Mississippi Valley Division

Numerical Sedimentation 

Investigation

Mississippi River

Cairo to Pilots Station

MRG&P Report No.30 • February 2020

Mississippi River Geomorphology & 

Potamology (MRG&P) Program 

MRG&P Report No. 30 

February 2020 

Numerical Sedimentation Investigation 

Mississippi River Cairo to Pilots Station

Ronald R. Copeland

U.S. Army Corps of Engineers

Vicksburg District

4155 Clay Street

Vicksburg, Mississippi 39183

Leslie Lombard

U.S. Army Corps of Engineers

New Orleans District

7400 Leake Avenue

New Orleans, Louisiana 70118

Roger A. Gaines

U.S. Army Corps of Engineers

Memphis District

167 N. Main St., Rm B-202

Memphis, Tennessee 38103-1894

Final report 

Approved for public release; distribution is unlimited. 

Prepared for U.S. Army Corps of Engineers

Washington, DC 20314-1000

Under Project No. 127672, “Mississippi River Geomorphology and Potamology 

Program”
MRG&P Report No. 30 ii

Abstract

A HEC-6T numerical model of the entire Lower Mississippi River between 

the end of Southwest Pass and the confluence of the Ohio River was 

developed. The model, which included over 1000 river miles, was 

calibrated to 1991-2002 measured data. The purpose of the numerical 

sedimentation model was to provide a tool to evaluate the long-term and 

system–wide effects of specific Mississippi River and Tributaries Project 

features. Model applications related to the effects of sediment diversions 

and the effects of dredging in the New Orleans District were demonstrated. 

The model demonstrated the effects of new constrictive works on the longterm and short-term river morphology. The model was used to test the 

effects of changes in upstream sediment inflow. The model’s ability to 

assess the effects of natural geomorphic changes, such as erosion of hard 

points, was demonstrated. Future application of this model to specific 

project sites should include the addition of more detailed geometry in the 

area of interest. 

DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. 

Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. 

All product names and trademarks cited are the property of their respective owners. The findings of this report are not to 

be construed as an official Department of the Army position unless so designated by other authorized documents.

DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.
MRG&P Report No. 30 iii

Contents

Abstract .......................................................................................................................................................... ii

Figures and Tables.........................................................................................................................................v

Preface........................................................................................................................................................... xi

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

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

Objective ................................................................................................................................... 2

Approach................................................................................................................................... 2

Questions and metrics ............................................................................................................. 3

2 Numerical Model Description.............................................................................................................4

HEC-6T description................................................................................................................... 4

Model network.......................................................................................................................... 4

Channel geometry .................................................................................................................... 8

New Orleans District channel geometry ..................................................................................... 9

Vicksburg District channel geometry ........................................................................................10

Memphis District channel geometry .........................................................................................11

St. Louis District channel geometry ..........................................................................................12

Dike Fields ..............................................................................................................................12

Southwest Pass ..........................................................................................................................12

Dikes in New Orleans District ....................................................................................................13

Dikes in Vicksburg and Memphis Districts ...............................................................................15

Hydrographs ...........................................................................................................................21

Distributary flows and flows around islands.........................................................................29

Southwest Pass ..........................................................................................................................29

Above Venice to Head of Passes ...............................................................................................32

Tarbert Landing to Above Venice discharge range ..................................................................38

Old River Complex ......................................................................................................................43

Water temperature .................................................................................................................45

Downstream water-surface elevations..................................................................................46

Datum and gages ...................................................................................................................48

Roughness coefficients..........................................................................................................50

Roughness coefficients for Ohio and Arkansas Rivers ........................................................64

Sediment transport................................................................................................................66

Sand and gravel transport function ..........................................................................................66

Silt and clay transport functions ...............................................................................................67

Sediment inflow......................................................................................................................70

Sediment inflow Middle Mississippi River at Thebes and Chester ..........................................73

Sediment inflow Ohio River .......................................................................................................78

Sediment inflow Obion and Hatchie Rivers ..............................................................................83

Sediment inflow St. Francis River .............................................................................................89
MRG&P Report No. 30 iv

Sediment inflow White River......................................................................................................92

Sediment inflow Arkansas River................................................................................................96

Sediment inflow Yazoo River .....................................................................................................99

Sediment inflow sources......................................................................................................102

Depth of bed sediment reservoir.........................................................................................103

Mississippi River bed material gradations..........................................................................104

Tributary bed gradations......................................................................................................109

Middle Mississippi River bed gradations ................................................................................109

Ohio River bed gradations .......................................................................................................109

Obion and Hatchie River bed gradations ................................................................................111

St. Francis River bed gradations .............................................................................................111

White River bed gradations .....................................................................................................112

Arkansas River bed gradations ...............................................................................................113

Yazoo River bed gradations .....................................................................................................114

Sediment concentrations in distributary flows ...................................................................114

Sediment distribution around islands.................................................................................124

3 Model Calibration and Verification...............................................................................................126

Selection of model parameters ...........................................................................................126

Computational time-step .........................................................................................................126

Exchange increment ................................................................................................................127

Sediment transport function ...................................................................................................127

Calibration tests ...................................................................................................................131

Steady-state, fixed-bed tests ...................................................................................................131

Steady-state, movable-bed tests .............................................................................................134

Quasi-unsteady movable-bed tests .........................................................................................138

Verification............................................................................................................................170

Deposition downstream from Old River ..................................................................................170

Degradation at Smithland Crossing ........................................................................................177

4 Model Results...................................................................................................................................188

Sediment yield......................................................................................................................188

Modified hydrograph 2003–2011 ......................................................................................190

Sediment inflow for the Middle Mississippi River 2003–2012.........................................191

Effect of declining sediment inflow at Thebes....................................................................197

Effect of hard points on degradation ..................................................................................198

Effects of dike construction.................................................................................................200

5 Summary and Recommendations ................................................................................................202

References................................................................................................................................................210

Unit Conversion Factors .........................................................................................................................213

Acronyms and Abbreviations.................................................................................................................215

Report Documentation Page
MRG&P Report No. 30 v 

Figures and Tables

Figures

Figure 1. Schematic of HEC-6T Stream Network in New Orleans and Vicksburg Districts..................5

Figure 2. Schematic of HEC-6T stream network in Memphis and St. Louis Districts...........................6

Figure 3. 1991–2002 hydrograph.............................................................................................................22

Figure 4. Prototype and initial model discharge at Helena. ...................................................................27

Figure 5. Prototype and initial model cumulative flow volume at Helena. ...........................................27

Figure 6. Flow decrease in downstream direction Memphis to Helena Reach...................................28

Figure 7. Measured Above Venice discharge in Pass a Loutre and South Pass..................................34

Figure 8. Measured Above Venice discharge in Cubits Gap...................................................................36

Figure 9. Measured Above Venice discharge in Grand Pass..................................................................37

Figure 10. Measured Above Venice discharge in Baptiste Collette.......................................................38

Figure 11. Caernarvon tailwater rating curve, 2001–2006...................................................................40

Figure 12. 2001 Stage-discharge rating curve Mississippi River at Caernarvon Inlet.......................41

Figure 13. Percentage of upstream discharge diverted at Caernarvon. ..............................................42

Figure 14. Tarbert Landing discharge diverted at Morganza and Bonnet Carré.................................43

Figure 15. Flow distribution at Old River, 1991–2002 and 2011 Flood..............................................44

Figure 16. Southwest Pass and Venice, 1991–1992, stage-discharge rating curves.......................46

Figure 17. Average monthly stages in Southwest Pass and at Grand Isle East...................................47

Figure 18. Venice rating curves, RM 10.7, 1991–2002. .......................................................................52

Figure 19. Empire rating curves, RM 29.5, 1991–2002. ......................................................................52

Figure 20. West Pointe a la Hache rating curves, RM 48.7, 1991–2002...........................................53

Figure 21. New Orleans rating curves, RM 102.8, 1991–2002...........................................................53

Figure 22. Reserve rating curves, RM 138.7, 1991–2002...................................................................54

Figure 23. Donaldsonville rating curve, RM 175.4, 1991–2002..........................................................54

Figure 24. Baton Rouge rating curves, RM 228.4, 1991–2002...........................................................55

Figure 25. Bayou Sara rating curves, RM 265.4, 1991–2002.............................................................55

Figure 26. Red River Landing rating curves, RM 302.4, 1991–2002. ................................................56

Figure 27. Measured and calculated stages, RM -19 to RM 320. ........................................................56

Figure 28. Stage-discharge for St. Joseph (RM 396.4) and Natchez (RM 363.0)..............................57

Figure 29. Stage-discharge for Lake Providence (RM 486.4) and Vicksburg (RM 437.4).................58

Figure 30. Stage-discharge for Arkansas City (RM 554.1) and Greenville (RM 531.5)......................58

Figure 31. Stage-discharge for Rosedale (RM 592)................................................................................59

Figure 32. Stage-discharge for historical floods on the Mississippi River at Vicksburg. ....................60

Figure 33. Stage-discharge for Helena (RM 663.1). ...............................................................................61

Figure 34. Stage-discharge for Memphis (RM 734.4). ...........................................................................61

Figure 35. Stage-discharge for Hickman (RM 922). ...............................................................................62
MRG&P Report No. 30 vi

Figure 36. Stage-discharge for the Ohio River at Metropolis (RM 990 AHP), 1991-2002. ...............65

Figure 37. Stage-discharge for the Ohio River at Cairo (RM 955.8 AHP), 1991-2002.......................66

Figure 38. Erosion rate characteristics. ....................................................................................................69

Figure 39. Deposition rate characteristics................................................................................................70

Figure 40. Total measured suspended sediment concentration at Thebes........................................74

Figure 41. Measured suspended sand concentration at Thebes. ........................................................74

Figure 42. Measured suspended total and sand concentrations at Thebes. .....................................75

Figure 43. Size class percentages for at Thebes, 1973-1991, and Chester, 1980–1991. ..............77

Figure 44. Total measured suspended sediment concentration at Dam 53. .....................................79

Figure 45. Measured suspended total and sand concentrations at Dam 53.....................................80

Figure 46. Measured size class percentages, at Louisville....................................................................81

Figure 47. Measured suspended total and sand concentrations Obion River near RM 62. .............85

Figure 48. Measured suspended total and sand concentrations Hatchie River.................................87

Figure 49. Combined measured suspended total and sand concentrations Hatchie River..............88

Figure 50. Measured suspended sediment concentrations, St. Francis River at Madison...............91

Figure 51. Measured suspended sediment concentrations at three gages, White River..................93

Figure 52. Measured suspended sand concentrations, White River....................................................94

Figure 53. Measured suspended sediment concentrations, White River............................................95

Figure 54. Measured sediment concentrations at two gages on the Arkansas River........................97

Figure 55. Measured sediment concentrations on the Arkansas River. ..............................................97

Figure 56. Sediment inflow rating curves for Arkansas River. ...............................................................98

Figure 57. Sediment concentration Yazoo River at Redwood and Steel Bayou................................ 100

Figure 58. Total sediment concentration trends Yazoo River.............................................................. 100

Figure 59. Sediment inflow rating curves for Yazoo River. .................................................................. 101

Figure 60. Lateral variation in bed material gradation at RM 265, August 2005. .......................... 105

Figure 61. Historic change in Mississippi River median bed grain size............................................. 106

Figure 62. Historic change in median bed grain size — gravel samples removed..............................107

Figure 63. 1989 bed gradations downstream from RM 306 with polynomial trend lines..............107

Figure 64. 1989 bed gradations upstream from RM 306, with polynomial trend lines................. 108

Figure 65. Initial bed calculated starting with Nordin polynomials after 30 days............................ 108

Figure 66. 1980–1989 average bed-material gradation at Thebes. ................................................ 109

Figure 67. Ohio River bed-material gradations...................................................................................... 110

Figure 68. Initial bed-material gradations used for the Obion and Hatchie Rivers.......................... 111

Figure 69. USGS bed gradations for St. Francis River at Madison and Riverfront...........................112

Figure 70. White River bed-material gradations collected by ERDC at RM 4. .................................. 113

Figure 71. Arkansas River bed-material gradations at Emerson and Camp Bends......................... 114

Figure 72. Sediment diversion coefficients at Caernarvon.................................................................123

Figure 73. Sand concentration at Belle Chasse. ..................................................................................130

Figure 74. Sand concentration at Tarbert Landing...............................................................................130
MRG&P Report No. 30 vii 

Figure 75. Sand concentration at Coochie (RM 317.3) and Union Point (326.6)............................ 131

Figure 76. Calculated channel velocity in the New Orleans District reach........................................132

Figure 77. Calculated channel velocity in the Vicksburg District reach.............................................133

Figure 78. Calculated channel velocity in the Memphis District reach. ............................................133

Figure 79. Calculated bed change in the New Orleans District reach...............................................135

Figure 80. Calculated bed change in the Vicksburg District. ..............................................................136

Figure 81. Calculated bed change in the Memphis District. ...............................................................136

Figure 82. Calculated bed change at five consecutive cross sections.............................................. 137

Figure 83. Calculated average bed change during the 1991–2002 hydrograph............................138

Figure 84. Specific gage at Venice, RM 10.7......................................................................................... 140

Figure 85. Specific gage at West Pointe A La Hache, RM 48.7. ..........................................................141

Figure 86. Specific gage at New Orleans, RM 102.8............................................................................141

Figure 87. Specific gage at Reserve, RM 138.7.................................................................................... 142

Figure 88. Specific gage at Donaldsonville, RM 175.4........................................................................ 142

Figure 89. Specific gage at Baton Rouge, RM 228.0. ......................................................................... 143

Figure 90. Specific gage at Bayou Sara, RM 265.4. ............................................................................ 143

Figure 91. Specific gage at Red River Landing, RM 302.4. ................................................................144

Figure 92. Specific gage at Natchez, RM 363.3...................................................................................144

Figure 93. Specific gage at Vicksburg, RM 435.7................................................................................. 145

Figure 94. Specific gage at Greenville, RM 531.1................................................................................ 145

Figure 95. Specific gage at Arkansas City, RM 554.1.......................................................................... 146

Figure 96. Specific gage at Rosedale, RM 592.2................................................................................. 146

Figure 97. Specific gage at Helena, RM 663.1.......................................................................................147

Figure 98. Specific gage at Memphis, RM 734.7. .................................................................................147

Figure 99. Specific gage at Hickman, RM 922..................................................................................... 148

Figure 100. Calculated average bed change, New Orleans District gages, 1991–2002............... 149

Figure 101. Calculated average bed change, Vicksburg District gages, 1991–2002. ...................150

Figure 102. Calculated average bed change, Memphis District gages, 1991–2002.....................150

Figure 103. 1982–1985 and 2005 USGS bed-material gradations................................................. 151

Figure 104. USGS and Nordin and Queen bed-material gradations..................................................152

Figure 105. Calculated active layer gradation compared to 2005 USGS gradations......................153

Figure 106. Calculated active layer gradation – Head of Passes to Cairo. .......................................154

Figure 107. Sand and fine concentrations at Tarbert Landing 1991–2002. ...................................155

Figure 108. Effect of model hydrographs on concentrations at Tarbert Landing. ........................... 157

Figure 109. Measured and calculated sediment concentrations at Belle Chasse..........................158

Figure 110. Measured and calculated sediment concentrations at Union Point and 

Coochie.......................................................................................................................................................159

Figure 111. Calculated energy slope between Tarbert Landing and Natchez.................................. 160

Figure 112. Measured fine sediment concentrations at Vicksburg (1984–2004)......................... 161

Figure 113. Measured fine sediment concentrations at Tarbert Landing (1984–2004). ............. 161
MRG&P Report No. 30 viii 

Figure 114. Measured sand concentrations at Vicksburg (1984–2004). ....................................... 162

Figure 115. Measured and calculated sediment concentrations at Vicksburg. .............................. 162

Figure 116. Measured and calculated sediment concentrations at Memphis................................ 163

Figure 117. Accumulated dredging in Southwest Pass, and from Head of Passes to RM 7........... 169

Figure 118. 1999 Hydrographic survey at Old River Control Complex. ............................................. 172

Figure 119. 2008 Hydrographic survey at Old River Control Complex. ............................................. 173

Figure 120. Navigation map of Smithland Crossing before construction of contraction 

works............................................................................................................................................................177

Figure 121. Navigation map of Smithland Crossing after construction. ........................................... 178

Figure 122. Looking upstream at Smithland Crossing after construction of dikes. The 

chute closure structure has not been completed, the river has not eroded to the trench fill 

revetment, and sediment has begun to deposit in the dike field....................................................... 179

Figure 123. Smithland Crossing after completion of chute closure structure. Looking 

downstream — the river has eroded back to the trench fill revetment, and sediment has 

deposited in dike field............................................................................................................................... 179

Figure 124. Calculated and measured degradation at Smithland Crossing, RM 300.3. ...............182

Figure 125. Calculated and measured degradation at Smithland Crossing, RM 299.5. ...............182

Figure 126. Calculated and measured degradation at Smithland Crossing, RM 298.9. ...............183

Figure 127. Calculated and measured degradation at Smithland Crossing, RM 298.1.................183

Figure 128. Calculated and measured degradation at Smithland Crossing, RM 297.45. .............184

Figure 129. Calculated bed changes at cross section 298.1 for 1991–2002................................186

Figure 130. Calculated accumulated sediment load for 1991–2002.............................................. 187

Figure 131. Calculated cumulative sand delivery for 1 year and 12 years.......................................189

Figure 132. Measured total suspended sediment concentration at Thebes...................................193

Figure 133. Measured suspended sand concentration at Thebes. ..................................................193

Figure 134. Mean daily measured total suspended sediment concentration at Thebes...............194

Figure 135. Measured total suspended sediment concentration, at Hermann. .............................196

Figure 136. Measured suspended sand concentration for the Missouri River at Hermann. ........196

Figure 137. Calculated cumulative sand delivery 1991–2011. ......................................................... 197

Figure 138. Effect of hard points at Hickman on calculated cumulative sand delivery..................199

Figure 139. Calculated difference in average bed with hard points at Hickman removed. ...........199

Figure 140. Effect of dike construction on calculated cumulative sand delivery............................. 201

Figure 141. Calculated difference in average bed change with dike construction.......................... 201

Tables

Table 1. Description of HEC-6T segments. .................................................................................................8

Table 2. Dikes in New Orleans District HEC-6T model, Pilots Station (RM -18.0) to Union 

Point (RM 326). ............................................................................................................................................15

Table 3. Dikes in Vicksburg District HEC-6T Model, Union Point (RM 326) to Rosedale 

(RM 92)..........................................................................................................................................................16

Table 4. Dikes in Memphis District HEC-6T Model, Rosedale (RM 592) to Cairo (RM 954). ............18
MRG&P Report No. 30 ix

Table 5. Reported water volume passing Mississippi River and Tributary gages, 1991–

2002. .............................................................................................................................................................23

Table 6. Annual discrepancy in recorded discharges at gages..............................................................24

Table 7. Calculated sediment delivery from the Ohio River. ...................................................................29

Table 8. Outflow from Southwest Pass distributaries, percentage of discharge immediately 

upstream from Diversion.............................................................................................................................32

Table 9. Distributary outflow between Above Venice and Head of Passes. .........................................33

Table 10. Calculated headwater upstream from Caemarvon Diversion Structure. ............................42

Table 11. Outflow at Old River distributaries, percentage of Union Point discharge. .........................45

Table 12. Average monthly water temperatures, 1992–2002..............................................................45

Table 13. Downstream water surface elevations at Pilots Station........................................................48

Table 14. Gages and datum used for water surface calibration. ..........................................................48

Table 15. HEC-6T roughness coefficients in New Orleans District........................................................63

Table 16. HEC-6T roughness coefficients in Vicksburg District. ............................................................63

Table 17. HEC-6T roughness coefficients in Memphis District...............................................................64

Table 18. Silt and clay coefficients for Parthenaides and Krone equations........................................69

Table 19. Percentage of the annual Mississippi River discharge at Vicksburg, 1991–

2002. .............................................................................................................................................................73

Table 20. Sediment inflow for Middle Mississippi River, Segment 25..................................................78

Table 21. Sediment inflow for Ohio River – Segment 24........................................................................82

Table 22. Sediment inflow for Obion River – Segment 16. ....................................................................86

Table 23. Sediment inflow for Hatchie River – Segment 14..................................................................89

Table 24. Sediment inflow for St. Francis River – Segment 12. ............................................................92

Table 25. Sediment inflow for White River – Segment 10......................................................................96

Table 26. Sediment inflow for Arkansas River – Segment 8..................................................................99

Table 27. Sediment inflow for Yazoo River – Segment 6. .................................................................... 102

Table 28. Source of Mississippi River water and sediment loads. 1991–2002

by percentage – based on HEC 6T input. .............................................................................................. 103

Table 29. Sediment diversion coefficients at Old River Control Complex from Catalyst-Old 

River Hydroelectric (1999)....................................................................................................................... 116

Table 30. Sediment diversion coefficients, Burrwood Bayou. ............................................................ 119

Table 31. Sediment diversion coefficients – outlet W-2 and overlfows............................................. 119

Table 32. Sediment diversion coefficients – Joseph Bayou................................................................120

Table 33. Sediment diversion coefficients – Southwest Pass at Mile 3.0........................................120

Table 34. Sediment diversion coefficients – South Pass and Pass a Loutre...................................120

Table 35. Sediment diversion coefficients – Cubits Gap. ................................................................... 121

Table 36. Sediment diversion coefficients – Baptiste Collette...........................................................122

Table 37. Sediment diversion coefficients – Caenarvon. ....................................................................123

Table 38. Sediment diversion coefficients – Bonnet Carré. ............................................................... 124

Table 39. Island sediment concentration ratios in secondary channel.............................................125
MRG&P Report No. 30 x 

Table 40. Sand size class fractions. Measured versus calculated using different sediment 

transport function, 1991–2002. ............................................................................................................129

Table 41. Measured and calculated size class distributions average percentages.........................158

Table 42. 12-year calculated sand yield between 1991 and 2002................................................... 164

Table 43. Reported and calculated* dredging 1991–2002. ............................................................. 167

Table 44. Bed and area changes downstream from Old River Control Complex, 1991–

2002. ...........................................................................................................................................................174

Table 45. Effects of sediment inflow and roughness on bed change.................................................176

Table 46. Roughness coefficients, falling limb of 2002 hydrograph, RM 267–306.3. ...................177

Table 47. Calculated and measured erosion at Smithland Crossing, 1991–2002. ........................185

Table 48. Calculated sediment loads from tributaries and distributaries, 1991–2002.................189

Table 49. 2003–2011 calculated sediment delivery...........................................................................198
MRG&P Report No. 30 xi

Preface

This study was conducted for the U.S. Army Corps of Engineers (USACE) 

as part of the Mississippi River Geomorphology and Potamology 

(MRG&P) Program, under Project 127672; “Mississippi River 

Geomorphology and Potamology Program.” The MRG&P Program is part 

of the Mississippi River and Tributaries Program (MR&T) and is 

managed by the USACE, Mississippi Valley Division (MVD), and 

Districts. At the time of publication of this report, the MRG&P Program 

Director was Dr. James W. Lewis. The MVD Commander was MG R. 

Mark Toy. The MVD Director of Programs was Mr. James A. Bodron.

This investigation was led by the U.S. Army Engineer Vicksburg District 

with support from the St. Louis District, Memphis District, and New 

Orleans District.
MRG&P Report No. 30 1 

1 Introduction

Background 

This report incorporates findings from an unpublished interim report 

entitled Numerical Sedimentation Investigation – Mississippi River 

Vicksburg to Pilots Station dated 27 October 2009. The interim study 

was conducted first to help address pressing issues related to flow 

diversions and dredging in the New Orleans District. This interim model 

was subsequently used by other investigators as a starting point for 

numerical studies for the State of Louisiana and the U.S. Army Corps of 

Engineers (USACE). It was also used as the starting point for the 

numerical model described in this report and is referred to herein as the 

Regional Model.

The original scope of work for the Regional Model called for producing a 

numerical model of the entire Lower Mississippi River that was calibrated 

to the 1991–2002 time period. This work was completed in 2010. To 

demonstrate the applicability of the Regional Model, it was decided to 

expand the study to evaluate (1) effects of changing sediment inflow from 

the Middle Mississippi River, (2) construction of a dike field, and (3) 

removal of the hard point at Hickman. Then, the 2011 flood produced 

record stages up and down the Lower Mississippi River. As part of the 

extended study, data from this flood were used to re-calibrate roughness 

coefficients at flood flows in the Vicksburg District. Also, additional 

sediment data through 2012 were used to extend the sediment inflow data 

base. A draft report describing this work was prepared in 2014, and the 

Regional Model is frequently referred to as the 2014 Report. Before review 

of the Regional Model was completed, focus was diverted to completing a 

numerical sediment study for the USACE Flowline Study for the 

Mississippi River and Tributaries Project. The Flowline Model used the 

Regional Model as a starting point, incorporating enhancements from the 

State of Louisiana and USACE models and incorporating additional data 

obtained after completion of the Regional Model study. The Flowline 

Model Report (Copeland 2018) was actually reviewed and completed 

before the Regional Model Report. Hence, there is a somewhat confusing 

chronology when publication dates are compared. 
MRG&P Report No. 30 2 

The Regional Model does not try to study specific areas in detail. The 

model is constructed so that more refinement can be added to study 

specific problem areas. The model can then be used to assess the systemwide effects of changes at the project site. The model extends from 

Chester, IL, on the Middle Mississippi River and Metropolis on the Ohio 

River to Pilots Station at the end of Southwest Pass – over 1000 miles.

Objective 

The purpose of this study was to develop a numerical sedimentation model 

that can identify and predict the effects of planned Mississippi River and 

Tributaries Project features and dredging strategies on long-term 

sediment trends between Cairo, IL, and Pilots Station, LA. The New 

Orleans, Vicksburg, Memphis, and St. Louis Districts were responsible for 

developing the numerical model in their respective reaches of 

responsibility along the Mississippi River. 

Approach 

The study approach was to develop a one-dimensional (1D) computational 

model using the computer program HEC-6T. This program has been 

applied successfully to evaluate long-term sedimentation responses to 

various engineering projects along the Lower Mississippi River. These 

applications have included river response to dredging, river response to 

flow diversions through distributaries, stability of a low-flow sediment sill, 

and the effect of contraction works on navigation depth. It is recognized 

that river response to dikes, especially overtopping dikes, is more complex 

than a 1D steady-flow problem. Specific reaches will need multidimensional modeling, or perhaps physical modeling, to determine design 

details; however, 1D computations were one of the approaches used to link 

these specific reaches together during the planning and design of the 

Arkansas River Flood Control and Navigation project in the 1950s and 

60s. That design included 450 miles of dikes and revetments that created 

an effective navigation channel. The project has performed exceptionally 

well in terms of evaluating maintenance requirements by dredging. The 

application of the computational model in the current study, by engineers 

who understand river behavior, will be equally successful in determining 

the appropriate length, height, and longitudinal extent for dike field 

construction, and it will give feedback on the long-term trends, due to 

sedimentation processes, that result from such projects.
MRG&P Report No. 30 3 

Questions and metrics 

Dredging and sediment diversion significantly alter morphologic processes 

in the river system. The numerical model can be used to calculate the 

short-term and long-term effects of proposed dredging activities and the 

effectiveness of a dredging program. The model can calculate the increased 

deposition rates associated with dredging and the length of time required 

to refill the navigation channel back to a critical elevation. The model can 

be used to calculate the effectiveness of in-channel dredge disposal versus 

disposal outside of the channel. The timing of dredging activities with 

respect to annual flood peaks can be evaluated. Similarly, the short-term 

and long-term effects of sediment diversions can be calculated using the 

numerical model. Although the quantity of sediment diverted must be 

determined external to the numerical model, the morphologic changes 

induced by a specified quantity of sediment diversion can be determined. 

The most useful feature of the numerical model analysis is that systemwide effects of several diversions and dredging activities can be evaluated 

together so that the effect of each feature on the system can be 

determined. These effects can be evaluated using calculated bed elevation 

and corresponding water-surface elevation changes in the river channel, 

sediment yields past designated cross sections, sediment diversion 

quantities through designated diversions, and required dredging 

quantities to maintain project depths.

Dike fields are constructed to hold alignment and increase navigation 

depths. In addition to the intentional bed changes in the dike field, there 

will be additional morphological changes in the upstream and downstream 

river reaches. The numerical model can be used to calculate both the 

short-term and long-term bed and water-surface elevation changes in the 

dike field itself and in the river system as a whole. The model also 

calculates short-term and long-term changes in sediment yield upstream 

and downstream from proposed dike fields.

The effects of imposed hydrologic and sedimentation conditions on the 

river system can be evaluated using the numerical model. Changes in the 

sediment supply will affect the aggradation/degradation rates in the river 

system. The numerical model can be used to determine the calculated bed 

changes and the reach length affected. The effects of sea-level rise, 

temperature changes, and removal of riverbed hard points can also be 

calculated. The primary calculated metrics are bed elevation change and 

changes in sediment yield.
MRG&P Report No. 30 4 

2 Numerical Model Description

HEC-6T description 

The HEC-6T 1D numerical sedimentation model was used in this study 

(MBH 2002). Mr. William A. Thomas initiated development of this 

computer program at the U.S. Army Engineer District, Little Rock, in 1967. 

Further development at the U.S. Army Engineer Hydrologic Engineering 

Center by Mr. Thomas produced the widely used HEC-6 generalized 

computer program for calculating scour and deposition in rivers and 

reservoirs. Additional modification and enhancement to the basic program 

by Mr. Thomas and his associates at the U.S. Army Engineer Research and 

Development Center (ERDC) led to the HEC-6W program. The HEC-6T 

program used in this study is the product of additional modification and 

enhancement conducted by Mr. Thomas at Mobile Boundary Hydraulics 

PLLC. Version nine of the HEC-6T code was used to make calculations in 

this study. The model is proprietary and can be obtained from Mobile 

Boundary Hydraulics.

The HEC-6T program produces a 1D model that simulates the response of 

the riverbed profile to sediment inflow, bed-material gradation, and 

hydraulic parameters. The model simulates a series of steady-state 

discharge events, their effects on the sediment transport capacity at cross 

sections and the resulting degradation or aggradation. The program 

calculates hydraulic parameters using a standard-step backwater method.

HEC-6T is a state-of-the-art program for use in mobile bed channels. The 

numerical model computations account for all the basic processes of 

sedimentation: erosion, entrainment, transportation, deposition, and 

compaction of the bed for the range of particle sizes found in the 

Mississippi River. The model calculates aggradation and degradation of 

the streambed profile over the course of a hydrologic event. It does not 

simulate bank erosion or natural adjustments in channel widths. When 

applied by experts using good engineering judgment, the HEC-6T program 

will provide good insight into the behavior of mobile bed rivers.

Model network 

The New Orleans, Vicksburg, Memphis, and St. Louis Districts were 

responsible for developing the numerical model in their respective reaches 

of responsibility along the Mississippi River. 
MRG&P Report No. 30 5 

The model network consists of 25 segments that are connected by control 

points. The network is shown in Figure 1 and Figure 2. In the figures, 

control points are designated with circles with a numerical designation, and 

segments are labeled inside of parentheses. For reference purposes, Figure 1

and Figure 2 also show tributaries, river miles, and loops. River miles are 

set using the 1962 Hydrographic Survey Index. River Mile (RM) 0 is at 

Head of Passes. Cross sections upstream from Head of Passes are positive 

values, and if there is any doubt, AHP (i.e., Above Head of Passes) is 

appended to the label. Cross sections along Southwest Pass are labeled as a 

negative values, and BHP (i.e., Below Head of Passes) is appended to those 

labels. 

Figure 1. Schematic of HEC-6T Stream Network in New Orleans and Vicksburg Districts.
MRG&P Report No. 30 6 

Figure 2. Schematic of HEC-6T stream network in Memphis and St. Louis Districts. 

Segments 1 through 4 are in New Orleans District. The model begins at 

RM -18 (BHP), which is just inside the jetties of Southwest Pass at Pilots 

Station. The downstream boundary is designated as Control Point 1. 

Segment 1 extends from Pilots Station to Profit Island, which is designated 

as Control Point 2. Segments 2 and 3 model the loop at Profit Island. 

Segment 2 is the main channel side, and Segment 3 is the chute. Control 

Point 2 joins Segments 2 and 3 to the downstream segment (Segment 1),

and Control Point 3 joins them to the upstream segment (Segment 4). 

Control Point 5, at the upstream end of Segment 4, is the gage at Tarbert 
MRG&P Report No. 30 7 

Landing (RM 306.3). It is located just downstream from the Old River 

Control Complex. 

Segments 5 through 9 are primarily located in the Vicksburg District. 

However, the Old River Diversion Complex, which is located between 

RM 311 and 316 AHP, is in the New Orleans District. Segment 5 begins at 

RM 306.3, and Segment 9 ends at RM 598. There are no loops in 

Vicksburg District, but the network schematic shows two major 

tributaries. They are the Yazoo River (Segment 6) at RM 438.39 AHP and 

the Arkansas River (Segment 8) at RM 580.8 AHP. 

Segments 10 through 23 are primarily in the Memphis District with 

Control Points 9 and 21 representing the downstream and upstream 

boundaries, respectively. Tributaries in the Memphis District include the 

White River (Segment 10) at RM 672.6, the Hatchie River (Segment 14) at 

RM 772.76, and the Obion River (Segment 16) at RM 819.39. The model 

contains the Island 8 Loop (Segments 18 and 19) and the Wolf Island Loop 

(Segments 21 and 22).

The Middle Mississippi River (Segment 25) is in the St. Louis District. 

The downstream control point is at Cairo (Control Point 21), and the 

upstream control point is at Chester (Control Point 23), which is located 

109.9 miles upstream.

Approximately 37 miles of the Ohio River are included in the model. The 

Ohio River is Segment 24. The downstream end of the segment is at 

Cairo, and the upstream end of the segment is located at Metropolis 

(Control Point 22.) Ohio River stationing starts at the confluence of the 

Allegheny and Monongahela Rivers in Pittsburgh, PA, and moves 

downstream to Cairo IL. However, in this report Ohio River stationing is 

sometimes referenced (for convenience) to River Miles Above Head of 

Passes (AHP).

The number of cross sections in each segment and the description of the 

segment boundaries are given in Table 1.
MRG&P Report No. 30 8 

Table 1. Description of HEC-6T segments. 

