U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5230

Prepared in cooperation with the Missouri Department of Transportation

Two-Dimensional Simulation of Flow and Evaluation of 

Bridge Scour at Structure A-1700 on Interstate 155 over 

the Mississippi River near Caruthersville, Missouri
Cover photograph. Main-channel spans of structure A-1700 on Interstate 155 over the Mississippi River near Caruthersville, Missouri, 

as viewed from the downstream left (southeast) bank looking toward the upstream right (northwest) bank on January 23, 2007.
Two-Dimensional Simulation of Flow 

and Evaluation of Bridge Scour at 

Structure A-1700 on Interstate 155 over 

the Mississippi River near Caruthersville, 

Missouri

By Richard J. Huizinga

Prepared in cooperation with the Missouri Department of Transportation

Scientific Investigations Report 2007–5230

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Huizinga, R.J., 2007, Two-dimensional simulation of flow and evaluation of bridge scour at structure A-1700 on Interstate 155 over the Mississippi River near Caruthersville, Missouri: U.S. Geological Survey Scientific Investigations 

Report 2007–5230, 33 p. 
iii

Contents

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

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

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

Description of Study Area ...................................................................................................................2

Acknowledgements..............................................................................................................................6

Two-Dimensional Simulation of Flow .........................................................................................................6

Model Development .............................................................................................................................6

Calibration of Model to a Known Flood.............................................................................................9

Simulation of 100-Year Flood.............................................................................................................10

Simulation of Project Design Flood..................................................................................................13

Evaluation of Bridge Scour.........................................................................................................................13

Scour Depth Computations in the Two-Dimensional Model........................................................18

Scour Depth Computations Using Two-Dimensional Simulation Results..................................18

Summary........................................................................................................................................................32

References Cited..........................................................................................................................................33

Figures

1. Photograph showing main-channel spans of structure A-1700 on Interstate 

155 over the Mississippi River near Caruthersville, Missouri, as viewed from the

upstream left (northeast) bank facing downstream (southwest) on January 23, 2007.....2

2. Map showing location of the study area on the Mississippi River near

Caruthersville, Missouri...............................................................................................................3

3. Aerial photograph showing study area on the Mississippi River near

Caruthersville, Missouri...............................................................................................................4

4. Graph showing cross section, substructural and superstructural details, and 

key features of structure A-1700 over the Mississippi River near Caruthersville, 

Missouri..........................................................................................................................................5

5. Map showing finite-element mesh used in flow simulations on the Mississippi

River near Caruthersville, Missouri ...........................................................................................7

6. Aerial photograph showing land-surface elevations from the model of the

Mississippi River near Caruthersville, Missouri......................................................................8

7. Map showing land-use coverages used in flow simulations on the Mississippi

River near Caruthersville, Missouri .........................................................................................11

8–11. Aerial photographs showing—

8. Measured, estimated, and simulated water-surface elevations for the

calibration flood of April 4, 1975, on the Mississippi River near Caruthersville,

Missouri...............................................................................................................................12

9. Rated and simulated water-surface elevations for the 100-year flood on the

Mississippi River near Caruthersville, Missouri...........................................................14

10. Rated and simulated water-surface elevations for the project design flood 

on the Mississippi River near Caruthersville, Missouri...............................................15

11. Simulated depths and velocity vectors in the vicinity of structure A-1700 

for the project design flood on the Mississippi River near Caruthersville, 

Missouri...............................................................................................................................16
iv

12. Aerial photograph showing simulated velocity magnitudes for project design flood

and flux lines used for scour parameter determinations on the Mississippi River

near Caruthersville, Missouri ...................................................................................................17

13–16. Graphs showing—

13. Predicted contraction and local pier scour depths under the

Tennessee-approach (left overbank) spans for the project design flood on

the Mississippi River near Caruthersville, Missouri ....................................................27

14. Predicted contraction and local pier scour depths under the main-channel

and Missouri-approach (right overbank) spans for the project design flood 

on the Mississippi River near Caruthersville, Missouri...............................................28

15. Predicted total scour depths under the Tennessee-approach (left overbank)

spans for three floods on the Mississippi River near Caruthersville, Missouri ......29

16. Predicted total scour depths under the main-channel and Missouri-approach

(right overbank) spans for three floods on the Mississippi River near

Caruthersville, Missouri....................................................................................................30

17. Photograph showing abutment and part of the guidebank upstream from the right

(northwest) end of structure A-1700 over the Mississippi River near Caruthersville, 

Missouri, January 23, 2007........................................................................................................32

Tables

1. Material and hydraulic properties of various land-use coverages in the model of

the Mississippi River near Caruthersville, Missouri, resulting from the calibration

flood of April 4, 1975 ...................................................................................................................10

2. Measured and simulated water-surface elevations for the calibration flood of

April 4, 1975, on the Mississippi River near Caruthersville, Missouri ................................13

3. Predicted live-bed contraction scour depths and parameters used to compute

main-channel contraction scour on the Mississippi River near Caruthersville,

Missouri........................................................................................................................................19

4. Predicted clear-water contraction scour depths and parameters used to compute

overbank contraction scour on the Mississippi River near Caruthersville, Missouri.....20

5. Predicted local pier scour depths and parameters used to compute pier scour for

the calibration flood of April 4, 1975, on the Mississippi River near Caruthersville,

Missouri........................................................................................................................................21

6. Predicted local pier scour depths and parameters used to compute pier scour for

the 100-year flood on the Mississippi River near Caruthersville, Missouri ......................23

7. Predicted local pier scour depths and parameters used to compute pier scour for

the project design flood on the Mississippi River near Caruthersville, Missouri ............25

8. Predicted abutment scour depths and parameters used to compute abutment

scour on the Mississippi River near Caruthersville, Missouri ............................................31
v

Conversion Factors and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2

)

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

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

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Kinematic viscosity

square foot per second (ft2

/s) 0.09290 square meter per second (m2/s) 

Unit discharge*

cubic foot per second per foot

[(ft3

/s)/ft]

0.09290 cubic meter per second per meter 

[(m3/s)/m]

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

*Unit discharge: The standard unit for unit discharge is cubic foot per second per foot [(ft3/s)/

ft]. In this report, the mathematically reduced form, square foot per second (ft2/s), is used for 

convenience.

In this report, the words “left” and “right” generally refer to directions that would be reported 

by an observer facing downstream.

Abstract

The evaluation of scour at bridges throughout the State 

of Missouri has been ongoing since 1991, and most of these 

evaluations have used one-dimensional hydraulic analysis and 

application of conventional scour depth prediction equations. 

Occasionally, the complex conditions of a site dictate a more 

thorough assessment of the stream hydraulics beyond a onedimensional model. This was the case for structure A-1700, 

the Interstate 155 bridge crossing the Mississippi River near 

Caruthersville, Missouri. To assess the complex hydraulics at 

this site, a two-dimensional hydrodynamic flow model was 

used to simulate flow conditions on the Mississippi River in 

the vicinity of the Interstate 155 structure A-1700. The model 

was used to simulate flow conditions for three discharges: a 

flood that occurred on April 4, 1975 (the calibration flood), 

which had a discharge of 1,658,000 cubic feet per second; the 

100-year flood, which has a discharge of 1,960,000 cubic feet 

per second; and the project design flood, which has a discharge of 1,974,000 cubic feet per second. The project design 

flood was essentially equivalent to the flood that would cause 

impending overtopping of the mainline levees along the Mississippi River in the vicinity of structure A-1700. Discharge 

and river-stage readings from the flood of April 4, 1975, were 

used to calibrate the flow model. The model was then used to 

simulate the 100-year and project design floods.

Hydraulic flow parameters obtained from the three flow 

simulations were applied to scour depth prediction equations 

to determine contraction, local pier, and abutment scour depths 

at structure A-1700. Contraction scour and local pier scour 

depths computed for the project design discharge generally were the greatest, whereas the depths computed for the 

calibration flood were the least. The maximum predicted total 

scour depth (contraction and local pier scour) for the calibration flood was 66.1 feet; for the 100-year flood, the maximum 

predicted total scour depth was 74.6 feet; for the project 

design flood, the maximum predicted total scour depth was 

93.0 feet. If scour protection did not exist, bent 14 and piers 15 

through 21 would be substantially exposed or undermined by 

the predicted total scour depths in all of the flood simulations. 

However, piers 18 through 21 have a riprap blanket around the 

base of each, and the riprap blanket observed on the right bank 

around bent 14 is thought to extend around the base of pier 

15, which would limit the amount of scour that would occur at 

these piers. Furthermore, the footings and caissons that are not 

exposed by computed contraction scour may arrest local pier 

scour, which will limit local pier scour at several bents and 

piers. Nevertheless, main-channel piers 16 and 17 and all of 

the bents on the left (as viewed facing downstream) overbank 

are moderately to substantially exposed by the predicted scour 

depths from the three flood simulations, and there is no known 

scour protection at these piers or bents. Abutment scour depths 

were computed for structure A-1700, but abutment scour 

is expected to be mitigated by the presence of guidebanks 

upstream from the bridge abutments, as well as riprap revetment on the abutment and guidebank faces.

Introduction

In 1988, the Federal Highway Administration (FHWA) 

recommended that “every bridge over a scourable stream, 

whether existing or under design, should be evaluated as to its 

vulnerability to floods in order to determine the prudent measures to be taken for its protection” (U.S. Federal Highway 

Administration, 1988). In 1991, the U.S. Geological Survey 

(USGS) and the Missouri Department of Transportation 

(MoDOT) began a cooperative study to accomplish two goals: 

(1) to develop and use a suitable screening process to identify 

“scour-susceptible” bridges, and (2) for bridges identified 

as “scour-susceptible,” perform a detailed hydraulic evaluation and estimate values of scour using accepted hydraulic 

techniques. The term “scour-susceptible” describes a bridge 

that is deemed potentially unstable because abutment or pier 

foundations have the potential to be undermined by erosion of 

the channel bed or banks (U.S. Federal Highway Administration, 1988). Nearly 3,100 bridges throughout Missouri were 

screened for scour-susceptibility, and nearly 400 bridges have 

undergone a detailed hydraulic evaluation and estimation of 

scour depths (Huizinga and Rydlund, 2004).

Two-Dimensional Simulation of Flow and Evaluation of 

Bridge Scour at Structure A-1700 on Interstate 155 over 

the Mississippi River near Caruthersville, Missouri

By Richard J. Huizinga
2 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

The detailed hydraulic evaluations have been performed 

using techniques outlined in Hydraulic Engineering Circular No. 18 (Richardson and Davis, 2001), which generally 

entails the application of predictive scour-depth computations 

using parameters from a one-dimensional hydraulic analysis. 

Occasionally, however, the simplifying assumptions that must 

be made to apply a one-dimensional hydraulic analysis to 

a two-dimensional flow scenario are deemed unreasonable. 

This is the case at structure A-1700 on Interstate 155 over the 

Mississippi River near Caruthersville, Missouri (hereinafter 

referred to as “structure A-1700”; fig. 1). The Mississippi 

River meanders in the immediate vicinity of structure A-1700, 

with associated bends in the mainline levees on the adjacent 

flood plains. Rock dikes built and maintained by the U.S. 

Army Corps of Engineers (USACE) in the bend upstream 

from structure A-1700 further contribute to the two- and threedimensional nature of the flow around structure A-1700. This 

unique configuration is beyond the reasonable bounds for a 

one-dimensional hydraulic analysis, indicating the need for a 

two-dimensional hydraulic analysis of the site.

Purpose and Scope

This report describes the two-dimensional simulation 

of flow and evaluation of bridge scour at structure A-1700. 

The report contains the description of the development of and 

results from a two-dimensional hydrodynamic flow model 

that represents part of the Mississippi River at Interstate 155 

near Caruthersville, Mo., using the depth-averaged flow 

model Flo2DH [part of the Federal Highway Administration’s 

Finite Element Surface-Water Modeling System (FESWMS) 

designed for hydraulic structures and flood plains (Froehlich, 

2002)]. The model was calibrated to the flood of April 4, 

1975, and used to simulate the 100-year recurrence flood as 

well as the project design flood (PDF), which is the flood that 

causes impendent overtopping of the USACE mainline levees 

at some point in the stretch of river between Hickman, Ky., 

and Memphis, Tenn. (Barry Bruchman, U.S. Army Corps of 

Engineers, oral commun., 2007). The model was used to compute the hydraulic parameters needed to determine the contraction scour, local pier scour, and abutment scour that might 

occur at structure A-1700 for the three flood discharges.

Description of Study Area

The study area is located along the eastern edge of 

Pemiscot County, and covers part of the Mississippi River and 

associated flood plains between the USACE mainline levees 

upstream and downstream from Interstate 155 near Caruthersville (figs. 2 and 3). The study area begins at river mile 

(mi) 832.5, near a local constriction in the mainline levees 

at Cottonwood Point, Mo., and ends at river mi 846.8, near 

the upstream edge of Caruthersville. In addition to Pemiscot 

County in Missouri, the study area also covers parts of Lake 

and Dyer Counties in Tennessee, and includes such features 

as the Towhead of Island No. 18, Blaker Towhead, and the 

Linwood Bend (U.S. Army Corps of Engineers, 2007a; figs. 2 

and 3). Numerous rock dikes and other revetments are present 

along the banks of the river in the study area.

