Prepared in cooperation with the

ALASKA DEPARTMENT OF TRANSPORTATION AND PUBLIC FACILITIES

Methodology and Estimates of Scour at

Selected Bridge Sites in Alaska

Water-Resources Investigations Report 00-4151

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY
Cover photograph: Bridge over Castner Creek, Richardson Highway mile 217.2. View

from right downstream bank, west end of bridge. Right abutment (left side of photograph)

was eroded and required emergency repair. Photograph was taken by author D.E.

Langley, approximately 8 hours after peak flow, August 13, 1997.
Methodology and Estimates of Scour at 

Selected Bridge Sites in Alaska

By Thomas A. Heinrichs, Ben W. Kennedy, Dustin E. Langley, and 

Robert L. Burrows

U.S. GEOLOGICAL SURVEY

Anchorage, Alaska

2001

Prepared in cooperation with the

ALASKA DEPARTMENT OF TRANSPORTATION AND PUBLIC FACILITIES

Water-Resources Investigations Report 00ñ4151
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

Any use of trade, product, or firm names in this publication is for descriptive

purposes only and does not imply endorsement by the U.S. Government

For additional information Copies of this report can be

contact: purchased from:

District Chief U.S. Geological Survey 

U.S. Geological Survey Information Services

4230 University Drive, Suite 201 Building 810

Anchorage, AK 99508ñ4664 Box 25286, Federal Center

Denver, CO 80225ñ0286

http://ak.water.usgs.gov
CONTENTS III

CONTENTS

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

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

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

Purpose and Scope ..................................................................................................................................................... 2

Methodology.......................................................................................................................................................................... 2

Magnitude of 100- and 500-Year Floods ................................................................................................................... 3

Cross Sections and Hydraulic Properties .................................................................................................................. 3

Computation of Water-Surface Profile Using WSPRO Step-Backwater Model ....................................................... 16

Estimates of Contraction Scour and Pier Scour..................................................................................................................... 16

Summary and Conclusions .................................................................................................................................................... 17

References Cited.................................................................................................................................................................... 30

Appendix: Summary Examples of Four Phase I Bridge-Scour Analyses ............................................................................. 31

FIGURE

1. Plan view showing approach, bridge, full-valley, and exit cross sections used in water-surface-profile

computational model WSPRO ............................................................................................................................... 16

TABLES

1. Basin characteristics at selected bridge sites in Alaska ......................................................................................... 4

2. Computed Phase I contraction- and pier-scour depths at selected bridge sites in Alaska ..................................... 18

CONVERSION FACTORS and VERTICAL DATUM

Multiply by To obtain

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer

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

cubic foot per second (ft3

/s) 0.02832 cubic meter per second

foot per foot (ft/ft) 1.000 meter per meter

In this report, temperature is reported in degrees Fahrenheit (°F), which can be converted to degrees Celsius (°C) by the equation

°C = (°F – 32) / 1.8

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called “Sea-Level 

Datum of 1929”), which is derived from a general adjustment of the first-order leveling networks of the United States and Canada. In the 

adjustment, sea levels from selected tide stations in both countries were held fixed. The year indicates the time of the last 

general adjustment. This datum should not be confused with mean sea level. Altitudes are the same in both the local coordinate 

system and the Universal Transverse Mercator system.
INTRODUCTION 1

Abstract

The U.S. Geological Survey estimated scour 

depths at 325 bridges in Alaska as part of a cooperative agreement with the Alaska Department of 

Transportation and Public Facilities. The department selected these sites from approximately 806 

State-owned bridges as potentially susceptible to 

scour during extreme floods. Pier scour and contraction scour were computed for the selected 

bridges by using methods recommended by the 

Federal Highway Administration. The U.S. Geological Survey used a four-step procedure to estimate scour: (1) Compute magnitudes of the 100- 

and 500-year floods. (2) Determine cross-section 

geometry and hydraulic properties for each bridge 

site. (3) Compute the water-surface profile for the 

100- and 500-year floods. (4) Compute contraction 

and pier scour. This procedure is unique because 

the cross sections were developed from existing 

data on file to make a quantitative estimate of 

scour. This screening method has the advantage of 

providing scour depths and bed elevations for 

comparison with bridge-foundation elevations 

without the time and expense of a field survey. 

Four examples of bridge-scour analyses are summarized in the appendix.

INTRODUCTION

The Federal Highway Administration (FHWA) 

has established a requirement that all State highway 

agencies evaluate the bridges on the Federal Aid System for susceptibility to scour-related failure. In 1994, 

the U.S. Geological Survey (USGS), in cooperation 

with the Alaska Department of Transportation and 

Public Facilities (ADOT&PF), began a cooperative 

study of bridge scour in Alaska. The project was part 

of a national cooperative effort among the States, the 

FHWA, and the USGS to analyze scour potential 

at existing bridge sites. The ADOT&PF screened 

approximately 800 bridge sites in Alaska, selected 520 

sites as scour susceptible, and assigned 340 of these 

scour-susceptible sites to the USGS for assessment. To 

date, assessment of scour has been completed for 325 

of the 340 sites.

Background

A bridge is described as “scour-critical” if the 

abutment or pier foundations or both have been determined to be, or have the potential to be, undermined or 

to become unstable because of hydraulic erosion of the 

channel bed or banks (Federal Highway Administration, 1988). Scour processes are accelerated during 

high-flow conditions, and the potential for scourMethodology and Estimates of Scour at Selected Bridge 

Sites in Alaska

By Thomas A. Heinrichs, Ben W. Kennedy, Dustin E. Langley, and Robert L. Burrows
2 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

related problems at a bridge tends to increase during 

floods. Bridge-scour processes are classified into three 

components: (1) general long-term aggradation or degradation of the stream channel, (2) contraction scour, 

and (3) local scour at piers and abutments. The total 

scour that can occur at a bridge is the sum of these 

components. 

General scour refers to geomorphic processes 

that cause degradation, such as long-term adjustments 

of a channel that result from changes in basin hydrology, hydraulics, or sediment movement. Contraction 

scour refers to the general lowering of the channel bed 

under the bridge. Contraction scour is initiated by 

increased flow velocities through the bridge opening, 

change in local base-level elevation, or flow around a 

bend. The most common cause of contraction scour is 

the contraction of flow by bridge-approach embankments that encroach on the flood plain, the main channel, or both (Richardson and Davis, 1995). Local 

scour is the removal of material around piers, abutments, spur dikes, and embankments caused by flow 

acceleration and turbulence near bridge substructural 

elements and embankments.

Purpose and Scope

Evaluation of the selected 325 bridge sites is 

being accomplished in two phases. Phase I, which is 

described in this report, is the preliminary assessment 

of scour, floods, and basin characteristics for each 

of the selected sites. Phase II evaluation consists of 

detailed field surveys, inspections, and additional 

hydraulic modeling of those bridges that have a high 

potential for scour as determined by ADOT&PF from 

reported Phase I results. The results of Phase II scour 

assessments will be published in a subsequent report.

The purpose of this report is (1) to document the 

general methodology used to evaluate scour for the 

selected bridge sites in Alaska and (2) to summarize 

preliminary scour results, basin characteristics, and 

calculated estimates of 100- and 500-year peak flows 

for each of the 325 bridge sites analyzed to date. Fifteen additional sites were not completed because they 

either are affected significantly by tidal activity or do 

not have bridge plans readily available.

This study is focused on estimating maximum 

contraction scour and local pier scour at selected 

bridge sites associated with floods having annual 

exceedence probabilities of 0.01 and 0.002, referred to 

hereafter as the 100- and 500-year floods, respectively. 

The scour analyses do not include other factors that 

can affect bridge scour, such as channel migration or 

long-term aggradation or degradation that may be 

occurring at the bridge site.

The maximum-scour equations used for this 

study are those presented in an FHWA report, Hydraulic Engineering Circular 18, by Richardson and Davis 

(1995)—hereafter referred to as “HEC–18.”

METHODOLOGY

An estimate of the maximum scour that may 

occur at a site during a high-flow event can be made 

by determining the hydraulic properties of the channel 

and bridge opening for a flood and using appropriate 

scour equations. 

The techniques developed by the USGS for 

this Phase I study were in response to requests from 

ADOT&PF for a low-cost, quantitative scour-estimation technique. When this project was initiated in 

1994, two methods were in general use for screening 

bridge sites for scour potential, and both required initial site visits: (1) Using data entered into a standardized qualitative form to assess geomorphic features of 

the site, to determine certain bridge parameters, and to 

identify and rate scour potential for the bridge (Robinson and Thompson, 1993; Huizinga and Waite, 1994). 

(2) Surveying the cross sections required to develop 

a hydraulic model of flood flow through the bridge 

opening, modeling the flow, and extracting variables 

from the model output to compute scour by empirical 

techniques described in HEC–18 (Richardson and 

Davis, 1995).

Doing site-specific field surveys and producing 

hydraulic models are relatively expensive and time 

consuming but do provide a quantitative estimate of 

scour based on current physical conditions at the site. 

In the past, the less expensive method using standardized qualitative forms commonly was used as a 

screening method (Phase I) to select sites that may 

require a more detailed and expensive quantitative 

estimate of scour (Phase II).
METHODOLOGY 3

A new technique developed by the USGS provides a relatively low cost, preliminary (Phase I) but 

quantitative estimate of scour. Channel cross sections 

and hydraulic models were developed from bridge 

as-built plans or plans-of-record (provided by 

ADOT&PF) and other existing bridge and hydrologic information such as bridge inspections, USGS 

discharge measurements, and USGS indirect flood 

computations as well as from topographic maps. Scour 

was computed from these models by the accepted 

FHWA techniques as described in HEC–18 (Richardson and Davis, 1995).

Phase I scour-estimation techniques described in 

this report are composed of four essentially discrete 

steps: (1) Compute magnitudes of the 100- and 500-

year floods from regional regression equations or published flood-frequency analyses. (2) Determine cross 

sections and hydraulic properties for each bridge site 

based on existing bridge plans and available hydrologic information. (3) Compute the water-surface profile for the 100- and 500-year floods by using Shearman’s (1990) step-backwater water-surface profile 

(WSPRO) model. (4) Compute contraction scour and 

pier scour by using variables generated by the WSPRO 

model and techniques recommended by the FHWA in 

HEC–18 (Richardson and Davis, 1995).

Because of the repetitive and complex nature of 

the computations, software was developed to automate 

each of the four steps. This software allowed timely 

and accurate analyses of sites by automating repetitive 

tasks and providing quality-assurance tools.

Magnitude of 100- and 500-Year Floods

Alaska has a relatively sparse stream-gaging

network. For bridge sites having a sufficient streamgaging record, floods were estimated by using both 

standard flood-frequency analyses (Interagency Advisory Committee on Water Data, 1982) and regional 

regression flood estimates (Jones and Fahl, 1994). 

Specifically, at sites where both the standard frequency 

and regression flood estimates were available, floods 

were combined by using a logarithmic-weighting factor based on the number of years of stream-gaging data 

and an equivalent factor for the regression-computed 

floods (Jones and Fahl, 1994).

For ungaged sites, the 100- and 500-year floods 

were computed by using regional regression equations, 

which required drainage basin characteristics as outlined by Jones and Fahl (1994). Statistically significant 

basin characteristics that vary by region throughout the 

State include basin area, mean basin elevation, mean 

annual precipitation, mean minimum January temperature, percentage of basin covered by forest or covered 

by lakes or ponds. Basin characteristics are summarized in table 1. Of more than 300 basins characterized 

during Phase I of this study, many had no previous 

data on record. Scour assessments were not done for 

all the sites included in table 1, such as Chilkoot River 

bridge 387; scour assessments were done at other sites 

that do not appear in table 1, such as the Chena River 

bridge sites where maximum flow is regulated. A geographic-information system (spatial database) was 

used to automate the process of extracting basin characteristics from maps, and a spreadsheet incorporating 

regional regression equations was used to automate 

flood computations.

Cross Sections and Hydraulic Properties

To model water-surface profiles accurately, cross 

sections and hydraulic properties for the bridge and 

channel must be determined by surveying or be estimated by other techniques. In this study, nearly all 

cross sections were derived from existing bridge plans. 

Almost all bridges in the State were built in the last 60 

years, and bridge plans are readily available. These 

plans generally include an elevation view of the bridge 

showing the angle of attack (skew) of channel flow relative to the bridge at the time of construction and commonly contain a detailed topographic map showing the 

shape of the channel and overbank near the bridge.

Some bridge sites have available additional information such as discharge measurements at or near the 

bridge, stream-gaging records, bridge inspections, surveys for indirect flood computations, and photographs. 

When possible, such additional information was combined with the bridge-plan information to produce 

representative cross sections, determine channel-flow 

angle of attack at the bridge, and delineate breaks 

between the main channel and overbank.
4

MethodologyandEstimatesofScouratSelectedBridgeSitesinAlaska

Table 1. Basin characteristics at selected bridge sites in Alaska[Bridge ADOT&PF number: Bold indicates that corresponding basin-characteristics data are from Jones and Fahl (1994). Flood-frequency area designations are from Jones and Fahl (1994Transportation and Public Facilities. —, not applicable]

Bridge

Floodfrequency

area

Route or junction Basin Mean 

annual

precipitation

(inches)

Mean 

minimum

January

temperature

(degrees

Fahrenheit)

ADOT&PF

number Name Name Mile Area (square miles) Mean elevation (feet) 

201 Tanana River North Slough 3 Parks Highway 305.3 25,600 3,920 16.0 -15 202 Tanana River at Nenana 3 Parks Highway 305.0 25,600 3,920 16.0 -15 205 Copper River at Chitina 3 McCarthy Road 34.6 12,600 3,370 20.5 -7 208 Roslyn Creek 1 Cape Chiniak Road 36.7 5.9 531 120.0 24 

211 Little Willow Creek 2 Parks Highway 74.7 155 1,840 30.0 2 

212 Kashwitna River 2 Parks Highway 83.2 341 3,368 22.0 -1 215 Montana Creek 2 Parks Highway 96.5 164 1,930 30.0 0 217 Mendenhall River 1 Mendenhall Loop Road .0 84.8 2,236 145.4 21 230 Sheridan Glacier No. 3 1 Copper River Highway 14.7 106 2,216 177.2 16 232 North Fork Chena River 3 Chena Hot Springs Road 37.8 941 2,270 16.0 -19 233 North Fork Chena River 3 Chena Hot Springs Road 39.5 939 2,270 16.0 -19 234 North Fork Chena River 3 Chena Hot Springs Road 44.0 351 2,293 17.0 -19 235 North Fork Chena River 3 Chena Hot Springs Road 45.7 346 2,293 18.0 -19 238 Angel Creek 3 Chena Hot Springs Road 49.8 38.1 2,292 15.0 -19 240 Little Susitna River 2 Parks Highway 57.1 172 2,298 19.0 2 242 North Fork Chena River 3 Chena Hot Springs Road 55.3 120 2,460 18.0 -19 254 Susitna River at Sunshine 2 Parks Highway 104.2 11,100 3,480 35.0 -4 259 Honolulu Creek 2 Parks Highway 178.1 66.7 3,586 40.0 -5 260 East Fork Chulitna River 2 Parks Highway 185.1 154 3,717 40.0 -5 261 Middle Fork Chulitna River 2 Parks Highway 194.5 53.0 3,838 35.0 -6 266 Cripple River 3 Nome–Teller Road 19.4 32.6 797 25.7 -3 268 Fox River 3 Nome–Council 68.2 37.2 675 17.7 -5 269 Bear River 3 Nome–Council 71.7 30.5 644 17.4 -5 270 Little Chena River 3 Chena Hot Springs 11.9 372 1,480 15.0 -16 272 Hot Springs Slough 3 Elliot Highway 150.9 36.0 627 15.0 -16 274 Hutlinana Creek 3 Elliot Highway 129.3 88.0 1,791 15.0 -16 275 North Fork 12 Mile Creek 3 Steese Highway 93.4 23.0 3,239 19.3 -22 277 Taylor Creek 5 Taylor Highway 50.3 40.7 2,479 15.0 -24 281 Jack River 3 Cantwell Road — 315 3,459 30.0 -6 284 American River 1 Kodiak Island Highway 22.2 24.9 1,047 100.0 24 
METHODOLOGY 5