Segment 

Number of 

Cross 

Sections Description River Miles 

1 133 Mississippi River - Pilots Station to Profit Island -18.0 to 246,3

2 6

Mississippi River - Main Channel (West) Profit 

Island 246.9 to 251.8

3 6

Mississippi River - Chute Channel (East) Profit 

Island 246.8 to 248.6

4 27 Mississippi River - Profit Island to Tarbert Landing 253.0 to 306.3

5 72 Mississippi River - Tarbert Landing to Yazoo River 306.3 to 437.3

6 3 Yazoo River 1.5 to 16.7

7 81 Mississippi River - Yazoo River to Arkansas River 438.4 to 580.8

8 19 Arkansas River 0.6 to 29.0

9 9 Mississippi River - Arkansas River to White River 580.8 to 598.0

10 69 White River 0.0 to 100.0

11 45 Mississippi River - White River to St. Francis River 600.1 to 672.6

12 19 St. Francis River 0.5 to 17.7

13 38 Mississippi River - St. Francis River to Hatchie River 674.7 to 772.8

14 3 Hatchie River 0.1 to 2.0

15 18 Mississippi River - Hatchie River to Obion River 774.0 to 819.4

16 3 Obion River 0.1 to 2.0

17 35 Mississippi River - Obion River to Island 8 820.0 to 910.0

18 5 Mississippi River - East Loop Island 8 910.5 to 914.6

19 5 Mississippi River - West Loop Island 8 910.5 to 914.6

20 9 Mississippi River - Island 8 to Wolf Island 915.6 to 930.8

21 3 Mississippi River - East Loop Wolf Island 931.5 to 934.4

22 3 Mississippi River - West Loop Wolf Island 931.5 to 934.4

23 8 Mississippi River - Wolf Island to Cairo 934.4 to 953.0

24 37 Ohio River – Cairo to Metropolis

955.to 0 990.0

AHP

25 46 Middle Mississippi River - Cairo to Chester 0.8 to 109.90

Channel geometry 

The cross-section geometry in the HEC-6T model was developed from 

hydrographic survey data taken between 1987 and 1992 (USACE MVN 

1993; USACE MVK 1990; USACE MVM 1990). The hydrographic surveys 
MRG&P Report No. 30 9 

were conducted at different times in the different districts. There is a time 

discontinuity in the cross sections surveyed in individual districts as the 

hydrographic surveys in each district were conducted over a period of a year 

or more. One of the consequences of this anomaly is that direct comparisons 

between historical surveys at individual cross sections or even short reaches 

may be misleading. This factor makes model calibration to changes in 

surveyed bed volumes difficult and most likely unreliable.

Most of the cross sections in the 1987–1989 hydrographic survey for the 

Memphis District were obtained in 1988 and 1989. Gaps were filled by 

surveys obtained in 1985 through1987. Ten of the model cross sections 

came from these earlier dates. These were located at RMs 847.96, 792.1, 

777.3, 748.94, 744.98, 632.6, 628.66, 627.1, 602.95, and 600.1. 

Elevations from the hydrographic survey were related to mean sea level. 

Areas above the water line were obtained by photogrammetric methods 

from aerial photos taken between 1987 and 1988. River miles relate to 

distance AHP (1962).

The cross sections in the 1988–1989 hydrographic survey for the Vicksburg 

District were obtained between January 1988 and January 1989. Elevations 

from the hydrographic survey were related to National Geodetic Vertical 

Datum (NGVD) of 1929. Areas above the water line were obtained by 

photogrammetric methods from aerial photos taken between February and 

March 1988. River miles relate to distance AHP (1962).

The cross sections in the New Orleans District 1991-1992 hydrographic 

survey were obtained between October 1991 and September 1992. 

Elevations from the hydrographic survey were related to NGVD of 1929. 

Planimetry was from aerial photographs flown in November 1991. River 

miles relate to distance AHP (1962).

New Orleans District channel geometry 

Two existing HEC-6T models of the Mississippi River through the New 

Orleans District were available. The first model extended from East Jetty 

to Tarbert Landing and was constructed by Kevin Fagot at the USACE, 

New Orleans District (Barbe et al. 2000). The second model extended from 

Donaldsonville, LA, to Vicksburg, MS, and was constructed by Dr. Ronald 

Copeland at the USACE, ERDC (Catalyst-Old River Hydroelectric 1999). 

Both of these models were constructed using the 1983 Mississippi River 

Hydrographic Survey. A new model was developed for this study using 
MRG&P Report No. 30 10

essentially the same cross-section locations but replacing the 1983 channel 

survey data with the 1991–92 hydrographic survey data. This was done to be 

consistent with the survey data dates used upstream through the Vicksburg, 

Memphis, and St. Louis Districts. Overbanks in the new model were taken 

from various sources such as Hydrographic Survey Contours, U.S. 

Geololgical Survey (USGS) Quad Maps, and Louisiana DOQQ1 and lidar. 

However, some overbanks were taken from the original 1983 models and 

were not changed with the 1992 channel conversion. At some cross sections, 

overbank elevations were artificially raised to the upstream or downstream 

natural levee elevation to restrict overbank conveyance. 

Vicksburg District channel geometry 

The initial Mississippi River channel geometry through the Vicksburg 

District was developed from 1988–89 hydrographic survey data. Most of 

the overbank elevations came from the hydrographic survey. For cross 

sections without overbank elevations, USGS quad maps were used to 

develop overbank geometry. The Vicksburg District channel and overbank 

cross sections came from a previously developed HEC-2 model. At some 

cross sections, overbank elevations were artificially raised to the upstream 

or downstream natural levee elevation to restrict overbank conveyance.

The Yazoo River Segment in the HEC-6T model was poorly defined due to 

lack of channel geometry data. This condition was deemed acceptable 

because the sole purpose of the Yazoo River Segment was to provide 

sediment inflow to the Mississippi River. Data were insufficient for 

calibration and determination of morphologic changes in the Yazoo River. 

Three cross sections were used to define the Yazoo River. Cross sections at 

Yazoo RMs 1.51 and 3.69 were taken from the 1988–1989 hydrographic 

survey of the Mississippi River. A cross section at RM 16.7 was developed 

from geometry data obtained from the USGS gage at Redwood.

The HEC-6T model includes 28.2 miles of the Arkansas River downstream 

from Dam No. 2 to the Mississippi River. Cross-section geometry was 

obtained from a HEC-RAS backwater model labeled ArkWhite_seed1.G13

provided by Little Rock District. Cross sections in the HEC-RAS model 

were surveyed in May 2003. The channel alignment reflects cutoffs in the 

Lower Arkansas River that took place in the mid-1990s. The Arkansas 

River confluence with the Mississippi River moved to RM 580.5 from 

 

1 DOQQ is an abbreviation derived from the following: Digital Orthophoto Quarter Quadrangle.
MRG&P Report No. 30 11

RM 585 in 1989. This alignment and the location of the confluence are 

considerably different from that shown on the 1989 hydrographic survey.

Overbank geometry for Arkansas River cross sections where the overbank 

was shared with the Mississippi River was based on elevations from the 

1989 and 1995 Hydrographic Surveys modified to account for the new 

Arkansas River channel. Farther upstream, overbank widths and 

elevations were based on USGS quad elevations. At some cross sections, 

overbank elevations were artificially raised to the upstream or downstream 

natural levee elevation to restrict overbank conveyance. 

The purpose of the Arkansas River Segment in the HEC-6T model was to 

provide sediment inflow to the Mississippi River. Data are insufficient for 

calibration of the Arkansas River segment, and calculated morphologic 

changes should be treated with caution. 

Memphis District channel geometry 

The initial Mississippi River channel geometry for the Memphis District 

came from the 1988–89 hydrographic survey. USGS quads or lidar data 

were used to define overbank geometry. At some cross sections, overbank 

elevations were artificially raised to the upstream or downstream natural 

levee elevation to restrict overbank conveyance.

One hundred miles of the White River are included in the HEC-6T model. 

The channel cross sections were based on the 1997 hydrographic survey. 

Overbank elevations were taken from a 2000 survey and USGS quad 

maps. Data were insufficient for calibration and determination of 

morphologic changes in the White River.

Cross sections for the St. Francis River were taken from a previously 

developed HEC-6T model, which used 1997–1998 surveys for crosssection geometry. Overbank data came from 1997–1998 survey data and 

USGS quad maps. The Saint Francis River segment is 17.2 miles long.

There were no available survey data for the Obion and Hatchie Rivers, and 

therefore these segments were poorly defined. This condition was deemed 

acceptable because the sole purpose of these segments was to provide 

sediment inflow to the Mississippi River. Data were insufficient for 

calibration and determination of morphologic changes. Three cross 

sections were used to define 2 miles on the Obion and Hatchie River 
MRG&P Report No. 30 12

segments. The shape of the cross sections was determined from a 

discharge range at the Rialto gage on the Hatchie River. Elevations were 

determined by adjustments using the valley slope. Widths were adjusted 

using aerial photographs. 

The 37-mile-long Ohio River segment was based on a Louisville District 

HEC-2 model. Cross sections in this model were surveyed in the 

mid-1960s. The Ohio River is relatively stable and has not experienced 

significant bed changes since 1960, which justifies use of the 1960s survey 

data. However, it is recommended that more recent survey data be 

obtained for the Ohio River, especially, for any detailed study of reaches in 

the vicinity of the confluence of the Ohio and Mississippi Rivers. The 

purpose of the Ohio River segment in the HEC-6T model was to provide 

sediment inflow to the Mississippi River. Data are insufficient for 

calibration of the Ohio River Segment, and calculated morphologic 

changes should be treated with caution. 

St. Louis District channel geometry 

The St. Louis District channel cross sections came from the 1986–1988 

hydrographic survey. The cross sections were obtained between March 

1986 and June 1988. Elevations from the hydrographic survey were 

related to NGVD of 1929.

Dike Fields 

Southwest Pass 

The dike fields in Southwest Pass consist of pile dikes. The dimensions and 

stationing of these dikes were taken from drawings and information 

provided by the New Orleans District General Engineering Branch and 

Civil Branch Channel Stabilization Section. In addition, the pile dike 

locations and lengths were verified using the 1991–1992 Mississippi River 

Hydrographic Survey. All of the pile dikes were originally built to elevation 

of +6.0 ft (NGVD). The dikes were coded in the geometry to this elevation. 

Cross-section geometry was adjusted to account for the effects of the dikes. 

The dikes were coded into the model using a 1:1 contraction rate and a 1:4 

expansion rate. These rates were taken from the 2001 HEC-RAS Reference 

Manual (HEC 2001) for general modeling guidelines for modeling bridges. 

The coefficients for contraction and expansion losses, 0.1, and 0.3, 

respectively, were also taken from the HEC-RAS Reference Manual.
MRG&P Report No. 30 13

Dikes in New Orleans District 

There are three crossings with dike fields in the New Orleans District. 

These dike fields are located in the Medora Crossing, Red Eye Crossing, 

and Smithland Crossing at Hog Point. The dimensions and stationing of 

the dikes in Medora, Red Eye, and Smithland crossings were taken from 

drawings and information provided by the New Orleans District Civil 

Branch Channel Stabilization Section. These dike locations were also 

verified using the 1991–1992 Mississippi River Hydrographic Survey. As

with Southwest Pass, the dikes were coded into the model using a 1:1 

contraction rate and a 1:4 expansion rate for the affected cross sections. 

The coefficients for contraction and expansion losses were 0.1 and 0.3, 

respectively.

Medora Crossing 

Medora Crossing is located between RMs 211 and 213. There are three 

dikes located within the crossing. The effects of these dikes are felt on 

cross sections 210.8 through 212.2. The dikes are coded from left to right 

beginning at the left descending bank.

The left top of bank begins at the end of the dikes as they extend into the 

channel. Points in the cross section from the 1992 Hydrographic Survey 

whose elevations were higher than those in the dikes’ geometry were 

retained. Points whose elevations were lower than those for the dikes were 

raised to match the dikes’ geometry.

Dike Number 3 is coded into the geometry for cross sections 210.8 and 

211.6 to its crest elevation of +2 feet (ft) (NGVD). Cross section 212 is 

affected by both dikes Numbers 1 and 2. The average length of 460 ft and 

average crest elevation of -7 ft (NGVD) is coded into the geometry for this 

cross section. Dike Number 1 is coded into the geometry of cross section 

212.6 to its crest elevation of -10 ft (NGVD). 

Red Eye Crossing 

Red Eye Crossing is located between RMs 223 and 225. There are six dikes 

located within the crossing. The effects of these dikes are felt on cross 

sections 223.0 through 224.4.
MRG&P Report No. 30 14

The dikes are coded from left to right beginning at the left descending 

bank. The left top of bank begins at the end of the dikes as they extend into 

the channel. Points in the cross sections from the 1992 Hydrographic 

Survey whose elevations were higher than those in the dikes’ geometry 

were retained. Points whose elevations were lower than those for the dikes 

were raised to match the dikes’ geometry.

Dike Number 6 is coded into the geometry for cross section 223.0 to its 

crest elevation of zero ft (NGVD). Dike Number 3 is coded into the 

geometry for cross section 224.1 to its crest elevation of zero ft (NGVD). 

Dike Number 1 is coded into the geometry for cross section 224.4 to its 

crest elevation of -4 ft (NGVD). Dikes Numbers 2, 4, and 5 are not coded 

into the geometry because no cross sections in the model are affected by 

them. 

Smithland Crossing (Hog Point) 

Smithland Crossing is located between RMs 297 and 301. There are five 

dikes and one closure chute located within the crossing. The effects of the 

dikes and chute are felt on cross sections 297.45 through 300.3.

Initially, the cross sections in this reach were modeled using the geometry 

from the 1992 Hydrographic Survey. However, it was determined during 

the calibration phase of the study that changes due to the dikes had not 

occurred when the 1992 hydrographic survey was conducted. Therefore, 

this reach was used during the verification phase of the study to assess the 

numerical model's reliability for predicting degradation. The verification 

analyses are discussed in the section entitled "Degradation at Smithland 

Crossing" in this report. Following the verification phase of the study, the 

2002 cross sections were used through Smithland Crossing.

The dikes are coded from left to right beginning at the left descending 

bank. The left top of bank begins at the end of the dikes as they extend into 

the channel. The chute is coded from right to left beginning at the right 

descending bank. The right top of bank begins at the end of the chute as it 

extends into the river. Points in the cross sections from the 2004 

Hydrographic Survey whose elevations were higher than those in the 

dikes’ and chutes’ geometry were retained. Points whose elevations were 

lower than those for the dikes and chute were raised to match the dikes’ 

and chutes’ geometry.
MRG&P Report No. 30 15

The locations of the dikes that are present in the New Orleans District 

reach of the HEC-6T model are listed in Table 2.

Table 2. Dikes in New Orleans District HEC-6T model, 

Pilots Station (RM -18.0) to Union Point (RM 326). 

Cross Section Dike Field Descending River Bank 

-18.0 Southwest Pass Left and Right

-16.5 Southwest Pass Left and Right

-14.7 Southwest Pass Left and Right

-13.3 Southwest Pass Left and Right

-11.9 Southwest Pass Left and Right

-10.7 Southwest Pass Left and Right

-9.3 Southwest Pass Right

-7.7 Southwest Pass Right

-5.8 Southwest Pass Right

-1.9 Southwest Pass Right

211.6 Medora Dikes Left

212 Medora Dikes Left

212.2 Medora Dike Left

223.0 Red Eye Dikes Left

224.1 Red Eye Dikes Left

224.4 Red Eye Dikes Left

297.45 Smithland Dikes Left

298.1 Smithland Dikes Left

298.9 Smithland Dikes Left

299.5 Smithland Dikes Left

300.3 Smithland Dikes Left

Dikes in Vicksburg and Memphis Districts 

There are numerous dike fields in the Vicksburg and Memphis Districts. 

The list of dikes that were implemented in the HEC-6T model are listed in 

Table 3 and Table 4. Due to the large number of dike fields, the level of 

detail in the Vicksburg and Memphis Districts was not as great as was 

applied in the New Orleans District reach. Cross sections where dikes were 

present in 1992 were modified to reflect the projections of both upstream 

and downstream dikes in the vicinity of the cross section. This is 
MRG&P Report No. 30 16

equivalent to assuming that cross sections in the dike field are filled to the 

top of dike elevations. At the time the HEC-6T model was constructed, it 

was not possible to change the geometry of cross sections to reflect 

changes to existing dikes or construction of new dikes as the simulation 

progressed. Therefore, changes to cross-section geometry due to 

construction in dike fields after 1992 is not simulated in the HEC-6T 

model. Recent enhancement of the HEC-6T model allows for changing 

cross-section geometry during the course of the historical simulation. 

Future studies should take advantage of this option. 

Table 3. Dikes in Vicksburg District HEC-6T Model, Union Point (RM 326) to Rosedale 

(RM 592). 

Cross Section Dike Field 

Descending 

River Bank 

330.61 Jackson Point Left

337.00 Fritz Island Right

346.81 Esperance Point Right

351.12 Opposite Warnicott Landing Left

352.98 Opposite Warnicott Landing Left

357.00 Natchez Island Right

358.63 Natchez Island Right

374.59 Chute Restricted by Waterproof Bar Dikes Right

377.00 Chute Restricted by Waterproof Bar Dikes Right

378.59 Waterproof Bar Right

385.01 Spithead Towhead Left

387.41 Chute Restricted by Browns Field Dikes Right

389.01 Cottage Bed Left

389.01 Browns Field Right

391.40 Chute Restricted by Browns Field Dikes Right

393.00 Bondurant Right

394.61 Bondurant Towhead Right

398.80 Below Grand Gulf Left

402.80 Coffee Point Right

405.18 Upstream from Coffee Point Right

407.62 Yucatan Cutoff Restricted by Closure Dike Right

409.03 Yucatan Cutoff Restricted by Closure Dike Right

415.00 Togo Island Left

429.20 Below Racetrack Left

431.00 Below Racetrack Left

438.39 Chute Restricted by Upstream Dikes Right

440.80 False Point Right
MRG&P Report No. 30 17

Cross Section Dike Field 

Descending 

River Bank 

447.20 Marshall Point Cutoff Right

448.79 Forest Home Towhead Left

451.20 Forest Home Towhead Left

460.80 Willow Cutoff Right

468.97 Arcadia Point Left

470.13 Arcadia Point Left

470.13 Cottonwood Right

471.40 Arcadia Point Left

477.20 Point Lookout Right

478.00 Point Lookout Right

481.06 Ajax Bar Left

483.00 Ajax Bar Left

484.80 Ben Lomond Left

486.40 Ben Lomond Left

487.80 Ben Lomond Left

489.00 Ben Lomond Left

490.80 Baleshed Landing Left

492.69 Baleshed Landing Left

494.59 Baleshed Landing Left

495.59 Cutoff Restricted by Wilson Point Dike 3-R Right

497.20 Cutoff Restricted by Wilson Point Dike 3-R Right

499.59 Wilson Point Right

502.80 Corregidor Left

504.66 Corregidor Left

507.29 Chute Restricted by Cracraft Dike 3-R Right

509.20 Cracraft Right

509.20 Caroline Left

510.00 Cracraft Right

512.80 Leota Left

512.80 Cracraft Right

515.03 Leota Left

515.03 Chute Restricted by Island 86 Dikes Right

516.60 Chute Restricted by Island 86 Dikes Right

518.21 Chute Restricted by Island 86 Dikes Right

518.21 Island 86 Right

521.19 Chute Restricted by Island 86 Dikes Right

522.76 Seven Oaks Right

524.40 Seven Oaks Right

524.40 Walnut Point Left
MRG&P Report No. 30 18

Cross Section Dike Field 

Descending 

River Bank 

526.00 Cutoff Restricted by Refuge Dikes Left

526.00 Anconia Chute Dike Right

527.80 Cutoff Restricted by Refuge Dikes Left

529.20 Refuge Left

532.20 Island 84 Left

533.13 Island 84 Left

535.17 Longitudinal Dikes Right

537.25 Leland Bar Right

538.56 Leland Bar Right

540.38 Leland Neck Left

540.38 Tarpley Cutoff Dikes Right

543.21 Island 82 – Miller Bend Right

544.72 Island 82 – Miller Bend Right/Left

546.83 Ashbrook- Miller Bend Right/Left

549.00 Ashbrook Cutoff Left

560.00 Chute Restricted by Chicot Landing Dikes Right

562.40 Chute Restricted by Chicot Landing Dikes Right

565.19 Chute Restricted by Chicot Landing Dikes Right

569.03 Chute Restricted by Catfish Point Dikes Left

576.21 Chute Restricted by Below Prentiss Dikes Left

578.80 Below Prentiss Left

584.86 Malone Field Right

589.07 Terrene Left

590.40 Terrene Left

591.99 Montgomery Point Towhead Right

Table 4. Dikes in Memphis District HEC-6T Model, Rosedale (RM 592) 

to Cairo (RM 954). 

Cross Section Dike Field 

Descending 

River Bank 

600.10 Smith Point Left

602.95 Henrico Right

606.00 Island 70 Left

607.17 Island 70 Left

610.94 Below Knowlton Right

613.60 Below Knowlton Right

614.58 Below Knowlton Right

616.07 Below Knowlton Right
MRG&P Report No. 30 19

Cross Section Dike Field 

Descending 

River Bank 

621.03 Island 67 Left

623.12 Below Ludlow Left

627.10 Sunflower Left

637.91 Island 62 Right

637.91 Chute Restricted by Closure Dike Left

639.73 Island 62 Right

648.47 Kangaroo Point Right

649.00 Kangaroo Point Right

651.91 Friars Point Left

654.23 Chute Restricted by Upstream Dike Right

656.21 Montezuma Towhead Right

658.06 Montezuma Bar Left

666.01 Chute Restricted by Closure Dike Right

666.01 Prairie Point Right

667.00 Chute Restricted by Closure Dike Right

667.00 Prairie Point Right

668.22 Prairie Point Right

668.22 Flower Lake Left

670.00 St. Francis Towhead Left

676.20 Below Walnut Bend Right

681.00 Bordeaux Point Left

682.06 Bordeaux Point Left

691.40 Chute Restricted by Commerce Dike Left

692.43 Commerce Left

696.80 Porter Lake Right

700.28 Porter Lake Right

702.30 Porter Lake Right

704.08 Pickett Left

710.60 Cat Island Right

711.00 Cat Island Right

719.67 Armstrong Right

723.85 Dismal Point Right

735.90 Hopefield Point Right
MRG&P Report No. 30 20

Cross Section Dike Field 

Descending 

River Bank 

737.00 Robinson Crusoe Right

738.00 Robinson Crusoe Right

738.95 Robinson Crusoe Right

738.95 Loosahatchie Bar Right

740.00 Robinson Crusoe Right

741.00 Above Loosahatchie Left

744.98 Randolph Point Left

748.94 Poker Point Right

752.98 Corona Bar Right

756.97 Densford Left

766.90 Below Richardson Landing Left

770.60 Lookout Bar Right

772.76 Lookout Bar Right

783.50 Plum Point Left

784.00 Plum Point Left

788.13 Keyes Point Left

790.00 Keyes Point Left

792.10 Keyes Point Left

792.10 Kat Aubrey Right

796.01 Ashport Goldust Right

800.04 Forked Deer Left

803.84 Island 25 Right

807.79 Nebraska Point Left

812.44 Below Tamm Bend Left

818.00 Wrights Point Right

819.39 Wrights Point Right

820.80 Wrights Point Right

823.46 Chute Restricted by Island 21 Dike Left

828.24 Head of Island 21 Left

831.72 Island 20 Right

835.86 Island 18 Towhead Left

839.82 Caruthersville - Linwood Bend Right

841.50 Tennemo Left
MRG&P Report No. 30 21

Cross Section Dike Field 

Descending 

River Bank 

841.50 Caruthersville - Linwood Bend Right

844.20 Caruthersville - Linwood Bend Right

846.40 Opposite Caruthersville Left

847.96 Sandy Hook Dike #2 Right

851.97 Hathaway Left

851.97 Robinson Bayou Right

864.70 Below Cherokee Left

869.08 Steward Towhead Right

872.40 Steward Towhead Right

873.04 Ruddles Point Dikes Right

874.20 Ruddles Point Dikes Right

880.00 Island 11 Right

881.89 Island 11 Right

885.40 Kentucky Point Left

886.40 Kentucky Point Left

887.20 Kentucky Point Left

888.20 Chute Restricted by Dike Left

895.00 Hotchkiss Bend Right

899.27 Below Island 9 Left

903.45 Donaldson Point Right

905.60 Donaldson Point Right

914.60 Below Island 7 and 8 Right

915.59 Below Island 7 and 8 Right

925.00 Below Williams Left

927.50 Moore Island Right

944.75 Island No. 1 Left

944.75 Pritchard Dikes Right

947.40 Island No. 1 Left

949.00 Island No. 1 Left

Hydrographs 

Discharge hydrographs are simulated in the numerical model by a series of 

steady-state events. The duration of each event is chosen such that the 
MRG&P Report No. 30 22

changes in bed elevation, due to deposition or scour, do not significantly 

change the hydraulic parameters during that event. In this study, 

computational time-steps of one day were used. A one-day time-step is not 

necessary to meet the requirement of insignificant bed change but was 

chosen for convenience because available data were reported as mean 

daily flows.

The approach used in HEC-6T approximates unsteady flow by stepping 

through a time-sequence of steady discharges. This method does not take 

into consideration flow routing or backwater storage effects, introducing 

the potential for timing issues in flow propagation through the model. 

Thus, HEC-6T may not be appropriate for predicting flood hydrographs 

and stages, but experience has shown that it is successful in predicting 

long-term sedimentation processes. 

Reported daily discharges are available at several gages within the study 

reach. The 12-year discharge hydrographs at Hickman, Vicksburg, and 

Tarbert Landing, between October 1990 and September 2002, are shown 

in Figure 3. 

Figure 3. 1991–2002 hydrograph. 

Uncertainty is associated with the choice of discharge data for the inflow 

hydrograph because there are discrepancies in the reported data. Continuity 

of the discharge record is inconsistent with both time and distance. 

Discrepancies in reported discharge volumes, between October 1990 and 

September 2002, at various points on the Mississippi River are listed in 

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1,800,000

2,000,000

1-Oct-90 1-Oct-91 30-Sep-92 30-Sep-93 1-Oct-94 1-Oct-95 30-Sep-96 30-Sep-97 1-Oct-98 1-Oct-99 30-Sep-00 30-Sep-01 1-Oct-02 Discharge CFS

Hickman

Vicksburg

Tarbert Landing
MRG&P Report No. 30 23

Table 5. The total volumes listed in Table 5 were calculated from USGS or 

USACE annual and mean daily discharge data. The 12-year volume of water 

flowing past Thebes on the Mississippi River above Cairo is approximately 

2 percent greater than the combined volumes for the Mississippi River at 

Chester and from the Big Muddy River. Big Muddy discharges had to be 

estimated from upstream gages, and local inflow could account for some of 

the difference. The 12-year volume of water passing Memphis is consistent 

with the sum of the flow volumes from the Mississippi River at Thebes, the 

Ohio River at Metropolis, and the Obion and Hatchie Rivers. There is 

approximately a 4 percent loss in flow volume at Helena when compared to 

the sum of Memphis and St. Francis River flows. The 12-year volume of 

water passing Arkansas City is consistent with the sum of the flow volumes 

from the Mississippi River at Helena and the White and Arkansas Rivers. 

There is approximately a 2 percent increase in flow volume at Vicksburg 

when compared to the sum of Arkansas City and Yazoo River flows. This 

increase helps to balance out the decrease recorded at Helena. Flow past 

Vicksburg and Natchez is relatively consistent. The largest discrepancy is at 

the Old River Control Complex where the sum of reported discharges in the 

Old River Outflow Channel and in the Mississippi River at Tarbert Landing 

is approximately 8 percent higher than the reported discharge upstream at 

Natchez and Vicksburg. 

Table 5. Reported water volume passing Mississippi River and Tributary 

gages, 1991–2002. 

Total Volume 

million acre-feet 

Discrepancy 

with Upstream Gage(s) 

million acre-feet % 

Ohio River 2559

Chester 2122

Big Muddy River 20

Thebes 2188 46 2.15%

Hickman (calculated) 4747

Obion River 22

Hatchie River 33

Memphis 4797 -5 -0.10%

St. Francis River 69

Helena 4679 -187 -3.84%

White River 247
MRG&P Report No. 30 24

Total Volume 

million acre-feet 

Discrepancy 

with Upstream Gage(s) 

million acre-feet % 

Arkansas River 461

Arkansas City 5387 0 0.00%

Yazoo River 179

Vicksburg 5678 112 2.01%

Natchez 5671 -7 -0.12%

Old River Outflow 1340

Tarbert Landing 4770 439 7.74%

Total 398

The discrepancies between reported discharges are not consistent 

annually. As shown in Table 6, there is an annual variation in the 

discrepancies between Natchez and Old River Control Complex and 

Vicksburg and Natchez. The differences between Vicksburg and Natchez 

are insignificant, but the differences between Natchez and Old River 

Control Complex are puzzling. These discrepancies at Old River Control 

Complex produce a conundrum with respect to determining a 

hydrograph for the HEC-6T model. Additional study, which should 

include evaluation of data at the Baton Rouge gage, is recommended to 

address these issues.

Table 6. Annual discrepancy in recorded discharges at gages. 

Water 

Year 

Mean Annual Flow, -cfs Discrepancy 

Mean Annual 

Flow, cfs Discrepancy 

Tarbert+C89* Natchez 

Natchez/ 

Tarbert+C89* Vicksburg 

Vicksburg/ 

Natchez 

1991 775,973 710,782 8.4% 720,087 -1.3%

1992 567,992 544,152 4.2% 548,801 -0.9%

1993 950,403 872,373 8.2% 886,602 -1.6%

1994 817,121 807,858 1.1% 809,301 -0.2%

1995 672,033 629,302 6.4% 612,695 2.6%

1996 673,667 585,902 13.0% 587,385 -0.3%

1997 849,170 749,047 11.8% 751,032 -0.3%

1998 752,027 679,636 9.6% 679,671 0.0%

1999 700,016 638,434 8.8% 638,328 0.0%
MRG&P Report No. 30 25

Water 

Year 

Mean Annual Flow, -cfs Discrepancy 

Mean Annual 

Flow, cfs Discrepancy 

Tarbert+C89* Natchez 

Natchez/ 

Tarbert+C89* Vicksburg 

Vicksburg/ 

Natchez 

2000 426,175 427,524 -0.3% 416,737 2.5%

2001 555,901 523,638 5.8% 519,355 0.8%

2002 695,422 651,952 6.3% 665,697 -2.1%

2003 649,492 605,962 6.7% 616,508 -1.7%

2004 685,139 635,481 7.2% 645,596 -1.6%

2005 701,797 676,948 3.5% 682,081 -0.8%

2006 406,762 403,920 0.7% 396,292 1.9%

2007 616,545 638,307 -3.5% 630,790 1.2%

2008 846,169 804,268 5.0% 799,308 0.6%

2009 695,614 696,099 -0.1% 672,233 3.4%

2010 875,167 885,645 -1.2% 878,661 0.8%

2011 799,482 795,681 0.5% 801,581 -0.7%

*Old River Outflow Channel near Knox Landing

The hydrograph used in the 2009 interim study of the Mississippi River 

between Vicksburg and Pilots Station was based on the reported 

discharges at Vicksburg. The 12-year hydrograph extended between 1 

October 1990 and 30 September 2002 (Water Years 1991–2002). Initially, 

this hydrograph was adjusted for use in the entire Regional Model study 

reach by setting tributary discharges upstream from Vicksburg as a 

constant percentage of the mean daily discharges at Vicksburg. The 

percentage was based on the percentage of the 12-year total volume of flow 

from the tributary with respect to the 12-year volume of flow at Vicksburg. 

One advantage of this approach is the relative simplicity associated with 

hydrograph development. One significant disadvantage is that the effects 

of high flows on the tributaries at low Mississippi River stages are not 

simulated. The effect of using this simplified hydrograph on sedimentation 

processes is evaluated in this report.

A second hydrograph used in the Regional Model was based on recorded 

mean daily inflows at the boundary gages, which are primarily in the 

Memphis District. Because tributary backwater effects extended as much 

as 100 miles from the Mississippi River, tributary flow could not easily be 

determined from existing tributary stream gages. Long reaches of some 

tributary streams were not included in the current modeling effort because 
MRG&P Report No. 30 26

survey data for tributary streams were limited or non-existent. The initial 

approach adopted for developing model boundary conditions was to limit 

the number of tributary inflow points to tributaries that are expected 

sources of geomorphic change. Here, sources of geomorphic change meant 

locations where observed geomorphic features in the main channel 

resulted from tributary sediment inflows. These features persisted for 10 

or more miles in the Mississippi River. The numerical model included 

inflows for the Ohio, Obion, Hatchie, St. Francis, White, Arkansas, and 

Yazoo Rivers. The model network utilized a representative reach of the 

tributary channel as a boundary condition. Initial flow was estimated from 

historical stream discharge measurement stations located outside zones of 

backwater influence. The resulting inflow hydrograph provided the initial 

flows for model simulation.

After model assembly, annual water volumes and daily discharges were 

compared between model and prototype at measured discharge stations 

along the main-stem Mississippi River in the Memphis District. There was 

good agreement at the confluence of the Ohio and Middle Mississippi 

Rivers. However, downstream control points did not maintain the close 

agreement. Figure 4 highlights the discrepancies between measured and 

calculated daily discharge at Helena. Figure 5 shows the discrepancy 

between measured and calculated total cumulative volumes at Helena. 

These differences may be attributed to measurement error, unsteady flow 

effects and/or to assumptions related to the timing and magnitude of 

tributary inflows. Another possibility for the differences is that some 

reaches of the Mississippi River could lose flow between upstream and 

downstream measurement points. For example, the gage at Memphis, TN,

shows more discharge than observed at the next downstream gage at 

Helena, AR, during some historical periods in the data record (Table 5).

The reason for the decrease in discharge between these two stations is 

unknown. Several hypotheses exist including flow lost to the alluvial and 

deeper aquifers and extensive attenuation due to large backwater areas 

along the lower St. Francis basin. Nonetheless, the current model effort 

required an accurate representation of water in terms of flow rate and 

volume to calculate sediment transport over the simulation period. To 

achieve discharges and volumes that matched measured data along the 

Mississippi main-stem in the Memphis District, tributary flow magnitudes 

were adjusted to account for variances that resulted from using the quasisteady flow steps that were estimated using tributary stream gauges. The 

modified hydrologic data are shown in Figure 6.
MRG&P Report No. 30 27 

 Figure 4. Prototype and initial model discharge at Helena. 

Figure 5. Prototype and initial model cumulative flow volume at Helena. 

100,000

300,000

500,000

700,000

900,000

1,100,000

1,300,000

1,500,000

1,700,000

Jan1989 Mar1989 May1989 Jul1989 Sep1989 Nov1989 Jan1990 Mar1990 May1990 Jul1990 Sep1990 Nov1990 Jan1991

Date Computed Discharge, cfs

Historical

Model

0

500,000,000

1,000,000,000

1,500,000,000

2,000,000,000

2,500,000,000

3,000,000,000

3,500,000,000

1988 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Date Cumulative Volume, cfs-day

Historical

Initial Model
MRG&P Report No. 30 28

Figure 6. Flow decrease in downstream direction Memphis to Helena Reach. 

