Appendix B, Yaquina Bay ODMDS Evaluation/EA B-i

APPENDIX B

Physical Processes and Geologic Features

CONTENTS

 Page

EXECUTIVE SUMMARY

1. INTRODUCTION B-1

Entrance to Yaquina Bay - Physical Setting B-1

Yaquina Bay Navigation Project Background B-2

Ocean Dredged Material Disposal Sites B-3

2. MANAGEMENT OF YAQUINA BAY ODMDS B-7

Yaquina Bay Ocean Dredging Disposal before 1977 B-7

Yaquina Bay Ocean Dredging Disposal 1977 to 1985 B-7

Yaquina Bay Ocean Dredging Disposal 1986 to 2000 B-9

Management Actions for Yaquina Bay ODMDSs B-10

3. PAST BATHYMETRIC CHANGE AND RELATED IMPACTS AT YAQUINA

 BAY ODMDS B-11

Interim ODMDS B-11

Nearshore Section 103 ODMDS B-15

Observed Sediment Dispersion at Yaquina ODMDS B-16

Capacity Limitations for Interim and Nearshore Section 103 ODMDS B-17

4. SITING AND MANAGEMENT REQUIREMENTS FOR PROPOSED ODMDS

 AT YAQUINA BAY B-21

ODMDS Requirements B-21

ODMDS Capacity – General Considerations B-22

ODMDS Selection – Specific Considerations B-23

Littoral Considerations B-25

5. SIMULATING THE FATE OF DREDGED MATERIAL PLACED AT ODMDS

 Coupled Strategy for Numerical Modeling and ODMDS Management B-26

Fate of Dredged Sediment Placed in Open Water B-26

Predictive Methods: Applicable Numerical Models B-27

ODMDS Modeling Strategy B-28

Short-term FATE Model B-29

Long-term FATE Model B-29

Calculating Bottom Sediment Transport Potential B-30

Hallermeier Sediment Transport Limits B-30

Modified Ackers-White Sediment Transport Estimates B-31

Limitations of Simple Sediment Transport Estimates B-32

FATE Model Data Requirements B-34
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-ii

CONTENTS (continued)

 Page

6. FATE MODELING RESULTS AND IMPACT ASSESSMENT FOR

 PROPOSED ODMDS LOCATIONS B-35

Vertical Limit for Dredged Material Mound Height B-35

General Location for North and South ODMDS and Required Size B-37

Short-Term FATE Modeling - Bathymetry Impact Assessment B-37

STFATE Results B-39

STFATE Conclusions B-45

Specification of Proposed ODMDS Size and Location B-46

Long-Term FATE Modeling - Typical Disposal Year B-48

Long-Term FATE Modeling - 20-Year Life Cycle B-50

 ODMDS Disposal Placement Grid B-50

 Year One of 20-Year Disposal Sequence B-50

 Complete 20-year Disposal Sequence B-52

Summary of FATE Modeling Results B-52

Physical Impacts at ODMDS due to Dredged Material Disposal B-54

7. OCEANOGRAPHIC PROCESSES B-56

Offshore Regional-Scale Circulation B-56

California and Davidson Currents B-57

Shelf Circulation B-57

 Inner-Shelf Circulation B-57

 Mid-Shelf Circulation B-58

 Littoral Sediment Transport B-58

Summary of Seasonal Changes in Circulation B-60

Cross-shore Circulation B-60

Long-Period Waves B-61

 Offshore Rotary Currents B-63

8. MEASURED OCEANOGRAPHIC DATA B-64

Hydrographic Survey Data B-64

 Survey Error Assessment B-64

Sediments at Yaquina Bay Proposed ODMDSs B-65

Dredged Sediment Characteristics B-65

Physical Properties of Dredged Material Placed at ODMDSs B-65

 Dredged Material Solids Content and Void Ratio B-66

 Subaqueous Angle of Repose - Avalanching of Dredged Sediments B-67

Summary of Yaquina Dredged Material Parameters B-68

Surface Waves - Simulated Data B-68

 Mean WIS Parameters B-68

Simulated Shelf Tidal Elevations and Currents B-69

Observed Currents Applicable for Yaquina Bay ODMDSs B-69

 Bottom Currents due to Estuarine Discharge and Jetty Effects B-72

 Surface Currents at the North Reef B-73

 Bottom Current at the Interim ODMDS B-73

 Surface Currents 10 miles Offshore of Newport B-73

 Geostrophic Currents B-73

 Currents Observed at a Similar Nearshore Location – Coos Bay B-73

Calculation of Residual Current for Yaquina Bay ODMDSs B-74
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-iii

CONTENTS (continued)

 Page

9. GEOLOGIC FEATURES B-75

Introduction B-75

General Geology B-75

Unconsolidated Marine Deposits B-78

 Seabed Sediments near Yaquina Bay B-78

 Sediment Accretion B-80

Geophysical Explorations B-80

1995 Side-scan Sonar Survey Results B-80

2000 Side-scan Sonar Survey Results B-81

10. REFERENCES B-82

LIST OF FIGURES

NUMBER Page

Section 1

B-1. Yaquina Bay and Harbor, Oregon B-2

B-2. ODMDS feature map and approach bathymetry B-6

Section 3

B-3. Approach and ODMDS bathymetry offshore of Yaquina Bay for 1983 and 1985 B-12

B-4. Bathymetric change at Yaquina Bay ODMDS during 1983 and 2000 B-13

B-5. Approach bathymetry offshore of Yaquina Bay in 1983 and 1999 B-14

B-6. Mounded bathymetry in 1985 dredging season and resultant wave amplification B-18

B-7. Mounded bathymetry in Section 103 ODMDS in 2000 and potential amplification B-19

Section 5

B-8. Results from Ackers-White sensitivity test for sediment transport potential B-33

Section 6

B-9. RCPWAVE estimates for maximum limiting mound height B-36

B-9a. Four phases of dredged material behavior during placement in open water B-38

B-10. Predicted disposal footprint geometry as a function of disposal vessel speed B-41

B-11. Predicted disposal footprint thickness for dredges Westport and Yaquina B-42

B-12. Predicted disposal footprint geometry as a function of current speed B-43

B-13. Predicted bottom distribution resulting from release of one load of sandy

 dredged material in water depth of 100 feet for Westport and Yaquina B-44

B-14. Proposed new locations for Yaquina Bay ODMDSs B-47

B-15. Accumulation of dredged sand placed in center of proposed North ODMDS

 for split-hull hopper dredge and multi-bin hopper dredge B-49

B-16. Baseline bathymetry at proposed North ODMDS and estimated accumulation

 after 1 year of dredged material placement B-51

B-17. Predicted bathymetry at proposed North ODMDS after 20 years of dredged

 material placement and corresponding vertical accumulation B-53
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-iv

CONTENTS (continued)

NUMBER Page

Section 7

B-18. Mean circulation in the coastal upwelling region off central Oregon B-62

Section 8

B-19. Wave environment offshore of Yaquina Bay simulated from WIS-II data B-70

B-20. ADCIRC simulated tidal elevation and current at Yaquina Bay ODMDS B-71

Section 9

B-20A. Geologic map of the Yaquina Bay area, Newport, Oregon B-76

B-21. Generalized geologic cross section at Newport, Oregon B-77

B-22. Surface features and sediment cover of continental shelf off central Oregon B-79

LIST OF TABLES

NUMBER Page

Section 1

B-1. Volume of dredged material placed at Yaquina Bay ODMDS B-5

B-2. Observed dispersion potential at Yaquina ODMDS based on survey differencing B-16
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-v

APPENDIX B - Physical Processes and Geologic Features

EXECUTIVE SUMMARY

Geographic Location: Northwest Pacific Coast of continental United States, deep draft

ocean entrance to Newport at Yaquina Bay along Central Oregon.

Organizational Oversight: U.S. Army Corps of Engineers - Portland District and U.S.

 Environmental Protection Agency - Region X.

Project Features Addressed: Ocean Dredged Material Disposal Sites 2 miles Offshore

 of Yaquina Bay.

Appendix B describes the physical evaluation of dredged sediment placed at Yaquina Bay 

Ocean Dredged Material Disposal Sites (ODMDS). This appendix presents assessments 

highlighting the shortcomings of the historic ODMDS (the Interim and Section 103 Sites) and 

develops analyses that support the optimal selection of new ODMDS locations.

Two ODMDSs (North Site and South Site) are proposed. Each site was conservatively 

designed to be capable of providing at least 20-years of capacity for dredged material 

disposal. The proposal for two sites is based on the need to provide for up to 50 years of 

disposal capacity and to accommodate operational flexibility. Additional consideration was 

given to providing enough ODMDS area for distributing dredged material to a relatively thin 

(vertical) accumulation on an annual basis, if needed. This approach was considered for 

minimizing the vertical accumulation resulting from repeated disposal at one location. The 

proposed North and South ODMDSs are located offshore of the historic sites, at an average 

water depth of 135 ft with a minimum depth of 120 feet and a maximum depth of 160 feet, 

and within the 4.5-mile zone of siting feasibility.

Siting criteria used to assess new ODMDSs are discussed. Physical assessments of open 

water dredged material disposal are performed with regard to the in situ conditions at 

proposed ODMDS sites. Potential physical impacts resulting from the long-term use of the 

proposed North and South ODMDSs are identified.

Appendix B is composed of nine sections. Section 1 describes the relevant navigation project 

features at Newport, Oregon (Yaquina Bay). Section 2 reviews the life cycle of Yaquina Bay 

ODMDSs and identifies deficiencies of the historic ODMDSs. Section 3 assesses bathymetric 

change at the historic ODMDSs and related affects on the local wave climate. Section 4

identifies the need for new larger ODMDSs and formulates site selection criteria necessary for 

successful long-term ODMDS management. Section 5 describes the FATE modeling 

approach used to select the new ODMDS. Section 6 proposes ODMDS locations based on 

FATE modeling results. Sections 7 and 8 describe the oceanographic process affecting 

Yaquina Bay ODMDSs. Section 9 describes relevant geologic resources.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-1

Ocean Dredged Material Disposal Sites at Yaquina Bay

Utilization of Historic ODMDS

and

Proposed New ODMDS

Section 1

INTRODUCTION

Entrance to Yaquina Bay - Physical Setting

The Yaquina River enters the Pacific Ocean near the city of Newport, Oregon, approximately 

115 miles south of the Columbia River (Figure B-1). Yaquina Bay is the fourth largest

estuary in Oregon in terms of area. The estuary is fed mainly by the Yaquina River, which 

drains 253 square miles and is 59 miles long from its mouth to headwaters. The river’s 

annual discharge is marked by a high seasonal variability, typically ranging from 100 cubic 

feet per second (cfs) to 2,500 cfs. Highest discharges occur during November through 

February due to rain runoff. Lowest flows occur during July through September [USGS 

1990]. The tidal prism of the Yaquina estuary is about 40 square miles/foot [Jarrett 1976].

The shoreline and nearshore vary from wide sand beaches to rocky headlands. Offshore rocks 

and neritic reefs attest to the retreat of the coastline from erosive ocean forces. Part of this 

shoreline retreat has been due to a sea level rise of over 30 feet in the past 6,000 years. This is 

only the latest in a long series of fluctuations in sea level that have affected the area.

The sea cliffs and headlands as well as the rock underlying all the beach and nearshore sands 

are many millions of years old. The beach nearshore sands are less than one million years 

old. Coastal rivers deposited some of these sands when sea level was lower (>6,000 years 

ago). Other sources include erosion from rock outcrops and bluffs as sea level rose and fell. 

Little, if any, sand is presently escaping from coastal estuaries. In fact, the Yaquina Bay 

estuary is being filled by marine sand entering from the ocean and deposition of fluvial 

sediment entering the estuary from upland sources [Komar 1997]. In the nearshore area, 

wave energy has removed any fine silts and clays from sediments leaving only medium-fine 

sand covering an area 3 to 10 miles offshore along much of the Oregon coast.

The continental shelf off Oregon is widest from Siuslaw River to Siletz Bay, extending over 

30 miles offshore. This is due to a large rocky outcrop complex (Stonewall Bank) beginning 

about 15 miles offshore of Yaquina Bay and trending southwest (refer to Figure B-22). Little

silt and clay is found inshore of this bank and sediments are predominantly fine sand out to 

depths of 300 feet. This sand zone narrows rapidly south of Siuslaw River and less rapidly 

north of Yaquina Bay. In three dimensions, this inner shelf sand zone is a wedge or lens of 

sediment overlying much older rock. See Section 9, Geologic Resources for additional 

discussion of seabed and related geological characteristics.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-2

Figure B-1. Yaquina Bay and Harbor, Oregon.

Yaquina Bay Navigation Project Background

The deep draft navigation project located at the Yaquina Bay consists of a dredged entrance 

channel that is 40-feet deep, 400-feet wide, and 4,280-feet long, which extends through a 

jettied entrance between the Yaquina River and the Pacific Ocean (Figure B-1). A smaller

channel (30-feet deep and 300-feet wide) continues from the landward end of the entrance 

channel [river mile (RM) 0] and proceeds 2 miles northeast into Yaquina Bay, where the 

channel leads to a turning basin that is 1,200-feet wide at McLean Point.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-3

The process of maintaining a jettied navigation channel at an estuary entrance such as 

Yaquina Bay involves the periodic relocation of sediment that shoals within the entrance 

channel. The activity of removing shoaled sediment is called dredging. At the ocean 

entrance to Yaquina Bay, the shoaled sediment is marine sand and originates from littoral 

areas on the ocean-side of the entrance. Shoaling of the navigation channel occur throughout 

the year and is driven by waves and currents. The dredged sediment is placed into designated 

ocean dredged material disposal sites (ODMDS) that are located in open water within 1-3

miles of the entrance channel. Dredging is typically performed during the summer, when 

ocean waves are small and dredging can be safely performed at the jettied entrance channel.

Federal navigation improvements at Yaquina Bay began in 1879 when Congress authorized 

the Portland District USACE to begin construction of the south jetty. In 1896, the north jetty 

was constructed, with the intention of maintaining a 12-foot project depth over the entrance 

bar. The natural channel had averaged about 7 feet deep and shifted frequently both during 

and between seasons. Appreciable quantities of sediments have been dredged from Yaquina 

Bay and the entrance channel since 1928, when consistent dredging was initiated to establish 

and maintain an 18-foot deep channel across the entrance bar.

In 1949, the entrance channel was deepened to 26 feet. Additional entrance channel 

deepening to 40 feet was authorized in 1958 and completed in 1969. Presently, the north jetty 

is 1.3 miles long and the south jetty is 1.6 miles long.

Typically, the Yaquina Bay deep draft project has two main shoaling areas. The sediment 

dredged from the 40-foot deep entrance channel and associated bar crossing is composed of 

fine-medium sand [median grain size is 0.18 millimeters (mm) with fines content less than 

2%] and accounts for 95% of the annual dredging volume. The interior 30-foot channel (and 

turning basin) accounts for 5% of the total annual dredging and dredged material properties 

are more variable, than the entrance channel and bar [see Section 8 of this appendix]. In its 

present configuration, the entrance channel up to the turning basin require annual dredging of 

up to 370,000 cubic yards (cy) of shoaled sediment (fine-medium sand with some silt) to 

maintain the authorized depth. Up to an additional 25,000 cy of material may be removed 

from the South Beach Marina access channel and up to 100,000 cy of material may be 

removed from Depot Slough every 5-8 years. The amount and frequency of maintenance 

dredging depends on the volume of sediments transported into the project area by storm 

conditions. The sandy dredged material is placed in ocean dredged material disposal sites 

(ODMDS). Dredging and disposal is typically performed by hopper dredges.

Ocean Dredged Material Disposal Sites

The consistent use of an ocean site for disposal of sediment dredged from Yaquina Bay began 

in the 1920s and has continued to the present. Prior to EPA Interim site designation in 1977, 

the location of the ocean disposal site was not precisely specified and the placement of 

dredged material within the disposal site was not strictly controlled, in terms of vessel 

positioning. The volume of dredged material placed at Yaquina Bay ODMDSs since 1928 is 

summarized in Table B-1.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-4

In January 1977, the Yaquina Bay ocean disposal site received interim designation when EPA 

issued the final Ocean Dumping Regulations (40 CFR 228). At this time, the Interim site was 

classified as an ocean dredged material disposal site (ODMDS). At the time of interim site 

designation, the boundaries for the rectangular ODMDS were fixed geographically in terms of 

corner coordinates. Figure B-2 denotes the boundaries for the EPA interim-designated

disposal site (solid line). The Interim ODMDS was “sized” based on the policy of 

minimizing the areal extent over which dredged sediments would affect the receiving water 

column and seabed during disposal. Smaller sites were considered more environmentally 

acceptable than larger sites.

A Corps-sponsored site evaluation report [USACE 1985] prepared in April 1985, 

recommended final EPA-approval of the Interim ODMDS. In late 1985, it became apparent 

that significant mounding of dredged sediments placed at the Interim ODMDS was occurring. 

The mounding was affecting incoming waves, resulting in unstable (breaking) wave 

conditions at the jetty entrance to Yaquina Bay. The mounding of dredged placed material 

was completely unexpected and was contrary to the assumptions advanced in the USACE 

1985 site evaluation report.

To avert additional dredged material mounding and wave-related impacts at the Interim site, 

the Portland District selected a nearshore ODMDS (Figure B-2) under the authority of Section 

103 of the Marine Protection, Research and Sanctuaries Act (MPRSA). The nearshore 

Section 103 ODMDS, situated north of the Interim ODMDS, was used for dredged material 

disposal after 1985 (no dredged material was placed in the Interim ODMDS again until 1999). 

By 1995, it became apparent that dredged material was accumulating within the nearshore

103 ODMDS; as of 1998, a significant mound feature was forming within the site. To avert 

additional mounding within the nearshore Section 103 site, the nearshore Section 103 site was 

expanded in 1999 - southward into the previously used Interim site in 1999 (material 

previously placed within the Interim site had been completely dispersed by 1999). Between 

1999 and 2000, use of the nearshore Section 103 site (the only disposal site available) was

reduced to the minimum necessary, due to concerns of mounding. This limited the volume of 

dredging that can be performed at Yaquina Bay entrance.

In June 2001, the USACE Portland District, under its Section 103 authority, selected the two 

proposed ODMDSs (North and South) for the disposal of dredged material. EPA concurred 

in a July 2001 letter for a 5-year period. The North Site was first used during the 2001 

dredging season. EPA issued a second Section 103 site use concurrence letter in April 2007. 

This allowed continued use of the North Site through the 2011 dredging season. The South 

Site has not been used so is still available for use.

Between 2001-2009 all dredged material was placed in the northern half of the North Site. 

Maximum mound height in 2007 reached 5 feet and 6 feet in 2008. In 2009-2010, material 

from Depot Slough was dredged by clam-shell and barged to the North Site. A portion of the 

material from the Yaquina Bay federal project was placed in the southern half of the North 

Site. Portions of the North Site mounded 10-12 feet above the 2001 baseline bathymetry. In 

2011, all material was placed in the southern half of the North Site.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-5

Table B-1. Volume of dredged material placed at Yaquina Bay ODMDS.

