Hydraulic Survey and Scour Assessment of

Bridge 524, Tanana River at Big Delta, Alaska

Scientific Investigations Report 2006–5282

Prepared in cooperation with the Alaska Department of Transportation and Public Facilities 

U.S. Department of the Interior

U.S. Geological Survey

Hydraulic Survey and Scour Assessment of 

Bridge 524, Tanana River at Big Delta, Alaska

By Thomas A. Heinrichs, Dustin E. Langley, Robert L. Burrows, and Jeffrey S. Conaway

Prepared in cooperation with the

Alaska Department of Transportation and Public Facilities

Scientific Investigations Report 2006–5282

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Heinrichs, T.A., Langley, D.E., Burrows, R.L., and Conaway, J.S., 2007, Hydraulic survey and scour assessment of 

Bridge 524, Tanana River at Big Delta, Alaska: U.S. Geological Survey Scientific Investigations Report 2006-5282, 

66 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Background.....................................................................................................................................................1

Purpose and Scope .......................................................................................................................................3

Data Collection...............................................................................................................................................4

Computation of Water-Surface Profiles.....................................................................................................6

Scour Computations......................................................................................................................................8

Channel Changes and Bank Erosion ........................................................................................................15

Conclusions...................................................................................................................................................16

References Cited..........................................................................................................................................16

Appendix A. Water-Surface Profile Model Data Files........................................................................17

Appendix B. Survey Data ........................................................................................................................47

Figures

Figure 1. Map showing location of the Tanana River at Big Delta study unit, Alaska ......... 2

Figure 2. Schematic showing surveyed cross sections at the Tanana River at Big

Delta, Alaska ................................................................................. 3

Figure 3. Graph showing upstream cross sections and pier soundings at bridge 524,

Tanana River at Big Delta, Alaska ......................................................... 3

Figure 4. Graphs showing depth-velocity profiles (A) near bluff downstream of bridge,

(B) at cross section Slough 1, 10 feet from right edge of water, (C) at cross

section Slough 1, 20 feet from right edge of water, (D) at cross section Slough

2, 10 feet .................................................................................... 5

Figure 5. Graph showing estimated pier-scour magnitudes for the 100-year-flood

discharge computed from model output with starting water-surface

elevations from 985.0 to 993.5 feet at the Tanana River at Big Delta, Alaska......... 13

Figure 6. Graph showing channel changes at cross section Exit 1 from 1971 to 1996,

Tanana River at Big Delta, Alaska ......................................................... 15

Tables

Table 1. Bed material samples, Tanana River at Big Delta, Alaska.............................. 4

Table 2. Water-surface profiles computed with WSPRO, Tanana River at Big Delta, 

Alaska ....................................................................................... 7

Table 3. Bridge-scour computations, Scenario 1, Tanana River at Big Delta, Alaska,

Bridge 524 .................................................................................... 9

Table 4. Bridge-scour computations, Scenario 2, Tanana River at Big Delta, Alaska,

Bridge 524 .................................................................................... 10
iv

Conversion Factors, Datum, and Abbreviations and 

Acronyms

Conversion Factors

Multiply By To obtain

cubic foot per second (ft3

/s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter

foot per second (ft/s) 0.3048 meter per second

inch (in.) 2.54 centimeter 

inch (in.) 25.4 millimeter

mile (mi) 1.609 kilometer

pounds per square foot (lb/ft2

) 0.04788 kilopascal

square foot (ft2

) 929.0 square centimeter

square mile (mi2

) 2.590 square kilometer

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F - 32)/1.8

Vertical Datum

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929—A 

geodetic datum derived from a general adjustment of the first-order level nets of the United 

States and Canada, formerly called Sea Level Datum of 1929.

Abbreviations and Acronyms

Abbreviations and 

Acronyms Meaning

ADOT&PF Alaska Department of Transportation and Public Facilities

USGS U.S. Geological Survey

WSPRO Computer model for water-surface profile

Tables—continued

Table 5. Bridge scour computations, Scenario 3, Tanana River at Big Delta, Alaska,

Bridge 524 .................................................................................... 11

Table 6. Bridge-scour computations, Scenario 4, Tanana River at Big Delta, Alaska,

Bridge 524 .................................................................................... 12

Table 7. Estimated pier-scour depths for the 100-year-flood discharge computed from

model output with starting water-surface elevations from 985.0 to 993.5 feet

at the Tanana River at Big Delta, Alaska ................................................ 13

Table 8. Pier-scour computations for discharge measurements, Tanana River at Big

Delta, Alaska, August 26, 1996 ............................................................ 14
Abstract

Bathymetric and hydraulic data were collected 

August 26–28, 1996, on the Tanana River at Big Delta, 

Alaska, at the Richardson Highway bridge and Trans-Alaska 

Pipeline crossing. Erosion along the right (north) bank of the 

river between the bridge and the pipeline crossing prompted 

the data collection. A water-surface profile hydraulic model 

for the 100- and 500-year recurrence-interval floods was 

developed using surveyed information. The Delta River enters 

the Tanana immediately downstream of the highway bridge, 

causing backwater that extends upstream of the bridge. Four 

scenarios were considered to simulate the influence of the 

backwater on flow through the bridge. Contraction and pier 

scour were computed from model results. Computed values 

of pier scour were large, but the scour during a flood may 

actually be less because of mitigating factors. No bank erosion 

was observed at the time of the survey, a low-flow period. 

Erosion is likely to occur during intermediate or high flows, 

but the actual erosion processes are unknown at this time.

Introduction

Alaska Department of Transportation and Public 

Facilities’ (ADOT&PF) bridge 524 crosses the Tanana River, 

a major tributary of the Yukon River, at milepost 275.4 on 

the Richardson Highway (fig. 1). The Delta River flows into 

the Tanana immediately downstream of the highway bridge, 

and the Trans-Alaska Pipeline crosses the river about 500 ft 

upstream (fig. 2). Backwater on the Tanana River from the 

confluence with the Delta River can extend upstream of bridge 

524. The extent of backwater and its effects on river hydraulics 

through the bridge depends on the discharge in both rivers. 

The ADOT&PF commissioned the U.S. Geological Survey 

(USGS) to complete a bathymetric and hydraulic survey of 

the Tanana River at Big Delta, Alaska, simulate the river 

hydraulics, and investigate streambed-scour problems at the 

site. 

The USGS initially identified a potential streambedscour problem at bridge 524 in 1975 (Norman, 1975). Norman 

(1975) was able to observe the site at high flows, and some 

findings are contained in the analysis in section, “Scour 

Computations.” Potential scour was investigated again for 

a statewide scour assessment (Heinrichs and others, 2001). 

Pier-scour computations from this preliminary study for the 

100-year recurrence-interval flood were more than 35 ft. In 

the spring of 1996, the right (north) bank of the river began 

to erode substantially. About 10 ft of the bank had sloughed 

into the river by mid-April 1996, and the concern was that the 

continued erosion could affect both the highway bridge and 

the pipeline crossing. Hydraulic data and computations were 

needed to design a proposed protective dike on the north bank.

Background

The Tanana River is a glacier-fed river that carries large 

sediment loads. The basin area upstream of the bridge is 

13,500 mi2 with an average elevation of 3,440 ft. Six percent 

of the basin is glaciated; 2 percent is lakes, ponds, and 

swamps; and 50 percent is forest. Mean annual precipitation is 

22 in. and mean January minimum temperature is -14°F (Jones 

and Fahl, 1994.)

A slough of the Tanana branches off the main channel 

approximately 8,000 ft upstream of the bridge and then 

reenters approximately 500 ft upstream of the bridge. The 

Delta River enters the Tanana River immediately downstream 

of the bridge on river left. The Delta River has formed a 

braided delta at this confluence and forces the majority of 

the flow in the Tanana River towards its right bank, thus 

accelerating flow and exacerbating streambed scour. The 

confluence with the Delta River also creates backwater that 

propagates upstream through the bridge reach. The shape of 

the delta and extent of backwater are constantly changing and 

influencing the hydraulics at the bridge.

Hydraulic Survey and Scour Assessment of Bridge 524, 

Tanana River at Big Delta, Alaska

By Thomas A. Heinrichs, Dustin E. Langley, Robert L. Burrows, and Jeffrey S. Conaway
AKASC19-5014_Figure 01

Tanana

River

Susitna River

Paxon

Glennallen

Delta Junction

Fairbanks

Nenana

Tok

George

Parks

Highw

ay

3

1

8

Denali

Highway

4

2 5

Alaska Highway

Copper

River

Taylor Hig

hway

Ric

h

ardson

High

w

a

y

D

elta

River

Richardson

Highway

Base from U.S. Geological Survey digital data, 1:63,360

Universal Transverse Mercator projection

Figure

location

ALASKA

YUKON

Bridge 524

63°

64°

65°

149° 147° 145° 143°

0 20

0 20 40 60 80 100 120 KILOMETERS

40 60 80 100 MILES

Figure 1. Location of the Tanana River at Big Delta study unit, Alaska.

   Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
_fig02

Figure 2. Surveyed cross sections at the Tanana River at Big Delta, Alaska.

Cross sections are referred to in text by name and corresponding number in 

the figure.

Bridge 524 was constructed in 1966. It 

consists of a 399-ft, steel-through truss span and 

4 steel-girder spans, each about 95 ft long (fig. 3). 

The piers are not aligned directly with the flow, 

therefore the river strikes them at an angle. This 

“angle of attack” of the flow at the piers has 

the potential to increase the local scour at the 

piers significantly and is discussed in the Scour 

Computations section.

Purpose and Scope

This report presents the results of a field 

survey of the Tanana River at Big Delta, 

Alaska, water-surface profile hydraulic-model 

computations, and bridge-scour computations. 

Some interpretation is made of the scour results, 

and erosion processes are considered. The 

report’s primary purposes are to present the actual 

observations made during the field survey and the 

hydraulic and scour results that follow from the 

observations. These observations and computations 

are intended to support the planning and design 

efforts of all parties who have an interest in this 

reach of the Tanana River. The Tanana and Delta 

Rivers are very dynamic; therefore, the survey, 

hydraulic models, and scour computations are 

representative of the conditions during the time of 

the survey. 

Bathymetric and hydraulic data were 

collected during August 26-28, 1996, by the USGS 

as a cooperative effort with ADOT&PF. Eighteen 

channel cross sections were surveyed, velocity 

profiles and discharge were measured, soundings 

were made at the piers, and bed material was 

sampled. Cross-sectional and other surveyed data 

were used as input to the step-backwater watersurface profile (WSPRO) model (Shearman, 1990). 

Using this model, the water-surface profiles for the 

100- and 500-year recurrence-interval floods were 

computed, and potential scour at the bridge was 

calculated.

DISTANCE FROM LEFT BANK, IN FEET

0 200 400 600 800

1010

1000

990

980

970

960

950

940

ELEVATION, IN FEET

5/14/1971

7/16/1971

8/26/1996

UPSTREAM SOUNDINGS

DOWNSTREAM SOUNDINGS

PIER 5 PIER 4 PIER 3

PIER 2

Figure 3. Upstream cross 

sections and pier soundings at 

bridge 524, Tanana River at Big 

Delta, Alaska. Pier soundings 

were made on August 26, 1996.

Purpose and Scope   
Data Collection

A total station was used to survey points on the bank, 

road, and bridge, and to locate the ends of the cross sections 

measured in the river channel. Distance across the channel was 

measured using a microwave-frequency distance meter and 

depths were measured with a fathometer or sounding weight.

All surveyed points and channel soundings were 

referenced to a single arbitrary coordinate system. The origin 

of this system is (Easting, Northing)=(10,000 ft, 10,000 ft) 

at the center of the south end of the bridge. The system was 

aligned with north using the bridge azimuth listed on the asbuilt plans (S36°26’52”E). The elevation was referenced to a 

brass cap listed on the plans as 998.94 ft (location E=9,986.6, 

N=9,991.4).