Adjusting the tributary discharges in an attempt to better simulate 

recorded Mississippi River discharges in the Memphis District did not 

necessarily provide accurate results at downstream gages. In future 

studies, this approach should be modified to focus on the particular reach 

of the river where project features are to be evaluated. The significant 

discrepancy in reported discharges downstream from the Old River 

Structure suggests that a different hydrograph based on Tarbert Landing 

discharges should be used in the New Orleans District.

Differences in calculated results using the two model hydrographs is not 

confined to just the differences in flow magnitudes. For example, the 

calculated sediment delivery from the Ohio River, during the 1991–2002 

simulation period, is significantly affected by the choice of hydrograph. 

Table 7 shows the different results calculated for 12-years of sediment 

delivery to the Mississippi River from the Ohio River. The calculations 

used the same sediment discharge rating curves with the two model 

hydrographs. Even though the accumulated water inflows are essentially 

the same, the sediment delivery is significantly greater with the 

hydrograph developed from the recorded Ohio River discharges at 

Metropolis and Mississippi River discharges at Chester than with the 

hydrograph based on the average annual percentages of the Vicksburg 

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

900,000

1,000,000

1,100,000

1,200,000

1-Apr-01 1-Jun-01 1-Aug-01 1-Oct-01 1-Dec-01 31-Jan-02 2-Apr-02

Date Computed Daily Discharge, cfs

MS River @ Helena, AR

MS River @ Memphis, TN
MRG&P Report No. 30 29

discharge. It is concluded that studies in the Memphis District should use 

a hydrograph that accounts for the differences in tributary flood peaking. 

Calculated results using both hydrographs are presented in this report. 

These results will be useful in selection of hydrographs for future studies. 

Table 7. Calculated sediment delivery from the Ohio River. 

 

Tributary Flow Based on 

Annual Percentage of 

Vicksburg Discharges 

Tributary Flow Based on 

Adjusted Measured 

Discharges 

Percent of the Delivery 

Lost using Annual 

Percentage of Vicksburg 

Discharges 

acre-feet acre-feet

Clay 214,000 277,000 23

Silt 85,000 118,000 28

Sand 17,000 30,000 43

Water 2,543,000,000 2,558,000,000 1

Distributary flows and flows around islands

Flows out the distributaries in the New Orleans District were calculated as 

a percentage of Mississippi River flow at a station upstream from the 

tributary. The location of this station was a function of the location of 

available data. Simple percentages were used rather than actual measured 

discharges to make model application easier for a wide range of projects 

located up and down the 1000-mile study reach. Future studies related to 

a specific diversion on the Mississippi River may require a more detailed 

treatment of the flow through the diversion or diversions of interest. 

The reference cross section used to determine the distributary discharge in 

HEC-6T is specified on the PM record (PM is a label used within the 

software input properties) by sequence number in the HEC-6T version used 

for this study. Future users are cautioned that values on the PM record need 

to be changed if cross sections are added or deleted from this model. Newer 

versions of HEC-6T eliminate this issue for distributaries (but not return 

flows) by use of the PS record (PS is a label used within the software input 

properties) that directly identifies the reference cross section. 

Southwest Pass 

Four distributaries are included in the HEC-6T numerical model in 

Southwest Pass: Burrwood Bayou (RM -14.4), Outlet W – 2 (RM -9.8), 
MRG&P Report No. 30 30

Joseph Bayou (RM -4.5), and Southwest Pass at Mile 3.0 West (RM -3.0). 

In addition, flow is lost over the natural levees in Southwest Pass during 

flood events. 

The water discharges diverted at each distributary were computed using a 

percentage of the water discharge in the Mississippi River approaching 

that distributary. The percentages were estimated from available 

measured data in Burrwood Bayou. Measurements were made between 

March 2003 and April 2005, so no analysis of variation with respect to 

time could be made. Measured data were not available for the other 

distributaries.

Burrwood Bayou 

Nineteen pairs of flow measurements were made. One measurement was 

in the Burrwood Bayou diversion, and the other was in Southwest Pass just 

upstream of the diversion. The diverted discharge was expressed as a 

percentage of the approaching flow. These measurements were made 

between March 2003 and April 2005 in conjunction with repair of a stone 

closure dike constructed as a result of a blowout through the distributary. 

Only nine of the measurements were taken with the closure structure in 

place. These nine measurements showed no apparent trend between the 

percentage of flow diverted and upstream discharge. Therefore, the 

percentages were simply averaged giving a value of 12 percent. No other 

measurements are available, so 12 percent was used in the HEC-6T model. 

Outlet W-2 and overbank flows

There were no available flow measurements in Outlet W-2. It was 

therefore assumed that the diverted flow percentages at Burrwood Bayou 

and Outlet W-2 could be directly related to the widths of the outlets. Using 

this assumption, 7 percent of the upstream flow in Southwest Pass is 

diverted through Outlet W-2.

No data were available for other time periods, so the 7 percent diversion 

percentage was used in the HEC-6T model. 

During floods, water flows over the natural levees in Southwest Pass into 

East Bay and West Bay. There were no measurements available to estimate 

the magnitude of this overbank flow. However, a TABS-2 two-dimensional 

(2D) numerical model study was conducted at the USACE Waterways 
MRG&P Report No. 30 31

Experiment Station (Richards and Trawle 1988) in which overbank flow 

from Southwest Pass was calculated. Using results from that study, 

overbank flow percentages were estimated for flood conditions and 

assigned to Outlet W-2. This is the same approach employed in two 

previous numerical sedimentation studies in Southwest Pass (Copeland 

1991; Copeland and Thomas 1992). In these studies, overflow discharges 

were determined to be 2 percent of the discharge Above Venice when the 

Above Venice discharge was 900,000 cubic feet per second (cfs) and 5 

percent of the discharge Above Venice when the Above Venice discharge 

was 1,300,000 cfs. Converting these percentages to percentage of flow 

above Outlet W-2 and considering the changes in distributary flow 

distribution that occurred since 1992, the combined Outlet W-2 and 

Southwest Pass overbank flows were 7 percent of the upstream flow when 

the upstream flow was 300,000 cfs or less, 10 percent of the upstream 

flow when the upstream flow was 400,000 cfs, and 19 percent of the 

upstream flow when the upstream flow was 500,000 cfs or greater. 

Joseph Bayou 

There were no available flow measurements in Joseph Bayou. It was 

therefore assumed that the diverted flow percentages at Burrwood Bayou 

and Joseph Bayou could be directly related to the widths of the outlets. 

Using this assumption, 12 percent of the upstream flow in Southwest 

Pass is diverted through Joseph Bayou. No data are available for other 

time periods, so the 12 percent diversion percentage was used in the 

HEC-6T model.

Southwest Pass at Mile 3.0 West 

There were no available flow measurements in this distributary. It was 

therefore assumed that the outflow that was measured at Burrwood Bayou 

could be directly related to the distributary at RM -3.0 by using the width 

ratio of the two outlets. Using this assumption, 4 percent of the flow 

entering Southwest Pass is diverted through the distributary at RM -3.0. 

No data are available for other time periods, so the 4 percent diversion 

percentage was used for all time periods in the HEC-6T model. 

The percentage of upstream flow diverted out of the four Southwest Pass 

distributaries in the HEC-6T model is listed in Table 8.
MRG&P Report No. 30 32

Table 8. Outflow from Southwest Pass distributaries, percentage of discharge immediately 

upstream from Diversion. 

Above Venice to Head of Passes 

Four distributaries are included between the Above Venice discharge 

range at RM 12 and Head of Passes: combined South Pass and Pass a 

Loutre (RM 0.0), Cubits Gap (RM 3.0), Grand Pass (RM 10.5), and 

Baptiste Collette (RM 11.5). In addition, flow is lost over the natural levees 

in this reach. West Bay Diversion (RM 4.9) was not opened until 2004 and 

is not included in the 1992–2002 calibration simulations.

Flows that are diverted through the various distributaries in this reach 

were treated as a percentage of the Mississippi River discharge at the 

Above Venice discharge range. The diversion percentages at Cubits Gap 

and Head of Passes were calculated from measurements made between 

1979 and 2004. Measurements made between 1979 and 2006 were used 

for Grand Pass and Baptiste Collette. 

Between 1979 and 2004, there were 28 sets of measurements at two 

ranges in the Mississippi River: the Above Venice Discharge Range and the 

Pilottown Discharge Range at RM 2.0. Discharges in Baptiste Collette, 

Grand Pass, Cubits Gap, Pass a Loutre, South Pass, and Southwest Pass 

were also included in these measurements. Measurements at RM 2.0 were 

used to check flow continuity with respect to inflow at the Above Venice 

discharge range and outflow at Baptiste Collette, Grand Pass and Cubits 

Gap. If an error greater than 10 percent was found, then data from that set 

were not included in the analysis. This left 23 measurements that satisfied 

the continuity requirement. 

Data collected between 2005 and 2006 at Grand Pass and Baptiste 

Collette were included in the analysis to increase the size of the data base 

Distributary River Mile 

Discharge Upstream from Distributary, cfs 

10,000 300,000 400,000 500,000 

Burrwood Bayou -14.4 12% 12% 12% 12%

Outlet W-2 and Overbank Flows -9.8 7% 7% 10% 19%

Joseph Bayou -4.5 12% 12% 12% 12%

Southwest Pass at Mile 3.0 West -3.0 4% 4% 4% 4%
MRG&P Report No. 30 33

and because these distributaries are upstream from West Bay Diversion, 

and the new diversion’s effect on discharge percentages were deemed to be 

negligible. Inclusion of the 2005–2006 measurements added 16 data 

points to the Grand Pass and Baptiste Collette analysis. 

The data were analyzed to determine trends with both time and discharge 

using linear regression curves in EXCEL to help define trends. The results 

are shown in Table 9 as a percentage of discharge at the Above Venice 

discharge range, and the analysis is discussed in the following paragraphs.

At the time the calibration study was conducted, diversion percentages 

could not be changed over time in the simulation hydrograph. Studies of 

different time periods might require modification of the average 

percentage values. If new diversions are added to this reach (e.g., West Bay 

Diversion), flow percentages will need to be modified so that the 

percentages reflect conditions immediately upstream from the distributary 

rather than in the Mississippi River at the Above Venice discharge range. 

Table 9. Distributary outflow between Above Venice and Head of Passes. 

Distributary 

River 

Mile 

Discharge at Above Venice Discharge Range, cfs 

50,000 200,000 600,000 1,000,000 1,300,000

South Pass and Pass a Loutre 0.0 30% 30% 26% 23% 23%

Cubits Gap and Overbank 

Flows 3.0 14% 14% 14% 17.5% 22%

Grand Pass 10.4 13% 13% 11% 9% 9%

Baptiste Collette 11.4 11% 11% 11% 11% 11%

South Pass and Pass a Loutre 

Outflow through South Pass and Pass a Loutre was combined and treated 

as a single distributary in the HEC-6T numerical model. Figure 7 shows 

the variations in the flow percentage out combined South Pass and Pass a 

Loutre with time and discharge. Figure 7 suggests a significant decrease in 

distributary flow percentage with time. However, there were only four 

measurements between 1979 and 1990. There were only six measurements 

taken during the 1991–2002 calibration period. Thirteen measurements 

taken between 2003 and 2004 indicate a continuing decrease in the 

combined flow percentage out South Pass and Pass a Loutre. This 

continuing decrease may be due to the disposal of dredged material in 
MRG&P Report No. 30 34

Pass a Loutre, or a change in dredging practices in South Pass and 

Southwest Pass. The linear regression lines shown in Figure 7 also show a 

decrease in combined flow percentage out the distributaries with an 

increase in discharge at the Above Venice discharge range, although 

measured high flows do not appear to follow this trend. 

The flow distribution percentages for the combined flows through South 

Pass and Pass a Loutre were varied with discharge in the HEC-6T model. 

The percentages are from the linear regression line labeled 1996–2002 in 

Figure 7.

Studies of different time periods may require modification of the flow 

distribution percentages. If new diversions are added to this reach (e.g., 

West Bay Diversion), flow percentages will need to be modified so that the 

percentages reflect conditions immediately upstream from the 

distributaries rather than in the Mississippi River Above Venice. 

Figure 7. Measured Above Venice discharge in Pass a Loutre and South Pass. 

Cubits Gap and overbank flows 

The measured data at Cubits Gap show a relatively constant relationship 

between the distributary discharge and time and Above Venice discharge. 

A constant distributary percentage of 14 percent of the Above Venice 

10

15

20

25

30

35

40

45

50

55

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000

Discharge CFS Percent of Discharge Above Venice

WY1979-84

1990

WY1996-2002

WY2003-04

HEC-6T
MRG&P Report No. 30 35

discharge was assigned for Cubits Gap. Figure 8 shows the variations in 

flow percentage out Cubits Gap with time and Above Venice discharge. If 

new diversions are added to this reach (e.g., West Bay Diversion), flow 

percentages will need to be modified so that the percentages reflect 

conditions immediately upstream from the distributary rather than in the 

Mississippi River Above Venice.

During floods, water flows over the natural levees between Venice and 

Head of Passes. There were no measurements available to estimate the 

magnitude of this overbank flow. However, a TABS-2 2D numerical model 

study was conducted at the USACE Waterways Experiment Station 

(Richards and Trawle 1988) in which overbank flow was calculated. Using 

results from that study, overbank flow percentages were estimated for 

flood conditions and assigned to Cubits Gap. This is the same approach 

employed in two previous numerical sedimentation studies in this reach of 

the Mississippi River (Copeland 1991; Copeland and Thomas 1992). In 

these studies, overflow discharges were determined to be 5 percent of the 

discharge Above Venice when the Above Venice discharge was 900,000 cfs 

and 12 percent of the discharge Above Venice when the Above Venice 

discharge was 1,300,000 cfs. Adjusting these percentages to account for 

the changes in distributary flow distribution upstream that has occurred 

since 1992, the combined Cubits Gap distributary and overbank flows were 

16 percent of the discharge at Above Venice when the Above Venice flow 

was 900,000 cfs and 22 percent of the discharge at Above Venice when the 

Above Venice flow was 1,300,000 cfs. 
MRG&P Report No. 30 36

Figure 8. Measured Above Venice discharge in Cubits Gap. 

Grand Pass (The Jump) 

Measurements taken between 2005 and 2006 were included in the 

analysis of flow distribution out Grand Pass because this distributary is 

upstream from West Bay, and West Bay’s effect on diversion percentages 

was deemed to be negligible. However, subsequent AdH modeling (Sharp 

et al. 2013) indicated that the West Bay diversion has reduced flows into 

Grand Pass due to a reduction in head. The reduction was described but 

not quantified and may be small. Additional measurements should be 

taken to better estimate future diversion percentages at Grand Pass.

The measured data at Grand Pass show an increasing trend in the 

distributary discharge with time, expressed as a percentage of Above 

Venice discharge, between 1979 and 2006. The measured data also show a 

decreasing trend in the distributary discharge, expressed as a percentage 

of the Above Venice discharge, with increasing discharge Above Venice. 

Figure 9 shows the variations in flow percentage out Grand Pass with time 

and Above Venice discharge.

The average flow distribution percentages for Grand Pass were varied with 

discharge in the HEC-6T model. The percentages correspond to an average 

of all the data shown in Figure 8. 

0

5

10

15

20

25

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000

Discharge CFS Percent of Discharge Above Venice

1984

WY1990-2002

WY 2003-2004

HEC-6T
MRG&P Report No. 30 37

Figure 9. Measured Above Venice discharge in Grand Pass. 

Baptiste Collette 

Measurements taken between 2005 and 2006 were included in the 

analysis of flow distribution out Baptiste Collette because this distributary 

is upstream from West Bay, and West Bay’s effect on diversion 

percentages was deemed to be negligible. This added significantly more 

data points to the analysis. The measured data at Baptiste Collette show an 

increase in the distributary discharge after 1997. However, the measured 

data also show a relatively constant relationship between the distributary 

discharge and the discharge at the Above Venice discharge range after 

1997. The measured variations in flow percentage out Baptiste Collette 

with time and Above Venice discharge are shown in Figure 10.

A constant distributary percentage of 11 percent of the Above Venice 

discharge was assigned for Baptiste Collette in the HEC-6T model for the 

calibration study. Studies of different time periods will require 

modification of the flow distribution percentages in Baptiste Collette.

4

6

8

10

12

14

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000

Discharge cfs Percent of Discharge Above Venice

WY1979-84

WY1990-91

WY1997-2002

WY2003-06

HEC-6T
MRG&P Report No. 30 38

Figure 10. Measured Above Venice discharge in Baptiste Collette. 

Tarbert Landing to Above Venice discharge range 

Four distributaries are included between the Above Venice discharge 

range and Tarbert Landing: Bohemia Spillway (RMs 33 - 45), Caernarvon 

(RM 81.4), Bonnet Carré Diversion Structure (RMs 127– 129) and the 

Morganza Spillway (RM 280). Davis Pond Diversion (RM 118.4) was not 

opened until March 2002 and is not included in the 1992–2002 

calibration simulations.

Flow diversion discharges for the Bohemia Spillway and the Caernarvon 

diversion structure were determined as a percentage of the Mississippi 

River discharge immediately upstream from the diversions. Flow diversion 

discharges for the Bonnet Carré and Morganza Spillways were determined 

as a percentage of the flow at Tarbert Landing. 

Bohemia Spillway 

The Bohemia Spillway extends for 12 miles along the left descending bank 

of the Mississippi River between RMs 33 and 45. It is a constructed feature 

of the Mississippi River and Tributaries Project, but it has not been 

maintained. Flow presently occurs over the spillway during flood flows. It 

was determined from the analysis that flow over the spillway commenced 

2

4

6

8

10

12

14

16

18

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000

Discharge CFS Percent of Discharge Above Venice

WY1979-84

WY1990-91

WY1997-2002

WY2003-2006

HEC-6T
MRG&P Report No. 30 39

when the Mississippi River flow exceeded 927,000 cfs. The maximum 

river flow approaching the Bohemia Spillway is 1,250,000 cfs. It is 

controlled by operations at the Old River Control Complex, Morganza 

Spillway, and Bonnet Carré Spillway. Therefore, the computation of 

outflows at the Bohemia Spillway was made for river flows between 

937,000 cfs and 1,250,000 cfs.

Diversion percentages were calculated using the broad-crested weir 

equation. The weir heights in these calculations were determined by 

superimposing the left outer bank elevations over water surface profiles 

determined from stage gage records. The bank elevations were taken 

from the 1992 Hydrographic Survey. Water surface profiles were 

determined from recorded stages at West Pointe A La Hache, Port 

Sulphur, and Empire. The profiles were taken on dates that correspond 

to discharges of 800,000 cfs, 1,000,000 cfs, and 1,250,000 cfs at Tarbert 

Landing. Discharges were calculated incrementally along the spillway 

using the equation Q = CLH3/2, with C = 3.0. The calculated discharge for 

the project flood, 1,250,000 cfs, was approximately 50,000 cfs or 4 

percent of the river discharge approaching RM 45. 

There are four cross-sections in the model for the spillway. These cross 

sections extend from RM 33 to RM 45. The 50,000 cfs was divided into four 

1.0 percent diversions — one increment for each of the four cross sections. 

Caernarvon 

The Caernarvon Diversion Structure is located at RM 81.4. Flow through the 

Caernarvon Diversion Structure is controlled and is not a unique function of 

Mississippi River discharge. For the calibration study, it was assumed that 

the gates would remain opened during the simulation. Flow through the 

diversion was calculated as a function of the Mississippi River stage, head 

loss through the structure with the gates open, and tailwater downstream 

from the structure. A maximum flow of 6,000 cfs was allowed.

Controlled conditions are not compatible with the HEC-6T option of 

assigning a percentage to determine the diversion discharge. However, for 

the systematic study purpose, the unique relationship is adequate. For 

studies relating to the operation of the Caernarvon Diversion Structure 

and its effect on downstream conditions and/or sediment delivery to the 

Gulf of Mexico, more detailed definition of diversion flows in the 

numerical model hydrograph is required.
MRG&P Report No. 30 40

A tailwater rating curve for the structure was derived from stage-discharge 

gage data in the outflow channel from the period of record between 

January 2001 and December 2006 and is shown in Figure 11. Discharges 

ranged between 6,000 and 500 cfs. The stage data were converted from 

NAVD88 to NGVD29. Differential heads for 100 percent gate openings 

were determine from the discharge rating curve found in the Caernarvon 

Design Memorandum. The differential heads were added to values from a 

polynomial regression curve of the tailwater stage-discharge data to obtain 

a headwater stage-discharge rating curve through the structure.

Figure 11. Caernarvon tailwater rating curve, 2001–2006. 

A stage-discharge curve in the Mississippi River at the Caernarvon 

Diversion Structure was developed from January-December 2001 stage 

data at Algiers Lock and Braithwaite and January-December 2001 

discharge data at Tarbert Landing. Trend lines were computed through 

each data set. The stage for the riverside at Caernarvon was interpolated 

between those trend lines. The trend lines and the interpolated rating 

curve are shown in Figure 12. Maximum flow upstream from Caernarvon 

is 1,250,000 cfs and is controlled by operations at the Old River Control 

Complex, Morganza Spillway, and Bonnet Carré Spillway. 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

Caernarvon Discharge (cfs) Caernarvon Stage (ft, NGVD)
MRG&P Report No. 30 41

Figure 12. 2001 Stage-discharge rating curve Mississippi River at Caernarvon Inlet. 

The Mississippi River discharges at Tarbert Landing that are required to 

achieve specified discharges through the Caernarvon Diversion Structure 

are shown in Table 10. Specified discharges through Caernarvon are in the 

first column. The headwater elevations required for those discharge are 

shown in the fourth column. The Mississippi River flows required to provide 

the headwater elevations were read from the interpolated rating curve in 

Figure 12 and recorded in the fifth column. For example, the headwater 

elevation required to provide a diversion flow of 1,000 cfs is 1.8 ft. The 

Tarbert Landing discharge required to provide that head is 190,000 cfs. 

Expressing those discharges as a percent gives a diversion coefficient of 0.5 

percent. When the Mississippi River discharge is 430,000 cfs, the head at 

Caernarvon is 3.7 ft. This will provide a diversion discharge of 6,000 cfs, 

and that is 1.4 percent of the Mississippi River flow. As the Mississippi River 

discharge increases above 430,000 cfs, the diverted percentage must 

decrease because the maximum discharge from Caernarvon is 6,000 cfs. 

The resulting diversion coefficients are shown in Figure 13. 

0

2

4

6

8

10

12

14

100 200 300 400 500 600 700 800 900 1000

Tarbert Discharge (cfsx1000) Stage (ft, NGVD)

Braithwaite 

Algiers Lock

Caernarvon

Poly. (Braithwaite )

Poly. (Algiers Lock)

Poly. (Caernarvon)
MRG&P Report No. 30 42

Table 10. Calculated headwater upstream from Caemarvon Diversion Structure. 

Discharge through 

Structure (cfs) 

Tailwater 

NGVD (ft) 

Head Differential 

(ft) 

Headwater 

NGVD (ft) 

Discharge 

Mississippi River 

(cfs) 

6,000 2.8 0.9 3.7 430,000

5,000 2.55 0.7 3.25 385,000

4,000 2.3 0.55 2.85 340,000

3,000 2.05 0.4 2.45 290,000

2,000 1.8 0.3 2.1 240,000

1,000 1.6 0.2 1.8 190,000

500 1.5 0.1 1.6 <190,000

Figure 13. Percentage of upstream discharge diverted at Caernarvon. 

Bonnet Carré and Morganza Spillways 

Flows over the Bonnet Carré and Morganza Spillways only occur when 

discharge upstream exceeds 1,250,000 cfs and 1,500,000 cfs, respectively. 

The Bonnet Carré structure is operated such that the downstream discharge 

does not exceed 1,250,000 cfs, and the Morganza Spillway is operated such 

that the downstream discharge does not exceed 1,500,000 cfs. Diversion 

percentages at Bonnet Carré and Morganza were assigned in the numerical 

model to match the operation schedule. The flow diversion percentages are 

0.00%

0.20%

0.40%

0.60%

0.80%

1.00%

1.20%

1.40%

1.60%

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300

Upstream Discharge 1000 CFS Percent Diverted 
MRG&P Report No. 30 43

calculated in the numerical model as a function of the Tarbert Landing 

discharge as shown in Figure 14. The Morganza Spillway was not operated 

during the 1992–2002 calibration simulation. 

Figure 14. Tarbert Landing discharge diverted at Morganza and Bonnet Carré. 

Old River Complex 

The Old River Complex is operated to maintain a Congressionally mandated 

30- to 70-percent split of both water and sediment between the Atchafalaya 

River at Simmesport and the Mississippi River at Tarbert Landing, 

respectively. The fraction of Mississippi River flow above Old River diverted 

through the complex is a function of several factors, including the 

discharges in the Red River and the Mississippi River, hydropower demand, 

the state of the river bed (e.g., bathymetry and bed material gradation), the 

shape of the hydrograph, and the distribution of the flow allocated to each 

diversion structure. There is no simple rule curve to predict the diversion 

percentage through the individual structures. The poor relationships 

between diversion percentages and Mississippi River discharge are shown 

in Figure 15. Historical diversion discharges are available and could have 

been used in the model calibration. However, future daily diversion 

percentages cannot be predicted. Model diversion percentages should be 

determined using the same methodology in both the calibration and 

predictive phase of the study. 

0

5

10

15

20

25

30

1,000,000 1,250,000 1,500,000 1,750,000 2,000,000

Discharge at Tarbert Landing CFS Percent Diverted

Morganza

Bonnet Carre
MRG&P Report No. 30 44

The study purpose was to provide a numerical model that could determine 

long-term sediment trends over the entire 1000-mile reach of the 

Mississippi River between the Gulf of Mexico and Cairo, IL, and to provide 

a model that can be used to evaluate the effect of particular project design 

modifications at a specific location on the entire Lower Mississippi River 

system. Detailed diversion percentages at the Old River Complex are not 

required to meet study objectives and are only necessary for specific 

studies relating to operation of the complex itself. For the general case, 

average historical diversion percentages are appropriate.

Average historical percentages for flow distribution through the Auxiliary 

Structure, Low Sill Structure, Old River Spillway, and Hydropower 

Structure were determined from reported daily discharges for 1991–2002 

and for May-June 2011. There was no flow over the Old River Spillway 

during this period. Averages were determined for three distinct discharge 

ranges — 100,000 to 800,000 cfs; 800,000 to 1,600,000 cfs; and 

1,600,000 to 2,200,000 cfs. An average trend line was determined for the 

combined flow from the Auxiliary and Low Sill Structures, and then a 

straight average of the flow fraction within each data range was used to 

determine Auxiliary and Low Sill fractions. The daily data points and the 

average trend line are shown in Figure 15. Percentages used in the HEC-6T 

model are tabulated in Table 11. 

Figure 15. Flow distribution at Old River, 1991–2002 and 2011 Flood. 

0

0.05

0.1

0.15

0.2

0.25

0.3

0 500,000 1,000,000 1,500,000 2,000,000 2,500,000 Fraction

Discharge at Union Point CFS

Hydropower

Aux +Low Sill

Average Hydro

Average Aux +Low Sill
MRG&P Report No. 30 45

Table 11. Outflow at Old River distributaries, percentage of Union Point discharge. 

Water temperature 

The assigned water temperatures in the numerical model were based on 

measurements reported by the USGS on its water quality web site. 

Temperature data were typically collected at the same time that sediment 

data were collected and are inadequate for determining daily values for 

water temperature. Average monthly values were determined from the 

available data at model inflow boundaries to account for seasonal 

variations in water temperature. Mean monthly temperatures for the Ohio 

River and the Mississippi River at Thebes are listed in Table 12. Also 

shown in Table 12 are the reported mean monthly temperatures at Tarbert 

Landing. This comparison demonstrates the seasonally and longitudinal 

variability in water temperature.

Table 12. Average monthly water temperatures, 1992–2002. 

Month 

Ohio River 

at Dam 53 

Mississippi 

River 

at Thebes 

Mississippi River 

at Tarbert Landing 

January 42.0 41.0 43.9

February 42.3 38.8 44.5

March 48.7 44.8 50.4

April 55.5 54.3 59.6

May 68.6 66.1 67.4

June 76.4 73.5 76.0

July 83.9 82.3 83.9

August 83.6 81.6 84.4

September 80.6 77.7 80.7

October 65.8 64.0 67.8

November 54.9 46.9 58.1

December 47.4 39.2 50.2

Distributary River Mile 

Discharge at Union Point, cfs 

100,000 800,000 1,600,000 2,200,000

Auxiliary Structure 312 4.0% 4.0% 6.8% 3.7%

Low Sill Structure 314.6 0.6% 0.6% 3.9% 17.0%

Old River Spillway 315.2 0 0 0 0

Hydropower 

Structure 315.9 17.6% 17.6% 8.6% 7.2%
MRG&P Report No. 30 46

Downstream water-surface elevations 

Stages at the end of Southwest Pass and routed discharges from Tarbert 

Landing show no stage-discharge correlation. Therefore, downstream 

water-surface elevations at Pilots Station in Southwest Pass (RM -18.0) 

were set based on average monthly stages. This is consistent with the 

approach taken in two previous studies (Copeland 1991; Copeland and 

Thomas 1992.) The simplifying assumption of an average monthly stage at 

the downstream boundary of the model is adequate for purposes of the 

generalized model developed in this study. However, studies of specific 

morphologic changes in the Mississippi River below Belle Chasse, 

especially in response to river diversions, may require a more detailed 

description of the downstream stages.

National Oceanic and Atmospheric Administration (NOAA) tide gage data 

were used to determine the average monthly stages at Pilots Station due to 

inconsistencies discovered in the USACE reported stage elevations in 

Southwest Pass. These inconsistencies are shown in Figure 16, which 

shows plots of reported daily stages versus routed discharges from Tarbert 

Landing for water years 1991 and 1992. A comparison of linear regression 

curves for the gages shows stages at East Jetty (RM -20.6) and Mile 9.2 

(RM -9.2) to be higher than stages at Head of Passes (RM 0.0) and Venice 

(RM 10.7) for low discharges. The physically possible progression of stage 

elevations where water surface increases in an upstream direction does not 

occur until discharges at Tarbert Landing exceed 1,100,000 cfs. Therefore, 

the East Jetty and Head of Passes gage data were not used in this study.

Figure 16. Southwest Pass and Venice, 1991–1992, stage-discharge rating curves. 

0.00

1.00

2.00

3.00

4.00

5.00

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 DISCHARGE @ TARBERT (CFS) STAGE (FT, NGVD)

East Jetty Mile 9.2 HOP

Venice
MRG&P Report No. 30 47

NOAA tide gage data were obtained from http://tidesandcurrents.noaa.gov. Data 

from Pilots Station East, Southwest Pass, LA (Station 8760922), which is 

located at the downstream boundary of the numerical model, were 

available for the months between September 2004 and September 2008. 

Data from Pilot Station, Southwest Pass, Louisiana (Station 8760943) 

were available the months between November 1996 and December 1998 

and for the months between September 2002 and February 2004. The 

nearest station with a complete record between 1992 and 2008 was Grand 

Isle, East Point, LA (Station 876174). As shown in Figure 17, 2004 to 2008 

average monthly stages at Pilots Station East correlated well to average 

monthly stages from Grand Isle East Point. The favorable correlation did 

not seem to be affected by the fact that mean sea level (MSL) at Pilots 

Station East was based on the 1983–2001 epoch and MSL at Grand Isle 

East Point was based on the 2002–2006 epoch. The 1997–1998 average 

monthly stages at Pilot Station did not correlate as well to average monthly 

stages at Grand Isle East Point. Therefore, the data from Pilot Station were 

dropped from further consideration. Due to the good correlation with the 

2004–2008 average monthly stages at Pilots Station East, the 1992–2002 

data at Grand Isle East Point were used to determine average monthly 

stages for the HEC-6T calibration runs. Data from Pilots Station East can 

be used for simulations starting in water year 2005.

Figure 17. Average monthly stages in Southwest Pass and at Grand Isle East. 

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

1 2 3 4 5 6 7 8 9 10 11 12

Month Elevation Feet MSL

97-98 Pilot Sta

97-98 Grand Isle 

04-08 Pilots Sta East

04-08 Grand Isle

92-02 Grand Isle

92-02 East Jetty

Pilots Station and SW Pass MSL 1983-

2001 Epoch

Grand Isle MSL 2002-2006 Epoch

NGVD = MSL + 0.8 ft
MRG&P Report No. 30 48

NOAA Stages are reported in MSL elevation. NGVD29 elevations are 

obtained by adding 0.8 ft to the MSL values. Downstream water-surface 

elevations used in the numerical model are listed in Table 13.

Table 13. Downstream water surface elevations 

at Pilots Station. 

Month 

NGVD 

feet Month 

NGVD 

feet 

January 0.3 July 0.6

February 0.3 August 0.9

March 0.5 September 1.2

April 0.7 October 1.1

May 0.7 November 0.7

June 0.8 December 0.4

Datum and gages 

The datum used in the model is NGVD29. This is the datum used for the 

1991–92 hydrographic survey in the New Orleans District and for the 

stages reported on New Orleans District web site. This is also the datum 

used for the 1988–89 hydrographic survey in the Vicksburg District. Mean 

sea level was used at the datum for the 1988–1989 survey in the Memphis 

District. In Memphis District, mean sea level is theoretically equivalent to 

NGVD29. Stage elevations between 1991 and 2002 reported in Vicksburg 

District Annual Stages and Discharges reports are given in NGVD29. 

Stage elevations from the USACE website RiverGages.com, which includes 

stage gages in all three districts, are also given in NGVD29. Gages used to 

calibrate the model's roughness coefficients are listed in Table 14. 

Table 14. Gages and datum used for water surface calibration. 

 River Mile 

AHP 

Gage Zero 

feet, NGVD29 1 

Venice 10.7 0

Empire 29.5 0

West Pointe a La Hache 48.7 0

New Orleans 102.8 0

Reserve 138.7 0

Donaldsonville 175.4 0

Baton Rouge 228.0 0
MRG&P Report No. 30 49

 River Mile 

AHP 

Gage Zero 

feet, NGVD29 1 

Bayou Sara 265.4 0

Red River Landing 302.4 0

Natchez 363.3 17.28

St. Joseph 396.4 33.12

Vicksburg 435.7 46.23

Lake Providence 487.2 69.71

Greenville 531.1 74.92

Arkansas City 554.1 96.66

Rosedale 595.2 108.73

Helena 663.1 141.70

Memphis 734.7 183.91

Hickman 922.0 264.73

Cairo 955.8 (AHP) 2 270.47

Metropolis 990.5 (AHP) 3 276.60

Thebes 43.7 4 300.00

Chester 109.9 4 341.05

12014 from Rivergages.com

2Ohio RM 978.8 – 2 miles upstream from Mississippi River confluence 

3Ohio RM 944.1 – 37 miles upstream from Mississippi River confluence

4River Miles upstream from Ohio River confluence

Daily stage data are available for most of the gages for the entire 1991–2002 

simulation period. The gage at St. Joseph was discontinued in January 

1996. When daily stages were missing from the record, linear interpolation 

was used to fill in the gaps. 