286 Deadman (Small) Creek 1 Kodiak Island Highway 31.0 1.1 1,398 100.0 24 

287 Olds River 1 Kodiak Island Highway 30.2 15.6 862 100.0 24 

288 Tonsina River (Lower) 3 McCarthy Road 19.3 827 3,170 58.0 -5 

290 East Fork Twin Creek 3 Cape Chiniak Road 40.8 3.5 507 120.0 24 

291 Kalsin Creek 1 Kodiak Island Highway 1.0 8.3 580 100.9 24 

292 Myrtle Creek 1 Cape Chiniak Road 33.3 4.9 725 113.9 24 

293 Pass Creek 3 Parks Highway 208.0 29.0 2,956 28.8 -6 

297 Forty Mile River 3 Taylor Highway 112.5 5,880 2,940 17.0 -22 298 O’Brien Creek 5 Taylor Highway 113.2 362 2,772 15.1 -22 299 Walker Fork 40 Mile River 5 Taylor Highway 81.8 388 3,039 15.2 -24 

302 Jack River 3 Parks Highway 209.5 200 3,821 30.0 -6 

303 O’Connor Creek 3 Goldstream Road .0 12.7 1,227 15.0 -18 310 Pilgrim River 3 Nome–Taylor Road 60.4 313 972 28.0 -5 

311 Bear Creek 3 Parks Highway 269.4 21.8 1,955 16.0 -9 

312 Jenny M Creek 3 Chena Hot Springs Road 20.0 13.4 1,041 15.0 -18 

313 Panguingue Creek 3 Parks Highway 252.5 17.1 2,076 25.0 -8 

323 Penny River 3 Nome–Teller Road 12.6 18.9 721 21.5 -3 

324 Snake River 3 Nome–Teller Road 7.3 85.7 632 30.0 -2 

325 West Fork Tolovana River 3 Elliot Highway 74.9 289 1,512 15.0 -17 

327 Station 355 Creek 1 Halibut Point Road 7.0 2.0 961 100.0 28 

328 Granite Creek 1 Halibut Point Road 4.6 2.2 1,167 100.0 28 

348 Scott Glacier No. 1 1 Copper River Highway 7.8 154 2,262 188.9 16 

349 Scott Glacier No. 2 1 Copper River Highway 7.9 154 2,262 188.9 16 

350 Scott Glacier No. 3 1 Copper River Highway 8.4 154 2,262 188.9 16 

351 Scott Glacier No. 4 1 Copper River Highway 8.8 154 2,262 188.9 16 

352 Scott Glacier No. 5 1 Copper River Highway 9.6 154 2,262 188.9 16 

355 Birch Creek 3 Steese Highway 147.1 2,160 2,250 16.8 -22 

357 Goldstream Creek 3 Sheep Creek Road — 96.7 1,200 15.0 -16 359 Spinach Creek 3 Goldstream Road .0 9.9 1,186 15.0 -18 367 Sheridan Glacier East Channel 1 Copper River Highway 16.4 106 2,216 177.2 16 

381 Eyak River 1 Copper River Highway 5.9 40.2 1,360 174.4 16 

383 Peterson Creek 1 Dotson Landing Road .0 9.4 1,037 80.0 22 386 Felton Creek 1 Kodiak Island Highway 22.0 2.3 873 100.0 24 

387 Chilkoot River 1 Lutak Spur .0 127 3,127 64.7 12 395 Alaganik Slough 1 Copper River Highway 22.5 27.8 1,248 144.0 16 

396 Deception Creek 2 Fishhook/Willow Road 48.4 58.9 1,128 22.7 2 

399 King Salmon Creek 2 Naknek–King Salmon 13.2 170 769 24.5 7 

400 Leader Creek 2 Naknek–King Salmon 3.3 2.4 83 20.0 7 

401 Moose Creek 21 Petersville Road 7.1 52.3 800 35.0 -3 402 Pauls Creek 2 Naknek–King Salmon 9.5 122 359 23.4 7 
6 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 1. Basin characteristics at selected bridge sites in AlaskaóContinued [Bridge ADOT&PF number: Bold indicates that corresponding basin-characteristics data are from Jones and Fahl (1994). Flood-frequency area designations are from Jones and Fahl (1994)

Transportation and Public Facilities. —, not applicable] Bridge Flood- frequency area Route or junction Basin Mean annual precipitation (inches) Mean minimum January temperature (degrees Fahrenheit) 

ADOT&PF number Name Name Mile Area (square miles) Mean elevation (feet) 

403 Portage Creek Overflow No. 1 2 Portage Glacier Road 3.1 45.9 2,046 152.2 11 404 Portage Creek Overflow No. 2 2 Portage Glacier Road 3.5 45.1 2,064 153.0 11 405 Portage Creek Overflow No. 3 2 Portage Glacier Road 4.1 42.1 2,099 156.0 11 406 Scott Glacier No. 6 1 Copper River Highway 9.8 154 2,262 188.9 16 407 Scott Glacier No. 7 1 Copper River Highway 10.0 154 2,262 188.9 16 

411 Scott Glacier No. 11 1 Copper River Highway 11.4 154 2,262 188.9 16 

419 Gold Run Creek 3 Nome–Teller Road 53.3 24.5 818 15.0 -4 

421 Feather River 3 Nome–Teller Road 35.5 27.6 1,272 18.6 -3 

422 Tisuk River 3 Nome–Teller Road 46.9 35.7 1,012 16.5 -4 

423 Eldorado Creek 3 Nome–Teller Road 46.2 6.0 1,262 17.0 -4 

429 Blind Slough 1 Crystal Lake Hatchery Road .0 8.3 1,015 94.5 26 

430 Faith Creek 3 Steese Highway 69.1 61.1 2,800 18.0 -20 

432 Sawmill Creek 1 Sawmill Creek Road 6.0 38.5 2,127 167.8 28 440 Tolovana River 3 Elliott Highway 57.1 140.3 1,436 14.0 -15 

441 Mosquito Fork 5 Taylor Highway 64.3 1,120 2,980 15.3 -22 

442 West Fork Dennison River 5 Taylor Highway 49.1 623.8 2,645 15.0 -22 

455 Anchorage Port Access Overhead 1 Loop Road/C Street .0 116 2,344 30.7 3 460 Nome River 3 Nome–Taylor Road 13.1 77.7 903 25.0 -3 

467 Ganes Creek 3 Sterling Lake–Ophir Road .0 94.1 1,440 25.0 -10 470 Small Creek 1 Kodiak Island Highway 20.5 1.0 1,179 100.0 24 

478 Goldstream Creek 3 Goldstream Road .0 40.9 1,472 15.0 -16 503 Gardiner Creek 3 Alaska Highway 1,246.7 308 2,396 15.0 -24 504 Beaver Creek 3 Alaska Highway 1,268.1 31.6 2,706 15.0 -24 505 Tanana River Near Tanacross 3 Alaska Highway 1,303.3 6,800 3,860 18.0 -22 506 Tok River 3 Alaska Highway 1,309.4 912 3,844 15.0 -21 507 Yerrick Creek 3 Alaska Highway 1,333.6 33.5 4,190 15.3 -13 508 Cathedral Rapids No. 1 3 Alaska Highway 1,338.1 9.0 3,614 15.1 -15 509 Robertson River 3 Alaska Highway 1,345.3 576 4,589 15.0 -15 510 Cathedral Rapids Creek No. 2 3 Alaska Highway 1,338.7 5.2 4,337 15.0 -15 

511 Cathedral Rapids Creek No. 3 3 Alaska Highway 1,338.8 3.9 4,114 15.0 -15 
METHODOLOGY 7

513 Bear Creek 3 Alaska Highway 1,357.3 84.1 3,792 15.4 -12 

514 Chief Creek 3 Alaska Highway 1,358.6 34.5 2,312 15.0 -13 515 Berry Creek 3 Alaska Highway 1,371.4 65.1 3,168 15.1 -12 516 Sears Creek 3 Alaska Highway 1,374.4 8.4 2,037 15.0 -12 517 Dry Creek 3 Alaska Highway 1,378.1 55.4 3,209 15.0 -12 518 Johnson River 3 Alaska Highway 1,380.4 381 5,143 15.0 -12 519 Little Gerstle River 3 Alaska Highway 1,388.4 66.6 3,577 15.0 -12 520 Gerstle River 3 Alaska Highway 1,392.7 219 4,684 15.0 -12 524 Tanana River Big Delta 3 Richardson Highway 275.4 13,500 3,440 22.0 -14 

525 Shaw Creek 3 Richardson Highway 286.5 393.0 1,612 15.0 -16 

526 Banner Creek 3 Richardson Highway 295.4 20.2 1,709 15.0 -15 

527 Salcha River 3 Richardson Highway 323.3 2,170 2,520 15.0 -19 

528 Clear Creek 3 Richardson Highway 324.0 1.3 780 15.0 -16 

529 Munsons Slough 3 Richardson Highway 325.4 1.6 785 15.0 -16 

530 Little Salcha River 3 Richardson Highway 328.4 73.5 1,275 15.0 -16 

532 Chena River (North Hall Street) 3 Steese Highway — 2,000 1,770 15.0 -18 534 Ship Creek 2 Glenn Highway 133.5 92.2 2,923 33.0 2 

535 Eagle River North Crossing 2 Glenn Highway 140.1 192.0 3,120 40.0 6 

538 Goat Creek 2 Old Glenn Highway 6.1 15.0 3,579 28.0 7 

539 Knik River 2 Old Glenn Highway 8.6 1,180 4,000 100.0 9 

541 Moose Creek 2 Glenn Highway 54.7 61.4 2,849 30.0 5 

542 Eska Creek 2 Glenn Highway 60.9 14.0 2,720 38.0 5 

543 Granite Creek 2 Glenn Highway 62.4 61.9 3,925 30.0 4 

544 King River 2 Glenn Highway 66.4 153 4,029 51.1 4 

546 Puritan Creek 2 Glenn Highway 89.0 8.6 3,260 30.0 3 

547 Hicks Creek 2 Glenn Highway 96.5 46.0 4,295 30.0 4 

548 Caribou Creek 2 Glenn Highway 106.9 289.0 4,190 25.0 2 

549 Little Nelchina River 3 Glenn Highway Spur .0 283 3,700 20.0 2 551 Mendeltna Creek 3 Glenn Highway 152.8 193 2,682 16.5 -5 

552 Tolsona Creek 3 Glenn Highway 173.1 193 2,472 15.0 -8 

556 Valdez Glacier Stream 1 Richardson Highway .9 158 4,032 150.0 8 557 Lowe River Lower Crossing 1 Richardson Highway 14.8 222 3,533 82.0 7 

558 Lowe River Upper Crossing 1 Richardson Highway 16.5 201 3,520 80.0 6 

559 Sheep Creek 1 Richardson Highway 18.7 29.4 4,050 110.5 8 

565 Stuart Creek 3 Richardson Highway 45.5 37.6 4,120 83.8 2 

569 Tonsina River (Upper) 3 Richardson Highway 79.2 420 3,584 89.0 -4 

570 Squirrel Creek 3 Richardson Highway 79.6 70.5 3,100 15.0 -9 

572 Klutina River 3 Old Rich–Copper Cent — 880 3,500 30.0 -7 573 Tazlina River 3 Richardson Highway 110.7 2,670 3,450 30.0 4 574 Gulkana River 3 Richardson Highway 126.9 1,910 2,716 18.0 -6 
8 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 1. Basin characteristics at selected bridge sites in AlaskaóContinued [Bridge ADOT&PF number: Bold indicates that corresponding basin-characteristics data are from Jones and Fahl (1994). Flood-frequency area designations are from Jones and Fahl (1994). 

Transportation and Public Facilities. —, not applicable] Bridge Flood- frequency area Route or junction Basin Mean annual precipitation (inches) Mean minimum January temperature (degrees Fahrenheit) 

ADOT&PF number Name Name Mile Area (square miles) Mean elevation (feet) 

575 Sourdough Creek 3 Richardson Highway 147.7 75.5 2,244 17.0 -10 577 One Mile Creek 3 Richardson Highway 184.7 8.8 3,281 25.0 -7 589 Lower Suzy Q Creek 3 Richardson Highway 224.5 1.0 3,295 40.0 -7 591 One Mile Creek 3 Richardson Highway 228.4 4.8 4,006 35.0 -7 592 Darling Creek 3 Richardson Highway 231.0 6.3 4,514 35.0 -7 593 Bear Creek 3 Richardson Highway 233.3 6.8 4,355 34.1 -7 594 Ruby Creek 3 Richardson Highway 234.7 5.2 3,392 25.0 -7 595 Jarvis Creek 3 Richardson Highway 264.8 246 3,242 20.0 -8 596 Resurrection River No. 1 1 Seward Highway 2.8 169 2,270 100.0 12 597 Resurrection River No. 2 1 Seward Highway 3.0 169 2,270 100.0 12 598 Resurrection River No. 3 1 Seward Highway 3.1 169 2,270 100.0 12 599 Clear Creek 1 Seward Highway 3.8 12.8 2,407 110.0 11 600 Salmon Creek 1 Seward Highway 5.9 23.9 1,569 110.0 12 601 Bear Creek 1 Seward Highway 6.6 6.8 1,066 110.0 12 603 Snow River West Channel 2 Seward Highway 17.1 163 2,670 158.0 11 

605 Snow River Center Channel 2 Seward Highway 17.5 163 2,670 158.0 11 

608 Ptarmigan Creek 2 Seward Highway 23.1 32.6 2,800 90.0 10 

609 Falls Creek 2 Seward Highway 25.0 11.8 3,480 80.0 10 

610 Trail River 2 Seward Highway 25.4 181 2,470 90.0 6 

612 Canyon Creek 2 Seward Highway 56.4 96.3 2,183 53.4 10 

613 Dry Gulch Creek 2 Seward Highway 57.0 5.0 993 50.0 8 

627 Placer River Overflow 2 Seward Highway 77.9 122 2,083 113.6 11 

629 Placer River Main Crossing 2 Seward Highway 78.3 122 2,083 113.6 11 

630 Portage Creek No. 1 2 Seward Highway 79.0 55.8 1,886 138.6 11 

634 Twenty Mile River 2 Seward Highway 80.7 163 2,200 112.0 11 

639 Glacier Creek 2 Seward Highway 89.7 58.2 2,610 70.0 10 

643 Bird Creek 2 Seward Highway 101.4 75.9 2,645 49.0 6 644 Indian Creek 2 Seward Highway 102.9 17.6 2,331 34.0 6 646 Gakona River 3 Tok Cutoff Highway 1.8 620 3,030 25.0 -9 648 Sinona Creek 3 Tok Cutoff Highway 34.6 157.8 2,758 18.5 -12 
METHODOLOGY 9