In the vicinity of the study area, the dominant physiographic feature is the Mississippi Alluvial Plain, which is 

approximately 70 mi wide measured in a west-northwest 

direction from the eastern bluffs at Lenox, Tenn., (about 7 mi 

west of Dyersburg, Tenn.) to the western bluffs at Harviell, 

Mo., (about 7.5 mi southwest of Poplar Bluff, Mo.). To control 

flooding over this vast area of minimal relief, the USACE 

built and maintains mainline levees along both sides of the 

Mississippi River. For the downstream part of the study area, 

these mainline levees are about 2.8 to 3.5 mi apart, but flare 

out to nearly 7 mi apart in the upstream part of the study area 

because of a large meander bend in the river (fig. 2).

Interstate 155 crosses the Mississippi River from northwest to southwest at about river mi 839.0, at the approximate 

midpoint of the study area. Structure A-1700 is a 7,100-foot 

(ft) long bridge, with the main spans consisting of a 1,440-ft 

cantilevered through-truss span, eight 235-ft steel I-beam 

spans, and two 132-ft steel I-beam spans with concrete piers 

founded on caissons and piles (fig. 4). The Tennessee-apFigure 1. Main-channel spans of structure A-1700 on Interstate 155 over the Mississippi River near Caruthersville, 

Missouri, as viewed from the upstream left (northeast) bank facing downstream (southwest) on January 23, 2007.
Introduction 3

MISSISSIPPI

RIVER

MISSISSIPPI RIVER

White Lake

Everett Lake

Obion River

Rock

Slough

Running

Half Moon Bayou

Reelfoot

Blue Bank Bayou

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832

835

833

834

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837

838

839

840

841

842

843

844

845

846

848

849

850

851

852 853

854

855 856

857

858

859

847

831

830

829

155

155

55

84

84

O

Y

D

164

181

181

103

181

79

20

LAKE COUNTY

DYER COUNTY

PEMISCOT COUNTY

MISSOURI

TENNESSEE

Blaker

Towhead

Towhead

Structure

A-1700

Linwood

Bend

of

Island

No. 18

Cottonwood Point

Caruthersville

Caruthersville gage

EXPLANATION

Boundary of study area

Primary highway

Minor roadway

Mainline levee

Rock dike (within study area)

River-mile marker—Number is distance

 upstream from Gulf of Mexico

U.S. Army Corps of Engineers

 river stage gaging station

>841

Cottonwood Point gage

MISSOURI

TENNESSEE

LOCATION MAP

Map area

Dyersburg

KENTUCKY

Memphis

Hickman Poplar Bluff

89°40' 89°35'

36°15'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000, 1996

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American

 Datum of 1983 (NAD 83)

Figure 2. Location of the study area on the Mississippi River near Caruthersville, Missouri.
4 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

>

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835

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837

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839

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846

847

155

155

20

103

164

D

O

84

84

Y

181

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

Primary highways

Study area boundary

EXPLANATION

River-mile marker—Number is distance upstream from

 Gulf of Mexico

U.S. Army Corps of Engineers river stage gaging station

Cottonwood

Point gage

Structure

A-1700

Caruthersville

gage Caruthersville

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 3. Study area on the Mississippi River near Caruthersville, Missouri.
Introduction 5

Bent 59

Bent 60 (Abutment)

Bent 58

Bent 57

Bent 56

Bent 55

Bent 54

Bent 53

Bent 52

Bent 51

Bent 50

Bent 49

Bent 48

Bent 47

Bent 46

Bent 45

Bent 44

Bent 43

Bent 42

Bent 41

Bent 40

Bent 39

Bent 38

Bent 37

Bent 36

Bent 35

Bent 34

Bent 33

Bent 32

Bent 31

Bent 30

Bent 29

Bent 28

Bent 27

Bent 25

Bent 24

Bent 23

Bent 22

Pier 21

Bent 26

Bent 9

Bent 8

Bent 7

Bent 6

Bent 5

Bent 4

Bent 3

Bent 2

Bent 1

(Abutment)

Bent 10

Bent 11

Pier 19

Pier 18

Pier 17

Pier 16

Pier 15

Bent 14

Bent 13

Bent 12

Pier 21

Pier 20

3,600 3,800 4,000 5,400 5,600 5,800 6,000 4,200 4,400 4,600 4,800 5,000 5,200 6,400 6,600 6,200 6,800 7,000 7,200

DISTANCE FROM FILL FACE OF LEFT (SOUTHEASTERN) ABUTMENT, IN FEET

500400

300200

100

ELEVATION, IN FEET ABOVE NGVD 29 B. Main-channel spans and Missouri-approach spans (right overbank) 0 200 400 600 800 1,000 2,400 2,600 2,800 3,000 1,200 1,400 1,600 1,800 2,000 2,200 3,400 3,600 3,200

500400

300200

100

A. Tennessee-approach spans (left overbank) LOCATION MAP

A B

Current (2004) land surfaceLand surface 1973Riprap protection

Current (2004) land surfaceLand surface 1973Riprap protection

Footing

Piles

Column

Pedestal

Caisson

Ice

breaker

Column

Footing

Piles

CapColumn

Piles

SealcoursePiles

Footing Footing

Column

Cap

PedestalCaisson

Ice

Column

breaker

Ice

Column

breaker

Caisson

Riprap scour protection

blanket

Ice

Column

breaker Left bank covered with articulating

concrete mattress and riprap

on bridge plans

Bents 26 through 59 consist of three cylindrical columns,

ranging from 3.5 to 5.5 feet in diameter supporting 70-foot

and 90-foot concrete I-beam spans

Bents 2 through 14 consist of three cylindrical columns,

ranging from 4.5 to 6.0 feet in diameter supporting 70-foot

and 90-foot concrete I-beam spans Piers 15 through 18 consist of two cylindrical columns

6.5 feet in diameter on top of 7.5-foot wide ice breakers,

supporting 132-foot and 235-foot steel I-beam spans

Piers 19 through 21 consist of two cylindrical columns ranging

from 11 to 16 feet in diameter on top of ice breakers ranging

from 14 to 21 feet wide, supporting 1,440-foot truss span

Bents 22 through 25 consist of two cylindrical

columns 6.5 feet in diameter supporting 132-foot

and 235-foot steel I-beam spans

Figure 4. Cross section, substructural and superstructural details, and key features of structure A-1700 over the Mississippi River near Caruthersville, Missouri.
6 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

proach spans on the eastern side consist of twenty-nine 70-ft 

and five 90-ft concrete I-beam spans on concrete bents with 

pile foundations. The Missouri-approach spans on the western side consist of seven 70-ft long and six 90-ft long concrete I-beam spans on concrete bents with pile foundations. 

Both abutment faces are covered with large cobble riprap, 

and there are riprap-covered guidebanks upstream from both 

abutments. Elevated, level road embankments extend to the 

mainline levees from both of the approach spans of structure 

A-1700. Both road embankments curve gently to the left as 

they approach the mainline levees from the bridge (figs. 2 

and 3), and descend to an elevation about 3 ft above the surrounding flood plain outside of the confines of the mainline 

levees.

In the study area, the flood plain predominantly consists 

of agricultural land used for growing cotton and corn, with 

areas of timber and brush (fig. 3). A thick riparian corridor is 

present along the Mississippi River, and wetland areas with 

surrounding timber border the mainline levees and various 

minor levees throughout the study area. The Towhead of 

Island No. 18 and Blaker Towhead are covered with timber 

and brush.

Acknowledgements

The author appreciates the assistance of two individuals 

with the U.S. Army Corps of Engineers, Memphis District. 

Barry Bruchman provided information about various historic 

floods that have occurred on the Mississippi River, along 

with information from the stage gage at Caruthersville, Missouri. Derrick Smith provided detailed elevation data for the 

flood plain in the vicinity of Interstate 155, recent hydrographic surveys of the channel, and information about the 

rock dikes built in the channel bend upstream from Interstate 

155.

Two-Dimensional Simulation of Flow

The FESWMS Flo2DH model simulates flow in two 

dimensions in the horizontal plane. It uses a finite-element 

mesh and the Galerkin finite-element method of solving three 

partial-differential equations representing conservation of 

mass and momentum (Froehlich, 2002). This two-dimensional 

model can simulate longitudinal and lateral variations in 

water-surface elevations and velocities and can accommodate 

geometric features such as highway embankments, bridge 

structures, channel bends, berms, buildings, and other flow 

obstructions. A graphic user interface called the Surface-Water 

Modeling System (SMS; Environmental Modeling Research 

Laboratory, 1999) was used to construct the two-dimensional 

finite-element mesh, facilitate assignment of roughness coefficients and other hydraulic and material parameters to the mesh 

elements, execute the model, and evaluate the model output 

numerically and graphically.

Model Development

The extent of the model mesh was from a point of 

constriction in the mainline levees near Cottonwood Point, at 

river mi 832.5 to the upstream (north) edge of Caruthersville, 

at river mi 846.8 (figs. 2 and 3). The model mesh extended 

from Tennessee Highway 181 along the mainline levee on the 

left (east) flood plain, to the mainline levee on the right (west) 

flood plain (figs. 2 and 3).

Ground-elevation information for the study area was 

provided by the USACE (Derrick Smith, U.S. Army Corps of 

Engineers, written commun., 2007) as a combination of Light 

Detection and Ranging (LiDAR) data for the flood plains and 

bathymetric data from a recent hydrographic survey for the 

channel. These data formed the base topographic data for the 

model. 

Mesh elements were designed with consideration to computational speed and the level of detail of the hydraulic information required from the simulation results (fig. 5). The area 

around structure A-1700 and the approach road embankments 

were of critical interest, so smaller elements were used in this 

part of the study area, whereas larger elements were used to 

represent the channel and flood plains toward the upstream 

and downstream ends of the study area (fig. 5). Secondary 

levees (such as the Boothspoint and Tennemo levees; fig 6) 

and older levees within the confines of the mainline levees 

were included with a moderate amount of detail to represent 

these local features more accurately (fig. 6). Elevation data 

were available for most of the dikes along the right (west) 

bank in the Linwood Bend upstream from structure A-1700 

(Derrick Smith, written commun., 2007), and these dikes were 

included with a moderate amount of detail to improve the simulation of flow near these features (fig. 6). Other dikes were 

present upstream and downstream from the Linwood Bend 

dikes, but elevation data for several of these dikes were not 

readily available (Derrick Smith, written commun., 2007), or 

the elevation of the channel bed near the dike essentially was 

the same as the elevation of the dike, so that the dike would 

not substantially affect flow. Specific elevation details from 

these dikes generally were not included in the mesh; therefore, 

these dikes do not appear in figure 6.

Piers and bents for structure A-1700 were incorporated 

into the model mesh using the pier module in Flo2DH. Position, orientation, and dimensions of each pier and bent were 

obtained from bridge plans (Missouri Department of Transportation, 1974) to accurately position and size the piers and 

bents. All piers and bents were coded based on their cross section at the interface with the current (2004) land surface on the 

bridge plans. Typically, piers were coded as solid, round-nosed 

columns with a width and length equal to the overall width and 

length from the bridge plans. To be consistent with guidelines 

for the computation of pier scour in Richardson and Davis 

(2001), bents with multiple columns spaced less than 5 times 

the column diameter apart were analyzed as a round-nosed 

column with a width equal to a single column and a length 

equal to the number of columns multiplied by the width of a 
Two-Dimensional Simulation of Flow 7

White Lake

Everett Lake

MISSISSIPPI RIVER

Half Moon Bayou

Blue Bank Bayou

Obion

River

155

155

20

103

164

D

O

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Study area boundary Primary highways Minor roads

EXPLANATION

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000, 1996

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American

 Datum of 1983 (NAD 83)

Figure 5. Finite-element mesh used in flow simulations on the Mississippi River near Caruthersville, 

Missouri.
8 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

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Guidebank I-155

approach

embankment

I-155

approach

embankment

Rock dikes

Linwood

Bend

Guidebank

levee

levee

Tennemo

Boothspoint

Study area boundary

Primary highways

EXPLANATION

Land-surface elevation, in

 feet above NGVD 29

290

270

250

230

210

190

170

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 6. Land-surface elevations from the model of the Mississippi River near Caruthersville, Missouri.
Two-Dimensional Simulation of Flow 9

single column, whereas bents with multiple columns spaced 

more than 5 times the column diameter apart were coded as a 

single cylindrical column with a width and length equal to the 

diameter of a single column. 

The finite-element mesh consisted of 25,550 elements 

that ranged in size from 522 square feet (ft2) to 13.86 acres. 

Each element had a node at each corner and at the midpoint of 

each side, which created a total of 58,833 nodes. 