Eighteen river cross sections were surveyed. Four of 

these cross sections were located downstream of the bridge, 

one each at the upstream and downstream sides of the bridge, 

five upstream of the bridge, and four in the slough near its 

mouth. The remaining two cross sections were about 8,000 ft 

upstream—one across the mouth at the head of the slough and 

the other across the main channel just upstream of the head of 

the slough (fig. 2).

The two sections surveyed about 8,000 ft upstream were 

made only to evaluate channel capacity at the head of the 

slough and the main channel, as well as to document existing 

conditions. These sections were not referenced to the same 

coordinate system as the other surveyed points and channel 

soundings.

Two discharge measurements were made on 

August 26, 1996—one measuring the full flow of the 

Tanana River just upstream of the bridge (21,500 ft3/s), and 

the second measuring the flow in the slough (2,570 ft3/s). 

Depth soundings were made around the piers (fig. 3). Debris 

obstructed some areas around the piers, making some 

soundings unfeasible. Sounding elevations indicated the 

downstream left end of the pier 5 footing was exposed.

Water velocity was measured at several locations using 

a current meter (fig. 4A-F). The current was extremely slow 

along the right bank upstream of the bridge abutment and 

downstream of the mouth of the slough—the section of bank 

that was eroding at the time of this study. At the time of the 

survey, a silt bar was forming 50–100 ft off the bank in this 

reach. The velocity profile measured near the right bank 

several hundred feet downstream of the bridge had the largest 

average velocity (6.5 ft/s) (fig. 4A-F). Water velocity along 

the right bank of cross section Slough 4 was too slow to be 

measured

Bed material was sampled under the bridge and in the 

channel about 700 ft upstream of the bridge (table 1). A sieve 

analysis was not performed because the samples were too 

small to give a statistically valid distribution. Norman (1975) 

also sampled the bed material under the bridge in the scour 

hole on the left side of pier 5 and found a median diameter 

(D50) of 30 mm (coarse gravel) and a 90th percentile diameter 

(D90) of 50 mm (very coarse gravel). He suggested that the 

streambed material probably is generally coarser at the other 

scour holes under the bridge that had swifter, deeper flow. He 

also sampled the bed upstream of the bridge and found a D50

of 14 mm (medium gravel) and D90 of 58 mm (very coarse 

gravel).

Table 1. Bed material samples, Tanana River at Big Delta, Alaska. 

[Sieve analysis not performed; this data to be used only as an estimate of material size. Sizes were measured along the 

B-axis using calipers. (B-axis is the mid-length axis—the one that limits the passage through a sieve.)]

Location Material

Bridge cross section

Right one-half of Span 1 (abutment 1 to pier 2) Gravel and cobble (largest clast: 65 millimeters)

Left one-half of Span 1 (abutment 1 to pier 2) Sand

Span 2 (pier 2 to pier 3) Sand and gravel (largest clast: 35 millimeters)

Span 3 (pier 3 to pier 4) Small amount of sand and one 40-millimeter piece of gravel

Span 4 (pier 4 to pier 5) Obtained no sample - bed is armored

Span 5 (pier 5 to abutment 6) Obtained no sample - bed is armored

Approach cross section

Right one-third of channel Sand and gravel (largest clast: 40 millimeters)

Middle one-third of channel Gravel and cobble (largest clast: 70 millimeters)

Left one-third of channel Small amount of fine gravel (~3 millimeters) and

one piece of coarse gravel (55 millimeters)

   Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Figure 4. Depth-velocity profiles (A) near bluff downstream of bridge, (B) at cross section Slough 1, 10 feet from right edge of 

water, (C) at cross section Slough 1, 20 feet from right edge of water, (D) at cross section Slough 2, 10 feet from right edge of 

water, (E) at cross section Slough 3, 10 feet from right edge of water, and (F) at cross section Slough 4, 10 feet from right edge of 

water, Tanana River at Big Delta.

0.0

0.2

0.4

0.6

0.8

1.0

0.0 2.0 4.0 6.0 8.0 10.0

VELOCITY IN FEET PER SECOND

RELATIVE DEPTH

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

DEPTH BELOW SURFACE,

IN FEET

AVERAGE

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0

VELOCITY, IN FEET PER SECOND

RELATIVE DEPTH

0.0

1.0

2.0

3.0

4.0

DEPTH BELOW SURFACE,

IN FEET

AVERAGE

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0 4.0

VELOCITY, IN FEET PER SECOND

RELATIVE DEPTH

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

DEPTH BELOW SURFACE,

IN FEET

AVERAGE

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0 4.0

VELOCITY, IN FEET PER SECOND

RELATIVE DEPTH

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

DEPTH BELOW SURFACE,

IN FEET

AVERAGE

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0 4.0

VELOCITY, IN FEET PER SECOND

RELATIVE DEPTH

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

DEPTH BELOW SURFACE,

IN FEET

AVERAGE

0.0

0.2

0.4

0.6

0.8

1.0

0.0 1.0 2.0 3.0 4.0

VELOCITY, IN FEET PER SECOND

RELATIVE DEPTH

0.0

1.0

2.0

3.0

4.0

5.0

DEPTH BELOW SURFACE,

IN FEET

AVERAGE

A B

C D

E F

Data Collection   
Computation of Water-Surface Profiles

The magnitudes of the 100- and 500-year recurrenceinterval discharges were computed for both the Tanana River 

at the bridge and for the Delta River. The discharges for 

the Tanana River were computed as a weighted average of: 

(1) flood-frequency analysis of discharge data from 1948 

to 1957 by use of techniques described in the Interagency 

Advisory Committee on Water Data Bulletin 17B (1982), and 

(2) from regression equations based on basin characteristics 

developed by Jones and Fahl (1994). The recurrence-interval 

discharges for the Delta River were computed entirely from a 

regression of basin characteristics because limited discharge 

information was available. The computed 100- and 500-year 

recurrence-interval discharges for the Tanana River at the 

bridge are 86,700 and 95,600 ft3/s, respectively, and 36,300 

and 41,300 ft3/s, respectively, for the mouth of the Delta River.

Two WSPRO models were created using some of the 

surveyed cross sections—the first was for the main channel 

through the bridge and the second was for the slough. 

Surveyed cross sections used to generate the model of the 

main channel were: Exits 2, 3, and 4, the upstream bridge 

section, the discharge measurement section, and the approach 

section upstream of the mouth of the slough (cross section 

Approach 8000) (fig. 2). 

Measured discharge in the slough during the field 

survey was 12 percent of the total discharge in the Tanana. 

This percentage likely varies with discharge, but was used 

in the models of the high discharges because it was the only 

available observation. The volume and distribution of the 

flow entering from the Delta River affected the WSPRO 

computations upstream on the Tanana River. These results 

in turn affected the scour computations at the bridge. Four 

scenarios were modeled to account for a range of backwater 

effects on the Tanana River:

Scenario 1: 18 percent of the Delta River flow enters 

upstream of Exit 2, 47 percent upstream of Exit 3, 

65 percent upstream of Exit 4, and the remainder 

enters downstream of Exit 4. This scenario represents 

hydraulic conditions at the time of the field survey.

Scenario 2: 100 percent of the Delta River flow enters 

upstream of Exit 2. This scenario would create the 

most backwater in the Tanana River through the 

bridge, and hence the highest water surface and lowest 

velocities upstream.

•

•

Scenario 3: 100 percent of the Delta River flow enters 

between Exit 3 and Exit 4. This scenario would create 

moderately high backwater.

Scenario 4: no flow entering, and therefore, no 

backwater caused by the Delta River, resulting in the 

lowest water surface and highest velocities. This is 

a worst-case scenario, because the Delta River will 

contribute some flow for all likely scenarios.

For each scenario, a corresponding model was run in 

the slough, using the water surface in the main channel at the 

mouth of the slough to start the profile computations. The 

model was calibrated using the discharge measurement of 

21,500 ft3/s and influence from the Delta River described by 

Scenario 1. Discharge of the Delta River was not measured. 

A discharge of 9,150 ft3/s was estimated for the Delta River 

at the time of the discharge measurement of the Tanana by 

applying the ratio (43 percent) of the calculated 500-year 

recurrence interval flows for the Delta and Tanana Rivers. The 

surveyed water surface at the cross section Exit 4 was used as 

the initial water surface for profile computations and resulted 

in good agreement between modeled and observed watersurface elevations (table 2).

An important input parameter to WSPRO is the initial 

water surface at the farthest downstream cross section (Exit 4). 

The WSPRO model determined the initial water surface at the 

downstream-most section by solving the Manning’s equation 

for depth, given user-defined energy slope, discharge, and 

geometry at cross section Exit 4. Roughness values were 

calibrated from measured discharge (21,500 ft3/s) by matching 

the modeled water surface to the observed water surface. 

The energy slope (0.0005) was computed from the calibrated 

model, when water surfaces were within 0.6 ft (table 2 and 

appendix A).

Model results for all four scenarios for both the 100- and 

500-year flood flows indicate there would be a significant 

ponding upstream of bridge 524. Downstream, the braided 

channel of the Delta River would be submerged for nearly 0.5 

mile up the delta. Upstream, the banks would be under several 

feet of water and the downstream end of the island formed by 

the slough would be submerged. The Richardson Highway 

would be submerged about 1,000 ft south of the end of the 

bridge, but the model indicates a very low water-surface slope, 

so the flow over the road would be minor. The water-surface 

elevations are summarized in table 2, and the output from the 

WSPRO model runs is attached in appendix A.

•

•

 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Table 2. Water-surface profiles computed with WSPRO, Tanana River at Big Delta, Alaska.

[Abbreviations: ft3/s, cubic foot per second; DS, downstream; Q mmt, discharge measurement]

Test Case A

Surveyed water surface at Exit 4; 

for measured discharge

Test Case B

Water surface computed using friction slope 

at Exit 4; for measured discharge

Cross section Discharge

(ft3

/s)

Water-surface 

elevation (ft) Cross section Discharge (ft3/s)

Water-surface 

elevation (ft)

Exit 4 27,400 979.7 Exit 4 27,400 980.3

Exit 3 25,800 979.9 Exit 3 25,800 980.5

Exit 2 23,100 980.6 Exit 2 23,100 981.1

Bridge (DS) 21,500 980.9 Bridge (DS) 21,500 981.2

Q mmt 21,500 981.1 Q mmt 21,500 981.5

Approach 1 18,900 981.5 Approach 1 18,900 981.5

Case 1: 100-year flood Case 1: 500-year flood

Cross section Discharge

(ft3

/s)

Water-surface

 elevation (ft) Cross section Discharge(ft3/s)

Water-surface

 elevation (ft)

Exit 4 110,000 991.3 Exit 4 122,000 992.1

Exit 3 104,000 991.6 Exit 3 115,000 992.3

Exit 2 93,200 992.3 Exit 2 103,000 993.0

Bridge (DS) 86,700 992.1 Bridge (DS) 95,600 992.8

Q mmt 86,700 992.6 Q mmt 95,600 993.3

Approach 1 76,300 992.9 Approach 1 84,200 993.7

Case 2: 100-year flood Case 2: 500-year flood

Cross section Discharge

(ft3

/s)

Water-surface

 elevation (ft) Cross section Discharge(ft3/s)

Water-surface

 elevation (ft)

Exit 4 123,000 992.1 Exit 4 136,900 992.1

Exit 3 123,000 992.3 Exit 3 136,900 993.1

Exit 2 123,000 993.0 Exit 2 136,900 993.7

Bridge (DS) 86,700 993.0 Bridge (DS) 95,600 993.7

Q mmt 86,700 993.4 Q mmt 95,600 994.1

Approach 1 76,300 993.7 Approach 1 84,200 994.5

Case 3: 100-year flood Case 3: 500-year flood

Cross section Discharge

(ft3

/s)

Water-surface

 elevation (ft)

Cross section Discharge

(ft3/s)

Water-surface

 elevation (ft)

Exit 4 123,000 992.1 Exit 4 136,900 992.9

Exit 3 86,700 992.7 Exit 3 95,600 993.5

Exit 2 86,700 993.0 Exit 2 95,600 993.8

Bridge (DS) 86,700 992.8 Bridge (DS) 95,600 993.5

Q mmt 86,700 993.2 Q mmt 95,600 994.0

Approach 1 76,300 993.5 Approach 1 84,200 994.3

Case 4: 100-year flood Case 4: 500-year flood

Cross section Discharge

(ft3

/s)

Water-surface

 elevation (ft)

Cross section Discharge

(ft3/s)

Water-surface

 elevation (ft)

Exit 4 86,700 989.6 Exit 4 95,600 990.3

Exit 3 86,700 989.8 Exit 3 95,600 990.5

Exit 2 86,700 990.6 Exit 2 95,600 991.3

Bridge (DS) 86,700 990.5 Bridge (DS) 95,600 991.1

Q mmt 86,700 991.0 Q mmt 95,600 991.7

Approach 1 76,300 991.4 Approach 1 84,200 992.2

Computation of Water-Surface Profiles 
Scour Computations

Pier scour was calculated according to procedures 

outlined in HEC–18 (Richardson and Davis, 1995) for the 

100- and 500-year floods for all four scenarios described in 

tables 3–6. The USGS scour-evaluation procedure is outlined 

in detail by Heinrichs and others (2001) and summarized here. 