649 Chistochina River No. 1 3 Tok Cutoff Highway 35.4 623 3,761 40.0 -10 

650 Chistochina River No. 2 3 Tok Cutoff Highway 35.6 623 3,761 40.0 -10 

651 Indian River 3 Tok Cutoff Highway 43.9 108 3,468 19.0 -16 

653 Porcupine Creek 3 Tok Cutoff Highway 64.1 23.6 3,957 25.4 -18 

654 Slana River 3 Tok Cutoff Highway 75.6 327 3,962 42.2 -18 

658 Little Tok River 3 Old Tok Highway .0 263 3,720 34.8 -19 663 Tok River 3 Tok Cutoff Highway 104.1 762 4,049 34.7 -21 

666 South Fork Anchor River 2 Sterling Highway 161.0 137 1,147 24.8 16 

668 Deep Creek 2 Sterling Highway 136.7 221 1,326 23.0 12 

669 Ninilchik River 2 Sterling Highway 135.0 141 650 21.1 11 

670 Kasilof River 2 Sterling Highway 109.4 738 1,810 50.0 10 

671 Kenai River at Soldotna 2 Sterling Highway 96.0 2,010 1,750 50.0 8 

673 Kenai River at Schooners Bend 2 Sterling Highway 53.1 758 2,704 96.6 10 

674 Cooper Creek 3 Sterling Highway 50.6 48.6 2,486 59.7 9 

675 Kenai River Cooper Land 2 Sterling Highway 47.8 642 2,736 104.5 10 

678 Little Goldstream Creek 3 Parks Highway 314.8 41.7 678 15.0 -17 

685 Maclaren River 2 Denali Highway 41.9 274 4,367 47.7 -6 

686 Clearwater Creek 3 Denali Highway 55.9 126 4,036 29.4 -5 

687 Susitna River 2 Denali Highway 79.2 919 4,421 51.7 -6 

688 Canyon Creek 3 Denali Highway 94.8 15.0 3,429 25.0 -6 

690 Seattle Creek 3 Denali Highway 110.9 34.7 3,464 25.0 -6 

693 Carlo Creek 3 Parks Highway 224.0 18.7 3,979 26.0 -7 

694 Nenana River Park Bend 3 Parks Highway 231.2 1,180 3,545 32.6 -6 

695 Riley Creek 3 Parks Highway 237.2 130 3,716 31.9 -7 

697 Kingfisher Creek 3 Parks Highway 238.2 .6 3,043 25.0 -6 

732 Gold Creek 1 Egan Drive 1.1 9.8 2,242 125.7 22 

735 Eagle River 1 Glacier Highway 28.3 48.9 3,061 96.9 22 

736 Herbert River 1 Glacier Highway 27.6 56.7 2,787 108.0 22 

737 Mendenhall River 1 Glacier Highway .0 105 2,891 134.0 21 742 Chilkat River 1 Haines Highway 23.8 794 3,920 85.3 -2 

749 Carlanna Creek 1 North Tongass Highway .0 2.5 1,323 180.0 28 799 Long Creek 3 Steese Highway 45.5 9.2 1,874 15.0 -18 

816 Crooked Creek 3 Steese Highway 40.4 9.1 1,800 15.0 -18 

819 Deadwood Creek 3 Circle Hot Springs 2.8 35.3 2,334 15.0 -24 

822 Belle Creek 3 Steese Highway 41.5 18.1 1,917 15.0 -17 

823 McKay Creek 3 Steese Highway 42.7 7.4 1,909 18.0 -18 

826 Reed Creek 3 Steese Highway 88.6 4.3 3,254 20.0 -22 

827 Willow Creek 3 Steese Highway 95.7 3.3 2,950 20.0 -22 

828 Bear Creek 3 Steese Highway 97.6 9.9 3,304 18.3 -22 

831 Mammoth Creek 3 Steese Highway 116.5 40.4 2,869 15.0 -23 
10 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 1. Basin characteristics at selected bridge sites in AlaskaóContinued [Bridge ADOT&PF number: Bold indicates that corresponding basin-characteristics data are from Jones and Fahl (1994). Flood-frequency area designations are from Jones and Fahl (1994)

Transportation and Public Facilities. —, not applicable] Bridge Flood- frequency area Route or junction Basin Mean annual precipitation (inches) Mean minimum January temperature (degrees Fahrenheit) 

ADOT&PF number Name Name Mile Area (square miles) Mean elevation (feet) 

832 Boulder Creek 3 Steese Highway 125.3 9.8 4,300 40.0 0 

833 Albert Creek 3 Steese Highway 131.2 113 1,757 15.0 -23 

836 Chatanika River 3 Elliott Highway 11.0 529 1,921 17.3 -18 838 Washington Creek 3 Elliott Highway 18.3 46.2 1,490 15.0 -17 

839 South Fork 40 Mile River 5 Taylor Highway 75.3 2,730 2,777 15.1 -22 

844 Heney Creek 1 Point Whitshed Road .0 1.8 958 158.4 17 

851 Dry Creek 3 Parks Highway 249.8 38.3 3,284 25.0 -12 

852 Dry Creek Overflow 3 Parks Highway 249.3 3.0 2,141 25.0 -12 

853 Salmon Creek 1 Nash Road 3.3 41.3 1,542 110.0 12 

854 Small Creek 1 Nash Road 1.9 10.7 1,850 110.0 12 

855 Small Creek 1 Nash Road 2.0 10.7 1,850 110.0 12 

857 Nenana River at Healy 3 Healy Road 3.2 1,910 3,500 34.0 -8 

858 Slana River 3 Nabesna Road 1.5 720 3,707 34.0 -15 

861 Jack Creek 3 Nabesna Road 37.1 115 4,340 30.0 -19 

864 Trollers Creek 1 Knudson Cove Road .0 1.2 466 114.7 29 865 Indian River 1 Sawmill Creek Road 1.0 12.0 1,275 105.9 28 

868 Falls Creek 1 Mitkof Highway 10.8 16.6 720 98.6 25 

888 Carlson Creek 3 Tok Cutoff Highway 67.8 10.4 3,832 25.0 -18 

940 Fish Camp Creek 3 Northway Road 2.6 19.3 1,706 15.0 -23 

969 Campbell Creek Lake Otis 2 Lake Otis Parkway .0 45.2 2,387 24.4 6 970 Campbell Creek Arctic 2 Arctic Boulevard .0 69.7 1,879 23.0 5 971 Campbell Creek 2 C Street Northbound — 69.7 1,921 23.0 5 979 North Fork Anchor River 2 Chakok Road — 224 1,111 23.0 14 983 Red Cloud River 1 Kodiak Island Highway 7.9 3.8 1,137 100.0 24 

986 Buskin River No. 5 1 Kodiak Island Highway 6.8 18.9 878 100.0 23 

988 Buskin River No. 7 1 Kodiak Island Highway 1.5 12.0 928 100.0 23 

989 Sargent Creek 1 Kodiak Island Highway 10.3 11.7 1,399 100.0 24 

992 Salonie Creek No. 1 1 Kodiak Island Highway 12.4 16.2 1,249 100.0 24 

999 Glacier Creek 2 Alyeska Road 2.3 45.9 2,525 70.0 10 

1008 Cripple Creek 3 Chena Ridge/Pump Road 12.1 40.9 959 15.0 -18 
METHODOLOGY 11

1009 Goldstream Creek 3 Ballaine Road .0 74.8 1,249 15.0 -18 

1025 Resurrection Creek 2 Hope Road 16.9 161 2,584 25.0 7 

1075 Dragonfly Creek 3 Parks Highway 242.4 .7 3,021 25.0 -8 

1085 Hartney Bay 1 Point Whitshed Road 2.2 8.0 837 106.9 17 

1092 Little Tok River 3 Tok Cutoff 83.1 353 3,733 20.0 -19 

1094 Situk River 1 Yakut/Alsek Road 8.7 35.8 379 140.0 18 1098 Smith Creek 3 Deering Road 25.7 22.3 34 10.0 -16 

1121 Knik River No. 1 2 Glenn Highway 30.3 1,220 3,926 100.0 9 1124 Matanuska River 2 Glenn Highway 31.4 2,100 3,950 35.0 4 1131 Ketchikan Creek Fair Street 1 Ketchikan City Street .0 12.3 1,455 189.4 28 

1132 Ketchikan Creek Park–Upper Crossing 1 Ketchikan City Street .0 12.4 1,440 189.0 28 1141 Antler Creek 3 Parks Highway 244.6 1.4 2,965 29.0 -8 1142 Bison Gulch 3 Parks Highway 243.6 1.1 3,250 29.0 -9 1143 Nenana River at Moody 3 Parks Highway 242.8 1,890 3,703 34.0 -7 1145 Hornet Creek 3 Parks Highway 240.2 2.2 3,410 25.0 -9 1146 Iceworm Gulch 3 Parks Highway 240.0 1.5 3,381 25.0 -9 1147 Nenana River Park Station 3 Parks Highway 237.9 1,870 3,713 34.0 -7 1149 Kenai River at Kenai 2 Kenai River Road — 2,140 1,655 50.0 8 

1153 Whipple Creek 1 North Tongass Highway 11.6 5.4 989 140.3 29 

1155 Peters Creek–North Crossing 2 Glenn Highway 149.3 87.8 3,436 36.0 2 

1156 Wasilla Creek 2 Parks Highway 37.8 38.9 796 19.0 5 1157 Campbell Creek East Frontage 2 Brayton Drive 124.9 46.0 2,353 24.3 5 1193 Chokosna River 3 McCarthy Road 60.6 37.6 4,089 24.0 -7 1194 Gilahina River 3 McCarthy Road 62.7 50.2 3,635 19.0 -6 1196 Lost River 1 Lost River Road .0 19.3 46 140.0 19 

1203 Solomon Creek 1 Dayville Road .0 19.2 2,239 116.2 9 

1204 Abercrombie Creek 1 Dayville Road .0 6.8 2,325 110.0 9 

1207 Lowe River Main Channel 1 Dayville Road .0 358 3,211 125.7 7 

1208 Lowe River North Channel 1 Dayville Road .0 358 3,211 125.7 7 

1213 Hess Creek 3 Dalton Highway 23.8 666 1,362 14.9 -16 

1220 Cowee Creek 1 Glacier Highway 1.9 43.1 2,072 89.6 22 1222 Tiekel River No. 2 3 Richardson Highway 50.7 99.9 3,572 104.1 -2 

1228 Antlen River 1 Yakut/Alsek Road 24.9 1.7 96 160.0 18 

1229 Ahrnklin River 1 Yakut/Alsek Road 25.3 31.5 1,238 160.4 18 

1230 Eklutna River Northbound 2 Glenn Highway 26.3 170 3,340 47.0 6 

1234 Ketchum Creek 3 Circle Hot Springs 5.7 12.3 2,047 15.0 -24 1241 Little Nelchina River 3 Glenn Highway 137.4 283 3,687 20.0 -8 

1243 Nenana River at Windy 3 Parks Highway 215.6 710 3,506 33.0 -6 

1250 Tulsona Creek 3 Tok Cutoff Highway 17.6 93.9 2,162 17.0 -12 

1255 Fish Creek 3 Dalton Highway 114.0 102 2,199 17.7 -18 
12 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 1. Basin characteristics at selected bridge sites in AlaskaóContinued [Bridge ADOT&PF number: Bold indicates that corresponding basin-characteristics data are from Jones and Fahl (1994). Flood-frequency area designations are from Jones and Fahl (1994)

Transportation and Public Facilities. —, not applicable] Bridge Flood- frequency area Route or junction Basin Mean annual precipitation (inches) Mean minimum January temperature (degrees Fahrenheit) 

ADOT&PF number Name Name Mile Area (square miles) Mean elevation (feet) 

1256 North Fork Bonanza Creek 3 Dalton Highway 125.7 100 2,123 18.5 -17 

1257 South Fork Bonanza Creek 3 Dalton Highway 124.7 122 1,994 18.2 -18 

1258 Prospect Creek 3 Dalton Highway 135.1 108 1,826 17.2 -18 

1259 Jim River No. 1 3 Dalton Highway 140.1 258 2,456 17.7 -17 

1260 South Fork Koyukuk River 3 Dalton Highway 156.1 696 2,417 19.9 -17 

1261 Middle Fork Koyukuk River No. 1 3 Dalton Highway 188.5 1,160 3,267 27.7 -17 

1273 Chester Creek 1 C Street .0 29.2 658 22.1 5 

1274 Monashka Creek 1 Pillar Creek Road 10.8 5.3 881 100.0 24 1282 Middle Fork Koyukuk River No. 2 3 Dalton Highway 190.8 904 3,287 27.4 -17 

1283 Middle Fork Koyukuk River No. 3 3 Dalton Highway 204.3 801 3,420 27.7 -17 

1284 Middle Fork Koyukuk River No. 4 3 Dalton Highway 204.5 801 3,420 27.7 -17 

1295 Box Canyon Creek 1 Resurrection River Road .0 2.1 1,567 110.0 11 1320 Ship Creek 2 Reeve Boulevard .0 109 2,488 31.3 6 1329 Little Chena River 3 Nordale Road .0 399 1,506 15.0 -18 1332 Slate Creek 3 Dalton Highway 175.1 74.1 2,299 24.2 -17 

1333 Atigun River No. 2 3 Dalton Highway 271.1 297.4 4,448 23.0 -16 

1334 No Name Creek 3 Dalton Highway 79.1 123 1,125 16.9 -18 1335 Minnie Creek 3 Dalton Highway 187.2 52.1 3,221 25.0 -17 

1336 Hammond River 3 Dalton Highway 190.6 246 3,207 28.9 -17 

1337 Dietrich River 3 Dalton Highway 207.0 349 3,554 29.8 -17 

1338 Kanuti River 3 Dalton Highway 105.7 159 2,095 17.9 -17 

1341 Eagle River South Crossing 2 Glenn Highway 139.9 192 3,120 40.0 6 

1344 Peters Creek Southbound 2 Glenn Highway 149.2 87.8 3,436 36.0 2 

1350 Campbell Creek West Frontage 2 Homer Drive 124.9 46.0 2,353 24.3 5 

1355 Harris River 1 Hydaburg Road .0 13.2 1,367 100.0 30 1356 Fubar Creek 1 Hydaburg Road .2 3.8 1,033 100.0 30 1363 Steelhead River 1 Big Salt Lake Road 12.3 16.5 1,102 100.0 30 1383 Lowe River Lower Keystone 1 Richardson Highway 15.3 218 3,538 82.0 7 1384 Lowe River Upper Keystone 1 Richardson Highway 15.4 218 3,538 82.0 7 1389 Unnamed Creek 1 Exit Glacier Road — 3.0 2,735 110.0 12 
METHODOLOGY 13

1390 Resurrection River 1 Exit Glacier Road — 106 2,391 106.0 12 1394 Globe Creek 3 Elliott Highway 37.0 31.1 1,614 15.0 -17 1400 Tatalina River 3 Elliott Highway 44.9 86.9 1,251 15.0 -16 1436 Jim River No. 2 3 Dalton Highway 141.0 257 2,457 17.8 -18 1437 Jim River No. 3 3 Dalton Highway 144.1 224 2,580 17.7 -17 1439 Atigun River No. 1 3 Dalton Highway 253.1 48.8 4,899 27.3 -16 1443 Campbell Creek 2 Minnesota Drive Southbound .0 67.4 1,750 23.3 5 

1444 Campbell Creek at Minnesota Drive 2 Minnesota Drive Frontage .0 67.4 1,750 23.3 5 

1445 Campbell Creek at Minnesota Drive 2 Minnesota Drive Frontage .0 67.4 1,750 23.3 5 

1455 Control Creek 1 Thorne Bay Road 1.4 9.6 867 100.0 29 

1461 Goose Creek 1 Thorne Bay Road 11.7 19.3 787 104.7 29 

1462 Thorne River 1 Thorne Bay Road 13.4 151 852 103.2 30 1508 Campbell Creek Dimond Drive 2 Dimond Drive .0 69.3 1,704 23.2 5 

1513 Fort Hamlin Hills Creek 3 Dalton Highway 72.6 36.0 1,249 16.1 -17 1514 Gold Creek 3 Dalton Highway 197.0 16.4 2,737 25.0 -17 1519 Roche Moutonnee Creek 3 Dalton Highway 265.1 31.7 5,097 25.0 -16 1520 Holden Creek 3 Dalton Highway 267.5 11.0 4,534 17.0 -16 1521 Dan Creek 3 Dalton Highway 330.8 34.8 1,424 10.0 -16 1536 False Pass Creek 1 Airfield Road .0 7.3 1,177 70.0 27 

1560 Douglas Creek 3 Dalton Highway 141.8 16.5 2,051 17.0 -17 1629 Chester Creek 1 A Street .0 29.2 658 22.1 5 

1676 Starrigavan Creek 1 Rodman Bay Road .6 6.4 1,247 104.2 28 

1694 Campbell Creek 2 Minnesota Drive Northbound .0 67.4 1,750 23.3 5 

1746 Klutina River 3 Richardson Highway .0 890 3,371 82.4 -7 

1786 Jordan Creek, Juneau 1 Trout Street .0 .9 315 90.0 22 

1820 Salmon Creek 1 Bruno Road .0 6.2 2,746 110.0 12 

1864 Eklutna River Southbound 2 Glenn Highway 26.3 170 3,340 47.0 6 
14 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Manning’s n values (roughness coefficients) 

were assumed to be 0.035 in the main channel and 

0.10 in the overbank area. These typical values were 

changed if information from photographs, site visits, 

surveys, or other sources indicated a more appropriate 

value. In general, winding natural streams filled with 

weeds have n values of about 0.035 and mountain 

streams flowing over rocky beds have n values on the 

order of 0.04–0.05 (Fetter, 1994).