Calibration of Model to a Known Flood

The model was calibrated to the flood that occurred on 

the Mississippi River in April 1975. Based on information 

provided by the USACE (Barry Bruchman, oral commun., 

2007; U.S. Army Corps of Engineers, 2007b), the gage heights 

recorded on April 4, 1975, at the USACE stage-gaging stations at Caruthersville (river mi 846.4; hereinafter referred to 

as “the Caruthersville gage”) and Cottonwood Point (river mi 

832.7; hereinafter referred to as “the Cottonwood Point gage”) 

were 277.89 ft and 270.08 ft, and the discharge computed at 

Hickman, Ky. (the nearest discharge station upstream from 

Caruthersville, at river mi 921.4), was 1,658,000 cubic feet 

per second (ft3

/s). No major inflow tributaries to the Mississippi River exist between Hickman and Cottonwood Point, 

and no substantial flood storage or attenuation occurs on this 

reach according to the USACE; therefore, the peak discharge 

measured at Hickman can be associated with the peak stages 

measured at Caruthersville and Cottonwood Point (Barry 

Bruchman, oral commun., 2007). The water-surface elevation at structure A-1700 was estimated as 273.67 ft using the 

average slope of the water surface between the Caruthersville 

and Cottonwood Point gages for the flood, which was approximately 0.57 feet per mile (ft/mi).

The simulation of a particular flow scenario with Flo2DH 

requires an iterative process called spindown (Huizinga, 

2007; Huizinga and Rydlund, 2001). In a subcritical flow 

regime (deep, slow flow typical of non-alpine streams and 

rivers), spindown involves initializing the model with the 

desired discharge as the upstream boundary condition and a 

downstream water-surface elevation that is higher than the 

highest land-surface elevation in the mesh. This ensures that 

all nodes in the model are “wet” (having a positive depth of 

flow) and produces a flat water-surface elevation across the 

model grid, which promotes numerical stability for the initial 

model computations. The model is run with these conditions 

for a sufficient number of iterations to cause the water-surface 

elevation changes between iterations to be minimized within 

a preset limit. Once the limit is reached, the model is said to 

have “converged.” The downstream water-surface elevation is 

then decreased by some finite amount, the model is restarted 

using the results of the previous run—called a hotstart—as 

the starting point for the new run, and the model is run until 

convergence occurs. This process is repeated until the desired 

downstream water-surface elevation is reached, as dictated by 

high-water marks, flood profiles, or other known site parameters. During the spindown process, if the simulated water-surface elevation at a particular node is less than the land-surface 

elevation assigned to the node, then the node is said to “go 

dry.” If one or more of the nodes for a particular element go 

dry, then the element goes dry, and the element is not included 

in the computations during that iteration. As the simulation 

proceeds through iterations, an element can oscillate between 

wet and dry, which can lead to solution instability and a loss of 

convergence. To limit this instability, the user sets a tolerance 

on the depth of flow over a node (the storativity depth, table 

1); however, if an element goes dry and stays dry for several 

iterations, it can and should be manually disabled to prevent 

model instability. Once the spindown process is complete, 

the model calibration can be refined by adjusting other model 

parameters such as Manning’s roughness coefficient and kinematic eddy viscosity.

For the current model, the upstream boundary was set 

to the flood discharge of 1,658,000 ft3

/s and the downstream 

boundary initially was set to 306.0 ft. The model then was 

spun down to a downstream boundary condition of 270.0 ft, 

which was the estimated water-surface elevation based on the 

water-surface slope of 0.57 ft/mi between the Caruthersville 

and the Cottonwood Point gages. 

Material and hydraulic properties were assigned to the 

model based on land use from aerial photography (fig. 7), and 

initial Manning’s roughness coefficients were assigned based 

on published guidance (Chow, 1959; Barnes, 1967; Arcement 

and Schneider, 1989) and previously calibrated models of 

similar river reaches (Huizinga and Rydlund, 2001). A depthdependent Manning’s roughness coefficient (n-value) method 

was used, wherein the “lower depth” n-value is applied when 

the water depth over the nodes around an element is less than 

the lower depth, and the “upper depth” n-value is applied 

when the water depth is greater than the upper depth; when the 

water depth is between the lower and upper depths, the n-value 

is interpolated linearly from the upper and lower n-values 

(Froehlich, 2002). Depth-dependent n-values were used to 

account for changes in the roughness with increased depth of 

flow; generally, the roughness decreases with increased depth 

because the effect of the physical features causing the roughness decreases as the depth of flow increases (for example, 

grass and crops that lie over in high flows). In addition, all of 

the coverages initially were assigned a large value of kinematic eddy viscosity that would promote model stability [75 

square feet per second (ft2

/s)] during the spindown process. 

After spinning the model down to the desired boundary conditions, the eddy viscosity was adjusted to a more appropriate 

value (the “Mississippi River channel” and “Riprap banks and 

dikes” coverages were adjusted to 30 ft2/s and all other coverages were adjusted to 10 ft2

/s) consistent with guidelines in 

Froehlich (2002).

To refine the model calibration, the material properties 

were adjusted to the values in table 1 to cause the watersurface elevations in the model to match the observed watersurface elevations at Caruthersville and Cottonwood Point 

from the April 1975 flood. Matching the observed elevations 
10 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

at the two gages was the priority in the calibration; however, 

an extremely close match to the estimated elevation at the 

bridge also was obtained. Measured and simulated watersurface elevations for the flood are shown in figure 8 and 

table 2.

Simulated results indicate that the maximum velocity in 

the main channel was 10.7 feet per second (ft/s) and occurred 

on the mid-left side of the main channel immediately downstream from structure A-1700. The maximum depth was 95.1 

ft and occurred about 3 mi downstream from structure A-1700 

along the right bank. The maximum depth near structure 

A-1700 was 92.5 ft at the base of the left bank immediately 

downstream from structure A-1700. The mean water-surface 

elevation at structure A-1700 was 273.70 ft.

Simulation of 100-Year Flood

The 100-year flood is the discharge that has a 1 in 100 

chance of occurring during any given year. It is used as a standard value in flood-plain assessment and bridge design and 

is a recommended event for assessing scour potential (Richardson and Davis, 2001). Therefore, the 100-year flood was 

simulated to provide hydraulic parameters for the computation 

of scour at structure A-1700.

At the Caruthersville gage, the USACE has determined 

the stage for the 100-year flood to be 281.80 ft plus or minus 

(+/-) 0.05 ft, with a corresponding discharge of 1,960,000 

ft3

/s; stage and discharge for the 100-year flood at the Cottonwood Point gage have not been determined (Barry Bruchman, 

oral commun., 2007). Consequently, the upstream boundary 

condition (discharge) for the 100-year flood simulation was 

known, but the downstream boundary condition (water-surface 

elevation) was not. The simulation of the 100-year flood used 

the material and hydraulic properties determined in the calibration simulation and a known upstream boundary discharge of 

1,960,000 ft3/s; however, a downstream boundary condition 

was assumed and adjusted until the simulated water-surface 

elevation at the Caruthersville gage matched the known 

water-surface elevation of 281.80 ft (+/- 0.05 ft). The downstream boundary for the 100-year flood simulation initially 

was spun down to 273.9 ft, using the water-surface slope from 

the calibration simulation (0.57 ft/mi); however, the simulated 

water-surface elevation at the Caruthersville gage for this 

downstream condition was 282.00 ft. Lowering the downstream 

water-surface elevation to 273.7 ft resulted in a simulated 

water-surface elevation at the gage of 281.87 ft, and lowering 

the downstream water-surface elevation to 273.6 ft resulted in 

a simulated water-surface elevation at the gage of 281.80 ft. 

The latter downstream condition corresponds to a water-surface 

slope of 0.59 ft/mi, which is slightly greater than the calibration 

simulation slope of 0.57 ft/mi, but compares favorably with it. 

The simulated water-surface elevations for the entire study area 

for the 100-year flood are shown in figure 9.

Simulated results indicate that the maximum velocity in 

the main channel was 11.7 ft/s and occurred on the mid-left 

side of the main channel immediately downstream from structure A-1700. The maximum depth was 98.4 ft and occurred 

approximately 3 mi downstream from structure A-1700 along 

the right bank. The maximum depth near structure A-1700 was 

96.1 ft at the base of the left bank immediately downstream 

from structure A-1700. The average water-surface elevation at 

structure A-1700 was 277.42 ft.

Table 1. Material and hydraulic properties of various land-use coverages in the model of the Mississippi River near 

Caruthersville, Missouri, resulting from the calibration flood of April 4, 1975.

[ft, feet]

Lower depth Upper depth Storativity 

depth

(ft) Land-use coverage

Manning’s 

n

Depth

(ft)

Manning’s 

n

Depth

(ft)

Channel and bank

Mississippi River channel 0.035 15 0.028 30 1.0

Riprap banks and dikes .100 5 .043 30 2.0

Thick timber and thick brush .180 10 .150 30 1.5

Timber and brush .150 10 .120 25 1.5

Flood plain

Row crops (cotton and corn) 0.090 3 0.060 20 1.5

Grassy area with interspersed trees .050 1 .040 3 1.0

Grassy embankment .040 1 .035 3 2.0

Pavement and gravel .020 1 .015 2 .5

Thick brush (small trees and scrub) .150 5 .100 15 1.5

Wetlands .065 10 .040 25 3.0
Two-Dimensional Simulation of Flow 11

White Lake

Everett Lake

MISSISSIPPI RIVER

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Blue Bank Bayou

Obion

River

Half Moon Bayou

Study area boundary Primary highways Minor roads

EXPLANATION

Area of no flow

Mississippi River channel

Riprap banks and dikes

Thick timber and thick brush

Timber and brush

Thick brush (small trees and scrub)

Row crops (cotton and corn)

Grassy area with interspersed trees

Grassy embankment

Pavement and gravel

Wetlands

LAND USE

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000, 1996

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American

 Datum of 1983 (NAD 83)

Figure 7. Land-use coverages used in flow simulations on the Mississippi River near Caruthersville, 

Missouri.
12 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

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Study area boundary

Primary highways

Observation point

Measured, 277.89 ft

Simulated, 277.88 ft

Measured, 270.08 ft

Simulated, 270.08 ft

270.0

270.5

271.0

271.5

272.0

276.0

276.5

277.0

277.5

278.0

272.5

273.0

273.5

274.0

Estimated, 273.67 ft

Simulated, 273.70 ft

EXPLANATION

Simulated water-surface elevation,

 in feet above NGVD 29

278.5

277.5

276.5

275.5

274.5

273.5

272.5

271.5

270.5

269.5

274.5

275.0

275.5

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 8. Measured, estimated, and simulated water-surface elevations for the calibration flood of April 4, 

1975, on the Mississippi River near Caruthersville, Missouri.
Evaluation of Bridge Scour 13

Simulation of Project Design Flood

The project design flood (PDF) is a generic term used 

by the USACE to designate the maximum flood that will be 

safely contained by the mainline levees in a particular area 

(Barry Bruchman, oral commun., 2007). The impendent levee 

overtopping discharge is a situation where maximum scour at 

a bridge possibly can occur because all the flow is contained 

within the levees and forced through the bridge opening. If 

the levees are overtopped, the flow can expand across the vast 

flood plains beyond the mainline levees, which allows a part 

of the total flow to bypass the bridge and causes the water-surface elevation and velocities at the bridge to decrease, reducing the potential for scour at the bridge. Another situation for 

the possibility of maximum scour exists when approach road 

embankments are about to be overtopped because all of the 

flow on the adjacent flood plain is forced through the bridge 

opening instead of being able to flow over the road embankment (Richardson and Davis, 2001). At structure A-1700, the 

impendent road overtopping discharge would approximately 

equal the PDF because the road embankment elevations are 

similar to the mainline levee elevations near structure A-1700; 

therefore, the PDF was simulated to provide hydraulic parameters for a possible worst-case scenario for scour at structure 

A-1700.

As with the 100-year flood, the USACE has determined 

the stage and discharge for the PDF at the Caruthersville gage, 

but not at the Cottonwood Point gage; therefore, a similar 

scheme was employed for the simulation of the PDF as was 

used for the 100-year flood. At the Caruthersville gage, the 

USACE has determined the stage for the PDF to be 283.80 ft 

(+/- 0.05 ft), with a corresponding discharge of 1,974,000 ft3

/s 

(Barry Bruchman, oral commun., 2007). The simulation of the 

PDF used the material and hydraulic properties determined 

in the calibration simulation and a known upstream boundary 

discharge of 1,974,000 ft3

/s; however, a downstream boundary 

condition again was assumed and adjusted until the simulated 

water-surface elevation at the Caruthersville gage matched the 

known water-surface elevation of 283.80 ft (+/- 0.05 ft). The 

downstream boundary for the PDF simulation initially was 

spun down to 275.9 ft, using the water-surface slope from the 

calibration simulation (0.57 ft/mi); however, the simulated 

water-surface elevation at the Caruthersville gage for this 

downstream condition was 283.41 ft. Raising the downstream 

water-surface elevation to 276.8 ft resulted in a simulated 

water-surface elevation at the gage of 283.74 ft, and raising 

the downstream water-surface elevation to 276.9 ft resulted in 

a simulated water-surface elevation near the gage of 283.82 

ft. This latter downstream condition corresponds to a surfacewater slope of 0.50 ft/mi, which is somewhat lower than the 

calibration simulation slope of 0.57 ft/mi. The change in slope 

likely is the result of decreasing flow resistance with increasing depth, particularly on the flood plain. The simulated 

water-surface elevations for the entire study area for the PDF 

are shown in figure 10.