Flow at the bridge was divided into 20 stream tubes of equal 

conveyance by using an option in the WSPRO model program. 

The highest-velocity stream tube was selected and assumed 

to be directed at the widest pier. This assumption provides the 

maximum estimate of pier scour. This worst-case analysis is 

useful for screening purposes, whereas actual scour events 

may have mitigating factors that would reduce the actual 

scour. 

The HEC–18 pier-scour equation (Richardson and 

Davis, 1995) is recommended for both live-bed and clearwater sediment-transport conditions and is relatively sensitive 

to changes in pier geometry and angle of attack. Scour was 

computed using model results from the 100-year recurrenceinterval discharge and a 35o angle of attack over a range of 

water-surface elevations from 985.0 to 993.5 ft. A range of 

starting water-surface elevations was used in the model to 

evaluate this variable’s effect on pier-scour computations. 

Computed pier scour varied in magnitude from 43.3 to 35.9 ft 

(fig. 5, table 7) or about 20 percent for the range of starting 

water-surface elevations. The reference surface for these 

computations was the streambed elevation determined from 

the as-built survey plans. Of the four scenarios considered to 

represent the input from the Delta River, Scenario 4, with no 

modeled backwater and consequently higher flow velocities 

at the bridge, resulted in the greatest computed pier scour 

(tables 3–6). Because the pier-scour values computed at the 

Tanana River at Big Delta are large, the bridge may be in need 

of scour countermeasures. Therefore, the factors that may 

mitigate the actual scour at piers must be considered.

Mitigating factors that affect scour depths include 

reduced effective pier length, reduced angle of attack, and 

bed armor. If the entire length of the pier is not subject to the 

flow attacking from an angle, the length used for the scour 

computations must be reduced to an “effective length” or 

the scour may be over-predicted significantly (Richardson 

and Davis, 1995). The angle of attack may differ across the 

width of the bridge and be lower at some piers. The bed may 

be armored, resulting in a possible reduction of pier scour 

by as much as 30 percent (Richardson and Davis, 1995). At 

bridge 524, all three factors may apply, but caution is needed 

applying field observations made at relatively low flow 

(21,500 ft3/s) to 100- and 500-year recurrence-interval floods.

An important factor for pier-scour computations is pier 

alignment relative to the flow direction. The piers at bridge 

524 are as much as 35o misaligned with the flow. Applying 

the pier-scour computation equations using this angle, without 

considering possible mitigating factors, increases computed 

scour by a factor of 3.2 more than the scour computed for 

a 0o angle of attack. This 35o angle of attack was observed 

at higher flows by Norman (1975) and confirmed by the 

August 1996 survey. Considering effective flow length, at 

the time of this survey, only the front 50 percent of the pier 

was subject to this angle of attack. The vortex near the nose 

deflected the flow that otherwise would have struck at an angle 

farther back on the pier, and the flow was aligned with the pier 

from the midpoint back.

During the field survey, the angle of attack was the full 

35o at the left piers, but it decreased to the right with an angle 

of about 20o at pier 2, the largest pier. At higher flows, this 

situation is different. A discharge measurement of 51,600 ft3

/s 

made on August 13, 1971, indicates the angle of attack of the 

flow near all the piers was approximately 32o. Norman (1975) 

found that at high stages, the angle of attack varies between 

35o and 40o.

Bed armoring also occurs to some extent at the bridge 

site. Bed material sampled during the field survey showed the 

left half of the channel through the bridge was substantially 

armored, and the right portion of the channel consisted of sand 

and gravel. A pipe dredge consisting of a 20-pound cylinder 

with an 8-inch-diameter opening surrounded by teeth to rip 

material from the bed was not able to drag up a sample from 

the armored sections of the bed. The quantitative formulas 

presented by Richardson and Davis (1995) apply a bed armor 

correction factor (K4) for median particle diameters coarser 

than 2 mm. Norman (1975) found a D50 of 30 mm on the left 

side of pier 5, but could not sample at other piers. 

The depths observed at the time of the survey at a flow 

of 21,500 ft3/s also can be used to check the validity of the 

scour computations. The average bed elevation for the cross 

section on the upstream side of the bridge was 973 ft. The 

channel was deepest on the left side of pier 5. Soundings at 

the upstream end of the pier found an average bed elevation 

of 967 ft, indicating about 6 ft of pier scour. The effects of 

various combinations of mitigating factors are shown in 

table 8. A 35o angle of attack with a 50-percent effective pier 

length and maximum armoring (30-percent scour reduction) 

gives a computed pier scour of 11.4 ft—an over-estimate of 

5.4 ft compared to the observation.

Additional observations at higher flows would give 

more information about present conclusions. Although it 

is unlikely the information about the angle of attack would 

change substantially from Norman’s (1975) result, it would be 

possible to get a better estimate of the effective pier length and 

better description of the flow pattern through the bridge.

 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Table 3. Bridge-scour computations, Scenario 1, Tanana River at Big Delta, Alaska, Bridge 524.

[Flow from the Delta River is added in proportion to channel width above the exit section. Exit 2: 18 percent; Exit 3: 45 percent; Exit 4: 65 percent. The 

remaining 35 percent of the flow enters downstream of Exit 4. Abbreviations: ft, foot; ft/ft, foot per foot; lbs/ft2, pounds per square foot; ft/s, foot per second; 

ft3/s, cubic foot per second; ft/s2, foot per second squared; s, second; deg, degree; g, gravity (32.2 ft/s2)]

LIVE-BED CONTRACTION SCOUR

y 100 Year 500 Year

y

Q

Q

W

W

y y y

K

cs

2

1

2

1

6

7 1

2

2 1

1

= 



 



 



 





= − = (average scour depth)

Computed floods: total discharge (ft3/s) Q 86,700 95,600

Hydraulic radius of approach section (ft) R 16.66 17.29

Friction slope (ft/ft) S .001 .001

Average shear stress at bed (lbs/ft2

) t=ρgRS .52 .54

Shear velocity (ft/s) V*=(τ/ρ)

1⁄2 .52 .53

Fall velocity of bed material (ft/s) w 2.60 2.60

Ratio V*/w .20 .20

Exponent determined from mode of bed material transport k1

=f(V*/w) .59 .59

Discharge in main channel of approach section (ft3

/s) Q1 86,700 95,600

Percentage of total discharge 100 100

Discharge in main channel of contracted (bridge) section (ft3

/s) Q2 86,700 95,600

Percentage of total discharge 100 100

Width of main channel of approach section (ft) W1 666 666

Width of main channel of contracted (bridge) section (ft) W2 603 608

Average depth of main channel of approach section (ft) y1 20.2 21.1

Average depth in contracted (bridge) section (ft) y2 21.4 22.2

CONTRACTION SCOUR (ft) Ycs 1.2 1.1

PIER SCOUR

y 100 Year 500 Year

y

K K K a

y

Fr ps

1

1 2 3

1

0 65

0 43 = 2 0 



 



 .

.

.

Speed of maximum velocity stream tube (ft/s) v1 8.77 9.39

Depth of maximum velocity stream tube (ft/s) y1 18.4 18.4

Froude number of maximum velocity stream tube Fr=v1

/(gy1)

1⁄2 .37 .39

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 35 35

Pier width (ft) a 5.0 5.0

Pier length (ft) L 47 47

Ratio L/a 9 9

Angle of attack correction factor K2

=f(AA,L/a) 3.3 3.3

Bed condition (dunes) correction factor K3 1.1 1.1

PIER SCOUR (ft) Yps 36.4 37.9

TOTAL SCOUR

 100 Year 500 Year T y y s cs ps = +

Contraction scour (ft) Ycs 1.2 1.1

Pier scour (ft) Yps 36.4 37.9

TOTAL SCOUR (ft) Ts 37.6 39.0

Scour Computations   
Table 4. Bridge-scour computations, Scenario 2, Tanana River at Big Delta, Alaska, Bridge 524.

[Entire flow from the Delta River is added above the farthest upstream exit section. This creates the most backwater. Exit 2: 100 percent, Exit 3: 0 percent, 

Exit 4: 0 percent. Abbreviations: ft, foot; ft/ft, foot per foot; lbs/ft2, pounds per square foot; ft/s, foot per second; ft3/s, cubic foot per second; ft/s2, foot per 

second squared; s, second; deg, degree; g, gravity (32.2 ft/s2)]

LIVE-BED CONTRACTION SCOUR

 

 100 Year 500 Year y

y

Q

Q

W

W

y y y

K

cs

2

1

2

1

6

7 1

2

2 1

1

= 



 



 



 





= − = (average scour depth)

Computed floods: total discharge (ft3/s) Q 86,700 95,600

Hydraulic radius of approach section (ft) R 17.37 18.04

Friction slope (ft/ft) S .001 .001

Average shear stress at bed (lbs/ft2

) τ=ρgRS .54 .56

Shear velocity (ft/s) V*=(τ/ρ)

1⁄2 .53 .54

Fall velocity of bed material (ft/s) w 2.60 2.60

Ratio V*/w .20 .21

Exponent determined from mode of bed material transport k1

=f(V*/w) .59 .59

Discharge in main channel of approach section (ft3

/s) Q1 86,700 95,600

Percentage of total discharge 100 100

Discharge in main channel of contracted (bridge) section (ft3

/s) Q2 86,700 95,600

Percentage of total discharge 100 100

Width of main channel of approach section (ft) W1 666 666

Width of main channel of contracted (bridge) section (ft) W2 610 612

Average depth of main channel of approach section (ft) y1 21.2 22.1

Average depth in contracted (bridge) section (ft) y2 22.3 23.2

CONTRACTION SCOUR (ft) Ycs 1.1 1.1

PIER SCOUR 

y 100 Year 500 Year

y

K K K a

y

Fr ps

1

1 2 3

1

0 65

0 43 = 2 0 



 



 .

.

.

Speed of maximum velocity stream tube (ft/s) v1 8.41 8.92

Depth of maximum velocity stream tube (ft/s) y1 18.6 18.8

Froude number of maximum velocity stream tube Fr=v1

/(gy1)

1⁄2 .34 .36

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 35 35

Pier width (ft) a 5.0 5.0

Pier length (ft) L 47 47

Ratio L/a 9 9

Angle of attack correction factor K2

=f(AA,L/a) 3.3 3.3

Bed condition (dunes) correction factor K3 1.1 1.1

PIER SCOUR (ft) Yps 35.9 36.9

TOTAL SCOUR

T y y s cs ps = + 100 Year 500 Year

Contraction scour (ft) Ycs 1.1 1.1

Pier scour (ft) Yps 35.9 36.9

TOTAL SCOUR (ft) Ts 37.0 38.0

10 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Table 5. Bridge scour computations, Scenario 3, Tanana River at Big Delta, Alaska, Bridge 524.

