also require a Water Quality Modification from

WDOE. This grants the applicant a short-term modification from compliance

with the State of Washington's water quality standards. The modification will be

issued simultaneously with the Water Quality Certification for a minimum 1-year

period. Longer periods are common.

The WDOE also establishes guidelines for State and local administration of

the Washington Shoreline Management Act (SMA). The WDOE ensures that

permits issued by local Governments are consistent with the SMA. If a permit

H-12 Appendix H Willapa Bay Dredged Material
does not appear to be consistent, WDOE may appeal the permit to the Shorelines

Hearing Board.

Washington Department of Natural Resources. The WDNR acts as the

proprietor and manager of State-owned aquatic lands, which include all subtidal

lands within 3 miles of the Washington coastline. For each open-water disposal

site located on State lands, WDNR is required by the SMA to obtain a Shoreline

Substantial Development (SSD) permit from the local jurisdictions (Pacific

County). This permitting process allows for public review at the local level,

including private interests and Government agencies. As the SSD permit

applicant, WDNR is also the lead agency under State Environmental Policy Act

(SEPA).

The WDNR issues dredged material disposal site use authorizations for each

disposal operation. The WDNR sends the proponent an application upon their

request. The proponent submits the disposal site use application to WDNR. The

WDNR does not issue the authorization until the applicant has obtained all

required regulatory permits (i.e., the Corps permit, WDOE Water Quality

Certification, and WDFW Hydraulic Project Approval).

Corps navigation projects are exempt from WDNR's dredged-material

disposal site use authorization requirements. For Corps projects having local

sponsors, the sponsors must obtain the disposal permit for their berthing area

dredging volumes, but not for Federal channel dredging volumes.

Washington Department of Fish and Wildlife. The WDFW has the

responsibility to issue a Hydraulic Project Approval (HPA) under a process

outlined in Chapter 75.08.012 (The Fisheries Code), 75.20.100 Revised Code of

Washington (RCW), and Chapter 220-100 Washington Administrative Code.

The WDFW issues most HPAs in saltwater areas. The purpose of the HPA is to

protect fish life.

Under RCW 65.20.100, WDFW must approve or deny the HPA application

within 45 days of receiving a complete application, providing the project has

achieved SEPA compliance. The WDFW accepts the Corps' Public Notice as

the application for the HPA.

Local Governments. Under the SMA, local Governments have the

responsibility for general land use planning for shoreline development. Local

Governments control shoreline land use planning through the issuance of

Shoreline Substantial Development permits.

Environmentally sensitive areas

The entire Willapa Bay estuary contains a wide variety of valuable and

sensitive aquatic habitat areas. These areas include sand shoals, eelgrass beds,

mudflats, oyster beds, and salt marshes that provide habitat for a range of species.

More than a half dozen species listed as endangered or threatened under the

Endangered Species Act reside or visit for feeding, nesting, or resting at the

surrounding beaches and dunes. Environmentally sensitive areas of the Willapa

Bay estuary were determined for the SR-105 ESP Environmental Assessment

(Federal Highway Administration and WDOT 1997) and are shown in

Figure H-3.

Appendix H Willapa Bay Dredged Material H-13
During construction of the SR-105 ESP beach nourishment, resource

agencies required a minimum one-half mile buffer between the edge of Sand

Island and any proposed construction activities. Similar restrictions may apply to

other islands in Willapa Bay.

Potential sensitive areas are the former Cape Shoalwater location of the

Willapa National Wildlife Refuge (NWR) and Leadbetter Point Park. NWR had

two locations along Washaway Beach prior to being lost to erosion. The first

was located halfway between SR-105 ESP rock dike and the beach nourishment

borrow site. The second site was located at the outer bar of the North Channel

just offshore from Cape Shoalwater. The SR-105 ESP features were required to

be outside of the NWR boundaries. Similar restrictions may apply to disposal

actions associated with channel dredging.