ODMDS Location Year Year Total

(cy)

Average

at Site (cy)

Total Placed

at Site (cy)

Interim Site

1928-1940* 1,040,000

252,379 14,638,036

1941-1967* 5,400,000

1968-1981* 6,440,000

1982 331,180

1983 453,319

1984 670,773

1985 302,764

Nearshore

Section 103 Site

1986 242,468

310,240 4,653,596

1987 537,843

1988 324,519

1989 333,807

1990 216,696

1991 316,956

1992 321,652

1993 358,407

1994 206,971

1995 393,641

1996 314,636

1997 370,000

1998 351,000

1999 260,000

2000 105,000

North ODMDS

2001 198,284

217,379 2,173,790

2002 179,427

2003 320,455

2004 241,293

2005 282,596

2006 223,150

2007 192,352

2008 175,031

2009 161,678

2010 199,524

Total 21,465,422

*Volumes are approximate
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-6

Figure B-2. ODMDS Feature Map and Approach Bathymetry.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-7

Section 2

MANAGEMENT OF YAQUINA BAY ODMDS

Between 1977 and 2000, two nearshore ODMDSs were utilized by the Portland District for 

disposal of sediments dredged from the Yaquina Bay navigation project (Table B-1). Prior to 

1986, only the Interim ODMDS had been used. In 1986, the nearshore 103 ODMDS was 

selected and used in place of the Interim site to increase disposal site capacity and reduce 

hazards associated with the mounding of placed dredged material at the Interim site. In 1998, 

mounding of placed dredged material within the nearshore 103 ODMDS became an issue of 

concern motivating the need for a new and much larger ODMDS. Note that from 1928-1981, 

12 million cubic yards (mcy) of dredged material had been placed at (or within the vicinity of) 

the Interim ODMDS resulting in little mounding of placed dredged material. During 1982-

1985, there was 1.7 mcy placed at the Interim ODMDS and from 1986 to 2000 approximately 

4.6 mcy was placed at the nearshore 103 ODMDS, resulting in pronounced mounding of 

dredged material within both sites.

Dredged material mounding at the Yaquina Bay ODMDSs was attributed to changes in 

disposal site utilization. The rationale for ODMDS management has changed significantly 

since the initial use of an ocean disposal area in 1928. The transition in ODMDS 

management at Yaquina Bay is characterized by three important shifts in USACE and EPA 

policy which are outlined below.

Yaquina Bay Ocean Dredging Disposal Before 1977

Prior to formal designation of the Interim ODMDS in 1977, the offshore dredged material 

disposal area was located only in terms of approximate location and areal configuration. 

Placement of dredged material within the disposal area was governed by the need to minimize 

dumped dredged material being transported back into the navigation channel and minimize 

haul distance. Mounding did not appear to be a concern due to the spatial variability of 

dredged material disposal within a given site; the site boundaries were not fixed and it was not 

required to place material strictly within the disposal site. The operational “flexibility” of 

disposal site boundaries and vessel control during material placement resulted in a higher 

degree of dredged material dispersal than at present. Prior to 1977, dredged material was 

placed over a wider areal expanse than the configuration of the ODMDS indicates.

Yaquina Bay Ocean Dredging Disposal 1977 to 1985

Between 1977 and 1985, management of the offshore dredged material disposal site at 

Yaquina Bay was characterized by the transition from unregulated dredged material disposal 

to a regulated program. In January 1977, the active ocean disposal site at Yaquina Bay 

received interim designation as an ODMDS when EPA issued the final Ocean Dumping 

Regulations (40 CFR 228). The Interim ODMDS configuration was governed by the 

requirement to minimize the benthic area of impact due to open-water disposal of dredged 

sediments. The areal size of the Interim ODMDS at Yaquina Bay was based on:
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-8

ODMDS length = average dumping run for one dump

 = (disposal vessel speed while dumping) x (time to empty disposal vessel)

ODMDS width = average turn during one dump = disposal vessel turning radius while dumping

ODMDS long axis orientation = preferential approach heading during dredged material disposal (site

orientation is set by disposal vessel operators based on dumping

efficiency and vessel sea-keeping due to incident wave direction).

The lineal dimensions, boundary coordinates, and water depth variation for the Interim 

ODMDS are described below. Disposal boundary coordinates are in state plane, Oregon 

north zone, NAD 27 (feet). Geographic coordinates are in NAD 27. These boundaries apply 

to the Interim ODMDS configuration, as shown in Figure B-2.

“Interim” ODMDS: dimensions = 3,600 feet x 1,400 feet, azimuth = 270o, average depth = 60 feet

 1996 elevation variation = -72 MLLW to -42 MLLW

Northwest corner - Easting=1,062,478 ft, Northing=364,249 ft Lat=44 36 31 N, Lng= -124 06 04 W

Northeast corner: - Easting=1,065,939 ft, Northing=364,146 ft Lat=44 36 31 N, Lng= -124 05 16 W

Southwest corner: - Easting=1,062,411 ft, Northing=362,885 ft Lat=44 36 17 N, Lng= -124 06 04 W

Southeast corner: - Easting=1,065,879 ft, Northing=362,730 ft Lat=44 36 31 N, Lng= -124 05 16 W

The Interim ocean disposal site was intended to receive final EPA designation as an ODMDS 

in August 1986, but did not due to the rapid accumulation of placed dredged material between 

1982 to 1985. The unintended consequence of using the aerially restricted Interim ODMDS 

has been creation of potentially adverse impacts to navigation at the Yaquina Bay entrance, by 

mounding of placed dredged material. The reason for dredged material mounding in the 

Interim site was not associated with increased dredging/disposal volumes. The average 

annual volume of dredged material placed in the Interim ODMDS between 1982 and 1985 

was 251,150 cy/yr, which is lower than the 14-year year average of 460,000 cy/yr between 

1968 and 1982. The reason for rapid accumulation (mounding) of dredged material within the 

Interim ODMDS has been attributed to two factors:

(1) The restriction of dredged material disposal within relatively small EPA-designated 

ODMDSs, rather than in larger unconfined areas and in a dispersive manner of placement.

(2) Increased use of contractor operated split-hull hopper dredges in 1982, which enhanced 

the vertical extent of dredged material placed on the seabed within the ODMDSs.

Prior to the 1982, sediment dredged at the Yaquina Bay and placed in the ODMDS was 

accomplished using government hopper dredges. Government hopper dredges utilize a series 

of “doors” located on the hull bottom to release each load of dredged material. The bottom 

doors are sequentially opened during disposal until the entire load of dredged material is 

released from the vessel, resulting in a gradual release of dredged material from the vessel.

Between 1982 and 1985, more than 80% of the material dredged at Yaquina Bay was 

accomplished using contractor split-hull hopper dredges. Contractor split-hull hopper 

dredges release their load of dredged material by opening (splitting) the entire hull of the 

vessel. The split-hull method of disposal is more rapid than bottom-door hopper dredges. 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-9

While the use of split-hull hopper dredges reduces the time required for material disposal, 

split-hull dredges reduce the horizontal dispersal of dumped dredged material on the seabed 

while increasing the vertical extent of accumulation per dump.

In addition to the type of hopper dredge used, the capacity (volume per dump) of the hopper 

dredge also affects the amount of vertical accumulation. Since 1982, the bottom-door hopper 

dredge Yaquina (capacity 850-1,000 cy) has been used as the government dredge at Yaquina 

Bay. Between 1982-1984, the split-hull dredge Westport (capacity 1,000 cy) was used as the 

contractor dredge at Yaquina Bay. Beginning in 1985, larger split-hull dredges such as the 

Padre Island and Newport (capacity 2,600 cy) were used as contractor dredges.

To comply with Ocean Dumping Regulations (40 CFR 228), Portland District contract 

specifications required dredges to place dredged material entirely in ODMDS boundaries. 

The ODMDS corner coordinates and a single disposal location (coordinate or buoy) were 

given as a reference for disposal position within the ODMDSs. Conceptually, placement of 

dredged material was done randomly at some “radius” about the assigned disposal point. 

Dredged material was usually placed on the side of the disposal area (or specified disposal 

point) closest to the location of dredging to shorten the haul distance. This effectively 

minimized aerial extent over which dredged material was dispersed in the ODMDS. This 

method of dredged material disposal is referred to as “point dumping.” Point dumping 

enhanced the vertical accumulation of dredged material in a small area of the ODMDS.

In 1985, mounding of dredged material at the Interim ODMDS began causing incoming 

waves to shoal and break at the approaches to the jettied entrance channel of Yaquina Bay. 

Numerous reports by commercial and private mariners and the Coast Guard had implicated 

the dredged material mounding to the hazardous wave conditions at the jettied entrance.

Yaquina Bay Ocean Dredging Disposal 1986 to 2000

The Interim ODMDS which was designated by EPA in 1977 was not given “final” approval 

by EPA in 1986, as recommended by a Portland District report compiled early in 1985 

[USACE 1985]. Rather, another ODMDS was selected by the Portland District under the 

Section 103 authority of MPRSA. This nearshore 103 ODMDS was located directly north of 

the Interim site in an average water depth of 70 feet (10 feet deeper than the Interim site). 

The nearshore 103 ODMDS was sized with 80% greater area than the Interim site. The lineal 

dimensions, boundary coordinates, and water depth variation for the nearshore 103 ODMDS 

are described below. Disposal boundary coordinates are in state plane, Oregon north zone, 

NAD 27 (feet). Geographic coordinates are in NAD 27. These boundaries apply to present 

nearshore 103 ODMDS configuration as shown in Figure B-2.

“103” ODMDS: dimensions = 4,070 feet x 2,220 feet, azimuth = 270o, average depth = 70 feet

 1996 elevation variation = -90 MLLW to -50 MLLW

Northwest corner - Easting=1,061,352 ft, Northing=366,679 ft Lat=44 36 32 N, Lng= -124 06 21 W

Northeast corner: - Easting=1,065,463 ft, Northing=366,501 ft Lat=44 36 54 N, Lng= -124 06 21 W

Southwest corner: - Easting=1,061,249 ft, Northing=364,459 ft Lat=44 36 32 N, Lng= -124 05 24 W

Southeast corner: - Easting=1,065,372 ft, Northing=364,276 ft Lat=44 36 54 N, Lng= -124 05 24 W
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-10

Beginning in 1986, all sediment dredged from the Yaquina Bay deep draft navigation channel 

was placed within the nearshore 103 ODMDS. Additionally, disposal site management 

became increasingly proactive in the year-to-year operation of the Yaquina Bay ODMDS. 

Proactive disposal site management was required to maximize site capacity utilization of the 

Corps-designated nearshore 103 ODMDS and minimize mounding within the site. Refer to 

Section 4 of this appendix for definition of ODMDS capacity. Important facets of ODMDS 

management now include consistent site monitoring and uniform distribution of dredged 

material within the entire site during placement.

Management Actions for Yaquina Bay ODMDSs

Bathymetric surveys serve as the method of choice to monitor the physical environment at 

ODMDSs. Consistent annual bathymetric surveys have been conducted at Yaquina ODMDSs 

and vicinity since 1983; the x,y,z data have been digitally stored. The annual monitoring is 

necessary to track bathymetric change at the ODMDS, ensure that the Corps of Engineers 

does not un-intentionally worsen a mounding problem, or place dredged material outside of 

the active ODMDS boundaries.

Since 1997, bathymetric monitoring of the nearshore 103 ODMDS has been used to direct the 

location of dredged material disposal within the site and avoid “hitting” high spots created by 

the previous years’ disposal operation. Despite the effort to evenly distribute dredged 

material within the nearshore 103 ODMDS, dredged material has slowly accumulated within 

this site since 1986 when the nearshore 103 ODMDS was first used. While exclusively 

utilizing the nearshore 103 site for dredged material disposal between 1986 and 1996, the 

mound at the Interim ODMDS was completely dispersed by waves and currents to an 

elevation consistent with the ambient seabed.

In 1995, shoaling (breaking) waves associated with mounding at the nearshore 103 ODMDS 

were reported by anglers and the US Coast Guard. Bathymetric surveys of the nearshore 103 

ODMDS indicated the formation of a mound within the site. In 1998, the size of the dredged 

material mound in the nearshore 103 ODMDS was sufficient to warrant adjustments to site 

management. See Section 3 of this appendix for an analysis of mound-induced wave 

amplification at Yaquina Bay ODMDSs. Starting in 1998, use of the nearshore 103 ODMDS 

was restricted to isolated areas that had not exhibited mounding. By 2001, it was estimated 

that the nearshore 103 ODMDS would have no capacity for receiving additional dredged 

material.

Between 2001 and 2010, all dredged material was placed in the northern half of the North 

Site. Maximum mound height in 2007 reached 5 feet and 6 feet in 2008. In 2009-2010,

material from Depot Slough was dredged by clam-shell and barged to the North Site. Some 

of the material from the Yaquina Bay federal project in 2010 was placed in the southern half 

of the North Site for the first time. Portions of the north half of the North Site has mounded 

10-12 feet above the 2001 baseline bathymetry. In 2011, all material was scheduled to be 

placed in the southern half of the North Site.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-11

Section 3

PAST BATHYMETRIC CHANGE AND RELATED IMPACTS 

AT YAQUINA BAY ODMDS

This section discusses site-specific bathymetric change at Yaquina Bay ODMDSs, in terms of 

the accumulation (or mounding) of dredged material placed within the sites. The change in 

wave conditions at the entrance due to the dredged material mounding also is discussed.

Interim ODMDS

Prior to formal designation of the Interim ODMDS in 1977, approximately 10.6 mcy of 

dredged sediment had been placed within or in vicinity of the Interim ODMDS. Between 

1977 and 1981, approximately 2.3 mcy of dredged material was placed within the boundaries 

of the Interim ODMDS. During this time, no mounding of dredged material was reported or 

observed within the Interim site boundary. Prior to 1982, dredged material was placed using 

government-operated multiple bottom-door hopper dredges.

Between 1982 and 1985, approximately 1.8 mcy of dredged material was placed within the 

western half of the Interim ODMDS boundaries; 88% of which was placed by Contractoroperated split-hull hopper dredges. The baseline condition (1983) bathymetry for Yaquina 

Bay ODMDSs and vicinity is shown in the top of Figure B-3. In 1985, significant mounding 

of dredged material was observed within the western half of the Interim ODMDS as shown in 

the bottom of Figure B-3 and top of Figure B-4.

The top graphic of Figure B-4 shows the “difference” between the 1983 survey and the 1985

survey. The mound feature associated with 3 years (1983-1985) accumulation of dredged 

material disposal was 20-feet high and 1,800-feet wide at the base with respect to the 1983 

site bathymetry. Note that 1,430,000 cy was placed within the Interim ODMDS between 

1983-1985 (annualized average of 285,000 cy/yr). Approximately 780,000 cy was estimated 

to have been contained within the 20-foot high mound, or 55% of the total placed between 

1983 and 1985. The other 45% of dredged material unaccounted was likely dispersed by 

waves and currents to a thickness below the survey detection threshold (±1.5 feet). This 

dispersion rate translates into 214,000 cy/yr, which defines the estimated “dynamic” capacity 

of the Interim ODMDS (the volume that can be placed per year without accumulating; refer to 

Section 4 for capacity definitions). Note that the above estimated dispersion rate is based in 

part on the presence of the dredged material mound. Waves and currents interact with the 

mound to enhance dispersion: The higher the mound for a given water depth, the greater the 

potential sediment dispersion rate. Dispersion of dredged material placed on a “flat” bottom 

at the Interim ODMDS would likely be significantly less than on a “mounded” bathymetry. 

Despite the dispersiveness of the Interim ODMDS, rapid accumulation of dredged material 

occurred during 1983-1985. This is because the volume of dredged material placed at the 

Interim ODMDS during 1983-1985 exceeded the site’s dispersive capacity (i.e., 285,000 cy/yr 

was “placed” vs. 214,000 cy/yr “dispersed”) resulting in the formation of a pronounced 

mound, approximately 20 feet high.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-12

Figure B-3. Approach and ODMDS bathymetry for 1983 (A) and 1985 (B).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-13

Figure B-4. Bathymetric change at Yaquina ODMDS during 1983 and 2000. Top graphic (A) is 

bathymetry change for 1983-1985, bottom (B) is bathymetry change from 1985 to 2000.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-14

Figure B-5. Approach bathymetry offshore of Yaquina Bay in 1983 (A - top) and 1999 (B - bottom)
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-15

The rapid accumulation of dredged material at the Interim site indicates that changes in 

ODMDS management likely contributed to the mounding of placed material from 1982-1985. 

Initially, the “stage was set” in 1977 when the disposal of dredged material was formally 

restricted to the boundaries of ODMDSs. During 1982-85, the extensive use of Contractoroperated split-hull hopper dredges and point dumping within the confines of the Interim

ODMDS resulted in rapid accumulation of dredged material within the site (i.e. mounding). 

In 1985, the placement of dredged material disposal within the Interim ODMDS was halted 

due to concern of potential wave shoaling associated with the dredged material mound.

By 1999, the mound within the Interim ODMDS was completely obliterated (negative contour 

values shown in the bottom graphic of Figure B-4). In fact, complete dispersal of the Interim

ODMDS mound was achieved by 1990. Note that the Interim site is aligned with the Yaquina 

Bay jetty entrance. The high dispersion rate of the Interim ODMDS appears to be due to 

localized currents generated by the Yaquina Bay jetties. The jetties act to funnel the Yaquina 

Bay estuarine (ebb tide) flow over the Interim site. Additionally, the jetties act on the littoral 

current redirecting the littoral current oceanward over the Interim site. The direction of 

sediment transport at the Interim site could not be inferred from observed bathymetry change. 

Based on the curvature of the -90 to -130 feet contours (bottom Figure B-5), it is likely that 

some of the dredged material placed within the Interim ODMDS was transported offshore to

an undetectable thickness (±1.5 feet). The jetty intensification of the estuarine and littoral 

current is assumed to be the main cause for the high rate of dredged material dispersion within 

the Interim ODMDS. This assessment infers that other sites (such as the nearshore 103

ODMDS) would be expected to have a lower dispersion rate than the Interim ODMDS.

Nearshore Section 103 ODMDS

After 1985, the nearshore Section 103 ODMDS was used for disposal of sediments dredged 

from Yaquina Bay project. Between 1986 and 2000, approximately 4.7 mcy of dredged 

sediment was placed within the nearshore 103 ODMDS, 30% of which was placed using 

Contractor-operated split-hull hopper dredges. Despite the enhanced use of a more dispersive 

(government, bottom-door) type of hopper dredge and avoidance of point dumping, 

progressive accumulation of placed dredged material occurred at the nearshore 103 ODMDS. 

Within the nearshore 103 ODMDS, bathymetric change between the baseline condition 

(1983) and 1999 is shown by comparing the contours in the top and bottom of Figure B-5.

The mounding of dredged material that has occurred within the western half of the nearshore

103 ODMDS during 1986-2000 is shown in the bottom of Figure B-4 (positive values).

During 1986-2000, the average annual volume of dredged material placed within the

nearshore 103 ODMDS was 310,000 cy/yr. The mound feature associated with 15 years 

(1986-2000) accumulation of dredged material disposal was 18-feet high and 2,000-feet wide 

x 3,500-feet long at the base with respect to the 1985 site bathymetry. As of 2000,

approximately 2.5 mcy was estimated to have been contained within the 18-foot high mound, 

or 53% of the total placed between 1986 and 2000. The other 47% of dredged material 

unaccounted was likely dispersed by waves and currents to a thickness below the survey 

detection threshold (±1.5 feet). This dispersion rate translates into 157,000 cy/yr, which 

defines the estimated dynamic capacity of the nearshore 103 ODMDS (the volume that can be 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-16

placed per year without accumulating). Recall that this apparent dispersion rate is in part due 

to the presence of the dredged material mound within the nearshore 103 ODMDS: Without 

the high relief of the dredged material mound, the dispersion rate (due to waves and currents) 

would likely be much lower.

Despite the moderate dispersiveness of the nearshore 103 ODMDS, accumulation of dredged 

material occurred during 1986-2000. This is because the volume of dredged material placed 

at the nearshore 103 ODMDS during 1986-2000 exceeded the site’s dispersive capacity (i.e. 

310,000 cy/yr “placed” vs. 157,000 cy/yr “dispersed”) resulting in the formation of a 

pronounced mound.

Based on the zero contour interval (bottom of Figure B-4), it appears that dredged material 

dispersal at the nearshore 103 ODMDS is dependent upon location within site. Dredged 

material placed in the western half of the site appears to be transported to the north and west. 

Dredged material placed in the eastern half of the site appears to be transported to the south 

and east. The jetty intensification of the estuarine current (during ebb flow) is assumed to 

have some contribution for the moderate rate of dredged material dispersion within the

nearshore 103 ODMDS. It is likely that the estuarine current is stronger in the southeastern 

part of the site.