The only discharge measurements in New Orleans District, for the 

calibration period, are at Tarbert Landing. They were used to develop the 

stage discharge rating curves at all gages in the New Orleans District

In Vicksburg District, discharge measurements were available at Natchez, 

Vicksburg, and Arkansas City during the calibration period. Daily 

discharge estimates, calculated from the measurements, were published in 

annual Stages and Discharges Reports until 1997. Subsequent daily 

discharge estimates are available from the Vicksburg District Water 

Control Branch. The stage-discharge curve at St. Joseph was developed 
MRG&P Report No. 30 50

using an average of the Vicksburg and Natchez calculated daily discharges. 

The stage-discharge curve at Lake Providence was developed using 

calculated daily discharges at Arkansas City that were lagged 1 day. The 

stage-discharge curve at Greenville was developed using calculated daily 

discharges at Arkansas City without any lag. The stage-discharge curve at 

Rosedale was developed using calculated daily discharges at Arkansas City 

and Dam No. 2 on the Arkansas River. The daily discharges on the 

Arkansas River were obtained from the USACE Little Rock District. The 

daily discharge at Rosedale was taken to be the difference between the 

Arkansas City and Dam No. 2 discharges. A 1-day lag was assumed 

between Arkansas City and Rosedale and between Dam No. 2 and 

Arkansas City. 

Discharge measurements are taken at Helena, Memphis, and Hickman. 

Daily discharge estimates, calculated from the measurements, were 

provided by the Memphis District Water Control Office . Discharge data 

were not available at Hickman for 2001 and were not available at Helena 

for 2002. Daily stages are available from USACE website RiverGages.com.

Roughness coefficients 

Model roughness coefficients were initially determined early in the 

calibration phase of the study using the initial cross-section geometry with 

a fixed-bed. The 1991–92 stage data were used to develop regression 

equations at each gage to which roughness coefficients were adjusted. At 

the end of the calibration phase of the study, the calculated water surface 

profiles at the end of the first year of simulation, 1991, and at the end of 

the 12-year simulation, 2002, were compared to average regression curves 

developed from the 12-year measured stage data reported between 1991 

and 2002. These three regression curves were developed to determine if 

there were any obvious aggradation or degradation trends that could be 

identified from the gage data. Changes in the HEC-6T calculated rating 

curves between 1991 and 2002 would suggest aggradation or degradation 

trends in the reach associated with the gage. The annual scatter in the 

measured data makes it difficult to identify any geomorphic trends during 

the calibration period. However, results suggest that there was no 

significant change in the annual rating curves between 1991 and 2002. 

Specific gage analyses were conducted for each gage and are discussed 

later in this report. 
MRG&P Report No. 30 51

It is apparent from the measured data that there is significant variability 

about the regression line relating stage to discharge. In the coastal zone, 

some of this variability can be attributed to tidal effects. However, bed 

forms and unsteady flow effects account for most of the variability. There 

is an identifiable loop effect in the rating curves. The height and 

distribution of bed forms lag the rise and fall of hydrographs so that there 

is no distinct relationship between bed-form shape and discharge. In the 

steady-state 1D sediment model, the objective is to simulate average 

conditions to best replicate the movement of sediment over time. This is 

different from the approach taken to establish flow lines for maximum 

water surface elevations (e.g., for levee design). With the levee design 

approach, roughness coefficients would be chosen to match a regression 

curve through the maximum water surface elevation values. 

The 1991–2002 measured data at nine gages in the New Orleans District 

and the computed regression curves for the 12-year period are shown in 

Figure 18 through Figure 26. Also shown on these figures are HEC-6T 

calculated rating curves at the end of the first and twelfth year of the 

movable-bed simulation. Figure 27 shows water surface profiles calculated 

by the movable-bed model for Tarbert Landing discharges of 150,000; 

300,000; 500,000; 900,000; and 1,500,000 cfs at the end of the first and 

twelfth year. Also shown on Figure 27 are water surface elevations 

calculated from the 1991–2002 regression equations from Figure 18

through Figure 26. Roughness coefficients determined during the initial 

fixed-bed calibration were found to produce reasonable results during the 

movable bed simulation. At the end of the 12-year simulation, the rating 

curves suggest aggradation at high flows between Venice (RM10.7) and 

Reserve (RM 138.7). The calculated stages between Donaldsonville (RM 

174.5) and Red River Landing (RM 302.4) show no significant difference 

between the 1992 and 2002 rating curves. Although the 2002 rating curves 

are well within the data scatter of the measured stages and discharges, the 

measured stage data do not support the aggradation trend shown in the 

calculated results downstream from Donaldsonville. One explanation for 

this inconsistency is that there was only 1 high-water year (1997) during the 

calibration period and the last 4 years of the calibration hydrograph (1998–

2002) were relatively low-flow years. Another explanation is that the rating 

curves calculated by the model were developed by running an instantaneous 

discharge over the calculated bed conditions in September 2002. These are 

not necessarily the conditions that would be expected at peak flows where 

the ascending limb of the flood hydrograph would tend to change bed 
MRG&P Report No. 30 52

conditions. Nevertheless, this inconsistency must be considered with other 

calibration data from the river. 

Figure 18. Venice rating curves, RM 10.7, 1991–2002. 

Figure 19. Empire rating curves, RM 29.5, 1991–2002. 

0

1

2

3

4

5

6

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)

0

2

4

6

8

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2003-04

Calculated 1991

Calculated 2002

Poly. (1991-2002)
MRG&P Report No. 30 53

Figure 20. West Pointe a la Hache rating curves, RM 48.7, 1991–2002. 

Figure 21. New Orleans rating curves, RM 102.8, 1991–2002. 

0

1

2

3

4

5

6

7

8

9

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)

0

1

2

3

4

5

6

7

8

9

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)
MRG&P Report No. 30 54

Figure 22. Reserve rating curves, RM 138.7, 1991–2002. 

Figure 23. Donaldsonville rating curve, RM 175.4, 1991–2002. 

0

2

4

6

8

10

12

14

16

18

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)

0

5

10

15

20

25

30

35

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calcilated 2002

Poly. (1991-2002)
MRG&P Report No. 30 55

Figure 24. Baton Rouge rating curves, RM 228.4, 1991–2002. 

Figure 25. Bayou Sara rating curves, RM 265.4, 1991–2002. 

0

5

10

15

20

25

30

35

40

45

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)

0

5

10

15

20

25

30

35

40

45

50

55

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)
MRG&P Report No. 30 56

Figure 26. Red River Landing rating curves, RM 302.4, 1991–2002. 

Figure 27. Measured and calculated stages, RM -19 to RM 320. 

10

15

20

25

30

35

40

45

50

55

60

65

100,000 300,000 500,000 700,000 900,000 1,100,000 1,300,000 1,500,000 1,700,000

DISCHARGE @ TARBERT (CFS) STAGE FT, NGVD

1991-92

1993-94

1995-96

1997

1998-99

2000-01

2002

Calculated 1991

Calculated 2002

Poly. (1991-2002)

0

10

20

30

40

50

60

70

-20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320

River Mile Stage Ft, NGVD

1991 150K

1991 300K

1991 500K

1991 900K

1991 1500K

2002 150K

2002 300K

2002 500K

2002 900K

2002 1500K

Discharge

at Tarbert 

Landing

Downstream Stage at 

Pilots Station = 0.7 FT NGVD

♦ Average Stage from 

Regression of 1991-2002 

Measured Stages 
MRG&P Report No. 30 57

The 1991–2002 measured data for seven gages in Vicksburg District are 

shown in Figure 28 through Figure 31. Also shown on these figures are 

calculated rating curves at the end of the first year of the movable-bed 

simulation (1991) and at the end of the 12-year simulation (2002). 

Roughness coefficients determined during the initial fixed-bed calibration 

and after the 12-year simulation were found to produce reasonable results 

during the movable bed simulation. The significant variability about the 

regression lines relating stage to discharge in Vicksburg District is 

consistent with the measurements downstream in New Orleans District. 

This spread is attributed to bed forms and unsteady flow effects and 

demonstrates that stage is not a unique function of discharge. During flood 

events, there is an identifiable loop effect in the rating curves. In the 

steady-state 1D sediment model the objective is to simulate average 

conditions to best replicate the movement of sediment over time. 

Figure 28. Stage-discharge for St. Joseph (RM 396.4) and Natchez (RM 363.0). 

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 400,000 800,000 1,200,000 1,600,000 2,000,000 2,400,000 Elevation Feet NGVD

Discharge CFS

St Joseph Measured 1991-96

St Joseph Calculated 1991

St Joseph Calculated 2002

St Joseph Calculated 2011

Natchez Measured 1991-02

Natchez Calculated 1991

Natchez Calculated 2002

Natchez Measured 2011

Natchez Calculated 2011
MRG&P Report No. 30 58

Figure 29. Stage-discharge for Lake Providence (RM 486.4) and Vicksburg (RM 437.4). 

Figure 30. Stage-discharge for Arkansas City (RM 554.1) and Greenville (RM 531.5). 

40

50

60

70

80

90

100

110

120

130

0 400,000 800,000 1,200,000 1,600,000 2,000,000 2,400,000 Elevation Feet NGVD

Discharge CFS

Lake Providence Measured 1991-0 2

Lake Providence Calculated 1991

Lake Providence Calculated 2002

Lake Providence Measured 2011

Lake Providence Calculated 2011

Vicksburg Measured 1991-0 2

Vicksburg Calculated 1991

Vicksburg Calculated 2002

Vicksburg Measured 2008

Vicksburg Measured 2011

Vicksburg Calculated 2011 80

90

100

110

120

130

140

150

160

0 400,000 800,000 1,200,000 1,600,000 2,000,000 2,400,000 Elevation Feet NGVD

Discharge CFS

ArkCityMeas1991-0 2

ArkCityMeas2008

ArkCityMeas2011

ArkCityCalc1991

ArkCityCalc2002

ArkCityCalc2011

Greenville Measured 1991-0 2

Greenville Calculated 1991

Greenville Calculated 2002

Greenville Measured 2011

Greenville Calculated 2011
MRG&P Report No. 30 59

Figure 31. Stage-discharge for Rosedale (RM 592). 

There were no significant flood events during the calibration period. 

Therefore, data from 1973 were initially used to estimate roughness 

coefficients in the Vicksburg District for large floods. Then, between 

completion of the modeling effort and this report documentation, the flood 

of record (in terms of stage) occurred at Vicksburg in 2011. Although this 

study was not intended to evaluate river response outside the 1991–2002 

time frame, since 2011 flood data became available, it was deemed 

appropriate to use the more recent 2011 stage-discharge discharges to 

estimate roughness coefficients for high flows that will occur in future longterm studies. Stage-discharge relationships for floods in 1973, 1989, 1991, 

2008 are compared to 2011 in Figure 32. Roughness coefficients calculated 

using the 2011 average rating curve were higher than originally used in the 

HEC-6T model, which had been calibrated using an extrapolation of the 

1973 flood rating curves. This analysis is incomplete because the model was 

not used to simulate aggradation/degradation between 1973 and 2011, and 

the apparent increase in roughness could be due to a long-term loss in 

channel capacity, increase in vegetation on bars, or other factors. More 

study on these issues should be addressed in future studies. 

100

110

120

130

140

150

160

170

0 500,000 1,000,000 1,500,000 2,000,000 2,500,000 Elevation Feet NGVD

Discharge CFS

Rose Meas 1991-02

Rose Meas 2011

Rose Calc 2011

Rose1991_Jun10

Rose Calc 91-02

Poly. (Rose Meas 1991-02)

Poly. (Rose Calc 91-02)
MRG&P Report No. 30 60

Figure 32. Stage-discharge for historical floods on the Mississippi River at Vicksburg. 

The 1991–2002 measured data for three gages in the Memphis District are 

shown in Figure 33 through Figure 35. The bottom row of points in Figure 

35 is not an error; it represents stages during the rising limb of the 

hydrograph in December 1990. A similar row of low points can be 

identified in Figure 34 and represents the rising limb of the hydrograph in 

March 1993. Large variations in the stage discharge relationship is typical 

of the Mississippi River where the combination of unsteady flow effects 

and bed form changes significantly influence the energy slope and 

channel-bed roughness. 

Also shown on these figures are calculated rating curves at the end of the 

first year of the movable-bed simulation (1991) and at the end of the 12-year 

simulation (2002). Roughness coefficients determined during the initial 

fixed-bed calibration were found to produce reasonable results during the 

movable bed simulation. 

76

80

84

88

92

96

100

104

1,000 1,200 1,400 1,600 1,800 2,000 2,200 2,400 Elevation ft NGVD

Discharge 1000 cfs

1973

1989

1991

2008

2011
MRG&P Report No. 30 61

Figure 33. Stage-discharge for Helena (RM 663.1). 

Figure 34. Stage-discharge for Memphis (RM 734.4). 

135

145

155

165

175

185

195

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 Elevation Feet NGVD

Discharge 1000 CFS

Meas Helena 91-01

Calc Hlelena 91

Calc Helena 2001

170

180

190

200

210

220

230

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 Elevation Feet NGVD

Discharge 1000 CFS

Meas Memphis 91-02

Calc Memphis 91

Calc Memphis 02
MRG&P Report No. 30 62

Figure 35. Stage-discharge for Hickman (RM 922). 

Roughness coefficients in the numerical model varied with both discharge 

and distance along the river. Overbank and channel roughness coefficients 

used in the HEC-6T model in the New Orleans District are shown in 

Table 15, in the Vicksburg District in Table 16, and in the Memphis District 

in Table 17. In the HEC-6T model, roughness values at a cross section are 

used at all subsequent upstream cross sections until changed. When the 

discharges are greater or less than those shown in the table, the last 

roughness coefficient shown in the table is used in the model. The 

discharges shown in the tables refer to the discharge at each specific river 

mile shown in column one of the table. The table discharges were chosen 

to account for any breaks in the regression of the measured stage data and 

do not relate to any specific frequency or event. Unreasonable coefficient 

magnitudes were not used for the sake of achieving a better fit to 

measured data.
MRG&P Report No. 30 63

Table 15. HEC-6T roughness coefficients in New Orleans District. 

River 

Mile Overbanks

Channel

250,000 

cfs 

550,000 

cfs 

850,000 

cfs 

950,000 

cfs 

1,500,000 

cfs 

-18.0 0.05 0.0165 0.0165 0.0165 0.0165 0.0165

0.0 0.15 0.032 0.022 0.0165 0.0165 0.0165

11.05 0.20 0.024 0.019 0.015 0.014 0.014

35.1 0.20 0.024 0.023 0.022 0.022 0.015

53.0 0.20 0.027 0.026 0.024 0.023 0.0205

105.0 0.20 0.029 0.026 0.0253 0.025 0.021

141.6 0.20 0.028 0.026 0.0245 0.024 0.022

177.3 0.20 0.026 0.026 .025 0.022 0.021

195.3 0.20 0.026 0.026 .025 0.022 0.021

229.7 0.20 0.027 0.027 .025 0.025 0.024

267.0 0.20 0.029 0.027 .024 0.0237 0.020

306.3 0.15 0.034 0.031 .031 0.0303 0.0275

Table 16. HEC-6T roughness coefficients in Vicksburg District. 

River 

Mile Overbanks 

Channel 

200,000

cfs

400,000

cfs

900,000

cfs

1,400,000

cfs

1,800,000

cfs

328.6 0.14 0.034 0.031 0.031 0.028 0.028

365.0 0.14 0.034 0.029 0.028 0.028 0.028

396.4 0.14 0.028 0.027 0.029 0.028 0.028

438.4 0.14 0.029 0.028 0.027 0.028 0.028

487.8 0.14 0.028 0.027 0.026 0.027 0.028

531.7 0.14 0.028 0.027 0.026 0.027 0.029

557.2 0.14 0.033 0.030 0.029 0.027 0.025

 
MRG&P Report No. 30 64

Table 17. HEC-6T roughness coefficients in Memphis District. 

River Mile Overbanks 

Channel -1000 cfs 

200 400 600 1,400 1,800

580.8 0.14 0.033 0.030 0.026 0.027 0.025

100 500 750 1,000 2,000

598 0.15 -0.25 0.033 0.029 0.029 0.029 0.028

600.1 0.15 -0.25 0.033 0.031 0.031 0.030 0.029

666.01 0.15 -0.25 0.035 0.031 0.030 0.030 0.029

100 500 1,000 1,250 2,000

738 0.10 – 0.19 0.034 0.033 0.033 0.033 0.028

741 0.10 – 0.25 0.036 0.033 0.033 0.033 0.028

752.98 0.15 -0.25 0.036 0.029 0.028 0.028 0.029

784 0.15 -0.25 0.036 0.030 0.030 0.030 0.031

796.01 0.15 -0.25 0.036 0.030 0.029 0.029 0.032

803.84 0.10 - 0.25 0.036 0.027 0.029 0.029 0.032

828.24 0.15 -0.25 0.036 0.027 0.029 0.029 0.034

846.4 0.10 0.036 0.032 0.031 0.031 0.034

864.7 0.10 0.036 0.027 0.029 0.029 0.034

873.04 0.10 0.036 0.027 0.029 0.029 0.036

880 0.20 0.036 0.028 0.029 0.029 0.036

881.89 0.20 0.036 0.028 0.033 0.033 0.040

882.6 0.15 – 0.25 0.036 0.030 0.033 0.033 0.040

910.54 0.15 – 0.25 0.036 0.036 0.036 0.036 0.036

915.59 0.15 0.036 0.030 0.033 0.033 0.040

923.46 0.15 0.033 0.025 0.028 0.028 0.034

927.5 0.15 0.031 0.025 0.024 0.024 0.031

934.41 0.15 – 0.25 0.031 0.025 0.024 0.024 0.031

949 0.12 0.031 0.025 0.023 0.023 0.029

953.03 0.12 0.031 0.025 0.023 0.023 0.027

Roughness coefficients for Ohio and Arkansas Rivers 

Roughness coefficients for the Arkansas River were transferred from the 

Little Rock District HEC-RAS model. A roughness coefficient of 0.031 was 

used in the channel. Overbank roughness coefficients ranged between 

0.08 and 0.14.

Roughness coefficients for the Ohio River were adjusted until the 

computed water surface elevations reproduced average measured data 

from the USGS gage Ohio River at Metropolis, Illinois (0361150), which is 

located at RM 944.1 below Pittsburgh (The Point), which is equivalent to 
MRG&P Report No. 30 65

RM 990.5 (AHP) and is 37 miles upstream from the Mississippi River 

confluence. A roughness coefficient of 0.026 was used for the channel. 

Overbanks were assigned a roughness coefficient of 0.230. Daily stages 

and discharges were obtained from the USGS website 

http://nwis.waterdata.usgs.gov/nwis. Using discharges from Metropolis, a stagedischarge plot was also developed at Cairo (RM 955.8 AHP).

Daily stages reported at Metropolis for 1991–2002 are compared to daily 

stages calculated by HEC-6T in Figure 36. Based on scatter in plotted 

points in Figure 36, Metropolis appears to be in the backwater from the 

Mississippi River. As such, the rating curve is not strictly friction 

controlled. However, the selected roughness coefficients for the Ohio River 

reproduced both the scatter and the average regression documented by the 

measured data and is considered appropriate for use in the numerical 

model. Using a single event to calibrate roughness coefficients is not 

desirable when it is known that individual events produce significantly 

different looped rating curves. In the sediment analysis, it is average 

conditions that are appropriate. 

Daily stage data at Cairo, shown in Figure 37, were obtained from the 

USACE website Rivergages.com. 

Figure 36. Stage-discharge for the Ohio River at Metropolis (RM 990 AHP), 1991-2002. 

280

290

300

310

320

330

340

350

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000 ELEVATION FT NVGD29

DISCHARGE CFS

USGS METROPOLIS

HEC-6T RM 990

Poly. (USGS METROPOLIS)

Poly. (HEC-6T RM 990)
MRG&P Report No. 30 66

Figure 37. Stage-discharge for the Ohio River at Cairo (RM 955.8 AHP), 1991-2002. 

Sediment transport 

The grain sizes of sediment particles transported by the Mississippi River 

range over several orders of magnitude. The small sizes behave much 

differently from the large sizes. Therefore, it is necessary to classify 

sediment material into groups for application of different sediment 

transport functions. The four basic classes considered in this study are 

clay, silt, sand, and gravel. The groups are identified and subdivided based 

on the American Geophysical Union classification scale (Lane 1947). 

Sediments smaller than 0.004 millimeter (mm) are classified as clay. 

Sediments between 0.004 and 0.0625 mm are classified as silt. Sediments 

between 0.0625 and 2.0 mm are classified as sand. Sediments between 2 

and 64 mm are classified as gravel. This study included one clay, four silt, 

five sand, and five gravel size classes. 

Sand and gravel transport function 

The sand sediment transport function in the HEC-6T numerical model 

calculates transport of the total sand and gravel sediment loads. This 

includes the sand and gravel bed-material load and the sand wash load. 

The bed-material load includes size classes found in substantial quantities 

in the bed and moves as bed load and suspended load. The armoring and 

sorting algorithm in the numerical model also allows for transport of sand 

sizes, not found in the bed, as suspended wash load. 

280

290

300

310

320

330

340

350

0 200,000 400,000 600,000 800,000 1,000,000 1,200,000 1,400,000 ELEVATION FT NVGD29

DISCHARGE CFS

USGS CAIRO 91-02

HEC-6T RM 955.8 91-02

Poly. (USGS CAIRO 91-02)

Poly. (HEC-6T RM 955.8 91-02)
MRG&P Report No. 30 67

The sediment transport function for sand and gravel chosen for this study 

was the Toffaleti-Meyer-Peter Muller function. With this function, bed 

load is calculated using the Toffaleti (1968) and Meyer-Peter Muller (1948) 

methods, and the larger of the two is used. Suspended bed-material load is 

then calculated using the Toffaleti method. The Toffaleti-Meyer-Peter 

Muller function is capable of calculating sand and gravel transport rates by 

size class. The Toffaleti equation was developed for large rivers like the 

Mississippi River. The Meyer-Peter Muller equation was used to facilitate 

the transport of gravel size classes known to be in the river bed in the 

Memphis District reach. 

Silt and clay transport functions 

The equation for silt and clay deposition used in HEC-6T is the Krone 

(1962) equation. The required calibration coefficient is the critical bed 

shear stress below which deposition occurs. In HEC-6T, this coefficient 

has a variable name DTCL for clay and DTSL for silt.

tk

o

e

C

C  



D

k

d

b

3.2

1 









 

 







where:

C = concentration at end of time step

Co = concentration at beginning of time step

t = time = reach length/flow velocity

ω = settling velocity of sediment particle

τb = bed shear stress

τd = critical bed shear stress for deposition (DTCL and DTSL) 

D = water depth.

Erosion in HEC-6T is calculated using the Parthenaides (1965) equation as 

adapted by Ariathurai and Krone (1976). Initial erosion coefficients for the 

equation were taken from previous numerical model work by Thomas et 

al. (1989). These were modified during model calibration. It is the cohesive 

properties of the clay that determine the erosion thresholds. For this 
MRG&P Report No. 30 68

reason, the same erosion coefficients are used for silt and clay in HEC-6T. 

Particle erosion is determined by the following: 

o

s

ba C

Q

SM

C 











  1

1







where:

M1 = erosion rate for particle scour [ τb *ERME/(STME-STCD)] 

(STCD< τb <STME)

Sa = surface area exposed to scour

Q = water discharge

τs = critical bed shear stress for particle scour (STCD)

γ = specific weight of water.

As the bed shear stress increases, particle erosion gives way to mass 

erosion, and the erosion rate increases. Because the mass erosion can 

theoretically be infinite, a characteristic time, Tc, is used. With a 

computation time interval of Δt, the mass erosion becomes the following:

o

a c C

t

T

Q

SM

C 







2

where:

M2 = erosion rate for mass erosion (ERME + ER2 {τb – STME}) Δt/ 

Tc

Tc = characteristic time of erosion

Δt = duration of time-step.

Silt and clay deposition coefficients were varied in the model. One set of 

coefficients was used in Southwest Pass, another in the reach between 

Head of Passes and RM 11.0, and another upstream from RM 11.0. Varying 

these coefficients was deemed reasonable to account for the effects of 

salinity on sediment deposition. Silt and clay coefficients used in the 

numerical model were determined during model calibration and are 

shown in Table 18. The erosion coefficients for Southwest Pass and 

upstream from RM 11.0 are the same as those used in two previous 

numerical sedimentation studies of the Lower Mississippi River (Copeland 
MRG&P Report No. 30 69

1991; Copeland and Thomas 1992).The relationships of erosion and 

deposition coefficients are shown in Figure 38 and Figure 39.

Table 18. Silt and clay coefficients for Parthenaides and Krone equations. 

Coefficient 

Variable Name 

in HEC-6T 

Southwest 

Pass 

River Miles 

0.0 to 11.05 Fresh Water Units 

Shear threshold for clay 

deposition DTCL .005 .003 .001 lbs/ft2

Shear threshold for silt 

deposition DTSL .014 .014 .002 lbs/ft2

Shear threshold for erosion of 

silt and clay particles STCD .025 .020 .020 lbs/ft2

Shear threshold for mass 

erosion STME .04 .04 .04 lbs/ft2

Erosion rate at STME ERME .001 .001 .001 lbs/ft2/hr

Slope of the erosion rate curve 

for mass erosion ER2 .03 .03 .03 1/hr

Figure 38. Erosion rate characteristics. 

ERME
MRG&P Report No. 30 70

Figure 39. Deposition rate characteristics. 

Sediment inflow 

A combination of measured and calculated data was used to establish 

sediment inflow boundary conditions. To model sedimentation trends in the 

Mississippi River, it is necessary to account for movement and storage of 

each sediment size class. HEC-6T allows for this accounting; however, the 

required input data are generally lacking. Long-term size class sediment 

data are available in the study reach, on the Middle Mississippi River at 

Thebes, located 44 miles upstream from the Ohio River, and Chester, 

located 110 miles upstream from the Ohio River. Long-term size class data 

are also available at Union Point (RM 326.6 AHP) and Coochie (RM 317.3 

AHP), which are located upstream from the Old River Control Complex and 

at Tarbert Landing (RM 306.3 AHP), which is located downstream from the 

Old River Control Complex. A shorter record is available at Belle Chasse, 

located 76 miles AHP. Data for the major tributaries, including the Ohio 

River, are generally limited to the sediment concentrations greater and less 

than 0.062 mm. The lack of boundary condition data required that size class 

percentages be estimated by calculation and/or judgment. A continuing 

sediment data collection program is essential to verify and enhance future 

sediment inflow predictions.
MRG&P Report No. 30 71

Sediment concentration is typically measured by mechanical samplers so 

that only a very small fraction of the actual load is physically measured. 

However, convention defines the measured suspended load as the 

sediment load that can be approximated from measured samples. The 

accuracy of the sediment measurement depends on the sampling 

collection method, the laboratory analysis of the samples and the protocol 

used to calculate average sediment concentration from the sample 

concentrations. The unmeasured load typically refers to the bed load plus 

the suspended load between the bed surface and the lowest sampled depth 

of the sampler’s intake nozzle.

In this study, sediment transport rating curves at model boundaries and at 

gages within the study reach were based on the measured (reported) 

sediment data. Near the upstream boundary of the numerical model, at 

Thebes, sediment samples are collected using a depth-integrated sampler 

at five verticals using the equal-discharge increment (EDI) method. The 

unsampled zone is approximately 4 inches (in.). At this boundary, the 

unmeasured load includes the bed load and the suspended load in the first 

4 in. above the bed. At Tarbert Landing, downstream from the Old River 

Control Complex, and at Coochie and Union Point, upstream from the Old 

River Control Complex, sediment samples are collected using a point 

sampler. Over the years, the number of verticals and the number of 

sampling points along each vertical has varied. Theoretically, the entire 

suspended load is considered to be measured. Practically, this is doubtful 

for the coarser sediment particles because the concentration profile for 

coarser particles increases exponentially near the bed, and the lowest 

point samples were taken between 70 and 95 percent of the depth. 

Nevertheless, only the bed load is considered unmeasured at the three 

gages near the Old River Control Complex. At Belle Chasse, samples are 

collected approximately 16 times a year with depth-integrated samplers 

and approximately 18 times a year with a point sampler. The depth 

integrated samplers have an unmeasured zone of approximately 4 in., and 

samples are collected at three fixed verticals. The point samples have been 

collected at four fixed verticals (changed to four EDI in April 2017) with 

points at 0.1, 0.3, 0.5, 0.7, and 0.9 of total depth at each vertical.

The unmeasured load has been historically estimated to be 15 percent of 

the total measured load. This approximation was first suggested by 

Dr. Hans Einstein in a personal communication in the 1960s. Based on 

subsequent studies and investigations, the New Orleans District concluded 
MRG&P Report No. 30 72

that the 15 percent estimate was appropriate (USACE MVN 1980, page 15).

Numerical sediment studies conducted on the Lower Mississippi River 

increased the measured bed material load by 10 to 15 percent to account 

for unmeasured load at upstream model boundary (Copeland 1991; 

Copeland and Thomas 1992; Catalyst-Old River Hydroelectric 1999; 

Thomas 2012, page 124; Sharp et al. 2013). Uncertainty related to the 

unmeasured load decreases as the distance between the area of interest 

and the upstream boundary increases. This occurs because the numerical 

model calculates the total bed-material load. As the sediment calculations 

move in a downstream direction, the sediment continuity equation is 

solved, extracting material from the streambed as required to meet the 

total bed-material load transport capacity. However, the uncertainty 

increases as the simulation time increases.

Recent development of the ISSDOTv2 methodology (Abraham et al. 2011) 

has made it possible to physically measure the bed-form component of bed 

load by mapping the movement of dunes using sonar equipment. 

Measurements taken in the Mississippi River in the vicinity of the Old 

River Control Complex (Heath et al. 2015) demonstrated that the bed load 

percentage of the bed-material load varied with discharge. The bed load 

percentage of the bed-material load varied from highs near 45 percent to 

low vales of approximately 10 percent.

The relative importance of boundary condition precision at each model 

boundary is related to the contribution of water and sediment from that 

tributary. The percent of the annual Mississippi River discharge at 

Vicksburg for the years 1989–2003 is shown in Table 19. Over 80 percent 

of the annual discharge at Vicksburg comes from the Ohio and Middle 

Mississippi Rivers. Boundary conditions for these two rivers are by far the 

most important in the model study.
MRG&P Report No. 30 73

Table 19. Percentage of the 

annual Mississippi River 

discharge at Vicksburg, 

1991–2002. 

Ohio River 45.1

Middle Mississippi 

River

37.4

Arkansas River 8.2

White River 4.4

Yazoo River 3.0

St. Francis River 0.8

Hatchie River 0.6

Obion River 0.5

Sediment inflow Middle Mississippi River at Thebes and Chester 

Sediment data are available for the Mississippi River at Thebes, IL 

(07022000), located 44 miles upstream from the Ohio River, and at 

Chester, IL (07020500), which is located 110 miles upstream from the 

Ohio River. The number of measurements at Chester is much smaller than 

at Thebes. Total measured suspended sediment and measured suspended 

sand data were collected at Thebes between 1973 and 2010 and at Chester 

between 1982 and 1985. Size class data were collected at Thebes between 

1973 and 1991 and at Chester between 1980 and 1991. 

During the 37 years between 1973 and 2010, 396 measurements of the total 

sediment load and 366 measurements of the sand load were available from 

the Thebes gage. Only 17 concentration measurements were available at 

Chester for this period and were omitted from the analysis of 

concentrations. Average daily sediment concentrations were determined for 

days when multiple samples were reported. Power regression curves that 

were developed from the Thebes data are plotted by decade in Figure 40

and Figure 41. The curves suggest that the total load and the sand load have 

declined over the 37-year period. However, considering the data scatter, 

there is considerable uncertainty associated with this conclusion. Data were 

insufficient to evaluate measured sediment concentration trends for 

individual size classes including silt and clay.
MRG&P Report No. 30 74

Figure 40. Total measured suspended sediment concentration at Thebes. 

Figure 41. Measured suspended sand concentration at Thebes. 

Measured total suspended sediment load and measured suspended sand 

load data collected at Thebes between 1991 and 2002 were used to 

calculate power regression curves for the HEC-6T sediment inflow rating 

table. These years correspond to the calibration time period. Later in the 

study, during sensitivity evaluations, a sediment inflow curve based on 

2003–2012 data was employed. Average daily sediment concentrations 

were determined for days when multiple samples were reported. There 

10

100

1000

10000

10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

1973-1979

1980-1989

1990-1999

2000-2012

1

10

100

1000

10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

1973-1979

1980-1989

1990-1999

2000-2012
MRG&P Report No. 30 75

were 106 measurements in this data set. The data are plotted in Figure 42. 

When the sediment concentrations are plotted against discharge, there is

considerable scatter, indicating that concentration is a function of more 

variables than just the discharge. A simple power regression fit of the data 

produced the following equations, with an R2 value of 0.65 for the total 

load and 0.54 for the sand load:

292.1 Ctotal  00002992.0 Q

.1 334 Csand  .0 000003533 Q

where: 

C = concentration, mg/l

Q = discharge, cfs.

Figure 42. Measured suspended total and sand concentrations at Thebes. 

A statistical correction factor was applied to the power regression 

equations to account for bias created by using a least-squares regression 

for the logarithm of concentration. This bias occurs because the power 

regression produces a geometric mean instead of an arithmetic mean. The 

geometric mean is necessarily lower than the arithmetic mean, so 

concentrations are underestimated using the biased equation. The bias 

increases with the degree of scatter about the regression. A correction 

y = 2.992E-05x1.292E+00

R2 = 6.524E-01

y = 2.857E-06x1.334E+00

R2 = 5.359E-01

Unbiased Total

y = 3.379E-05x1.292E+00

Unbiased Sand

y = 3.533E-06x1.334E+00

1

10

100

1000

10000

10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

Total Thebes 91-02

Sand Thebes 91-02

Power (Total Thebes 91-02)

Power (Sand Thebes 91-02)

Power (Unbiased Total)

Power (Unbiased Sand)
MRG&P Report No. 30 76

factor proposed by Ferguson (1986) was used to produce an unbiased 

estimator for both the total measured load and the sand load. The 

correction factor is given in the following equation:

2-n

( C - C )

s = 

C = C (2.651 s )

2

i

i

n

2 1=i

2

i i

loglog ˆ

ˆ exp



where:

Ci = unbiased concentration at discharge event i

Ci

ˆ = concentration from biased regression curve 

Ci = measured concentration

N = number of measurements.