Biological Resources. Biological and environmental assessments were

conducted for the SR-105 ESP. These documents were reviewed and the

following biological resources for the Willapa Bar area were identified:

a. Brown pelican: Currently on Endangered Species List. Critical habitat

located at Sand Island. No construction activities were allowed within

one-half mile of the island.

b. Dungeness crab: Crab present within Willapa Bay at the open-water

disposal site locations. Mitigation of impacts caused by dredging and

disposal were required.

c. Snowy plover: Currently on the Endangered Species List. Nesting

habitat located along Leadbetter Point and Gunpowder Island.

d. Marine fish: Juvenile salmon migration period within Willapa Bay from

1 March to 14 June. Adult salmon migration period during 16 August to

15 October.

e. Herring: Some locations within Willapa Bay may require shutdown of

construction activities from 1 February to 14 March for the herring

spawning period.

Resource agency requirements

The existing environmental documentation for the SR-105 Emergency

Stabilization Project, Willapa Harbor 1997 Test Hopper Agitation Dredging

Project, and the Tokeland Marina Maintenance Dredging were reviewed for

applicability to this project. These are possible restrictions on the disposal of

dredged sediment, which could apply to all of the evaluated disposal sites.

Possible restrictions for each of the disposal site alternatives are as follows (EPA

1995):

a. Beach nourishment: No disposal of dredged material above the 30-ft

depth from 1 March to 15 June of any year to avoid the adult salmon

migration period and possible mitigation.

b. North Channel disposal: Possible restrictions on disposal of dredged

material from 16 August to 15 October of any year (adult salmon

migration period).

H-14 Appendix H Willapa Bay Dredged Material
c. Sediment nourishment site: No disposal of dredged material above the

30-ft depth from 1 March to 15 June of any year to avoid the juvenile

salmon mitigation period.

d. Agitation dredging: Unknown.

Dredging alternatives may be limited by restrictions on Hopper dredging from

16 August to 15 October of any year.

Development of Disposal Site Alternatives

A range of disposal site alternatives was developed to accommodate

placement of dredged material from each of the bar navigation channel dredging

design alternatives. The development of the disposal site alternatives was

evaluated based upon the following criteria: technical feasibility of disposal, cost

of disposal, environmental impact, permit acquisition process, site capacity, and

equipment requirements.

Assumptions

Alternatives for disposal sites were developed under the following

assumptions:

a. The Port of Willapa Harbor is the local sponsor for all features of the

Federal navigation project except for the Nahcotta boat basin, which is

sponsored by the Port of Peninsula. As a local sponsor, the ports are

required to furnish all lands, easements and rights-of-way needed for the

dredged material disposal.

b. Dredging will be conducted during summer to early fall. Dredging and

disposal must be performed during 1 year.

c. The sediment dredged from the entire bar navigation channel dredging

alternatives is suitable for open-water disposal as well as for beneficial

use. The Willapa Bay area is classified as a low ranking area for

presence of chemicals of concern (U.S. Army Engineer District, Seattle

1994). Materials dredged from Willapa Bar, according to the Unified

Soil Classification System (USGS), ranges from poorly graded beach

sands with less than 5 percent passing the No. 200 sieve (SP), and sands

with more than 12 percent passing the No. 200 sieve (SM) to finegrained and well-sorted sand on the outer bar. Very poorly graded

clayey silts are present in Willapa River, and very poorly graded silty

clays in the marinas (Jackson, Allen, and Lowell 1997).

d. Willapa Bay hydrodynamic conditions at the disposal site locations are

based on the data from the SR-105 ESP Monitoring Program from 1997

through 1999, and the data collected for the Willapa Bay Navigation

Project Study from fall 1998 to summer 1999.

e. The part of the North Channel in the vicinity of the SR-105 project has

changed its alignment since the project was constructed. The channel

was relocated toward the south end of the dike, and a scour hole formed

at the toe of the dike. Seaward from the SR-105 project, a channel has

Appendix H Willapa Bay Dredged Material H-15
developed indicateing a potential new westerly branch formation

(Figure H-2). This branch is an active branch of the channel. However,

further development of the branch depends on the dynamics of the

existing, northerly channel branch. Closure (filling) of the northerly

branch of the channel may contribute to the rate of development of the

westerly channel branch.

f. Both direct beach and nearshore placement of dredged material can help

reduce the rate of erosion along the North Cove shoreline. The volume

of beach nourishment should not exceed 350,000 cu yd/year, as

authorized for the previous project. The nearshore berm should be

placed at a depth shallower than 20 ft to provide wave attenuation and

simultaneously minimize sand loss to the deep-water channel. Crest

elevation of nearshore berm should be above a depth of 5 ft, but not

higher than 0.0 ft so that all placed material is located on the slope in the

vicinity of a wave-breaking zone. A high level of energy dissipation

characterizes this slope. Dredged material placed at this area will

provide a benefit by reducing wave energy that drives longshore and

cross-shore sediment transport.