Observed Sediment Dispersion at Yaquina ODMDS

Table B-2 summarizes the estimated annual dispersion rate and associated bathymetric change

at the Interim and nearshore 103 ODMDS, based on surveys during 1983 to 2000. Note that 

the values shown in Table B-2 arise from: (1) the presence of the dredged material mounds 

within the ODMDSs, (2) an energetic current and wave environment associated with a jettied 

estuary entrance, and (3) relatively shallow water depth. Without the high relief of a dredged 

material mound in shallow water near an estuary entrance, the dispersion rates at the Interim

and nearshore 103 ODMDSs (due to waves and currents) would have been much lower.

Table B-2. Observed dispersion potential at Yaquina ODMDS based on survey differencing.

Disposal Site Observed Vertical

Erosion Rate (ft/yr)

Estimated Net Erosion

Volume (cy/yr)

Average Water Depth

at Erosion Area (ft)

Interim ODMDS 5 214,000 60

Nearshore Section 

103 ODMDS 3 157,000 70

At its greatest extent, the volume of dredge material mound contained within the nearshore

103 ODMDS (2.5 mcy) was 3.2 times larger than the mound that had formed within the 

Interim ODMDS (780,000 cy). The 20-foot high dredged material mound that had formed 

within the Interim ODMDS during 1983-1985 was dispersed within 5 years after dredged 

material placement was discontinued at the site (1985). This was in accordance with the 

214,000 cy/yr dispersion rate observed during 1983-1985. With use of the nearshore 103

ODMDS discontinued in 2001, it was estimated that the 18-foot high 103 mound would be 

dispersed within 16 years, based on the observed dispersion rate of 157,000 cy/yr.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-17

By comparing the erosion rates of dredged material placed at the Interim and nearshore 103

ODMDSs during the active periods of site use, it was estimated that the Interim site was 36% 

more dispersive than the nearshore 103 site. The higher dispersion rate for the Interim

ODMDS is likely due to the site’s shallower water depth and the more direct exposure to tidal 

and littoral currents associated with the Yaquina jetties.

If the Interim and nearshore Section 103 sites could be relied upon for their combined full 

dispersive capacity (214,000 cy/yr + 157,000 cy/yr), those ODMDSs could hypothetically 

accept up to 370,000 cy/yr of dredged material. This would require that the sites maintain 

pronounced mounding to provide full dispersion potential: Likely, an unacceptable 

proposition to the navigation community.

It must be stressed that without the presence of the high relief mounds, the rate of dredged 

material dispersion within Yaquina Bay ODMDS would be significantly lower (less than half 

the rates shown in Table B-2). While a highly dispersive ODMDS may be desirable from the 

standpoint of continual renewing site capacity, the presence of large dredged material mounds 

capable of adversely affecting navigation is not. Without the presence of pronounced 

mounding, the historic Yaquina ODMDSs are not large enough to accommodate the 

placement of annual O&M dredged material (up to 370,000 cy/yr).

Capacity Limitations for Interim and Nearshore Section 103 ODMDS

Since the 1980s, the volume (per year) of dredged material placed within Yaquina Bay 

ODMDS has been at least twice the rate at which the dredged material was eroded out of the 

sites. The result has been rapid accumulation of dredged material within the ODMDSs and 

associated undesirable effects.

Yaquina Bay ODMDSs were intended to be moderately dispersive, but have reached capacity 

within 10 years of initial designation. ODMDS capacity is defined as that quantity of material 

that can be placed within the legally designated disposal site without extending beyond the 

site boundaries or interfering with navigation [Poindexter-Rollings 1990]. Exceedence of 

ODMDS capacity at Yaquina Bay creates a serious operational problem for the users of the 

deep-draft navigation project. Dredged material within the ODMDSs has accumulated to an 

areal and vertical extent which creates adverse sea conditions. In some cases, mounds rise 20 

feet above ambient bathymetry producing depth-limited wave conditions. Mariners report 

that the ODMDS "mounds" cause waves to steepen or break in vicinity of the ODMDSs. 

These wave conditions are hazardous to navigation at the entrance to Yaquina Bay and may 

contribute to the degradation of the north jetty.

Figures B-6 and B-7 illustrate the creation of potentially undesirable wave conditions at the

Yaquina Bay entrance due to unanticipated mounding of dredged material placed within 

ODMDSs.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-18

Figure B-6. Mounded bathymetry in 1985 (final year of Interim site use) dredging season (A - top) 

and resultant wave amplification for 12 second wave period (B - bottom).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-19

Figure B-7. Mounded bathymetry in Section 103 ODMDS in 2000 (A - top) and potential 

amplification for 12 second waves (B - bottom).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-20

Figure B-6 documents the potential change (amplification) in wave height due to the change

in bathymetry at the Interim ODMDS between 1983 and 1985. The top graphic of Figure B-6 

shows the change in bathymetry within the Interim ODMDS. The bottom graphic shows the 

corresponding estimated change in wave height, in terms of an amplification factor, due to the 

bathymetric change (mounding of dredged material) within the Interim ODMDS from 1983 to 

1985. Based results shown in Figure B-6, the dredged material mound at the Interim ODMDS 

may have increased the height of incident waves by 40% for 12-second waves as compared to 

the (baseline) 1983 bathymetry.

Figure B-7 documents the potential change (amplification) in wave height due to the change

in bathymetry at the nearshore 103 ODMDS between 1983 and 1999. The top graphic of 

Figure B-7 shows the change in bathymetry within the 103 ODMDS. The bottom graphic 

shows the corresponding estimated change in wave height, in terms of an amplification factor, 

due to the bathymetric change within the nearshore 103 ODMDS from 1983 to 2000. Based 

on results shown in Figure B-7, the dredged material mound at the nearshore 103 ODMDS 

may have increased the height of incident waves by 50% for 12 second waves as compared to 

the (baseline) 1983 bathymetry. Note that the effect of wave amplification at the Interim and

nearshore Section 103 ODMDS was estimated to extend into the Yaquina Bay entrance 

channel. The method used to estimate the above wave amplification is discussed in Section 5, 

Simulating the Fate of Dredged Material Placed at ODMDSs.

The issue of dredged material accumulating at the Interim ODMDS (and associated affects on 

wave conditions) was temporarily resolved by USACE selecting an additional ODMDS (the

nearshore Section 103 site). This was only a short-term solution to the ODMDS site capacity 

problem at Yaquina. As of 2000, an 18 ft high dredged material mound had formed within 

the nearshore 103 ODMDS and is believed to be negatively affecting the wave climate at the 

entrance to Yaquina Bay. By 2001, the nearshore 103 ODMDS was expected to have no 

remaining capacity for accepting additional dredged material. Due to mounding-related 

problems at the Interim and nearshore Section 103 ODMDSs, the local navigation community 

had voiced strong opposition to continued use of either site (for the purpose of dredged 

material disposal), whether mounds are present or not.

The North and South ODMDS are needed to avert additional mounding and related navigation 

consequences at the historic ODMDSs. Based on past experience with the Interim and 

nearshore 103 sites, that new ODMDSs must be much larger than their predecessors to 

reliably handle years of dredging disposal without creating additional mounding issues. The 

new ODMDSs must be large enough to allow distribution of dredged material over a large 

enough area so that excessive vertical accumulation of placed dredged material is averted.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-21

Section 4

SITING AND MANAGEMENT REQUIREMENTS

FOR PROPOSED ODMDS AT YAQUINA BAY

The operational performance of the historic ODMDSs at Yaquina Bay indicates that past site 

selection objectives and management practices are unreliable. If ODMDS selection methods 

are unreliable, an expensive re-designation process could still result in unacceptable future 

conditions. The key to successful ODMDS designation and long-term management is 

knowing in advance or reliably predicting the fate of dredged material placed at the ODMDS. 

This is especially true if a new ODMDS is required to have the minimum dimensions 

necessary to provide adequate site capacity.

ODMDS Requirements

The operational requirements for future site use were assessed to ensure that expanded or new 

ODMDSs fulfill a minimum life cycle of 20 years. The total volume of dredged material 

expected to be placed within Yaquina ODMDSs for the next 20 years for this assessment was 

estimated to be 6.2 mcy (or 310,000 cy/yr based on Table B-1). ODMDS site capacity should 

be sufficient to handle the expected volume of placed dredged material without negatively 

affecting the environment outside the ODMDS boundaries. Objectives for successful 

ODMDS designation and management at Yaquina Bay will:

 Provide ODMDS(s) with a combined 40-year capacity for disposal of dredged 

material originating from the Yaquina Bay navigation project.

 Avoid disposal of dredged material on rocky reefs, outcrops, or on substrate that is 

dissimilar (gravel or silt/clay) to the dredged material.

 When placing dredged material within the ODMDS, the deposition of dredge material 

(on the seabed) should be confined within the formal ODMDS boundaries.

 Locate ODMDS so that average haul distance is within the zone of siting feasibility 

(ZSF).1The ZSF for hopper dredges is a 4.5 nautical mile radius from RM 0.

 Avoid navigation impacts at the new ODMDS due to excessive accumulation of 

placed dredged material over the life cycle of the proposed ODMDSs. Designate new 

ODMDSs with large areal configuration and reserve capacity. If needed, manage subunits of the new ODMDS on an annual rotational basis to minimize cumulative 

environmental impacts within the ODMDS.

 If large displacement split-hull hopper dredges are used at Yaquina Bay (i.e., the 

Newport @ 3,000 cy/load vs. the Westport @ 1,000 cy/load), attention should be 

focused on ensuring dispersal of dredged material during the disposal process. Large 

displacement dredges can produce rapid mounding of placed dredged material.

 

1 Zone of feasibility is defined by the capacity of the available dredging plant, average annual dredging quantity, 

and limited dredging time period. 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-22

 Enhance the distribution of dredged material placed at new ODMDSs by evenly 

distributing dredged material on the seabed. Dredged material mound height must be 

managed to prevent excessive amplification of waves due to shoaling. The new 

ODMDS could be divided into several sub-areas and each sub-area would be used 

until the height of accumulated dredged material reaches the maximum vertical limit.

 Ensure that new ODMDS conform to the four general and eleven specific criteria for 

the selection of ocean disposal sites (40 CFR 228.5), as specified in the main report.

Where the need exists and it was practical and possible, consideration was given to locating 

new ODMDSs in nearshore waters 60 feet deep or less, to facilitate introduction of dredged 

material into the littoral zone. Consideration for locating new ODMDSs nearshore was 

warranted, since the majority of sediment dredged from the Yaquina entrance channel is 

marine sand and originates from the adjacent littoral environment. However, due to the 

presence of rock outcrops (reefs) parallel to shore in water depth of 45-50 feet, this initiative 

was precluded from additional consideration.

ODMDS Capacity – General Considerations

The total site capacity for a given ODMDS consists of two components – static site capacity 

and dynamic site capacity.

Total ODMDS site capacity = dynamic site capacity + static site capacity

Dynamic ODMDS capacity is defined as the volume of placed dredged material which is 

transported out of an ODMDS, by waves and currents. The shallower an ODMDS location, 

the greater the potential for dispersing placed dredged sediments and the higher its dynamic 

capacity. Generally, the deeper an ODMDS location, the lower its dynamic capacity. For a 

given water depth, dynamic capacity may be higher for areas closer to an estuary inlet (such 

as the Interim ODMDS near the Yaquina entrance), than in areas further offshore.

Dynamic capacity is specified in terms of a volume rate (cy/year) at which sediment leaves a 

given site. Dynamic capacity at a given site can change with time based on changes in site 

bathymetry (mounding increases dynamic capacity) or changes in waves/currents (winter 

storms disperse more sediment than summer calm).

Static ODMDS capacity is defined as the limiting volume of dredged material which can be 

placed within a given area before the resultant mound feature begins to have a negative 

impact on either navigation or the ambient environment. Navigation impacts associated with 

static capacity include reducing vessel keel clearance to an unsafe margin or degrading the sea 

state by causing waves to steepen, amplify in height, or break. Environmental impacts 

associated with static capacity, include exceeding a pre-determined burial depth over the site’s 

pre-disposal substrate or promoting down-slope distribution of placed material onto areas 

beyond the designated ODMDS boundaries. 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-23

For the case of Yaquina ODMDS, static site capacity is governed by the need to avoid 

navigation impacts. This focuses on wave shoaling constraints: Wave amplification effects on 

the approaches to the navigation entrance, jetties, and channel. To meet wave amplification 

constraints, a given ODMDS mound must not significantly amplify incident waves with 

respect to a baseline (pre-disposal) bathymetric condition. The wave amplification criteria are

generally more restrictive than keel clearance. Generally, the shallower an ODMDS location, 

the lower its static capacity and vice versa.

ODMDS Selection – Specific Considerations

Dredging and dredged material disposal practices at Yaquina Bay continually balance the 

competing interests of providing a safe navigation channel, minimizing adverse impacts to the 

environment, optimizing dredging and disposal efficiency, and using dredged material as a 

littoral resource (when it is practical and when required). The over-riding considerations 

governing the selection of a new ODMDS include the avoidance of mound-induced wave 

shoaling, avoidance of impacts on sensitive benthic areas (rock “reefs”), and locating the new 

ODMDS within the ZSF. The new ODMDS should be located away from the Interim and 

nearshore 103 sites, due to the mounding issues associated with the historic sites and attendant 

wave shoaling problems.

Management of new Yaquina ODMDS will avoid the amplification of incoming waves, due 

to the formation of large dredged material mounds. At a minimum, new Yaquina ODMDSs 

should be large enough to permit the distribution of 20- to 50-years of dredged material 

disposal (facilitate the distribution of 6-15 mcy of dredged material on the seabed) without 

allowing the accumulated material to exceed a height which would cause significant wave 

amplification. At any given location within a proposed ODMDS, accumulation of dredged 

material will be controlled so that incident waves are not significantly amplified as compared 

to the baseline condition, due to dredged material mounding. The baseline condition for new 

ODMDSs refers to the bathymetry and associated wave environment BEFORE the ODMDS 

becomes operational (is used).

The placement strategy has a large influence on the overall impact of dredged material 

disposal in an ODMDS. Therefore, the size/location of the proposed ODMDS(s) must 

accommodate various potential site management scenarios and placement strategies for the 

purpose of minimizing mounding of placed dredged material and minimizing impacts to the 

benthic environment (infauna/epifauna). Such management scenarios may be mutually 

exclusive in approach. Two examples are described below:

1. The annual operational footprint (area affected by disposal) would be minimized. This 

placement method would concentrate dredged material within a small footprint, on an annual 

basis, while avoiding the formation of excessively high dredged material mounds. An ODMDS 

would be divided into several sub-areas; each sub-area would be used on an annual rotational 

basis. One sub-area would be used in any given disposal year, after which the cell would be left 

“fallow” for a number of years until it would again be used for dredged material disposal. This 

would allow benthic recovery within each cell following disposal
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-24

2. The annual operational footprint (seabed area affected by disposal) would be maximized. This 

placement method would distribute dredged material over a wide area annually (perhaps an entire 

ODMDS), minimize vertical accumulation, and promote immediate benthic recovery within the 

area affected by dredge material disposal. If two new ODMDS were available, each ODMDS 

could be used alternatively, on an annual basis. This would allow the area of an entire ODMDS to 

be left “fallow” for a year, similar to management scenario 1 above but much less vertical 

accumulation of dredged material in any given year.

To ensure that the new Yaquina ODMDS provides adequate capacity, the size of the proposed 

site(s) was based solely upon static capacity criteria. In other words, the dynamic capacity for 

proposed new ODMDS(s) was assumed to be zero. Although the proposed site(s) will exhibit 

some degree of dynamic capacity, the sites were assumed to be non-dispersive as a 

conservative measure for ensuring sufficient life-cycle capacity. Results of static capacity 

estimates are presented in Section 6, FATE Modeling and Impact Assessment for Proposed 

ODMDS Locations. Additionally, the proposed ODMDSs should facilitate redundant site 

capacity. For example, if at sometime in the future ocean disposal of dredged material is 

restricted within one ODMDSs, say a site located north of the Yaquina Bay entrance, another 

ODMDS located south of the entrance would have sufficient capacity to handle all dredged 

material disposal and vice-versa. For this reason, two new ODMDSs were proposed: a North 

ODMDS and a South ODMDS. Each new site would have capacity for more than 20 years of 

dredged material disposal. Refer to Figure B-14 for location and layout of the proposed North

and South ODMDS.

The management of the proposed ODMDS may change with time, depending on monitoring 

results, changes in resources agency criteria, or other unforeseen conditions. For example, at 

sometime in the future, it may be required that dredged material be dispersed to minimize 

vertical accumulation on the seabed, per disposal season. This would maximize the area over 

which dredged material would be placed. Therefore, proposed ODMDSs must be “sized” to 

permit adaptive management practices; hence, the large areal configuration and redundancy in 

capacity.

The objective of this appendix was to determine the size for each new ODMDS sufficient to 

handle 6.2 mcy of dredged sediment (placed over a period of 20 years) and to locate the new 

ODMDSs in terms of the required size vs. other competing criteria. Consideration of 

proposed ODMDSs in terms of size and location is described in Sections 5 and 6 of this 

appendix. Development of a management plan for proposed ODMDSs, to ensure that new 

sites meet operational requirements, is described in Appendix F, Site Management and

Monitoring Plan.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-25

Littoral Considerations

Although hopper dredge access to the littoral zone may be attained by transiting 4-5 miles 

north or south of the Yaquina Bay entrance (the height of the north or south reef may diminish 

at that point), the long transit distance would render hopper dredge disposal in the littoral zone 

uneconomical. Other potential biological and operational restrictions also preclude 

designation of a new ODMDS within the littoral zone (nearshore waters less than 60 feet 

deep).

The proposed ODMDS(s) will be located offshore of the reefs (active littoral zone) and not 

facilitate re-introduction of dredged material into the littoral zone. Dredged material placed 

within the proposed North or South ODMDS will in all likelihood be removed from the 

littoral zone for an extended period of time (10-20 years). Other statutory authorities may be 

invoked to permit USACE to place dredged material in the nearshore (littoral zone), but will 

require local-sponsorship to address cost-sharing arrangements and permitting issues.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-26

Section 5

SIMULATING THE FATE OF DREDGED MATERIAL 

PLACED AT ODMDS

Coupled Strategy for Numerical Modeling and ODMDS Management

The key to successful ODMDS designation and management is knowing in advance or 

reliably predicting the fate of dredged material placed at the ODMDS. The Ocean Dumping 

Act require that field-verified, state of the art procedures be used for the assessment of 

possible physical impacts due to the operation of proposed ODMDSs

During the USACE Dredging Research Program (DRP), several sediment FATE numerical 

models were developed or enhanced in order to improve the reliability of ODMDS 

management. These FATE models incorporate state-of-the-art techniques for simulating the 

behavior of dredged material placed in open water, and account for a variety of disposal 

operations and environmental conditions. Results from FATE model application at Yaquina 

Bay were used to guide site selection for the North and South ODMDS and facilitate lifecycle management of the proposed site in terms of operational requirements. Site physical 

impact assessments focused on:

Wave conditions - The use of ODMDSs would not significantly increase (worsen) the 

wave environment at the ODMDS location or adjacent areas, with respect to the site’s 

baseline condition.

Impacts to biologic community - The use of ODMDSs would minimize potential 

biological impacts (refer to Appendix A, Living Resources). Proposed sites are located to 

avoid placement of dredged material on a limited habitat or seabed substrate (rock reef) 

that is significantly different from the sediment dredged at the navigation channel. If 

needed, proposed ODMDSs may be managed to minimize areas of impact or degradation. 

Transport of dredged material into the littoral zone - It is desirable for ODMDSs to 

promote the littoral re-introduction of placed dredged material along the coast. Shallower 

portions of ODMDSs can be located in water depths of 30-60 feet to facilitate dredge 

material being transported by waves and currents to the littoral zone. For the Yaquina 

ODMDS North and South sites, the presence of rocky reefs and substrate and operational 

constraints preclude designation of a new ODMDS within the littoral zone.