The unbiased estimators for the measured total and sand concentrations 

are given by the following equations. Note that the exponent is the same in 

the biased and unbiased equations so that the regression curves on log-log 

plots are parallel.

Ctotal = Q

.1 292 00003379.0

C = Q

.

sand

1 334 000003533.0

Size class percentages for each size class were determined using the 

measured suspended data at Thebes and Chester. Linear regression 

equations were calculated in EXCEL from 35 samples from Thebes, 

collected between 1973 and 1991, and 36 samples from Chester, collected 

between 1980 and 1991. Multiple samples collected at the two stations on 

the same day in June 1984 were not included in the analysis to avoid bias. 

There were no size class data available for the 1991–2002 time period 

simulated in the HEC-6T calibration study. Plots of the regression curves 

are shown in Figure 43. Although there was considerable scatter for 

individual measurements, the regression analysis showed little variation in 

the size class percentage with discharge. 
MRG&P Report No. 30 77

Figure 43. Size class percentages for at Thebes, 1973-1991, and Chester, 1980–1991. 

The sediment inflow rating curves for the Middle Mississippi River are 

shown in Table 20. The discharge range used to develop the sediment 

inflow regression curves was between 100,000 and 800,000 cfs. In 

Table 20, the calculated concentration at 800,000 cfs was used for 

higher discharges. Assuming a flat concentration curve at higher 

discharges is generally closer to prototype behavior than an extrapolation 

of the regression curve. Size class percentages calculated from the 

regression curves at the 100,000 and 800,000 cfs were held constant for 

discharges beyond the data limits. In the HEC-6T sediment inflow table, 

fine sand through very coarse sand size class percentages were increased by 

15 percent to account for unmeasured load. The very-coarse sand to veryfine gravel size classes were adjusted during the calibration process so that 

transport of these size classes into and out of the segment were equal.

0

10

20

30

40

50

60

70

80

90

100

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

Discharge cfs

0.002

0.004

0.016

0.0625

0.125

0.25

0.5

Linear (0.002)

Linear (0.004)

Linear (0.016)

Linear (0.0625)

Linear (0.125)

Linear (0.25)

Linear (0.5)
MRG&P Report No. 30 78

Table 20. Sediment inflow for Middle Mississippi River, Segment 25. 

Discharge, cfs 10,000 50,000 100,000 300,000 500,000 800,000 1,200,000 

Concentration 

mg/l 4.97 39.80 97.45 402.9 779.6 1431 1431

Fractions 

Clay 0.4011 0.4011 0.4011 0.0451 0.4090 0.4150 0.4150

Very Fine Silt 0.0733 0.0733 0.0733 0.0669 0.0605 0.0510 0.0510

Fine Silt 0.0733 0.0733 0.0733 0.0669 0.0605 0.0510 0.0510

Medium Silt 0.0861 0.0861 0.0861 0.0911 0.0961 0.1035 0.1035

Coarse Silt 0.0861 0.0861 0.0861 0.0911 0.0961 0.1035 0.1035

Very Fine Sand 0.0397 0.0397 0.0397 0.0403 0.0410 0.0419 0.0419

Fine Sand .02155 0.2155 0.2155 0.2011 0.1868 0.1653 0.1653

Medium Sand 0.0578 0.0578 0.0578 0.0626 0.0674 0.0746 0.0746

Coarse Sand 0.0031 0.0031 0.0031 0.0106 0.0180 0.0292 0.0292

Very Coarse Sand 0.0000 0.0000 0.0008 0.0016 0.0025 0.0039 0.0039

Very Fine Gravel 0.0000 0.0000 0.0003 0.0006 0.0010 0.0015 0.0015

Fine Gravel 0.0000 0.0000 0.0001 0.0002 0.0003 0.0005 0.0005

Medium Gravel 0.0000 0.0000 0.0000 0.0001 0.0001 0.0002 0.0002

Coarse Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Very Coarse 

Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Sediment inflow Ohio River 

Sediment inflow from the Ohio River was determined from measured 

suspended sediment data collected at two USGS gages. The gage closest to 

the upstream model boundary is at Dam 53 near Grand Chain, IL, 

(03612500), which is 17 miles upstream from Cairo (Ohio River RM 

962.6). The second gage is considerably upstream from the model 

boundary at Louisville, KY (03294500), which is approximately 372 miles 

upstream from Cairo (Ohio River RM 607.3). Total measured suspended 

sediment concentration and sand percentages were collected at Dam 53, 

between 1973 and 2010. Size class percentage data for clay through 

medium sand were collected at Louisville, between 1979 and 1982. The 

Louisville gage is located a considerable distance upstream from the 

Mississippi River confluence at Cairo, and the available data were collected 

10 years prior to the calibration simulation period. However, the Louisville 

data are the only suspended size class data available. The Ohio River in the 
MRG&P Report No. 30 79

study reach essentially has a rigid boundary where most of the boundary 

materials do not actively exchange with the suspended load. Although, 

sand frequently moves as bed load throughput over a primarily gravel bed, 

calculation of suspended bed material load from available bed material 

gradations is not reliable.

During the 37 years between 1973 and 2010, 366 measurements of the 

total sediment load and 264 measurements of the sand load were available 

from the Dam 53 gage. Power regression curves were determined from the 

Dam 53 data for 4 decades covering the span of the measured data. When 

the sediment concentrations are plotted against discharge in Figure 44 it is 

apparent that there is considerable scatter, indicating that concentration is 

a function of more variables than just the discharge. The most obvious 

external variable is the backwater effect from the Mississippi River. In this 

model, there was no attempt at data segregation to exclude backwater 

effects because the study objective was to obtain long-term average values 

of sediment inflow. The data plotted in Figure 44 also suggest no longterm trend in the total concentration over the 37-year period. However, 

the data indicate that the 1990s had a slightly lower average sediment 

inflow than the preceding and following decades. Considering the data 

scatter, this conclusion is accompanied with considerable uncertainty. 

Figure 44. Total measured suspended sediment concentration at Dam 53. 

1

10

100

1,000

10,000 100,000 1,000,000 10,000,000

Concentration mg/l

Discharge CFS

1973-1979

1980-1989

1990-1999

2000-2010
MRG&P Report No. 30 80

Measured total suspended sediment load and measured suspended sand 

load data collected at Dam 53 between 1991 and 2002 were used to 

calculate power regression curves for the HEC-6Tsediment inflow rating 

table. There were 158 measurements for the total suspended concentration 

and 108 measurements for the sand concentration. The data are plotted in 

Figure 45. A simple power regression fit of the data produced the following 

equations, with a R2 value of 0.59 for the total suspended concentration 

and 0.50 for the sand concentration:

0505.1 Ctotal  0001008.0 Q

4368.1 Csand  .0 0000000374 4 Q

The unbiased power regression curves are the following:

.1 0505 Ctotal  .0 00012437 Q

.1 4368 Csand  .0 0000000654 24 Q

Figure 45. Measured suspended total and sand concentrations at Dam 53. 

y = 1.0080E-04x1.0505E+00

R2 = 5.9366E-01

y = 3.7440E-08x1.4368E+00

R2 = 5.0443E-01

Unbiased Total

y = 1.2437E-04x1.0505E+00

Unbiased Sand 

y = 6.5424E-08x1.4368E+00

0.1

1.0

10.0

100.0

1,000.0

10,000 100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Suspended

sand
MRG&P Report No. 30 81

There were no suspended sediment size class data available for the 1991–

2002 calibration period. In the HEC-6T model, size class percentages for 

each size class were estimated using the measured suspended data at 

Louisville collected between 1979 and 1982. Samples were collected on 11 

days during these 4 years, with a discharge range between 200,000 and 

450,000 cfs. Multiple samples collected on the same day were averaged to 

avoid bias. Linear regression equations were calculated in EXCEL to 

obtain percentages at specific discharges in the sediment input table. Plots 

of the regression curves are shown in Figure 46. 

Figure 46. Measured size class percentages, at Louisville. 

The sediment inflow rating curves used in the HEC-6T model, for the Ohio 

River, are shown in Table 21. Sand loads for very-fine, fine, and medium 

sand were determined from the sand regression curve, and fine load was 

determined from the difference between the total and sand load regression 

curves. The range of discharges used to develop the sediment inflow 

regression curves was between 50,000 and 1,200,000 cfs. In Table 21 the 

calculated concentration at 1,200,000 cfs was used for discharges greater 

than 1,200,000 cfs. Assuming a flat concentration curve at higher 

discharges is generally closer to prototype behavior than an extrapolation 

of the regression curve. 

20

30

40

50

60

70

80

90

100

200,000 250,000 300,000 350,000 400,000 450,000 500,000 Percent Finer

Discharge cfs

.002 mm

.004 mm

.008 mm

.016 mm

.032 mm

.062 mm

.125 mm

.25 mm
MRG&P Report No. 30 82

Table 21. Sediment inflow for Ohio River – Segment 24. 

Discharge 

1000 cfs 10 50 100 200 450 800 1000 1200 2000

Concentration

mg/l 1.98 10.74 22.24 46.07 108.0 197.7 249.9 302.6 302.6

Fractions 

Clay 0.6035 0.5938 0.5873 0.5788 0.4280 0.4187 0.4145 0.4108 0.4108

VF Silt 0.1349 0.1327 0.1313 0.1294 0.1256 0.1229 0.1216 0.1205 0.1205

F Silt 0.1377 0.1355 0.1340 0.1321 0.1557 0.1523 0.1508 0.1494 0.1494

M Silt 0.0818 0.0805 0.0796 0.0785 0.1287 0.1259 0.1247 0.1235 0.1235

C Silt 0.0235 0.0231 0.0229 0.0225 0.0817 0.0799 0.0791 0.0784 0.0784

VF Sand 0.0112 0.0208 0.0272 0.0355 0.0527 0.0658 0.0718 0.0770 0.0770

F Sand 0.0092 0.0171 0.0223 0.0292 0.0293 0.0366 0.0399 0.0428 0.0428

M Sand 0.00090 0.00168 0.00347 0.0137 0.0174 0.0361 0.0326 0.0279 0.0279

C Sand 0.0 0.0 0.00118 0.00621 0.0113 0.0137 0.0137 0.0120 0.0120

VC Sand 0.0 0.0 0.0 0.00307 0.00667 0.00898 0.00867 0.00806 0.0806

VF Gravel 0.0 0.0 0.0 0.0 0.00068 0.00230 0.00226 0.00209 0.00209

F Gravel 0.0 0.0 0.0 0.0 0.0 0.00050 0.00101 0.00118 0.00118

M Gravel 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00015 0.00015

C Gravel 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

VC Gravel 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Size class percentages were calculated from the size class regression curves 

between 200,000 and 450,000 cfs. Percentages were held constant for 

discharges beyond the data limits. Sediment inflow for the sand size 

classes determined from regression curves was increased by 15 percent to 

account for unmeasured load. The coarse-sand to medium-gravel size 

classes were transported in the unmeasured zone, so inflow fractions for 

these sediment sizes was determined using the recirculation option in 

HEC-6T. With this option, a series of steady state discharges are run for a 

period of time (in this case 25 days) where the sediment load calculated at 

the downstream end of the segment is re-introduced at the upstream end 

of the segment for the next time-step until the calculated inflow and 

outflow of sediment is approximately equal during a time-step. This is 

equivalent to assuming that the reach is in equilibrium with respect to 

sediment continuity. 
MRG&P Report No. 30 83

Uncertainty exists with this approach because these calculations are 

directly dependent upon the designated bed gradation. In this case, the 

bed gradation came from an average of multiple samples collected at 

Olmstead Lock and Dam located at RM 970.5 (mileage calculated by 

adding to Mississippi River mileage at Cairo). Medium sand load was 

determined using the larger of the fractions calculated from the regression 

equations or the recirculation option. 

Sediment inflow Obion and Hatchie Rivers 

The purpose of the Obion and Hatchie River Segments in the HEC-6T 

model was to provide sediment inflow to the Mississippi River. Measured 

suspended sediment data from both rivers are available from USGS gages 

located considerable distances upstream from the HEC-6T model 

boundaries. Total suspended and sand inflow concentrations were 

available from these gages for a wide range of discharges. However, 

individual size class percentages of the suspended load were lacking. Bed 

material samples were collected for this study on the Hatchie River near 

Rialto (RM 34) and near Bogota on the Obion River (RM 36.7). Samples 

were collected at three transects at a crossing using a 6 in. clam-shell 

sampler in June 2005. There were no geometric data available between 

the Mississippi River and upstream sediment gages. A 2-mile study reach 

was included in the model based on estimated cross-section geometry. No 

calibration was attempted for these segments, and no conclusions can be 

made with respect to calculated morphologic changes in these segments. 

In the HEC-6T model, the beds of the Obion and Hatchie Rivers were not 

allowed to scour below the initial cross-section elevations. Therefore, the 

river bed was not allowed to contribute any sediment to the Mississippi 

River. However, deposition was allowed in the model so that sediment 

inflow at the model boundary could be computationally reduced if 

hydraulic conditions were favorable. 

Measured suspended sediment concentrations from two gages on the 

Obion River were used to determine sediment inflow concentrations for 

the HEC-6T model. The USGS reported sediment data at gage number 

07026000, Obion River at Obion, Tennessee, from samples collected 

between 1975 and 1990, and from USGS gage number 07026040, Obion 

River at Hwy 51 near Obion, Tennessee, from samples collected between 

1990 and 1995. These gages are essentially at the same location at 

approximately RM 62, which is approximately 60 miles upstream from the 
MRG&P Report No. 30 84

HEC-6T model boundary. There were only 19 measurements at the 

Highway 51 near Obion gage. Considering the data scatter and the small 

number of samples collected during the 1991–2002 calibration period, it 

was deemed appropriate to use the measurements from the entire 1975–

1995 record and from both gages to develop the best estimate of average 

sediment inflow rating curves. 

Measured total suspended sediment concentrations and measured 

suspended sand concentrations collected at Hwy 51 near Obion and at 

Obion between 1975 and 1995 were used to calculate power regression 

curves for the HEC-6Tsediment inflow rating table. There were 149 

measurements of the total suspended concentration and 122 

measurements of the sand concentration. The data are plotted in Figure 

47. A simple power regression fit of the data produced the following 

equations, with an R2 value of 0.2204 for the total suspended 

concentration and 0.1558 for the sand concentration:

.0 6081 Ctotal  .1 890 Q

.0 5768 Csand  .0 2244 Q

The unbiased power regression curves are the following:

.0 6081 Ctotal  .3 381 Q

.0 5768 Csand  .0 5520 Q
MRG&P Report No. 30 85

Figure 47. Measured suspended total and sand concentrations Obion River near RM 62. 

The measured Obion River data included a sand-silt break, and these data 

were used to determine the inflow concentrations for fines and sand. 

However, there were no additional size class percentage data available. 

The sand size class percentages were taken to be the same as the average 

sand size class percentages at Thebes and Chester. Likewise, the clay and 

silt size class percentages were taken to be the same as the average clay 

and silt size class percentages at Thebes and Chester. These were 

determined by summing the percent finer data from 71 Chester and 

Thebes samples collected between 1973 and 1991. These percentages are 

independent of discharge. 

The sediment inflow rating curves used in the HEC-6T model, for the 

Obion River, are shown in Table 22. The discharge range used to develop 

the sediment inflow regression curves was between 400 and 30,000 cfs. In 

Table 22, the calculated concentration at 30,000 cfs was used for higher 

discharges. A flat concentration curve at higher discharges is generally 

closer to prototype behavior than an extrapolation of the regression curve. 

In the HEC-6T sediment inflow table, fine sand through coarse sand size 

class percentages were increased by 15 percent to account for unmeasured 

load. 

y = 1.8899x0.6081

R2 = 0.2204

y = 0.2244x0.5768

R2 = 0.1558

Unbiased Total

y = 3.3809x0.6081

Unbiased Sand

y = 0.5520x0.5768

0.1

1

10

100

1000

10000

100 1000 10000 100000 Concentration mg/l

Discharge CFS

1975-95 Total

1975-95 Sand

Power (1975-95 Total)

Power (1975-95 Sand)

Power (Unbiased Total)

Power (Unbiased Sand)
MRG&P Report No. 30 86

Table 22. Sediment inflow for Obion River – Segment 16. 

Discharge 1 50 500 2,000 5,000 30,000 200,000

Concentration

mg/l 3.4 36.5 148.0 343.9 600.3 1784.7 1784.7

Fractions 

Clay 0.4735 0.4842 0.4898 0.4931 0.4951 0.4990 0.4990

VF Silt 0.0733 0.0750 0.0758 0.0763 0.0767 0.0773 0.0773

F Silt 0.0751 0.0768 0.0777 0.0782 0.0786 0.0792 0.0792

M Silt 0.1074 0.1098 0.1111 0.1118 0.1123 0.1132 0.1132

C Silt 0.1074 0.1098 0.1111 0.1118 0.1123 0.1132 0.1132

VF Sand 0.0237 0.0209 0.0195 0.0187 0.0181 0.0171 0.0171

F Sand 0.1150 0.1018 0.0947 0.0907 0.0881 0.0833 0.0833

M Sand 0.0379 0.0335 0.0312 0.0299 0.0290 0.0274 0.0274

C Sand 0.0072 0.0063 0.0059 0.0056 0.0055 0.0052 0.0052

VC Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VF Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

F Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

M Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

C Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Measured suspended sediment concentrations from two gages on the 

Hatchie River were used to determine sediment inflow concentrations for 

the HEC-6T model. The USGS reported sediment data at gage number 

07029500, Hatchie River at Bolivar, Tennessee, from samples collected 

between 1977 and 1995. This gage is at RM 135, considerably upstream 

from the model boundary. Downstream, at RM 34, a smaller data set was 

collected at USGS gage number 07030050, Hatchie River at Rialto, 

Tennessee. Data at this gage extend between 1977 and 1978 and between 

2004 and 2008. Measured total sediment concentrations and measured 

sand concentrations from the two gages are compared in Figure 48. The 

figure shows considerable scatter for the total suspended concentrations 

and the sand concentrations. There were only 40 measurements at the 

Rialto gage, and 10 of these were collected during a 5-day period in 

September 1977. Only 17 measurements at Bolivar were collected during 

the 1991–2002 calibration period. Considering the data scatter, it was 

deemed appropriate to use the measurements from the entire 1977–2008 
MRG&P Report No. 30 87

record and from both gages to develop the best estimate of average 

sediment inflow rating curves. Future studies to assess downward trends 

in sand and fine sediment yields to downstream reaches of the Mississippi 

River will require the collection of additional sediment data on tributaries, 

such as the Obion and Hatchie Rivers. 

Figure 48. Measured suspended total and sand concentrations Hatchie River. 

Measured total suspended sediment concentrations and measured 

suspended sand concentrations collected at Rialto and Bolivar between 

1977 and 2008 were used to calculate power regression curves for the 

HEC-6Tsediment inflow rating table. There were 171 measurements of the 

total suspended concentration and 128 measurements of the sand 

concentration. The data are plotted in Figure 49. A simple power 

regression fit of the data produced the following equations, with an R2

value of 0.054 for the total suspended concentration and 0.045 for the 

sand concentration:

.0 2388 Ctotal  13.09 Q

2595.0 Csand  659.1 Q

0.1

1

10

100

1000

10000

100 1,000 10,000 100,000 Concentration MG/L

Discharge CFS

Rialto-Total

Bolivar - Total

Rialto - Sand

Bolivar- Sand

Rialto RM 34 - 1977-1978

Bolivar RM 135 - 1977-1995
MRG&P Report No. 30 88

The unbiased power regression curves are the following:

.0 2388 Ctotal  23.39 Q

.0 2595 Csand  .3 750 Q

Figure 49. Combined measured suspended total and sand concentrations Hatchie River. 

The measured Hatchie River data included a sand-silt break, and these 

data were used to determine the inflow concentrations for fines and sand. 

However, there were no additional size class percentage data available. 

The sand size class percentages were taken to be the same as the average 

sand size class percentages at Thebes and Chester. Likewise, the clay and 

silt size class percentages were taken to be the same as the average clay 

and silt size class percentages at Thebes and Chester. These were 

determined by summing the percent finer data from 71 Chester and 

Thebes samples collected between 1973 and 1991. These percentages are 

independent of discharge. 

The sediment inflow rating curves used in the HEC-6T model, for the 

Hatchie River, are shown in Table 23. The discharge range used to develop 

the sediment inflow regression curves was between 200 and 30,000 cfs. In 

Table 23, the calculated concentration at 30,000 cfs was used for higher y = 13.092x0.2388

R2 = 0.0536

y = 1.6586x0.2595

R2 = 0.0446

Unbiased Total

y = 23.39x0.2388

Unbiased Sand

y = 3.7496x0.2595

0.1

1

1 0

100

1000

10000

100 1,000 10,000 100,000 Concentration MG/L

Discharge CFS

Total

Sand

Power (Total)

Power (Sand)

Power (Unbiased Total)

Power (Unbiased Sand)
MRG&P Report No. 30 89

discharges. A flat concentration curve at higher discharges is generally 

closer to prototype behavior than an extrapolation of the regression curve. 

In the HEC-6T sediment inflow table, fine sand through coarse sand size 

class percentages were increased by 15 percent to account for unmeasured 

load. 

Table 23. Sediment inflow for Hatchie River – Segment 14. 

Discharge 1 50 200 1000 5000 30,000 200,000

Concentration mg/l 23.4 59.5 82.9 121.7 178.8 274.3 274.3

Fractions 

Clay 0.4752 0.4675 0.4647 0.4612 0.4577 0.4536 0.4536

VF Silt 0.0736 0.0724 0.0719 0.0714 0.0709 0.0702 0.0702

F Silt 0.0754 0.0742 0.0737 0.0732 0.0726 0.0720 0.0720

M Silt 0.1078 0.1060 0.1054 0.1046 0.1038 0.1029 0.1029

C Silt 0.1078 0.1060 0.1054 0.1046 0.1038 0.1029 0.1029

VF Sand 0.0232 0.0252 0.0259 0.0268 0.0277 0.0288 0.0288

F Sand 0.1130 0.1225 0.1261 0.1303 0.1347 0.1398 0.1398

M Sand 0.0372 0.0403 0.0415 0.0429 0.0444 0.0460 0.0460

C Sand 0.0070 0.0076 0.0078 0.0081 0.0084 0.0087 0.0087

VC Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VF Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

F Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

M Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

C Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Sediment inflow St. Francis River 

The purpose of the St. Francis River Segment in the HEC-6T model is to 

provide sediment inflow to the Mississippi River. Considerable sediment 

data are available for the St. Francis River and were used to calibrate a 

Memphis District HEC-6T study. Additional data were collected by the 

USGS subsequent to the 2000 study and were used to develop sediment 

inflow curves for this study. Total suspended sediment and suspended 

sand concentrations were available for a wide range of discharges. In 

almost all cases, bed material gradation data were also collected when the 

suspended samples were collected. Individual sand size class percentages 

were determined in the laboratory for almost all of the suspended samples 
MRG&P Report No. 30 90

Measured suspended sediment concentrations from the USGS gage 

number 07047907, St. Francis River at Madison, Arkansas, were used to 

determine sediment inflow concentrations for the HEC-6T model. The 

USGS reported sediment data at the Madison gage between 1977 and 

2009. This gage is located at RM 37.9, which is approximately 20 miles 

upstream from the upstream model boundary. 

Measured total suspended sediment concentrations and measured 

suspended sand concentrations collected at Madison between 1991 and 

2002 were used to calculate power regression curves for the HEC6Tsediment inflow rating table. There were 139 measurements of the total 

suspended concentration and 127 measurements of the sand 

concentration. The data are plotted in Figure 50. A simple power 

regression fit of the data produced the following equations, with an R2

value of 0.112 for the total suspended concentration and 0.100 for the sand 

concentration:

.0 1765 Ctotal  30.704 Q

0..3774 Csand  2688.0 Q

The unbiased power regression curves are the following:

.0 1765 Ctotal  37.594 Q

.0 3774 Csand  .0 6344 Q
MRG&P Report No. 30 91

Figure 50. Measured suspended sediment concentrations, St. Francis River at Madison. 

The measured St. Francis River data included a sand-silt break, and these 

data were used to determine the inflow concentrations for fines and sand. 

In addition, sand size class data were available for nearly all the sediment 

measurements. There was considerable scatter in the size class data, and 

no reliable relationship between size class and discharge was discernible. 

Due to the large data scatter, all the data between 1977 and 2009 were 

used to estimate the average percentage in each sand size class. There were 

no size class percentage data available for the silts and clays. The clay and 

silt size class percentages were taken to be the same as the average clay 

and silt size class percentages at Thebes and Chester. These were 

determined by summing the percent finer data from 71 Chester and 

Thebes samples collected between 1973 and 1991. These percentages are 

independent of discharge. 

The sediment inflow rating curves used in the HEC-6T model, for the 

St. Francis River, are shown in Table 24. The discharge range used to 

develop the sediment inflow regression curves was between 100 and 

40,000 cfs. In Table 24 the calculated concentration at 40,000 cfs was 

used for higher discharges. A flat concentration curve at higher 

discharges is generally closer to prototype behavior than an extrapolation 

of the regression curve. In the HEC-6T sediment inflow table, fine sand y = 30.704x0.1765

R2 = 0.1118

y = 0.2688x0.3703

R2 = 0.0995

y = 37.594x0.1765 y = 0.6344x0.3774

0.1

1

10

100

1000

10000

100 1,000 10,000 100,000 Concentration mg/l

Discharge CFS

Total 91-02

Sand 91-02

Power (Total 91-02)

Power (Sand 91-02)

Power (Unbiased Total)

Power (Unbiased Sand)
MRG&P Report No. 30 92

through coarse sand size class percentages were increased by 15 percent 

to account for unmeasured load. 

Table 24. Sediment inflow for St. Francis River – Segment 12. 

Discharge 1 50 500 2000 10000 40000 60000

Concentration

mg/l 37.6 75.0 112.6 143.8 191.0 244.0 244.0

Fractions 

Clay 0.5564 0.5449 0.5326 0.5219 0.5051 0.4856 0.4856

VF Silt 0.0861 0.0844 0.0825 0.0808 0.0782 0.0752 0.0752

F Silt 0.0883 0.0865 0.0845 0.0828 0.0801 0.0771 0.0771

M Silt 0.1262 0.1236 0.1208 0.1184 0.1146 0.1101 0.1101

C Silt 0.1262 0.1236 0.1208 0.1184 0.1146 0.1101 0.1101

VF Sand 0.0055 0.0121 0.0193 0.0254 0.0351 0.0464 0.0464

F Sand 0.0079 0.0174 0.0276 0.0364 0.0503 0.0665 0.0665

M Sand 0.0047 0.0104 0.0165 0.0218 0.0302 0.0399 0.0399

C Sand 0.0004 0.0008 0.0013 0.0018 0.0024 0.0032 0.0032

VC Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VF Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

F Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

M Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

C Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Sediment inflow White River 

The purpose of the White River Segment in the HEC-6T model is to 

provide sediment inflow to the Mississippi River. Sediment data for the 

White River were limited and are insufficient for calibration of the White 

River Segment. Total suspended and sand inflow concentrations were 

available for a wide range of discharges. However, bed material gradation 

data and individual size class percentages of the suspended load were 

lacking. In the HEC-6T model, the White River bed was not allowed to 

scour below the initial cross-section elevations. Therefore, the river bed 

was not allowed to contribute any sediment to the Mississippi River. 

However, deposition was allowed in the model so that sediment inflow at 

the model boundary could be computationally reduced if hydraulic 
MRG&P Report No. 30 93

conditions were favorable. Calculated morphologic changes in the White 

River are not reliable. 

Measured suspended sediment concentrations from three gages on the 

White River were used to determine sediment inflow concentrations for 

the HEC-6T model. The USGS reported sediment data at gage number 

07077800, White River at Clarendon, Arkansas, between 1974 and 1986. 

This gage is at the upstream boundary of the model at RM 99.1. A more 

recent record was reported by the USGS at gage number 07077000, White 

River at DeValls Bluff, Arkansas, which is located at RM 121.8. Data at this 

gage extend between 2001 and 2011. At RM 255.0 is USGS gage number 

07074500, White River at Newport, Arkansas. Data were collected at this 

gage between 1978 and 1994. Measured total sediment concentrations and 

measured sand concentrations from the three gages are compared in 

Figure 51 and Figure 52, respectively. The figures show considerable 

scatter for the total and the sand concentrations. Power regression 

equations were included on the two figures to help identify data 

differences at the gages. There were only 12 measurements at DeValls Bluff 

and 23 measurements at Newport collected during the 1991–2002 

calibration period. Considering the data scatter, it was deemed 

appropriate to use the measurements from the entire 1974–2001 time 

period and from all three gages to develop sediment inflow rating curves. 

Figure 51. Measured suspended sediment concentrations at three gages, White River. 

1

10

100

1000

1,000 10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

Total Clarendon

Total Devalls

Total Newport

Power (Total Clarendon)

Power (Total Devalls)

Power (Total Newport)
MRG&P Report No. 30 94

Figure 52. Measured suspended sand concentrations, White River. 

Measured total suspended sediment concentrations and measured 

suspended sand concentrations collected at Clarendon, DeValls Bluff, 

and Newport between 1974 and 2011 were used to calculate power 

regression curves for the HEC-6Tsediment inflow rating table. There 

were 264 measurements of the total suspended concentration and 258 

measurements of the sand concentration. The data are plotted in Figure 

53. A simple power regression fit of the data produced the following 

equations, with an R2 value of 0.052 for the total suspended 

concentration and 0.042 for the sand concentration:

2132.0 Ctotal  1875.7 Q

.0 3294 Csand  .0 3237 Q

The unbiased power regression curves are the following:

.0 2132 Ctotal  9356.8 Q

.0 3294 Csand  .0 6232 Q

0

1

10

100

1000

1,000 10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

Sand Clarendon

Sand Devalls

Sand Newport

Power (Sand Clarendon)

Power (Sand Devalls)

Power (Sand Newport)
MRG&P Report No. 30 95

Figure 53. Measured suspended sediment concentrations, White River. 

The measured White River data included a sand-silt break, and these data 

were used to determine the inflow concentrations for fines and sand. 

However, there were no additional size class percentage data available. 

The sand size class percentages were taken to be the same as the average 

sand size class percentages at Thebes and Chester. Likewise, the clay and 

silt size class percentages were taken to be the same as the average clay 

and silt size class percentages at Thebes and Chester. These were 

determined by summing the percent finer data from 71 Chester and 

Thebes samples collected between 1973 and 1991. These percentages are 

independent of discharge. 

The sediment inflow rating curves used in the HEC-6T model, for the 

White River, are shown in Table 25. The discharge range used to develop 

the sediment inflow regression curves was between 3000 and 300,000 cfs. 

In Table 25 the calculated concentration at 300,000 cfs was used for 

higher discharges. A flat concentration curve at higher discharges is 

generally closer to prototype behavior than an extrapolation of the 

regression curve. In the HEC-6T sediment inflow table, fine sand through 

coarse sand size class percentages were increased by 15 percent to account 

for unmeasured load. 

Total

y = 7.1875x0.2132

R2 = 0.0518

Sand

y = 0.3237x0.3294

R2 = 0.0418

Unbiased Total

y = 8.9356x0.2132

Unbiased Sand

y = 0.6232x0.3294

0.1

1

10

100

1000

1,000 10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

Total

Sand

Power (Total)

Power (Sand)

Power (Unbiased Total)

Power (Unbiased Sand)
MRG&P Report No. 30 96

Table 25. Sediment inflow for White River – Segment 10. 

Discharge 1000 3000 10,000 50,000 100,000 300,000 800,000

Concentration

mg/l 39.0 49.3 63.7 89.7 104.0 131.5 131.5

Fractions 

Clay 0.4778 0.4658 0.4508 0.4271 0.4155 0.3950 0.3950

VF Silt 0.0740 0.0721 0.0698 0.0661 0.0643 0.0612 0.0612

F Silt 0.0758 0.0739 0.0715 0.0678 0.0659 0.0627 0.0627

M Silt 0.1084 0.1057 0.1022 0.0969 0.0942 0.0896 0.0896

C Silt 0.1084 0.1057 0.1022 0.0969 0.0942 0.0896 0.0896

VF Sand 0.0226 0.0256 0.0295 0.0356 0.0385 0.0438 0.0438

F Sand 0.1097 0.1246 0.1433 0.1728 0.1873 0.2128 0.2128

M Sand 0.0361 0.0410 0.0472 0.0569 0.0617 0.0701 0.0701

C Sand 0.0068 0.0077 0.0089 0.0107 0.0116 0.0132 0.0132

VC Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VF Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

F Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

M Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

C Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Sediment inflow Arkansas River 

The purpose of the Arkansas River Segment in the HEC-6T model is to 

provide sediment inflow to the Mississippi River. Data are insufficient for 

calibration of the Arkansas River Segment, and calculated morphologic 

changes should be treated with caution. Sediment data for the Arkansas 

River were limited. Sand and fine inflow concentrations were available for 

a wide range of discharges. However, bed material gradation data and 

individual size class percentages of the suspended load were lacking. 

Measured suspended sediment measurements from two gages on the 

Arkansas River were used to determine sediment inflow. The USGS 

reported sediment data at gage number 0765283, Arkansas River at Dam 

No. 2, near Gillett, Arkansas, between 1979 and 1986. This gage is at the 

upstream end of the modeled reach. A much longer record was reported by 

the USGS, 95 miles upstream at gage number 07266283, Arkansas River 

at David D Terry Lock and Dam below Little Rock, Arkansas. Data at this 
MRG&P Report No. 30 97

gage extend between 1974 and 2010. Data from the two gages, for the 

years when both were operating, are compared in Figure 54. Regression 

equations for the total load and the sand load are similar. Because of this 

similarity, data from both gages were confidently used to develop 

sediment inflow rating curves for the HEC-6T model. Unbiased power 

regression curves were calculated for the total measured load and 

measured sand load and are shown in Figure 55. 

Figure 54. Measured sediment concentrations at two gages on the Arkansas River. 

Figure 55. Measured sediment concentrations on the Arkansas River. 