g. Formation of tidal flats at the entrance of Willapa Bay (similar to that at

Sand Island, locally called Deadman's Island) occurs periodically

following a breach in the North Cove bar. During this geomorphologic

cycle, a significant amount of sand is released from the North Cove bar

and migrates into Willapa Bay under transport by tidal currents and

waves. Disposal of a large amount of dredged material at certain areas of

the entrance of the bay (feeder zone) may simulate post-breach

conditions and result in formation of tidal flats. Location of the

placement zone would be selected based on the analysis of numerical

hydrodynamic modeling and available depth for hopper dredge access.

The disposal site is considered to be dispersive. Waves and currents will

disperse dredged material placed at the site. The rate of dispersion

depends on disposal site location and technology of dredged material

placement. The preliminary and final designs will be required to address

specific dispersivity issues for each of the disposal sites.

h. Because of variability of the South Channel alignment and depth

limitation, disposal at the South Channel has not been considered.

i. Hopper dredging with or without cutterhead dredging is the preferred

method of dredging for each of the design alternatives. Final

combination of hopper and cutterhead dredging is dependent on site

conditions of dredging and disposal site. For development of disposal

site alternatives, hopper dredging was categorized into three classes:

large class (6,000+ cu yd) hopper dredges with a loaded draft of 27 ft,

medium class (3,300 to 3,800 cu yd) with a draft of 20 ft, and small class

(1,500 to 2,000 cu yd) with a draft of 15 ft.

j. All distances referenced from the Outer Bar were measured from the

center of dredging alternatives to each of the disposal sites.

Based on these assumptions, a list of disposal site alternatives was developed and

preliminarily screened relative to feasibility, cost, beneficial use, and disposal

technology. Preliminary screening reduced the number of disposal site

H-16 Appendix H Willapa Bay Dredged Material
alternatives to 12 sites that are described in the following paragraphs. These sites

are identified in Figure H-4 and summarized in Table H-2.

Beach nourishment at SR-105

Location. This disposal site (referenced in Table H-2 as Alternative A) is

located at the existing SR-105 ESP beach nourishment site and approximately

3.5 n.m. inland from the outer bar of the North Channel. Placement of dredged

materials would occur between elevations of +3 and +10 ft. Disposal at this

location would require the use of a hydraulic dredge or a direct pump-out (from a

hopper dredge) with 1,500-ft of submerged pipeline. A direct pump-out

operation would require the use of either a mooring barge or a mooring buoy to

be positioned along the north edge of the North Channel for the hopper dredge to

connect to the submerged pipeline. Wave and currents at the disposal site are

assumed to be within the operating parameters of the equipment from June to

September.

Authorization. This site is authorized under the WDOT SR-105 ESP

construction permits. The existing permits authorizing placement of dredged

material along the SR-105 ESP shoreline will expire in March 2001.

Comment. Dredged material placement at this location would provide

beneficial use by reducing the volume of SR-105 beach nourishment

maintenance dredging. Placement of dredged material at this site may be

possible any time of the year except between 1 March and 15 June. Minimal

adverse impacts to biological resources would result from this alternative;

therefore, mitigation might be avoided. The recipient of this beneficial use of the

dredged sand will have to pay the incremental cost exceeding the cost of openwater disposal.

Beach nourishment along North Cove

Location. This disposal site (referenced in Table H-2 as Alternative B) is

located along the shoreline of North Cove, approximately 1 mile west of the

SR-105 ESP site and 2.5 n.m. inland from the outer bar of the North Channel.

Disposal of dredged material would be similar to that described for SR-105 ESP

Beach Nourishment.

Authorization. This site is not authorized for disposal of dredged material

under existing permits and has not been used as a disposal site in the past.

Comment. Placement of dredged material would provide beneficial use by

slowing the erosion of the shoreline along North Cove. This site would be

subject to the same environmental constraints as identified in Alternative A.