FATE model results that were used to assess the long-term suitability of the proposed 

Yaquina Bay ODMDS are described in Section 6, FATE Modeling Results and Impact 

Assessment for Proposed ODMDS Locations. The following paragraphs describe FATE 

model components and the strategy for using the FATE models in this ODMDS assessment.

Fate of Dredged Sediment Placed in Open Water

The physical processes affecting dredged material placed in open water include gravity, 

surface waves, and currents. At the point of release from the disposal vessel, dredged 

material falls through the water column, convects/diffuses laterally, and eventually comes to 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-27

rest on the seafloor. This scenario characterizes the short-term fate of dredged material 

placed in open water. Figure B-11a illustrates dredged material behavior, when placed in

open water by a hopper dredge or split-hull barge. During the disposal operation, dredged 

material can be spread out on the seabed to varying degrees, depending upon the speed of the 

disposal vessel, water depth, water column current, ambient bathymetry, and other variables.

The timeframe for processes affecting the short-term fate of placed dredged material is during 

and immediately after the disposal operation (minutes to hours).

After dredged material has come to rest on the seabed, it can be eroded by waves and currents. 

If the dredged material is cohesive, it can experience self-consolidation due to gravity. If 

many loads of dredged material are placed one on top of another such that a steep aggregate 

mound develops on ambient bathymetry, the mound will avalanche and material will be 

transported downslope. The combination of these processes defines the long-term fate of 

dredged material placed in open water. The timeframe for processes affecting the long-term 

fate of placed dredged material is after the disposal operation (days to years).

Predictive Methods: Applicable Numerical Models

STFATE, LTFATE, and MDFATE are numerical models which incorporate state-of-the-art 

techniques for simulating short- and long-term bathymetric change due to dredging disposal 

operations and environmental processes. The models were developed at USACE, Waterways 

Experiment Station (WES) and are briefly described below.

Short-Term FATE: Predicts the distribution of dredged material thru the water column and 

bathymetric distribution of dredged material on the seabed after it has passed through the water 

column, on an individual "dump" (disposal vessel load) basis. The timeframe of interest for the 

STFATE model is on the scale of minutes to hours, during dredged material disposal. The 

model accounts for various disposal vessel, water column, and material parameters. In this 

investigation, STFATE was used in a 2-dimension capacity.

Long-Term FATE: Simulates bathymetric change due to self-weight consolidation and 

sediment transport arising from the interaction of waves and currents. The timeframe of interest 

for the LTFATE model is from days to years, after dredged material disposal. The model 

accounts for waves, currents, tidal, and material parameters. LTFATE is a 2-dimensional 

model.

Multiple-Dump FATE: Predicts the change in bathymetry at an ODMDS resulting from a 

series of "dumps" and simulates long-term change of the resultant bathymetry. MDFATE uses 

components of STFATE and LTFATE to simulate a disposal operation, which could extend over 

a year and consist of hundreds of dumps. The model accounts for overall disposal operation and 

long-term environmental processes. The timeframe of interest for the MDFATE model is from 

minutes to years, and simulates processes during and after dredged material disposal. MDFATE 

is a 2-dimensional model and uses the same parameters as used in STFATE and LTFATE.

Predictions of dredged sediment behavior, when it is placed into the open waters of the ocean, 

can only be as good as the poorest estimate for the forcing environment (i.e., waves, currents, 

and other processes). To address this need for input data, tide and wave prediction techniques 

were developed by WES to provide realistic wave and current data to the FATE models.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-28

The computer programs HPDPRE and HPDSIM were used to simulate a time series 

representation for wave height, period, and direction [Borgman and Scheffner 1991]. The 

ADCIRC model was used to simulate equilibrium Newtonian tide in terms of ocean surface 

elevations and current [Hench et al. 1994].

The numerical model RCPWAVE [Ebersol et al. 1986] was used in this investigation to 

assess the effect of bathymetry change (dredged material mounds) upon the wave 

environment at the historic and proposed Yaquina Bay ODMDSs. RCPWAVE is a 2-

dimensional numerical model that simulates the transformation of wind-generated waves, as 

the waves propagate into shallow water and eventually break. The model accounts for the 

two dimensional behavior of wind-generated waves (shoaling and refraction) as the waves are 

affected by an irregular (mild-sloping) seabed. The model does not include the effects of 

current, wind, or wave-wave interaction upon the wave transformation process. Therefore, 

the results presented in this wave analysis consider ONLY the effect of waves interacting with 

bathymetry (the seabed). It has been observed that the RCPWAVE model overestimates the 

amplification of waves due to shoaling (the model is conservative). Since USACE would 

rather "err" by overestimating the potential wave amplification (rather than underestimating), 

a conservative estimator of potential wave amplification is desirable. If we err, it would be 

such that wave amplification would be predicted to occur, when in fact, waves would not 

actually be affected by dredged material accumulation (mounding).

The above models have been calibrated, verified, and successfully applied at several locations 

within and outside of the Portland District [USACE 1999 and 1995, Clausner et al. 1998 (a 

and b), Moritz and Randall 1995, Johnson 1978, Johnson and Fong 1995, Thevenot and 

Johnson 1994, Scheffner 1992, EPA 1978, and Schubel et al. 1978]. Collectively, the above 

numerical models were used to resolve future ODMDS site management issues related to 

physical aspects.

ODMDS Modeling Strategy

As a first step toward modeling sediment fate at ODMDSs, existing oceanographic 

information was consolidated for use in the modeling effort. The year 1996 was chosen as the 

“base year” for simulating the behavior of dredged material mounds at candidate Yaquina Bay 

ODMDSs. This was based on the availability of the most recent bathymetric survey for the 

Yaquina Bay approaches and ODMDSs.

For modeling purposes, the annual dredging and disposal season at Yaquina Bay was broken 

into two discrete time periods. Dredging disposal at the Yaquina Bay ODMDS normally 

begins during June and continues through the summer until July or August. After August, the 

ODMDSs are generally not used and are affected by the energetic wave/current environment 

until the following May when dredged disposal again commences. The schematic shown 

below describes how the MDFATE model was applied to simulate dredged material disposal 

at the proposed Yaquina Bay ODMDS.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-29

 Modeling of the Annual Dredged Material Disposal Cycle at Yaquina ODMDS

 DUMPING Simulate Remaining Part of 

 Simulate Disposal Season Year: Long-term FATE Only

 (1) model a series of 1 week dump episodes model bathymetric change

 for short-term fate processes due to sediment transport

 (2) follow-on with long-term FATE

 calculations for 1 week after each

 dump episode

 June July May

During a given ODMDS year, short-term fate processes (dredged material disposal) were 

simulated for a 2-month period (June-July). Long-term fate processes were then simulated for 

a 10-month period, until the following year when the annual cycle was repeated.

Short-term FATE Model

The STFATE model was used to estimate the geometry of dredged material deposited on the 

seafloor, on an individual dump basis. These results determined whether flat or peaked 

"mounds" are produced from dredged material disposal, on an individual dump basis. The 

above estimates were be performed for the two dredging vessels which have been most used 

at Yaquina Bay. Results are described in Section 6 of this exhibit. STFATE results were 

used to optimize ODMDS capacity based on the need to distribute dredged material within the 

site in terms of thickness, deposition rate, and areal extent per load placed.

Long-term FATE Model

The LTFATE and MDFATE models were used to estimate the capacity of proposed 

ODMDSs for a 20-year life cycle. The definition of ODMDS site capacity is discussed in 

Section 4 of this appendix. The MDFATE model was used to simulate the long-term 

accumulation of dredged material placed at various locations within proposed ODMDSs. 

MDFATE results were used to determine the ODMDS dimensions required to “acceptably” 

operate a site over the life cycle. MDFATE model results were also used to ensure that lifecycle management of the proposed ODMDS would meet operational requirements (based on 

the need to distribute dredged material within a given site, in terms of verifying accumulation 

thickness and areal extent per year). Results are described in Section 6, FATE Modeling 

Results and Impact Assessment for Proposed ODMDS Locations.

Future management of Yaquina ODMDS will prevent the amplification (shoaling) of incident 

waves due to the formation of new dredged material mounds by limiting the size (height and 

plan-form) of new dredged material mounds. Dredged material mound accumulation will be 

restricted to prevent wave amplification. The RCPWAVE model was used to assess waveshoaling characteristics of various dredged material mound sizes vs. water depth and wave 

parameters. The wave amplification criteria were used for purposes of minimizing 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-30

undesirable wave conditions due to excessive accumulation of dredged material mounds. 

Results are described in Section 6, FATE Modeling Results and Impact Assessment for the 

Proposed ODMDS and in Appendix F, Site Management and Monitoring Plan.

Calculating Bottom Sediment Transport Potential

The calculation of closure depths [Hallemeier 1981] gives a qualitative indication of the depth 

limit for sediment transport rate due to shoaling waves for average and storm wave 

conditions. Sediment transport closure depths give a general indication for the extent (water 

depth) of sediment transport, but do not define how much sediment transport will occur.

Hallermeier Sediment Transport Limits

The nearshore region of the seabed can be divided into different transport zones based upon 

relative rates of littoral sediment transport. Two water depth zonal limits, dand dsare 

typically used to describe the transportability of sediment at the seabed due to shoaling waves 

[Hallemeier 1981]. These depth values are commonly referred to as closure depths.

(1) The water depth corresponding to d gives a seaward limit for sediment transport 

associated with highly turbulent surf-zone (or littoral) effects. This depth is a function of the 

annual mean significant wave height (H1/3) and defines the littoral zone for which all 

significant alongshore/cross-shore transport occurs. Algebraically, the littoral closure depth 

(d) for typical nearshore sand is defined as:

d = 2H1/3 + 11σ where H1/3 = average annual significant wave height applicable at d

 σh = annual standard deviation of H1/3

The H1/3 used for the dcalculation for Yaquina Bay was determined by transforming the 

deepwater H1/3 (specified by WIS-II station 46, H1/3 = 9.0 ft and σh = 4.2 feet) to a water 

depth of 60 feet. The resultant annualized nearshore H1/3 = 8.8 feet with σh = 3.8 feet. Using 

the nearshore wave criteria, d was calculated to be 59 feet (say 60 feet).

(2) The water depth corresponding to ds gives the extreme seaward (outer) limit of waveinduced sediment motion due to extreme waves (storm effects) and is a function of annual 

mean significant wave height, the annual mean significant wave period, and median sediment 

grain size. The nearshore zone located seaward of dand landward of ds(between the two 

depths) defines the shoal zone. The shoal zone between dand dsis a “gray” area where 

typical waves have neither a strong nor a negligible effect on the bottom sediment transport 

during a typical year of wave action [Hallemeier 1981].
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-31

ds = (H1/3 - 0.3σ)Ts(g/5000D50)

1/2 where H1/3 = 9 feet, estimated average annual significant

wave height applicable at ds 

 Ts = wave period (associated with H1/3) = 11 sec

 g = 32.2 ft/sec2

D50 = median sediment grain size = 0.15-0.25 mm =

 0.000492 - 0.00082 feet

The median grain size for dredged material to be placed at Yaquina ODMDSs was estimated 

to be 0.20 mm (Section 8, Measured Oceanographic Data). The median grain size for native 

in situ material at candidate areas for new ODMDSs was estimated to be 0.15 mm. The 

corresponding values for closure depths were calculated to be:

d = seaward limit of active littoral zone at (all sediments) = -60 feet MSL

ds = extreme seaward limit for wave-induced sediment motion (0.15 mm) = -250 feet MSL

ds = extreme seaward limit for wave-induced sediment motion (0.25 mm) = -200 feet MSL

In terms of closure depth, the Interim and 103 ODMDSs should experience littoral sediment 

transport at locations shallower than d = -60 feet MSL (about -57 feet MLLW). This in fact 

has been the case (Section 3 of this appendix). Using closure depths as general criteria for 

selecting an ODMDS is illustrated as follows. If a new Yaquina ODMDS was needed to 

prevent any long-term transport of placed dredged material, then the non-dispersive site 

should be located in water depths deeper than -200 feet MLLW. These criteria would provide 

for a completely non-dispersive ODMDS, if placed dredged material had a median grain size 

of 0.25 mm. Conversely, if a dispersive ODMDS was required to promote rapid transport of 

placed dredged material back into the littoral environment, then the proposed site should be 

located in water depths equal to or shallower than -55 feet MLLW.

If new proposed ODMDSs were to be located in average water depth of 135 feet, dredged 

sand placed at the sites would be dispersed slowly during infrequent storm events. This 

would be the case for the proposed North and South ODMDSs.

Modified Ackers-White Sediment Transport Estimates

To obtain a more detailed description of sediment behavior, several relationships have been 

developed to quantitatively estimate sediment transport rates [Ackers and White 1973]. The 

LTFATE model uses the “modified” Ackers and White [1973] equations as the basis for the 

non-cohesive (total load) sediment transport model. The equations are applicable for 

uniformly graded non-cohesive sediment in the range of 0.06-0.4 mm. The Ackers-White 

equations are based on depth-averaged current. Because many ODMDSs are located in 

relatively shallow water (less than 200 feet), a modification of the Ackers-White equations 

was made to reflect an increase in the transport rate when ambient currents are accompanied 

by surface waves [Scheffner et al 1995]. The net direction of sediment transport is governed 

by current direction only; wave direction has no effect on sediment transport direction.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-32

Several sensitivity tests were conducted to demonstrate the sensitivity of the sediment 

transport rate with respect to wave height, current speed, water depth, and sediment grain size. 

Results of the of the Ackers-White sensitivity tests are shown in Figure B-8 (six graphs).

Wave height and current are the governing parameters for sediment transport (upper left and 

bottom two graphs). If wave height is increased from 7 feet to 20 feet in 48 feet of water 

depth, sediment transport potential increases by a factor of 10 for a current of 1.5 ft/sec (such 

would be the case of the eastern part of the Interim site during a storm). For water depth less 

than 125 feet, depth is equally important as wave height in controlling the magnitude of 

sediment transport (upper right and bottom two graphs), assuming other parameters remain 

constant. For a water depth of 48 feet (high point of Interim ODMDS mound in 1985) with a 

20-foot wave and current of 1.5 ft/sec, sediment transport rate is estimated to be about 7 times 

higher than at 125-foot depth (eastern part of the proposed North or South ODMDSs, see 

Section 6). Note that regardless of the wave height or water depth, if the depth-averaged 

current is lower than a threshold value of 0.5 ft/sec, there is no net sediment transport 

predicted by Ackers-White formulation.

Sediment grain size has some effect upon sediment mobility (middle left graph Figure B-8), 

but only at high values of depth-averaged current. The variability in wave period (middle left 

graph Figure B-8) does not appear to have an appreciable effect upon sediment transport rates.

Limitations of Simple Sediment Transport Estimates

Even though the modified Ackers-White equations may provide a realistic estimate of 

sediment transport potential, the result is only 1-dimensional. The actual (2-dimensional) 

response of dredged material placed at an ODMDS would remain uncertain, until hindsight 

from the actual disposal operation is gained through post-disposal condition surveys.

Reliance on 1-dimensional estimates for characterizing sediment transport can be a costly 

proposition for disposal site selection, if selection does not provide a disposal site with 

intended dispersive properties or sufficient static capacity. The FATE models use the AckersWhite and other equations to estimate physical processes affecting 2-dimensional sediment 

transport on the seabed. Application of the FATE models provides the needed predictive 

means to reliably select a new site or expand the historic ODMDS. The FATE models can 

also be used to optimize dredged material management at an ODMDS.

It must be noted that the FATE models are only tools that provide estimates of sediment 

behavior and related processes. The accuracy of FATE model-generated results is highly 

dependent upon the parameters input to the models. Controlling parameters are physical 

characteristics of the dredged material, disposal operation sequencing, and forcing 

environment (waves and currents). As discussed in Sections 7 and 8, much effort was 

expended to develop reliable input for FATE modeling. Based on previous applications of 

FATE models and data development outlined above, it is assumed that FATE model results 

obtained for the Yaquina ODMDSs will meet an accuracy standard of 80% (the difference 

between predicted and actual conditions is expected to be within  20%).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-33

Figure B-8. Results from Ackers-White sensitivity test for sediment transport potential.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-34

FATE Model Data Requirements

Before reliable modeling of dredged material fate could be conducted, environmental 

processes which govern sediment transport at Yaquina Bay ODMDSs had to be defined. The 

following prioritization of various environmental parameters is presented in terms of the 

requirement for FATE model result accuracy:

First Priority = Depth-averaged current magnitude and direction, resolve into seasonal regimes.

Second Priority = Wave height time series, year-long data record with 3-hour record interval.

Third Priority = Characteristic physical properties for dredged sediment and ambient bottom

 sediments at ODMDSs.

Fourth Priority = Wave period time series, year-long data record with 3-hour record interval.

Section 7, Oceanographic Processes provides a general description of regional oceanographic 

process offshore of Yaquina Bay. Section 8, Measured Oceanographic Data quantitatively 

describes site-specific parameters relevant to FATE modeling.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-35

Section 6

FATE MODELING RESULTS AND IMPACT ASSESSMENT

FOR PROPOSED ODMDS LOCATIONS

This section describes procedures that were used to define ODMDS site selection criteria 

based on physical processes relevant to Yaquina Bay offshore. The physical process criteria 

were used, in conjunction with other considerations, to evaluate the proposed ODMDS 

location. Proposed ODMDSs were assessed for life-cycle performance, in terms of physical 

processes, using the fate models. Long-term management for proposed ODMDSs is 

discussed in Appendix F, Site Management and Monitoring Plan.

Vertical Limit for Dredged Material Mound Height

As stated in Section 4, Siting and Management Requirements for New ODMDS at Yaquina 

Bay, the areal size of new ODMDS was determined based upon the site requirement to 

provide static capacity for 6.2 mcy of dredged material over a 20-year life cycle without 

significantly affecting baseline wave conditions. Management of the North and South 

Yaquina ODMDSs will avoid the amplification of incident waves (sea and swell), due to the 

formation of large dredged material mounds. The management of the North site for the past 

10 years has achieved this goal. At any given location within a proposed ODMDS, 

accumulation of dredged material will be controlled so that incident waves are not 

significantly amplified over the baseline (pre-disposal) condition. Biological considerations 

may impose additional controls to limit annual accumulation rates.

The RCPWAVE model was used to determine the maximum limiting height of a (dredged 

material) mound feature for various conditions. Figure B-9 summarizes the RCPWAVE 

results from estimating limiting mound height for several mound geometries in water depths 

from 40 to 200 feet. The lower bold solid line applies to a large mound feature (2,000-feet 

wide x 4,000-feet long with 1.2 or 1V:50H side slopes) and was used to determine to 

maximum mound height applicable for the North and South ODMDS.

Specification of the (baseline condition) water depth of the proposed ODMDS determines the 

limiting mound height, based on Figure B-9. Once the limiting mound height is determined,

the required areal extent of the ODMDS can be calculated from geometric constraints based 

on the desired volume of static capacity. Refer to Section 4 of this exhibit for the definition of 

static capacity. All that is needed to begin the ODMDS size calculation is the water depth at 

the candidate ODMDS location. An example is shown below.