[Entire flow from the Delta River is added in above the farthest downstream exit section. Exit 2: 0 percent; Exit 3: 0 percent; Exit 4: 100 percent. Abbreviations:

ft, foot; ft/ft, foot per foot; lbs/ft2, pounds per square foot; ft/s, foot per second; ft3/s, cubic foot per second; ft/s2, foot per second squared; s, second; deg, degree; 

g, gravity (32.2 ft/s2)]

LIVE-BED CONTRACTION SCOUR

100 Year 500 Year y

y

Q

Q

W

W

y y y

K

cs

2

1

2

1

6

7 1

2

2 1

1

= 



 



 



 





= − = (average scour depth)

Computed floods: total discharge (ft3/s) Q 86,700 95,600

Hydraulic radius of approach section (ft) R 17.21 17.86

Friction slope (ft/ft) S .001 .001

Average shear stress at bed (lbs/ft2

) t=ρgRS .54 .56

Shear velocity (ft/s) V*=(t/ρ)

1⁄2 .53 .54

Fall velocity of bed material (ft/s) w 2.60 2.60

Ratio V*/w .20 .21

Exponent determined from mode of bed material transport k1

 =f(V*/w) .59 .59

Discharge in main channel of approach section (ft3

/s) Q1 86,700 95,600

Percentage of total discharge 100 100

Discharge in main channel of contracted (bridge) section (ft3

/s) Q2 86,700 95,600

Percentage of total discharge 100 100

Width of main channel of approach section (ft) W1 666 666

Width of main channel of contracted (bridge) section (ft) W2 608 612

Average depth of main channel of approach section (ft) y1 21.0 21.9

Average depth in contracted (bridge) section (ft) y2 22.1 23.0

CONTRACTION SCOUR (ft) Ycs 1.1 1.1

PIER SCOUR

y

y

K K K a

y

Fr ps

1

1 2 3

1

0 65

0 43 = 2 0 



 



 .

.

. 100 Year 500 Year

Speed of maximum velocity stream tube (ft/s) v1 8.52 9.01

Depth of maximum velocity stream tube (ft/s) y1 18.4 18.6

Froude number of maximum velocity stream tube Fr=v1

/(gy1)

1⁄2 .35 .37

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 35 35

Pier width (ft) a 5.0 5.0

Pier length (ft) L 47 47

Ratio L/a 9 9

Angle of attack correction factor K2

=f(AA,L/a) 3.3 3.3

Bed condition (dunes) correction factor K3 1.1 1.1

PIER SCOUR (ft) Yps 36.2 37.2

TOTAL SCOUR

T y y s cs ps = +

100 Year 500 Year

Contraction scour (ft) Ycs 1.1 1.1

Pier scour (ft) Yps 36.2 37.2

TOTAL SCOUR (ft) Ts 37.3 38.3

Scour Computations 11
Table 6. Bridge-scour computations, Scenario 4, Tanana River at Big Delta, Alaska, Bridge 524.

[No flow from the Delta River is added to the exit sections. No backwater—worst case assumption for pier scour. Exit 2: 0 percent; Exit 3: 0 percent; Exit 4: 0 

percent. Abbreviations: ft, foot; ft/ft, foot per foot; lbs/ft2, pounds per square foot; ft/s, foot per second; ft3/s, cubic foot per second; ft/s2, foot per second squared; 

s, second; deg, degree; g, gravity (32.2 ft/s2)]

LIVE-BED CONTRACTION SCOUR

 y 100 Year 500 Year

y

Q

Q

W

W

y y y

K

cs

2

1

2

1

6

7 1

2

2 1

1

= 



 



 



 





= − = (average scour depth)

Computed floods: total discharge (ft3/s) Q 86,700 95,600

Hydraulic radius of approach section (ft) R 15.29 15.88

Friction slope (ft/ft) S .001 .001

Average shear stress at bed (lbs/ft2

) t=ρgRS .48 .50

Shear velocity (ft/s) V*=(t/r)

1⁄2 .50 .51

Fall velocity of bed material (ft/s) w 2.60 2.60

Ratio V*/w .19 .19

Exponent determined from mode of bed material transport k1

 =f(V*/w) .59 .59

Discharge in main channel of approach section (ft3

/s) Q1 86,700 95,600

Percentage of total discharge 100 100

Discharge in main channel of contracted (bridge) section (ft3

/s) Q2 86,700 95,600

Percentage of total discharge 100 100

Width of main channel of approach section (ft) W1 666 666

Width of main channel of contracted (bridge) section (ft) W2 591 595

Average depth of main channel of approach section (ft) y1 18.3 19.2

Average depth in contracted (bridge) section (ft) y2 19.7 20.5

CONTRACTION SCOUR (ft) Ycs 1.3 1.3

PIER SCOUR

y 100 Year 500 Year

y

K K K a

y

Fr ps

1

1 2 3

1

0 65

0 43 = 2 0 



 



 .

.

.

Speed of maximum velocity stream tube (ft/s) v1 9.64 10.26

Depth of maximum velocity stream tube (ft/s) y1 16.1 16.6

Froude number of maximum velocity stream tube Fr=v1

/(gy1)

1⁄2 .42 .44

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 35 35

Pier width (ft) a 5.0 5.0

Pier length (ft) L 47 47

Ratio L/a 9 9

Angle of attack correction factor K2

=f(AA,L/a) 3.3 3.3

Bed condition (dunes) correction factor K3 1.1 1.1

Submerged low steel multiplier f(Frapproach)

PIER SCOUR (ft) Yps 37.5 38.7

TOTAL SCOUR

T y y s cs ps = +

100 Year 500 Year

Contraction scour (ft) Ycs 1.3 1.3

Pier scour (ft) Yps 37.5 38.7

TOTAL SCOUR (ft) Ts 38.8 40.0

12 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Table 7. Estimated pier-scour depths for the 100-year-flood 

discharge computed from model output with starting watersurface elevations from 985.0 to 993.5 feet at the Tanana River at 

Big Delta, Alaska.

[Abbreviations: ft, foot; ft/s, foot per second]

Watersurface 

elevation 

(ft)

Average 

velocity 

of entire 

section 

(ft/s)

Stream 

tube 

depth

(ft)

Stream 

tube 

velocity

(ft/s)

Froude 

number

Pier scour 

for 35° angle 

of attack

(ft)

985.0 12.6 12.1 14.8 0.8 43.3

985.5 12.1 12.5 13.9 .7 42.4

986.0 11.6 12.9 13.5 .7 42.0

986.5 11.2 13.2 12.9 .6 41.4

987.0 10.8 13.6 12.4 .6 40.8

987.5 10.4 14.1 11.9 .6 40.4

988.0 10.0 14.4 11.4 .5 39.7

988.5 9.7 14.8 11.0 .5 39.3

989.0 9.4 15.2 10.6 .5 38.8

989.5 9.1 15.7 10.3 .5 38.5

990.0 8.8 16.1 10.0 .4 38.1

990.5 8.5 16.1 9.6 .4 37.5

991.0 8.3 16.5 9.4 .4 37.2

991.5 8.0 16.9 9.1 .4 36.8

992.0 7.8 17.8 8.9 .4 36.7

992.5 7.6 18.4 8.8 .4 36.4

993.0 7.4 18.4 8.5 .4 36.2

993.5 7.2 18.6 8.4 .3 35.9

Figure 5. Estimated pier-scour magnitudes for the 100-

year-flood discharge computed from model output with 

starting water-surface elevations from 985.0 to 993.5 feet 

at the Tanana River at Big Delta, Alaska.

34.0

35.0

36.0

37.0

38.0

39.0

40.0

41.0

42.0

43.0

44.0

984.0 986.0 988.0 990.0 992.0 994.0

WATER-SURFACE ELEVATION AT CROSS SECTION

EXIT 4, IN FEET

PIER-SCOUR MAGNITUDE, IN FEET

Scenario 4

Scenario 2

Scenario 3

Scenario 1

Scour Computations 13
Table 8. Pier-scour computations for discharge measurements, Tanana River at Big Delta, Alaska, August 26, 1996.

[Assessment of effective pier length, angle of attack, and bed armor factors; Bridge 524: Tanana River at Big Delta. Abbreviations: ft3/s, cubic foot per second; 

ft, foot; ft/s, foot per second. (pier-scour equation is presented in tables 3–6)]

Discharge (ft3/s) 21,500 Froude number, Fr 0.35

Stream tube depth, y 1

 (ft) 8.7 Pier shape factor, K1 1

Stream tube velocity (ft/s) 5.79 Bed condition factor, K3 1.1

Pier

No.

Pier

length,

L (ft)

Effective

pier

length

(percent)

Effective

pier

length,

(ft)

Pier

width, a

 (ft)

Effective

length/width

ratio

Angle of

attack

 (degrees)

Angle of

attack

factor, K2

Bed armor 

correction 

factor, K4

Pier scour 

(ft)

2 47 100 47.0 5.0 9.4 35 3.3 1.0 27.9

2 47 50 23.5 5.0 4.7 35 2.3 1.0 19.2

2 47 33 15.5 5.0 3.1 35 1.9 1.0 15.8

2 47 100 47.0 5.0 9.4 35 3.3 .7 19.5

2 47 50 23.5 5.0 4.7 35 2.3 .7 13.5

2 47 33 15.5 5.0 3.1 35 1.9 .7 11.1

2 47 100 47.0 5.0 9.4 25 2.8 1.0 23.8

2 47 50 23.5 5.0 4.7 25 2.0 1.0 17.0

2 47 33 15.5 5.0 3.1 25 1.7 1.0 14.3

2 47 100 47.0 5.0 9.4 25 2.8 .7 16.7

2 47 50 23.5 5.0 4.7 25 2.0 .7 11.9

2 47 33 15.5 5.0 3.1 25 1.7 .7 10.0

2 47 100 47.0 5.0 9.4 15 2.2 1.0 18.8

2 47 50 23.5 5.0 4.7 15 1.7 1.0 14.1

2 47 33 15.5 5.0 3.1 15 1.4 1.0 12.3

2 47 100 47.0 5.0 9.4 15 2.2 .7 13.2

2 47 50 23.5 5.0 4.7 15 1.7 .7 9.9

2 47 33 15.5 5.0 3.1 15 1.4 .7 8.6

3-5 36 100 36.0 4.0 9.0 35 3.2 1.0 23.5

3-5 36 50 18.0 4.0 4.5 35 2.2 1.0 16.3

3-5 36 33 11.9 4.0 3.0 35 1.8 1.0 13.4

3-5 36 100 36.0 4.0 9.0 35 3.2 .7 16.5

3-5 36 50 18.0 4.0 4.5 35 2.2 .7 11.4

3-5 36 33 11.9 4.0 3.0 35 1.8 .7 9.4

3-5 36 100 36.0 4.0 9.0 25 2.7 1.0 20.1

3-5 36 50 18.0 4.0 4.5 25 2.0 1.0 14.4

3-5 36 33 11.9 4.0 3.0 25 1.7 1.0 12.1

3-5 36 100 36.0 4.0 9.0 25 2.7 .7 14.1

3-5 36 50 18.0 4.0 4.5 25 2.0 .7 10.1

3-5 36 33 11.9 4.0 3.0 25 1.7 .7 8.5

3-5 36 100 36.0 4.0 9.0 15 2.2 1.0 16.0

3-5 36 50 18.0 4.0 4.5 15 1.6 1.0 12.0

3-5 36 33 11.9 4.0 3.0 15 1.4 1.0 10.5

3-5 36 100 36.0 4.0 9.0 15 2.2 .7 11.2

3-5 36 50 18.0 4.0 4.5 15 1.6 .7 8.4

3-5 36 33 11.9 4.0 3.0 15 1.4 .7 7.4

14 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Channel Changes and Bank Erosion

Scour and fill occurs seasonally on the Tanana River. At 

higher flows, the sand- and silt-size material is scoured from 

the bed and transported in suspension as well as bedload. If the 

flow declines and velocities decrease in parts of the channel, 

the fine material may drop out and be deposited. This seasonal 

change may explain the bar that has formed adjacent to the 

right bank—high flow washes out the bar and the flow pattern 

changes along the right bank—causing lateral erosion. The bar 

re-forms as the flow declines.

Documenting long-term channel change through 

comparisons of surveyed cross sections was difficult because 

of the dynamic nature of the river and the fact that these 

survey data only captured pieces of the change over time. 