Total Dam 2

C = 0.06821 Q0.6130

R2 = 0.422

Sand Dam 2

C = 0.2185 Q0.3638

R2 = 0.0915

Total Terry L&D

C= 0.2168Q0.5019

R2 = 0.464

Sand Terry L&D

C= 0.1344Q0.4258

R2 = 0.1871

0.1

1

10

100

1000

1,000 10,000 100,000 1,000,000

Concentration mg/l

Discharge CFS

Total Dam2

Sand Dam2

Total TerryL&D

Sand Terry L&D

Power (Total Dam2)

Power (Sand Dam2)

Power (Total TerryL&D)

Power (Sand Terry L&D)

Total

C = 0.1493Q0.5236

Unbiased Sand

C = 0.1436Q0.4408

Sand

C = 0.0489Q0.4408

Unbiased Total

C = 0.2039Q0.5236

0.1

1

10

100

1000

10000

100 1,000 10,000 100,000 1,000,000

Concentration mg/l

Discharge CFS

Total

Sand

Power (Total)
MRG&P Report No. 30 98

The measured Arkansas River data included a sand-silt break. These data 

were used to determine the inflow concentrations for fines and sand. 

However, there were no additional size class percentage data available. 

Measured percentages from Mississippi River gage data at Coochie and 

Union Point (Mississippi RMs 317 and 326, respectively) were assigned for 

clay and silt sizes on the Arkansas River. 

Sediment transport for each sand size class was calculated for a series of 

steady state discharges at five upstream cross sections. Due to the small 

percentage of very fine sand in the bed, very fine sand was considered to 

be wash load. Very fine sand transport was assumed to be the difference 

between the measured sand transport from the unbiased sand regression 

curve and the calculated sand transport for the fine sand through very 

coarse sand size classes. Sand size class percentages were then determined 

from these calculated sand loads. The calculated percentages were then 

smoothed using regression analysis in EXCEL. Fine sand through very 

coarse sand size class percentages was increased by 15 percent to account 

for unmeasured load. 

Arkansas River sediment inflow rating curves, for each size class, are 

shown in Figure 56. HEC-6T sediment inflow is shown in Table 26.

Figure 56. Sediment inflow rating curves for Arkansas River. 

0.01

0.1

1

1 0

100

100 1,000 10,000 100,000 1,000,000 Concentration MG/L

Discharge CFS

Clay

VF Silt

F Silt

M Silt

C Silt

VF Sand

F Sand

M Sand

C Sand

VC Sand
MRG&P Report No. 30 99

Table 26. Sediment inflow for Arkansas River – Segment 8. 

Discharge 300 1000 4000 8,000 16,000 64,000 200,000 1,000,000

Concentration mg/l 4.0 7.6 15.7 22.5 32.4 67.0 121.6 121.6

Fractions 

Clay 0.2129 0.2287 0.2451 0.2526 0.2597 0.2727 0.2823 0.2823

VF Silt 0.0779 0.0837 0.0897 0.0924 0.0950 0.0998 0.1033 0.1033

F Silt 0.0604 0.0649 0.0696 0.0717 0.0762 0.0774 0.0802 0.0802

M Silt 0.0987 0.1061 0.1137 0.1171 0.1245 0.1265 0.1309 0.1309

C Silt 0.1108 0.1191 0.1276 0.1315 0.1352 0.1419 0.1470 0.1470

VF Sand 0.1248 0.1273 0.1260 0.1254 0.1248 0.1236 0.1225 0.1225

F Sand 0.1259 0.1101 0.0919 0.0829 0.0738 0.0556 0.0407 0.0407

M Sand 0.2227 0.1988 0.1714 0.1577 0.1439 0.1165 0.0939 0.0939

C Sand 0.0000 0.0021 0.0050 0.0065 0.0079 0.0108 0.0132 0.0132

VC Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0005 0.0008 0.0008

VF Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

F Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

M Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

C Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Sediment inflow Yazoo River 

The purpose of the Yazoo River Segment in the HEC-6T model is to 

provide sediment inflow to the Mississippi River. Data are insufficient for 

calibration of the Yazoo River Segment, and calculated morphologic 

changes should be treated with caution. There are significant suspended 

sediment measurements of the total and sand load available for a wide 

range of discharges. However, only two bed samples were available, and 

there were no data defining the individual size class percentages in the 

suspended load.

The USGS has measured suspended sediment at Redwood (RM 16.7) and 

downstream from Steel Bayou (RM 9.5). Suspended sediment samples 

were collected at the Yazoo River at Redwood, Mississippi gage (USGS 

07288800) between 1978 and 1993. Suspended sediment samples were 

collected at the Yazoo River below Steele Bayou near Long Lake, 

Mississippi gage (USGS 07288955) between 1995 and 2010. The data 

from both gages were plotted together to determine power regression 
MRG&P Report No. 30 100 

equations for the total load and the sand load. Unbiased regression 

equations were calculated for both. The measured data and regression 

curves are shown in Figure 57.

Figure 57. Sediment concentration Yazoo River at Redwood and Steel Bayou. 

The total measured load data were used to evaluate the possibility of a 

declining or increasing trend in the sediment delivery to the Mississippi 

River. Power regression curves were calculated for the 1991–2002 and 

2003–2010 time periods. These curves were found to be very close to the 

regression curve for the entire 1978–2010 period as shown in Figure 58.

Figure 58. Total sediment concentration trends Yazoo River. 

Total

y = 7.7025x0.3255

Unbiased Total

y = 11.511x0.3255

Sand

y = 0.5900x0.1937

Unbiased Sand

y = 1.0238x0.1937

0.1

1

10

100

1000

10000

100 1,000 10,000 100,000

Concentration mg/l

Discharge CFS

Total

sand

Power (Total)

Power (unbiased total)

Power (sand)

Power (unbiased sand)

Total

y = 7.7025x0.3255

Unbiased Total

y = 11.511x0.3255

1

10

100

1000

10000

100 1,000 10,000 100,000

Concentration mg/l

Discharge CFS

Total

91-02

'02-10

Power (Total)

Power (unbiased total)

Power (91-02)

Power ('02-10)
MRG&P Report No. 30 101

The inflowing sediment load size class percentages for fines and sands 

were assumed to be the same as the measured size class percentages from 

the 1991–2002 data at Coochie and Union Point. These sediment gages 

are located at Mississippi RMs 317 and 326, respectively, and are the 

closest gages with size class data. The total fine sediment concentration 

was determined from the measured Yazoo River data, and then the fine 

sediment size class distribution was taken from the Coochie and Union 

Point fine sediment size class distribution data. Similarly, the total sand 

concentration was determined from the measured Yazoo River data, and 

then the sand size class distribution was taken from the Coochie and 

Union Point data. This methodology results in a significant discontinuity 

between coarse silt and very fine sand concentrations in the inflowing 

sediment load rating curves. The sand concentrations were arbitrarily 

increased by 15 percent to account for the unmeasured load. The 

sediment inflow rating curves for the Yazoo River are shown in Figure 59

and Table 27.

Figure 59. Sediment inflow rating curves for Yazoo River. 

Only two bed material samples were available for the Yazoo River. The 

USGS collected these samples at the Steele Bayou Gage. Both samples 

were collected in August: one in 1995 that contained only 8 percent sand 

and one in 1997 that contained 5 percent sand. These data suggest that the 

bed of the Yazoo River is primarily cohesive. Therefore, the bed sediment 

reservoir in the HEC-6T model was set to zero. The initial bed gradation in 

the Yazoo River was determined based on the two measurements, 

0.1

1

10

100

1000

100 1,000 10,000 100,000

Concentration mg/l

Discharge CFS

Clay

VF Silt

F Silt

M Silt

C Silt

VF Sand

F Sand

M Sand
MRG&P Report No. 30 102 

normalizing them to 100 percent sand. Since the bed sediment reservoir 

has been given a zero depth, this bed gradation only serves as a starting 

point in the numerical solution of the sediment continuity equation.

Table 27. Sediment inflow for Yazoo River – Segment 6. 

Discharge 10 100 1000 10,000 50,000 100,000 350,000

Concentration mg/l 44.6 44.6 97.6 213.4 368.8 466.8 466.8

Fractions

Clay 0.3482 0.3482 0.3522 0.3554 0.3573 0.3580 0.3580

VF Silt 0.1224 0.1224 0.1237 0.1249 0.1255 0.1258 0.1258

F Silt 0.1035 0.1035 0.1047 0.1057 0.1062 0.1064 0.1064

M Silt 0.1694 0.1694 0.1713 0.1729 0.1738 0.1742 0.1742

C Silt 0.1976 0.1976 0.1999 0.2017 0.2028 0.2032 0.2032

VF Sand 0.0118 0.0118 0.0096 0.0079 0.0069 0.0065 0.0065

F Sand 0.0218 0.0218 0.0178 0.0146 0.0127 0.0120 0.0120

M Sand 0.0253 0.0253 0.0207 0.0170 0.0148 0.0139 0.0139

C Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Sand 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VF Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

F Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

M Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

C Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

VC Gravel 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Sediment inflow sources 

Cumulative sediment inflows to the Mississippi River from the 

tributaries were calculated for the 1991–2002 calibration period. Using 

the sediment inflow rating curves described in the preceding sections, the 

calculated sediment inflowing sediment load percentages from each 

tributary are tabulated in Table 28. The table shows the calculated inflow 

from the tributary, which includes any calculated supply or deposition in 

the tributary between the upstream boundary and the confluence. 

Calculations show that 69.0 percent of the total sediment and 80.4 

percent of the sand are supplied by the Middle Mississippi River, even 

though most of the water is supplied by the Ohio River.
MRG&P Report No. 30 103 

Table 28. Source of Mississippi River water and sediment loads. 1991–2002 

by percentage – based on HEC 6T input. 

 Water Total Clay Silt Sand 

Ohio River 45.1 21.0 21.7 26.6 11.5

Middle Mississippi River 37.4 69.0 68.9 61.0 80.4

Arkansas River 8.2 3.1 1.7 3.1 6.3

White River 4.4 1.3 1.4 1.1 0.5

Yazoo River 3.0 3.2 3.2 5.8 0.3

St. Francis River 0.8 0.5 0.7 0.4 0.0

Hatchie River 0.6 0.4 0.5 0.4 0.2

Obion River 0.5 1.5 1.9 1.6 0.8

Depth of bed sediment reservoir 

The Exner 7 sorting and armoring algorithm used in this study assumes 

that the bed sediment reservoir provides an infinite supply unless a 

bottom elevation is prescribed. Sediment continuity is maintained in three 

separate bed layers during the computer simulation, and the bed sediment 

reservoir only comes into play during the initial time-step and when 

erosion of the three surface layers occurs. If the supply of bed sediment is 

limited in the prototype then that limit must be set in HEC-6T.

The bed sediment reservoir depth was limited at several locations in the 

Mississippi River where erosion is known to be limited by cohesive 

deposits, bedrock, gravel deposits, or constructed sills. A bed sediment 

reservoir depth of 1 ft was assigned in the model between RMs 12.5 and 57. 

This reflects the presence of a cohesive layer underlying the Mississippi 

River over which sand is transported (Kolb 1962). A bed sediment 

reservoir of 0.01 ft was specified in the Profit Island Chute (RMs 248.38 

and 248.56) and the Wolf Island Chute (RM 934.4) to account for closure 

structures constructed in the chutes. The bed sediment reservoir was also 

limited to 1 ft at RM 734.56 (I-55 Bridge at Memphis), 0.1 ft at RM 911.2 

(Island No. 8 main channel), 1.0 ft at RM 917.6, and 0.01 ft at RM 922. 

The bed sediment reservoir was also limited in some of the tributaries. The 

bed of the Ohio River was limited to 1 ft at the Metropolis Bridge, located 

approximately 41 miles upstream from Cairo. The Middle Mississippi 

River bed sediment reservoir was limited between RMs 32.84 and 44.29, 

and at 109.90 to account for exposed bed rock at these locations. The bed 

sediment reservoir in the St. Francis River was set at 20 ft because that 

was used in a previous HEC-6T study conducted for that river. The entire 
MRG&P Report No. 30 104 

White River and Yazoo River segments were assigned a bed sediment 

reservoir depth of only 0.01 ft. This was due to a lack of bed-material 

gradation data. These tributary segments are intended to provide a 

reasonable estimate of sediment inflow from the tributary. By setting a bed 

sediment reservoir depth of 0.01 ft, only deposition is allowed in the 

tributary so that there is no sediment contribution from the river bed. Data 

are insufficient for calibration of the White and Yazoo River segments, and 

calculated morphologic changes should be treated with caution. The cross 

sections on the Hatchie and Obion Rivers were assigned bed sediment 

reservoir depths of 0.01 ft. 

The dredging algorithm in HEC-6T requires that a bed sediment reservoir 

depth be prescribed. At non-dredging sites, the bed sediment reservoir 

depth is calculated by the hydraulic sorting and armoring algorithm. A bed 

sediment reservoir depth of 20 ft was assigned in the HEC-6T model in the 

New Orleans District between RMs -18.0 and 5.5 where dredging was 

calculated during the simulation. A bed sediment reservoir depth of 50 ft 

was assigned in the HEC-6T model in the Memphis District at all of the 

dredging sites. However, in the calibration study there was no dredging 

calculated in the Memphis District reach. The sensitivity of the depth of 

bed sediment reservoir assumption should be tested in future studies 

where the model is being used to test project impacts at specific dredging 

sites. A bed sediment reservoir depth will need to be included in any future 

studies using this model if new dredging sites are specified. 

Mississippi River bed material gradations 

Bed material sampling programs of the Mississippi River have indicated 

significant longitudinal and lateral variability in the bed material 

gradations. An example of lateral variability is shown in Figure 60 where 

samples were taken from transects at quarter points at a river bend at 

Bayou Sara (RM 265). In Figure 60 the point bar is on the right side of the 

river. Longitudinal variability is primarily due to the differences in bed 

shear stresses associated with the natural bends and crossings along the 

course of the river. Variability over short distances of 1 or 2 miles can 

equal the average variability over the entire 950 miles between Head of 

Passes and Cairo. This variability makes it difficult to determine if there 

has been any long-term change in the bed material gradation. Nordin and 

Queen (1992) compared thalweg bed-material samples that they collected 

in 1989 to thalweg bed-material samples collected in 1932 (WES 1935) and 

concluded the following:
MRG&P Report No. 30 105 

1. The 1989 samples were more uniform than the 1932 samples, containing 

less coarse sand and gravel and less very fine sand than the 1932 samples. 

The significant decrease in gravel is shown in Figure 61 which plots the 

median grain diameters of both the 1932 and 1989 samples.

2. Between Cairo and Vicksburg, the median grain diameter was generally 

smaller in 1989 than it was in 1932. This small difference in shown in 

Figure 62 which plots the median grain diameters of only the sand 

samples. Without the linear regression lines it would be difficult to 

determine any difference in the median size between 1932 and 1989. The 

average difference is contained within the data scatter.

3. Downstream from Vicksburg, the median grain diameter of the bed 

material was essentially the same in 1989 and 1932. 

Figure 60. Lateral variation in bed material gradation at RM 265, August 2005. 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 Percent Finer

Grain Size mm

Left

Center

Right
MRG&P Report No. 30 106 

Figure 61. Historic change in Mississippi River median bed grain size. 

Initial bed-material gradations in the numerical model were adjusted to 

allow for variability associated with cross-section shape and velocity. The 

Nordin and Queen (1992) data were used to develop polynomial regression 

curves of the bed material gradations to determine an average longitudinal 

variability. These are shown in Figures 63 and 64. Initial bed gradations 

for each model cross section were calculated using a bankfull discharge of 

1,436,000 for 30 days at Vicksburg. The Vicksburg bankfull discharge was 

calculated from assigned bankfull discharges from tributaries in the 

Memphis District. These new calculated bed gradations were then set as 

initial conditions in the numerical model. The calculated initial bed 

gradations are shown in Figure 65. 

0.01

0.10

1.00

10.00

100.00

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 Median Grain Size mm

River Mile

1932

1989

Data from Nordin and Queen (1992)
MRG&P Report No. 30 107 

Figure 62. Historic change in median bed grain size — gravel samples removed. 

Figure 63. 1989 bed gradations downstream from RM 306 with polynomial trend lines. 

0.01

0.10

1.00

10.00

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 Median Grain Size mm

River Mile

1932

1989

Linear (1932)

Linear (1989)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 50 100 150 200 250 300 350 400 450 Percent Finer

River Mile

1mm

0.5mm

.25mm

.125mm

Poly. (1mm)

Poly. (0.5mm)

Poly. (.25mm)

Poly. (.125mm)

Data from Nordin and Queen (1992)
MRG&P Report No. 30 108 

Figure 64. 1989 bed gradations upstream from RM 306, with polynomial trend lines. 

Figure 65. Initial bed calculated starting with Nordin polynomials after 30 days. 

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

200 300 400 500 600 700 800 900 1000 Percent Finer

River Mile

2mm

1mm

0.5mm

.25mm

.125mm

Poly. (2mm)

Poly. (1mm)

Poly. (0.5mm)

Poly. (.25mm)

Poly. (.125mm)

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000 Percent Finer

River Mile

Calc Initial .125mm

Calc Initial .25mm

Calc Initial .5mm

Calc Initial 1.0 mm

Calc Initial 2.0 mm

Nordin Poly .125 mm

Nordin Poly .25 mm

Nordin Poly .5 mm

Nordin Poly 1.0 mm

Nordin Poly 2.0 mm
MRG&P Report No. 30 109 

Tributary bed gradations 

Middle Mississippi River bed gradations 

The initial bed material gradations for the Middle Mississippi River 

segment between Cairo and Chester were developed from the USGS 

measured data at Thebes. Fourteen bed material gradations, taken 

between 1980 and 1989, were reported by the USGS on its water quality 

web site. The average of these gradations, and the maximum and 

minimum curves, are shown in Figure 66. The average Thebes bed 

gradation was assigned at all cross sections on the Middle Mississippi 

River segment. These initial bed-material gradations in the numerical 

model were then adjusted to allow for variability associated with crosssection shape and velocity by running a bankfull discharge of 413,000 cfs 

for 30 days. 

Figure 66. 1980–1989 average bed-material gradation at Thebes. 

Ohio River bed gradations 

The initial bed material gradations for the Ohio River segment between 

Cairo and Metropolis were developed from the average of multiple 

samples collected from three transects in the vicinity of Olmstead Lock 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100 Percent Finer

Sieve Diameter mm

Average

Miaximum

Minimum
MRG&P Report No. 30 110 

and Dam (Ohio RM 964.6, RM 970.4 AHP). The bed sampling site is 

approximately 17 miles upstream from Cairo. These samples were 

normalized to eliminate fines. The average of these gradations is shown in 

Figure 67. The average Olmstead bed gradation was assigned at all of the 

cross sections in the Ohio River segment. A bankfull discharge of 552,000 

cfs was run for 30 days to determine the initial bed-material gradations for 

the numerical model. The calculated initial gradations at the upstream end 

of the segment (Ohio RM 945, RM 990 AHP) and the downstream end of 

the segment (Ohio RM 981, RM 954 AHP) are shown in Figure 67. The 

calculated initial bed gradation for the Mississippi River at Cairo 

(Mississippi RM 953) is also shown in the figure. The figure shows that the 

adjusted bed material gradations are coarser than the average gradation at 

Olmstead; however, the downstream Ohio River cross section has an 

adjusted bed gradation that is very close to the Olmstead gradation. Figure 

67 also shows that the Ohio River bed is considerably coarser than the 

Mississippi River bed calculated at Cairo.

Figure 67. Ohio River bed-material gradations. 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100 Percent Finer

Grain size mm

Average Olmsted Meas

Calculated Miss RM 953

Calculated Ohio RM 945

Calculated Ohio RM 981
MRG&P Report No. 30 111

Obion and Hatchie River bed gradations 

Bed material samples for the Hatchie and Obion Rivers were collected for 

this study at Highway 51 near Rialto, TN, on the Hatchie River (RM 34) 

and at Highway 78 near Bogota, TN, on the Obion River (RM 36.7). 

Samples were collected at three transects at a crossing using a 6 in. clamshell sampler in June 2005. The transects were near the right bank, in the 

center of the channel, and near the left bank. The sample collection sites 

were located well upstream of the model boundary to escape the influence 

of backwater effects from the Mississippi River. The assigned bed material 

gradations for the numerical model are shown in Figure 68. 

Figure 68. Initial bed-material gradations used for the Obion and Hatchie Rivers. 

St. Francis River bed gradations 

The USGS has collected an extensive set of bed material gradation data on 

the St. Francis River at Madison and Riverfront. Madison is at RM 37.4, 

approximately 20 miles upstream from the HEC-6T model boundary, and 

Riverfront is at RM 58.0. The initial HEC-6T bed material gradation used 

for the St. Francis River was taken from the average of 139 samples 

collected between 1991 and 2002 at Madison. The gradation was 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 Percent Finer

Grain Size mm

Obion 0.1

Obion 2.0

Hatchie 0.1

Hatchie 2.0
MRG&P Report No. 30 112

normalized to represent 100 percent sand. The average 1991 and 2002 

gradation is compared to the 1977–2009 average gradation, which was 

determined from 377 samples, in Figure 69. Also shown are average 

gradations from the similar data set at Riverfront. The data suggest that 

there is no long-term variation in the bed gradation in the St. Francis River.

Figure 69. USGS bed gradations for St. Francis River at Madison and Riverfront. 

White River bed gradations 

Bed material samples were available at one site on the White River in the 

reach between Clarendon and the Mississippi River. The samples were 

collected at RM 4 from the bed, the point bar, and the bank by ERDC in 

2003 as part of a geomorphic assessment of the Arkansas and White 

Rivers. The median grain diameter of the bed was 0.18 mm, and the 

median grain diameter of the point bar was 0.17 mm. The bank was 

composed of entirely silts and clays. Bed gradations are shown in Figure 

70. An average of the bed and point bar samples was used as an initial bed 

gradation for the White River in the HEC-6T model. However, early in the 

movable bed calibration it was determined that the calculated degradation 

was unreasonable with this initial bed gradation. To eliminate scour, the 

bed sediment reservoir was set at 0.01 ft, allowing the model to calculate a 

bed gradation based on the inflowing sediment load. With these 

constraints, HEC-6T could calculate deposition but not erosion below the 

initial bed elevation. 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 Percent Finer

Grain Size mm

Madison 91-02 Ave

Madison 77-09 Ave

Riverfront 91-02

Riverfront 77-09
MRG&P Report No. 30 113

Figure 70. White River bed-material gradations collected by ERDC at RM 4. 

Arkansas River bed gradations 

Only two Arkansas River bed material samples were available in the reach 

between Lock and Dam 2 and the Mississippi River. This reach of the 

Arkansas River does not have designated river miles, and the reach length 

varies with time due to lateral migration and cutoffs. The numerical model 

represents 2003 conditions when the approximate distance between Lock 

and Dam 2 and the Mississippi River was 29 miles. The bed samples were 

collected from point bars in 2003 as part of a geomorphic assessment of 

the Arkansas and White Rivers. The two samples were collected at 

Emerson Bend, which is located approximately 10 miles upstream from 

the mouth of the Arkansas River; and Camp Bend, which is located 

approximately 19 miles upstream from the mouth of the Arkansas River. 

Bed gradations are shown in Figure 71 . An average of these two samples 

was used to develop an initial bed gradation that was used for entire 

Arkansas River reach. The bed gradation was adjusted at each cross 

section using a 30-day bankfull simulation. The adjusted values were then 

used as the initial bed gradation for the calibration simulation. 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 Percent Finer

Sieve Diameter mm

Bed

Point Bar
MRG&P Report No. 30 114

Figure 71. Arkansas River bed-material gradations at Emerson and Camp Bends. 

Yazoo River bed gradations 

Two bed material samples were available from the USGS gage at Steele 

Bayou on the Yazoo River. The samples, which were collected during 

August 1995 and August 1997, contained only 3 and 4 percent sand, 

respectively. The gage is in the Mississippi River backwater area, and the 

data may not reflect the actual bed gradation during channel forming 

events. An average of the two samples was normalized to 100 percent sand 

and used as the initial bed gradation for the Yazoo River in the HEC-6T 

model. However, early in the movable bed calibration it was determined 

that the calculated degradation was unreasonable with this initial bed 

gradation. To eliminate scour, the depth of the bed sediment reservoir was 

set at 0.01 ft, which allowed the model to calculate a bed gradation based 

on the inflowing sediment load. With these constraints, HEC-6T could 

freely calculate deposition, but erosion was limited to 0.01 ft.

Sediment concentrations in distributary flows 

The sediment concentrations that are diverted into distributaries are 

boundary conditions in a 1D model. The ratio of the sediment 

concentration in the distributary to the sediment concentration in the 

Mississippi River is called the sediment diversion coefficient and must be 

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10

Sieve Diameter mm Percent Finer

Emerson

Camp
MRG&P Report No. 30 115 

determined externally and coded as input data to the program. At the Old 

River Control Complex, sediment diversion coefficients for each size class 

were extracted from a previous study (Catalyst-Old River Hydroelectric, 

1999). The sediment diversion coefficients from the 1999 study had been 

developed from available measured data and numerical model calibration. 

Due to the wide scatter in the measured data, no attempt was made to vary 

the sediment diversion coefficients with changes in discharge or with 

variations in operation schedules. 

For the remaining distributaries, estimates of vertical sediment 

concentrations were computed using the Rouse (1937) equation. Sediment 

diversion coefficients were calculated for each size class by comparing the 

average Mississippi River bed elevation with the diversion sill or inlet 

channel elevation. This method accounts for the vertical variation in 

sediment concentrations, but it does not account for the lateral variation 

due to river meanders or for variable depths in a river cross section.

Sediment diversion coefficients for the Auxiliary Structure were 

determined from measured data in the 1999 study. Measurements from 

Tarbert Landing, taken between 1991 and 1998, were used to determine 

Mississippi River concentrations. The Tarbert Landing measurements 

were collected using standardized methods. Measurements at the 

Auxiliary Structure, taken between 1991 and 1997, were taken using nonstandard methods. That is, the suspended sediment samples were 

collected from three pumping samplers that were located on the 

downstream side of the gate piers. Additional measurements from the 

Auxiliary Structure inflow channel were made in 1998 using standardized 

methods. Sediment concentrations through the Auxiliary Structure were 

determined using measured averages. These concentrations were 

supplemented by hydrographic surveys of the inlet channel before and 

after flushing flows to include the sediment load passing the structure 

during flushing operations. When the measured data were combined with 

the survey data, the resulting ratio approximated the total sediment 

diverted through the structure. 

Sediment diversion coefficients for the Low Sill Structure were determined 

from measured data in the 1999 study. Mississippi River measurements at 

both Tarbert Landing and Coochie/Union Point were collected between 

1991 and1998 using standardized methods. Average concentrations 

calculated for these Mississippi River stations were compared to average 
MRG&P Report No. 30 116 

concentrations calculated from pumping sampler data collected from the 

downstream side of the gate piers at the Low Sill Structure. The data from 

the pumping samplers were supplemented using inlet channel 

hydrographic survey data as described above for the Auxiliary Structure. 

Additional measurements were made, using standardized methods, in 

1998 in the Low Sill Structure inflow channel and between 1989 and 1991 

in the Low Sill Structure outflow channel. Data collected during the period 

from 1976 to 1979, at Tarbert Landing and at gage C-89, which is located 

in the Outlet Channel approximately 2 miles downstream from the 

diversion structures, were used to supplement the more recent data. Both 

of these data sets were collected using standardized methods. 

In the 1999 study, sediment diversion coefficients for the Hydropower 

Plant were determined from the 1991–1998 average measured suspended 

loads at Coochie/Union Point and the 1991–1997 measured data from the 

Hydropower Plant. The measured suspended sediment loads at 

Coochie/Union Point were calculated from samples collected using 

standardized methods. The measured suspended loads at the Hydropower 

Structure were taken from pumping samplers located on the top of the 

power plant draft tubes. In 1998, measured suspended sediment data were 

collected from the Hydropower Structure inflow channel using 

standardized methods. 

The final adopted sand sediment diversion coefficients from the 1999 

study are tabulated in Table 29. These assignments were adopted in this 

study. Clay and silt sediment sizes and sediment larger than coarse sand 

were not considered in the 1999 study. In this study, fine sediments were 

assigned a sediment diversion coefficient of 1.0, and sediments coarser 

than coarse sand were assigned a sediment diversion coefficient of 0.0.

Table 29. Sediment diversion coefficients at Old River Control Complex from Catalyst-Old 

River Hydroelectric (1999). 

 

Hydropower 

RM 315.9 

Spillway 

RM 315.2 

Low Sill 

RM 314.6 

Auxiliary 

RM 312.0 

Very-fine sand 0.8 0.5 0.9 0.9

Fine sand 0.4 0.2 0.8 0.8

Medium sand 0.2 0.0 0.6 0.8

Coarse sand 0.2 0.0 0.6 0. 8
MRG&P Report No. 30 117 

As mentioned in the opening paragraph of this section, sediment diversion 

coefficients are specified as boundary conditions in the numerical model. 

A sediment diversion coefficient is specified for each sediment size class. 

Typically, inlet channels at diversions are at a higher elevation than the 

average bed of the river and draw flow from the upper portion of the water 

column in the river. Coarse sediment concentrations are higher at the 

bottom of the water column while fine sediment is more evenly distributed 

in the water column. Thus, the sediment diversion coefficients will be 

higher for finer sediment than for coarser sediment.

If the vertical velocity distribution and the vertical concentration 

distributions for each size class are known, then the sediment diversion 

coefficients for the sediment load can be calculated from the following 

equation:













 Dy

ay

iy y

Dy

hy

iy y

i

uC dy

uC dy

Sediment Diversion tCoefficien

where:

Ci = concentration of sediment size class i.

D = depth of flow in the main channel

h = height of diversion invert above average river bed

a = reference height near the stream bed – taken to be zero for 

these calculations

uy = velocity at depth y.

Using the Rouse (1937) equation for calculating sediment concentration, 

the following equation is derived by substitution. 















































Dy

ay

y

Z

ia

Dy

hy

y

Z

ia

i

u dy

aD

a

y

yD

C

u dy

aD

a

y

yD

C

Diversion Sediment tCoefficien
MRG&P Report No. 30 118

where:

Cia=concentration at the reference elevation

and

*

uk

z

























yk

uu

s

y

30 1.

*

.5 75 log

where:

ω = particle fall velocity

β = ratio of sediment and momentum exchange coefficients – 

taken to be 1.0

k = Von Karman constant – taken to be 0.4 

u* = shear velocity

ks = roughness height.

Removing the constant terms and converting from sediment load to 

concentration leaves the following equation, which can be solved using 

numerical integration. Hydraulic terms for this equation were determined 

at upstream river cross sections from HEC-6T backwater calculations for a 

range of discharges. Other terms are known.























 











 





Dy

ay

y

Z

Dy

hy

y

Z

i

u dy

y

yD

D

u dy

y

yD

hD

Sediment Diversion tCoefficien

1

1

The Rouse (1937) equation describes sediment concentration due to 

vertical diffusion. It does not account for convective sediment transport or 

for lateral diffusion. Thus, this analysis does not account for sediment that 

may ramp up into the diversion inflow channel. Ramping may not be a 

significant contributor of sediment for diversions located on the outside of 

meander bends, but ramping may be significant on the inside of bends or 

at bar locations. Actual measurements at diversions and in the upstream 
MRG&P Report No. 30 119 

main channel are the most reliable means of determining existing 

sediment diversion coefficients. Establishing a sediment measurement 

program that includes use of standardized methods is recommended at 

significant distributary locations for use in future studies.

The invert elevation in the four Southwest Pass distributaries was 

estimated to be at elevation -10 ft. The best available data to make this 

estimate were the 1992 and 2002 hydrographic surveys. Sills that may 

have been placed across these structures are accounted for only if they 

showed up in the hydrographic survey. At Outlet W-2, the sediment 

diversion coefficients represent a combination of flow over the levees at 

high flow and flow through the distributary channel. The elevation of the 

natural levee was estimated to be 1.2 ft based on digital data used to 

develop the cross sections for HEC-6T. Sediment diversion coefficients 

used in Southwest Pass are tabulated in Table 30 through Table 33. Ratios 

for sediment coarser than fine sand were 0.0.

Table 30. Sediment diversion coefficients, Burrwood Bayou. 

Discharge CFS 24,000 18,000 10,600 7,500 3,000 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 0.98 0.92 0.64 0.30

Coarse silt 0.90 0.85 0.65 0.50 0.09 0.0

Very fine sand 0.49 0.38 0.12 0.03 0.0 0.0

Fine sand 0.06 0.02 0.0 0.0 0.0 0.0

Table 31. Sediment diversion coefficients – outlet W-2 and overlfows. 

Discharge CFS 84,000 36,000 10,600 7,500 3,000 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 0.98 0.92 0.64 0.30

Coarse silt 0.88 0.85 0.65 0.50 0.09 0.0

Very fine sand 0.44 0.34 0.12 0.03 0.0 0.0

Fine sand 0.05 0.03 0.0 0.0 0.0 0.0
MRG&P Report No. 30 120 

Table 32. Sediment diversion coefficients – Joseph Bayou. 

Discharge CFS 24,000 18,000 10,600 7,500 3,000 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 0.98 0.92 0.64 0.30

Coarse silt 0.90 0.85 0.65 0.50 0.09 0.0

Very fine sand 0.49 0.38 0.12 0.03 0.0 0.0

Fine sand 0.06 0.02 0.0 0.0 0.0 0.0

Table 33. Sediment diversion coefficients – Southwest Pass at Mile 3.0. 

Discharge CFS 12,000 9,000 5,300 3,800 1,500 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 0.98 0.92 0.64 0.30

Coarse silt 0.90 0.85 0.65 0.50 0.09 0.0

Very fine sand 0.49 0.38 0.12 0.03 0.0 0.0

Fine sand 0.06 0.02 0.0 0.0 0.0 0.0

The invert elevations in South Pass and Pass a Loutre were estimated to be 

at elevations -31 ft and -17 ft, respectively. This estimate was based on the 

2002 hydrographic survey. Sediment diversion coefficients were 

calculated separately for the two major diversions and combined for the 

HEC-6T model. The combined ratios are tabulated in Table 34. Ratios for 

sediment coarser than medium sand were 0.0.

Table 34. Sediment diversion coefficients – South Pass and Pass a Loutre. 

Discharge CFS 270,000 225,000 160,000 76,000 40,000 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 1.0 1.0 0.97 .93

Coarse silt 0.99 0.97 0.96 0.91 0.65 .37

Very fine sand 0.76 0.70 0.65 0.49 0.09 0.0

Fine sand 0.29 0.22 0.16 0.05 0.0 0.0

Medium sand 0.03 0.02 0.01 0.0 0.0 0.0
MRG&P Report No. 30 121 

The average inlet channel elevation in Cubits Gap was taken to be -13 ft 

based on 2009 surveyed cross sections. These surveys were conducted by 

ERDC. The 1992 hydrographic survey shows a sill across Cubits Gap. 

However, the existence of this sill was not confirmed by the recent surveys. 