Additionally, impacts to Dungeness crab may require mitigation for losses

associated with burial. The recipient of this beneficial use of the dredged sand

will have to pay the incremental cost exceeding the cost of open-water disposal.

Appendix H Willapa Bay Dredged Material H-17
Table H-2

DeveloDment of Alternatives

Disposal Site

Alternatives

(Depth of

Placement, ft)

Relative

Cost

Status of

Authorization/

Permitting

Capacity

cuyd

Equipment

Requirements Feasibility

Beneficial

Use

Possible

A - Beach

Nourishment

(elev. +3 to+10)

High Currently

authorized

360,000 Small Hopper

with Pumpout

Medium -

increased cost

to pump,

beneficial use

Yes

B - Beach

Nourishment

(elev.+3 to+10)

High Not authorized 780,000 Large Hopper

with Pumpout

Medium -

increased cost

to pump,

beneficial use,

restricted const,

period

Yes

C - Nearshore Berm

West (depth 20

and shallower)

Med. Not authorized, 500,000 Small Hopper

Dredge

Low - shallow

water/high cost,

restricted const,

period

Yes

D - Nearshore Berm

East (depth 20

and shallower)

Med. Not authorized 330,000 Small Hopper

Dredge Cost

Low - shallow

water/high cost,

restricted const,

period

Yes

D-1 - Beach

Nourishment

East (elev. +3

to+10 and

higher)

High Not authorized 200,000 Small Hopper

Dredge Cost

Medium -

increased cost

to pump,

beneficial use,

restricted const,

period

Yes

E - North Channel

(depth 70)

Low Authorization

expired

1,600,000 Large Hopper

with direct

disposal

High - low cost,

beneficial use

Yes

F - Goose Point

(depth 20-30)

Med. Authorization

expired Permit

renewal

pending

900,000 Medium

Hopper with

direct disposal

Medium -large

haul distance

No

G - Interim Ocean

(depth greater

than 50)

Low Not authorized N/A Large Hopper

with direct

disposal

Medium -

subject to

operation in

ocean swell

No

H - Sediment

Nourishment

(depth 20 to 30)

High Not authorized 900,000 Small Hopper

Dredge

Low-shallow

water; wave

cond

Yes

I - Middle Channel

Agitation

Low Not authorized Small Hopper

Dredge

No

J - Rehandling Med. Not authorized N/A Cutterhead

Dredge

High to medium Yes

K - Proposed Cape

Shoalwater open

water

Low Pending

authorization

N/A Medium

Hopper with

direct disposal

High Yes

H-18 Appendix H Willapa Bay Dredged Material
Nearshore berm west of SR-105 ESP

Location. The west nearshore berm disposal site (referenced in Table H-2 as

Alternative C) is located along the west side of the SR-105 ESP groin and dike

structures, approximately 2.7 n.m. inland from the North Channel outer bar.

Dredged sediments would be placed initially by hopper dredge or bottom dump

barge, followed by pipeline disposal (or other method) above a depth of 20 ft to a

maximum depth of 5 ft. Waves and currents at the disposal site are assumed to

be within the operating parameters of the equipment from June to September.

Authorization. This site is not presently authorized for disposal of dredged

material. The location of this alternative is partially within the historical location

of the Cape Shoalwater disposal site referenced to the USCG Buoy No. 10.

Comment. Dredged material placed at this location may provide the benefit

of erosion protection for a currently retreating stretch of shoreline. The recipient

of the beneficial use of the dredged sand will have to pay the incremental cost

exceeding the cost of open-water disposal.

Nearshore berm east of SR-105 ESP groin/dike

Location. The east nearshore berm disposal site (referenced in Table H-2 as

Alternative D) is located along the east side of the SR-105 ESP groin and dike

structures, approximately 4.3 n.m. inland from the North Channel outer bar.

Dredged sediments would be placed initially by hopper dredge or bottom dump

barge, followed by pipeline rehandling (or other method) at a depth of 20 ft up to

a limiting depth of 5 ft. Waves and currents at the disposal site are assumed to be

within the operating parameters of the equipment from June to September.

Authorization. This disposal site is not authorized for disposal. It may

provide beneficial use as described in the alternative nearshore berm west of

SR-105 ESP. If a beneficial use is identified, the recipient of the dredged sand

will have to pay the incremental cost exceeding the cost of open-water disposal.