Simulated results indicate that the mean water-surface 

elevation at structure A-1700 was 279.98 ft (fig. 10) and the 

maximum depth was 101.1 ft about 3 mi downstream from 

structure A-1700 along the right bank. Simulated depths and 

velocities from the simulation of the PDF in the vicinity of 

structure A-1700 are shown in figures 11 and 12. The maximum depth near structure A-1700 was 98.8 ft at the base of 

the left bank immediately downstream from structure A-1700 

(fig. 11). The velocity vectors (velocity magnitudes and direction computed at various points) indicate the direction of flow 

around the left and right abutments and guidebanks and also 

show flow at an angle across the flood plain near the bridge 

(fig. 11). Velocity magnitudes reach a maximum of 11.2 ft/s 

immediately downstream from structure A-1700 on the left 

side of the main channel (fig. 12). Velocity magnitudes around 

the left guidebank are similar to the main channel upstream 

from the bridge (fig. 12). Similar results were observed for the 

calibration flood and 100-year flood simulations.

Evaluation of Bridge Scour

Scour is the removal of the channel bed and bank material 

by flowing water and is the leading cause of bridge failures in 

the United States (Richardson and Davis, 2001). Total scour is 

divided into three primary components: general scour, which 

refers to long-term geomorphicological processes that cause 

degradation (lowering), aggradation (filling), or lateral shifting 

Table 2. Measured and simulated water-surface elevations for the calibration flood of April 4, 1975, on the Mississippi River near 

Caruthersville, Missouri.

[ft, feet]

Water-surface elevation

Location

Measured 

(ft)

Simulated 

(ft)

Simulated minus measured

(ft)

Gage at Caruthersville, Missouri (near upstream boundary of model) 277.89 277.88 -0.01

Interstate 155 bridge over the Mississippi River (structure A-1700) a

273.67 273.70 .03

Gage at Cottonwood Point, Missouri (near downstream boundary of model) 270.08 270.08 0

a

Water-surface elevation estimated using the average slope of the water surface between the gages at the peak of the flood.
14 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

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Observation point

Rated, 281.80 ft

Simulated, 281.80 ft

282.0

281.5

281.0

280.5

280.0

279.5

277.0

276.5

276.0

275.5

275.5

273.5

275.0

274.5

274.0

279.0

278.5

278.0

277.5

EXPLANATION

Simulated water-surface elevation,

 in feet above NGVD 29

282.5

281.5

280.5

279.5

278.5

277.5

276.5

275.5

274.5

273.5

272.5

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 9. Rated and simulated water-surface elevations for the 100-year flood on the Mississippi River 

near Caruthersville, Missouri.
Evaluation of Bridge Scour 15

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Study area boundary

Primary highways

Observation point

Rated, 283.80 ft

Simulated, 283.82 ft

284.0

281.5

281.5

279.5

279.0 279.0

278.0

277.5

279.0

278.5

278.5 278.5

277.0

283.0

283.5

282.5

282.0

281.0

280.0

280.5

EXPLANATION

Simulated water-surface elevation,

 in feet above NGVD 29

284.5

283.5

282.5

281.5

280.5

279.5

278.5

277.5

276.5

LAKE COUNTY

DYER COUNTY

MISSOURI

TENNESSEE

PEMISCOT COUNTY

89°40' 89°35'

36°10'

36°05'

0 1 2 MILES

0 1 2 3 KILOMETERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 10. Rated and simulated water-surface elevations for the project design flood on the Mississippi 

River near Caruthersville, Missouri.
16 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

Structure

A-1700

Grain bins

(disabled elements)

EXPLANATION

Simulated depth, in feet

100

90

80

70

60

50

40

30

20

10

0

Simulated velocity, in

 feet per second

12

9

6

3

0

89°37'30" 89°37' 89°36'30" 89°36'

36°07'

36°06'30"

36°06'

0 1,000 2,000 FEET

0 250 500 METERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 11. Simulated depths and velocity vectors in the vicinity of structure A-1700 for the project design flood on the 

Mississippi River near Caruthersville, Missouri.
Evaluation of Bridge Scour 17

FLUX LINES Study area boundary

Left overbank

Bridge main channel

Right overbank

Approach main channel

Left embankment blocked

Right embankment blocked

EXPLANATION

Simulated velocity magnitude,

 in feet per second

12

10

8

6

4

2

0

Grain bins

(disabled elements)

89°37' 89°36' 89°35'

36°08'

36°07'

36°06'

0 1,000 2,000 FEET

0 250 500 METERS

Base from Center for Agricultural, Resource and Environmental Systems (CARES), 2004

Universal Transverse Mercator projection, Zone 16

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83)

Figure 12. Simulated velocity magnitudes for project design flood and flux lines used for scour parameter 

determinations on the Mississippi River near Caruthersville, Missouri.
18 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

of the natural channel; contraction scour, which refers to the 

erosion of material that occurs when the cross-sectional flow 

area of the stream is decreased or contracted; and local scour, 

which refers to the localized erosion of material caused by 

flow vortex action that forms near bridge piers and abutments 

(Richardson and Davis, 2001). Although scour processes continually are at work, the processes are accelerated during highflow conditions, and the potential for scour-related concerns at 

a bridge tend to increase during such floods.

Using techniques outlined in Hydraulic Engineering Circular No. 18 (HEC-18), entitled “Evaluating Scour at Bridges” 

(Richardson and Davis, 2001), the various components of 

scour can be estimated from hydraulic parameters determined 

from numerical models and bridge parameters obtained from 

bridge plans and surveys done of the site. Long-term degradation or aggradation can be determined from a comparison of 

the present channel cross section at the bridge with the channel cross section at the time of bridge construction. General 

contraction scour depths can be estimated using the ratio of 

the discharge in the approach channel to the discharge in the 

bridge opening and the ratio of the width of the approach 

channel to the width of the bridge opening. Local pier scour 

depths can be estimated at each pier or bent using flow velocity, flow depth, pier width, pier length, and flow approach 

angle. Abutment scour depths can be estimated for the road 

embankment on each side of the bridge using the discharge 

and flow area on the flood plain that is blocked by each road 

embankment.

Scour Depth Computations in the TwoDimensional Model

The Flo2DH model is able to compute general contraction scour at each node, using a critical bed shear stress 

(τ0, the stress that must be overcome to move a soil particle by the flow) and various other parameters computed 

by the model during the simulation. Chow (1959) defines 

τ0

 as “permissible tractive force” or “permissible shear 

force” and provides several tables for estimating τ0

 based 

on material type, particle size, and cohesion. Furthermore, 

Froehlich (2002) provides guidance for estimating τ0 based 

on soil cover. However, the critical bed shear stress was 

difficult to estimate with confidence. The critical bed shear 

stress for the material in the Mississippi River channel 

and on the adjacent flood plain was estimated based on 

the median particle diameter (D50, the particle diameter at 

which 50 percent of the material is coarser and 50 percent 

is finer) of the material and the type of vegetative cover 

present. Based on the assigned critical bed shear stress, the 

general scour depths in the channel computed by the model 

were exceptionally large (about 1,000 ft of scour in some 

locations); therefore, the general contraction scour depths 

computed by the model were not used, even though the general scour depths computed for the flood plain were more 

reasonable.

Local pier scour also can be computed by the model 

when the user defines the location, size, alignment, and 

various other parameters for each pier or bent. However, the 

pier scour depths computed by the model are for the existing 

channel configuration. Historically, the scour assessments performed for MoDOT are for the most severe conditions, which 

allows for a dynamic channel configuration such as a shift in 

the channel thalweg during a flood (Huizinga and Rydlund, 

2004); therefore, the pier scour depths computed by the model 

were not used as the pier scour depths for structure A-1700.

Scour Depth Computations Using TwoDimensional Simulation Results

To obtain the parameters required for scour depth computations from the simulation results, flux lines were delineated 

at critical locations of interest in the finite-element mesh. The 

various node strings used as flux lines are indicated in figure 

12. Flux lines were delineated across the flood plain under 

the left (east) approach spans of structure A-1700 from the 

left abutment to top of the left bank (left overbank); the main 

channel of the Mississippi River from the top of the left (east) 

bank to the top of the right (west) bank under the main spans 

of structure A-1700 (bridge main channel); the flood plain 

under the right (west) approach spans of structure A-1700 

from the right abutment to top of the right bank (right overbank); the upstream channel of the Mississippi River from the 

top of the left (east) bank to the top of the right (west) bank 

about 4,750 ft upstream from structure A-1700 (approach 

main channel); the left (east) flood plain upstream from the 

left (east) embankment from the east mainline levee to a point 

where the velocity vector flow lines (if extended) would intersect the toe of the left abutment (left embankment blocked); 

and the right (west) flood plain upstream from the right (west) 

embankment from the west mainline levee to a point where 

the velocity vector flow lines (if extended) would intersect the 

toe of the right abutment (right embankment blocked). The 

velocity magnitude, depth of flow, and water-surface elevation 

assigned to each node in the flux lines were obtained from the 

simulations and used to determine the cross-sectional area of 

flow, average depth, and average flow velocity at each flux 

line. Additionally, the average elevation of the energy grade 

line (the sum of the land-surface elevation, the depth of flow, 

and the velocity head, V2

/2g, where V is the mean velocity of 

flow in feet per second and g is the acceleration of gravity in 

feet per second squared) was determined at the bridge main 

channel and approach main channel flux lines for use in the 

contraction scour computations.

A cross section of the bridge opening of structure A-1700 

is shown in figure 4, along with bridge substructure and superstructure details and other information pertaining to the scour 

analysis. The channel shows some long-term aggradation in 

the thalweg and degradation on the right side, as indicated by 

the difference in the land surface in 1973 from MoDOT plans 

(Missouri Department of Transportation, 1974) and the current 
Evaluation of Bridge Scour 19

(2004) land surface obtained from the USACE ground-elevation data. The left overbank has an area of degradation near the 

left abutment, and the right overbank has an area of degradation near the top of the right bank and an area of aggradation 

in the middle of the overbank.

Core logs from boreholes (hereinafter referred to as “bore 

logs”) drilled by the USACE on the left bank upstream from 

structure A-1700 (Derrick Smith, written commun., 2007) 

indicate the material near the land surface is composed of 

sandy silt and silty clay, and transitions into a fine to medium 

sand [D50 ranging from 0.60 to 0.90 millimeters (mm)] about 

50 to 60 ft below the land surface. Bore logs from MoDOT 

plans (Missouri Department of Transportation, 1974) for the 

flood plain under both approach spans also indicate the material on the flood plain consists of a sandy silt and clay near the 

surface, changing to fine and medium sand below the surface. A sample collected from the land surface under the left 

approach spans of structure A-1700 confirmed the material on 

the left flood plain is a sandy silt with clay (D50 = 0.04 mm) as 

indicated by the USACE and MoDOT bore logs. The material 

in the channel was assumed to consist of the fine to medium 

sand present at depth in the USACE bore logs (D50 = 0.90 

mm), based on MoDOT bore logs near the main-channel piers 

and visual inspection of material deposited on the banks and 

on bars in the channel.

The estimated contraction scour depths for structure 

A-1700 were computed using Laursen’s live-bed contraction 

scour equation for the main channel (table 3) and Laursen’s 

clear-water contraction scour equation for the left and right 

overbanks (table 4), assuming an infinite depth of erosive 

material and a homogeneous particle-size distribution (Richardson and Davis, 2001). Based on the velocities and depths 

obtained from the Flo2DH analysis and the median diameter 

of the material in the channel (D50 = 0.90 mm), a critical 

velocity of incipient motion, Vc, in the main channel was 

calculated using Laursen’s equation (Richardson and Davis, 

2001) for each of the three simulations. Because the critical 

velocity, Vc, was less than the mean velocity in the approach 

main channel for all three of the discharge simulations used in 

this analysis, a live-bed scour scenario was assumed to exist in 

the main channel. Conversely, because of the extensive vegetation on the flood plain upstream from the bridge and the lower 

velocities on the flood plain near the bridge, a clear-water 

scour scenario (wherein no bed material is transported) was 

assumed to exist on the overbank areas under the approach 

spans of structure A-1700. The median particle diameter of the 

surface material on the left flood plain (D50 = 0.04 mm) also 

was used to represent the right flood plain.

The predicted contraction scour depths for the calibration 

flood were 13.8 and 5.0 feet for main channel and left overbank, respectively; a value of 0 feet was predicted for the contraction scour depth on the right overbank for the calibration 

flood. The predicted main-channel contraction scour depth 

for the 100-year flood was 17.7 feet, with predicted overbank 

contraction scour depths of 14.4 and 2.6 feet for the left and 

right overbanks, respectively. The predicted main-channel 

Table 3. Predicted live-bed contraction scour depths and parameters used to compute main-channel contraction scour 

on the Mississippi River near Caruthersville, Missouri.