The data collected for this study and the hydraulic model 

represent the conditions at the time of the August 1996 

field survey. Substantial changes in channel geometry have 

occurred in this river system and may occur regularly. Norman 

(1975) surveyed four cross sections in 1971—upstream 

and downstream sides of the bridge and a section near the 

1996 cross section Exit 1. Direct comparison between cross 

sections used in this study and Norman (1975) are complicated 

further by the fact that the pipeline crossing and its associated 

revetment that encroaches on the channel had not been 

constructed in 1971. Norman’s cross sections measured at the 

bridge at varying discharges indicated substantial changes in 

the bed over a few months (fig. 3). The delta formed by the 

Delta River probably is in a constant state of flux (note the 

changes in fig. 6). It is likely the channel downstream of the 

bridge is constantly changing shape as the flow and sedimenttransport rates change in both the Tanana and Delta Rivers. 

This is not unusual on rivers carrying large amounts of fine 

sediment and has been observed at other sites on the Tanana 

River with comparable channel changes occurring in as little 

as a week (Burrows and others, 1981).

The cause of the accelerated lateral erosion on the right 

bank is unknown. Two effects appear to occur at varying 

flows. First, as mentioned previously, as the flow decreases, 

the bar re-forms. Although this bar may buffer the bank from 

direct attack, the main channel also shifts to the left as the 

flow decreases, thereby lowering the velocities directed to the 

right bank. Second, at higher flows, an eddy forms on the right 

bank upstream from the bridge and reverse flow occurs on the 

right bank and through the bridge. This was observed during 

the 1971 high-flow measurement of 51,600 ft3

/s and during 

a discharge measurement from the bridge of 49,500 ft3/s on 

August 19, 1967—the 100-year flood flow is 86,700 ft3/s. The 

bank erosion that prompted this study occurred during early 

spring and continued into the early part of summer, a period of 

intermediate flows. The morphology of the Delta River’s delta 

at this time is unknown. Changes in its shape and extent could 

influence the velocities along the right bank upstream from 

the bridge. The bar that protects the right bank easily could 

be eroded if the flow of the Tanana were directed at it. There 

were no observations of these intermediate flows in 1996. 

At the time of the August 1996 survey, velocities 

along the right bank were very slow. One goal of the survey 

was to determine what maximum velocities might be 

expected—a velocity of 9.5 ft/s was measured at the rock bluff 

downstream of the bridge. During a discharge measurement 

of 51,600 ft3/s made at the bridge on August 13, 1971, the 

highest velocity measured was 9.9 ft/s at 20 percent of the 

total depth near pier 3.

Figure 6. Channel changes at cross section Exit 1 from 1971 

to 1996, Tanana River at Big Delta, Alaska. See figure 2 for 

cross-section location. ELEVATION, IN FEET

7/16/71

8/27/96

DISTANCE FROM THE LEFT BANK, IN FEET

Channel Changes and Bank Erosion 15
Conclusions

Hydraulic conditions at bridge 524 are complex because 

the Delta River enters immediately downstream of the bridge. 

The varying discharge and shape of the delta formed by the 

Delta River affect the flow of the Tanana River as it passes 

through the bridge. A water-surface profile model was 

developed and calibrated to the relatively low flow observed at 

the time of the field survey. However, given the complications 

and variations of the channel at different discharges, the model 

results should be considered an estimate.

Computed pier scour varied from 43.3 to 35.9 ft. Possible 

mitigating factors, such as effective pier length and bed 

armoring, reduced the computed pier-scour magnitude to 

11.4 ft. Maximum observed pier scour during the field survey 

at a relatively low flow was 6.0 ft.

The cause of the accelerated lateral erosion on the right 

bank is unknown. At the time of the field survey, a bar had 

formed between the main channel and the right bank. The 

erosion occurred at flows higher than those observed. The 

circumstances at the time of active erosion are uncertain—

erosion may occur at an intermediate flow or higher flows. At 

higher flows an eddy has been observed under the right side 

of the bridge. The extent and shape of the delta downstream 

of the bridge, as well as the discharge of the Delta River, 

affect the flow and channel configuration of the Tanana River 

upstream of the bridge.

Both the pier-scour computations and the determination 

of the bank-erosion process would benefit from observations at 

higher flows. Previous work by Norman (1975) lacks detailed 

observations of high flow at the piers. Hydraulic data gathered 

at a high flow, and/or a period of active bank erosion, would 

be useful for understanding and attempting to predict both of 

these processes.

References Cited

Burrows, R.L., Emmett, W.W., and Parks, Bruce, 1981, 

Sediment transport in the Tanana River near Fairbanks, 

Alaska, 1977–79: U.S. Geological Survey Water-Resources 

Investigations 81–20, 56 p.

Heinrichs, T.A., Kennedy, B.W., Langley, D.E., and Burrows, 

R.L., 2001, Methodology and estimates of scour at selected 

bridge sites in Alaska: U.S. Geological Survey WaterResources Investigations Report 2000–4151, 44 p.

Interagency Advisory Committee on Water Data, 1982, 

Guidelines for Determining Flood Flow Frequency: 

Hydrology Subcommittee Bulletin 17B, 28 p. 

Jones, S.H., and Fahl, C.B., 1994, Magnitude and frequency of 

floods in Alaska and conterminous basins of Canada: U.S. 

Geological Survey Open-File Report 93–4179, 122 p.

Norman, V.W., 1975, Scour at selected bridge sites in Alaska: 

U.S. Geological Survey Water-Resources Investigations 

32–75, 160 p.

Richardson, E.V., and Davis, S.R., 1995, Evaluating scour 

at bridges, (3rd ed.): U.S. Department of Transportation 

Hydraulic Engineering Circular 18, 132 p.

Shearman, J.O., 1990, Users Manual for WSPRO—A 

computer model for Water-Surface Profile computations: 

Federal Highway Administration Publication FHWA–IP–

89–027, 177 p.

16  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A. Water-Surface Profile Model Data Files
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18  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 19
20 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 21
22 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 23
24 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 25
26  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 27
28  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 29
30 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 31
32 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 33
34 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 35
36  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 37
38  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 39
40 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 41
42 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 43
44 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix A 45
46  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Appendix B. Survey Data
This page is intentionally left blank.

48  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B1. Cross section Approach 1 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -20.1 998.7 extended up

– – -19.6 986.7 estimated overbank

10,753.1 9,894.0 -9.6 986.7 rebar

10,751.3 9,903.4 0.0 981.5 left edge of water

10,753.6 9,913.5 10.3 976.4 channel sounding

10,757.3 9,929.5 26.7 973.4 channel sounding

10,761.0 9,945.5 43.1 973.2 channel sounding

10,764.6 9,961.5 59.5 973.4 channel sounding

10,768.3 9,977.5 75.9 973.7 channel sounding

10,772.0 9,993.4 92.3 973.6 channel sounding

10,775.7 10,009.4 108.7 973.7 channel sounding

10,779.3 10,025.4 125.1 973.7 channel sounding

10,783.0 10,041.4 141.6 974.3 channel sounding

10,786.7 10,057.4 158.0 974.3 channel sounding

10,790.4 10,073.4 174.4 974.2 channel sounding

10,794.0 10,089.4 190.8 973.9 channel sounding

10,797.7 10,105.4 207.2 973.5 channel sounding

10,801.4 10,121.3 223.6 973.5 channel sounding

10,805.1 10,137.3 240.0 973.6 channel sounding

10,808.7 10,153.3 256.4 974.8 channel sounding

10,812.4 10,169.3 272.8 974.4 channel sounding

10,816.1 10,185.3 289.2 974.0 channel sounding

10,819.8 10,201.3 305.6 973.8 channel sounding

10,823.4 10,217.3 322.0 973.9 channel sounding

10,827.1 10,233.3 338.4 974.2 channel sounding

10,830.8 10,249.3 354.8 974.8 channel sounding

10,834.5 10,265.2 371.2 975.6 channel sounding

10,838.1 10,281.2 387.6 975.8 channel sounding

10,841.8 10,297.2 404.0 976.0 channel sounding

10,845.5 10,313.2 420.4 976.4 channel sounding

10,849.2 10,329.2 436.8 976.7 channel sounding

10,852.8 10,345.2 453.2 977.1 channel sounding

10,856.5 10,361.2 469.7 977.6 channel sounding

10,860.2 10,377.2 486.1 977.0 channel sounding

10,863.8 10,393.1 502.5 977.3 channel sounding

10,867.5 10,409.1 518.9 977.2 channel sounding

10,871.2 10,425.1 535.3 977.6 channel sounding

10,874.9 10,441.1 551.7 977.5 channel sounding

10,877.1 10,450.7 561.5 978.4 channel sounding

10,888.3 10,482.3 594.8 981.4 right edge of water

10,889.4 10,488.7 601.3 982.3 toe of bank

10,890.3 10,491.1 603.9 986.3 rebar

– – 1,603.9 986.3 estimated overbank

– – 1,613.9 996.3 extended up

Appendix B 49
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Sur veyed 

Surveyed Water 

Surface

Table B2. Cross section Approach 2 at the Tanana River at Big 

Delta.

[Points surveyed Aug. 27, 1996. See Figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

10,753.1 9,894.0 -9.1 987.2 bank

10,751.3 9,903.4 .0 981.5 left edge of water

10,747.6 9,909.9 7.4 976.2 channel sounding

10,739.5 9,924.1 23.8 974.5 channel sounding

10,731.3 9,938.4 40.2 973.4 channel sounding

10,723.2 9,952.6 56.7 973.3 channel sounding

10,715.0 9,966.8 73.1 973.4 channel sounding

10,706.9 9,981.1 89.5 973.5 channel sounding

10,698.7 9,995.3 105.9 973.6 channel sounding

10,690.6 10,009.6 122.3 973.5 channel sounding

10,682.4 10,023.8 138.7 973.4 channel sounding

10,674.3 10,038.0 155.1 973.4 channel sounding

10,666.1 10,052.3 171.5 973.4 channel sounding

10,658.0 10,066.5 187.9 973.3 channel sounding

10,649.8 10,080.7 204.3 972.9 channel sounding

10,641.6 10,095.0 220.7 972.9 channel sounding

10,633.5 10,109.2 237.1 972.9 channel sounding

10,625.3 10,123.4 253.5 973.3 channel sounding

10,617.2 10,137.7 269.9 973.9 channel sounding

10,609.0 10,151.9 286.3 974.1 channel sounding

10,600.9 10,166.2 302.7 974.1 channel sounding

10,592.7 10,180.4 319.1 973.5 channel sounding

10,584.6 10,194.6 335.5 972.9 channel sounding

10,576.4 10,208.9 351.9 972.6 channel sounding

10,568.3 10,223.1 368.3 972.8 channel sounding

10,560.1 10,237.3 384.8 973.3 channel sounding

10,552.0 10,251.6 401.2 973.1 channel sounding

10,543.8 10,265.8 417.6 973.4 channel sounding

10,535.7 10,280.1 434.0 974.7 channel sounding

10,527.5 10,294.3 450.4 975.5 channel sounding

10,519.4 10,308.5 466.8 975.8 channel sounding

10,511.2 10,322.8 483.2 976.0 channel sounding

10,503.1 10,337.0 499.6 976.5 channel sounding

10,494.9 10,351.2 516.0 976.7 channel sounding

10,486.8 10,365.5 532.4 977.1 channel sounding

10,478.6 10,379.7 548.8 977.2 channel sounding

10,470.5 10,393.9 565.2 977.7 channel sounding

10,462.3 10,408.2 581.6 977.8 channel sounding

10,454.2 10,422.4 598.0 978.2 channel sounding

10,446.0 10,436.7 614.4 978.7 channel sounding

10,437.9 10,450.9 630.8 978.0 channel sounding

10,429.7 10,465.1 647.2 978.4 channel sounding

10,421.6 10,479.4 663.6 978.0 channel sounding

10,413.4 10,493.6 680.0 978.5 channel sounding

10,405.3 10,507.8 696.4 978.9 channel sounding

10,397.1 10,522.1 712.9 978.4 channel sounding

10,393.8 10,527.8 719.4 978.4 channel sounding

10,372.6 10,584.6 779.3 981.0 right edge of water

10,357.8 10,615.9 813.7 982.0 bank

10,346.9 10,643.1 842.8 980.9 bank

10,325.4 10,675.3 881.5 980.9 bank

10,319.2 10,701.7 907.5 983.9 bank

50 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B3. Cross section Approach 3 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, feet]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