Beach nourishment east of SR-105 ESP groin/dike

Location. This disposal site (referenced in Table H-2 as Alternative D-l) is

located along the east side of the SR-105 ESP groin and dike structures,

approximately 4.3 n.m. inland from the North Channel outer bar. Placement of

dredged material would be similar to that described for SR-105 ESP Beach

Nourishment.

Authorization. This site is not authorized for disposal of dredged material

under existing permits and has not been used as a disposal site in the past.

Comment. Placement of dredged material at this site may help to nourish a

shoreline dune that was breached during a 1998 extreme tide.

North Channel open water disposal

Location. The North Channel disposal site (referenced in Table H-2 as

Alternative E) is located along the North Channel thalweg at the SR-105 ESP,

located approximately 2.5 n.m. inland of the outer bar. Dredged material could

Appendix H Willapa Bay Dredged Material H-19
be placed at this site by bottom dumping from the hopper dredge in depths as

great as 70 ft. Because of the significant bottom changes that are presently

occurring, the specific location of disposal would be evaluated immediately prior

to the placement of dredged material. General location of the disposal can be

assumed to be downstream and upstream of SR-105 underwater dike, and at the

south end of the dike where the bottom is presently deepening. The proximity of

this disposal site to the underwater dike structure is a potential navigation safety

concern.

Authorization. This disposal site coincides with the historical location of

the Cape Shoalwater open-water disposal site near USCG Buoy No. 10. The site

permits expired on 7 July 1999.

Comment. The North Channel thalweg at the dike location has shifted

approximately 2,000 ft to the south since the completion of SR-105 ESP

construction and current velocity reduction in this vicinity has been documented.

Current velocities increase with distance from the north side slope southward

toward the channel. Therefore, placement of dredged material along the north

side slope of the North Channel could result in beneficial use by stabilizing the

channel side slope and lower portion of the beach and assisting the growth of

upper beach profile. Possible impacts to Dungeness crab may require mitigation.

Goose Point open water disposal

Location. The Goose Point open water disposal site (referenced in

Table H-2 as Alternative F) is located approximately 2.3 n.m. east of Leadbetter

Point and 8 n.m. from the North Channel outer bar. Placement of dredged

materials would occur by bottom dumping from a hopper dredge at existing

depths greater than 20 ft. Wave and current conditions at the disposal site are

within the operating parameters of the dredging equipment that would be used for

this alternative.

Authorization. This site is currently designated as the Goose Point openwater disposal site. Coordinates of the proposed disposal site are latitude

46°39'28" and longitude 123°59'46" located in 36 to 60 ft of water depth of the

Nahcotta Channel thalweg. Disposal site depths will be greater resulting in an

increased disposal site capacity. Previous disposal site coordinates from a dated

NOAA chart resulted in shallower disposal site depths and increased concerns

about site capacity.

Comment. This disposal site would provide no beneficial use of dredged

material. Biological resources impacts would be minimal.

Interim ocean disposal site

Location. This disposal site alternative (referenced in Table H-2 as

Alternative G) is an ocean site located approximately 1 mile outside the Willapa

outer bar.

1 Personal communication with Mr. Ted Benson, WDNR, describing status of disposal site

authorization at Goose Point and Cape Shoalwater sites, 13 September 1999.

H-20 Appendix H Willapa Bay Dredged Material
Authorization. This site is not authorized for ocean disposal and requires

Corps and EPA designation and approval of dredged sediments. Placement of

dredged material at this location would not provide a beneficial use.

Sediment nourishment site

Location. This disposal site (referenced in Table H-2 as Alternative H) is

located inshore from the outer bar along the middle shoal between the North and

Middle Channels of Willapa Bay. The site is approximately 1 n.m. inland from

the outer bar of the North Channel. A small hopper dredge would be required for

this site for bottom dump disposal of dredged sediments at existing depths of

20 to 30 ft.

Authorization. This site is not currently authorized for disposal of dredged

sediments under existing permits and is not within one of the designated openwater disposal sites in Willapa Bay. Placement of dredged material at this

location would provide some beneficial use. Material placed within the sediment

nourishment site would serve as a feeder for the formation of tidal flats for

additional habitat. Site designation would require EPA designation and approval.