[ft3/s, cubic feet per second; ft/s, feet per second; ft, feet]

Flood

Parameter required to compute scour depth Calibration 100-year Project design

Flood discharge (ft3

/s) 1,658,000 1,960,000 1,974,000

Critical velocity of incipient motion (ft/s) 3.11 3.15 3.17

Average velocity in approach main channel (ft/s) 5.94 6.23 5.85

Type of scour Live-bed Live-bed Live-bed

Approach section (fig. 12)

Discharge (ft3

/s) 1,533,000 1,732,000 1,696,000

Channel width (ft) 4,840 4,840 4,840

Average depth (ft) 53.3 57.4 59.9

Energy grade line elevation (ft) 275.65 279.66 282.02

Bridge section (fig. 12)

Discharge (ft3

/s) 1,610,000 1,849,000 1,820,000

Channel width minus pier/bent widths (ft) 2,600 2,600 2,600

Average depth (ft) 69.1 72.9 75.6

Energy grade line elevation (ft) 274.84 278.72 281.18

Computed contraction scour depth (ft) 13.8 17.7 19.4
20 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

contraction scour depth for the project design flood was 19.4 

feet, with predicted overbank contraction scour depths of 20.6 

and 5.2 feet for the left and right overbanks, respectively.

The local pier scour depths were computed using the 

Colorado State University (CSU) pier scour equation (Richardson and Davis, 2001). The piers of the main span consist 

of round-nosed columns on caisson foundations and were analyzed as round-nosed columns using their overall length and 

width according to HEC-18 guidelines (Richardson and Davis, 

2001). The bents of the main span consist of two cylindrical 

columns 6.5 ft in diameter spaced 46 ft on center supported on 

pile foundations; these bents were analyzed as a single column 

because the spacing between the columns was greater than 5 

times the column diameter, and HEC-18 guidelines state that 

for multiple columns spaced 5 column-diameters or greater 

apart the predicted scour depth should be limited to 1.2 times 

the local scour of a single column if debris is not a concern 

at the site (Richardson and Davis, 2001). The bents of the 

left and right approach spans consisted of three cylindrical 

columns ranging from 3.5 to 6.0 ft in diameter and spaced 29 

ft on center; the bents with a column diameter of 4.5 ft or less 

were analyzed as a single column because the spacing between 

the columns was greater than 5 times the column diameter, and 

the bents with a column diameter of greater than 4.5 ft were 

analyzed as an equivalent round-nosed pier with a length equal 

to the 3 times the column diameter. The piers and bents in the 

main channel were analyzed using the maximum velocity and 

the maximum depth of flow in the channel under the bridge 

to account for possible changes in the thalweg during a flood, 

whereas the piers and bents on the left and right banks and 

overbanks were analyzed using the depth and velocity at the 

pier or bent (tables 5–7). The flow angle of attack as determined by Flo2DH for each pier or bent was included in the 

local pier scour depth computation (tables 5–7).

The predicted contraction scour depths on the left 

overbank and in the main channel resulted in footing exposure at the bents on the left overbank and on the right bank, 

as well as at several of the main-channel piers. Therefore, 

the local pier scour depths computed using the CSU pier 

scour equation were superseded by local pier scour depths 

computed using the equations for complex pier foundations (Richardson and Davis, 2001) at these piers and bents 

(tables 5–7).

The predicted contraction and local pier scour depths 

computed for the PDF are shown in figures 13 and 14, and the 

predicted total scour depths (the sum of contraction scour and 

local pier scour) for the three flood simulations are shown in 

figures 15 and 16. Predicted scour depths are shown in relation 

to the current (2004) land surface taken from the groundelevation data provided by the USACE, assuming no scour 

protection. Predicted total scour depths (contraction and local 

pier scour) for the calibration flood were the least, whereas the 

predicted total scour depths for the project design flood generally were the greatest.

The maximum predicted total scour depth for the calibration flood was 66.1 ft, occurring at pier 18. The maximum 

predicted total scour depth for the 100-year flood was 74.6 ft, 

also occurring at pier 18. The maximum predicted total scour 

depth for the project design flood was 93.0 ft, occurring at pier 

20. Based on the predicted total scour depths (figs. 15 and 16), 

piers 15 through 21 in the main channel and bent 14 on the 

right bank may be substantially exposed or undermined by a 

flood equal to or greater than the calibration flood of April 4, 

1975, in the absence of scour protection. On the left overbank, 

nearly all of the bents show footing undermining with moderate pile exposure for the calibration flood of April 4, 1975, and 

all of the bents show footing undermining with moderate to 

substantial pile exposure for the 100-year flood and PDF. The 

Table 4. Predicted clear-water contraction scour depths and parameters used to compute overbank contraction scour 

on the Mississippi River near Caruthersville, Missouri.

[ft3/s, cubic feet per second; ft, feet]

Flood

Parameter required to compute scour depth Calibration 100-year Project design

Flood discharge (ft3

/s) 1,658,000 1,960,000 1,974,000

Left overbank section (fig. 12)

Discharge (ft3

/s) 40,000 91,800 129,600

Section width minus pier/bent widths (ft) 3,320 3,320 3,320

Average depth (ft) 7.7 11.4 14.0

Computed contraction scour depth (ft) 5.0 14.4 20.6

Right overbank section (fig. 12)

Discharge (ft3

/s) 9,140 19,400 25,200

Section width minus pier/bent widths (ft) 916 916 916

Average depth (ft) 14.3 17.9 20.5

Computed contraction scour depth (ft) 0 2.6 5.2
Evaluation of Bridge Scour 21

Table 5. Predicted local pier scour depths and parameters used to compute pier scour for the calibration flood of April 4, 1975, on the 

Mississippi River near Caruthersville, Missouri.—Continued

[ft, feet; ft/s, feet per second; deg, degrees]

Pier/

bent 

numbera

Stationing along 

centerline from 

left (southeast) 

end of bridgeb 

(ft) Location

Pier/bent 

width at 

ground 

elevation

(ft)

Pier/bent 

length at 

ground 

elevation

(ft) Pier/bent shape

Flow parameters at upstream bridge 

face from Flo2DH Computed 

pier scour 

depth

(ft)

Depth

(ft)

Velocity

(ft/s)

Angle of 

attack 

(deg)

Bent 59 71.0 Left overbank 3.5 c3.5 Single columnc 5.90 2.23 1.8 d8.9

Bent 58 141.0 Left overbank 3.5 c

3.5 Single columnc 8.99 2.85 5.6 d6.2

Bent 57 211.0 Left overbank 3.5 c

3.5 Single columnc 9.37 2.71 8.0 d6.2

Bent 56 281.0 Left overbank 3.5 c

3.5 Single columnc 9.50 2.55 9.7 d11.8

Bent 55 351.0 Left overbank 3.5 c3.5 Single columnc 9.06 2.40 10.7 d5.9

Bent 54 421.0 Left overbank 3.5 c

3.5 Single columnc 9.14 2.27 10.3 d5.7

Bent 53 491.0 Left overbank 3.5 c

3.5 Single columnc 9.20 2.12 8.6 d5.3

Bent 52 561.0 Left overbank 3.5 c

3.5 Single columnc 8.71 2.02 6.4 d9.3

Bent 51 631.0 Left overbank 4.0 c4.0 Single columnc 8.55 1.93 3.4 d8.5

Bent 50 701.0 Left overbank 3.5 c3.5 Single columnc 8.76 1.86 3.7 d8.5

Bent 49 771.0 Left overbank 3.5 c

3.5 Single columnc 9.23 1.82 2.9 d8.5

Bent 48 841.0 Left overbank 4.0 c

4.0 Single columnc 8.47 1.78 1.4 d8.5

Bent 47 911.0 Left overbank 4.0 c

4.0 Single columnc 8.62 1.70 2.0 d8.8

Bent 46 981.0 Left overbank 4.0 c4.0 Single columnc 9.08 1.64 1.6 d8.7

Bent 45 1,051.0 Left overbank 4.0 c4.0 Single columnc 9.20 1.60 2.4 d8.8

Bent 44 1,121.0 Left overbank 4.0 c

4.0 Single columnc 8.88 1.57 4.9 d8.4

Bent 43 1,191.0 Left overbank 4.0 c4.0 Single columnc 8.75 1.47 4.6 d8.2

Bent 42 1,261.0 Left overbank 4.0 c

4.0 Single columnc 8.91 1.44 5.4 d8.3

Bent 41 1,331.0 Left overbank 4.0 c

4.0 Single columnc 8.56 1.43 5.0 d8.2

Bent 40 1,401.0 Left overbank 4.0 c

4.0 Single columnc 8.20 1.40 4.3 d7.9

Bent 39 1,471.0 Left overbank 4.0 c

4.0 Single columnc 7.83 1.40 5.1 d8.1

Bent 38 1,541.0 Left overbank 4.0 c

4.0 Single columnc 7.44 1.38 7.8 d8.5

Bent 37 1,611.0 Left overbank 4.0 c

4.0 Single columnc 7.09 1.38 11.8 d9.0

Bent 36 1,681.0 Left overbank 4.0 c

4.0 Single columnc 7.08 1.37 12.8 d9.1

Bent 35 1,751.0 Left overbank 4.0 c4.0 Single columnc 7.49 1.38 12.9 d9.0

Bent 34 1,821.0 Left overbank 4.0 c4.0 Single columnc 7.50 1.37 12.9 d9.2

Bent 33 1,891.0 Left overbank 4.0 c4.0 Single columnc 7.47 1.35 14.7 d9.3

Bent 32 1,961.0 Left overbank 4.0 c4.0 Single columnc 7.39 1.34 15.7 d9.4

Bent 31 2,031.0 Left overbank 4.5 c

4.5 Single columnc 7.17 1.29 16.6 d9.8

Bent 30 2,121.0 Left overbank 5.5 16.5 Multiple columns 6.87 1.25 16.7 d

11.7

Bent 29 2,211.0 Left overbank 5.5 16.5 Multiple columns 6.94 1.24 17.6 d11.8

Bent 28 2,301.0 Left overbank 5.5 16.5 Multiple columns 7.25 1.23 15.9 d11.7

Bent 27 2,391.0 Left overbank 5.5 16.5 Multiple columns 7.66 1.27 17.3 d12.0

Bent 26 2,481.0 Left overbank 5.0 15.0 Multiple columns 6.19 1.39 17.8 d

12.2

Bent 25 2,613.4 Left overbank 6.5 c6.5 Single columnc 3.71 0.94 62.7 c6.0

Bent 24 2,848.3 Left overbank 6.5 c

6.5 Single columnc 4.23 0.78 88.1 c4.7

Bent 23 3,083.2 Left overbank 6.5 c6.5 Single columnc 6.77 1.58 55.3 c8.3

Bent 22 3,318.2 Top of left bank 6.5 c6.5 Single columnc 6.38 2.29 42.5 c9.7
22 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

Table 5. Predicted local pier scour depths and parameters used to compute pier scour for the calibration flood of April 4, 1975, on the 

Mississippi River near Caruthersville, Missouri.—Continued

[ft, feet; ft/s, feet per second; deg, degrees]

Pier/

bent 

numbera

Stationing along 

centerline from 

left (southeast) 

end of bridgeb 

(ft) Location

Pier/bent 

width at 

ground 

elevation

(ft)

Pier/bent 

length at 

ground 

elevation

(ft) Pier/bent shape

Flow parameters at upstream bridge 

face from Flo2DH Computed 

pier scour 

depth

(ft)

Depth

(ft)

Velocity

(ft/s)

Angle of 

attack 

(deg)

Pier 21 3,556.1 Left bank 17.0 100.5 Round-nosed 35.65 5.34 7.8 32.2

Pier 20 4,476.0 Main channel 21.0 104.5 Round-nosed e

92.73 e10.53 2.2 42.5

Pier 19 4,995.9 Main channel 14.0 97.5 Round-nosed e

92.73 e10.53 0.3 29.4

Pier 18 5,233.8 Main channel 7.5 53.5 Round-nosed e92.73 e10.53 0.7 d52.3

Pier 17 5,468.8 Main channel 7.5 53.5 Round-nosed e

92.73 e10.53 3.1 d33.0

Pier 16 5,703.7 Main channel 7.5 53.5 Round-nosed e92.73 e10.53 3.8 d34.2

Pier 15 5,938.6 Right bank 7.5 53.5 Round-nosed 52.25 7.21 3.3 d41.2

Bent 14 6,071.0 Right bank 6.0 18.0 Multiple columns 25.47 3.82 3.6 d

10.6

Bent 13 6,161.0 Top of right bank 6.0 18.0 Multiple columns 20.38 0.71 44.9 8.5

Bent 12 6,251.0 Right overbank 6.0 18.0 Multiple columns 14.51 0.70 72.9 8.7

Bent 11 6,341.0 Right overbank 6.0 18.0 Multiple columns 12.56 0.79 63.8 8.9

Bent 10 6,431.0 Right overbank 6.0 18.0 Multiple columns 13.70 0.79 50.2 8.7

Bent 9 6,521.0 Right overbank 6.0 18.0 Multiple columns 12.83 0.76 39.1 7.9

Bent 8 6,611.0 Right overbank 5.5 16.5 Multiple columns 12.86 0.80 30.5 7.1

Bent 7 6,681.0 Right overbank 5.0 15.0 Multiple columns 13.62 0.86 23.5 6.4

Bent 6 6,751.0 Right overbank 5.0 15.0 Multiple columns 14.22 0.90 16.5 6.0

Bent 5 6,821.0 Right overbank 5.0 15.0 Multiple columns 14.74 0.93 9.4 5.3

Bent 4 6,891.0 Right overbank 5.0 15.0 Multiple columns 15.09 0.99 5.1 4.9

Bent 3 6,961.0 Right overbank 4.5 c

4.5 Single columnc 15.56 1.14 1.6 c5.2

Bent 2 7,031.0 Right overbank 4.5 c

4.5 Single columnc 9.94 1.43 1.0 c5.4

a

Pier/bent number corresponds to bridge plans from Missouri Department of Transportation (1974).