Given:

Water depth at a hypothetical ODMDS = D = 120 ft

Desired static capacity volume = Vs = 6.2 mcy = 167.4 million cubic feet

Side slope for accumulated dredged material = theta = 1.2  =1V:50H = 0.020

Required:

Maximum limiting mound height = Hm 

Areal Dimensions for ODMDS (assume square site boundaries, length=width) = Ls = Ws.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-36

Solution:

Hm = 14 ft (obtained from Figure B-9, lower curve using 120 feet water depth)

Vs = 1/6*Hm*(A +4B+C), where A = (Ls-2*Hm/theta)*(Ws-2*Hm/theta)

 = volume of a prismatoid B = [(Ls-2*Hm/theta) + Ls]*[(Ws-2*Hm/theta) + Ws]/4

 C = Ls*Ws

  0.95 * Volume of a solid trapezoid 

 Volume of a solid trapezoid = 1⁄2*Hm[Ws+( Ws-2*Hm/theta)]*Ls

Vs  0.95* {1⁄2*Hm[Ws+( Ws-2*Hm/theta)]*Ls}, since Ws = Ls

Vs  0.95* {Ls2 *Hm – Hm2*Ls/theta}, at this point Vs can be solved for, or if Vs is known then Ls can

 be determined by 0 = Ls 2– Hm*Ls/theta – Vs/(0.95*Hm), by solving

 for Ls in terms of the quadratic solution for the root. 

for this example, Ls = {14/0.02 + [(14/0.02) 2 + 4*167,400,000/(0.95*14)] 1/2 }/2 = 3,900 ft

The length of each side of ODMDS (assuming a square ODMDS layout), = Ls = 3,900 ft 

Figure B-9. RCPWAVE estimates for maximum limiting mound height.

Note that if Figure B-9 were applied to the designation of an “appropriately sized” Section

103 ODMDS (located in average water depth 70 feet), the maximum mound height should 

have been limited to 5 feet. This would have required that the length of each side (for a 

square site) of the site to be at least 6,100 feet, resulting in an ODMDS 4 times larger than the 

nearshore Section 103 ODMDS.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-37

General Location for North and South ODMDS and Required Size

Locating the North and South ODMDS was accomplished by a method of default. As stated 

in Section 5, the North and South ODMDS could not be located shoreward of the “reefs.” 

Nor should the new site be located over any exposed bottom rock areas offshore of the north 

and south “reefs.” Finally, it was desirable for the new ODMDS not to be located near the 

historic ODMDSs or near the “mounded” bathymetry located 1 mile due west of the entrance 

channel. The above restrictions lead to the new ODMDS being located either northwest or 

southwest of the nearshore 103 site and west of the exposed rock area shown in Figure B-2. 

Additionally, it was determined that the boundary of a new ODMDS should be located at least 

1,000 feet away from any exposed bottom rock area to avoid habitat impacts. This set the 

location of the landward boundary of the new ODMDS. The width (east-west) and length 

(north-south) dimensions of the new ODMDS were set such that the middle of the ODMDS 

would be located as close as possible to the entrance channel. These restrictions confined the 

general location of the proposed ODMDS to an area either north or south of the bathymetric 

“bulge” located 0.75 miles due west of the Interim ODMDS, having sandy-bottom, and a 

minimum water depth of about 120 feet.

Based on a water depth of 120 feet and the limiting mound height criteria in Figure B-9, the 

maximum vertical accumulation of dredged material placed in the new ODMDS was

determined to be 14 feet (see above calculation for Hm). The data used in the example static 

capacity calculation (water depth and required static capacity, shown above) was also applied 

to determine the minimum area needed for the proposed ODMDS. The length per side 

(assuming a square site) must be at least 3,900 feet or have an area of 350 acres.

To accommodate for the variable operational aspects of dredged material disposal and other 

life-cycle uncertainties, the new ODMDS should be “sized” to provide more than the 

minimum capacity requirement. The following FATE assessments address these 

considerations.

Short-Term Fate Modeling: Bathymetry Impact Assessment

When dredged material is released in open water by a disposal vessel, the material falls 

through the water column, mixes with ambient water, and forms a plume. This process is 

called convective descent. When the diluted dredged material plume encounters the seabed, 

the plume spreads radially along the seabed. This process is called dynamic collapse. After 

the plume has expended all of its momentum along the seabed, the dredged material slowly 

settles under the influences of gravity and the ambient current environment. This process is 

called passive transport and diffusion. Figure B-9a illustrates dredged material behavior,

when placed in open water by a hopper dredge.

Bathymetric impacts were defined in terms of the short-term behavior of dredged material on 

a per dump basis; as dredged material is released from the disposal vessel and accumulates on 

the seabed. The objectives of the short-term fate assessment were to:
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-38

Figure 9a. (Top) Four phases of dredged material behavior during placement in open water. 

(Bottom) Computational phases of the short-term fate model.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-39

Estimate the disposal footprint geometry (per dump) in terms of thickness and 

areal extent after the placed material comes to rest on the seabed. This data 

describes the coverage of dredged material on the seabed data and provides insight 

to the potential bathymetric impacts in the immediate vicinity of disposal.

Determine the distance that placed dredged material is displaced away from 

the point of release during disposal. This parameter describes the size of the 

ODMDS “buffer” zone that is located along the site’s perimeter. The buffer zone 

inscribes the outer area of the ODMDS and is intended to prevent transport of 

dredged material (by currents or bottom surge motion) beyond the formal site 

boundary during placement operations.

Short-term fate simulations were conducted for the disposal of dredged material from two 

types of hopper dredges: (1) split-hull hopper dredge Westport, and (2) a multiple bottom 

door hopper dredge Yaquina. Since 1982, about half of all dredging disposal at Yaquina Bay 

ODMDSs has been performed by the Yaquina. The Westport has performed about 30% of the 

Yaquina Bay dredging disposal. Operating parameters for each dredge that has recently been 

used at Yaquina Bay are shown below.

DREDGE

OVERALL DIMENSIONS WORKING

CAPACITY

average (cy)

VESSEL SPEED

during disposal

(knots)

DISPOSAL

vessel type

(doors/size of each)

DURATION

placement of

each load

(minutes)

Length

(ft)

Beam

(ft)

Draft (ft)

loaded/empty

Westport 270 50 14/8 1,000 2 to 6 split hull/160 x 25 ft 2 to 6

Padre Island 281 52 19/8 2,600 2 to 6 split hull/190 x 30 ft 4 to 6

Atchafalya 197 41 15/6 1,300 2 to 6 split hull/120 x 20 ft 4 to 6

Yaquina 200 58 14/10 1,000 2 to 8 bottom doors (6)/

4 x 4 ft 2 to 6

For simulation purposes, the vessel speed during disposal was assumed to be 2 knots (3.5 

ft/sec) for both dredges. The duration of placement for an individual load of dredged material 

was assumed to be 3 minutes for the Westport and the Yaquina. Short-term fate simulations 

were conducted for disposal water depths ranging from 40 to 200 ft. Three types of current 

conditions were also tested: No current, a 1 ft/sec current, and a 4 ft/sec current. Currents 

were modeled as being oriented 45° into the heading of the disposal vessel. The current 

regime at Yaquina ODMDSs ranges from 0.5 ft/sec to 3 ft/sec. The characteristics of 

sediment dredged from the Yaquina Bay project and placed at ODMDSs are described in 

Section 8, Measured Oceanographic Data.

STFATE Results

As dredged material is released from a disposal vessel and falls through the water column, the 

material mixes with ambient environment and forms a plume. The dredged material plume 

slowly settles to the seabed under the influences of gravity and the ambient current 

environment. The time required for dredged material to fall to the seabed and completely 

settle out of suspension is largely dependent upon the water column environment and the 

material type placed at a given disposal site. At Yaquina Bay ODMDSs, approximately 98% 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-40

of dredged material placed is composed of sand and 2% is composed of fines (silt), on a per 

load basis. Based on STFATE results for typical conditions, the time required for sand to 

completely settle out of the water column during dredged material disposal and deposit onto 

the seabed is approximately 200 seconds (after the completion of the disposal operation). The 

time required for silt to completely settle out of the water column and deposit onto the seabed 

is approximately 2,000 seconds (after the completion of the disposal operation). The above 

results were obtained for 100-foot water depth with no current. Short-term FATE modeling 

results are summarized graphically in Figures B-10 to B-13 and are described below for

parameters governing mound height, mound width, and displacement distance.

Mound length is directly related to disposal vessel speed during disposal (Figure B-10). For

normal operating conditions in water depth of 70 feet, the Yaquina and Westport produce a 

dump footprint 600 to 3,200 feet long for vessel speeds ranging from 1-10 ft/sec, respectively. 

Mound thickness is also affected by vessel speed. For normal operating conditions in water 

depth of 70 feet, the Yaquina (Westport) produces a dump footprint 0.2 to 0.05 (0.3 to 0.1) 

feet thick for vessel speeds ranging from 1-10 ft/sec, respectively.

For similar operating conditions (vessel speed, vessel capacity, water depth, and currents), 

split-hull hopper dredges produce a thicker (higher) resultant mound footprint than multiple 

bottom-door hopper dredges (Figure B-11). For average operating conditions in 100 feet of

water, without a current, the dredge Yaquina will produce a deposition mound with maximum 

height of 0.17 feet. The Westport will produce a mound with maximum height of 0.3 feet.

The most significant parameter affecting mound geometry (width and height) is water depth. 

Increasing the water depth by a factor of three (60 to 180 feet) will decrease disposal mound 

height for a single dump by a factor of three for both types of hopper dredges (Figure B-12). 

Increasing the water depth by a factor of three (60 to 180 feet) will increase disposal mound 

width for a single dump by a factor of three for both types of hopper dredges (Figure B-13). 

This applies to dredges disposing in all current conditions tested.

Increasing current speed from 1-4 ft/sec (in 100 feet of water) reduces mound height by a 

factor of three for both dredges (Figure B-12). The presence of a current act to displace 

placed dredged material away from the location of release, before the material impacts the 

seabed (Figure B-13). For disposal in a water depth of 100 feet, a 1 ft/sec current will 

displace dredged material 400 feet from the site of disposal before most of the material hits

the seabed. For the same water depth, a 4 ft/sec current may displace dredged material 1,600 

feet from the site of disposal before most of the material hits the seabed.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-41

Figure B-10. Predicted disposal footprint geometry as a function of disposal vessel speed. Top 

graphic is for mound thickness vs. speed; bottom is for mound length vs. speed.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-42

Figure B-11. Predicted disposal footprint thickness for dredges Westport and Yaquina as a 

function of current speed. Top graphic is for the dredge Yaquina and bottom is for Westport.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-43

Figure B-12. Predicted disposal footprint geometry as a function of current speed. Top graphic is 

for footprint width vs. current speed and bottom is for displacement distance of footprint from point 

of disposal vs. current speed.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-44

Figure B-13. Predicted bottom distribution resulting from release of one load of sandy dredged 

material in water depth of 100 feet for two hopper dredges: (A) Westport and (B) Yaquina.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-45

The nominal configuration of a dredged material mound resulting from disposal of one load 

by the dredge Westport and Yaquina in 100 feet water depth with a current of 1 ft/sec is 

shown in Figure B-13. The estimated areal coverage of a mound resulting from a single load

placed by the Westport in 100 feet water depth is about 17 acres with maximum mound height 

of 0.22 feet; however, 90% of the mounded area is less than 0.10 feet (1.2 inches). The 

estimated areal coverage of a mound resulting from a single load placed by the Yaquina in 

100 feet water depth is about 21 acres with maximum mound height of 0.12 feet; however, 

90% of the mounded area is less than 0.07 feet (0.84 inches). The Westport’s dump footprint 

is smaller aerially and thicker than the Yaquina’s dump footprint. The Yaquina’s footprint is 

more uniform in terms of deposition (thickness).

For locations offshore of Yaquina Bay where water depths range between 60-150 feet and 

currents are 1 ft/sec, the mound resulting from an individual dump could be expected to have 

the following configuration:

Mound Length: 1,200 - 2,400 feet

Mound Width: 400 - 1,300 feet

Maximum Mound Thickness: 0.1 - 0.3 feet

Displacement of Mound During Disposal: 200 - 700 feet

STFATE Conclusions

The bottom encounter processes associated with dredged material disposal (convective 

descent and dynamic collapse) are mainly a function of disposal water depth. For shallow 

water disposal (in 50 feet of depth), the “impact” of the dredged material plume on the seabed 

is more concentrated (in terms of dredged material plume velocity and density at the seabed) 

than for disposal in 100 feet of water. However, disposal at deeper water depths increases the 

areal extent of bottom impact as compared to disposal in shallower water depths. The seabed 

area affected by the convective descent phase is about 10% of the total dredged material 

footprint (resulting from completion of the passive transport and diffusion phase).

The thickest area of bottom accumulation for an individual dump represents a small fraction 

(10% or less) of the overall footprint coverage. For a typical disposal event, most of the 

disposal footprint area is composed of a thin apron of dredged material (less than 0.1 feet 

thick, depending on disposal water depth).

Based on the characteristics of dredging vessels typically used at Yaquina Bay, split-hull 

hopper dredges (Westport) are estimated to produce a disposal footprint per dump that has a 

maximum thickness 50% greater than the multiple bottom-door hopper dredge (Yaquina). 

Dredged material can be dispersed (spread-out on the seabed) by increasing the speed of the 

disposal vessel while it is placing the dredged material. If the hopper dredge speed is 

increased while dumping, the mound thickness of individual dumps can be significantly 

reduced at the expense of increasing mound length. Mound height can be reduced by 45% by 

increasing the speed of the disposal vessel from 2 ft/sec (1 knot) to 6 ft/sec (3.5 knots). Based 

on STFATE results assessing displacement of placed dredged material from the point of 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-46

release, an ODMDS “buffer zone” of 500 feet (minimum) is recommended to prevent the drift 

or deposition of dredged material on areas outside of the ODMDS boundary, during disposal.

Specification of Proposed ODMDS Size and Location

The size, location, and layout of the proposed ODMDSs was based on the “site selection and 

management criteria” described in Section 4 of this appendix and the “general location and 

required size” discussed above. To summarize:

A. Based on mound height restrictions and simple geometry, the minimum size of each proposed 

ODMDS (for static capacity) was calculated to be 3,900 feet x 3,900 feet. See Section 6.

B. To reduce the risk of dredged material being placed outside of the ODMDS boundaries, a 500-foot 

“buffer” zone was inscribed within the formal site boundary. No dredged material disposal is 

proposed within the site’s “buffer zone” although it is formally part of ODMDS. The “buffer” 

zone functions to keep material within the ODMDS while the placed material is falling through 

the water column.

C. The orientation of the proposed ODMDSs was such that the primary axis of the sites was aligned 

with the bathymetry contours.

D. Two ODMDS (identical in size) are proposed to facilitate adaptive management and variable 

dredged material placement strategies. The proposed sites are referred to as the “North” ODMDS 

and the “South” ODMDS.

Discounting the buffer zone, the effective usable area for each proposed ODMDS was set at 

5,500 feet x 2,800 feet. This is equivalent to the minimum required size of 3,900 feet x 3,900 

feet (see the ODMDS “size” calculation in Section 6). The buffer zone along the northern, 

southern, and western perimeters of the ODMDSs was set at 500 feet. For the purpose of 

FATE modeling, a larger buffer zone (800 feet) was applied to eastern perimeter of the 

proposed ODMDSs to account for the presence of potentially sensitive rocky bottom areas 

east of the proposed ODMDSs. If FATE model results show that 800 feet of buffer is not 

needed along the eastern perimeter of the ODMDS, the buffer can be reduced to 500 feet. 

Including the offset buffer zone, the overall dimensions of each proposed ODMDS is 6,500 

feet x 4,000 feet.

The lineal dimensions, boundary coordinates, and water depth variation for the proposed 

North and South ODMDS are described below and shown in Figure B-14. Disposal boundary 

coordinates in state plane are Oregon north zone, NAD 27 (feet). Disposal boundary 

coordinates in geographic coordinates are in latitude-longitude, NAD83 (deg min sec).

Proposed “North” ODMDS: dimensions = 6,500 ft x 4,000 ft, area = 597 acres, axis azimuth = 10o, 

average depth = 135 feet. Baseline bathymetry elevation variation = -115 MLLW to -150 MLLW

Northwest corner - Easting=1,057,355 ft, Northing=375,434 ft Lat=44 38 17.98 N, Lng= -124 07 25.95 W

Northeast corner: - Easting=1,061,294 ft, Northing=374,740 ft Lat=44 38 12.86 N, Lng= -124 06 31.10 W

Southwest corner: - Easting=1,056,226 ft, Northing=369,033 ft Lat=44 37 14.33 N, Lng= -124 07 37.57 W

Southeast corner: - Easting=1,060,166 ft, Northing=368,339 ft Lat=44 37 09.22 N, Lng= -124 06 42.73 W
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-47

Figure B-14. Proposed new locations for Yaquina Bay ODMDSs.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-48

Proposed “South” ODMDS : dimensions = 6,500 ft x 4,000 ft, area = 597 acres, axis azimuth = 

10o, average depth = 135 ft. Baseline bathymetry elevation variation = -115 MLLW to -150 MLLW

Northwest corner - Easting=1,054,819 ft, Northing=362,018 ft Lat=44 36 04.50 N, Lng= -124 07 52.66 W

Northeast corner: - Easting=1,058,758 ft, Northing=361,323 ft Lat=44 35 59.39 N, Lng= -124 06 57.84 W 

Southwest corner: - Easting=1,053,890 ft, Northing=355,617 ft Lat=44 35 00.85 N, Lng= -124 08 04.27 W

Southeast corner: - Easting=1,057,629 ft, Northing=354,922 ft Lat=44 34 55.75 N, Lng= -124 07 09.47 W

Long-Term Fate Modeling: Typical Disposal Year

Assessment of life-cycle capacity for the proposed ODMDSs was based on applying the 

FATE models to the “North” ODMDS. Since the physical environment is basically the same 

at the North and South sites, similar FATE results are expected for the “South” ODMDS.

The bottom accumulation of dredged material placed within the proposed North ODMDS was 

estimated based on an annualized sequence of disposal. This was done using two different 

types of dredging equipment: split-hull and multiple-bottom door hopper dredges. The 

MDFATE model was used to predict the bathymetric distribution of dredged material in 

response to a year-long disposal cycle. The focus of this endeavor was to assess the 

“operational dispersiveness” of the multiple-door hopper dredge (Yaquina) and the split-hull 

dredge (Westport). Factors under consideration include the areal extent of placed dredged 

material and the maximum mound height attained after a given year-long disposal cycle. 

Disposal parameters assumed for both types of dredging vessels are:

 Volume placed = 310,000 cy or 310 loads (annual average 1986-2000).

 Dredged material placed randomly about the center of the proposed ODMDS, using a 

maximum placement radius of 1,000 feet from the centroid. Water depth at the 

centroid of the ODMDS was about 135 feet.

 The hopper dredge approaches the disposal release point from the southeast for each 

dump placed.

 Other operational parameters are as stated above or in Section 8, Measured 

Oceanographic Data.

Results from the year-long simulations are shown in Figure B-15 in terms of accumulated

placed dredged material, resulting from a one-year disposal scenario. The left-hand graphic 

(A) applies to the split-hull dredge Westport placing 310,000 cy and the right-hand graphic 

(B) applies to the multiple bottom-door dredge Yaquina placing 310,000 cy. Note that the 

dredge Westport produced a 40% taller and more compact mound (13% smaller), than did the 

dredge Yaquina. This result is consistent with the short-term FATE results described above. 

Both disposal vessels produced an aggregate mound that was higher than 5 feet.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-49

Figure B-15. Accumulation of dredged sand placed in center of proposed North ODMDS for a 

split-hull hopper dredge (A) and multi-bin hopper dredge (B), 1,000 cy per load.

Given the above results, it would be hard to prevent accumulation of dredged material to 

heights less than 14 feet during a 20-year life cycle (assuming dredged material is placed in a 

similar manner each year). Discrete mounds would likely overlap and accumulate to heights 

greater than 14 feet. Recall from the ODMDS “size” calculation shown in Section 6 (Figure 

B-9) that for a large mound 135 feet in depth the maximum mound height that will not affect 

waves is 14 feet.