Friction slope and valley slope were estimated 

from topographic information (from 1:63,360-scale 

USGS quadrangle maps or from bridge-plan maps), 

from discharge measurements (by back-calculation 

using Manning’s equation), or from information 

derived through surveying or by a site visit. Slopes for 

many of the Phase I sites were estimated from USGS 

topographic maps and have associated uncertainties on 

the order of ±50 percent.

Bridge hydraulic parameters—including bridge 

width, embankment slope and elevation, low-steel elevation, pier widths, and bridge type—were obtained 

from existing bridge plans.

Automated procedures were developed to 

increase the efficiency and accuracy of entering this 

information. The process is outlined as follows:

(1) Digitize bridge, full-valley, and pier information 

from existing bridge plans using AutoCAD. 

Export data to a spreadsheet.

(2) Modify cross sections with improved information from measurements or surveys.

(3) Enter additional hydraulic parameters into the 

Excel workbook.

(4) Run a series of Visual Basic for Applications programs that use the hydraulic data to create a 

WSPRO input file.

(5) Export the WSPRO input file to the UNIX system for model processing.

Computation of Water-Surface Profile Using 

WSPRO Step-Backwater Model

Water-surface profiles for the 100- and 500-year 

flood discharges were calculated using the WSPRO 

step-backwater model (Shearman, 1990), which is a 

water-surface profile computational model for onedimensional, gradually varied, steady flow in open 

channels.

Typical cross sections used in the WSPRO model 

are shown in figure 1 and were described in detail by 

Shearman (1990). Cross sections are referenced as follows: Sections upstream from the bridge are called 

approach sections; sections at the bridge location without the bridge structure, full-valley sections; sections 

with the bridge structure in place, bridge sections; and 

sections downstream from the bridge, exit sections. 

One bridge length (b) is the recommended distance 

between cross sections (Shearman, 1990).

Hydraulic models resulting from WSPRO computations can vary depending on the information available; however, most of the models used in this study 

were one of two types:

(1) Models based on the bridge and full-valley cross 

section. Three exit and one approach section 

were templated from the full-valley section.

(2) Models based on the bridge and full-valley cross 

section and an approach section read from the 

bridge plan topographic map. Three exit sections 

were templated from the full-valley section.

Channel slope is an important parameter for this 

method because it is used both to template the elevation change for the additional sections and to estimate 

the starting friction slope for the model. The chosen 

slope affects the depth and velocity of the flow, both 

of which are important factors in scour computations.

WSPRO model parameters are reviewed and adjusted 

as needed to ensure that model parameters, and the 

resulting output, are within known ranges of natural 

physical systems. Flow properties for the hydraulic 

sections were generated from WSPRO computations 

for use in scour equations.

Figure 1. Plan view showing approach, bridge, full-valley, 

and exit cross sections used in water-surface-profile computational model WSPRO. b, bridge length.

b

b bbb

Approach

Bridge

Full valley

Exit 1Exit 2Exit 3

Flow
ESTIMATES OF CONTRACTION SCOUR AND PIER SCOUR 15

ESTIMATES OF CONTRACTION SCOUR 

AND PIER SCOUR

Scour was estimated by applying FWHA techniques and equations presented in HEC–18 (Richardson and Davis, 1995), assuming WSPRO modelderived hydraulic properties. In this Phase I scour 

assessment, the USGS and ADOT&PF chose to compute the two principal types of scour that occur at 

bridges: contraction scour and local scour at piers. 

Although techniques for estimating abutment scour 

exist, they have large associated uncertainties. Furthermore, most abutments on Alaskan bridges are armored 

by riprap to inhibit local scour (Mark Miles, Alaska 

Department of Transportation and Public Facilities, 

oral commun., 1995).

Contraction scour is affected by the sedimenttransport characteristics of the stream; therefore, 

HEC–18 (Richardson and Davis, 1995) included contraction-scour equations for both live-bed and clearwater sediment-transport conditions. For this study, 

maximum contraction scour was estimated (table 2) 

assuming live-bed transport at all selected bridge sites. 

Live-bed transport is a reasonable assumption for 

Alaska’s alluvial streams and rivers and yields a more 

conservative estimate of scour. The bed material was 

assumed to have a median diameter of 10 millimeters 

(0.34 in), and an associated fall velocity of 2.60 ft/s, at 

all bridges except bridge 331 and 332 on the Copper 

River Delta. Median diameter grain size at bridge 331 

is 15 millimeters (0.59 in) and at bridge 332 is 0.4 millimeter (0.03 in) (Brabets, 1994). Bed-material fall 

velocities were derived according to methods presented in HEC–18 (Richardson and Davis, 1995, p. 

32), assuming a water temperature of 32°F. Thus, the 

derived fall velocity for bed material at bridge 331 is 

3.67 ft/s and at bridge 332 is 0.14 ft/s.

Pier scour (table 2) was calculated according to 

procedures outlined in HEC–18 (Richardson and 

Davis, 1995). 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. The HEC–18 pier-scour 

equation is recommended to be used for both live-bed 

and clear-water sediment-transport conditions and is 

relatively sensitive to changes in pier geometry and 

angle of attack. Scour computations were automated 

using Excel spreadsheet and Visual Basic programs

to extract the required variables from the WSPRO output.

At several sites, pressure scour is a potential 

problem because estimated floods partly or fully submerge the bridge. These sites are noted in the “Comments” column of table 2. However, pressure-scour 

values were not calculated because of the lack of a 

generally accepted method for estimating pressureflow scour under live-bed conditions, according to 

HEC–18 (Richardson and Davis, 1995).

Four selected examples of Phase I bridge-scour 

analyses are summarized in the appendix. The examples were selected to illustrate the wide range of information that may be available for a given site and the 

procedures used to estimate scour. Examples sites 

included in the appendix are bridge 528, Clear Creek; 

bridge 407, Scott Glacier No. 7; bridge 527, Salcha 

River; and bridge 857, Nenana River at Healy.

SUMMARY AND CONCLUSIONS

Potential scour computations were completed 

for 325 of the 340 sites selected for assessment by 

ADOT&PF. The 15 sites not completed either are 

affected tidally or do not have bridge plans readily 

available. Maximum contraction scour and local pier 

scour were calculated for each bridge by using FHWA 

scour equations from HEC–18 (Richardson and Davis, 

1995). The discharges used to calculate scour were the 

100- and 500-year floods. Floods were calculated 

using methods outlined in Jones and Fahl (1994).

Calculated scour depths reported herein represent 

conditions at a bridge at a single point in time. Channel migration and aggradation or degradation of the 

streambed that may have occurred during the period of 

streamflow since the bridge was constructed were not 

considered in this preliminary assessment. However, 

greater depths of scour suggest a greater likelihood of 

scour-related problems occurring at a bridge and, as 

such, the scour depths summarized in table 2 provide a 

valuable quantitative scour assessment that can help 

ADOT&PF identify the need for additional investigation at a particular site. This screening method has the 

advantage of providing scour depths and bed elevations for comparison with foundation elevations without the time and expense of a field survey. Examples 

of automated scour analysis for ADOT&PF bridges 

407, 527, 528, and 857 are included in the appendix.
1

6MethodologyandEstimatesofScouratSelectedBridgeSitesinAlaska

Table 2. Computed Phase I contraction- and pier-scour depths at selected bridge sites in Alaska[Manning’s roughness coefficients are for main channel at bridge. ADOT&PF, Alaska Department of Transportation and Public Facilities. Q100, 100-year flood; Q500, 500-year flood. —, not app

Bridge

Discharge

(cubic feet

per second) Angle of attack

(degrees)

Valley

slope

(feet

per

foot)

Manningís

roughness 

coefficient

n

Computed scour depth

(feet)

Contraction scour Pier scour 

ADOT&PF

number Name Q100 Q500 Q100 Q500 Q100 Q500

201 North Slough Tanana River 12,400 15,500 0 0.0080 0.035 0.3 0.4 8.5 9.0202 Tanana River at Nenana 162,000 203,000 15 .0010 .030 .2 .7 43.5 44.8205 Copper River at Chitina 126,000 151,000 0 .0010 .030 1.0 1.1 13.7 14.0206 Copper River 422,000 538,000 0 .0006 .030 .5 .4 32.8 34.8208 Roslyn Creek 2,390 2,950 0 .0070 .035 .0 .0 4.0 4.1209 Noyes Slough (Aurora) 2,100 2,100 0 .0005 .035 .8 .8 2.9 2.9210 Willow Creek 7,510 9,550 0 .0008 .035 .0 .0 4.8 5.0

211 Little Willow Creek 4,510 5,680 0 .0007 .035 .6 .6 4.4 4.6

212 Kashwitna River 3,920 4,650 0 .0020 .035 .0 .0 3.7 3.9213 Sheep Creek 3,120 3,820 0 .0022 .035 .1 .0 4.4 4.5215 Montana Creek 8,270 11,700 0 .0040 .035 .0 .0 5.7 6.1216 Nenana River at Rex 30,100 35,900 0 .0030 .035 6.0 7.3 — —217 Mendenhall River 17,200 20,700 0 .0023 .040 3.7 4.4 9.5 10.1230 Sheridan Glacier No. 3 16,300 20,200 20 .0015 .030 1.6 2.1 18.4 25.0 Press231 Chena River 12,000 12,000 0 .0002 .030 .1 .1 4.5 4.5232 North Fork Chena River 16,270 18,240 0 .0020 .030 .1 .1 4.1 4.2233 North Fork Chena River 22,100 27,400 10 .0015 .035 8.3 15.9 8.0 8.8234 North Fork Chena River 8,800 10,800 10 .0050 .035 4.9 7.4 6.5 6.7235 North Fork Chena River 9,240 11,200 0 .0030 .035 .5 .5 4.0 4.2237 North Fork Chena River 9,220 11,200 0 .0050 .035 .0 .0 3.8 3.9238 Angel Creek 1,630 2,090 0 .0120 .035 .0 .0 — —239 West Fork Chena River 9,380 11,300 0 .0070 .035 1.0 1.0 4.6 4.7240 Little Susitna River 3,800 4,570 30 .0003 .035 .0 .0 10.3 10.8242 North Fork Chena River 4,220 5,220 0 .0070 .045 .8 .8 4.5 4.7254 Susitna River at Sunshine 186,000 206,000 0 .0020 .030 6.2 6.5 16.7 17.3255 Chulitna River 83,200 103,000 20 .0080 .030 .4 .4 23.8 25.0256 Troublesome Creek 2,250 2,900 0 .0100 .040 .9 1.0 2.8 3.1257 Byers Creek 2,030 2,580 10 .0025 .035 1.0 1.2 3.2 3.4259 Honolulu Creek 3,180 3,900 5 .0500 .035 1.6 1.9 5.3 5.6260 East Fork Chulitna River 6,680 8,070 20 .0100 .045 .4 .4 9.1 9.7
ESTIMATES OF CONTRACTION SCOUR AND PIER SCOUR 17

261 Middle Fork Chulitna River 1,880 2,300 0 0.0080 0.045 0.0 0.0 2.3 2.4

263 Chena River University Ave. 12,000 12,000 0 .00015 .030 .4 .4 4.8 4.8

266 Cripple River 2,480 3,060 0 .0040 .035 .6 .8 3.4 3.6

268 Fox River 2,380 2,980 0 .0030 .035 .0 .0 3.3 3.5

269 Bear River 2,030 2,560 0 .0040 .035 .0 .0 — —

270 Little Chena River 7,050 11,000 10 .0005 .030 2.1 8.0 6.6 7.2

272 Hot Springs Slough 1,550 2,030 0 .0005 .035 .1 .1 4.9 5.2

274 Hutlinana Creek 3,290 4,130 0 .0050 .035 1.5 2.0 — —

275 North Fork 12 Mile Creek 1,150 1,470 0 .0200 .045 .9 1.3 2.7 3.0

277 Taylor Creek 1,350 2,360 0 .0027 .035 4.4 .9 — — Press

281 Jack River 6,750 8,230 0 .0050 .035 .0 .0 3.2 3.4

283 Noyes Slough (Illinois) 2,100 2,100 0 .0005 .035 .3 .3 2.8 2.8

284 American River 6,830 8,510 0 .0050 .035 .4 .4 3.8 4.0

286 Deadman (Small) Creek 911 1,130 0 .0170 .035 .3 .4 3.2 3.4

287 Olds River 4,230 5,270 0 .0065 .035 .4 .4 3.9 4.0

288 Tonsina River (Lower) 26,100 29,500 0 .0050 .035 .5 .5 8.5 8.7

290 East Fork Twin Creek 1,120 1,320 0 .0160 .035 .2 .2 3.4 3.5

291 Kalsin Creek 2,960 3,690 0 .0080 .035 .0 .0 3.4 3.4

292 Myrtle Creek 1,530 1,790 0 .0080 .047 .0 .0 2.5 2.7

293 Pass Creek 1,230 1,590 0 .0055 .035 1.8 2.2 2.4 2.6

295 Noyes Slough (Minnie Street) 2,100 2,100 10 .0005 .035 .3 .3 6.9 6.9

297 Forty Mile River 76,700 90,000 0 .0010 .035 .4 .3 15.5 16.0

298 O’Brien Creek 6,950 9,320 0 .0033 .040 .1 .1 6.0 6.4

299 Walker Fork 40 Mile River 7,440 9,850 0 .0017 .035 2.9 4.1 5.6 6.0

302 Jack River 6,090 7,380 0 .0040 .035 .0 .0 3.4 3.4

303 O’Connor Creek 827 1,080 0 .0072 .035 .1 .2 — —

310 Pilgrim River 11,700 13,900 0 .0020 .035 2.1 2.6 6.6 7.0

311 Bear Creek 704 957 0 .0280 .035 .3 .3 3.9 4.2

312 Jenny M Creek 895 1,160 0 .0120 .035 .1 .1 — —

313 Panguingue Creek 1,180 1,490 0 .0170 .035 .1 .2 3.3 3.5

323 Penny River 1,540 1,940 0 .0048 .035 2.7 3.1 — —

324 Snake River 5,060 5,830 0 .0008 .044 2.5 2.7 7.9 8.3

325 West Fork Tolovana River 8,380 10,200 0 .0035 .035 .3 .4 4.4 4.6

327 Station 355 Creek 1,040 1,290 0 .0050 .035 .6 .7 2.9 3.0

328 Granite Creek 1,100 1,360 0 .0050 .045 .9 1.2 2.8 3.0
18 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 2. Computed Phase I contraction- and pier-scour depths at selected bridge sites in AlaskaóContinued [Manning’s roughness coefficients are for main channel at bridge. ADOT&PF, Alaska Department of Transportation and Public Facilities. Q100, 100-year flood; Q500, 500-year flood. —, not app