b

Stationing is the distance from the left abutment fill face (as viewed facing downstream).

c

“Pier/bent length at ground elevation” and “Pier/bent shape” are for a single column of a multiple column bent because the spacing between the columns 

is greater than 5 times the column diameter. The computed pier scour depth at this bent is 1.2 times the local scour of a single column, based on guidelines 

in Hydraulic Engineering Circular No. 18 (Richardson and Davis, 2001), except for those with complex pier foundation exposure after contraction scour 

(footnote d).

d

Computed contraction scour depths resulted in footing or pile exposure at this pier or bent. Local pier scour depths were computed using equations for 

complex pier foundations (Richardson and Davis, 2001).

e

The maximum depth and velocity in the main channel were used to compute pier scour depth to account for the possibility of a shift in the channel thalweg. 
Evaluation of Bridge Scour 23

Table 6. Predicted local pier scour depths and parameters used to compute pier scour for the 100-year flood on the Mississippi River 

near Caruthersville, Missouri.—Continued

[ft, feet; ft/s, feet per second; deg, degrees]

Pier/

bent 

numbera

Stationing 

along centerline from left 

(southeast) 

end of bridgeb 

(ft) Location

Pier/bent 

width at 

ground 

elevation

(ft)

Pier/bent 

length at 

ground 

elevation

(ft) Pier/bent shape

Flow parameters at upstream bridge 

face from Flo2DH

Computed 

pier scour 

depth

(ft)

Depth

(ft)

Velocity

(ft/s)

Angle of 

attack 

(deg)

Bent 59 71.0 Left overbank 3.5 c3.5 Single columnc 9.36 3.61 2.2 d7.6

Bent 58 141.0 Left overbank 3.5 c

3.5 Single columnc 12.52 4.01 6.7 d8.2

Bent 57 211.0 Left overbank 3.5 c3.5 Single columnc 12.93 3.93 8.0 d8.7

Bent 56 281.0 Left overbank 3.5 c

3.5 Single columnc 13.08 3.67 8.3 d8.5

Bent 55 351.0 Left overbank 3.5 c

3.5 Single columnc 12.65 3.50 8.2 d8.6

Bent 54 421.0 Left overbank 3.5 c

3.5 Single columnc 12.74 3.32 7.3 d8.1

Bent 53 491.0 Left overbank 3.5 c

3.5 Single columnc 12.82 3.16 5.3 d7.4

Bent 52 561.0 Left overbank 3.5 c

3.5 Single columnc 12.33 3.04 3.5 d7.5

Bent 51 631.0 Left overbank 4.0 c4.0 Single columnc 12.17 2.96 0.7 d6.5

Bent 50 701.0 Left overbank 3.5 c

3.5 Single columnc 12.39 2.86 0.6 d6.7

Bent 49 771.0 Left overbank 3.5 c3.5 Single columnc 12.87 2.80 0.5 d6.7

Bent 48 841.0 Left overbank 4.0 c

4.0 Single columnc 12.10 2.76 1.8 d6.6

Bent 47 911.0 Left overbank 4.0 c

4.0 Single columnc 12.26 2.68 4.3 d7.1

Bent 46 981.0 Left overbank 4.0 c4.0 Single columnc 12.72 2.60 4.7 d7.0

Bent 45 1,051.0 Left overbank 4.0 c

4.0 Single columnc 12.84 2.51 5.6 d7.2

Bent 44 1,121.0 Left overbank 4.0 c4.0 Single columnc 12.52 2.53 7.7 d7.1

Bent 43 1,191.0 Left overbank 4.0 c

4.0 Single columnc 12.40 2.38 7.6 d6.9

Bent 42 1,261.0 Left overbank 4.0 c

4.0 Single columnc 12.55 2.33 9.0 d7.1

Bent 41 1,331.0 Left overbank 4.0 c4.0 Single columnc 12.20 2.32 8.7 d7.0

Bent 40 1,401.0 Left overbank 4.0 c

4.0 Single columnc 11.83 2.28 8.7 d6.8

Bent 39 1,471.0 Left overbank 4.0 c

4.0 Single columnc 11.46 2.29 9.6 d7.0

Bent 38 1,541.0 Left overbank 4.0 c

4.0 Single columnc 11.07 2.29 11.3 d7.3

Bent 37 1,611.0 Left overbank 4.0 c

4.0 Single columnc 10.72 2.28 14.3 d7.4

Bent 36 1,681.0 Left overbank 4.0 c4.0 Single columnc 10.70 2.28 14.8 d7.3

Bent 35 1,751.0 Left overbank 4.0 c

4.0 Single columnc 11.11 2.26 15.4 d7.2

Bent 34 1,821.0 Left overbank 4.0 c

4.0 Single columnc 11.12 2.25 15.8 d7.3

Bent 33 1,891.0 Left overbank 4.0 c4.0 Single columnc 11.09 2.24 17.1 d7.2

Bent 32 1,961.0 Left overbank 4.0 c4.0 Single columnc 11.00 2.23 18.0 d7.3

Bent 31 2,031.0 Left overbank 4.5 c4.5 Single columnc 10.78 2.17 19.0 d7.3

Bent 30 2,121.0 Left overbank 5.5 16.5 Multiple columns 10.47 2.12 19.8 d

8.0

Bent 29 2,211.0 Left overbank 5.5 16.5 Multiple columns 10.54 2.09 20.6 d

8.1

Bent 28 2,301.0 Left overbank 5.5 16.5 Multiple columns 10.84 2.06 19.9 d

8.0

Bent 27 2,391.0 Left overbank 5.5 16.5 Multiple columns 11.24 2.09 20.4 d

8.1

Bent 26 2,481.0 Left overbank 5.0 15.0 Multiple columns 9.77 2.28 21.7 d

8.5

Bent 25 2,613.4 Left overbank 6.5 c

6.5 Single columnc 7.30 1.59 34.0 d9.4

Bent 24 2,848.3 Left overbank 6.5 c

6.5 Single columnc 7.90 1.06 38.7 d16.7

Bent 23 3,083.2 Left overbank 6.5 c

6.5 Single columnc 10.46 2.17 37.7 d21.9

Bent 22 3,318.2 Top of left bank 6.5 c

6.5 Single columnc 10.06 3.21 35.4 d15.0
24 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

Table 6. Predicted local pier scour depths and parameters used to compute pier scour for the 100-year flood on the Mississippi River 

near Caruthersville, Missouri.—Continued

[ft, feet; ft/s, feet per second; deg, degrees]

Pier/

bent 

numbera

Stationing 

along centerline from left 

(southeast) 

end of bridgeb 

(ft) Location

Pier/bent 

width at 

ground 

elevation

(ft)

Pier/bent 

length at 

ground 

elevation

(ft) Pier/bent shape

Flow parameters at upstream bridge 

face from Flo2DH

Computed 

pier scour 

depth

(ft)

Depth

(ft)

Velocity

(ft/s)

Angle of 

attack 

(deg)

Pier 21 3,556.1 Left bank 17.0 100.5 Round-nosed 39.32 5.71 8.6 34.8

Pier 20 4,476.0 Main channel 21.0 104.5 Round-nosed e

96.40 e11.39 2.4 44.1

Pier 19 4,995.9 Main channel 14.0 97.5 Round-nosed e96.40 e11.39 0.1 30.6

Pier 18 5,233.8 Main channel 7.5 53.5 Round-nosed e

96.40 e11.39 1.0 d56.9

Pier 17 5,468.8 Main channel 7.5 53.5 Round-nosed e

96.40 e11.39 3.4 d34.0

Pier 16 5,703.7 Main channel 7.5 53.5 Round-nosed e

96.40 e11.39 4.4 d36.6

Pier 15 5,938.6 Right bank 7.5 53.5 Round-nosed 55.80 7.20 4.2 d

42.1

Bent 14 6,071.0 Right bank 6.0 18.0 Multiple columns 29.10 3.46 6.2 d

9.9

Bent 13 6,161.0 Top of right bank 6.0 18.0 Multiple columns 23.97 1.04 45.9 10.3

Bent 12 6,251.0 Right overbank 6.0 18.0 Multiple columns 18.11 1.08 60.0 10.7

Bent 11 6,341.0 Right overbank 6.0 18.0 Multiple columns 16.16 1.24 53.5 10.9

Bent 10 6,431.0 Right overbank 6.0 18.0 Multiple columns 17.32 1.29 43.3 10.6

Bent 9 6,521.0 Right overbank 6.0 18.0 Multiple columns 16.45 1.27 34.7 9.9

Bent 8 6,611.0 Right overbank 5.5 16.5 Multiple columns 16.49 1.36 28.4 9.0

Bent 7 6,681.0 Right overbank 5.0 15.0 Multiple columns 17.26 1.46 21.8 8.2

Bent 6 6,751.0 Right overbank 5.0 15.0 Multiple columns 17.87 1.58 16.5 7.9

Bent 5 6,821.0 Right overbank 5.0 15.0 Multiple columns 18.39 1.60 10.3 7.0

Bent 4 6,891.0 Right overbank 5.0 15.0 Multiple columns 18.73 1.76 3.8 6.4

Bent 3 6,961.0 Right overbank 4.5 c

4.5 Single columnc 19.19 1.81 1.7 c6.5

Bent 2 7,031.0 Right overbank 4.5 c4.5 Single columnc 13.57 1.64 3.6 c6.2

a

Pier/bent number corresponds to bridge plans from Missouri Department of Transportation (1974).

b

Stationing is the distance from the left abutment fill face (as viewed facing downstream).

c

“Pier/bent length at ground elevation” and “Pier/bent shape” are for a single column of a multiple column bent because the spacing between the columns 

is greater than 5 times the column diameter. The computed pier scour depth at this bent is 1.2 times the local scour of a single column, based on guidelines 

in Hydraulic Engineering Circular No. 18 (Richardson and Davis, 2001), except for those with complex pier foundation exposure after contraction scour 

(footnote d).

d

Computed contraction scour depths resulted in footing or pile exposure at this pier or bent. Local pier scour depths were computed using equations for 

complex pier foundations (Richardson and Davis, 2001).

e

The maximum depth and velocity in the main channel were used to compute pier scour depth to account for the possibility of a shift in the channel thalweg. 
Evaluation of Bridge Scour 25

Table 7. Predicted local pier scour depths and parameters used to compute pier scour for the project design flood on the Mississippi 

River near Caruthersville, Missouri.—Continued

[ft, feet; ft/s, feet per second; deg, degrees]

Pier/

bent 

numbera

Stationing along 

centerline from 

left (southeast) 

end of bridgeb 

(ft) Location

Pier/bent 

width at 

ground 

elevation

(ft)

Pier/bent 

length at 

ground 

elevation

(ft) Pier/bent shape

Flow parameters at upstream bridge face 

from Flo2DH Computed 

pier scour 

depth

(ft)

Depth

(ft)

Velocity

(ft/s)

Angle of 

attack 

(deg)