It is apparent from both the Westport and Yaquina disposal scenarios shown in Figure B-15, 

that “point” disposal methods (random placement about a specified point) are not sufficiently

distributive, in an operational sense, for the successful long-term management of site capacity 

within the configuration of the proposed ODMDSs. To avert future static site capacity 

problems at the proposed ODMDSs, it is recommended that a pro-active approach be used to 

enhance the uniform distribution of dredged material during disposal. Basically, this entails 

the use of a placement grid to evenly distribute the placement of dredged material within the 

ODMDS by assigning the “starting point” of each dump within specified grid cells. The 

“placement grid” method of dredged material disposal is discussed below and has been used 

since 2001 at the North site.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-50

Long-Term Fate Modeling: 20-Year Life Cycle

The “operational” capacity of the proposed North ODMDS was assessed for a 20-year life

cycle by conducting 20 back-to-back year-long disposal operations. The goal was to verify 

that by distributing the placement of dredged material throughout the usable part of the 

ODMDS was such that dredged material is not deposited outside the formal boundaries of the 

ODMDS during the placement, and dredged material does not accumulate higher than 14 feet 

after 20 years of site use. The MDFATE model was used for this series of simulations. For 

each year of simulation, disposal processes (short-term fate) and bottom transport processes 

(long-term fate) were included. The left graphic in Figure B-16 shows the baseline

bathymetry condition of the proposed North ODMDS.

ODMDS Disposal Placement Grid

For this life-cycle assessment, uniform thin-layer placement of dredged material was 

accomplished by using a grid of 32 cells that are 700 x 700 feet to establish the release point

for each load of dredged material. The “placement grid” was contained inside of the 

ODMDS. The “placement grid” was used to guide the distribution of dredged material 

disposal for each year.

Nine (dredge Westport) and 10 (dredge Yaquina) dumps per grid cell were needed to place 

310,000 cy of dredged material within the site per year. It was assumed that both the 

Westport (30%) and Yaquina (70%) would be used for dredging/disposal during the 20-year 

period. The selection of each simulated dump location was chosen randomly based on a 500-

foot radius from the center coordinate for each cell. The center of each grid cell is shown in 

Figure B-16 (left graphic “+”). Note that “usable” area of the ODMDS is inscribed by the

dashed line.

Year One of 20-Year Disposal Sequence

The first year of the 20-year “operational” capacity assessment was simulated based on the 

dredge Yaquina performing dredged material disposal within the proposed North ODMDS. 

The 32-cell placement grid described above was used to control the disposal of 310 loads of 

dredged material within the North ODMDS boundaries. The resultant dredged material 

accumulation, after 1 year of disposal, is show in the right graphic of Figure B-16. The 

maximum height of dredged material accumulation is estimated to be 1.2 feet and all placed 

dredged material is contained within the North ODMDS boundaries. Due to the low relief of 

the dredged material mound, very little material was affected by waves/currents during the 

first year of simulation.

Comparison of Figure B-16 (right graphic) with Figure B-15 (left graphic) clearly shows that 

the “placement grid” method of disposal control is superior to “point dump” methods for

dispersing material uniformly with an ODMDS.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-51

Figure B-16. Baseline (2000) bathymetry at the proposed North ODMDS (A) and estimated 

accumulation after 1 year of dredged material placement by hopper dredge Yaquina (B).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-52

Complete 20-year Disposal Sequence

The disposal of 6.2 mcy of dredged material (sand) was simulated based on the dredge 

Yaquina placing 70% of the material and the Westport placing 30%. Results of the 20-year 

disposal sequence are shown in Figure B-17. The left graphic in this figure shows the 

predicted 20-year bathymetry within the proposed ODMDS. Note that the depth contours are

displaced oceanward from the baseline condition. The right graphic of Figure B-17 shows the 

vertical and areal extent of the dredged material mound resulting from 6.2 mcy of disposal. 

Note that the maximum height of the resultant dredged material mound is estimated to be 12 

feet, which is 2 feet lower than the limiting mound height required to meet the wave 

amplification constraint (see the ODMDS “size” calculation in Section 6).

Based on the above long-term simulation results, each proposed ODMDS is expected to 

provide sufficient static capacity for at least a 20-year life cycle without impacting wave 

conditions at the site. Although the dynamic capacity of the proposed ODMDS (after 20 

years of dredged material accumulation) is estimated to be 100,000 cy/year, this was not 

considered part of the site’s operational capacity. Collectively, both the North and South sites 

are estimated to provide over 40 years of capacity for the placement of Yaquina Bay dredged 

material. The net direction and distance of sediment movement off of the mound is estimated 

to be toward the WNW (300) at 120 feet/year. Based on the estimated deposition pattern 

shown in Figure B-17B and the direction of dredged material movement (after placement at

the North or South sites), a uniform 500-foot setback area is appropriate for the proposed 

sites. In other words, the 800-foot setback area along the eastern perimeter of the proposed 

sites is not needed.

Summary of FATE Modeling Results

The proposed North ODMDS shown in Figure B-10 (and left graphic of Figure B-16) appears

to be capable of receiving 310,000 cy/yr of dredged material disposal for a period of 20 years 

(6.2 mcy total) without impacting the present wave climate. This assessment is based on 

results obtained using the MDFATE model. The South Site has similar capacity.

The 20-year capacity of each proposed ODMDS can only be met if a “placement grid” or 

equivalent method of disposal control is used to evenly distribute dredged material within the 

site during disposal. The “placement grid” would consist of 32 cells that are 700 x 700 feet to 

“distribute” the release point for each load of dredged material.

Net long-term movement of the dredged material placed at the proposed ODMDS would be 

toward the north-northwest, away from any known rock outcrop features. A 500-foot 

placement setback should be inscribed within the proposed North and South ODMDS 

boundaries to keep material within the ODMDS during dredged material placement.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-53

Figure B-17. Predicted bathymetry at proposed North ODMDS after 20 years of dredged material 

placement (A) and corresponding vertical accumulation (B).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-54

Physical Impacts at ODMDSs due to Dredged Material Disposal

Accumulation of Dredged Material Placed. The seabed at the proposed North and South 

ODMDSs will be subjected to various degrees of dredged material accumulation (burial) 

during dredged material disposal operations. On a per dump basis (individual disposal vessel 

load), the seafloor at the ODMDSs could be subjected to individual burial events ranging 

from 0.01 - 0.3 feet thick and covering 5-20 acres of seafloor. On a seasonal basis (after an 

entire dredging-disposal season), the sites may be subjected to dredged material accumulation 

ranging between 1-10 feet thick covering an area of 100-500 acres, depending upon the 

disposal scenario. Generally speaking, the more confined the area over which dredged 

material placement occurs, the higher the accumulation.

Modification of in situ Surface Sediment Gradation. There could be a slight change of the 

surface sediment texture (grain size) at the North and South ODMDSs, in response to dredged 

material disposal. Specifically, the average grain size of seabed sediment within the sites will 

likely increase due to the placement of dredged material that is slightly coarser than in situ

sediments. The overall physical properties of the pre-disposal seabed sediment within the 

proposed ODMDSs would not be changed. Sand (sediment dredged from the Yaquina Bay 

project is about 95% sand) will be placed on sand (in situ sediment residing on the seabed of 

proposed ODMDSs). The mean grain-size of in situ seabed sediment within the ODMDSs 

varies between 0.10 - 0.20 mm and has a fine-grain material content of 0-10%. The mean 

grain size of 95% of the dredged sediment to be placed in ODMDSs varies from 0.15 - 0.25 

mm and has a fine-grain material content of 1%-4%.

A small amount of fine-grained dredged sediment may be placed at the proposed ODMDSs. 

This dredged material originates from periodic dredging of South Beach marina, North Bay 

marina, Depot Slough, and potentially other permitted projects. The quantities of fine-grained 

sediment to be placed at the proposed ODMDSs are about 5% of the total volume dredged at 

Yaquina Bay. It is expected that placement of such small amounts of fine-grain sediment 

within the proposed ODMDSs will not significantly alter the characteristic grain size of native 

sediment within or outside the ODMDSs.

Modification of Existing Wave Environment. Use of the proposed North and South 

ODMDSs will not degrade the existing wave environment either within or outside the 

ODMDS boundaries.

Modification of Existing Current Environment. Placement of dredged material within the 

proposed North and South ODMDSs may have a minor affect on circulation within or outside 

of the site boundaries. Due to the size of the mound resulting from accumulated dredged 

material placed at the sites (10-14 feet high covering a 0.6 square mile area) over a period of 

20 years, it is possible that currents in vicinity of ODMDSs could be affected by disposal 

operations. A vertical accumulation of 14 feet of dredged material within a water depth of 

115 feet will directly affect 10% of the water column. This amount of “protrusion” may 

modify currents at the disposal site. If realized, the effects upon the site’s current field would 

not occur until a substantial volume of dredged material has been placed at the site (4-6 mcy, 

or after 15-20 years of disposal).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-55

Littoral Budget. Most of the sand dredged from the Yaquina Bay entrance channel originates 

from the marine environment. It is possible that dredged sand placed at the proposed North 

and South ODMDSs could be removed from the littoral budget for 10-20 years (until 

infrequent large storms can transport the sand back toward the shore). An important question 

related to the siting and long-term management of proposed ODMDSs at Yaquina Bay is:

Will the use of the proposed North and South ODMDSs affect the littoral sediment budget in 

vicinity of the Yaquina Bay entrance? If the littoral budget is affected, could there be an 

associated effect on coastal beaches near the jettied entrance? To address the above 

questions, the following assumptions must be made:

1. An undetermined but substantial percentage of the sand dredged from the entrance 

channel originates from active littoral area immediately north and south of the jettied 

entrance. The active littoral area is the upper shoreface, generally where depths are 

less than 60 feet. Further, assume that a percentage of dredged material that has been 

placed at past (Interim and nearshore Section 103 sites) ODMDSs was transported 

back to the active littoral budget.

2. The littoral budget was in equilibrium with past dredging and disposal practices. That 

is, use of past ODMDSs did not significantly altered the littoral budget or affected 

coastal beaches near the entrance.

3. The dredged sand placed at the proposed ODMDSs will be removed from the active 

littoral budget for a number of years (until infrequent large storms can transport the 

sand back onto the upper shoreface). Long-term removal of sand from the active 

littoral budget could produce a recession response of the upper shoreface.

Based on the assumptions, use of the proposed ODMDSs may remove a percentage of sand 

from the active littoral budget at the Yaquina entrance. If the active littoral budget is reduced, 

recession of the upper shoreface may occur. Using the proposed North and South ODMDSs 

for placement of all sediment dredged from the entrance channel could result in erosion of the 

upper shoreface (and possibly beaches) within close proximity to the jettied entrance. 

Although this finding is based on conjecture, engineering judgment and experience, it 

describes the potential for shoreface recession in response to the use of the proposed new 

ODMDSs for the placement of all sediment dredged from the Yaquina entrance channel.

Changes at the Historic ODMDSs. Since 2000, disposal of dredged material at the Interim or 

nearshore 103 sites has not occurred. Placement of material into the Interim Site was 

suspended in 1986 due to mounding. The mound, which reached a maximum of 22 feet, was 

essentially eroded by 1990. By November 2000, mounding in the nearshore 103 Site had 

reached a maximum of 20 feet; placement was suspended and subsequent material placed in 

the North Site beginning in 2001. As of 2006, the last year the nearshore 103 Site was

surveyed, the maximum mound height was reduced to 13 feet. When placement in this site 

was suspended, it was predicted that the mound height would be reduced 1-3 feet per annum. 

Further, it was predicted that the mound would be completely dispersed by waves and 

currents within 14 years. Sediment and contours would return to pre-placement conditions. 

This has occurred in the Interim Site and looks to be on track at the nearshore 103 Site.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-56

Section 7

OCEANOGRAPHIC PROCESSES

Offshore Regional-Scale Circulation

Circulation processes in the coastal waters near the Yaquina Bay result from an interaction of 

regional oceanic circulation, astronomical tides, wind-generated surface waves and currents, 

and estuarine flow. One of the direct effects of circulation processes at the entrance to 

Yaquina Bay is on the transport and seasonal distribution of sediments. These processes act 

on ebb-tidal shoal and littoral sediments (depths <120 feet) to produce the bathymetric 

condition observed at any particular time. Time scales for circulation processes range from 

seconds for wind-generated waves to months for seasonal weather patterns to years for largescale events such as El Nino.

From a sediment transport point of view, the Oregon continental shelf can be divided into 

three cross-shore regions [Sternberg 1986]. The first of these regions is the outer shelf (depth 

>300 feet) where shoaling internal waves and large-scale, wind-driven currents affect the 

movement of bottom sediments. The second cross-shore region is the mid-shelf (120-300 feet 

depth), over which wind-driven currents are the most important factor. The third and most 

active region is the inner shelf (depth <120 feet), on which shoaling waves and tidal (and 

estuarine) induced currents are at least as important as wind-driven currents for transport of 

bottom sediments. For the most part, the assessment of the historic and proposed Yaquina 

ODMDSs is limited to the inner and mid shelf region.

Circulation of the continental shelf waters off Oregon is thought to be nearly geostrophic, i.e.,

friction plays a minor role in determining the water column circulation when compared to 

sloping sea surfaces, sloping internal density surfaces, and the rotation of the earth. 

Consequently, mean circulation on the shelf tends to be along the bathymetric contours.

Circulation of coastal (inner shelf) waters is subject to seasonal reversal, being northward 

during winter and southward during summer. On time scales of several days, coastal 

circulation can be highly variable in direction and speed with fluctuations correlating with 

changes in sea level and the alongshore component of wind [Huyer 1977]. The alongshore 

component of the coastal current regime is substantially stronger and more responsive to 

changes in wind conditions than is the onshore-offshore component of current [Collins 1970]. 

Fluctuations in the mean alongshore circulation appear to be coherent over distances of 125 

miles and are independent of depth in both phase and magnitude to approximately 70 feet 

depth [Huyer 1977]. The magnitude of alongshore current fluctuations decreases rapidly with 

distance offshore and increasing water depth. Currents averaged over very long periods, e.g., 

longer than 50 days, correlate better with sea level changes than with winds to depths of 120 

feet. By 250 feet in depth, the influence of both sea level and winds appears to be 

substantially diminished and other processes such as tides, regional circulation, and internal 

waves control the current regime.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-57

California and Davidson Currents

Net regional circulation along the continental shelf of the Washington and Oregon coasts has 

been characterized in terms of two seasonal current regimes: summer and winter [Bourke 

1971]. Offshore of the continental shelf break (>20 miles from the coast), surface flow down 

to 500 feet in depth is dominated by the California current. The California current is a broad, 

shallow, slow moving current which flows southward throughout the year at speeds of 0.1 -

0.7 ft/sec as a diffuse band about 300 miles wide. Inshore (east) of the California is a 

seasonally varying flow called the Davidson current.

The Davidson current is a northward flowing current attaining speeds of 0.3 to 1.0 ft/sec over 

extensive distances. On the surface waters of the continental shelf, this current responds to 

the seasonal wind patterns of the northeast Pacific. The Davidson current develops off of the 

Oregon-Washington coast in September and becomes well established in January in response 

to southerly winds. The surface expression of the Davidson current diminishes towards the 

spring, disappears by May, and becomes incorporated into the permanent California current 

[Bourke 1971]. The subsurface part of the Davidson current is believed to flow northward 

throughout the year.

Shelf Circulation

A generalized model for the seasonal changes in the alongshore and offshore circulation along 

the Pacific Coast of Washington and Oregon has been developed [Huyer 1977]. The summer 

circulation of surface water on the continental shelf is influenced by the southward flowing 

California current which attains maximum strength during the summer when surface winds 

are consistently from the north-northwest. Winter circulation of shelf waters is dominated by 

the northward flowing Davidson current which attains maximum strength due to winter storm 

(wind stress) patterns. The subsurface part of the Davidson current (below 300 feet in depth) 

is believed to flow northward throughout the year, although the surface waters respond to 

seasonally varying wind stress patterns (reversals). Thus, the net direction of bottom currents 

on the mid and outer continental shelf is believed to be northward and along shore.

Inner-Shelf Circulation

Vertical mixing of the inner shelf waters is at a maximum during the winter (December -

March) when currents are nearly uniform in speed and direction throughout the water column. 

During winter, significant wind-generated currents develop in response to strong southerly 

storm winds. Wind-induced currents may exceed 2 ft/sec flowing northward with event 

persistence of 5 to 7 days. Wind-driven currents develop within a few hours of the onset of 

strong winds then decrease slowly over several days following cessation of the winds.

With the onset of southerly winter winds resulting in northward flow, surface coastal waters 

are directed northward and landward due to Coriolis deflection resulting in downwelling 

along the coast. Bottom water is directed offshore. The mean alongshore circulation of 

surface coastal waters during winter is northward at 0.3 - 0.8 ft/sec. The inner shelf current 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-58

can be highly variable over periods of several days: Southerly flow (north to south) can 

sometimes occur during the winter.

Mid-Shelf Circulation

The transition from the winter circulation regime to the spring and summer regime is abrupt 

along the middle and inner shelf, occurring only in about a week during a strong northerly 

wind event. The transition is the result of a large cumulative offshore transport of surface 

water caused by local wind stress and the establishment of strong offshore density gradients in 

the shelf waters. Upwelling is associated with the spring current transition and continues into 

July or August. The offshore density gradients are associated with the persistent southward 

surface current and upwelling due to the summer oceanographic season.

During the summer, southward surface currents can approach 1.3 ft/sec. Reversals in current 

direction rarely occur during summer. With onset of northerly summer winds (southward 

coastal current), surface coastal waters are directed offshore due to Coriolis deflection 

resulting in upwelling along the coast. Bottom water is directed onshore. 

During summer, a strong vertical gradient (shear) of the alongshore current can be found over 

the middle and outer shelf. The subsurface current is northward while the surface current is 

southward. Maximum surface current speed over the mid-shelf (5-10 miles offshore) occurs

during June when the southward flow is reinforced by strong northerly winds. The bottom 

current along the mid-shelf is reduced, due to the high gradient between surface and bottom 

waters. The bottom current for inner shelf waters is dominated by surface circulation ands 

tends to be stronger and more consistently southerly (during the summer) than the bottom 

circulation further offshore.

The transition between summer and winter nearshore circulation is gradual. The offshore 

shear zone between the northward flowing bottom waters of the outer-shelf and the southward 

flow of nearshore coastal waters expands upward and shoreward under the influence of fall 

and winter southerly winds. Reversal of surface water circulation over the shelf occurs when 

the winter regime of northward flow (Davidson current) is re-established throughout the water 

column [Sobey 1977].

Littoral Sediment Transport

Along the inner- and mid-shelf zone of the Oregon coast (water depths less than 300 feet), 

currents induced by wind, waves, and tides are primarily responsible for sediment transport 

through the water column and on the seafloor. Wave-induced currents tend to diminish 

inversely with (water depth)1/2 [Komar et al. 1972]. The closer one moves toward shore (the 

shallower the water depths), the more energetic the effects of wave shoaling will be 

throughout the water column. Increased wave shoaling accompanied by an ambient current 

can produce a high sediment transport potential (see Section 5, Hallermeier Sediment 

Transport Limits). The seaward limit of active littoral zone coincides with the Hallermeier 

closure depth d, which is 60 feet at Yaquina Bay. In water depths less than 60 feet along the 

project area coast, wind- and wave-induced currents dominate the transport of sediment along 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-59

the seabed. This area is called the littoral zone. Within the littoral zone of Oregon, the 

seabed sediment is primarily composed of sand, gravel, and cobbles. Sediments smaller than 

sand (silt and clay) generally do not reside within the littoral zone of the Pacific Northwest

due to the high mobility of fine-grain sediment. Near the Yaquina Bay entrance, littoral 

sediments are composed of fine-medium sand. In fact, much of the sediment dredged from 

the Yaquina Bay entrance is littoral sand or marine origin (the sand was either transported to 

the coast via rivers long ago or the sand is a product of bluff/rock outcrop erosion).