10,499.7 9,929.0 -63.6 987.1 bank

10,480.6 9,964.6 -23.2 986.8 rebar

10,477.3 9,989.5 .0 981.1 left edge of water

10,467.5 10,006.6 19.7 978.4 channel sounding

10,459.4 10,020.8 36.1 976.2 channel sounding

10,451.2 10,035.0 52.5 974.9 channel sounding

10,443.1 10,049.3 68.9 973.9 channel sounding

10,434.9 10,063.5 85.3 972.9 channel sounding

10,426.8 10,077.7 101.7 972.5 channel sounding

10,418.6 10,092.0 118.1 971.7 channel sounding

10,410.5 10,106.2 134.5 971.0 channel sounding

10,402.3 10,120.4 150.9 970.3 channel sounding

10,394.2 10,134.7 167.3 970.3 channel sounding

10,386.0 10,148.9 183.7 970.5 channel sounding

10,377.9 10,163.2 200.1 970.8 channel sounding

10,369.7 10,177.4 216.5 970.9 channel sounding

10,353.4 10,205.9 249.4 970.9 channel sounding

10,345.2 10,220.1 265.8 971.0 channel sounding

10,337.1 10,234.3 282.2 971.0 channel sounding

10,328.9 10,248.6 298.6 971.3 channel sounding

10,320.8 10,262.8 315.0 971.5 channel sounding

10,312.6 10,277.0 331.4 972.0 channel sounding

10,304.5 10,291.3 347.8 973.1 channel sounding

10,296.3 10,305.5 364.2 974.0 channel sounding

10,288.2 10,319.8 380.6 975.0 channel sounding

10,280.0 10,334.0 397.0 975.4 channel sounding

10,271.9 10,348.2 413.4 976.1 channel sounding

10,263.7 10,362.5 429.8 976.9 channel sounding

10,255.6 10,376.7 446.2 977.1 channel sounding

10,247.4 10,390.9 462.6 976.9 channel sounding

10,239.3 10,405.2 479.0 977.5 channel sounding

10,231.1 10,419.4 495.4 978.0 channel sounding

10,223.0 10,433.7 511.8 978.2 channel sounding

10,214.8 10,447.9 528.2 978.6 channel sounding

10,206.7 10,462.1 544.6 979.1 channel sounding

10,182.2 10,504.8 593.9 978.3 channel sounding

10,174.1 10,519.1 610.3 978.8 channel sounding

10,165.9 10,533.3 626.7 978.8 channel sounding

10,157.8 10,547.5 643.1 978.0 channel sounding

10,149.6 10,561.8 659.5 978.7 channel sounding

10,141.5 10,576.0 675.9 979.1 channel sounding

10,133.3 10,590.3 692.3 978.9 channel sounding

10,125.2 10,604.5 708.7 978.0 channel sounding

10,117.0 10,618.7 725.1 972.7 channel sounding

10,108.9 10,633.0 741.5 969.1 channel sounding

10,100.7 10,647.2 757.9 969.0 channel sounding

10,092.6 10,661.4 774.3 972.0 channel sounding

10,084.4 10,675.7 790.7 976.3 channel sounding

10,079.5 10,684.2 800.6 980.1 channel sounding

10,048.5 10,714.5 842.3 980.9 right edge of water

10,047.4 10,720.0 847.6 982.1 toe of bank

10,047.0 10,721.8 849.4 986.5 rebar

10,044.6 10,726.7 854.8 987.1 bank

10,026.5 10,758.0 890.9 988.3 bank

Appendix B 51
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B4. Cross section Approach 4 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

10,171.1 9,803.9 -2,15.9 995.5 road shoulder

10,190.3 9,815.9 -1,93.3 988.6 base road embank

10,221.0 9,893.1 -1,10.2 989.4 parking lot

10,206.1 9,952.5 -49.0 989.7 bank

10,205.9 9,955.3 -46.5 986.8 bank

10,206.7 9,957.2 -45.3 987.5 rebar

10,207.4 9,959.9 -43.3 984.4 toe of bank

10,202.3 10,007.0 .0 980.9 left edge of water

10,167.3 10,021.2 29.9 978.4 channel sounding

10,159.0 10,035.4 46.3 976.6 channel sounding

10,150.8 10,049.5 62.7 975.5 channel sounding

10,142.5 10,063.7 79.1 973.9 channel sounding

10,142.5 10,063.7 79.1 973.9 channel sounding

10,134.2 10,077.9 95.5 972.7 channel sounding

10,126.0 10,092.1 111.9 972.1 channel sounding

10,117.7 10,106.2 128.3 971.9 channel sounding

10,109.4 10,120.4 144.7 971.6 channel sounding

10,101.2 10,134.6 161.1 971.3 channel sounding

10,092.9 10,148.8 177.5 971.5 channel sounding

10,084.7 10,162.9 193.9 971.3 channel sounding

10,076.4 10,177.1 210.3 970.7 channel sounding

10,068.1 10,191.3 226.8 970.5 channel sounding

10,059.9 10,205.4 243.2 970.7 channel sounding

10,051.6 10,219.6 259.6 971.1 channel sounding

10,043.3 10,233.8 276.0 971.3 channel sounding

10,035.1 10,248.0 292.4 971.1 channel sounding

10,026.8 10,262.1 308.8 971.2 channel sounding

10,018.6 10,276.3 325.2 971.1 channel sounding

10,010.3 10,290.5 341.6 971.2 channel sounding

10,002.0 10,304.6 358.0 971.6 channel sounding

9,993.8 10,318.8 374.4 972.6 channel sounding

9,985.5 10,333.0 390.8 973.3 channel sounding

9,977.2 10,347.2 407.2 974.2 channel sounding

9,969.0 10,361.3 423.6 974.8 channel sounding

9,960.7 10,375.5 440.0 973.5 channel sounding

9,952.5 10,389.7 456.4 974.9 channel sounding

9,944.2 10,403.9 472.8 975.2 channel sounding

9,935.9 10,418.0 489.2 975.5 channel sounding

9,927.7 10,432.2 505.6 976.2 channel sounding

9,919.4 10,446.4 522.0 977.0 channel sounding

9,911.1 10,460.5 538.4 977.2 channel sounding

9,902.9 10,474.7 554.9 976.8 channel sounding

9,894.6 10,488.9 571.3 975.9 channel sounding

9,886.4 10,503.1 587.7 975.1 channel sounding

9,869.8 10,531.4 620.5 974.9 channel sounding

9,853.3 10,559.7 653.3 973.9 channel sounding

9,845.0 10,573.9 669.7 973.7 channel sounding

9,836.8 10,588.1 686.1 974.9 channel sounding

9,828.5 10,602.3 702.5 975.5 channel sounding

9,820.3 10,616.4 718.9 975.9 channel sounding

9,807.0 10,639.1 745.1 980.1 channel sounding

9,774.0 10,695.8 810.8 979.9 channel sounding

9,770.3 10,702.1 818.0 980.9 right edge of water

9,768.5 10,706.3 822.6 982.9 bank

9,767.8 10,707.0 823.6 985.3 bank

9,767.8 10,709.9 826.1 985.9 rebar

9,735.5 10,773.9 897.6 988.0 on gravel pad

52 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B5. Cross section Approach 5 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

10,136.9 9,963.9 -39.8 984.7 toe of bank

10,137.1 9,968.8 -35.9 984.6 rebar

10,134.3 10,010.1 .0 980.9 left edge of water

10,110.6 10,011.2 14.1 978.6 channel sounding

10,097.9 10,030.3 37.0 975.4 channel sounding

10,088.8 10,044.0 53.4 974.0 channel sounding

10,070.7 10,071.4 86.2 972.0 channel sounding

10,052.6 10,098.7 119.0 971.3 channel sounding

10,043.5 10,112.4 135.5 973.3 channel sounding

10,034.5 10,126.1 151.9 973.6 channel sounding

10,016.3 10,153.4 184.7 973.3 channel sounding

10,007.3 10,167.1 201.1 971.8 channel sounding

9,998.2 10,180.8 217.5 970.6 channel sounding

9,989.2 10,194.4 233.9 970.6 channel sounding

9,980.1 10,208.1 250.3 970.9 channel sounding

9,971.0 10,221.8 266.7 971.1 channel sounding

9,962.0 10,235.5 283.1 970.9 channel sounding

9,952.9 10,249.1 299.5 971.3 channel sounding

9,943.8 10,262.8 315.9 971.0 channel sounding

9,934.8 10,276.5 332.3 971.1 channel sounding

9,916.7 10,303.8 365.1 972.5 channel sounding

9,907.6 10,317.5 381.5 974.8 channel sounding

9,898.5 10,331.2 397.9 973.7 channel sounding

9,889.5 10,344.9 414.3 974.4 channel sounding

9,880.4 10,358.5 430.7 974.9 channel sounding

9,871.3 10,372.2 447.1 975.2 channel sounding

9,862.3 10,385.9 463.6 972.6 channel sounding

9,853.2 10,399.6 480.0 974.4 channel sounding

9,844.2 10,413.2 496.4 974.9 channel sounding

9,835.1 10,426.9 512.8 975.7 channel sounding

9,826.0 10,440.6 529.2 975.9 channel sounding

9,817.0 10,454.3 545.6 976.2 channel sounding

9,807.9 10,467.9 562.0 974.9 channel sounding

9,798.8 10,481.6 578.4 975.7 channel sounding

9,789.8 10,495.3 594.8 977.6 channel sounding

9,780.7 10,509.0 611.2 975.6 channel sounding

9,771.7 10,522.6 627.6 974.3 channel sounding

9,762.6 10,536.3 644.0 973.6 channel sounding

9,753.5 10,550.0 660.4 973.3 channel sounding

9,744.5 10,563.7 676.8 974.9 channel sounding

9,735.4 10,577.3 693.2 975.5 channel sounding

9,726.3 10,591.0 709.6 975.7 channel sounding

9,717.3 10,604.7 726.0 978.1 channel sounding

9,699.2 10,632.0 758.8 975.4 channel sounding

9,681.0 10,659.4 791.7 975.1 channel sounding

9,669.5 10,676.8 812.5 981.0 right edge of water

9,664.3 10,681.9 819.7 983.4 toe of bank

9,664.2 10,682.9 820.5 985.4 bank

9,657.9 10,691.9 831.6 985.5 bank

Appendix B 53
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B6. Cross section Discharge Measurement at the Tanana 

River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -52.1 998.4 bank

10,029.6 10,038.301 -19.0 989.6 rebar

10,031.1 10,057.3 .0 981.1 left edge of water

10,031.9 10,067.1 9.8 975.1 channel sounding

10,034.6 10,099.8 42.7 970.6 channel sounding

10,037.3 10,132.5 75.5 972.0 channel sounding

10,039.9 10,165.2 108.3 970.6 channel sounding

10,042.6 10,197.9 141.1 969.9 channel sounding

10,044.5 10,220.8 164.0 970.4 channel sounding

10,046.4 10,243.7 187.0 970.4 channel sounding

10,048.2 10,266.5 210.0 970.2 channel sounding

10,050.1 10,289.4 233.0 972.7 channel sounding

10,052.0 10,312.3 255.9 972.2 channel sounding

10,053.8 10,335.2 278.9 972.9 channel sounding

10,056.5 10,367.9 311.7 974.1 channel sounding

10,059.2 10,400.6 344.5 975.4 channel sounding

10,061.9 10,433.3 377.3 976.3 channel sounding

10,065.3 10,475.8 420.0 977.6 channel sounding

10,069.3 10,524.9 469.2 977.6 channel sounding

10,073.4 10,573.9 518.4 976.6 channel sounding

10,076.0 10,606.6 551.2 968.6 channel sounding

10,081.4 10,672.0 616.8 969.6 channel sounding

10,085.4 10,721.1 666.0 981.1 right edge of water

10,086.2 10,730.6 675.6 988.4 rebar

– – 741.2 988.3 estimated overbank

– – 761.2 988.3 estimated overbank

– – 773.2 999 extended up

54 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B7. Cross section Upstream Side Bridge at the Tanana 