Bent 59 71.0 Left overbank 3.5 c3.5 Single columnc 11.81 4.02 2.4 d7.6

Bent 58 141.0 Left overbank 3.5 c

3.5 Single columnc 14.98 4.31 6.8 d8.1

Bent 57 211.0 Left overbank 3.5 c

3.5 Single columnc 15.39 4.39 7.6 d8.8

Bent 56 281.0 Left overbank 3.5 c3.5 Single columnc 15.55 4.08 7.5 d8.6

Bent 55 351.0 Left overbank 3.5 c

3.5 Single columnc 15.12 3.93 7.0 d8.7

Bent 54 421.0 Left overbank 3.5 c3.5 Single columnc 15.22 3.75 6.1 d8.2

Bent 53 491.0 Left overbank 3.5 c3.5 Single columnc 15.30 3.59 4.0 d7.6

Bent 52 561.0 Left overbank 3.5 c

3.5 Single columnc 14.82 3.48 2.4 d7.6

Bent 51 631.0 Left overbank 4.0 c

4.0 Single columnc 14.66 3.41 0.2 d6.6

Bent 50 701.0 Left overbank 3.5 c3.5 Single columnc 14.88 3.29 0.3 d6.8

Bent 49 771.0 Left overbank 3.5 c

3.5 Single columnc 15.36 3.22 1.4 d6.8

Bent 48 841.0 Left overbank 4.0 c

4.0 Single columnc 14.60 3.17 2.6 d6.7

Bent 47 911.0 Left overbank 4.0 c

4.0 Single columnc 14.76 3.10 4.7 d7.3

Bent 46 981.0 Left overbank 4.0 c

4.0 Single columnc 15.23 3.02 5.1 d7.2

Bent 45 1,051.0 Left overbank 4.0 c4.0 Single columnc 15.35 2.91 6.0 d7.4

Bent 44 1,121.0 Left overbank 4.0 c

4.0 Single columnc 15.03 2.94 7.8 d7.3

Bent 43 1,191.0 Left overbank 4.0 c4.0 Single columnc 14.90 2.78 7.7 d7.1

Bent 42 1,261.0 Left overbank 4.0 c

4.0 Single columnc 15.06 2.72 9.2 d7.3

Bent 41 1,331.0 Left overbank 4.0 c

4.0 Single columnc 14.70 2.72 9.0 d7.3

Bent 40 1,401.0 Left overbank 4.0 c

4.0 Single columnc 14.34 2.67 9.1 d7.0

Bent 39 1,471.0 Left overbank 4.0 c4.0 Single columnc 13.97 2.68 10.0 d7.3

Bent 38 1,541.0 Left overbank 4.0 c

4.0 Single columnc 13.58 2.68 11.3 d7.6

Bent 37 1,611.0 Left overbank 4.0 c

4.0 Single columnc 13.23 2.68 13.9 d8.3

Bent 36 1,681.0 Left overbank 4.0 c

4.0 Single columnc 13.22 2.66 14.1 d8.5

Bent 35 1,751.0 Left overbank 4.0 c4.0 Single columnc 13.62 2.63 14.9 d8.5

Bent 34 1,821.0 Left overbank 4.0 c4.0 Single columnc 13.64 2.63 15.3 d8.7

Bent 33 1,891.0 Left overbank 4.0 c4.0 Single columnc 13.61 2.62 16.4 d8.9

Bent 32 1,961.0 Left overbank 4.0 c4.0 Single columnc 13.52 2.61 17.2 d9.0

Bent 31 2,031.0 Left overbank 4.5 c4.5 Single columnc 13.31 2.54 18.1 d8.5

Bent 30 2,121.0 Left overbank 5.5 16.5 Multiple columns 13.00 2.49 18.9 d

8.9

Bent 29 2,211.0 Left overbank 5.5 16.5 Multiple columns 13.07 2.45 19.7 d8.8

Bent 28 2,301.0 Left overbank 5.5 16.5 Multiple columns 13.37 2.42 19.5 d8.7

Bent 27 2,391.0 Left overbank 5.5 16.5 Multiple columns 13.78 2.43 20.0 d8.8

Bent 26 2,481.0 Left overbank 5.0 15.0 Multiple columns 12.30 2.62 21.7 d

9.8

Bent 25 2,613.4 Left overbank 6.5 c6.5 Single columnc 9.85 1.92 29.1 d10.4

Bent 24 2,848.3 Left overbank 6.5 c

6.5 Single columnc 10.47 1.29 26.8 d9.6

Bent 23 3,083.2 Left overbank 6.5 c6.5 Single columnc 13.05 2.51 32.3 d12.8

Bent 22 3,318.2 Top of left bank 6.5 c

6.5 Single columnc 12.65 3.58 32.1 d15.5
26 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

Table 7. Predicted local pier scour depths and parameters used to compute pier scour for the project design flood on the Mississippi 

River near Caruthersville, Missouri.—Continued

[ft, feet; ft/s, feet per second; deg, degrees]

Pier/

bent 

numbera

Stationing along 

centerline from 

left (southeast) 

end of bridgeb 

(ft) Location

Pier/bent 

width at 

ground 

elevation

(ft)

Pier/bent 

length at 

ground 

elevation

(ft) Pier/bent shape

Flow parameters at upstream bridge face 

from Flo2DH Computed 

pier scour 

depth

(ft)

Depth

(ft)

Velocity

(ft/s)

Angle of 

attack 

(deg)

Pier 21 3,556.1 Left bank 17.0 100.5 Round-nosed 41.92 5.54 9.1 34.7

Pier 20 4,476.0 Main channel 21.0 104.5 Round-nosed e

99.00 e10.82 2.4 d73.6

Pier 19 4,995.9 Main channel 14.0 97.5 Round-nosed e

99.00 e10.82 0.0 30.0

Pier 18 5,233.8 Main channel 7.5 53.5 Round-nosed e99.00 e10.82 1.1 d56.7

Pier 17 5,468.8 Main channel 7.5 53.5 Round-nosed e

99.00 e10.82 3.6 d33.1

Pier 16 5,703.7 Main channel 7.5 53.5 Round-nosed e99.00 e10.82 4.7 d35.4

Pier 15 5,938.6 Right bank 7.5 53.5 Round-nosed 58.44 6.45 4.7 d40.9

Bent 14 6,071.0 Right bank 6.0 18.0 Multiple columns 31.66 3.09 7.8 d

9.4

Bent 13 6,161.0 Top of right bank 6.0 18.0 Multiple columns 26.57 1.18 42.8 10.9

Bent 12 6,251.0 Right overbank 6.0 18.0 Multiple columns 20.71 1.21 54.1 11.2

Bent 11 6,341.0 Right overbank 6.0 18.0 Multiple columns 18.76 1.37 49.0 11.4

Bent 10 6,431.0 Right overbank 6.0 18.0 Multiple columns 19.91 1.44 40.4 11.2

Bent 9 6,521.0 Right overbank 6.0 18.0 Multiple columns 19.04 1.44 32.5 10.5

Bent 8 6,611.0 Right overbank 5.5 16.5 Multiple columns 19.07 1.53 27.0 9.6

Bent 7 6,681.0 Right overbank 5.0 15.0 Multiple columns 19.85 1.64 20.9 8.7

Bent 6 6,751.0 Right overbank 5.0 15.0 Multiple columns 20.45 1.79 16.3 8.4

Bent 5 6,821.0 Right overbank 5.0 15.0 Multiple columns 20.96 1.80 10.8 7.7

Bent 4 6,891.0 Right overbank 5.0 15.0 Multiple columns 21.31 1.99 4.3 6.8

Bent 3 6,961.0 Right overbank 4.5 c

4.5 Single columnc 21.75 1.97 1.6 c6.8

Bent 2 7,031.0 Right overbank 4.5 c

4.5 Single columnc 16.13 1.59 4.3 c6.1

a

Pier/bent number corresponds to bridge plans from Missouri Department of Transportation (1974).

b

Stationing is the distance from the left abutment fill face (as viewed facing downstream).

c

“Pier/bent length at ground elevation” and “Pier/bent shape” are for a single column of a multiple column bent because the spacing between the columns 

is greater than 5 times the column diameter. The computed pier scour depth at this bent is 1.2 times the local scour of a single column, based on guidelines in 

Hydraulic Engineering Circular No. 18 (Richardson and Davis, 2001), except for those with complex pier foundation exposure after contraction scour (footnote d).

d

Computed contraction scour depths resulted in footing or pile exposure at this pier or bent. Local pier scour depths were computed using equations for 

complex pier foundations (Richardson and Davis, 2001).

e

The maximum depth and velocity in the main channel were used to compute pier scour depth to account for the possibility of a shift in the channel thalweg. 
Evaluation of Bridge Scour 27

Bent 60(Abutment)Bent 59Bent 58Bent 57Bent 56Bent 55Bent 54Bent 53Bent 52Bent 51Bent 50Bent 49Bent 48Bent 47Bent 46Bent 45Bent 44Bent 43

Bent 27

Bent 25

Bent 24

Bent 23

Bent 22

Pier 21

Bent 26

Bent 43Bent 42Bent 41Bent 40Bent 39Bent 38Bent 37Bent 36

Bent 35

Bent 34

Bent 33

Bent 32

Bent 31

Bent 30

Bent 29

Bent 28

Bent 27

0 100 200 300 400 500 600 700 800 900 1,000 1,100 1200

200

220

240

260

280

300

320

340

ELEVATION, IN FEET ABOVE NGVD 29

1,200 1,300 1,400 1,500 1,600 1,700 1,800 1,900 2,000 2,100 2,200 2,300 2,400

200

220

240

260

280

300

320

340

DISTANCE FROM FILL FACE OF LEFT (SOUTHEASTERN) ABUTMENT, IN FEET

2,400 2,500 2,600 2,700 2,800 2,900 3,000 3,100 3,200 3,300 3,400 3,500 3,600

160

180

260

280

340

200

220

240

300

320

Predicted contraction scour

Predicted local pier scour Average water-surface elevation, 279.98 feet

Left bank covered with articulating concrete mattress

and riprap per bridge plans

LOCATION A

MAP

B C F

D E

A

B

C

D

B

C

Current (2004) land surface

Land surface 1973

Riprap or other revetment

Figure 13. Predicted contraction and local pier scour depths under the Tennessee-approach (left overbank) spans for the 

project design flood on the Mississippi River near Caruthersville, Missouri.
28 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri Pier 21 Pier 20 Pier 19 Pier 18 Pier 17 Pier 16 Pier 15 Bent 14 Bent 9 Bent 8 Bent 7 Bent 6 Bent 5 Bent 4 Bent 3 Bent 2 Bent 1 (Abutment) Bent 11 Bent 10 Bent 14 Bent 13 Bent 12

3,500 3,600 3,700 3,800 3,900 4,000 4,100 4,200 4,300 4,400 4,500 4,600 4,700 4,800

160

180

200

220

240

100

120

140

260

280

300

320

340

4,800 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6,000 6,100

160

180

200

220

240

100

120

140

260

280

300

320

340

ELEVATION, IN FEET ABOVE NGVD 29

6,100 6,200 6,300 6,400 6,500 6,600 6,700 6,800 6,900 7,000 7,100

DISTANCE FROM FILL FACE OF LEFT (SOUTHEASTERN) ABUTMENT, IN FEET

180

200

220

240

260

280

300

320

340

Predicted contraction scour

Predicted local pier scour

Average water-surface elevation, 279.98 feet

Riprap blanket for scour

protection around base

of ice breaker

Riprap blanket for

scour protection

around top of

seal course

Left bank covered with articulating

concrete mattress and riprap

per bridge plans

Riprap blanket for

scour protection

around base

of ice breaker

LOCATION A

MAP

B C F

D E

D

E

F

E

F

Current (2004) land surface

Land surface 1973

Riprap or other revetment

Figure 14. Predicted contraction and local pier scour depths under the main-channel and Missouri-approach 

(right overbank) spans for the project design flood on the Mississippi River near Caruthersville, Missouri.
Evaluation of Bridge Scour 29

Bent 60(Abutment)Bent 59Bent 58Bent 57Bent 56Bent 55Bent 54Bent 53Bent 52Bent 51Bent 50Bent 49Bent 48Bent 47Bent 46Bent 45Bent 44Bent 43

Bent 27

Bent 25

Bent 24

Bent 23

Bent 22

Pier 21

Bent 26

Bent 43Bent 42Bent 41Bent 40Bent 39Bent 38Bent 37Bent 36

Bent 35

Bent 34

Bent 33

Bent 32

Bent 31

Bent 30

Bent 29

Bent 28

Bent 27

0 100 200 300 400 500 600 700 800 900 1,000 1,100 1200

200

220

240

260

280

300

320

340

ELEVATION, IN FEET ABOVE NGVD 29

1,200 1,300 1,400 1,500 1,600 1,700 1,800 1,900 2,000 2,100 2,200 2,300 2,400

200

220

240

260

280

300

320

340

DISTANCE FROM FILL FACE OF LEFT (SOUTHEASTERN) ABUTMENT, IN FEET

2,400 2,500 2,600 2,700 2,800 2,900 3,000 3,100 3,200 3,300 3,400 3,500 3,600

160

180

260

280

340

200

220

240

300

320

Predicted total scour for calibration flood of

 April 4, 1975 (1,658,000 cubic feet per second)

Predicted total scour for 100-year flood

 (1,960,000 cubic feet per second)

Predicted total scour for project design

 flood (1,974,000 cubic feet per second)

Average water-surface elevation for

 project design flood, 279.98 feet

Average water-surface elevation for

 100-year flood, 277.42 feet

Average water-surface elevation for

 calibration flood of April 4, 1975, 273.70 feet

LOCATION A

MAP

B C F

D E

Current (2004) land surface

Land surface 1973

Riprap or other revetment

A

B

C

D

B

C

Left bank covered with

articulating concrete mattress

and riprap per bridge plans

Figure 15. Predicted total scour depths under the Tennessee-approach (left overbank) spans for three floods on the 