Bridge Discharge (cubic feet per second) Angle of attack (degrees) Valley slope (feet per foot) Manningís roughness coefficient

n

Computed scour depth

(feet)

Contraction scour Pier scour 

ADOT&PF

number Name

Q100

Q500

Q100

Q500

Q100

Q500

331 Copper River Delta 103,000 130,000 0 .00056 .030 3.4 3.9 13.3 14.1 Grain 

332 Copper River Delta 47,200 59,900 10 .00018 .030 2.6 2.8 10.3 10.8 Grain 

333 Copper River Delta 12,600 16,000 25 .0002 .030 .8 1.4 6.5 6.8

334 Copper River Delta 42,100 53,400 20 .0004 .030 1.2 .9 24.7 25.7

336 Copper River Delta 3,590 4,560 0 .0001 .030 1.0 1.1 4.8 4.9

339 Copper River Delta 30,800 39,000 0 .0007 .030 3.4 4.0 7.7 8.1

340 Copper River Delta 30,800 39,000 25 .0016 .030 5.0 6.0 9.6 10.4

342 Copper River Delta 144,000 182,000 0 .0005 .029 1.9 2.0 8.9 9.3 Pressu

344 Copper River Delta 3,080 3,900 0 .0005 .030 .1 .1 4.2 4.3

345 Copper River Delta 7,700 9,760 0 .0010 .030 .0 .0 4.8 5.1

348 Scott Glacier No. 1 1,880 2,320 0 .0014 .035 3.0 3.2 3.0 3.1

349 Scott Glacier No. 2 4,480 5,520 0 .0007 .035 6.1 7.2 3.7 3.8

350 Scott Glacier No. 3 — — — — — —— —— Site v351 Scott Glacier No. 4 — — — — — —— —— Site v352 Scott Glacier No. 5 — — — — — —— —— Site v355 Birch Creek 36,000 42,000 0 .0011 .030 .6 .8 9.1 9.5

357 Goldstream Creek 3,140 4,000 0 .0020 .035 .0 .0 3.7 4.1

359 Spinach Creek 687 902 0 .0050 .035 .6 .9 — —

367 Sheridan Glacier East Channel — — — — — —— ——381 Eyak River 4,980 6,160 0 .0002 .035 1.6 2.1 2.8 2.9

386 Felton Creek 1,050 1,300 0 .0070 .035 .1 .1 3.4 3.6

390 Chena River (Cushman) 12,000 12,000 0 .0006 .035 .0 .0 10.8 10.8

396 Deception Creek 1,600 2,060 0 .0040 .035 .3 .3 3.3 3.5

401 Moose Creek 4,360 7,010 0 .0100 .038 2.0 9.6 — — Pressu

403 Portage Creek Overflow No. 1 2,500 3,000 20 .0060 .035 .0 .0 3.1 4.7

404 Portage Creek Overflow No. 2 5,400 7,140 0 .0050 .035 .0 .0 6.3 7.0

405 Portage Creek Overflow No. 3 1,350 2,360 0 .0050 .035 4.4 .9 — — Pressu

406 Scott Glacier No. 6 13,600 16,800 0 .0018 .035 .2 .2 3.7 3.9

407 Scott Glacier No. 7 1,760 2,170 10 .0010 .035 3.9 4.5 4.6 4.9

408 Scott Glacier No. 8 5,430 6,690 0 .0010 .035 3.9 4.3 3.9 4.0
ESTIMATES OF CONTRACTION SCOUR AND PIER SCOUR 19

411 Scott Glacier No. 11 3,610 4,450 0 .0018 .035 .2 .3 3.4 3.5

419 Gold Run Creek 1,870 2,390 0 .0025 .035 .0 .0 2.8 3.0

421 Feather River 1,620 2,050 0 .0140 .035 .0 .0 3.6 3.8

422 Tisuk River 1,960 2,490 30 .0050 .035 1.2 1.4 7.3 7.8

423 Eldorado Creek 826 1,160 0 .0180 .038 9.1 10.9 — —

430 Faith Creek 5,750 9,480 0 0.0080 0.045 12.5 5.6 4.9 5.0 Press

440 Tolovana River 4,810 5,970 10 .0030 .035 .0 1.2 7.6 7.6

441 Mosquito Fork 17,400 22,700 0 .0023 .035 .4 .5 6.6 7.0

442 West Fork Dennison River 10,600 14,100 0 .0007 .035 2.9 3.4 5.3 5.7

455 Anchorage Port Access Overhead 5,780 7,970 0 .0050 .035 — — 8.7 9.8

460 Nome River 4,630 5,600 0 .0020 .035 .5 .6 4.3 4.5

470 Small Creek 542 673 0 .0860 .035 .2 .2 3.7 3.9

478 Goldstream Creek 1,920 2,450 0 .0060 .035 1.1 1.3 3.9 4.2

503 Gardiner Creek 6,870 8,530 0 .0020 .035 .0 .0 — —

504 Beaver Creek 1,350 1,740 0 .0010 .035 2.9 2.9 — —

505 Tanana River near Tanacross 51,900 59,700 30 .00016 .035 .0 .0 28.1 28.7

506 Tok River 13,400 16,400 0 .0035 .035 .0 .2 — —

507 Yerrick Creek 1,270 1,640 5 .0300 .035 .1 .0 6.4 6.5

508 Cathedral Rapids Creek No. 1 483 643 0 .0190 .040 .0 .0 — —

509 Robertson River 9,520 11,700 25 .0050 .040 — — 21.6 22.4

510 Cathedral Rapids Creek No. 2 303 410 0 .0960 .040 .3 .3 — —

511 Cathedral Rapids Creek No. 3 245 333 0 .0480 .040 .0 .0 — —

513 Bear Creek 2,360 3,020 0 .0110 .040 .0 .2 — —

514 Chief Creek 1,480 1,900 0 .0070 .035 1.9 2.8 — —

515 Berry Creek 3,240 4,720 0 .0480 .035 2.5 3.0 — —

516 Sears Creek 528 700 0 .0080 .035 3.0 3.8 — —

517 Dry Creek 2,720 3,350 0 .0060 .035 2.2 4.1 — — Press

518 Johnson River 7,520 9,250 40 .0110 .040 — — 26.6 28.1

519 Little Gerstle River 1,970 2,540 0 .0020 .035 .0 .0 3.7 3.9

520 Gerstle River 5,100 6,340 25 .0075 .060 .1 .2 18.5 19.0

524 Tanana River Big Delta 86,700 95,600 35 .0002 .030 1.3 1.3 37.5 38.7

525 Shaw Creek 6,090 7,820 0 .0010 .035 2.9 3.4 3.4 3.6

526 Banner Creek 1,570 2,320 0 .0130 .040 3.5 4.7 — —

527 Salcha River 50,600 64,900 10 .0012 .030 3.3 3.9 20.7 21.7

528 Clear Creek 162 221 0 .0030 .035 1.9 2.4 — —

529 Munsons Slough 188 256 0 .0020 .035 4.8 5.6 — —

530 Little Salcha River 3,130 3,920 15 .0050 .050 1.5 2.2 10.7 11.3

532 Chena River (North Hall Street) 12,000 12,000 0 .0005 .035 .3 .3 7.6 7.6

534 Ship Creek 3,180 3,960 0 .0100 .043 4.4 5.2 — —

535 Eagle River North Crossing 6,920 8,710 0 .0054 .040 2.1 3.0 9.9 10.6
20 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 2. Computed Phase I contraction- and pier-scour depths at selected bridge sites in AlaskaóContinued [Manning’s roughness coefficients are for main channel at bridge. ADOT&PF, Alaska Department of Transportation and Public Facilities. Q100, 100-year flood; Q500, 500-year flood. —, not app

Bridge Discharge (cubic feet per second) Angle of attack (degrees) Valley slope (feet per foot) Manningís roughness coefficient

n

Computed scour depth

(feet)

Contraction scour Pier scour 

ADOT&PF

number Name

Q100

Q500

Q100

Q500

Q100

Q500

538 Goat Creek 498 642 30 .0090 .035 .0 .0 — —

539 Knik River 79,400 104,000 0 .0006 .046 11.7 13.4 10.8 11.7

541 Moose Creek 1,630 2,060 0 .0050 .040 .7 .8 3.9 4.1

542 Eska Creek 1,060 1,860 10 .0070 .035 .7 2.4 — —

543 Granite Creek 1,920 2,390 55 .0150 .045 .4 .5 16.6 17.6

544 King River 7,600 9,310 15 .0090 .035 2.0 2.4 19.6 20.6

547 Hicks Creek 1,370 1,700 25 .0100 .045 .0 .0 12.0 12.5

548 Caribou Creek 9,550 11,800 25 .0060 .035 4.5 5.0 30.1 31.6

549 Little Nelchina River 6,760 8,300 30 .0080 .035 1.7 1.9 27.8 29.2

551 Mendeltna Creek 3,950 5,050 0 .0030 .035 .0 .0 — —

552 Tolsona Creek 3,730 4,810 0 .0068 .035 .0 .0 — —

556 Valdez Glacier Stream 24,400 30,600 0 .0060 .035 5.8 7.3 3.9 4.3

557 Lowe River Lower Crossing 22,100 28,500 0 .0080 .040 1.1 1.5 7.2 7.7

558 Lowe River Upper Crossing 19,400 25,100 20 .0040 .040 .3 .3 17.2 18.3

559 Sheep Creek 5,410 6,870 0 .0120 .040 .0 .0 — —

565 Stuart Creek 3,430 4,750 0 .0200 .050 .7 1.3 — —

569 Tonsina River (Upper) 10,400 12,300 0 .0050 .035 .3 .3 5.5 5.7

570 Squirrel Creek 1,210 1,630 0 .0080 .037 2.9 2.8 — —

572 Klutina River 10,700 11,800 0 .0070 .040 .6 .5 15.5 15.8

573 Tazlina River 79,400 109,000 35 .0020 .036 2.9 2.8 31.7 34.4

574 Gulkana River 18,400 22,200 0 .0006 .035 5.3 6.3 6.8 6.9

575 Sourdough Creek 2,330 3,570 0 .0060 .035 .0 .1 — —

577 One Mile Creek 529 696 0 .0320 .040 2.2 2.9 3.2 3.4

589 Lower Suzy Q Creek 155 205 0 .0740 .040 .1 .1 — —

592 Darling Creek 530 680 0 .0100 .040 .0 .0 — —

593 Bear Creek 558 716 0 .0470 .035 .8 .7 — —

595 Jarvis Creek 5,840 7,240 0 .0040 .040 4.3 4.8 7.1 7.5

596 Resurrection River No. 1 6,200 7,870 20 .0020 .040 .1 .1 12.0 12.6

597 Resurrection River No. 2 9,500 12,100 0 .0020 .040 .5 .9 5.0 5.2

598 Resurrection River No. 3 8,400 10,700 0 .0020 .040 .2 .4 4.5 4.7
ESTIMATES OF CONTRACTION SCOUR AND PIER SCOUR 21

599 Clear Creek 3,070 3,880 0 .0060 .035 2.2 2.5 — —

600 Salmon Creek 2,580 3,250 0 .0011 .040 1.7 1.2 — —

601 Bear Creek 765 964 0 .0100 .040 2.1 2.4 — —

603 Snow River West Channel 2,100 2,600 20 .0015 .035 .6 .7 8.7 9.1605 Snow River Center Channel 21,600 27,000 0 .0010 .040 1.2 1.2 7.5 7.9608 Ptarmigan Creek 1,610 2,070 0 0.0080 0.035 0.1 0.1 6.7 7.0

609 Falls Creek 1,220 1,750 0 .0120 .040 .5 .6 3.4 3.7610 Trail River 9,260 11,800 45 .0001 .030 1.9 2.1 2.9 3.0613 Dry Gulch Creek 560 789 0 .1800 .040 .4 .4 9.8 10.3634 Twenty Mile River 32,500 35,600 0 .0005 .035 4.1 4.4 4.1 4.2639 Glacier Creek 11,100 16,700 0 .0060 .035 .7 .9 6.3 6.9643 Bird Creek 4,390 5,560 0 .0010 .035 2.3 2.3 3.5 3.7644 Indian Creek 844 1,110 0 .0100 .035 .5 .7 3.1 3.3646 Gakona River 14,500 19,300 0 .0030 .035 .4 .4 — —

649 Chistochina River No. 1 15,000 17,700 0 .0050 .040 2.2 2.6 5.9 6.2650 Chistochina River No. 2 15,000 17,700 0 .0050 .040 2.2 2.6 5.9 6.2651 Indian River 3,730 4,630 5 .0100 .035 .0 .0 3.9 4.0653 Porcupine Creek 1,140 1,460 0 .0180 .040 .4 .5 — —

654 Slana River 5,980 7,020 0 .0014 .032 .0 .0 4.5 4.6658 Little Tok River 9,430 11,200 5 .0040 .035 .0 .0 4.5 4.7 Press663 Tok River 20,000 23,100 0 .0030 .035 3.6 3.6 5.1 5.3666 South Fork Anchor River 6,520 10,400 0 .0085 .038 3.1 1.8 — — Press

668 Deep Creek 2,170 2,740 0 .0060 .035 .5 .6 4.1 4.3669 Ninilchik River 2,010 2,720 0 .0069 .035 2.2 2.8 7.6 8.2670 Kasilof River 14,500 16,900 0 .0010 .035 .8 .8 7.1 7.3671 Kenai River at Soldotna 40,000 48,400 0 .0013 .035 .3 .4 8.2 8.5673 Kenai River at Schooners Bend 36,900 46,900 0 .0030 .035 .9 1.4 6.3 6.7674 Cooper Creek 2,680 3,290 0 .0190 .040 .0 .0 — —

675 Kenai River Cooper Land 34,400 44,000 0 .0006 .035 .2 .2 2.9 3.1678 Little Goldstream Creek 2,260 2,870 0 .0005 .040 2.5 1.8 3.5 3.7685 Maclaren River 10,900 13,200 0 .0015 .035 .1 .1 6.9 7.1686 Clearwater Creek 4,420 5,400 25 .0100 .035 1.1 1.6 11.3 11.8687 Susitna River 37,600 48,200 20 .0009 .030 .3 .5 18.4 19.1688 Canyon Creek 648 861 0 .0380 .045 .4 .5 — —

690 Seattle Creek 3,090 5,730 0 .0150 .045 5.9 .0 — — Press

693 Carlo Creek 1,080 1,380 0 .0180 .035 1.0 1.1 — —

694 Nenana River Park Bend 25,400 30,300 0 .0040 .035 .2 .2 12.5 12.9695 Riley Creek 5,220 6,290 0 .0140 .045 .1 .1 7.3 7.5697 Kingfisher Creek 84 115 0 .2300 .040 .0 .0 — —

735 Eagle River 10,400 13,000 20 .0050 .035 .0 .0 19.8 20.8
22 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 2. Computed Phase I contraction- and pier-scour depths at selected bridge sites in AlaskaóContinued [Manning’s roughness coefficients are for main channel at bridge. ADOT&PF, Alaska Department of Transportation and Public Facilities. Q100, 100-year flood; Q500, 500-year flood. —, not app