Middle channel agitation dredging site

Location. This type of disposal (Alternative I) would occur along the

alignment of the Middle Channel dredging alternative. Existing depths at the

dredging site vary from 5 to 28 ft. Side casting in this location would constitute

resuspension of the bottom sediments for dispersal by currents and waves.

Authorization. This site is not currently authorized for disposal of dredged

sediments under any existing permits and is not within one of the designated

open-water disposal sites in Willapa Bay. This alternative would not provide any

beneficial use of dredged material. Site designation would require EPA

designation and approval. Additionally, impacts to Dungeness crab may require

mitigation for losses.

Rehandling site

Location. This rehandling site (Alternative J) is located approximately

0.5 n.m. east of the SR-105 project at the south bank of the North Channel.

Authorization. This site has been authorized as a borrow site for the

SR-105 project. This site has not been designated as a disposal site.

Comment. This site is considered a potential rehandling site for beach

nourishment disposal.

Proposed Cape Shoalwater open water-disposal site

Location. The proposed open-water disposal site (Alternative K) is

northeast of the USCG Buoy No. 13. The buoy is located in about 45 ft of water.

The disposal area location will vary with movements of the buoy. Disposal area

Appendix H Willapa Bay Dredged Material H-21
depths vary from 15 to 50 ft. The shallower depths would be associated with

potential beach nourishment disposal uses of dredged material.

Authorization. The WDNR is finalizing a SMA application to Pacific

County for state approval and designation of a Cape Shoalwater open-water

disposal site.

The preceding disposal site information is summarized in Table H-2.

Disposal Sites/Navigation Channel Alternative

Combinations

More than one disposal site can be feasible for a dredging alternative. A

preliminary attempt was made to assign the disposal site alternatives to the

navigation channel dredging alternatives. The list of navigation channel

alternatives presented in Table H-2 served as the basis for assigning disposal site

alternatives. The matching of channel dredging and disposal site alternatives was

a logistical and iterative process that accounted for cost of disposal, schedule of

construction, site capacity and volume of dredging, and dredging and disposal

equipment compatibility. These preliminary dredging site and disposal site

combinations are presented in Table H-3. The cost for the disposal operation was

estimated using CEDEP software (Callan 1998) and is also presented.

In developing the cost estimate for dredged material disposal alternative the

following major assumptions were used:

a. Placement of dredged material to beach nourishment and nearshore berm

is provided by a hopper dredge only.

b. Capacity of a small hopper dredge is 2,100 cu yd. Capacity of a large

hopper dredge is 6,000 cu yd.

The identified disposal site, as well the combination of disposal sites and

navigation channel alternatives, are preliminary and should be specified during

permitting and design. These dredging site/disposal site combinations may be

modified after completing numerical modeling and if new information about

channel sedimentation and volume of future maintenance dredging becomes

available.

H-22 Appendix H Willapa Bay Dredged Material
Table H-3

Dredging Site/Disposal Site Combination Alternatives |

Alternative

Dredging

Volume, cu yd Description Disposal Sites

Estimated Dredging

and Disposal Cost1j

per cu yd

3A 800,000 Dredge primarily on

entrance bar, straight out

and fixed in position.

A, B, or D-1 - Beach

Nourishment

C or D - Nearshore Berm

E - North Channel Disposal

$8.70

$6.60

$4.30

3B 200,000 Modified S-curve (moderate

curve).

A, B, or D-1 - Beach

Nourishment

C or D - Nearshore Berm

E - North Channel Disposal

$8.70

$6.60

$4.30

3H-a, 3H-b 1,600,000 Added after 1999 survey to

coincide with the straight

path seaward from near SR105 project that had minimal

change since 1998 survey.

Two variations include

existing SR-105 (3H-a) and

SR-105 dike raised to -2 ft

(3H-b).

A, B, or D-1 - Beach

Nourishment

C or D - Nearshore Berm

E - North Channel Disposal

$8.70

$6.60

$4.30

4A 2,300,000 Dredge primarily on

entrance bar.

F - Goose Point

I - Agitation Side Casting

$6.80

$3.80

4E 12,600,000 Same as 4A, except dredge

to total depth of 38 ft and

with width 1,000 ft.