Mississippi River near Caruthersville, Missouri.
30 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri Pier 21 Pier 20 Pier 19 Pier 18 Pier 17 Pier 16 Pier 15 Bent 14 Bent 9 Bent 8 Bent 7 Bent 6 Bent 5 Bent 4 Bent 3 Bent 2 Bent 1 (Abutment) Bent 11 Bent 10 Bent 14 Bent 13 Bent 12

3,500 3,600 3,700 3,800 3,900 4,000 4,100 4,200 4,300 4,400 4,500 4,600 4,700 4,800

160

180

200

220

240

100

120

140

260

280

300

320

340

4,800 4,900 5,000 5,100 5,200 5,300 5,400 5,500 5,600 5,700 5,800 5,900 6,000 6,100

160

180

200

220

240

100

120

140

260

280

300

320

340

ELEVATION, IN FEET ABOVE NGVD 29

6,100 6,200 6,300 6,400 6,500 6,600 6,700 6,800 6,900 7,000 7,100

DISTANCE FROM FILL FACE OF LEFT (SOUTHEASTERN) ABUTMENT, IN FEET

180

200

220

240

260

280

300

320

340

Predicted total scour for project design flood (1,974,000 cubic feet per second)

Predicted total scour for 100-year flood (1,960,000 cubic feet per second)

Predicted total scour for calibration flood of April 4, 1975 (1,658,000 cubic feet per second)

LOCATION A

MAP

B C F

D E

D

E

F

Current (2004) land surface

Land surface 1973

Riprap or other revetment

Riprap blanket for scour

protection around base

of ice breaker

Riprap blanket for

scour protection

around top of

seal course

Left bank covered with articulating

concrete mattress and riprap

per bridge plans

Riprap blanket for

scour protection

around base

of ice breaker

E

F

Average water-surface elevation for

 project design flood, 279.98 feet

Average water-surface elevation for

 100-year flood, 277.42 feet

Average water-surface elevation for

 calibration flood of April 4, 1975, 273.70 feet

Figure 16. Predicted total scour depths under the main-channel and Missouri-approach (right overbank) spans 

for three floods on the Mississippi River near Caruthersville, Missouri.
Evaluation of Bridge Scour 31

bents on the right overbank are not substantially exposed in 

any of the flood simulations.

Abutment scour depths were computed for the three 

simulations (table 8) using the Highways in the River Environment (HIRE) scour equation (Richardson and Davis, 

2001). The abutment scour depths assume no protection on 

the abutment faces; however, guidebanks upstream from both 

abutments (fig. 6) likely will move the abutment scour hole 

away from the bridge substructure (Melville and Coleman, 

2000), and the abutment and upstream guidebanks are covered 

with large riprap boulders and stone revetment (fig. 17), which 

likely will provide resistance to abutment scour. Therefore, no 

abutment scour is shown on figures 13 through 16.

Resistance to contraction and local pier scour may be 

provided by revetment features around structure A-1700. 

Based on bridge plans (Missouri Department of Transportation, 1974) and visual observations, revetment in the form 

of riprap blankets and an articulated concrete mattress are 

present around the main-channel piers (piers 18 through 

21), on the left and upper right banks, and on abutments and 

guidebank faces (fig. 4 and figs. 13–16). These revetment 

features likely will limit the amount of scour that occurs at 

these locations; however, no revetment is present near the 

main-channel piers 16 and 17, and the total scour depths 

indicate these piers are substantially exposed or undermined 

in all three flood simulations. Riprap in the vicinity of pier 

15 is inferred from visual observation of riprap on the upper 

right bank around bent 14, but pier 15 also was substantially 

exposed or undermined in the three flood simulations in the 

absence of scour protection.

Additional resistance to local pier scour may be provided by the structure of the piers and bents. According to 

Richardson and Davis (2001), when the computed contraction 

scour depth does not cause exposure of the top of the footing 

at a pier or bent (such that the footing is not exposed to flow 

after contraction scour), the wider footing may arrest local 

pier scour. This may limit the local pier scour for several of 

the main-channel piers and the bents on the right overbank. 

For the bents on the right overbank, the computed contraction 

scour depths did not cause the exposure of any of the footings 

(figs. 14 and 16); therefore, the local pier scour at these bents 

may be limited to the tops of the footings. For the piers in the 

main channel, the tops of the pedestals or caissons at piers 19 

through 21 have no or limited exposure from the computed 

contraction scour depths for the three simulated floods (figs. 

14 and 16); therefore, the local pier scour may be limited 

to the tops of the pedestals or caissons at these piers. This 

additional resistance to pier scour would not apply to piers 

16, 17, and 18 because the footings and seal courses of these 

piers already were exposed to flow by the current (2004) land 

surface (figs. 4, 14 and 16).

Finally, the predicted contraction scour depths are based 

on the assumption of an infinite depth of erosive material and 

a homogeneous particle-size distribution; however, USACE 

and MoDOT bore logs indicate that the material on the flood 

plain changes with increased depth from sandy silt to sand. 

Table 8. Predicted abutment scour depths and parameters used to compute abutment scour on the Mississippi River near 

Caruthersville, Missouri.

[ft3/s, cubic feet per second; ft2, square feet; ft, feet; deg, degrees; ft/s, feet per second]

Flood

Parameter required to compute scour depth Calibration 100-year Project design

Flood discharge (ft3

/s) 1,658,000 1,960,000 1,974,000

Left embankment blocked section (fig. 12)

Discharge blocked by embankment (ft3

/s) 24,000 51,600 66,800

Area of blocked flow (ft2

) 52,400 73,000 85,600

Embankment length perpendicular to flow (ft) 5,140 5,140 5,140

Embankment skew (deg)a 15 15 15

Velocity at embankment toe near upstream edge of bridge (ft/s) 2.29 3.68 4.09

Computed abutment scour depth (ft) 14.3 24.1 30.0

Right embankment blocked section (fig. 12)

Discharge blocked by embankment (ft3

/s) 23,000 44,400 55,900

Area of blocked flow (ft2

) 42,200 58,600 68,700

Embankment length perpendicular to flow (ft) 4,020 4,020 4,020

Embankment skew (deg)a -40 -40 -40

Velocity at embankment toe near upstream edge of bridge (ft/s) 1.44 2.20 2.52

Computed contraction scour depth (ft) 23.6 32.3 37.4

a

A negative value for skew indicates the embankment points downstream.
32 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

Assuming the material on the left overbank was a fine to 

medium sand (D50 = 0.40 mm) and using identical hydraulic 

parameters from the PDF simulation to compute the contraction scour on the left overbank, the predicted overbank contraction scour depth is only 3.9 ft as compared to the predicted 

depth of 20.6 ft for sandy silt (D50 = 0.04 mm); therefore, the 

contraction scour depths may not reach the predicted values 

because of the non-homogeneous nature of the material, particularly on the overbanks.

Summary

A two-dimensional hydrodynamic flow model was used 

to simulate flow conditions on the Mississippi River in the 

vicinity of structure A-1700, the Interstate 155 crossing of 

the river near Caruthersville, Missouri. The model was used 

to simulate flow conditions for three discharges: a flood that 

occurred on April 4, 1975 (the calibration flood), the 100-

year flood, and the project design flood. The project design 

flood was essentially equivalent to the flood that would cause 

impending overtopping of the mainline levees along the Mississippi River in the vicinity of structure A-1700. Discharge 

and river-stage readings from the flood of April 4, 1975, were 

used to calibrate the flow model. The model was then used to 

simulate the 100-year and project design floods.

The flow conditions simulated in the model were used to 

estimate the contraction, local pier, and abutment scour depths 

for the three discharges. The predicted contraction scour 

depths for the calibration flood were 13.8 and 5.0 feet for main 

channel and left overbank (as viewed facing downstream), 

respectively; a value of 0 feet was predicted for the contraction 

scour depth on the right overbank for the calibration flood. 

The predicted main-channel contraction scour depth for the 

100-year flood was 17.7 feet, with predicted overbank contraction scour depths of 14.4 and 2.6 feet for the left and right 

overbanks, respectively. The predicted main-channel contraction scour depth for the project design flood was 19.4 feet, 

with predicted overbank contraction scour depths of 20.6 and 

5.2 feet for the left and right overbanks, respectively.

Predicted total scour depths (contraction and local pier 

scour) for the calibration flood were the least, whereas the predicted total scour depths for the project design flood generally 

were the greatest. The maximum predicted total scour depth 

(contraction and local pier scour) for the calibration flood was 

66.1 feet, occurring at pier 18. The maximum predicted total 

scour depth for the 100-year flood was 74.6 feet, also occurring at pier 18. The maximum predicted total scour depth for 

the project design flood was 93.0 feet, occurring at pier 20. 

The footings of the bents on the left overbank are undermined 

and the piles are moderately to substantially exposed in all 

three of the discharge simulations. The bents on the right 

overbank are minimally exposed in the three discharge simulations. Piers 15 through 21 in the main channel and bent 14 

on the right bank would be substantially exposed or undermined by the predicted total scour depths in all three of the 

discharge simulations in the absence of scour protection. Piers 

18 through 21 have scour protection in the form of a riprap 

blanket around the base of each according to bridge plans, and 

the riprap blanket observed on the right bank around bent 14 

is believed to extend around the base of pier 15; this revetment likely would limit the amount of scour that would occur 

at these piers. Furthermore, the footings and caissons that are 

not exposed by predicted contraction scour may arrest local 

pier scour, which may limit local pier scour at several bents 

and piers. Abutment scour depths were computed for structure 

A-1700, but are expected to be mitigated by the presence of 

guidebanks upstream from the abutments, as well as riprap 

revetment on the abutment and guidebank faces.

Abutment face

covered with riprap

Upstream guidebank

covered with riprap

Figure 17. Abutment and part of the guidebank upstream from the right (northwest) end of structure A-1700 over the 

Mississippi River near Caruthersville, Missouri, January 23, 2007.
References Cited 33

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selecting Manning’s roughness coefficients for natural channels and flood plains: U.S. Geological Survey Water-Supply 

Paper 2339, 38 p.

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1849, 213 p.

Chow, V.T., 1959, Open-channel hydraulics: St. Louis, Mo., 

McGraw-Hill Publishing Company, 678 p.

Environmental Modeling Research Laboratory, 1999, Surfacewater modeling system reference manual, version 8.0: 

Provo, Utah, Brigham Young University, 315 p. 

Froehlich, D.C., 2002, Two-dimensional depth-averaged flow 

and sediment transport model—Users manual for FESWMS 

Flo2DH: Federal Highway Administration, FHWA–RD–

03–053, 203 p.

Huizinga, R.J., 2007, Two-dimensional hydrodynamic modeling and analysis of the proposed channel modifications and 

grade control structure on the Blue River near Byram’s Ford 

Industrial Park, Kansas City, Missouri: U.S. Geological 

Survey Scientific Investigations Report 2007–5098, 45 p.

Huizinga, R.J., and Rydlund, P.H., Jr., 2001, Simulation of 

flow and evaluation of bridge scour at Horse Island Chute 

Bridge near Chester, Illinois: U.S. Geological Survey WaterResources Investigations Report 01–4176, 28 p.

Huizinga, R.J., and Rydlund, P.H., Jr., 2004, Potential-scour 

assessments and estimates of scour depth using different 

techniques at selected bridge sites in Missouri: U.S. Geological Survey Scientific Investigations Report 2004–5213, 

42 p.

Melville, B.W., and Coleman, S.E., 2000, Bridge scour: Highlands Ranch, Colo., Water Resources Publications, 550 p.

Missouri Department of Transportation, 1974, Bridge over 

Mississippi River near Caruthersville, Missouri: Jefferson 

City, Missouri State Highway Department, Project Nos. 

I–155–1(32–35), Bridge No. A-1700.

Richardson, E.V., and Davis, S.R., 2001, Evaluating scour at 

bridges (4th ed.): U.S. Federal Highway Administration 

Publication FHWA NHI 01–001 Hydraulic Engineering 

Circular No. 18, 378 p.

U.S. Army Corps of Engineers, 2007a, River Engineering 

Branch: Memphis District, U.S. Army Corps of Engineers, 

accessed May 24, 2007, at http://155.76.117.11/river/

default.htm.

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page: Memphis District, U.S. Army Corps of Engineers, 

accessed May 24, 2007, at http://155.76.117.11/hydraulics/

memphis.htm.

U.S. Federal Highway Administration, 1988, Scour at bridges: 

Washington, D.C., Federal Highway Administration Technical Advisory 5140.20, 4 p.
34 Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 near Caruthersville, Missouri

Prepared by: 

USGS Enterprise Publishing Network 

Rolla Publishing Service Center 

1400 Independence Road 

Rolla, MO 65401

For more information concerning this publication, contact:

Director

U.S. Geological Survey

Missouri Water Science Center

1400 Independence Road

Rolla, MO 65401

(573) 308–3667

Or visit the Missouri Water Science Center website at:

http://mo.water.usgs.gov 
References Cited 35
Huizinga—Two-Dimensional Simulation of Flow and Evaluation of Bridge Scour at Structure A-1700 —Scientific Investigations Report 2007–5230

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