Bridge Discharge (cubic feet per second) Angle of attack (degrees) Valley slope (feet per foot) Manningís roughness coefficient

n

Computed scour depth

(feet)

Contraction scour Pier scour 

ADOT&PF

number Name

Q100

Q500

Q100

Q500

Q100

Q500

736 Herbert River 10,100 12,400 10 .0020 .035 .3 .4 15.8 16.5737 Mendenhall River 18,900 23,200 0 .0010 .033 .1 .0 5.9 5.8742 Chilkat River 32,600 42,900 0 .0006 .035 .3 .3 4.2 4.5799 Long Creek 577 763 0 .0170 .040 .0 .0 — —

816 Crooked Creek 578 763 0 .0090 .035 .0 .0 — —

819 Deadwood Creek 1,530 1,970 0 .0110 .035 2.3 3.0 — —

822 Belle Creek 964 1,250 0 .0090 .035 2.1 2.8 3.1 3.3823 McKay Creek 534 703 0 .0240 .035 .0 .0 4.2 4.4826 Reed Creek 326 434 0 .0290 .035 .0 .0 — —

827 Willow Creek 269 360 0 .0260 .045 .2 .2 — —

828 Bear Creek 584 767 0 .0190 .035 .0 .0 — —

831 Mammoth Creek 1,610 2,060 0 .0140 .035 3.2 5.6 — —

832 Boulder Creek 2,130 3,840 0 .0145 .045 .7 .3 — — Press

833 Albert Creek 3,890 4,860 0 .0060 .035 2.2 2.8 — — Press836 Chatanika River 13,600 16,200 0 .0010 .035 .0 .0 4.4 4.5838 Washington Creek 4,210 6,710 0 .0120 .040 2.3 2.3 4.7 5.2839 South Fork 40 Mile River 37,200 48,700 0 .0015 .035 1.7 1.9 7.3 7.8851 Dry Creek 1,930 2,420 0 .0300 .040 .0 .0 2.8 3.0852 Dry Creek Overflow 307 404 0 .0300 .040 .0 .0 2.5 2.7853 Salmon Creek 4,190 5,290 0 .0060 .035 1.3 1.7 4.1 4.3854 Small Creek 903 1,140 0 .0250 .040 3.3 5.4 — — Press

855 Small Creek 1,520 1,910 0 .0250 .040 .8 1.0 — —

857 Nenana River at Healy 47,200 57,800 15 .0100 .040 7.3 9.6 33.9 36.2 Footi858 Slana River 18,400 21,400 0 .0026 .035 7.9 8.8 8.0 8.2868 Falls Creek 5,050 6,290 0 .0030 .035 2.6 3.4 5.7 6.2888 Carlson Creek 559 738 0 .0320 .040 .2 .2 — —940 Fish Camp Creek 637 871 0 .0005 .035 4.4 4.4 — —969 Campbell Creek Lake Otis 1,090 1,500 0 .0050 .035 .5 .7 4.1 4.4970 Campbell Creek Arctic 1,390 1,780 0 .0050 .035 .0 .0 3.3 3.5971 Campbell Creek 1,380 1,770 0 .0050 .035 .9 1.4 3.3 3.6
ESTIMATES OF CONTRACTION SCOUR AND PIER SCOUR 23

983 Red Cloud River 1,580 1,960 0 0.0200 0.045 0.0 0.0 3.2 3.3

986 Buskin River No. 5 3,460 4,330 0 .0015 .035 .2 .4 — —

999 Glacier Creek 7,020 10,200 20 .0150 .040 3.3 4.4 9.2 9.9

1008 Cripple Creek 1,920 2,470 0 .0040 .035 .0 .0 — —

1009 Goldstream Creek 3,190 3,990 0 .0020 .035 1.2 2.4 — — Press

1025 Resurrection Creek 4,590 6,520 0 .0100 .035 1.8 2.4 7.5 8.1

1075 Dragonfly Creek 95 130 0 .1400 .050 .0 .0 — —

1092 Little Tok River 7,970 9,750 0 .0020 .035 .0 .4 3.9 3.9

1094 Situk River 4,330 5,400 0 .0006 .035 .0 .0 5.7 6.2 Press

1131 Ketchikan Creek Fair Street 2,920 3,550 0 .0200 .035 .1 .1 6.8 7.2

1132 Ketchikan Creek Park–Upper Crossing 2,960 3,600 0 .0200 .035 .2 .2 6.8 7.2

1141 Antler Creek 169 226 0 .1030 .045 .0 .0 6.2 6.5

1142 Bison Gulch 136 183 0 .1040 .040 .1 .0 4.6 4.9

1143 Nenana River at Moody 43,700 54,400 0 .0050 .045 .0 .2 — —

1145 Hornet Creek 212 283 0 .1100 .040 .0 .0 — —

1146 Iceworm Gulch 164 221 0 .1100 .040 .3 .3 — —

1147 Nenana River Park Station 43,200 53,600 0 .0050 .040 .8 1.7 9.9 10.3

1153 Whipple Creek 3,500 4,740 0 .0320 .040 .2 .1 13.0 13.8

1155 Peters Creek North Crossing 2,260 2,890 0 .0270 .035 .3 .4 8.4 8.8

1156 Wasilla Creek 570 767 0 .0020 .035 .0 .0 — —

1157 Campbell Creek East Frontage 1,120 1,540 0 .0040 .035 .4 .4 — —

1187 Copper River Delta 54,400 69,000 35 .00015 .030 2.6 2.9 18.3 18.7

1191 Chena River (Peger Road) 12,000 12,000 0 .0002 .030 1.9 1.9 4.5 4.5

1196 Lost River 5,850 7,240 0 .0011 .030 .6 .6 3.6 3.9 Press

1203 Solomon Creek 3,300 4,090 0 .0054 .035 .0 .0 — —

1204 Abercrombie Creek 1,710 2,170 0 .2700 .040 .1 .2 — —

1207 Lowe River Main Channel 37,300 47,300 20 .0030 .035 .5 .7 14.9 15.8

1208 Lowe River North Channel 5,090 6,460 0 .0030 .035 .1 .1 4.6 4.8

1212 Chena River 12,000 12,000 0 .0010 .035 .0 .0 5.6 5.6

1213 Hess Creek 13,500 17,200 0 .0004 .035 3.6 3.5 — —

1220 Cowee Creek 9,870 12,400 0 .0040 .035 3.2 .7 4.9 5.0 Press

1222 Tiekel River No. 2 8,000 9,030 0 .0100 .040 .0 .0 12.8 13.1

1228 Antlen River 546 672 0 .0020 .035 .3 .3 3.4 3.6

1229 Ahrnklin River 9,690 11,900 0 .0030 .035 1.5 2.0 6.5 6.9

1230 Eklutna River Northbound 5,090 6,210 10 .0130 .040 8.2 8.7 — —

1234 Ketchum Creek 704 925 0 .0160 .040 1.2 1.7 — —

1241 Little Nelchina River 6,760 8,300 0 .0096 .040 1.2 1.6 8.5 8.9

1243 Nenana River at Windy 13,000 15,400 0 .0042 .050 .0 .0 6.9 7.2

1250 Tulsona Creek 2,400 3,110 0 .0050 .035 .0 .0 — —

1255 Fish Creek 3,800 4,710 20 .0060 .035 1.4 1.9 9.5 10.1
24 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska Table 2. Computed Phase I contraction- and pier-scour depths at selected bridge sites in AlaskaóContinued [Manning’s roughness coefficients are for main channel at bridge. ADOT&PF, Alaska Department of Transportation and Public Facilities. Q100, 100-year flood; Q500, 500-year flood. —, not app

Bridge Discharge (cubic feet per second) Angle of attack (degrees) Valley slope (feet per foot) Manningís roughness coefficient

n

Computed scour depth

(feet)

Contraction scour Pier scour 

ADOT&PF

number Name

Q100

Q500

Q100

Q500

Q100

Q500

1256 North Fork Bonanza Creek 3,870 4,790 0 .0050 .040 .9 1.5 2.8 3.0

1257 South Fork Bonanza Creek 4,530 5,590 0 .0040 .035 .0 .0 3.1 3.3

1258 Prospect Creek 7,210 8,980 0 .0030 .035 2.9 3.8 3.5 3.7

1259 Jim River No. 1 2,920 3,640 0 .0050 .035 1.7 2.0 2.8 3.0

1260 South Fork Koyukuk River 14,900 17,900 0 .0020 .030 .1 .2 3.0 3.2

1261 Middle Fork Koyukuk River No. 1 25,100 28,500 10 .0230 .028 .9 1.0 7.2 7.4

1273 Chester Creek 1,650 2,260 0 .0007 .035 1.0 1.4 3.5 3.7 Press

1282 Middle Fork Koyukuk River No. 2 20,300 23,400 10 .0030 .030 .3 .4 12.8 13.3

1283 Middle Fork Koyukuk River No. 3 10,300 12,000 0 .0013 .035 1.5 3.1 3.4 3.4 Press

1284 Middle Fork Koyukuk River No. 4 7,880 9,180 0 .0020 .035 1.5 1.6 3.1 3.2

1320 Ship Creek 3,520 4,550 0 .0060 .035 .5 .7 6.8 7.2

1329 Little Chena River 7,910 11,800 0 .0010 .035 .0 .0 5.1 5.8 Press

1332 Slate Creek 3,480 4,300 0 .0050 .035 1.3 1.3 3.2 3.3

1333 Atigun River No. 2 6,990 8,550 0 .0040 .035 1.0 1.1 2.6 2.7

1334 No Name Creek 4,930 6,080 0 .0030 .035 .0 .0 3.4 3.6

1335 Minnie Creek 2,230 2,790 0 .0040 .037 1.2 1.7 3.2 3.4

1336 Hammond River 8,560 10,200 0 .0030 .035 3.0 3.7 3.7 3.9

1337 Dietrich River 11,200 13,100 10 .0040 .035 .3 .4 6.3 6.5

1338 Kanuti River 5,140 6,340 15 .0010 .035 .9 1.3 6.3 6.7

1341 Eagle River South Crossing 6,920 8,710 0 .0120 .035 1.8 1.7 12.9 13.6

1344 Peters Creek Southbound 2,260 2,890 0 .0270 .035 .0 .0 8.4 8.8

1350 Campbell Creek West Frontage 1,120 1,540 0 .0040 .035 .1 .2 — —

1355 Harris River 4,380 5,420 0 .0070 .035 .7 .8 — —

1356 Fubar Creek 1,640 2,020 0 .0170 .040 2.7 3.2 — —

1383 Lowe River Lower Keystone 21,400 27,600 50 .0050 .040 .6 .4 15.4 16.3

1384 Lowe River Upper Keystone 21,400 27,600 35 .0070 .040 .0 .0 13.2 14.2

1389 Unnamed Creek 980 1,230 25 .0500 .035 .1 .1 3.5 3.7

1390 Resurrection River 14,100 17,800 0 .0012 .035 .0 .0 10.5 11.2 Press

1394 Globe Creek 1,520 1,960 0 .0060 .035 1.2 2.5 — —

1400 Tatalina River 3,570 4,460 0 .0050 .035 2.9 3.4 — —
ESTIMATES OF CONTRACTION SCOUR AND PIER SCOUR 25

1436 Jim River No. 2 2,910 3,620 20 0.0050 0.035 0.6 1.2 7.7 8.1

1437 Jim River No. 3 6,570 8,040 0 .0090 .035 1.2 1.4 3.3 3.4

1439 Atigun River No. 1 2,190 2,730 0 .0100 .035 4.9 5.9 2.8 2.9

1443 Campbell Creek 1,600 2,070 0 .0050 .035 .4 .5 — —

1444 Campbell Creek at Minnesota Drive 1,600 2,070 0 .0050 .035 .4 .5 — —

1445 Campbell Creek at Minnesota Drive 1,600 2,070 0 .0050 .035 .4 .5 — —

1455 Control Creek 2,480 3,070 0 .0010 .035 2.9 3.2 — —

1461 Goose Creek 4,240 5,250 0 .0005 .035 3.4 3.5 6.7 7.1

1462 Thorne River 23,500 29,100 0 .0020 .035 .0 .3 — —

1513 Fort Hamlin Hills Creek 1,830 2,330 0 .0050 .035 1.8 2.6 — —

1514 Gold Creek 1,060 1,350 0 .0170 .040 1.7 2.1 — —

1519 Roche Moutonnee Creek 1,250 1,480 0 .0360 .063 1.2 1.4 — —

1520 Holden Creek 563 743 0 .0380 .040 .2 .3 — —

1521 Dan Creek 1,000 1,360 0 .0110 .035 1.2 1.7 — —

1536 False Pass Creek 2,260 2,850 0 .0170 .040 .0 .0 4.3 4.5

1560 Douglas Creek 932 1,210 0 .0060 .040 1.8 3.2 — —

1629 Chester Creek 1,650 2,260 0 .0050 .035 .0 .0 — —

1694 Campbell Creek 1,600 2,070 0 .0050 .035 .4 .5 — —

1746 Klutina River 11,900 12,800 0 .0060 .035 .0 .0 8.4 8.5

1864 Eklutna River Southbound 5,090 6,210 0 .0130 .040 8.2 8.7 — —

tigations Report 94–4073, 57 p.

Alaska: U.S. Geological Survey Water-Resources InvesPoint to Million Dollar bridge, Copper River Highway, 

Federal Highway Administration, 1988, Scour at bridges: 

portation Technical Advisory 5140.20, 103 p.

Federal Highway Administration, Department of TransFetter, C.W., 1994, Applied Hydrogeology (3d ed.): New 

York, Macmillan College Publishing Company, 691 p.

Huizinga, R.J., and Waite, L.A., 1994, Methodology for the 

logical Survey Open-File Report 94–544, 23 p.

assessment of scour at bridge sites in Missouri: U.S. GeoInteragency Advisory Committee on Water Data, 1982, 

report PB–86–157278/AS].

from the National Technical Information Service as 

Hydrology Subcommittee, Bulletin 17B, 28 p. [available 

Guidelines for determining flood-flow frequency: 

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

Report 93–4179, 122 p.

U.S. Geological Survey Water-Resources Investigations 

of floods in Alaska and conterminous basins of Canada: 

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

HEC–18, 204 p.

Federal Highway Administration, FHWA–IP–90–017 

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

Robinson, B.A., and Thompson, R.E., 1993, An efficient 

Hydraulic Engineering ‘93, 

method for assessing channel instability near bridges: 

American Society of Civil 

Engineering Proceedings, 1993, v. 1, p. 513–518.

Shearman, J.O., 1990, Users manual for WSPRO—A comeral Highway Administra

puter model for water-surface profile computations: Fedtion Publication FHWA–IP–

89–027, 177 p.
APPENDIX
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 29

SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES

In this appendix are four examples of data summaries from Phase I bridge-scour 

analyses for four bridges (see location map, below). Examples of raw output from the bridgesite files (Excel spreadsheets), they were chosen to illustrate the wide range of information 

that may be available for a given site and the procedures used to estimate scour at the site. 

The examples are presented in ascending order according to the amount of useful hydraulic 

information available for the site. Thus, bridge 528 has very little background information 

available, whereas bridge 857 has information available that would be equivalent to a Phase 

II on-site survey including recent flood-discharge measurements. Examples of spreadsheet 

output, including summary information and automatic calculations, are provided as follows:

Example 1—Bridge 528, Clear Creek

Example 2—Bridge 407, Scott Glacier No. 7

Example 3—Bridge 527, Salcha River

Example 4—Bridge 857, Nenana River at Healy

Phase I site locations, bridges 407, 527, 528, and 857

Bridge 857

Bridge 527

Bridge 407

Bridge 528 

▲

▲

▲▲

Fairbanks

Anchorage

Cordova
30 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Example 1

Bridge 528, Clear Creek, Richardson Highway mile 324.0:

Bridge 528 is a single-span bridge at an ungaged site.