River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -31.6 993.9 low steel

10,016.7 10,014.7 -31.5 993.1 bank

10,006.2 10,030.6 -12.5 989.8 bank

9,997.3 10,039.5 .0 981.1 left edge of water

9,989.5 10,050.1 13.1 975.6 channel sounding

9,979.7 10,063.3 29.5 973.3 channel sounding

9,970.0 10,076.5 45.9 972.1 channel sounding

9,960.2 10,089.7 62.3 969.6 channel sounding

9,950.5 10,102.9 78.7 972.1 channel sounding

9,940.7 10,116.1 95.1 975.4 channel sounding

9,931.0 10,129.3 111.6 974.8 channel sounding

9,921.3 10,142.5 128.0 974.9 channel sounding

9,911.5 10,155.7 144.4 974.1 channel sounding

9,901.8 10,168.9 160.8 971.1 channel sounding

9,892.0 10,182.1 177.2 970.9 channel sounding

9,882.3 10,195.2 193.6 970.4 channel sounding

9,872.5 10,208.4 210.0 970.7 channel sounding

9,862.8 10,221.6 226.4 971.0 channel sounding

9,853.0 10,234.8 242.8 970.5 channel sounding

9,843.3 10,248.0 259.2 970.3 channel sounding

9,833.5 10,261.2 275.6 970.0 channel sounding

9,823.8 10,274.4 292.0 971.2 channel sounding

9,814.0 10,287.6 308.4 972.5 channel sounding

9,804.3 10,300.8 324.8 972.4 channel sounding

9,794.6 10,314.0 341.2 970.1 channel sounding

9,784.8 10,327.2 357.6 970.0 channel sounding

9,775.1 10,340.4 374.0 971.6 channel sounding

9,765.3 10,353.6 390.4 972.4 channel sounding

9,755.6 10,366.8 406.8 973.1 channel sounding

9,745.8 10,380.0 423.2 973.1 channel sounding

9,736.1 10,393.2 439.7 972.8 channel sounding

9,726.3 10,406.4 456.1 973.4 channel sounding

9,716.6 10,419.6 472.5 973.8 channel sounding

9,706.8 10,432.8 488.9 972.3 channel sounding

9,697.1 10,446.0 505.3 975.0 channel sounding

9,687.4 10,459.2 521.7 977.1 channel sounding

9,677.6 10,472.4 538.1 976.4 channel sounding

9,667.9 10,485.6 554.5 974.8 channel sounding

9,658.1 10,498.8 570.9 974.6 channel sounding

9,648.4 10,512.0 587.3 972.3 channel sounding

9,628.9 10,538.3 620.1 973.9 channel sounding

9,619.1 10,551.5 636.5 977.8 channel sounding

9,609.4 10,564.7 652.9 977.6 channel sounding

9,599.6 10,577.9 669.3 976.5 channel sounding

9,589.9 10,591.1 685.7 974.3 channel sounding

9,580.1 10,604.3 702.1 976.4 channel sounding

9,574.3 10,612.2 712.0 981.1 right edge of water

9,571.3 10,615.4 716.3 983.4 bank

9,563.7 10,620.9 725.2 990.4 bank

9,554.2 10,636.2 743.2 995.6 bank

9,553.6 10,637.0 744.2 1,001.2 low steel

Appendix B 55
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B8. Cross section Downstream Side Bridge at the Tanana 

River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

9,979.7 10,001.4 – 993.9 low steel

9,984.5 9,990.9 -33.1 993.1 bank

9,974.1 10,006.9 -14.1 989.8 bank

9,965.4 10,018.0 .0 980.8 left edge of water

9,942.7 10,049.8 39.1 972.8 channel sounding

9,931.0 10,065.6 58.8 967.1 channel sounding

9,927.1 10,070.9 65.3 968.2 channel sounding

9,913.4 10,089.4 88.3 971.8 channel sounding

9,903.7 10,102.6 104.7 973.5 channel sounding

9,893.9 10,115.7 121.1 975.4 channel sounding

9,884.2 10,128.9 137.5 973.2 channel sounding

9,878.3 10,136.9 147.3 971.8 channel sounding

9,872.5 10,144.8 157.2 968.7 channel sounding

9,858.8 10,163.3 180.1 968.9 channel sounding

9,845.2 10,181.7 203.1 963.6 channel sounding

9,835.4 10,194.9 219.5 964.3 channel sounding

9,825.7 10,208.1 235.9 965.8 channel sounding

9,821.8 10,213.4 242.5 965.0 channel sounding

9,810.1 10,229.2 262.2 964.4 channel sounding

9,806.2 10,234.5 268.7 966.8 channel sounding

9,796.5 10,247.7 285.1 971.9 channel sounding

9,786.7 10,260.9 301.5 972.6 channel sounding

9,777.0 10,274.1 318.0 973.9 channel sounding

9,755.5 10,303.1 354.0 963.3 channel sounding

9,753.6 10,305.8 357.3 973.6 channel sounding

9,738.0 10,326.9 383.6 974.8 channel sounding

9,728.2 10,340.1 400.0 972.5 channel sounding

9,718.5 10,353.3 416.4 972.2 channel sounding

9,708.8 10,366.5 432.8 971.1 channel sounding

9,699.0 10,379.7 449.2 971.3 channel sounding

9,689.3 10,392.9 465.6 971.3 channel sounding

9,679.5 10,406.1 482.0 972.1 channel sounding

9,669.8 10,419.3 498.4 972.7 channel sounding

9,660.0 10,432.5 514.8 971.0 channel sounding

9,650.3 10,445.7 531.2 974.3 channel sounding

9,640.5 10,458.8 547.6 973.8 channel sounding

9,630.8 10,472.0 564.0 972.7 channel sounding

9,621.0 10,485.2 580.4 969.5 channel sounding

9,611.3 10,498.4 596.8 964.8 channel sounding

9,601.5 10,511.6 613.2 964.4 channel sounding

9,591.8 10,524.8 629.6 964.8 channel sounding

9,582.1 10,538.0 646.1 971.9 channel sounding

9,574.4 10,548.3 658.9 981.1 right edge of water

9,563.8 10,557.4 672.4 988.3 bank

9,554.3 10,570.8 688.9 993.0 bank

9,522.1 10,613.6 742.5 998.9 bank

56  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B9. Cross section Exit 1 at the Tanana River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -6,020.0 1,020.0 extended up 

– – -6,000.0 1,000.0 estimated delta

– – -84.0 982.8 estimated delta

9,725.6 9,963.9 -14.8 981.2 rebar

9,722.8 9,980.8 .0 980.3 left edge of water

9,696.0 9,999.7 31.6 980.1 channel sounding

9,683.5 10,014.8 51.3 976.5 channel sounding

9,673.1 10,027.5 67.7 975.7 channel sounding

9,662.6 10,040.1 84.1 973.8 channel sounding

9,652.2 10,052.8 100.5 973.5 channel sounding

9,641.7 10,065.4 116.9 973.9 channel sounding

9,631.3 10,078.1 133.3 974.6 channel sounding

9,620.8 10,090.7 149.7 971.9 channel sounding

9,610.4 10,103.3 166.1 965.7 channel sounding

9,599.9 10,116.0 182.5 963.2 channel sounding

9,589.5 10,128.6 198.9 960.2 channel sounding

9,579.0 10,141.3 215.3 957.8 channel sounding

9,558.1 10,166.6 248.1 955.8 channel sounding

9,547.7 10,179.2 264.5 957.8 channel sounding

9,537.2 10,191.9 280.9 958.2 channel sounding

9,526.8 10,204.5 297.3 964.2 channel sounding

9,516.3 10,217.2 313.7 967.3 channel sounding

9,505.9 10,229.8 330.2 970.9 channel sounding

9,495.4 10,242.5 346.6 973.8 channel sounding

9,485.0 10,255.1 363.0 976.8 channel sounding

9,478.7 10,262.7 372.8 976.6 channel sounding

9,467.9 10,280.6 393.4 980.6 right edge of water

9,463.8 10,280.6 396.1 982.5 rebar

9,449.4 10,285.2 408.8 994.4 bank

– – 410.8 1,014.4 cliff face

Appendix B 57
945

955

965

975

985

995

1005

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B10. Cross section Exit 2 at the Tanana River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -6,020.0 1,020.0 extended up 

– – -6,000.0 1,000.0 estimated delta

– – -84.0 982.8 estimated delta

9,474.6 9,803.0 -10.0 980.5 rebar

9,470.5 9,812.4 .0 980.1 left edge of water

9,470.2 9,822.1 9.5 976.6 channel sounding

9,466.6 9,837.5 25.4 975.4 channel sounding

9,463.0 9,853.0 41.3 975.7 channel sounding

9,459.4 9,868.5 57.2 975.9 channel sounding

9,455.8 9,884.0 73.1 976.1 channel sounding

9,452.2 9,899.4 89.0 977.7 channel sounding

9,448.6 9,914.9 104.8 977.2 channel sounding

9,445.0 9,930.4 120.7 977.3 channel sounding

9,442.9 9,939.7 130.3 977.7 channel sounding

9,437.8 9,961.3 152.5 968.5 channel sounding

9,434.2 9,976.8 168.4 967.2 channel sounding

9,427.0 10,007.7 200.2 959.9 channel sounding

9,423.4 10,023.2 216.0 955.8 channel sounding

9,419.8 10,038.7 231.9 950.7 channel sounding

9,416.2 10,054.2 247.8 948.9 channel sounding

9,412.7 10,069.6 263.7 948.7 channel sounding

9,409.1 10,085.1 279.6 957.7 channel sounding

9,407.6 10,091.3 285.9 961.2 channel sounding

9,405.5 10,100.6 295.5 965.5 channel sounding

9,401.9 10,116.1 311.4 968.3 channel sounding

9,399.7 10,125.3 320.9 971.2 channel sounding

9,396.1 10,140.8 336.8 979.5 right edge of water

9,394.9 10,146.0 342.1 981.7 rebar

9,386.5 10,154.7 352.5 987.5 bank

– – 354.5 1,007.5 cliff face

58  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B11. Cross section Exit 3 at the Tanana River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft)

Notes

– – -6,020.0 1,020.0 extended up 

– – -6,000.0 1,000.0 estimated delta

– – -81.8 983.1 estimated delta

9,474.6 9,803.0 -12.6 981.5 rebar

9,470.5 9,812.4 -3.1 980.1 toe of bank

9,470.2 9,822.1 .0 979.2 left edge of water

9,466.6 9,837.5 22.7 979.0 channel sounding

9,463.0 9,853.0 39.1 972.6 channel sounding

9,459.4 9,868.5 55.5 969.4 channel sounding

9,455.8 9,884.0 71.9 968.2 channel sounding

9,452.2 9,899.4 88.4 967.7 channel sounding

9,448.6 9,914.9 104.8 967.9 channel sounding

9,445.0 9,930.4 121.2 969.1 channel sounding

9,442.9 9,939.7 137.6 968.8 channel sounding

9,437.8 9,961.3 154.0 968.2 channel sounding

9,434.2 9,976.8 170.4 967.3 channel sounding

9,427.0 10,007.7 186.8 966.5 channel sounding

9,423.4 10,023.2 203.2 965.5 channel sounding

9,419.8 10,038.7 219.6 964.3 channel sounding

9,416.2 10,054.2 236.0 962.5 channel sounding

9,412.7 10,069.6 252.4 959.3 channel sounding

9,409.1 10,085.1 268.8 958.6 channel sounding

9,407.6 10,091.3 285.2 966.5 channel sounding

9,405.5 10,100.6 301.6 975.1 channel sounding

9,401.9 10,116.1 324.3 979.3 right edge of water

9,399.7 10,125.3 326.8 980.2 toe of bank

9,396.1 10,140.8 330.5 984.3 rebar

9,394.9 10,146.0 333.5 987.3 estimated bank

– – 335.5 1,007.3 cliff face

Appendix B 59
950

960

970

980

990

1000

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B12. Cross section Exit 4 at the Tanana River at Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -6,020.0 1,020.0 extended up 