The sill may be buried, or it may have washed out. Flow occurs over the 

natural levee between Head of Passes and Venice. Sediment diversion 

coefficients for the overbank flow were calculated using the minimum endof-cross-section elevation between Venice and Head of Passes. This 

elevation was 1.7 ft. The combined sediment diversion coefficients were 

calculated by discharge weighted averaging. The sediment diversion 

coefficients for Cubits Gap are tabulated in Table 35. Ratios for sediment 

coarser than fine sand were 0.0.

Table 35. Sediment diversion coefficients – Cubits Gap. 

Discharge, cfs 243,700 148,800 74,800 53,400 32,200 16,100 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 1.0 1.0 0.97 0.84 0.70

Coarse silt 0.94 0.90 0.85 0.80 0.64 0.32 0.0

Very fine sand 0.57 0.48 0.37 0.27 0.09 0.0 0.0

Fine sand 0.12 0.05 0.02 0.0 0.0 0.0 0.0

The invert elevations in Grand Pass were very close to the average bed 

elevations in the Mississippi River according to the 2002 hydrographic 

survey. Sediment diversion coefficients were set equal to 1.0 for clay and 

silt and 0.9 for sands for all discharges. Diversion coefficients for sediment 

coarser than medium sand were 0.0.

The average invert elevation in Baptist Collette was taken from a 2009 

survey conducted by New Orleans District. The invert elevation in Baptiste 

Collette was -45 ft. The sediment diversion coefficients for Baptiste 

Collette are tabulated in Table 36. Diversion coefficients for sediment 

coarser than medium sand were 0.0.
MRG&P Report No. 30 122 

Table 36. Sediment diversion coefficients – Baptiste Collette. 

Discharge CFS 117,000 75,000 44,000 18,000 1

Clay 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 1.0 1.0 1.0

Coarse silt 1.0 1.0 0.98 0.84 0.70

Very fine sand 0.89 0.83 0.68 0.24 0.0

Fine sand 0.49 0.34 0.12 0.0 0.0

Medium sand 0.08 0.02 0.0 0.0 0.0

The elevation of the natural levee along the Bohemia Spillway was 

determined by New Orleans District using 2004 Louisiana lidar data. Top of 

levee elevations were found to vary between 5.3 and 11.8 ft NGVD29. 

Sediment diversion coefficients for the maximum discharge of 1,250,000 cfs 

were calculated using the average of the calculated water-surface elevation 

and the minimum levee elevation in each of the four reaches along the 

spillway. The sediment diversion coefficient for clay through medium silt 

was 1.0. The coarse silt sediment diversion coefficient was 0.96. The very 

fine sand diversion coefficient was 0.6, and the fine sand diversion 

coefficient was 0.14. The coefficient for sediment coarser than fine sand 

was 0.0.

The invert elevation in Caernarvon Diversion inlet channel is -12 ft. This 

elevation was obtained from the Operations and Maintenance Manual. 

Sediment diversion coefficients were calculated for a range of Mississippi 

River discharges up to 1,250,000 cfs. However, the maximum discharge 

through the Caernarvon structure was set at 6,000 cfs in the model 

simulations. This results in a non-unique relationship between discharge 

through the structure and the sediment diversion coefficient which is 

changing with depth in the Mississippi River. The calculated rating curve 

is shown in Figure 72. Average sediment diversion coefficients were used 

at Caernarvon and are tabulated in Table 37. Coefficients for sediment 

coarser than medium sand were 0.0.
MRG&P Report No. 30 123 

Figure 72. Sediment diversion coefficients at Caernarvon. 

Table 37. Sediment diversion coefficients – Caenarvon. 

Discharge,

cfs 6000 5400 3900 2300 1500 1000 1

Clay 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 1.0 1.0 0.96 0.90 0.0

Coarse silt 1.0 0.94 0.87 0.72 0.55 0.40 0.0

Very fine 

sand 0.70 0.53 0.38 0.16 0.05 0.0 0.0

Fine sand 0.22 0.08 0.02 0.0 0.0 0.0 0.0

Medium sand 0.02 0.0 0.0 0.0 0.0 0.0 0.0

The elevation of the Bonnet Carré inlet channel varies. Bank elevations 

along the Mississippi River at the spillway entrance channel were 

estimated from the 1992 hydrographic survey. The bank elevations were 

between 9.3 ft and 12.9 ft. Calculations for the sediment diversion 

coefficients were based on average river channel depths and bank 

elevations. Clay and silt sediment diversion coefficients of 1.0 were 

0

0.2

0.4

0.6

0.8

1

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000

Diversion Discharge cfs Concentration Ratio

Coarse Silt

VFS

FS

MS
MRG&P Report No. 30 124 

calculated. Sand coefficients are listed in Table 38. Coefficients for 

sediment coarser than medium sand were 0.0.

Table 38. Sediment diversion coefficients – Bonnet Carré. 

Discharge, cfs 250,000 125,000 11,500 1

Clay 1.0 1.0 1.0 1.0

Very fine silt 1.0 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0 1.0

Medium silt 1.0 1.0 1.0 1.0

Coarse silt 1.0 1.0 1.0 1.0

Very fine sand 0.75 0.72 0.69 0.67

Fine sand 0.30 0.27 0.23 0.20

Medium sand 0.04 0.03 0.02 0.01

Sediment distribution around islands 

There are three islands in the numerical model. Wolf Island is located 

between RMs 930.8 and 934.4. Island 8 is located between RMs 910 and 

915.59. Profit Island is located between RMs and 246.3 and 253. There are 

many more locations where divided flow occurs in the study reach, but 

only these three were included in the numerical model as separate looped 

segments. The other divided flow cross sections were assumed to have the 

same water surface elevation across the section. In some cases, geometry 

was adjusted to maintain appropriate flow distribution in the cross 

section. This treatment is deemed adequate for the general model. 

Detailed investigations of specific reaches may require the addition of 

additional looped segments.

Sediment distribution at the upstream end of looped segments is a model 

boundary condition. The model assumes equal sediment concentrations in 

both loops if no boundary condition is supplied. There were no measured 

suspended data available to calibrate the sediment distribution, so initially 

the model default was used in the calibration runs. The assignment of equal 

sediment concentrations in both loops produced deposition and erosion 

results inconsistent with known channel responses. Consequently, sediment 

inflow distributions were adjusted until reasonable channel responses were 

calculated. Without calibration data, the results remain questionable and 

are adequate for the general model but require more detailed investigation 

if the islands are part of a detailed reach investigation.
MRG&P Report No. 30 125 

The ratio of sediment concentration in the secondary loop to sediment 

concentration upstream from the island is specified for each sediment size 

class. The model then calculates the sediment concentration for the primary 

loop. The wash load, which constitutes all the sediment less than 0.125 mm, 

was assumed to have the same concentration in both loops. The remaining 

size classes were assigned sediment distributions shown in Table 39.

Table 39. Island sediment concentration ratios in secondary channel. 

 Profit Island Island 8 Wolf Island 

Clay 1.0 1.0 1.0

Very Fine Silt 1.0 1.0 1.0

Fine Silt 1.0 1.0 1.0

Medium Silt 1.0 1.0 1.0

Coarse Silt 1.0 1.0 1.0

Very Fine Sand 1.0 1.0 1.0

Fine Sand 0.8 0.75 0.9

Medium Sand 0.6 0.5 0.7

Coarse Sand 0.5 0.5 0.5

Very Coarse Sand 0.5 0.5 0.5

Very Fine Gravel 0.5 0.4 0.5

Fine Gravel 0.5 0.4 0.5

Medium Gravel 0.5 0.4 0.5

Coarse Gravel 0.5 0.4 0.5

Very Coarse Gravel 0.5 0.4 0.5
MRG&P Report No. 30 126 

3 Model Calibration and Verification

The calibration and verification procedure adopted for this study is the 

accepted USACE methodology described in Guidelines for Calibration and 

Application of HEC-6 (HEC 1982) and Chapter 14 of ASCE Manual 110 

(ASCE 2006). Terminology for the study process of preparing a numerical 

model for predictive use is not consistent. Calibration, circumstantiation, 

validation, and verification are common terms used in practice. 

Terminology from the above sources was adopted for use in this study. 

Calibration is defined herein to be the study process of arriving at 

roughness coefficients, a sediment transport function, model parameters, 

and representative data that will allow the model to calculate values that 

agree with values measured in the prototype. Verification is defined herein 

as the study process that demonstrates that the calibrated model will 

match the prototype when specified boundary conditions, such as time 

period or cross-section geometry, are changed. 

This chapter presents the selection of model parameters and the 

determination of coefficients that allow the model to reconstitute 

measured stages, sediment concentrations, sediment yields, and trends in 

aggradation and degradation of the channel cross sections. Verification is 

demonstrated by the application of the calibrated model to compute 

channel changes resulting from the diversion at the Old River Control 

Complex and the newly constructed dike field at Smithland Crossing. 

Selection of model parameters 

Some of the input parameters to HEC-6T are considered "model 

parameters." These include the computational time-step, the sorting and 

armoring time interval (SPI), and the sediment transport function. These 

parameters should not be changed without conducting new calibration 

tests.

Computational time-step

The computational time-step needs to be short enough so that changes in 

bed elevation, due to deposition or aggradation, do not significantly 

change the hydraulic parameters during the event. Previous studies on the 

Lower Mississippi River with similar cross section spacing (Copeland 1991; 

and Copeland and Thomas 1992) varied the computational time-step as a 
MRG&P Report No. 30 127 

function of discharge, using computational time-steps between 1 and 31 

days. A more recent study on the Lower Mississippi River with similar 

cross section spacing (Catalyst–Old River Hydroelectric 1999) used a 

constant computational time-step of 1 day. The 1-day time-step is not 

necessary to meet the requirement of insignificant bed change but was 

chosen for convenience in this study because available data were reported 

as mean daily flow. If additional cross sections are added to this model, 

which significantly reduces the cross section spacing, then new calibration 

tests are required.

Exchange increment 

The sorting and armoring time interval or exchange increment (SPI) is the 

parameter that determines how many times the Exner equation is solved 

during the computational time-step. If sediment transport capacity is 

greater than the sediment load entering the control volume defined by the 

upstream and downstream cross sections, available sediment is removed 

from the bed to satisfy continuity. Since sediment transport capacity for a 

given size class depends on the fraction of that size class on the bed, it is 

necessary to frequently recalculate fractions present as sediment is 

exchanged with the bed. The HEC-6T program will calculate SPI as a 

function of the computational time-step, Δt, average channel velocity, V, 

and the reach length, ΔL.

L

Vt

SPI







Usually, the number of exchange increments can be less than calculated 

using this equation without inducing bed change and sediment yield 

oscillations from one time-step to the next. Fewer exchange increments 

relates to less computational intensity (i.e., shorter computer runs). In this 

study the computed exchange increment was 20. If the assigned SPI 

parameter is increased or decreased in future studies using this model, 

then new calibration tests are required.

Sediment transport function 

The sediment transport function for sand and gravel chosen for this study 

was the Toffaleti-Meyer-Peter Muller function. With this function, bed 

load is calculated using the Toffaleti (1968) and the Meyer-Peter Muller 
MRG&P Report No. 30 128 

(1948) methods, and the larger of the two is used. Suspended bed-material 

load is then calculated using the Toffaleti method. 

The sediment transport function was selected by the project engineers 

from all four districts during the study scoping process. The ToffaletiMeyer-Peter Muller function was selected because it has the capability of 

transporting both sands and gravels and because the Toffaleti equation 

was developed for large sand-bed rivers and has been used successfully on 

previous Mississippi River studies. Gravel transport is not an issue in the 

New Orleans District portion of the model, but some reaches of the 

Mississippi River in the Memphis District are known to have significant 

quantities of gravel in the bed. 

There are no size class suspended sediment measurement data between 

the Middle Mississippi River gages upstream from Cairo and the Lower 

Mississippi River gages in the New Orleans District. Therefore, size class 

comparisons between measured and calculated sand yield could only be 

made in the New Orleans District reach. Sand yield calculated using the 

Toffaleti-Meyer-Peter Muller equation was compared to measured sand 

yield at three stations in the New Orleans District. The calculated size class 

distributions of the total sand yield from the 1991–2002 simulation at 

Belle Chasse, Tarbert Landing, and Union Point are compared to 

measured sand size class distributions in Table 40 The measured data do 

not include bed load or sediment load in the unmeasured zone (the zone 

beneath the lowest elevation of the sediment sampler nozzle.) The base 

test used the Toffaleti-Meyer-Peter Muller sediment transport function. In 

the base test, the calculated very fine sand fractions were lower than the 

measured very fine sand fractions at all three gages, and the calculated 

medium sand fractions were higher than the measured medium sand 

fractions at all three gages. This result may partially be explained by the 

fact that the coarser sediment is transported closer to the bottom of the 

water column and is more likely to found in the unmeasured zone and thus 

more likely to be underestimated in the measured load.

Three additional sediment transport functions that have been used in large 

sand-bed rivers were tested in the numerical model. These were the 

Toffaleti, Laursen-Madden and Laursen-Copeland functions. Both the 

calculated percentages of base test sand yield during the 1991–2002 

simulation and the sand fractions of the 1991–2002 sediment yield are 

tabulated in Table 40. Size class fractions calculated using the Toffaleti 
MRG&P Report No. 30 129 

equation were very similar to those calculated in the base test. Three to 

seven percent less sand yield was calculated with the Toffaleti equation. 

Size class fractions calculated using the Laursen-Madden and LaursenCopeland functions were closer to the measured values at all three gages. 

Total sand yield with the two Laursen-based equations was between 9 and 

30 percent less than calculated in the base test. 

Table 40. Sand size class fractions. Measured versus calculated using different 

sediment transport function, 1991–2002. 

 Measured 

Base 

Toffaleti and 

Meyer-Peter 

Muller Toffaleti 

LaursenMadden LaursenCopeland 

Belle Chasse RM 76.0 

VFS .55 .28 .29 .49 .36

FS .34 .69 .69 .49 .60

MS .08 .03 .02 .02 .04

CS .03 .00 .00 .00 .00

Sediment Yield as % of

Base 100 97.0 69.6 71.4

Tarbert Landing RM 306.3 

VFS .29 .25 .26 .35 .32

FS .60 .56 .59 .56 .51

MS .10 .18 .14 .09 .16

CS .01 .01 .01 .00 .01

Sediment Yield as % of

Base 100 94.9 91.4 78.5

Union Point RM 326.6 

VFS .32 .26 .28 .37 .33

FS .57 .44 .45 .46 .43

MS .11 .29 .25 .17 .22

CS .01 .01 .01 .00 .02

Sediment Yield as % of

Base 100 93.2 88.5 79.9

The sediment transport function tests indicate that the Laursen-Madden 

or Laursen-Copeland functions may be more appropriate for the New 

Orleans District reach of the Mississippi River in terms of reproducing size 

class fractions. However, the improved size class distribution result must 

be weighed against the lower transport rate of fine and medium sand 

obtained when the Laursen based equations are used. Calculated sand 

transport at Union Point, Tarbert Landing, and Belle Chasse are compared 
MRG&P Report No. 30 130 

to measured sand transport in Figure 73 through Figure 75. In these 

figures, the measured load does not include the bed load or the suspended 

load in the unmeasured zone.

Figure 73. Sand concentration at Belle Chasse. 

Figure 74. Sand concentration at Tarbert Landing. 

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Measured

Calc Toffaleti MPM

Calc Laursen Madden

Calc Laursen Copeland

Power (Measured)

Measured data 1978–2006

Calculated data 1991–2002

Measured and calculated 

data 1991–2002
MRG&P Report No. 30 131 

Figure 75. Sand concentration at Coochie (RM 317.3) and Union Point (326.6). 

Calibration tests 

The calibration procedure is organized into three steps: (1) steady-state 

fixed-bed tests, (2) steady-state, movable-bed tests, and (3) quasiunsteady movable-bed tests. 

Steady-state, fixed-bed tests 

As described in the section on channel roughness, water-surface profiles 

were calculated with the numerical model in a fixed-bed mode for a range 

of steady-state discharges. Model roughness coefficients were initially 

adjusted to 1991–92 stage data at several gages. Later in the quasiunsteady movable-bed tests, a final adjustment was made.

Channel velocity and channel discharge profiles were also plotted to 

ascertain if the model was reproducing acceptable hydraulic results. This 

test revealed a few cross sections with large spikes or valleys in channel 

velocity. Typically, this occurred where the 1992 channel geometry had 

not adjusted to superimposed dike fields or at deep-bend sections where 

the 1D assumption was invalid. At some locations, cross-section 

geometry was adjusted to reduce the spikes or the suspect cross section 

was removed from the numerical model. Calculated channel velocities for 

0.1

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Measured Sand

Calculated Toffaleti MPM

Calculated Laursen Madden

Calculated Laursen Copeland

Power (Measured Sand)

Calculated and measured data 

1991–2002

Calculated data at RM 326.6
MRG&P Report No. 30 132 

a range of steady state discharges at the end of 1 year are shown in Figure 

76 through Figure 78.

The discharges shown in the legend on Figure 76 through Figure 78 are the 

discharges at Vicksburg. Discharges at inflow boundaries were set as a 

constant percentage of the discharge at Vicksburg. The percentage was 

based on the percentage of the 12-year total volume of flow from the 

tributary with respect to the 12-year volume of flow at Vicksburg. 

Not all of the spikes were removed from the model as these occur naturally 

at some cross sections with variation in discharge. The large spike at 

RM 481.1 occurs at a narrow cross section constricted by the Ajax Bar Dike 

Field. The high calculated velocities at RM 637.9 and RM 645.9 occur at 

divided flow locations. The I-55 Bridge creates a high flow constriction at 

RM 734.6 where the overbank is blocked by the raised roadway. At this 

cross section, the bed sediment reservoir was limited to a 1 ft depth to avoid 

excessive scour calculations. The high velocity at RM 911.2 occurs at a 

constricted cross section in the main channel around the Island 8 loop and 

was assigned a bed sediment reservoir depth of 0.1 ft. 

Figure 76. Calculated channel velocity in the New Orleans District reach. 

0

1

2

3

4

5

6

7

8

-50 0 50 100 150 200 250 300 350 Velocity FPS

River Mile

200 K

500K

900K

1200K
MRG&P Report No. 30 133 

Figure 77. Calculated channel velocity in the Vicksburg District reach. 

Figure 78. Calculated channel velocity in the Memphis District reach. 

0

1

2

3

4

5

6

7

8

9

10

300 350 400 450 500 550 600 Velocity FPS

River Mile

200 K

500K

900K

1200K

0

1

2

3

4

5

6

7

8

9

10

550 600 650 700 750 800 850 900 950 Velocity FPS

River Mile

200 K

500K

900K

1200K
MRG&P Report No. 30 134 

Steady-state, movable-bed tests 

Model performance was evaluated for a channel-forming discharge and a 

movable bed. The movable-bed tests were conducted to adjust the initial 

bed material gradation to reflect reach-averaged conditions and to make 

sure that cross-section changes over time tend to stabilize with a channelforming discharge. 

The initial bed reservoir in the numerical model has an infinite depth, and 

bed gradation is best determined using the channel-forming discharge. 

During the course of a simulation, the sorting and armoring algorithm in 

HEC-6T adjusts the composition of the bed as a function of the 

composition of each bed layer at the previous time-step, the incoming 

sediment load, and the hydraulic conditions during the computational 

time step. Hydraulic parameters and bed gradations in the HEC-6T model 

are representative of a reach. However, sampled bed gradations are 

representative of a point. Therefore, some adjustment of initial bed 

material gradation is typically required to prevent rapid bed changes and 

changes in sediment transport at the beginning of the numerical 

simulation. Results of bed material adjustments were described in the 

section on bed material gradation.

A constant discharge was simulated for 1,780 days in the numerical model 

to assess model stability. The constant discharge was 1,060,000 cfs at 

Vicksburg, which had been determined to be the channel-forming 

discharge by Biedenharn and Thorne (1994). Accumulated average bed 

changes over the 1,780 days for several cross sections are plotted in Figure 

79 through Figure 81. These cross sections were chosen for display because 

they were cross sections that had significant bed elevation changes in the 

1991–2002 simulation. The 1,780-day duration provides time for the 

model to transport a sediment load equivalent to 10 years of average 

annual sand discharge. Although some cross sections in Figure 79 through 

Figure 81 show considerable bed change, especially at the beginning of the 

simulation, the rate of change generally decreases as time passes. Rapid 

changes in average bed elevation at some cross sections, during the first 

100 days, is related to the difficultly in choosing a representative cross 

section in a river reach where cross-section shapes are changing rapidly 

due to meanders or constrictions. At RMs 369 and 597 in Figure 80, an 

increasing trend begins after approximately 1,200 days. This can be 

attributed to problems with the equilibrium concept applied to a dynamic 

river system. Most important, there is not a numerical oscillation in the 
MRG&P Report No. 30 135 

calculations, and therefore it can be concluded that the computations are 

stable for the water discharge tested and that the model is robust.

The results from the channel-forming discharge movable-bed test do not 

show changes that will occur in the river. They are only useful for 

demonstrating that the model may generally converge on an equilibrium 

condition in response to a constant discharge simulation hydrograph. 

Such a model is then ready to be applied to non-steady, discharge 

hydrographs to predict changes in the river. In this case, a divergence from 

equilibrium occurs at some of the cross sections shown in Figure 79

through Figure 81. This suggests that the equilibrium concept is simplistic 

and is more applicable to the uniform canal channels from which the 

concept developed and not to dynamic alluvial rivers.

Figure 79. Calculated bed change in the New Orleans District reach. 

-8

-4

0

4

8

12

16

0 500 1000 1500 2000

Average Bed Change Ft

Days

21.6

141.6

143.7

195.3

203.6

212

218.9

253

306.1

311.6

315.4
MRG&P Report No. 30 136 

Figure 80. Calculated bed change in the Vicksburg District. 

Figure 81. Calculated bed change in the Memphis District. 

-15

-10

-5

0

5

10

0 200 400 600 800 1000 1200 1400 1600 1800 Average Bed Change FEET

DAYS

335

369

436

454.77

489

501.2

560

597

-15

-10

-5

0

5

10

15

20

0 200 400 600 800 1000 1200 1400 1600 1800 Average Bed Change FEET

DAYS

641.96

649.96

712.12

738.95

781.97

784

846.4

889.01

922
MRG&P Report No. 30 137 

Problems with assuming a constant channel-forming discharge is 

demonstrated in Figure 82, which shows calculated average bed changes 

in five consecutive cross sections with a channel-forming discharge for 

1,780 days. At the upstream cross section (578.8), the bed change trends 

toward equilibrium. However, at the next downstream cross section 

(576.21), there is a consistent degradation trend that accelerates after 

approximately 1,350 days of constant channel-forming discharge. This 

cross section is at a constriction, which tends to degrade at the channelforming discharge and may aggrade at other discharges. However, by 

simulating only a single discharge, the natural degradation and 

aggradation trend is masked. Average bed change at the next downstream 

cross section (574.8) is the reciprocal of bed change upstream. The 

sediment scoured from cross section 576.21 is deposited in cross section 

574.8. The expected trend toward equilibrium is displayed at the next two 

downstream cross sections (573.15 and 571.4). 

Figure 82. Calculated bed change at five consecutive cross sections. 

Calculated average bed changes at nine cross sections during the 1991–

2002 simulation are plotted in Figure 83. This figure shows the true 

dynamic nature of the alluvial river. Cross-sections 369 and 574.8, show 

a variation with discharge and a general increasing trend over time with 

-8

-6

-4

-2

0

2

4

0 200 400 600 800 1000 1200 1400 1600 1800 2000 BED CHANGE FEET

DAYS

571.4

573.15

574.8

576.21

578.8
MRG&P Report No. 30 138 

the actual annual hydrograph. Some cross sections (411.2) show 

significant variability in average bed change with discharge. Other cross 

sections (529.2 and 553) show little variation with the annual flood 

discharges.

Figure 83. Calculated average bed change during the 1991–2002 hydrograph. 

Quasi-unsteady movable-bed tests

Model performance was evaluated with a movable bed for the 1991–2002 

hydrograph. The quasi-unsteady movable-bed tests were conducted to 

assess changes in calculated water-surface elevations and bed material 

gradations over time. Tests were also conducted to assess calculated 

sediment concentrations and size class distributions and total sediment 

yield for the 12-year hydrograph. 

Stage variation with movable bed 

As described in the section on channel roughness, water-surface profiles 

were calculated with the numerical model at the end of the 1991–2002 

hydrograph for a range of steady-state discharges. The results of those 

calculations are shown in Figure 18 through Figure 37. The figures show 

that the calculated rating curves are slightly lower in 2002 than in 1991 in 

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 500 1000 1500 2000 2500 3000 3500 4000 4500 BED CHANGE FEET

DAYS

330.61

369

396.4

411.2

454.77

501.2

529.2

553

574.8
MRG&P Report No. 30 139 

most of the New Orleans District. However, the differences are well within 

the annual variations of the measured data. In the Vicksburg and Memphis 

Districts, the figures show that the calculated rating curves are well within 

the scatter of data and essentially unchanged between 1991 and 2002.

Specific gage analysis 

Specific gage analysis is sometimes used to assess the historical stability of 

a river system. A specific gage record is a graph of stage for a specific 

discharge at a particular gaging location plotted against time. A channel is 

considered to be in equilibrium if the specific gage record shows no 

consistent increasing or decreasing trends over time. An increasing or 

decreasing trend is indicative of aggradation or degradation, respectively. 

Annual variations in the specific gage record may obfuscate the true longterm trend, so care must be taken to ensure that a sufficient time record is 

evaluated. Specific gage records were used in this study to assess the 

numerical model’s predictive ability with respect to matching trends, or 

lack of trends, during the 1991–2002 calibration period. The specific gage 

record evaluated in this study was of insufficient length to make any longterm conclusions relative to river geomorphology, which is outside the 

scope of this study. 

In the New Orleans District reach, specific gage was calculated in HEC-6T 

by inserting a rating curve calculation at the end of each water year during 

the 1991–2002 simulation. In the Vicksburg and Memphis reaches, 

specific gage was calculated in HEC-6T during the 1991–2002 historical 

simulation using the specific gage option with a tolerance of 3,000 cfs. 

With this option, calculated water surface elevations for discharges within 

the tolerance range of specified discharges at specified cross sections are 

written to a Tape99 file. The specific gage option was an enhancement to 

the HEC-6T model that was unavailable when the New Orleans reach of 

the model was developed. Measured specific gage was calculated using 

statistical regression analyses in EXCEL. Third- or fourth-order 

polynomial regression curves were fit to the reported annual stage and 

discharge data at specific gages. Daily stage data are available for all the 

gages. In the New Orleans District, discharge measurements were not 

available at the gages, so the discharge from Tarbert Landing was used in 

the regression equations. The regression analysis produces questionable 

results for low discharges downstream from New Orleans because the 

stage is not a unique function of discharge and is influenced greatly by 

water surface elevations in the Gulf. Discharge measurements are taken at 
MRG&P Report No. 30 140 

Natchez, Vicksburg, Arkansas City, Helena, Memphis, and Hickman. 

Discharge at Greenville was taken to be the discharge at Arkansas City 

without any lag. The stage-discharge curves at Rosedale were developed 

using calculated daily discharges at Arkansas City and Dam No. 2 on the 

Arkansas River. The daily discharges on the Arkansas River were obtained 

from the USACE Little Rock District. The daily discharge at Rosedale was 

taken to be the difference between the Arkansas City and Dam No. 2 

discharges. A 1-day lag was assumed between Arkansas City and Rosedale 

and between Dam No. 2 and Arkansas City. 

The HEC-6T calculated specific gages are compared to measured specific 

gages determined from the regression curves in Figure 84 through Figure 

99. In the New Orleans District, upstream from New Orleans, the model 

results are consistent with the measured specific gage determined from the 

regression curves. Downstream from New Orleans, at lower discharges, 

the magnitude comparison between HEC-6 calculations and measured 

specific gage is not expected to be consistent due to the influence of the 

Gulf water-surface elevation. However, the trend comparison between 

HEC-6 calculations and measured specific gage may be useful. In the 

Vicksburg and Memphis Districts, calculated and measured specific gage is 

generally steady between 1991 and 2002, with no obvious aggradation or 

degradation trends displayed at any of the gages.

Figure 84. Specific gage at Venice, RM 10.7. 

1

2

3

4

5

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

DAYS ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K
MRG&P Report No. 30 141 

Figure 85. Specific gage at West Pointe A La Hache, RM 48.7. 

Figure 86. Specific gage at New Orleans, RM 102.8. 

0

1

2

3

4

5

6

7

8

9

10

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regresion 1200K

0

2

4

6

8

10

12

14

16

18

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K
MRG&P Report No. 30 142 

Figure 87. Specific gage at Reserve, RM 138.7. 

Figure 88. Specific gage at Donaldsonville, RM 175.4. 

0

5

10

15

20

25

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K

0

5

10

15

20

25

30

35

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K
MRG&P Report No. 30 143 

Figure 89. Specific gage at Baton Rouge, RM 228.0. 

Figure 90. Specific gage at Bayou Sara, RM 265.4. 

0

5

10

15

20

25

30

35

40

45

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K

0

10

20

30

40

50

60

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K
MRG&P Report No. 30 144

Figure 91. Specific gage at Red River Landing, RM 302.4. 

Figure 92. Specific gage at Natchez, RM 363.3. 

10

15

20

25

30

35

40

45

50

55

60

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ELEVATION FT NGVD

200K

500K

900K

1200K

Regression 200K

Regression 500K

Regression 900K

Regression 1200K

25

30

35

40

45

50

55

60

65

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

800K

1200K

Measured 300K

Measured 500K

Measured 800K

Measured 1200K
MRG&P Report No. 30 145 

Figure 93. Specific gage at Vicksburg, RM 435.7. 

Figure 94. Specific gage at Greenville, RM 531.1. 

50

55

60

65

70

75

80

85

90

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

800K

1200K

Measured 300K

Measured 500K

Measured 800K

Measured 1200K

85

90

95

100

105

110

115

120

125

130

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

800K

1200K

Measured 300K

Measured 500K

Measured 800K

Measured 1200K
MRG&P Report No. 30 146 

Figure 95. Specific gage at Arkansas City, RM 554.1. 

Figure 96. Specific gage at Rosedale, RM 592.2. 

95

100

105

110

115

120

125

130

135

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

800K

1200K

Measured 300K

Measured 500K

Measured 800K

Measured 1200K

105

110

115

120

125

130

135

140

145

150

155

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

700K

1200K

Measured 300K

Measured 500K

Measured 700K

Measured 1200K
MRG&P Report No. 30 147 

Figure 97. Specific gage at Helena, RM 663.1. 

Figure 98. Specific gage at Memphis, RM 734.7. 

140

145

150

155

160

165

170

175

180

185

190

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

700K

1200K

Measured 300K

Measured 500K

Measured 700K

Measured 1200K

185

190

195

200

205

210

215

220

225

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

700K

1000K

1200K

Measured 300K

Measured 500K

Measured 700K

Measured 1000K

Measured 1200K
MRG&P Report No. 30 148 

Figure 99. Specific gage at Hickman, RM 922. 

Average bed change 

Calculated average bed changes at the gages during the 1991–2002 

simulation are shown in Figure 100 through Figure 102. These plots show 

significant oscillation in the bed elevation at some gages, such as Bayou 

Sara and Greenville. General aggradation trends are calculated at Venice 

and Reserve. Some cross sections show significant change early in the 

simulation, such as New Orleans, Arkansas City, and Memphis. The rapid 

change in average bed elevation early in the simulation is most likely due 

to failure to select “reach-averaged” cross section for the numerical model. 

The calculated average bed changes at gages, and the results from the 

specific gage plots demonstrate the importance of looking at long reaches 

to access general aggradation and degradation and the danger of focusing 

on results from a single cross section in determining long-term or even 

short-term bed change. 

The purpose of showing these calculations is to provide insight into how 

the model responds to changing hydrologic and hydraulic conditions. 

Given the available survey data and the fact that the cross-section surveys 

are not taken at the same time, prototype average bed change at specific 

275

280

285

290

295

300

305

310

315

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Elevation Feet NGVD

Days

300K

500K

700K

1000K

1200K

Measured 300K

Measured 500K

Measured 800K

Measured 1000K

Measured 1200K
MRG&P Report No. 30 149 

cross sections was not determined. Comparing cross-section surveys at a 

specific location, taken 10 years apart, can lead to erroneous conclusions. 

For example, the crest of a bed form could be passing a specific cross 

section during one survey, and the trough of a bed form could be passing 

during the second survey. Comparing surveys at such a cross section could 

lead to the erroneous conclusion that aggradation/degradation is 

occurring, when in fact average conditions are unchanged. Proper analysis 

requires evaluating an entire reach of the river in the vicinity of the gage. 

This falls into the realm of a geomorphic study, which is beyond the scope 

of this study. 

Figure 100. Calculated average bed change, New Orleans District gages, 1991–2002. 

-2

-1

0

1

2

3

4

5

6

7

8

0 500 1000 1500 2000 2500 3000 3500 4000 4500 Calculated Average Bed Change Feet

Days

Venice

West Point a la Hache

New Orleans

Reserve

Donaldsonville

Baton Rouge

Bayou Sara

Red River Landing
MRG&P Report No. 30 150

Figure 101. Calculated average bed change, Vicksburg District gages, 1991–2002. 

Figure 102. Calculated average bed change, Memphis District gages, 1991–2002. 

-6

-4

-2

0

2

4

6

8

10

0 500 1000 1500 2000 2500 3000 3500 4000 4500 Calculated Average Bed Change Feet

Days

Natchez

Vicksburg

Greenville

Arkansas Ciity

Rosedale

-8

-6

-4

-2

0

2

4

6

8

10

0 500 1000 1500 2000 2500 3000 3500 4000 4500 Calculated Average Bed Change Feet

Days

Helena

Memphis

Hickman
MRG&P Report No. 30 151 

Bed gradation trends with movable bed 

Changes in calculated bed material gradation trends between Head of 

Passes (RM 0.0) and Vicksburg (RM 435.7), during the 12-year calibration 

simulation, were compared to trends measured by the USGS between 1982 

and 1985 (Demas and Curwick 1987) and in 2005. The 1982–85 data were 

collected at eight stations between Venice (RM 10.7) and Tarbert Landing 

(RM 306.3). At most stations, there were approximately 25 sets of data 

collected. Most sets consisted of three laterals, some sets had five laterals. 

In July 2005, the USGS collected bed material data at each of these eight 

stations at five laterals. In August 2005, the USGS collected samples at 

approximately 2-mile increments at three laterals between Head of Passes 

and Vicksburg. The data are shown in Figure 103. Samples that contained 

greater than 10 percent fines were excluded from the analysis. 

Figure 103 shows the variability in the composition of the bed with 

distance along the river. When the 0.25 mm data collected at a few specific 

stations in 1982–1985 and 2005 are compared with the data collected at 

2-mile increments in 2005, it is apparent that developing trend lines from 

a few stations can be problematic. 