Data available: As-built plans were provided by the Alaska Department of Transportation 

and Public Facilities.

Summary information included: Cross sections and scour computations.

Derivations, assumptions, and remarks: Geometry of the stream channel at the fullvalley and approach cross sections was derived from the as-built topographic map. A slope

of 0.0030 ft/ft was measured from a U.S. Geological Survey topographic-quadrangle map;

this slope was used as the valley slope for templating cross sections and as the initial friction 

slope for the WSPRO model run. We assumed a Manning’s n value of 0.035 and a bed-material grain size of 10 millimeters (0.39 in).
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 31

Clear Creek

Bridge 528

Alaska HIghway mile 258.5

X Z Notes

(feet) (feet)

Bridge geometry

3.2 637.1 from as-builts

3.3 636.1 from as-builts

4.1 636.2 from as-builts

15.1 628.1 from as-built topo

21.1 627.5 from as-built topo

23.1 628.1 from as-built topo

27.1 628.2 from as-built topo

31.0 628.8 from as-built topo

43.2 636.6 from as-builts

44.0 636.5 from as-builts

44.2 637.4 from as-builts

3.2 637.1 from as-builts

Full valley section

-100.0 638.2 extended up

-94.0 634.2 from as-built topo

-33.0 632.2 from as-built topo

-15.0 630.2 from as-built topo

9.0 628.2 from as-built topo

16.0 627.7 from as-built topo

23.0 628.2 from as-built topo

34.0 630.2 from as-built topo

44.0 632.2 from as-built topo

88.0 634.2 from as-built topo

94.0 638.2 extended up

Approach section

-75.0 644.0 extended up

-62.0 634.0 from as-built topo

-54.0 632.0 from as-built topo

-17.0 630.0 from as-built topo

3.0 628.0 from as-built topo

10.0 627.8 from as-built topo

17.0 628.0 from as-built topo

40.0 630.0 from as-built topo

68.0 632.0 from as-built topo

85.0 634.0 from as-built topo

100.0 644.0 extended up

Bridge 528

626

628

630

632

634

636

638

0 10 20 30 40 50

X, IN FEET

Z, IN FEET

Full Valley Section

626

628

630

632

634

636

638

640

-150 -100 - 50 0 50 100 150

X, IN FEET

Z, IN FEET

Bridge 528. Clear Creek bridge and 

full valley cross-sections. 

[X is an arbitrary horizontal coordinate. Z is the 

elevation read from the as-built bridge plans. 

Approach was measured 47 feet upstream of 

the bridge.]

Bridge 528 bridge cross-section.

Bridge 528 full valley cross-section.

Approach Section

625

630

635

640

645

-100 - 50 0 50 100 150

X, IN FEET

Z, IN FEET

Bridge 528 approach cross-section.

Clear Creek

Bridge 528

Alaska HIghway mile 258.5

X Z Notes

(feet) (feet)

Bridge geometry

3.2 637.1 from as-builts

3.3 636.1 from as-builts

4.1 636.2 from as-builts

15.1 628.1 from as-built topo

21.1 627.5 from as-built topo

23.1 628.1 from as-built topo

27.1 628.2 from as-built topo

31.0 628.8 from as-built topo

43.2 636.6 from as-builts

44.0 636.5 from as-builts

44.2 637.4 from as-builts

3.2 637.1 from as-builts

Full valley section

-100.0 638.2 extended up

-94.0 634.2 from as-built topo

-33.0 632.2 from as-built topo

-15.0 630.2 from as-built topo

9.0 628.2 from as-built topo

16.0 627.7 from as-built topo

23.0 628.2 from as-built topo

34.0 630.2 from as-built topo

44.0 632.2 from as-built topo

88.0 634.2 from as-built topo

94.0 638.2 extended up

Approach section

-75.0 644.0 extended up

-62.0 634.0 from as-built topo

-54.0 632.0 from as-built topo

-17.0 630.0 from as-built topo

3.0 628.0 from as-built topo

10.0 627.8 from as-built topo

17.0 628.0 from as-built topo

40.0 630.0 from as-built topo

68.0 632.0 from as-built topo

85.0 634.0 from as-built topo

100.0 644.0 extended up

Bridge 528

626

628

630

632

634

636

638

0 10 20 30 40 50

X, IN FEET

Z, IN FEET

Full Valley Section

626

628

630

632

634

636

638

640

-150 -100 - 50 0 50 100 150

X, IN FEET

Z, IN FEET

Bridge 528. Clear Creek bridge and 

full valley cross-sections. 

[X is an arbitrary horizontal coordinate. Z is the 

elevation read from the as-built bridge plans. 

Approach was measured 47 feet upstream of 

the bridge.]

Bridge 528 bridge cross-section.

Bridge 528 full valley cross-section.

Approach Section

625

630

635

640

645

-100 - 50 0 50 100 150

X, IN FEET

Z, IN FEET

Bridge 528 approach cross-section.
32 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Clear Creek

Bridge 528

Alaska Highway mile 258.5

LIVE-BED CONTRACTION SCOUR

100 Year 500 Year

Computed floods: total discharge (cfs) Q 162 221

Hydraulic radius of approach section (ft) R 1.64 1.88

Friction slope (ft/ft) S 0.0023 0.0024

Average shear stress at bed (lbs/ft2

) gRS 0.24 0.28

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

1⁄2 0.35 0.38

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

Ratio V*/w 0.13 0.15

Exponent determined from mode of bed material transport k1 =f(V*/w) 0.59 0.59

Discharge in main channel of approach section (cfs) Q1 162 221

Percentage of total discharge 100% 100%

Discharge in main channel of contracted (bridge) section (cfs) Q2 162 221

Percentage of total discharge 100% 100%

Width of main channel of approach section (ft) W1 78 90

Width of main channel of contracted (bridge) section (ft) W2 21 22

Average depth of main channel of approach section (ft) y1 1.6 1.9

Average depth in contracted (bridge) section (ft) y2 3.6 4.3

CONTRACTION SCOUR (ft) Ycs 1.9 2.4

PIER SCOUR

100 Year 500 Year

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

Depth of maximum velocity stream tube (ft) y1

Froude number of maximum velocity stream tube Fr=v1/(gy1)

1⁄2

Pier shape

Pier shape correction factor K1

Angle of attack (deg) AA

Pier width (ft) a

Pier length (ft) L

Ratio L/a

Angle of attack correction factor K2=f(AA,L/a)

Bed condition (dunes) correction factor K3

PIER SCOUR (ft) Yps n/a n/a

TOTAL SCOUR

100 Year 500 Year

Contraction scour (ft) Ycs 1.9 2.4

Pier scour (ft) Yps n/a n/a

TOTAL SCOUR (ft) Ts 1.9 2.4

y

y

Q

Q

W

W

y yy

K

cs

2

1

2

1

6

7

1

2

2 1

1

 



 



 



 





  = (average scour depth)

y

y

KKK a

y

Fr ps

1

123

1

0 65

0 43  2 0 



 

 . 

.

.

Ty y s cs ps  

Notes:

Notes: This bridge has no piers.

Bridge 528. Clear Creek bridge scour computations. 
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 33

Example 2

Bridge 407, Scott Glacier No. 7, Copper River Highway mile 10.0

Bridge 407 has piers and is at an ungaged site.

Data available: This bridge was surveyed for bridge-scour assessment on August 30, 

1996. As-built plans were provided by the Alaska Department of Transportation and Public 

Facilities.

Summary information included: Cross sections and scour computations.

Derivations, assumptions, and remarks: Flood flow was allocated among the 11 

Scott Glacier bridges by dividing flow computed from an August 30, 1996, discharge measurement among the 11 bridges. Approximately 6 percent of the total Scott Glacier discharge 

measured on that date passed through bridge 407. As a best approximation based on available data, we routed 6 percent of the Q100 and Q500 flows through the bridge, with the 

understanding that the actual percentage of flow through the bridge may vary significantly 

with changes in total flow.

Geometry from the as-built plans was combined with soundings made during the 

August 30, 1996, discharge measurement of 444 ft3

/s (25 percent of Q100) to construct the 

full-valley cross section. This geometry was used to template approach and exit sections for 

the WSPRO model. On the basis of field observations, the approach section was scaled to 

be 300 percent of the full-valley width at the bridge. Active sediment transport was assumed 

for two-thirds of the approach. Friction slope was back-calculated from the discharge measurement assuming a Manning’s n value of 0.035. This slope was used as the valley slope for 

templating cross sections and as the initial friction slope for the WSPRO model run.

Because the piles are separated by less than five pile diameters, pier scour was computed for a composite pier length.
34 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Scott Glacier No. 7

Bridge 407

Copper River HIghway mile 10.1

X Z Notes

(feet) (feet)

Bridge geometry

2.9 47.0 from as-builts

3.0 47.0 from as-builts

5.9 46.7 from as-builts

8.1 45.5 from as-builts

12.7 45.1 from as-builts

20.0 40.7 USGS sounding

30.0 39.8 USGS sounding

40.0 39.4 USGS sounding

60.0 38.3 USGS sounding

70.0 37.6 USGS sounding

90.0 38.3 USGS sounding

110.0 39.6 USGS sounding

130.0 39.8 USGS sounding

150.0 39.2 USGS sounding

162.0 40.7 USGS sounding

168.7 43.2 from as-builts

170.4 44.6 from as-builts

173.3 44.6 from as-builts

175.7 45.8 from as-builts

178.3 46.0 from as-builts

178.4 47.0 from as-builts

2.9 47.0 from as-builts

Full valley section

-54.2 57.4 extended up

-44.2 47.4 from as-builts

-16.5 47.4 from as-builts

6.2 46.7 from as-builts

16.1 40.9 from as-builts

20.0 40.7 USGS sounding

30.0 39.8 USGS sounding

40.0 39.4 USGS sounding

60.0 38.3 USGS sounding

70.0 37.6 USGS sounding

90.0 38.3 USGS sounding

110.0 39.6 USGS sounding

130.0 39.8 USGS sounding

150.0 39.2 USGS sounding

162.0 40.7 USGS sounding

182.7 46.7 from as-builts

204.8 46.5 from as-builts

227.6 45.5 from as-builts

249.6 45.1 from as-builts

259.6 55.1 extended up

Bridge 407

35

37

39

41

43

45

47

49

0 50 100 150 200

X, IN FEET

Z, IN FEET

Full Valley Section

35

40

45

50

55

60

-100 0 100 200 300

X, IN FEET

Z, IN FEET

Bridge 407. Scott Glacier No. 7 

bridge and full valley cross-sections. 

[X is an arbitrary horizontal coordinate. Z is the 

elevation read from the as-built bridge plans. 

USGS soundings made 8/30/96.]

Bridge 407 bridge cross-section.

Bridge 407 full valley cross-section.
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 35

Scott Glacier No. 7

Bridge 407

Copper River Highway mile 10.1

LIVE-BED CONTRACTION SCOUR

100 Year 500 Year

Computed floods: total discharge (cfs) Q 1760 2170

Hydraulic radius of approach section (ft) R 3.18 3.58

Friction slope (ft/ft) S 0.0007 0.0008

Average shear stress at bed (lbs/ft 2

) gRS 0.14 0.18

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

1⁄2 0.27 0.30

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

Ratio V*/w 0.10 0.12

Exponent determined from mode of bed material transport k1 =f(V*/w) 0.59 0.59

Discharge in main channel of approach section (cfs) Q1 1162 1432

Percentage of total discharge 66% 66%

Discharge in main channel of contracted (bridge) section (cfs) Q2 1760 2170

Percentage of total discharge 100% 100%

Width of main channel of approach section (ft) W1 307 311

Width of main channel of contracted (bridge) section (ft) W2 143 144

Average depth of main channel of approach section (ft) y1 3.2 3.6

Average depth in contracted (bridge) section (ft) y2 7.1 8.1

CONTRACTION SCOUR (ft) Ycs 3.9 4.5

PIER SCOUR

100 Year 500 Year

Speed of maximum velocity stream tube (ft/s) v1 5.20 5.64

Depth of maximum velocity stream tube (ft) y1 4.2 4.6

Froude number of maximum velocity stream tube Fr=v1/(gy1)

1⁄2 0.45 0.46

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 10 10

Pier width (ft) a 1.3 1.3

Pier length (ft) L 8 8

Ratio L/a 6 6

Angle of attack correction factor K2=f(AA,L/a) 1.5 1.5

Bed condition (dunes) correction factor K3 1.1 1.1

PIER SCOUR (ft) Yps 4.6 4.9

TOTAL SCOUR

100 Year 500 Year

Contraction scour (ft) Ycs 3.9 4.5

Pier scour (ft) Yps 4.6 4.9

TOTAL SCOUR (ft) Ts 8.6 9.3

y

y

Q

Q

W

W

y yy

K

cs

2

1

2

1

6

7

1

2

2 1

1

 



 



 



 





  = (average scour depth)

y

y

KKK a

y

Fr ps

1

123

1

0 65

0 43  2 0 



 

 . 

.

.

Ty y s cs ps  

Notes:

Notes:

Bridge 407. Scott Glacier No. 7 bridge scour 

computations. 
36 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Example 3

Bridge 527, Salcha River, Richardson Highway mile 323.3

Bridge 527 has piers and is near a U.S. Geological Survey gaging station.

Data available: An active U.S. Geological Survey gaging station (15484000, Salcha 

River near Salchaket, Alaska) is approximately 1,000 ft upstream from the bridge. The gaging station has been in operation since September 1948. Discharge measurements from the 

bridge are available. As-built plans were provided by the Alaska Department of Transportation and Public Facilities. Flood estimates are from Jones and Fahl (1994).

Summary information included: Cross sections and scour computations.

Derivations, assumptions, and remarks: Geometry from the as-built bridge plans 

was combined with soundings made during the September 23, 1993 discharge measurement 

(4,860 ft3

/s, or 10 percent of Q100). This geometry was used to template additional sections 

for the WSPRO model. Friction slope was back-calculated from the discharge measurement 

assuming a Manning’s n value of 0.035. This slope was used as the valley slope for templating cross sections and as the initial friction slope for the WSPRO model run. Good agreement was obtained between the model and a high discharge measurement.

The flood of record at the gaging station (97,000 ft3

/s on August 14, 1967) exceeded 

the Q500 discharge, so an additional WSPRO run and scour calculation were done for 

97,000 ft3

/s. Computed contraction scour was 4.7 ft, and pier scour, 23.7 ft.
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 37

Salcha River

Bridge 527

Alaska HIghway mile 255.2

X Z Notes

(feet) (feet)

Bridge geometry

0.0 656.9 from as-builts

0.0 656.0 from as-builts

6.0 656.0 from as-builts

45.0 640.0 USGS sounding

51.0 636.5 USGS sounding

60.0 635.7 USGS sounding

70.0 635.1 USGS sounding

80.0 634.3 USGS sounding

90.0 632.9 USGS sounding

100.0 632.8 USGS sounding

104.0 634.0 USGS sounding

109.0 634.0 USGS sounding

120.0 635.1 USGS sounding

140.0 633.8 USGS sounding

160.0 631.7 USGS sounding

165.0 631.4 USGS sounding

170.0 631.4 USGS sounding

180.0 631.0 USGS sounding

185.0 630.6 USGS sounding

200.0 630.5 USGS sounding

210.0 630.2 USGS sounding

215.0 630.3 USGS sounding

220.0 629.9 USGS sounding

235.0 629.6 USGS sounding

245.0 630.1 USGS sounding

250.0 631.5 USGS sounding

262.0 631.8 USGS sounding

324.0 638.0 from as-builts

422.0 638.0 from as-builts

446.0 640.0 from as-builts

464.0 641.0 from as-builts

494.0 656.0 from as-builts

500.0 656.0 from as-builts

500.0 656.9 from as-builts

0.0 656.9 from as-builts

continued next page

Bridge 527

625

630

635

640

645

650

655

660

0 100 200 300 400 500 600

X, IN FEET

Z, IN FEET

Bridge 527. Salcha River bridge and 

full valley cross-sections. 