F - Goose Point

I - Agitation Side Casting

$5.90

$3.50

1 Each cost estimate is based on disposal of amount shown in second column, though in some cases, it may be advantageous

to dispose of different portions of this amount at more than one site in a given year. Cost Estimate does not include

mobilization and demobilization. Mobilization and demobilization costs will vary depending on volume of dredged sediment

and dredged material disposal technique from $100,000 (small volume of sediment and small dredge to be used) up to

$2,000,000 (large volume of dredqe material and large dredge to be used).

Appendix H Willapa Bay Dredged Material H-23
References

Callan, Kim. (1998). Cost Estimate Dredging Engineering Program, CEPED,

U.S. Army Engineer District, Walla-Walla.

Environmental Protection Agency. (1995). Dredged MaterialEvaluation

Procedures and Disposal Site Management Manual, Washington State

Department of Natural Resources, U.S. Army Corps of Engineers,

Washington State Department of Ecology. Grays Harbor and Willapa Bay,

June 1995.

Federal Highway Administration and Washington State Department of

Transportation. (1997). "Environmental Assessment SR-105 Emergency

Stabilization Project, North Cove, Washington," Olympia, WA.

Jackson, D., Allen, T. M., and Lowell, S. M. (1997). "Vicinity of North Cove,

Washington, Willapa Bay Channel Restoration Project," SR-105 Geological

Study of the North Channel of Willapa Bay, Washington State Department of

Transportation, Olympia, WA, April 1997.

U.S. Army Engineer District, Seattle. (1994). Environmental documentation for

Operations and Maintenance of the Willapa Harbor navigation project,

CENPS-OP-NP, 30 March 1994.

H-24 Appendix H Willapa Bay Dredged Material
Appendix H Willapa Bay Dredged Material H-25
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AppendixH Willapa Bay Dredged Material H-27
REPORT DOCUMENTATION PAGE

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1. REPORT DATE (DD-MM-YYYY)

April 2000

2. REPORT TYPE

Final Report

4. TITLE AND SUBTITLE

Study ofNavigation Channel Feasibility,

Willapa Bay, Washington

6. AUTHOR(S)

Nicholas Kraus, editor

Edward B. Hands, Nicholas C. Kraus, Keith Kurrus, Adele Militello, William C. Seabergh,

Vladimir Shepsis, and Jane McKee Smith, Chuck Abbott, Hiram T. Arden,

Hugo Bermudez, Steven M. Bratos, Mitchell E. Brown, Bruce A. Ebersole, Scott Fenical,

Ken FitzGerald, Suzanne Giles, Norman W. SchefTher, Shane Phillips, and Carol Titus

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Army Engineer Research and

Development Center

Coastal and Hydraulics Laboratory

3909 Halls Ferry Road

Vicksburg, MS 39180-6199;

Evans-Hamilton, Inc.

Seattle, WA;

Pacific International Engineering PLLC

Edmonds, WA

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Army Engineer District, Seattle

P.O. Box 3755

Seattle, WA 98124-3755

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Approved for Public Release; distribution is unlimited.

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

The navigation channel reliability monitoring and evaluation study for Willapa Bay, Washington described in this report was

performed by the U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory for the U.S. Army Engineer

District, Seattle (NWS). The study was established under a Partnering Agreement between the NWS and the Willapa Port Commission for

deternrining the feasibility ofmamtaining a reliable navigation channel through the Willapa Bay entrance.

Willapa Bay is a large estuarine system located on the southern end ofthe Washington coast. Its spring or diurnal range tidal prism is

one of the largest of all inlets on the coast of the continental United States. The shifting channels at the entrance to Willapa Bay make

navigation unreliable, and the local port cannot maintain or attract commercial users. Local interests obtained Congressional support to

determine ifan economical deep-draft channel can be established through the entrance bar. An economical channel implies a route that can

be traversed safely under typical waves and tidal currents.

The study was conducted in a multi-disciplinary approach involving engineering analysis, field measurements, geomorphologic

analysis, and numerical modeling ofwaves, currents, and sediment transport in evaluation of alternative channel designs. These topics are

covered in the main text ofthe report, with additional details and data compilations contained in appendices.

15. SUBJECT TERMS

Cape Shoalwater Dredging Geomorphology

Currents Field measurement Navigation

Navigation channel

Sediment Transport

Washington

Waves

Willapa Bay

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UNCLASSIFIED

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