The transport of bottom sediment within the littoral zone, due to waves and currents, is called 

littoral transport. In general, littoral transport is a function of wave height and period, bottom 

sediment size, and strength of ambient current. There are two directional components of 

littoral transport: cross-shore or perpendicular to shore (onshore-offshore) and alongshore

(updrift-downdrift). As waves approach the coast, water depth becomes progressively 

shallower causing the waves to shoal. Eventually, the shore incident waves break due to 

bottom friction and conservation of momentum. The dissipation of energy due to wave 

shoaling and breaking acts to transport bottom sediment, (usually) in the direction of wave 

propagation. The angle at which waves approach the coast dictates the degree of alongshore 

and cross-shore littoral transport. For example, waves approaching the shore obliquely tend 

to produce more alongshore transport than waves which approach the shore straight on. 

Cross-shore transport is more complex than alongshore transport. Under some wave 

conditions bottom sediment can be transported offshore while at other times bottom sediment 

can be transport onshore. In general, the direction of cross-shore transport for sand-sized 

sediments along coastal areas of the Pacific Northwest is assumed to be onshore during 

summer and both onshore and offshore during winter.

Although the dominance of southerly waves (and associated northward littoral transport) 

during the 5-month period of December - March is a documented fact, the remainder of the 

year is characterized by northerly waves and an attending southward littoral transport. It is 

possible that the wave and current regime present during the remaining 7 months could 

generate littoral transport that approaches the transport experienced during the more energetic 

5-month period of the year. The onset of long-term climatic perturbations such as El Nino 

and La Nina can modify the directionality of waves making landfall on the northwest coast, 

greatly affecting the directionality and strength of the littoral current. Long-term changes in 

the littoral environment are likely responsible for whether littoral sediment (sand) is 

transported north or south along the northwest coast.

Estimates for gross alongshore transport (direction independent) along the OregonWashington coast exceed 1 mcy per year. In many locations along Oregon, the net long-term 

average long-shore transport rate is postulated to be close to zero [Komar 1997]. Due to the 

complexities of the nearshore reef system north and south of Yaquina Bay, a conclusive 

description for the net direction and magnitude of alongshore transport along coastal areas 

north and south of Yaquina Bay entrance is not available.

Based on long-term average annual conditions and the orientation of beach alignment north 

and south of the jettied entrance at Yaquina Bay, it appears that net littoral transport at 

Newport is slightly toward the north. The issue of “north vs. south” littoral transport at the 

Yaquina Bay entrance is an important consideration for an ODMDS which is to be located 
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-60

within the littoral zone. However, the proposed North and South ODMDSs are not located 

within the littoral zone (60 feet or less); minimum water depth for the proposed ODMDSs will 

be 115 feet. It is anticipated that “littoral transport” at the proposed ODMDSs will occur only 

during severe (storm) wave conditions. Dredged material placed within the proposed 

ODMDSs may be impounded from the littoral zone for 10-20 years.

If the opportunity arose for dredged material to be placed in the nearshore, it is recommended 

that an equal volume be placed north and south of the Yaquina Bay entrance at alongshore 

distances no closer than 2,000 feet from the entrance. If the opportunity arose to place 

dredged material directly on the beach, it is recommended that the dredged material be placed 

further than 300 feet to the north of the north jetty.

Summary of Seasonal Changes in Circulation

In general, there are three oceanographic seasons for circulation of coastal waters on the inner 

shelf of Oregon [Borgeld 1978]. These seasons are briefly defined as:

Fall - Winter: Onset of the Davidson current occurs and the coastal current is 

directed northward by southerly winds. The fall-winter season is generally defined 

as November - March.

Spring: Onset of the upwelling regime along the continental shelf. Transition 

between the Davidson and California current regimes occurs in offshore waters. 

The coastal current begins reversal from northward to southward flow. The spring 

season is defined as April - June.

Summer: Southerly circulation of shelf waters induced by the California current. 

The coastal water is directed southward by northerly winds. The summer season is 

generally defined as July - October.

Cross-shore Circulation

The upwelling and down-welling circulation due to Coriolis deflection induces seasonally 

varying cross-shore transport of shelf bottom water (Ekman transport) and sediments. 

Offshore transport of shelf bottom water occurs during winter and onshore transport occurs 

during summer. Within the immediate vicinity of Yaquina Bay, estuarine circulation also 

induces cross-shore transport during ebb-tide (offshore flow), flood-tide (onshore flow), and 

periods of high river discharge (offshore flow).

Significant cross-shore circulation occurs along the Oregon Coast during the upwelling 

(summer) season [Pillsbury 1972 and Huyer 1976]. This occurs when shelf bottom water 

moves onshore and converges with less dense (warmer) water of the inner shelf. The crossshore section shown in Figure B-18 illustrates the mean circulation induced by the upwelling

along Oregon continental shelf. The shaded zone is the permanent pycnocline (zone of rapid 

density change with depth), which is normally located at depths greater than 130 feet in 

offshore waters deeper than 200 feet deep (6-10 miles offshore).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-61

With the onset of coastal upwelling, the pycnocline rises and is pushed shoreward. When 

upwelling is fully developed, the pycnocline intersects the water surface within 10 miles from 

shore. Above and offshore of the pycnocline, mean flow is to the south as expected for the 

summer season. About 130 feet below the permanent pycnocline, flow is to the north. Under 

strong upwelling conditions, southward circulation is reinforced in the nearshore waters and 

the deeper north flowing current weakens and may disappear. Mean currents within 60 feet 

from the surface are south and offshore at speeds of 0.5 ft/sec due to the influence of the 

summer wind field combined with upwelling conditions.

Generally speaking, the proposed North and South sites are located within the area of coastal 

upwelling, but are well inshore of the “mixing” zone (or surface front) associated with the 

convergence of dense bottom water from the outer shelf and warmer less dense water from the 

inner shelf. While upwelling increases biological productivity along the coast, the location of 

the surface front is where intense biologic activity occurs.

Long-Period Waves

Superimposed upon the slowly varying regional or seasonal circulation are periodic currents 

due to tides, inertial currents, and internal waves. While variations in wind speed and 

direction at durations longer than 2 days are reflected in surface currents, shorter duration 

wind events can give rise to inertial currents that have 17-hour periods and speeds exceeding 

0.3 ft/sec [Huyer 1977].

Continental shelf waves are long waves typically generated by atmospheric pressure/system 

movements. These shelf waves have periods of 4-6 days and propagate toward the north 

along the western coast of North America. The magnitude of the current associated with shelf 

waves is on the order of 0.10 ft/sec [Moores 1968]. Shelf-wave flow is uniform throughout 

the water column and is directed along the shelf. This type of flow may have a significant 

long-term effect on the transport of fine (silt-clay) sediments, if placed in water depths greater 

than 120 feet.

Astronomical tides at the Yaquina Bay entrance have diurnal inequality typical of the Pacific 

Coast with long ebb from higher high to lower low water. Mean tidal elevation is + 4.15 feet 

mean low lower water (MLLW). The mean tidal range at the Yaquina Bay entrance is 5.9 

feet, the range from MLLW to MHHW is 7.9 feet. Extreme tides range from -3 feet MLLW 

to +11.5 feet MLLW [NOAA 1994]. Offshore Yaquina Bay, tidal currents are believed to 

account for more than half of the water motion over periods of several days [Stevenson 1974].
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-62

Figure B-18. Mean circulation in the coastal upwelling region off central Oregon
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-63

The tidal current for a given coastal location can be described in term of two components: (1) 

the shelf tidal current driven by the approach and passage of the tidal wave over the 

continental shelf and is uniform throughout the water column, and (2) the estuarine tidal 

current generated by flood and ebb flow from a nearby estuary/embayment, which is 

generally confined to depths shallower than 70 feet. Offshore of Yaquina Bay, the shelf tidal 

current is rotary. The estuarine (plume) driven tidal current at locations within 0.5 mile of the 

jettied entrance at Yaquina Bay is appreciable due to the size of Yaquina Bay and the 

constricting nature of the jettied entrance. The shelf tidal current offshore of the Yaquina Bay 

entrance may at times be partially or entirely masked by wind-driven, river discharge, or 

estuarine tidal currents.

Offshore Rotary Currents

Rotary currents are tidal currents that continually change direction, periodically with time, so 

that in 12.5 hours the current will have set in all directions of the compass. The rotary current 

offshore of Yaquina Bay generally floods towards 60 (T), and ebb towards 240 (T). Rotary 

current speeds have been measured at between 0.2 ft/sec and 0.5 ft/sec [Stevenson 1969].
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-64

Section 8

MEASURED OCEANOGRAPHIC DATA

Predictions of future ODMDS capacity requirements are highly dependent upon the quality of 

oceanographic data available. Analyses of the fate of dredged material placed in open water 

can only be as accurate as the poorest estimate for the forcing environment and dredged 

sediment composition. Relevant oceanographic data used in this appendix to simulate 

dredged material disposal at Yaquina Bay include:

 Bathymetric surveys at the historic and proposed ODMDS locations.

 Physical/textural properties for native seabed sediments at and dredged materials to be 

placed at ODMDSs.

 Wind-generated surface wave characteristics.

 Newtonian tidal signal (for surface elevation and currents).

 Residual currents for each oceanographic season.

Hydrographic Survey Data

Hydrographic surveys at the Yaquina Bay “approaches” and ODMDS have been digitally 

recorded since 1983. Areal coverage of the approach surveys is from the seaward jetty ends 

to 2 miles offshore and 2 miles north and south of the navigation channel. Survey frequency 

is about once every 2 years. Areal coverage of each disposal site survey typically extends 500 

feet beyond the sites’ formal boundary; the survey frequency is twice per year. Elevation (z) 

values for the hydrosurvey data are recorded in feet, MLLW which is -4.15 NGVD. The 

horizontal datum (x,y) is Oregon State Plane, north zone, NAD 27.

Survey Error Assessment

Horizontal control (x,y) for the Yaquina surveys is 3.3 feet (10 feet before 1987). The 

vertical accuracy of the wave motion compensator is 5% of the vertical displacement. For a 

6-foot swell, this is about 0.5 feet. The accuracy for vertical data (z), corrected for heavepitch-roll, at 100-foot water depth is 1.5 feet. This represents the random error inherent in 

the depth data (z) for hydrosurveys. In summary, the estimated accuracy statistics for the 

hydrographic surveys are:

Random error for X,Y data = 3.3 feet (10 feet before 1987)

Random error for Z data = 1.5 feet

Digital hydrographic survey data were used in this appendix to assess past and future 

bathymetric change at Yaquina ODMDSs. All results involving bathymetry change 

assessment, for both past and future conditions, should be assessed within the data accuracy 

limits stated above.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-65

Sediments at Yaquina Bay Proposed ODMDSs

The material that is dredged from the channel entrance to RM 1, closely resembles the 

ambient seafloor sediments in the vicinity of the ODMDSs. Sixteen samples collected within 

the 4.5-mile ZSF, at depths ranging from 44 to 144 feet, were all classified as fine sand. The 

average grain size of the seafloor sediment samples was 0.19 mm [USACE 1985]. Recent 

sediment sampling/testing specifically conducted to establish baseline conditions for the 

seabed within the proposed North and South ODMDSs produced the following results:

North ODMDS: D50 = 0.22 mm, sand content = 98.1%, fines content = 1.9%

South ODMDS: D50 = 0.20 mm, gravel content = 0.3%, sand content = 98.1%,

 fines content = 1.6%

The type of sediment in the federal channel is fine to medium sand with average grain size of 

0.22 mm, which is very similar to the ambient seafloor sediments.

Dredged Sediment Characteristics

The type of the sediment dredged from the Yaquina Bay Navigation project material depends 

on the location. More than 95% of dredged materials historically placed at the Yaquina 

ODMDSs has been dredged from the entrance channel and classified as poorly graded sand 

(SP sand, ASTM D 2487) with D50 = 0.17-0.23 mm [Appendix C]. A small amount of finer 

grain material is dredged from the turning basin (RM 2.0 to 2.4), South Beach marina, or 

Depot Slough and is placed in the ODMDSs.

Analysis of sediments from the channel entrance to the “outer” part of the bay (RM -1 to 2) 

indicates that these sediments are of uniform grain size and contain very little silts and clays 

(less than 2%). This sediment is composed of fine to medium sand having a mean grain size 

(D50) of 0.18 mm. The sediment is also low in organic content as measured by volatile solids 

(0.60%) [Appendix C].

Two samples taken from the turning basin at McLean Point (RM 2) in 1995 showed more 

variability. One sample had a large fines content of 72.3 percent and was classified as silt, 

while the other sample was classified as a medium sand with D50 =0.23 (and had a fines 

content of less than 2%). The amount of material dredged from the turning basin is small. 

Dredge logs indicate that 4% percent of the sediment placed at the ODMDs is dredged from 

the turning basin, on an average annual basis.

Physical Properties of Dredged Material Placed at ODMDSs

The specific gravity of the material dredged from the entrance channel at Yaquina was 

determined to be 2.65 and the resuspended density was 1,920 g/l from sediment analysis 

completed in 1990 [Appendix C]. The resulting resuspended void ratio (ess) for fine sand 

dredged from the channel entrance at Yaquina was calculated to be 0.815 using a standard 

volumetric method outline below:
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-66

t = s + v, assume t = 1.0 units

where v = volume of voids (entrained water) in sample

s =1-v s = volume of solids (sediment constituent) in sample

t = total unit volume of sediment in sample relating volume () to mass (M),

 Mt = Ms+Mv, Mv is due to entrained water = v*v

 tt = ss + vv t=ss =1920 g/l (lab data)

 t = ss + vv v = 1024 g/l, s = 2650 g/l (S.G = 2.65)

 t/s = (1-v ) + vv/s = S.G. *1,000 g/l

 0.7245 = (1-v ) + 0.3864*v

 v = 0.4490

 s = 1.0 - 0.4831 = 0.5510 

ess =v/s

ess = 0.815

Dredged Material Solids Content and Void Ratio

Normally, material which is dredged hydraulically has low solids content. The concentration 

of solids for hydraulically dredged sediments (Cs, by volume) varies from 0.18 to 0.35. Since 

hopper (hydraulic) dredges are used to remove channel sediments from Yaquina, it could be 

concluded that the solids content for each load of dredged material placed at the Yaquina 

ODMDS would be lower than 0.35. However, the operating practice of overflow dredging is 

used at Yaquina for sand-based dredged material placed at the ODMDS. This allows for 

water to be drained out of the hopper bins as dredged sediment is pumped in. The practice of 

overflow dredging can substantially increase the solids content of each load of dredged 

material placed at the ODMDS. The concentration of solids for sand in the hopper dredges 

operating at Yaquina (Cs in dredge) was assumed to be the same as for the resuspended 

sediment tests (i.e. ss = 1,920 g/l and ess=0.815) and was calculated by:

Cs in dredge = s in dredge /t in dredge = concentration ofsolids by volume in the hopper dredge

ess = v/s = 0.815, v in dredge = sin dredge *0.815

ess = resuspended void ratio

ein situ = in situ void ratio at site of dredging in channel

 = 0.68 (assumed value based on typical range) in a volumetric

analysis, t = s + v, assume t = 1.0 units

t = v in dredge + s in dredge

 = 0.815s in dredge + s in dredge

 = s in dredge (1+0.815)

since t = 1.0 , s in dredge = 1.0/(1+0.815) = 0.551

Cs in dredge = s in dredge /t = 0.551/1.0 = 0.551 similarly, Cs(in situ) = 0.595 (ein situ = 0.68)
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-67

Usually, the volume of sediment reported as placed at an ODMDS is different from the 

volume of sediment removed from the site of dredging. This is due to the cumulative 

difference between the: (1) the in situ void ratio of the sediment before dredging, (2) the 

resuspended void ratio of the dredged sediment after being placed into the disposal vessel 

(0.815 this case), and (3) the depositional void ratio of the dredged sediment after placement 

at an ODMDS. The change in specific volume of dredged material from the site of dredging 

to the site of disposal is commonly referred to as a “bulking factor.” The bulking factor for 

dredged sediments placed at Yaquina ODMDSs can be calculated by noting the relationship 

between the volume of sediment removed from the channel (in situ), the volume of dredged 

material in the disposal vessel (in dredge), and volume deposited on the seabed (d).

The depositional void ratio for dredged material placed on the seabed (ed) for sand-based 

dredged material placed at ODMDSs was assumed to be equivalent to the resuspended case 

(ed = ess).

t ss = Cs(in situ)*t in situ(1+ess) = t in dredge

t in dredge = Cs(in dredge)*t in dredge (1+ed) 

 = Cs(in situ)Cs(in dredge)t in situ(1+ess)(1+ed) = (0.595)(0.551)t in situ (1+0.815)(1+0.815)

 = 1.190t in situ 

where, ed = depositional void ratio

Bulking factor from dredging site to disposal vessel = 1.190

Bulking factor from disposal vessel to disposal site = 1.000 or seabed = disposal

The volume of dredged material hauled to the ODMDS is based on the “dredge logs” for each 

disposal vessel. The dredge log volume is the volume of dredged material in the disposal 

vessel before placement at a disposal site (disposal). It is not equivalent to the undisturbed 

volume of in situ sediment (in situ). The “dredge log” volume is equal to the volume of 

material placed on the seabed at the ODMDSs. Therefore, the dredging volume statistics 

reported in Table B-1 indicates the “actual” volume of dredged material placed at ODMDSs.

Subaqueous Angle of Repose - Avalanching of Dredged Sediments

As dredged sediments are continually placed (load by load) within a specific open water area, 

the material builds laterally and vertically. Geometrically, the extent to which the material 

accumulates is limited by the steepest angle at which the material can attain before gravity 

(and environmental forces) forces the material to avalanche and redistribute downslope. The 

avalanched sediment comes to rest when some equilibrium angle is reached. The limiting 

angle of repose (shearing angle, s) for subaqueous dredged sediments is steepest angle the 

material can attain before avalanching. The post-sheared angle (ps), defines the slope of the 

avalanched dredged material after is has come to rest [Larson and Krause 1989, Allen 1970]. 

The areal and vertical configuration of aggregate dredged material mounds at ODMDSs is

controlled by the shearing angle and post-sheared angle of the dredged material.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-68

The range in avalanche angles varies considerably with material type and the forcing 

environment. The angle of repose for dry loose sand is 26oto 30o from horizontal [Hough 

1957]. Reported values for the subaqueous angle of repose (shearing angle) for sand placed 

on the seabed range from 1.8o to 8o[USACE 1995 and Johnson 1995]. Reported values for 

the angle of repose for highly disturbed and minimally disturbed cohesive sediments placed 

on the seabed are 0.3o and 10o respectively.

At the Yaquina ODMDS, the angle at which sandy dredged material begins to avalanche 

(shearing angle, s) varies between 1.7o and 2.5o (tanf =z/x= z/y). These values are 

based upon the assessment of recent bathymetric surveys of the dredged material mound at 

the Section 103 ODMDS. The angle at which avalanching stops (post-sheared angle, ps) 

once it has begun was estimated to be 1.5o. These values will define the steepness at which 

dredged material is permitted to accumulate during the MDFATE simulation.

Summary of Yaquina Dredged Material Parameters

The following dredged material parameters will be used in the DRP fate models when 

simulation activities are pursued in later phases of this investigation:

Dredged material type = fine to medium sand, SP

D75 material dredged from channel = 0.20 mm.

D25 material dredged from channel = 0.15 mm.

Fines content (D<0.0625 mm) = 2 % (silt).

S.G. of dredged material solids = 2.65.

Cs (disposal) = concentration of solids by volume in the disposal vessel = 0.551.

ed = depositional void ratio = 0.815.

s = subaqueous shearing angle = 1.7o, ps = subaqueous post-shearing angle = 1.5o.

Surface Waves - Simulated Data

A synthetic time series for the annualized wave environment offshore of Yaquina Bay was 

generated using HPDSIM, a PC-program developed by USACE [Borgman and Scheffner 

1991]. The program uses a finite length wave record to compute a matrix of coefficient 

multipliers that can be used to generate arbitrarily long time sequences of simulated wave data 

which preserve the primary statistical properties of the source finite data set. The wave 

height, period, and direction for the synthetic data set are based upon the 20-year Wave 

Information Study (WIS) station 41 - Phase II database [Corson et al. 1987]. WIS station 41 

is located 30 miles offshore Yaquina Bay. The summary statistics for station 41 are: 

Mean WIS Parameters

Water depth at WIS II-41 = 1500 feet.