[X is an arbitrary horizontal coordinate. Z is the 

elevation read from the as-built bridge plans. 

USGS soundings made on 9/23/93]

Bridge 527 bridge cross-section.
38 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Full valley section

-100.0 650.0 extended up

-50.0 645.0 extended up

45.0 640.0 USGS sounding

51.0 636.5 USGS sounding

60.0 635.7 USGS sounding

70.0 635.1 USGS sounding

80.0 634.3 USGS sounding

90.0 632.9 USGS sounding

100.0 632.8 USGS sounding

104.0 634.0 USGS sounding

109.0 634.0 USGS sounding

120.0 635.1 USGS sounding

140.0 633.8 USGS sounding

160.0 631.7 USGS sounding

165.0 631.4 USGS sounding

170.0 631.4 USGS sounding

180.0 631.0 USGS sounding

185.0 630.6 USGS sounding

200.0 630.5 USGS sounding

210.0 630.2 USGS sounding

215.0 630.3 USGS sounding

220.0 629.9 USGS sounding

235.0 629.6 USGS sounding

245.0 630.1 USGS sounding

250.0 631.5 USGS sounding

262.0 631.8 USGS sounding

324.0 638.0 from as-builts

422.0 638.0 from as-builts

446.0 640.0 from as-builts

464.0 641.0 from as-builts

550.0 645.0 extended up

600.0 650.0 extended up

Full Valley Section

625

630

635

640

645

650

655

-200 0 200 400 600 800

X, IN FEET

Z, IN FEET

Bridge 527 full valley cross-section.

Bridge 527. Salcha River, continued
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 39

Salcha River

Bridge 527

Alaska Highway mile 255.2

LIVE-BED CONTRACTION SCOUR

100 Year 500 Year

Computed floods: total discharge (cfs) Q 50600 64900

Hydraulic radius of approach section (ft) R 15.99 18.24

Friction slope (ft/ft) S 0.0013 0.0014

Average shear stress at bed (lbs/ft 2

) gRS 1.30 1.59

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

1⁄2 0.82 0.91

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

Ratio V*/w 0.31 0.35

Exponent determined from mode of bed material transport k1 =f(V*/w) 0.59 0.59

Discharge in main channel of approach section (cfs) Q1 44912 56126

Percentage of total discharge 89% 86%

Discharge in main channel of contracted (bridge) section (cfs) Q2 44021 55357

Percentage of total discharge 87% 85%

Width of main channel of approach section (ft) W1 275 275

Width of main channel of contracted (bridge) section (ft) W2 195 195

Average depth of main channel of approach section (ft) y1 16.1 18.4

Average depth in contracted (bridge) section (ft) y2 19.4 22.2

CONTRACTION SCOUR (ft) Ycs 3.3 3.9

PIER SCOUR

100 Year 500 Year

Speed of maximum velocity stream tube (ft/s) v1 14.67 15.79

Depth of maximum velocity stream tube (ft) y1 19.3 21.6

Froude number of maximum velocity stream tube Fr=v1/(gy1)

1⁄2 0.59 0.60

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 10 10

Pier width (ft) a 4.0 4.0

Pier length (ft) L 30 30

Ratio L/a 8 8

Angle of attack correction factor K2=f(AA,L/a) 1.7 1.7

Bed condition (dunes) correction factor K3 1.1 1.1

Submerged low steel multiplier f(Frapproach)

PIER SCOUR (ft) Yps 20.7 21.7

TOTAL SCOUR

100 Year 500 Year

Contraction scour (ft) Ycs 3.3 3.9

Pier scour (ft) Yps 20.7 21.7

TOTAL SCOUR (ft) Ts 23.9 25.5

y

y

Q

Q

W

W

y yy

K

cs

2

1

2

1

6

7

1

2

2 1

1

 



 



 



 





  = (average scour depth)

y

y

KKK a

y

Fr ps

1

123

1

0 65

0 43  2 0 



 

 . 

.

.

Ty y s cs ps  

Notes:

Notes:

Bridge 527. Salcha River bridge scour computations.
40 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Example 4

Bridge 857, Nenana River at Healy, Healy Road, mile 3.2

Bridge 857 has piers and exposed footings. The bridge is near a U.S. Geological Survey gaging station that has available numerous U.S. Geological Survey discharge measurements.

Data available: A U.S. Geological Survey gaging station (15518000, Nenana River near 

Healy, Alaska) is approximately 1.2 mi upstream from the bridge. The gaging station was in 

operation during the years 1951–79. Another gaging station (15518040, Nenana River at 

Healy) that was located at the bridge was in operation during 1990–91. A flood survey was 

performed at the bridge from September 25 to October 2, 1990. Flood discharge was 31,200 

ft3/s. As-built plans were provided by the Alaska Department of Transportation and Public 

Facilities.

Summary information included: Cross sections and scour computations for contraction 

and pier and for contraction and footing.

Derivations, assumptions, and remarks: Geometry from the as-built bridge plans

was combined with the flood-survey data. Surveyed water-surface slope was used as the initial friction slope for the WSPRO model run. Manning’s n values were estimated in the field. 

Good agreement was obtained between the model and the surveyed water-surface profile.

This model is complicated by a railroad bridge located about 100 feet upstream. One 

span of the railroad bridge has been filled, thus reducing the channel width. To model this situation, the highway and railroad bridge were treated as one very wide bridge. Scour was 

computed for just the highway bridge.

The flood survey revealed that the pier footings were exposed. Local scour was computed for both the pier geometry and the footing geometry. Footing scour was greater and 

should be used as a worst-case scenario.
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 41

Nenana River at Healy

Bridge 857

Healy Road mile 3.2

X Z Notes

(feet) (feet)

Bridge geometry

114.0 1267.6 from as-builts

114.0 1250.7 from as-builts

118.0 1250.5 USGS sounding

143.0 1245.6 USGS sounding

158.0 1243.3 USGS sounding

163.0 1241.7 USGS sounding

168.0 1241.0 USGS sounding

173.0 1240.3 USGS sounding

178.0 1238.5 USGS sounding

183.0 1240.6 USGS sounding

188.0 1242.9 USGS sounding

198.0 1245.0 USGS sounding

203.0 1245.3 USGS sounding

208.0 1245.9 USGS sounding

213.0 1246.4 USGS sounding

218.0 1247.5 USGS sounding

228.0 1248.1 USGS sounding

238.0 1246.5 USGS sounding

245.0 1244.2 USGS sounding

246.0 1244.2 USGS sounding

256.0 1244.4 USGS sounding

261.0 1244.4 USGS sounding

273.0 1247.6 USGS sounding

283.0 1248.2 USGS sounding

303.0 1251.4 USGS sounding

318.0 1252.7 USGS sounding

341.0 1254.4 USGS sounding

353.0 1255.0 USGS sounding

363.0 1256.1 USGS sounding

373.0 1255.1 USGS sounding

381.0 1251.6 USGS sounding

391.0 1251.6 USGS sounding

393.0 1251.4 USGS sounding

403.0 1251.4 USGS sounding

418.0 1252.7 USGS sounding

433.0 1254.4 USGS sounding

443.0 1256.3 USGS sounding

453.0 1256.9 USGS sounding

463.0 1257.0 USGS sounding

473.0 1263.7 USGS sounding

483.0 1265.4 USGS sounding

500.0 1267.6 USGS sounding

114.0 1267.6 from as-builts

continued next page

Bridge 857

1235

1240

1245

1250

1255

1260

1265

1270

0 100 200 300 400 500 600

X, IN FEET

Z, IN FEET

Bridge 857. Nenana River at Healy, 

bridge and full valley cross-sections. 

[X is an arbitrary horizontal coordinate. Z is the 

elevation read from the as-built bridge plans. 

USGS sounding made on 9/7/90]

Bridge 857 bridge cross-section.
42 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Full valley section

-50.0 1270.5 extended up

43.0 1257.9 USGS sounding

53.0 1257.3 USGS sounding

63.0 1257.2 USGS sounding

73.0 1256.9 USGS sounding

83.0 1256.8 USGS sounding

93.0 1257.2 USGS sounding

103.0 1255.5 USGS sounding

106.0 1254.4 USGS sounding

118.0 1250.5 USGS sounding

143.0 1245.6 USGS sounding

158.0 1243.3 USGS sounding

163.0 1241.7 USGS sounding

168.0 1241.0 USGS sounding

173.0 1240.3 USGS sounding

178.0 1238.5 USGS sounding

183.0 1240.6 USGS sounding

188.0 1242.9 USGS sounding

198.0 1245.0 USGS sounding

203.0 1245.3 USGS sounding

208.0 1245.9 USGS sounding

213.0 1246.4 USGS sounding

218.0 1247.5 USGS sounding

228.0 1248.1 USGS sounding

238.0 1246.5 USGS sounding

245.0 1244.2 USGS sounding

246.0 1244.2 USGS sounding

256.0 1244.4 USGS sounding

261.0 1244.4 USGS sounding

273.0 1247.6 USGS sounding

283.0 1248.2 USGS sounding

303.0 1251.4 USGS sounding

318.0 1252.7 USGS sounding

341.0 1254.4 USGS sounding

353.0 1255.0 USGS sounding

363.0 1256.1 USGS sounding

373.0 1255.1 USGS sounding

381.0 1251.6 USGS sounding

391.0 1251.6 USGS sounding

393.0 1251.4 USGS sounding

403.0 1251.4 USGS sounding

418.0 1252.7 USGS sounding

433.0 1254.4 USGS sounding

443.0 1256.3 USGS sounding

453.0 1256.9 USGS sounding

463.0 1257.0 USGS sounding

550.0 1270.5 extended up

Full Valley Section

1235

1240

1245

1250

1255

1260

1265

1270

1275

-200 0 200 400 600

X, IN FEET

Z, IN FEET

Bridge 857 full valley cross-section.

Bridge 857. Nenana River at Healy, 

continued
SUMMARY EXAMPLES OF FOUR PHASE I BRIDGE-SCOUR ANALYSES 43

Nenana River at Healy

Bridge 857

Healy Road mile 3.2

LIVE-BED CONTRACTION SCOUR

100 Year 500 Year

Computed floods: total discharge (cfs) Q 47200 57800

Hydraulic radius (ft) R 14.05 16.34

Friction slope (ft/ft) S 0.0017 0.0018

Average shear stress at bed (lbs/ft 2

) gRS 1.49 1.84

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

1⁄2 0.88 0.97

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

Ratio V*/w 0.34 0.37

Exponent determined from mode of bed material transport k1 =f(V*/w) 0.59 0.59

Discharge in main channel of approach section (cfs) Q1 31574 36608

Percentage of total discharge 67% 63%

Discharge in main channel of contracted (bridge) section (cfs) Q2 47200 57800

Percentage of total discharge 100% 100%

Width of main channel of approach section (cfs) W1 390 390

Width of main channel of contracted (bridge) section (cfs) W2 345 346

Average depth of main channel of approach section (ft) y1 14.1 16.4

Average depth in contracted (bridge) section (ft) y2 21.4 26.0

CONTRACTION SCOUR (ft) Ycs 7.3 9.6

PIER SCOUR

100 Year 500 Year

Speed of maximum velocity stream tube (ft/s) v1 17.61 20.55

Depth of maximum velocity stream tube (ft) y1 20.7 21.3

Froude number of maximum velocity stream tube (ft/s) Fr=v1/(gy1)

1⁄2 0.68 0.79

Pier shape round nose

Pier shape correction factor K1 1.0 1.0

Angle of attack (deg) AA 15 15

Pier width (ft) a 3.0 3.0

Pier length (ft) L 32 32

Ratio L/a 11 11

Angle of attack correction factor K2=f(AA,L/a) 2.4 2.4

Bed condition (dunes) correction factor K3 1.1 1.1

PIER SCOUR (ft) Yps 26.4 28.3

TOTAL SCOUR

100 Year 500 Year

Contraction scour (ft) Ycs 7.3 9.6

Pier scour (ft) Yps 26.4 28.3

TOTAL SCOUR (ft) Ts 33.7 38.0

y

y

Q

Q

W

W

y yy

K

cs

2

1

2

1

6

7

1

2

2 1

1

 



 



 



 





  = (average scour depth)

y

y

KKK a

y

Fr ps

1

123

1

0 65

0 43  2 0 



 

 . 

.

.

Ty y s cs ps  

Notes: Using surveyed channel geometry.

Notes: 

Bridge 857. Nenana River at Healy bridge scour 

computations. 
44 Methodology and Estimates of Scour at Selected Bridge Sites in Alaska

Nenana River at Healy

Bridge 857

Healy Road mile 3.2

LIVE-BED CONTRACTION SCOUR

100 Year 500 Year

Computed floods: total discharge (cfs) Q 47200 57800

Hydraulic radius (ft) R 14.05 16.34

Friction slope (ft/ft) S 0.0017 0.0018

Average shear stress at bed (lbs/ft 2

) gRS 1.49 1.84

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

1⁄2 0.88 0.97

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

Ratio V*/w 0.34 0.37

Exponent determined from mode of bed material transport k1 =f(V*/w) 0.59 0.59

Discharge in main channel of approach section (cfs) Q1 31574 36608

Percentage of total discharge 67% 63%

Discharge in main channel of contracted (bridge) section (cfs) Q2 47200 57800

Percentage of total discharge 100% 100%

Width of main channel of approach section (cfs) W1 390 390

Width of main channel of contracted (bridge) section (cfs) W2 345 346

Average depth of main channel of approach section (ft) y1 14.1 16.4

Average depth in contracted (bridge) section (ft) y2 21.4 26.0

CONTRACTION SCOUR (ft) Ycs 7.3 9.6

PIER SCOUR

100 Year 500 Year

Speed of maximum velocity stream tube (ft/s) v1 14.28 16.59

Depth of maximum velocity stream tube (ft) y1 6.0 6.0

Froude number of maximum velocity stream tube (ft/s) Fr=v1/(gy1)

1⁄2 1.03 1.19

Pier shape square nose

Pier shape correction factor K1 1.1 1.1

Angle of attack (deg) AA 15 15

Pier width (ft) a 14.5 14.5

Pier length (ft) L 37 37

Ratio L/a 3 3

Angle of attack correction factor K2=f(AA,L/a) 1.3 1.3

Bed condition (dunes) correction factor K3 1.1 1.1

PIER SCOUR (ft) Yps 33.9 36.2

TOTAL SCOUR

100 Year 500 Year

Contraction scour (ft) Ycs 7.3 9.6

Pier scour (ft) Yps 33.9 36.2

TOTAL SCOUR (ft) Ts 41.2 45.8

y

y

Q

Q

W

W

y yy

K

cs

2

1

2

1

6

7

1

2

2 1

1

 



 



 



 





  = (average scour depth)

y

y

KKK a

y

Fr ps

1

123

1

0 65

0 43  2 0 



 

 . 

.

.

Ty y s cs ps  

Notes: Using surveyed channel geometry.

Notes: Footing scour.

Bridge 857. Nenana River at Healy bridge scour 

computations.