– – -6,000.0 1,000.0 estimated delta

8,391.010 9,525.970 -76.1 982.6 delta

8,405.1 9,593.7 -6.9 981.0 rebar

8,406.4 9,600.5 .0 979.7 left edge of water

8,409.1 9,613.3 13.1 978.3 channel sounding

8,415.1 9,642.2 42.7 977.6 channel sounding

8,421.8 9,674.4 75.5 965.7 channel sounding

8,428.5 9,706.5 108.3 962.2 channel sounding

8,435.1 9,738.6 141.1 962.7 channel sounding

8,441.8 9,770.7 173.9 962.7 channel sounding

8,448.5 9,802.8 206.7 962.9 channel sounding

8,455.2 9,835.0 239.5 963.8 channel sounding

8,461.8 9,867.1 272.3 965.9 channel sounding

8,469.8 9,905.6 311.7 966.1 channel sounding

8,475.8 9,934.6 341.2 979.7 right edge of water

– – 346.2 984.7 estimated bank

– – 348.2 1,004.7 cliff face

60 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-350 -250 -150 -50 50 150 250 350

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B13. Cross section Slough 1 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -2,50.3 1,001.2 estimated overbank

– – -2,35.3 986.2 estimated overbank

10,376.434 11,291.563 -35.3 986.2 bank

10,370.0 11,296.0 -27.7 985.5 rebar

10,361.8 11,301.0 -18.2 982.9 toe of bank

10,344.7 11,307.1 .0 980.8 left edge of water

10,337.1 11,310.4 8.2 978.8 channel sounding

10,331.1 11,313.0 14.8 976.3 channel sounding

10,325.1 11,315.6 21.3 975.7 channel sounding

10,319.0 11,318.2 27.9 975.1 channel sounding

10,313.0 11,320.7 34.5 974.5 channel sounding

10,307.0 11,323.3 41.0 973.9 channel sounding

10,301.0 11,325.9 47.6 973.0 channel sounding

10,294.9 11,328.5 54.1 972.8 channel sounding

10,288.9 11,331.1 60.7 972.0 channel sounding

10,282.9 11,333.7 67.3 971.6 channel sounding

10,276.8 11,336.3 73.8 970.9 channel sounding

10,270.8 11,338.9 80.4 970.4 channel sounding

10,264.8 11,341.5 87.0 970.4 channel sounding

10,258.8 11,344.1 93.5 970.4 channel sounding

10,252.7 11,346.7 100.1 971.1 channel sounding

10,246.7 11,349.2 106.6 971.5 channel sounding

10,240.7 11,351.8 113.2 973.0 channel sounding

10,234.6 11,354.4 119.8 974.5 channel sounding

10,228.6 11,357.0 126.3 976.6 channel sounding

10,216.6 11,362.2 139.5 980.8 right edge of water

10,212.8 11,363.5 143.4 988.4 rebar

– – 243.4 988.4 estimated overbank

– – 258.4 1,003.4 estimated overbank

Appendix B  61
950

960

970

980

990

1000

-350 -250 -150 -50 50 150 250 350

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B14. Cross section Slough 2 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -2,26.0 1,001.1 estimated overbank

– – -2,11.0 986.1 estimated overbank

10,302.530 11,121.440 -11.0 986.1 bank

10,298.1 11,121.7 -6.7 984.6 rebar

10,291.5 11,121.9 .0 980.8 left edge of water

10,288.2 11,122.1 3.3 979.0 channel sounding

10,262.0 11,123.6 29.5 974.1 channel sounding

10,245.6 11,124.5 45.9 973.6 channel sounding

10,229.3 11,125.4 62.3 972.6 channel sounding

10,212.9 11,126.3 78.7 970.2 channel sounding

10,196.5 11,127.3 95.1 969.3 channel sounding

10,180.1 11,128.2 111.6 969.4 channel sounding

10,163.7 11,129.1 128.0 977.1 channel sounding

10,159.1 11,128.8 132.6 980.8 right edge of water

10,153.8 11,129.7 137.9 986.2 rebar

– – 237.9 986.2 estimated overbank

– – 252.9 1,001.2 estimated overbank

62 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
950

960

970

980

990

1000

-350 -250 -150 -50 50 150 250 350

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B15. Cross section Slough 3 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -2,28.3 999.7 estimated overbank

– – -2,13.3 984.7 estimated overbank

10,278.7 10,925.2 -13.3 984.7 rebar

10,265.4 10,925.3 .0 981.1 left edge of water

10,260.3 10,924.4 5.2 979.1 channel sounding

10,250.5 10,923.9 15.0 978.1 channel sounding

10,243.9 10,923.6 21.6 977.1 channel sounding

10,237.4 10,923.2 28.1 975.7 channel sounding

10,230.8 10,922.9 34.7 975.2 channel sounding

10,224.2 10,922.5 41.3 973.9 channel sounding

10,211.1 10,921.8 54.4 972.0 channel sounding

10,204.6 10,921.5 60.9 971.3 channel sounding

10,198.0 10,921.2 67.5 970.9 channel sounding

10,191.5 10,920.8 74.1 970.9 channel sounding

10,184.9 10,920.5 80.6 970.3 channel sounding

10,178.4 10,920.1 87.2 969.8 channel sounding

10,171.8 10,919.8 93.7 969.6 channel sounding

10,165.3 10,919.4 100.3 969.1 channel sounding

10,158.7 10,919.1 106.9 969.0 channel sounding

10,152.2 10,918.8 113.4 969.3 channel sounding

10,145.6 10,918.4 120.0 975.6 channel sounding

10,135.8 10,917.9 129.8 979.0 channel sounding

10,133.9 10,917.8 131.7 981.0 right edge of water

10,127.8 10,917.3 137.9 985.7 rebar

10,093.1 10,925.1 173.4 999.9 bank

Appendix B  63
950

960

970

980

990

1000

-350 -250 -150 -50 50 150 250 350

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B16. Cross section Slough 4 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -324.6 1,001.4 estimated overbank

– – -309.6 986.4 estimated overbank

10,361.7 10,730.1 -109.6 986.4 bank

10,299.3 10,721.3 -46.6 985.7 rebar

10,287.5 10,721.8 -34.8 983.9 toe of bank

10,252.7 10,722.1 .0 981.0 left edge of water

10,246.2 10,722.2 6.6 977.6 channel sounding

10,233.1 10,722.2 19.7 974.9 channel sounding

10,223.2 10,722.2 29.5 972.5 channel sounding

10,216.7 10,722.2 36.1 972.9 channel sounding

10,206.8 10,722.2 45.9 972.6 channel sounding

10,200.2 10,722.3 52.5 972.3 channel sounding

10,187.1 10,722.3 65.6 972.6 channel sounding

10,180.6 10,722.3 72.2 972.6 channel sounding

10,167.4 10,722.3 85.3 972.5 channel sounding

10,164.2 10,722.3 88.6 972.3 channel sounding

10,151.0 10,722.4 101.7 971.9 channel sounding

10,141.2 10,722.4 111.6 971.7 channel sounding

10,134.6 10,722.4 118.1 972.2 channel sounding

10,128.1 10,722.4 124.7 973.0 channel sounding

10,118.2 10,722.4 134.5 973.9 channel sounding

10,114.9 10,722.4 137.8 975.5 channel sounding

10,108.4 10,722.5 144.4 975.9 right edge of water

10,101.8 10,722.5 150.9 981.0 right edge of water

10,047.0 10,721.8 205.8 986.0 rebar

10,044.6 10,726.7 211.2 987.1 bank

10,026.5 10,758.0 247.3 988.3 bank

– – 267.3 988.3 estimated overbank

– – 279.3 1,000.3 estimated overbank

64 Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
0

5

10

15

20

25

30

35

40

45

50

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B17. Cross section Approach 8000 at the Tanana River at 

Big Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -32.8 45.8 bank

– – 0.0 40.3 left edge of water

– – 16.4 37.3 channel sounding

– – 32.8 32.8 channel sounding

– – 49.2 34.0 channel sounding

– – 65.6 34.2 channel sounding

– – 82.0 37.6 channel sounding

– – 98.4 36.8 channel sounding

– – 114.8 35.7 channel sounding

– – 131.2 34.6 channel sounding

– – 147.6 31.6 channel sounding

– – 164.0 32.5 channel sounding

– – 180.4 29.6 channel sounding

– – 196.8 30.0 channel sounding

– – 213.2 31.7 channel sounding

– – 229.6 31.5 channel sounding

– – 246.0 31.9 channel sounding

– – 262.4 31.8 channel sounding

– – 278.8 31.5 channel sounding

– – 295.2 31.4 channel sounding

– – 311.6 31.7 channel sounding

– – 328.0 31.7 channel sounding

– – 344.4 31.7 channel sounding

– – 360.8 31.5 channel sounding

– – 377.2 31.6 channel sounding

– – 393.6 31.5 channel sounding

– – 410.0 31.4 channel sounding

– – 426.4 31.1 channel sounding

– – 442.8 31.2 channel sounding

– – 459.2 31.1 channel sounding

– – 475.6 31.5 channel sounding

– – 492.0 32.3 channel sounding

– – 508.4 33.1 channel sounding

– – 524.8 33.7 channel sounding

– – 541.2 34.1 channel sounding

– – 557.6 34.6 channel sounding

– – 574.0 35.0 channel sounding

– – 590.4 35.3 channel sounding

– – 606.8 34.2 channel sounding

Appendix B  65
0

5

10

15

20

25

30

35

40

45

50

-200 0 200 400 600 800 1000

DISTANCE FROM LEFT BANK, IN FEET

ELEVATION, IN FEET

Surveyed Water 

Surface

Table B18. Cross section Slough 8000 at the Tanana River at Big 

Delta.

[Points surveyed August 27, 1996. See figure 2 for location. See text for 

coordinate information; ft, foot]

Easting

(ft)

Northing

(ft)

Station

(ft)

Elevation

(ft) Notes

– – -85.3 44.1 bank

– – -36.1 43.1 bank

– – -34.5 41.6 bank

– – .0 39.4 left edge of water

– – 29.5 34.8 channel sounding

– – 39.4 34.4 channel sounding

– – 45.9 34.1 channel sounding

– – 52.5 34.3 channel sounding

– – 59.1 34.0 channel sounding

– – 65.6 34.2 channel sounding

– – 72.2 34.2 channel sounding

– – 78.7 34.3 channel sounding

– – 85.3 34.3 channel sounding

– – 91.9 34.0 channel sounding

– – 98.4 33.9 channel sounding

– – 105.0 34.1 channel sounding

– – 111.6 34.0 channel sounding

– – 118.1 34.2 channel sounding

– – 124.7 33.9 channel sounding

– – 137.8 34.3 channel sounding

– – 144.4 34.5 channel sounding

– – 150.9 34.2 channel sounding

– – 157.5 34.3 channel sounding

– – 170.6 39.2 right edge of water

– – 177.2 41.5 bank

– – 180.5 46.8 bank

– – 242.8 47.5 bank

66  Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska
Manuscript approved for publication, October 26, 2006

Prepared by the USGS Publishing Network, 

Publishing Service Center, Tacoma, Washington

Robert Crist

Christine Severtson

Sharon Wahlstrom

Bobbie Jo Richey

Publishing Service Center, Sacramento, California

Virginia Wenslaff

For more information concerning the research in this report, contact the 

Alaska Science Center

U.S. Geological Survey

4230 University Drive, Suite 201

Anchorage, Alaska 99508-4664

http://alaska.usgs.gov
SIR 2006–5282 Heinrichs and others Hydraulic Survey and Scour Assessment of Bridge 524, Tanana River at Big Delta, Alaska