H1/3 = average annual significant wave height = 9.8 feet.

σh = annual standard deviation of H1/3 = 4.2 feet.

Ts = wave period (associated with H1/3) = 11.2 sec.

σh = annual standard deviation of Ts = 2.5 sec.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-69

Most frequent wave direction band = 292°(T).

Wave direction for largest wave height = 209 °(T).

An example of the simulated wave environment for wave height (H1/3) and wave period (Ts) 

for a 1-year duration (time = 0 corresponds to January 1) is shown in Figure B-19. Note that

the waves are more severe during the late fall, winter, and early spring than other times of the 

year. The maximum and minimum significant wave heights (H1/3) for the synthetic wave year 

were about 30 feet and 3 feet, respectively. 

Based on favorable comparisons of synthetically generated wave data (WIS) and observed 

wave data for other locations on the Oregon coast [USACE 1995], the WIS data were 

considered adequate for simulating the wave environment at Yaquina Bay and for use as input 

for sediment fate modeling.

Simulated Shelf Tidal Elevations and Currents

The shelf tidal environment at the Yaquina Bay ODMDSs was simulated using the five

primary tidal constituents generated from the ADCIRC-derived database for the Eastern North 

Pacific Coast [Hench et al. 1994 and Luettich 1995]. ADCIRC (Advanced CIRCulation) is a 

two-dimensional finite-element model developed by USACE to simulate hydrodynamic 

circulation (tides) along shelves and coasts. The time series shown in the top of Figure B-20

represents a simulated equilibrium shelf tide 5 miles offshore Yaquina Bay for 1 month (720 

hours). The referenced tidal datum is MLLW. An equilibrium tide is harmonically correct to 

the actual case, but is not referenced to a specific date or time. The maximum tidal range for 

the simulated tide shown in Figure B-20 is 11 feet, which agrees with the observed range for 

the Yaquina bar. The tidal phasing of the simulated and observed tidal data also compared 

favorably.

Depth-averaged tidal currents (u,v) applicable for the Yaquina bar are shown in the bottom of 

Figure B-20 and were also produced using the ADCIRC model. The tidal current simulated

by the ADCIRC model accounts only for the shelf tidal current, based on the approach and 

passage of the tidal wave. The estuarine tidal current generated by flood and ebb flow from 

the Yaquina Bay estuary is not included in the ADCIRC-predicted tidal current. Based on 

favorable comparisons of synthetically-generated shelf tidal data (ADCIRC) and observed 

tidal data for other locations on the Oregon coast [USACE 1995], the ADCIRC data were 

considered adequate for simulating the wave environment at Yaquina Bay and for use as input 

for sediment fate modeling.

Observed Currents Applicable for Yaquina Bay ODMDSs

Definition of the residual current regime is of prime importance, since currents significantly 

affect the short-term fate of dredged material and completely control the long-term fate. For 

inner-shelf waters (depths <120 feet), the residual current regime is influenced by wind-stress, 

waves, tidal, and estuarine processes.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-70

Figure B-19. Wave environment offshore of Yaquina Bay simulated from WIS-II data. Top 

graphic is for wave height and bottom graphic is for wave period. Time 0 corresponds to January 1 

and Time 365 corresponds to December 31.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-71

Figure B-20. ADCIRC simulated tidal elevation and current at Yaquina Bay ODMDS for 2-week 

period. Top graphic is for tidal variation of water surface and bottom is for tidal-induced current.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-72

The term residual refers to a time-averaged or long-term net (over days, weeks, or months) 

result, which does not include short-term (hours to days) variations. A residual currents 

describes the net flow (direction and speed) for a given location during a given time interval 

and does not include shelf tidal currents, storm-induced currents, and other episodic events.

In close vicinity to the jetty entrance to Yaquina Bay, discharge from the estuary influences 

nearshore circulation from the surface to depths of 70 feet for distances of 1-2 miles offshore. 

Large scale oceanic currents such as the California or Davidson currents generally influence 

the direction of the shelf current regime, but do not directly affect the magnitude of inner shelf 

currents. Considerable effort was invested to reliably specify the residual current regime near 

the Yaquina Bay. Residual current data relevant to Yaquina Bay ODMDS designation and 

management are summarized below.

Bottom Currents due to Estuarine Discharge and Jetty Effects

On August 21, 1993, an acoustic Doppler current profiler (ADCP) was used to measure 

bottom velocities in the vicinity of the Yaquina Bay jetty entrance. The ADCP velocity data 

was measured 2 hours after high tide during an accelerating ebb-tide condition, but before 

maximum ebb tide. Point measurements of seaward flow at the mouth of the jetties reported 

near bottom velocities exceeding 3 ft/sec with total volume flow out of the jettied entrance 

measured by the ADCP at over 81,000 cfs [USACE 1993]. The riverine discharge from the 

Yaquina River was considered to have a negligible contribution to the observed estuarine 

discharge. Rainfall within the Yaquina River catchment was minimal during the time of data 

collection. The ADCP measured bottom current is summarized as:

VADCP = 3 ft/sec at 240° (T) during ebb-flow applicable throughout year

A mild wind out of the northeast was present producing a current velocity field tending 

toward the south-southwest (alongshore) during most measurements taken north and west of 

the northern jetty and north reef. Tidal outflow dominated the current filed at locations 

between the jetties and seaward of and in line with the entrance channel. Current 

measurements obtained north of the north jetty and inshore of the north reef showed a 

redirection of the alongshore flow in the offshore direction. Although a slight intensification 

of current velocity was observed at the north jetty head, potential for greater current velocities 

can be realized with a stronger alongshore wind (current) being present [USACE 1993].

The flow field observed at the Yaquina Bay jetty entrance on August 21, 1993, was assumed 

to represent typical estuarine ebb-flow conditions. Given that the alongshore wind field (and 

associated current) were minimal during the above measurement period, it is assumed that the 

combined current (estuarine flow + deflection of littoral current along jetties) at the jetty 

entrance is typically higher than that which was observed on August 21, 1993. Given that the 

combined current field is typically higher than the above measured data, the observed current 

is assumed to represent average conditions for the combined current field at the jetty entrance.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-73

Surface Currents at the North Reef

Oregon State University conducted circulation measurements inshore of the north reef 

between the north jetty and Yaquina Head [Neal 1969]. Wave approach angle and hydraulic 

(flow redirection) effects of the north jetty had significant affect upon the observed nearshore 

flow field. Observed currents in the near surface (upper 10 feet) of the water column are 

summarized below:

November - February: Vreef = 0.4 ft/sec @ 45° (T)

March - October: Vreef = 0.4 ft/sec @ 225° (T)

Bottom Current at the Interim ODMDS

Bottom currents in the Interim ODMDS were observed by SCUBA diver during June 1977 

[Montagne-Bierly Associates 1977]. Bottom currents were oriented toward the southwest and 

were heavily influenced by surge caused by waves passing overhead. The wave conditions 

during current observation were 4-foot swells from the northwest. Observed bottom currents 

are summarized below:

June: VODMDS = 0.62 ft/sec @ 225° (T)

Surface Currents 10 miles Offshore of Newport

A description of the seasonal mid-shelf surface current has been developed from transport 

data obtained by the transit of surface drift bottles released between 1959-1963 [Burt 1964]. 

The inferred surface currents are summarized below:

November - February: Voffshore = 0.82 ft/sec @ 0° (T)

March - October: Voffshore = 0.82 ft/sec @ 180° (T)

Geostrophic Currents

Estimates of geostrophic currents based on hydrographic observations from the Newport 

Hydro Line [Huyer 1977] agree well with seasonal observation of flow inferred from direct 

measurement [Huyer 1975]. In general, geostrophic currents were aligned with bottom 

contours with northerly mean flows deeper than 160 feet and southerly flows above. The 

summer geostrophic current at three varying cross-shore locations is summarized below:

June - September: VG70 = 0.6 ft/sec @ 187° (T) water depth = 70 feet

VG150 = 0.2 ft/sec @ 202° (T) water depth = 150 feet

VG200 = 0.2 ft/sec @ 63° (T) water depth = 200 feet

Currents Observed at a Similar Nearshore Location – Coos Bay

Detailed current measurements have been obtained from other similarly situated Oregon 

nearshore ODMDSs. The most thorough study has been conducted at Coos Bay, Oregon 

[Sollitt et al. 1984]. Seasonal measurements were made over two-week periods are 

summarized below (values reported from measurements at 1/3 total depth):
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-74

November - March: VCoos = 0.75 ft/sec @ 30° (T)

April - July: VCoos = 0.75 ft/sec @ 210° (T)

August - October: VCoos = 0.50 ft/sec @ 205° (T)

Calculation of Residual Current for Yaquina Bay ODMDSs

To represent the residual current at the proposed North and South ODMDSs, an annualized 

residual (depth averaged) current was developed based on a two-point value for seasonal 

representation. The individual current observations described above were vector-averaged 

according to the proper seasonal sequence of each current observation. This provided a 

realistic estimate for seasonally varying depth-averaged currents; data which was used to 

simulate the fate of dredged material to be placed at the proposed North and South ODMDSs. 

The annualized residual current applicable for locations within the 4.5-mile ZSF and where 

water depth is 100-150 feet is described below:

May - October: Vresidual = 0.53 ft/sec @ 202° (T)

November - April: Vresidual = 1.25 ft/sec @ 298° (T)

Note that the current affecting the proposed North and South ODMDSs is primarily a function 

of open coast flow, being influenced mainly by wind/waves, tide, and offshore processes. 

Estuarine current affects are, at best, weak within the North and South ODMDSs. This is 

reflected in the residual current described above.

The total depth-averaged current at any given point in time is estimated by adding the 

seasonal residual bottom current (above) to the simulated depth-averaged tidal (ADCIRC) 

current. The preceding section defined all oceanographic data required to successfully 

simulate dredged material behavior using the FATE models.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-75

Section 9

GEOLOGIC FEATURES

Introduction

Geologically speaking, the Oregon coast is young and active. Regional uplift of several 

hundred feet, intense volcanic activity, and tremendous erosion and sedimentation has 

occurred over the past several million years to change the shape of the coastline. Changes in 

sea level caused the ancient coastline to vary from several miles inland to over 10 miles 

offshore.

This history has resulted in the variety of coastal features we now see from massive volcanic 

headlands such as Cape Lookout to massive sand dunes such as the Oregon dunes near 

Florence. The Pacific Ocean has affected this geologic framework to produce spectacular 

effects within historic times. Coastal landslides and severe beach erosion are common in 

certain areas and there are numerous submerged nearshore reefs and exposed offshore rock 

islands or stacks.

General Geology

The geologic sequence at the outer portion of Yaquina Bay consists of over 50 feet of terrace 

deposits of semi-consolidated sands and silts and occasional gravel formed by marine forces 

less than one million years ago overlying much older, eroded sandstones, siltstones, and 

mudstones. These terrace deposits form the steep sea cliffs north of the north jetty but are 

absent for 1.5 miles to the south where modern sands form the South Beach area. A geologic 

map and generalized cross-section of the Yaquina Bay area are shown in Figures B-20A and 

B-21.

A limited number of borings and surface geology identifies the nature of the underlying rock. 

A succession of Miocene siltstones, mudstones, and sandstones form the bedrock material 

beneath the bay. The oldest sequence, the Nye Mudstone, comprises the majority of the 

bedrock portion of western Yaquina Bay. The Nye Mudstone is a predominantly medium to 

dark gray, massive-bedded sequence of mudstones with some siltstone and sandstone lenses. 

Within Yaquina Bay, the formation is approximately 4,400 feet thick and extends from near 

the eastern edge of the bay to a point about 2,400 feet west of the Highway 101 Bridge. West 

of the bridge these strata have an average strike of north 5 degrees west, and a dip of 18 

degrees toward the west. Beds of this formation are exposed at low tide on the north shore of 

the bay west of the highway bridge.

The Astoria Formation unconformably overlies the Nye Mudstone and is found in the outer 

navigation channel area from about 2,400 feet west of the highway bridge and westward. 

Precise location of the contact between the Nye and Astoria Formations is difficult to 

recognize, as the lower Astoria beds are very similar to the upper Nye beds. A small wedge 

of this formation is exposed near the base of the sea cliff on the north side of the bay.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-76

Figure B-20A. Geologic map of Yaquina Bay area, Newport, Oregon (from Snavely et al. 1964).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-77

Figure B-21. Generalized geologic cross section at Newport, Oregon.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-78

It has been determined through drill cores taken from navigation channel explorations in 1961 

that the strike of the beds is north 8 degrees east, with a dip of 15 degrees toward the west. 

The most common beds of this formation are olive-gray, fine- to medium-grained arkosic 

sandstones, carbonaceous siltstones, mudstones and claystones. These beds were deposited in 

a nearshore environment (Snavely et al. 1964).

Just offshore of the jetties is an unnamed unit that unconformably overlies the Astoria 

Formation. This unit consists of a basalt flow, water-laid fragmental basaltic debris, tuffs, and 

fine-grained sandstone. The more resistant basalt flow at the base of this unit forms 

northerly-trending Yaquina Reef, located about 4,000 feet offshore, which in this area is about 

55 feet thick. The Yaquina Reef is located immediately north and south of the Yaquina Bay 

jetties and appears to be offset by a north-south trending fault that might extend southward 

along the eastern margin of the project area (Snavely et al. 1964).

Figure B-21, which shows a generalized cross section applicable to Yaquina Bay and offshore

vicinity, was obtained using sub-bottom profiling techniques (Earth Sciences Associates et al.

1984). Recent marine sand forms a discontinuous cover over the underlying rock. At the 

contact between the less resistant mudstone and more resistant sandstone a thick lens of sand 

has accumulated. This has also happened at the basalt-sandstone contact. Not shown, but 

present are discontinuous layers of highly resistant tuff within the sandstone. The extent and 

type of rock are unknown beyond the basaltic layer. The sand layer ranges from 5-35 feet 

thick over an irregular rock surface throughout the nearshore area adjacent to Yaquina Bay.

Unconsolidated Marine Deposits

Sediment movement on the Oregon continental shelf consists of two mechanisms depending 

on the size of the sediment. Anything finer than sand size (0.0625 mm) is carried in 

suspension in the water column and removed far offshore. The almost total lack of silts and 

clays within ten miles or more of most of the Oregon coast attests to the efficiency of this 

mechanism. Sediments sand-size or coarser may be suspended by wave action near the 

bottom, and are moved by bottom currents as bedload transport. There is almost a complete 

lack of finer silts and clays offshore of Yaquina Bay. Silt appears offshore from Yaquina Bay 

at a depth of 300 feet. The lack of silt or clay is likely due to the high wave energy regime. 

Summer wave conditions produce bottom ripples to depths over 300 feet while winter storm 

waves can produce ripples to over 600 feet (Komar 1972). The generalized bathymetry and 

surface sediment coverage of the central Oregon continental shelf is shown in Figure B-22.

Seabed Sediments near Yaquina Bay

Fine sand underlies the major portion of area in the Yaquina Bay 4.5-mile ZSF. Figure B-10 

shows the seabed distribution of sand vs. exposed rock outcroppings within the 4.5-mile ZSF. 

Note the large area of seabed rock exposure occurs in the area directly to the north of the 

Section 103 disposal site. These seabed rock outcroppings contribute coarser sediment to the 

nearshore area as the rock surfaces are eroded by wave action. The classification of bottom 

sediments shown in Figure B-10 was developed from a high-resolution side-scan sonar survey

conducted during July 1995 (Geo Recon International Inc. 1995).
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-79

Figure B-22. Surface features and sediment cover of the continental shelf off central Oregon.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-80

The underlying geology, marine forces, and human action influence the nearshore bathymetry 

at Yaquina Bay. From the tip of the full-authorized end of the north jetty the Yaquina Reef 

extends northward to Yaquina Head. This reef, with depths less than twelve feet in places, is 

an eroded layer related to the basalt headland at Yaquina Head. There are numerous 

submerged rock outcrops between the reef and North Beach. Note the irregularity of this 

region shown in Figure B-10. These outcrops are probably part of the more resistant

sandstone layers. South of the jetties, the offshore reef turns seaward and is less continuous. 

There are few indications of submerged rock outcrops inshore of the reef and the South Beach 

area is a wide expanse of recent sand.

Sediment Accretion

A combination of littoral transport and jetty construction has resulted in significant beach 

advance south of the jetties (i.e. South Beach State Park). This accretionary process began in 

the 1882 with the first attempt to build the South Jetty and has continued as the jetty has been 

progressively extended. Beach accretion has not been apparent north from the jetties except 

for the area immediately adjacent to the North Jetty. The offshore reef apparently limits 

onshore sand transport in the area between the North Jetty and Yaquina Head (4 miles to the 

north).

Seaward of the reef complex, the bottom slopes about 60 feet per mile out to below elevation 

-120 feet (MLLW) where the slope flattens to about 20 feet per mile out to over -250 feet. 

There is a pronounced seaward bulge of bottom contours between -60 feet and -120 feet 

extending west from the Interim disposal site as shown on Figure B-10. This bulge feature is

composed of previously placed dredged material and sediment transported out of the Yaquina 

Bay estuary during high ebb-tide discharge conditions.

Geophysical Explorations

Geophysical explorations were conducted in 1993 in an area just offshore and adjacent to the 

North Jetty. These explorations were conducted in an effort to better identify the physical 

characteristics adjacent to the North Jetty, and to aid in determining the cause for repeated 

failures of the structure. Explorations consisted of side-scan sonar surveys, seismic reflection 

and seismic refraction techniques, sub-bottom profiling, and water jet probes. These 

techniques combined to map out better the location of the Yaquina Reef, show the sub-bottom 

characteristics of the different geologic units, and identify the presence and depth to bedrock 

in the vicinity of the North Jetty. Scattered bedrock exposures present within Yaquina Reef 

and on the north side of the North Jetty are located and shown on Figure B-10.

1995 Side-scan Sonar Survey Results

A side-scan sonar survey was conducted in 1995 of an area approximately 4-miles long by 2-

miles wide, of the area immediately offshore of the Yaquina jetties. The purpose of this study 

was to gain a better understanding of the surficial material types on the ocean floor for the 

potential of identifying future offshore disposal sites. Figure B-10 shows the location of the

different material types within the study area.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-81

This survey identified areas of bedrock outcroppings on the westward side of the Yaquina 

Reef, extending out a distance of up to a mile. These outcroppings follow the basic trend of 

the geology in the area, with beds dipping towards the west. The truncated edges of the more 

resistant layers provide the relief that is visible in side-scan images of the sea floor. A zone of 

coarse to medium sand is present adjacent to the westward side of the Yaquina Reef north of 

the North Jetty between the reef and outer rock exposures.

Surrounding the outcrops and the coarser sand is a blanket of fine to medium sand and silt, 

which is the most prevalent material seen offshore of this area. This material is also present 

immediately offshore of the jetties and entrance channel and obscures any bedrock exposures 

present there.

2000 Side-scan Sonar Survey

Additional surveys were conducted in 2000 to further identify material adjacent to the outer 

margins of the 1995 survey, but concentrating on two areas located both north and south of 

the jetties. The north area measured approximately 2-miles long by 1.25-miles wide, and the 

south area was 1.5-miles long by 1.25-miles wide. This survey utilized digital image 

processing techniques with a mosaic feature to more accurately define where the different 

material types occurred. Figure B-10 shows the location of the study area and the material

types represented.

Results of this survey verified the existence of rock outcroppings in the inner portion of the 

southern area. The predominant material type present on the bottom in both areas was also 

verified to be fine to medium sand and silt. This survey also showed the presence of gravel 

deposits, and gravel interspersed with sand and silt ribbons. Both of these material types 

occur mostly in the western portion of the study area.
Appendix B, Yaquina Bay ODMDS Evaluation/EA B-82

Section 10

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