Figure 103. 1982–1985 and 2005 USGS bed-material gradations. 

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400 450 Percent Finer

River Mile

1982-85 .125mm

1982-85 .25mm

1982-85 .5 mm

2005(5) .125mm

2005(5) .25mm

2005(5) .5mm

2005 (3) .125mm

2005(3) .25mm

2005 (3) .5 mm

Poly. (2005 (3) .125mm)

Poly. (2005(3) .25mm)

Poly. (2005 (3) .5 mm)

1982-85 25 sets of 3 

laterals at USGS stations 

2005(3) 3 laterals at about 2 

mile increments

2005(5) 5 laterals at USGS 

stations 
MRG&P Report No. 30 152

The USGS data are compared to polynomial regression curves of the 

Nordin and Queen (1989) data in Figure 104. The 1982–1985 USGS data 

and the Nordin and Queen data are similar, but the 2005 bed gradations 

appear to be slightly coarser.

Figure 104. USGS and Nordin and Queen bed-material gradations. 

A comparison of the 1982–85 and 2005 USGS data suggests that the very 

fine and coarse sand percentages in the river bed between Venice and 

Tarbert Landing have remained approxiamtely the same. The comparison 

also suggests that the fine sand percentage has decreased and the medium 

sand percentage has increased so that the river bed is coarser. However, it 

must be remembered that the 1982–1985 data include approximately 25 

sets of data that were collected over a 3-year period and that the 2005 data 

is one set of data collected during the summer months.

The calculated active layer gradations at the end of the 12-year simulation 

are compared to the 1982–1985 and 2005 USGS bed gradations Figure 

105. The calculated bed gradations indicate a slight coarsening of the bed 

over the 12-year period but not as much as suggested by comparing the 

1982–1985 and 2005 USGS data. Calculations also indicate a reduction in 

the very fine sand component downstream from RM 250, making this 

lower reach of the river more consistent with upstream reaches. The 

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400 450 Percent Finer

River Mile

1982-85 .125mm

1982-85 .25mm

1982-85 .5 mm

2005(5) .125mm

2005(5) .25mm

2005(5) .5mm

2005 (3) .125mm

2005(3) .25mm

2005 (3) .5 mm

Poly. (2005 (3) .125mm)

Poly. (2005(3) .25mm)

Poly. (2005 (3) .5 mm)

Poly. (Nordin 1.25mm)

Poly. (Nordin .25mm)

Poly. (Nordin .5 mm)

1982-85 25 sets of 3 

laterals at USGS stations 

2005(3) 3 laterals at about 2 

mile increments

2005(5) 5 laterals at USGS 

stations 
MRG&P Report No. 30 153

numerical model does not include sediment contributions from bank 

erosion or construction activities. These sources could be responsible for 

additional very fine sand in the sediment inflow. Another explanation 

could be that the initial gradations reflect low flow conditions where the 

very fine sand is a remnant of receding flood flows. Note that the 

numerical model’s active layer thickness can be quite small at lower 

discharges and that the gradation of underlying material can be finer. 

Upstream from RM 250, the calculated results show a slight increase in 

the medium sand percentage in the bed. It is noted that there were 20 

years between the USGS data collection efforts and the HEC-6T simulation 

was only 12 years. 

Figure 105. Calculated active layer gradation compared to 2005 USGS gradations. 

Calculated bed gradation changes between 1991 and 2002 for the entire 

Mississippi River reach between Head of Passes and Cairo are shown in 

Figure 106. The calculations do not show significant trends in the bed 

material gradations over the 12-year simulation. However, calculated bed 

gradations diffused some of the discontinuities in the initial bed 

gradations. The increase in the fine sand component upstream from 

RM 700 is interesting in that it is not typical for a river bed to become 

finer in an upstream direction. Measured and calculated data appear to be 

consistent in this reach, so it is suggested that this trend is due to 

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400 450 Percent Finer

River Mile

1982-85 .125mm

1982-85 .25mm

1982-85 .5 mm

2005(5) .125mm

2005(5) .25mm

2005(5) .5mm

CAL 2002 .125mm

CAL 2002 .25mm

CAL2002 .5mm

INITIAL .125mm

INITIAL .25mm

INITIAL .50mm

1982-85 Several sets of 3 

laterals at USGS stations 

2005(5) 5 laterals at USGS 

stations 
MRG&P Report No. 30 154 

geomorphic discontinuities such as gravel bars or hard points. It could 

also be related to the differential sediment contributions from the Ohio 

and Middle Mississippi Rivers.

Figure 106. Calculated active layer gradation – Head of Passes to Cairo. 

Available bed material data suggest a slight coarsening of the Mississippi 

River bed between RMs 100 and 400. Model results suggest a smaller 

coarsening trend. To increase the coarseness of calculated bed gradations, 

it would be necessary to significantly decrease the fine sediment 

contributions and increase the coarse sediment contributions at the 

upstream boundaries. The choice was made in this study to place more 

reliability on the sediment inflow measurements and to accept differences 

in the measured and calculated bed material changes as reasonable.

Sediment concentrations at Tarbert Landing and Belle Chasse 

Calculated sediment concentrations were compared to measured sediment 

concentrations at two gages downstream from the Old River Control 

Complex. Tarbert Landing is located at RM 306.3, just downstream from 

the Old River Complex, and Belle Chasse is located at RM 76.0, upstream 

from most of the distributaries and typically upstream from the influence of 

salt water intrusion. Measured suspended data were available at Tarbert 

Landing for the entire 1991 to 2002 calibration period. Data at Belle Chasse 

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

0 200 400 600 800 1000 Percent Finer

River Mile

INITIAL .125mm

INITIAL .25mm

INITIAL .50mm

CAL .125mm

CAL .25mm

CAL .5mm
MRG&P Report No. 30 155

were available between 1978 and 1997 and 2005 and 2007. Size class 

distribution data were available at Belle Chasse between 1982 and 1985. 

The calculated sediment concentrations at Tarbert Landing are compared 

to measured data in Figure 107. The calculated sand concentration at 

Tarbert Landing is consistent with the measured suspended sand load at 

discharges greater than 400,000 cfs. This is attributed to the greater 

concentration of sand in the unmeasured zone during low flow. 

Approximately 100 percent of the clay and 99 percent of the silt that enters 

the model from the tributaries is transported to Tarbert Landing. 

Therefore, the comparison of calculated and measured fine load is more of 

a check on boundary conditions than a test of model performance. 

Figure 107. Sand and fine concentrations at Tarbert Landing 1991–2002. 

The hydrograph used to develop the calculated sediment concentrations 

in Figure 107 was the adjusted hydrograph discussed in the report 

section on hydrographs in the Numerical Model Description (MVMQ). 

This hydrograph was based on recorded mean daily inflows at the 

boundary gages. However, some of the measured tributary discharges 

where adjusted to achieve discharges and volumes that better matched 

measured data on the main-stem Mississippi River. The modified 

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Calculated Sand

Measured Sand

Calculated Fines

Measured Fines
MRG&P Report No. 30 156

hydrologic data reproduced measured data within 1% at Hickman, KY, 

and within 3% at Helena, AR.

The hydrograph used in the 2009 interim study of the Vicksburg to Pilots 

Station reach was based on the reported discharges at Vicksburg. A 

simplified hydrograph, based on measured Vicksburg discharges (VickQ), 

was developed for the Regional Model by using a constant percentage of 

the Vicksburg discharge for each of the tributaries. The percentage was 

based on the percent of the total 1991–2002 volume of flow contributed by 

each tributary.

The calculated sediment concentrations at Tarbert Landing using the 

simplified hydrograph are compared to the calculated sediment 

concentration using the adjusted hydrograph in Figure 108. There are two 

significant observations made from Figure 108.

1. There is no scatter in the calculated fine concentration with the simplified 

hydrograph. This is because the discharge from each tributary is always 

the same percentage of the flow at Vicksburg (and Tarbert Landing) and 

there is essentially no deposition of silts and clays calculated between the 

boundaries and Tarbert Landing. Conversely, there is considerable scatter 

in the fine sediment concentrations using the adjusted hydrograph due to 

the irregularity in actual contribution from the tributaries — especially the 

Middle Mississippi and Ohio Rivers. 

2. The relationship between calculated sand concentration and discharge is 

essentially the same with both hydrographs. This is because the sand 

concentration is more closely related to transport potential in the river 

reaches immediately upstream than to inflow boundary conditions.

These two observations are especially useful in determining which 

hydrograph to use for a specific study. If the primary objective is to 

evaluate sedimentation processes driven by sand transport, or by the longterm effects of fine sediment, then the simplified hydrograph is adequate. 

However, if determining the effects of fine sediment processes associated 

with a specific event or events is the objective, then an adjusted 

hydrograph would be more appropriate.
MRG&P Report No. 30 157 

Figure 108. Effect of model hydrographs on concentrations at Tarbert Landing. 

The calculated sediment concentrations at Belle Chasse are compared to 

measured data in Figure 109. All of the measured data (1978–1997 and 

2005–2007) were used in the comparison because only 33 measurements 

were available from the 1991–2002 calibration period. The measured and 

calculated data are consistent for discharges greater than 400,000 cfs. 

Calculated fine sediment concentrations are higher than the measured fine 

concentrations at lower discharges. The measured sand concentrations at 

discharges below 400,000 cfs are characterized by significant scatter and 

are inconsistent with the calculated data. This inconsistency may be 

associated with the influence of salt water at low flow and/or difficulties in 

isokinetic sampling at low velocities.

Calculated size class percentages are compared to measured size class 

percentages in Table 41. The tabulated measured percentages were 

obtained by averaging all the available measurements — 1991–2002 at 

Tarbert Landing and 1982–1985 at Belle Chasse. The calculated 

percentages were obtained from the accumulated total transport of each 

size class past both gages during the 1991–2002 calibration simulation. 

Calculated percentages were calculated using the adjusted hydrograph 

(MVMQ) and the percentage of Vicksburg hydrograph (VickQ). The 

tabulated percentages indicate that appropriate quantities of each 

sediment size class are being transported through the study reach by the 
MRG&P Report No. 30 158

numerical model. The choice of hydrograph does not affect calculated 

percentages significantly.

Figure 109. Measured and calculated sediment concentrations at Belle Chasse. 

Table 41. Measured and calculated size class distributions average percentages. 

Grain Size

Tarbert Landing 

RM 306.3 

Belle Chasse 

RM 76.0 

Measured

Suspended 

Load

1991–2002

Calculated Total Load

1991–2002

Measured

Suspended

Load

1982–1985

Calculated Total Load

1991–2002

MVMQ VickQ MVMQ VickQ

Clay 30 38 37 44 41 41

Very fine silt 11 7 7 7 8 8

Fine silt 9 8 7 9 8 8

Medium silt 14 9 9 11 10 10

Coarse silt 17 9 8 8 9 9

Very fine sand 6 2 2 12 6 7

Fine sand 11 22 24 7 17 16

Medium sand 2 5 5 1 1 1

Coarse sand 0 0 0 1 0 0

MVMQ is adjusted hydrograph based on tributary gages.

VickQ is hydrograph based on constant percentage of Vicksburg discharge.

0.1

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Calculated Sand

Meas Sand 1978-97

Calculated Fines

Meas Fines 1978-97

Measured 1978–2007

Calculated 1991–2002
MRG&P Report No. 30 159

Sediment concentrations at Union Point 

Calculated sediment concentrations at Union Point were compared to 

measured sediment concentrations at Union Point and Coochie in Figure 

110. Union Point is located at RM 326.6, which is upstream from the Old 

River Control Complex. Coochie, also located above the Old River Control 

Complex, is at RM 317.3. Sediment data were collected at Union Point 

between 1993 and 2002 and at Coochie between 1991 and 1996. The most 

interesting observation from Figure 110 is the decline in calculated 

sediment concentration at discharges greater than 1,200,000 cfs. 

Measured data are insufficient to confirm this trend. Calculations at 

RM 326.6 show increasing velocity, effective depth, and effective width 

with discharge. However, the slope decreases with discharge at this station 

as shown in Figure 111. The consequence of decreasing slope is decreasing 

sediment concentration in the calculations. Figure 111 shows that the 

decreasing slope with discharge trend is not typical. However, this result 

points to the importance of reach analysis rather than focusing on results 

from a single cross section. 

Figure 110. Measured and calculated sediment concentrations at Union Point and Coochie. 

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Calc Sand Union Pt

Meas Sand Union Pt

Meas Sand Coochie

Calc fines Union Pt

Meas Fines Union Pt

Meas Fines Coochie

Measured Coochie 1991–1996

Measured Union Pt. 1993–2002

Calculated Union Pt. 1991–2002
MRG&P Report No. 30 160 

Figure 111. Calculated energy slope between Tarbert Landing and Natchez. 

Sediment concentrations at Vicksburg 

The reported 1992–2004 measured fine concentrations at Vicksburg and 

Natchez (RM 363.3) were found to be an order of magnitude less than the 

reported fine concentrations between 1984 and1989 at the same gages. 

This inconsistency, accompanied by a significant increase in 1992–2004 

measured sand concentrations, leads one to suspect a laboratory error in 

determining the sand-silt break point. Comparative fine sediment 

concentrations between 1984 and 2002 at Vicksburg are shown in Figure 

112. The Vicksburg and Natchez fine sediment concentrations between 

1992 and 2004 were also inconsistent with downstream measurements for 

the same period at Tarbert Landing (RM 306.3) as shown in Figure 113. 

When the measured sand data are plotted as in Figure 114, it is more 

difficult, but not impossible, to detect the error. According to reported 

sediment data at Vicksburg, between 1984 and 1989, 24 percent of the 

measured sediment load was sand, but between 1992 and 2004, 75 percent 

of the measured sediment load was sand. For this reason only, the 1984–

1989 data at Vicksburg were used to compare calculated and measured 

sediment load in Figure 115.

Q =1,070,000 cfs

RIVER MILE

Q= 1,900,000 cfs

Q= 1,479,000 cfs

SLOPE Feet / 1000 Feet
MRG&P Report No. 30 161

Figure 112. Measured fine sediment concentrations at Vicksburg (1984–2004). 

Figure 113. Measured fine sediment concentrations at Tarbert Landing (1984–2004). 

1

10

100

1000

100,000 1,000,000 10,000,000 Concnetration MG/L

Discharge CFS

84-89

92-94

95-04

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

1984-89

1992-94

1995-2004
MRG&P Report No. 30 162 

Figure 114. Measured sand concentrations at Vicksburg (1984–2004). 

Figure 115. Measured and calculated sediment concentrations at Vicksburg. 

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

84-89

92-94

95-04

Power (84-89)

Power (92-94)

Power (95-04)

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Calculated Sand

Calculated Fines

Meas Sand 1984-89

Meas Fines 1984-89

Measured 1984–90 and 1995–2004

Calculated 1991–2002
MRG&P Report No. 30 163 

Sediment concentrations at Memphis 

Calculated sediment concentrations were compared to measured sediment 

concentrations at the Memphis gage (USGS gage number 07032000), 

which is located at RM 734.4. Measured suspended data were collected by 

the USGS between 1974 and 1991. There were no available sediment data 

for the 1991–2002 calibration period. Calculated daily sediment 

concentrations of both the sands and fines at RM 734.4 are shown in 

Figure 116. There is good agreement in calculated and measured fine 

concentration, but the measured sand concentrations are considerably less 

than the calculated sand concentrations. The measured sand 

concentrations at Memphis are also considerably less than the measured 

sand concentrations at Vicksburg (Figure 115).

Figure 116. Measured and calculated sediment concentrations at Memphis. 

It is uncertain if the differences in measured and calculated sand 

concentrations are due to measurement errors or to problems with the 

numerical simulation. It is certain, however, that the reported sediment 

measurements represent an attempt to define sediment conditions at a 

single point on the river and do not require satisfaction of sediment 

continuity with upstream or downstream reaches. The numerical model, 

however, is governed by physical properties and requires that sediment 

continuity throughout the study reach be maintained. Sediment continuity 

1

10

100

1000

100,000 1,000,000 10,000,000 Concentration MG/L

Discharge CFS

Calculated Sand

Calculated Fines

Meas Sand 1974-91

Meas Fines 1974-91

Measured 1974–1991

Calculated 1991–2002
MRG&P Report No. 30 164 

is maintained by bed aggradation/degradation and sediment transport. 

The discrepancy in measured sand concentration at Memphis and 

Vicksburg highlights the need for coordinated sediment sampling 

programs for the entire Mississippi River reach. There should be 

consistency in collection methods and equipment. There should also be 

consistency in laboratory methodologies when the samples are analyzed. 

There is a need to compare sediment data collected at the various gages to 

ensure consistency and reasonableness in the reported data.

Comparison of calculated sand yields 

Sand yields at Tarbert Landing, Union Point, and Belle Chasse were 

calculated using regression equations developed from measured data and 

results from the HEC-6T simulation. Both calculations are subject to 

uncertainty. The sand yield calculated using the regression curve analysis 

should not be considered to be the true or measured sand yield. However, 

it is useful to compare sand yields calculated using the measured data with 

that calculated using the numerical model. Calculated sand yields using 

both methods are listed in Table 42. 

Table 42. 12-year calculated sand yield between 1991 and 2002. 

Regression Analysis 

HEC-6T 

MVM Hydrograph 

Vicksburg 

Hydrograph 

million tons million tons million tons

Belle Chasse 430 376 321

Tarbert Landing 438 504 469

Union Point 601 621 586

Vicksburg 405 685 641

Sand yield was calculated for each day between 1 October 1990 and 30 

September 2002 using published mean daily discharges and an unbiased 

power regression curve developed from measured sand data at each gage 

(http://www.mvn.usace.army.mil/eng/edhd/wcontrol/discharge.asp). 

At Belle Chasse, a sand power regression curve was developed from 35 

measurements collected between October 1990 and June 1997. Data 

collection at Belle Chasse was discontinued after June 1997 and did not 

resume until 2005. The unbiased power regression curve for sand 

concentration is the following:
MRG&P Report No. 30 165 

.3 866 C .1  21004 QE

where:

C =concentration mg/l

Q =discharge cfs.

The discharges at Belle Chasse were assumed to be the same as the mean 

daily discharges at Tarbert Landing unless the Tarbert Landing discharge 

was greater than 1,250,000 cfs. To account for flows over the Bonnet Carré 

Spillway, the maximum discharge at Belle Chasse was set at 1,250,000 cfs. 

The maximum discharge for which data were collected at Belle Chasse was 

1,060,000 cfs. The calculated concentration at this discharge was taken to 

be the maximum concentration for the sediment yield calculations (i.e., 

there was no extrapolation of the regression curve beyond the range of 

measured data). 

The regression curves at Tarbert Landing were developed from 243 

measurements taken between 1991 and 2002. Separate regression curves 

were developed for discharges greater than and less than 600,000 cfs. The 

maximum discharge for which data were collected at Tarbert Landing was 

1,470,000 cfs. The maximum daily discharge recorded between 1991 and 

2002 was 1,480,000 cfs, so there was no need to cap the regression curve 

at the highest discharges. The unbiased regression curves for sand 

concentration are the following:

For Q < 600,000

931.1 C 736.5  10 QE

For Q > 600,000

2862.0

C  694.1 Q

The regression curves at Union Point were developed from 223 

measurements taken between 1991 to 1996 at Coochie and between 1993 

to 2002 at Union Point. Discharge at Union Point was taken to be the sum 

of published discharges at Tarbert Landing and the Old River Outflow 

Channel. Separate regression curves were developed for discharges greater 

than and less than 600,000 cfs. The maximum discharge for which data 
MRG&P Report No. 30 166 

were collected at Coochie/Union Point was 1,300,000 cfs. The calculated 

concentration at this discharge was taken to be the maximum 

concentration for the sediment yield calculations (i.e., there was no 

extrapolation of the regression curve beyond the range of measured data). 

The unbiased regression curves for sand concentration are the following:

For Q < 600,000

.3 515 C 306.3  19 QE

For Q > 600,000

.1 078 C  .2 962 5 QE

The regression curves at Vicksburg were developed from 223 

measurements taken between 1984 and 1989. Discharge measurements 

were available at Vicksburg for each day when sediment data were 

collected. The maximum discharge for which data were collected at 

Vicksburg was 1,590,000 cfs. The calculated concentration at this 

discharge was taken to be the maximum concentration for the sediment 

yield calculations (i.e., there was no extrapolation of the regression curve 

beyond the range of measured data). The unbiased regression curve for 

sand concentration is the following:

8167.0

C   48681.7 QE

HEC-6T sand yields were calculated using the MVM hydrograph and the 

Vicksburg hydrograph. The MVM hydrograph was based on actual gage 

data from the tributaries adjusted to match measured data at the Memphis 

District Mississippi River gages. The Vicksburg hydrograph was based on 

measured data at Vicksburg, with tributary inflows assigned a constant 

percentage of the Vicksburg discharge based on average annual runoff 

volumes. It is expected that the Vicksburg hydrograph would produce 

better results downstream from Vicksburg because the Vicksburg 

hydrograph better represents the actual hydrograph in this part of the 

Mississippi River. Unfortunately, measured sediment data are lacking to 

compare sediment yield in the Memphis District reaches.
MRG&P Report No. 30 167 

Adjustment to dredging volumes 

The interim New Orleans District numerical model was calibrated to match 

reported dredging volumes in Southwest Pass and AHP between 1991 and 

2002. Sediment inflow for the interim model was developed from measured 

sediment concentration data at Union Point and Tarbert Landing. The 

reported dredging volumes were taken from New Orleans District dredging 

logs. The logs provide approximate locations of daily dredging activities. 

Annual dredging volumes for Southwest Pass between Pilots Station 

(RM -18) and Head of Passes (RM 0) and for the Mississippi River between 

Head of Passes and RM 7 were determined from the dredging logs. 

Estimated volumes of agitation dredging are not included in the reported 

volumes. Estimated volumes from operations where the dredged material 

was side cast out of the navigation channel onto a river bar are not included 

in the reported volumes. Annual reported dredging volumes in Southwest 

Pass and in the Mississippi River AHP are listed in Table 43.

Table 43. Reported and calculated* dredging 1991–2002. 

Annual Dredging 

(million cubic yards)

Southwest Pass RM -18 to 0 AHP RM 0 to 7 

Calculated 

Reported 

Calculated 

Interim Model Final Model Interim Model Final Model Reported 

1991 13.19 13.71 3.33 4.66 4.99 8.47

1992 3.66 4.84 8.23 0.91 1.21 1.31

1993 14.60 10.26 9.95 5.11 2.53 8.04

1994 13.15 11.66 7.68 9.30 5.13 6.97

1995 6.23 5.57 9.15 3.78 4.10 6.38

1996 6.51 6.17 8.09 7.78 4.07 4.32

1997 8.06 7.28 10.24 8.41 6.68 6.42

1998 4.85 6.22 7.50 4.68 2.18 6.01

1999 6.10 6.27 8.55 2.63 2.04 0.97

2000 4.66 3.41 2.32 0.59 1.25 0.60

2001 3.81 4.55 6.82 1.76 1.76 2.58

2002 5.45 6.54 8.37 8.22 6.44 5.43

Total 90.28 86.46 90.24 57.82 42.38 57.51

*Note: Annual calculated values include an equal distribution of the initial dredging that represents the difference 

between the 1992 and 2002 dredging templates. 
MRG&P Report No. 30 168 

Typically, the input parameters with the greatest uncertainty are chosen as 

calibration parameters in the numerical model. The primary calibration 

parameters for adjusting the model to reported dredging volumes are the 

fine sediment deposition coefficients. These coefficients affect the 

deposition of the silts and clays but do not affect sand deposition. Varying 

these coefficients was deemed reasonable to account for the effects of 

salinity on sediment deposition. Dredging volumes are also sensitive to the 

sediment diversion coefficients and the quantity of flow in the 

distributaries. Sediment diversion coefficients can also be used as 

calibration parameters. However, in this study a systematic procedure was 

developed to assign the sediment diversion coefficients and, lacking 

measured data, the systematic procedure was used to assign the 

coefficients. Distributary flows in the numerical model are based on 

measured data when available. In cases where data are not available, such 

as for flood flows, adjustments to the flow distribution percentages were 

made during the calibration phase of the study.

Simulated dredging in the model was set arbitrarily and does not represent 

an historical operation. To evaluate operation alternatives, specific 

dredging times and rates would need to be entered into the model. In the 

Regional Model dredging was performed at the beginning of June and 

December each year at a dredging rate of 100,000 cubic yards per day. 

The movable bed widths in the dredging reaches were set to be consistent 

with the dredging template in the navigation channel. This assignment in 

the numerical model allows for all deposited sediment to be subject to 

dredging. However, it does not allow for natural aggradation on bars 

outside the navigation channel. 

The dredging template for the calibration phase of the study was 

developed from the 2002 hydrographic survey. The survey indicated that 

the navigation channel had been dredged well below the 1992 elevations at 

several locations. The consequence of assigning the 2002 channel as the 

dredging template is that a significant quantity of calculated dredging 

occurs during the initial dredging operation. In Southwest Pass, the initial 

dredging was 25.1 million cubic yards. In the Mississippi River AHP, the 

initial dredging was 0.3 million cubic yards. Rather than assign this 1992 

and 2002 channel volume difference to a single year, the calculated initial 

dredging volumes were distributed equally among each of the 12 annual 

calculated volumes. Annual calculated dredging is shown in Table 43.
MRG&P Report No. 30 169 

Silt and clay deposition coefficients were adjusted in the numerical model 

to obtain a reasonable comparison between the total 12-year calculated 

and reported dredging volumes. A comparison of reported and calculated 

accumulated dredging volumes for the New Orleans District interim model 

is shown in Figure 117. Table 43 shows that the 12-year calculated 

dredging for the interim model is within 0.1 percent of the reported 

dredging in Southwest Pass and within 0.5 percent of the reported 

dredging AHP. Annual calculated and reported dredging volumes do not 

match as well as the overall volumes. This is to be expected because actual 

dredging operations are constrained by budgets, availability of dredges, 

weather, and other factors. 

Figure 117. Accumulated dredging in Southwest Pass, and from Head of Passes to RM 7. 

Calculated dredging AHP and in Southwest Pass did not match the 

reported data as well in the Regional Model. The difference is attributed to 

differences in the measured fine sediment data used to develop sediment 

inflow to the two models. The measured data indicates that fine sediment 

concentrations at Union Point and Tarbert Landing, which were used to 

develop sediment inflow for the interim New Orleans District model, are 

significantly greater at the lower discharges than reported at the upstream 

gages that were used to develop fine sediment inflow for the Regional 

Model. The consequence of this difference is that calculated dredging 

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

60,000,000

70,000,000

80,000,000

90,000,000

100,000,000

1990 1992 1994 1996 1998 2000 2002 2004 Accumulated Dredging cubic yards

SWP Calculated

SWP Reported

USHOP Calculated

USHOP reported

1991–2002

Calculations from interim study
MRG&P Report No. 30 170 

volumes are approximately 87% of reported volumes in the Regional 

Model. Table 43 shows that the 12-year calculated dredging is 

approximately 96 percent of the reported dredging in Southwest Pass and 

approximately 74 percent of the reported dredging AHP. Significant 

improvement in dredging volumes could not be achieved with additional 

adjustment of the cohesive sediment deposition coefficients. It was 

decided to use the cohesive deposition coefficients from the interim model. 

Options for improving the dredging simulation in the Regional Model 

include decreasing the fine sediment concentrations in the diversions AHP 

and in Southwest Pass and/or arbitrarily increasing fine sediment inflow at 

the upstream boundary or along the reach between Vicksburg and Union 

Point. One could justify the latter by attributing the increase to bank 

erosion. However, these modifications are not systematic and are left to 

future modelers addressing specific issues and objectives in future studies.

The calibrated numerical model is reliable for assessing the relative effect 

of upstream projects, such as channel constriction works or flow 

diversions, on dredging in Southwest Pass and AHP. Careful attention to 

sediment inflow assignment is required in order to assess calculated 

dredging magnitudes. Recalibration of the model may be required to 

assess project changes within the calibration reach itself or if the project to 

be evaluated requires modifying numerical model assignments, such as 

movable bed width, essential to the calibration. 

Verification 

Deposition downstream from Old River 

The numerical model was verified by simulating a deposition trend in the 

Mississippi River downstream from the Old River Control Complex. 

Measured deposition in the Mississippi River between RMs 310.1 and 

315.4 was obtained from the 1992 and 2002 hydrographic surveys. The 

numerical model geometry came from the 1992 hydrographic survey, and 

the 11-year time period between the hydrographic surveys was simulated 

in the model to determine calculated deposition. Deposition trends can be 

identified by comparing surveys taken in 1999 and 2008, which are shown 

in Figure 118 and Figure 119. 

The hydrograph simulated the 4,039 days between the 1992 and 2002 

hydrographic surveys. The cross sections of interest were surveyed on 
MRG&P Report No. 30 171 

2 November 1991 and on 20 November 2002. The comparison of 

measured and calculated deposition in the reach between RMs 310.1 and 

315.4 is shown in Table 44. Calculated deposition in the reach was 

26,461,000 cubic yards. Measured deposition was 29,360,000 cubic yards. 

The calculated deposition is 90 percent of the measured deposition. The 

comparison between calculated results and measured results are not as 

consistent when compared at individual cross sections. Calculated 

deposition was less than measured deposition at all cross sections except 

315.4 and 311.6. Cross section 315.4 is located downstream from the 

Hydropower Structure, and Cross section 311.6 is located downstream 

from the Auxiliary Structure. 

These results suggest that the numerical model is very successful in 

predicting deposition on a reach scale. If detailed information at a specific 

site is required then more detail in the vicinity of the site of interest needs 

to be added to the model geometry.
MRG&P Report No. 30 172 

Figure 118. 1999 Hydrographic survey at Old River Control Complex. 
MRG&P Report No. 30 173 

Figure 119. 2008 Hydrographic survey at Old River Control Complex.
MRG&P Report No. 30 174 

Table 44. Bed and area changes downstream from Old River Control Complex, 1991–2002. 

Cross Section 

RM 

Calculated Bed 

Change, ft 

Calculated Deposition 

cubic yards 

Measured Deposition 

cubic yards 

315.4 7.85 4,956,000 1,525,000

315.0 7.25 2,356,000 3,954,000

314.2 4.88 1,851,000 2,930,000

313.7 4.85 1,695,000 2,231,000

313.2 3.38 2,996,000 4,841,000

311.6 11.67 12,584,000 10,132,000

310.1 0.07 3,000 3,747,000

Total 26,461,000 29,360,000

The sensitivity of the numerical model results to several input 

parameters was evaluated using the measured deposition downstream 

from the Old River Control Complex. This sensitivity assessment was 

conducted chronologically before the calibration evaluation reported on 

above. At the time of the sensitivity assessment, roughness coefficients in 

the numerical model had been set using 1991 stage rating curves. 

Roughness coefficients in the final numerical model were set using an 

average of the 1991–2002 stage rating curves. The sensitivity assessment 

was conducted using a 14-year hydrograph between October 1988 and 

November 2002. Fines had not been added to the model at the time the 

sensitivity assessment was conducted. 

The effect of the sediment inflow rating curve on deposition downstream 

from the Old River Control Complex was evaluated. The sediment inflow 

rating curves for all the sand and gravel size classes at the upstream model 

boundary at Vicksburg was increased by a factor of 1.3. After a 14-year 

simulation, there was an insignificant change in deposition downstream 

from the Old River Control Complex as shown in Table 45. However, in 

this test, there was significant deposition downstream from the upstream 

boundary, which suggests that the inflow was too high. It was concluded 

that sediment inflow was not the primary factor influencing the increased 

deposition downstream from the Old River Control Complex. 

A test was made to see if changes in bed roughness due to wash-out of 

dunes would affect sediment deposition in the reach downstream from the 

Old River Control Complex. This effect is accounted for somewhat in the 

numerical model by varying bed roughness with discharge and calibrating 
MRG&P Report No. 30 175 

water-surface elevations to stages at gages. However, this approach 

ignores the loop effect as it assumes a unique roughness-discharge 

relationship. By using the Brownlie equations in HEC-6T, the bed 

roughness is calculated at each time-step as a function of the hydraulic 

conditions for that time-step. The Brownlie equations determine if dunes 

are present and account for increased roughness due to dunes. When the 

Brownlie equations were specified for the HEC-6T simulation for the 

falling limb of the 2002 hydrograph, there was an insignificant difference 

in calculated deposition downstream from Old River as shown in Table 46. 

A test was made to see if manually increasing the roughness on the falling 

limb of the 2002 hydrograph would significantly increase the deposition 

downstream from the Old River Control Complex. Roughness was 

increased between RMs 267 and 306.3 only on the falling limb of the 2002 

hydrograph. The increased roughness coefficients were determined by 

iteratively matching the falling limb of the stage-discharge rating curve at 

Red River Landing at RM 302.1. The revised roughness coefficients are 

shown in Table 46. Changes in bed elevation at the end of the 14-year 

simulation were insignificant as shown in Table 45. One reason is that the 

increased water surface elevations extend upstream and reduce sediment 

transport into the Old River Control Complex reach. 

The effect of increasing the roughness downstream from the Old River 

Control Complex for the entire 14-year simulation was evaluated. 

Roughness coefficients were increased to match the average 1989–2002 

stage data at Red River Landing. The roughness coefficients were higher 

for the long-term regression equations than for the 1991 rating curve used 

in the initial runs. Basically, this resulted in an insignificant increase in 

deposition during the 14-year simulation as shown in Table 45. 

The effect of the sediment diversion ratios at the Hydropower Structure 

was evaluated by reducing the sand diversion concentrations by 

50 percent. No diversion of very-coarse sand or larger grain sizes was 

allowed. This change resulted in a slight increase in deposition during the 

14-year simulation as shown in Table 45.

The effect of the sediment diversion ratios at the Low Sill and Auxiliary 

Structures was evaluated by reducing the sand diversion concentrations by 

50 percent. No diversion of very-coarse sand or larger grain sizes was 

allowed. This test was conducted to test the effect of reduced diversion of 
MRG&P Report No. 30 176 

coarse material that may occur due to shifting bar locations in the vicinity 

of the Old River diversion structures. This change resulted in a slight 

increase in deposition similar to that calculated when the sand diversion 

concentrations at the Hydropower Structure were reduced by 50 percent. 

Calculated results are shown in Table 45.

The sensitivity assessment demonstrates that numerical model results 

related to reach aggradation in this reach of the Mississippi River are not 

significantly affected by sediment inflow, bed roughness, or even sediment 

diversion concentrations at the Hydropower Structure if these input 

parameters are within a reasonable range. 

Table 45. Effects of sediment inflow and roughness on bed change. 

HEC-6T 

Section 

Base 

Test 

Increase 

Sediment 

Inflow × 

1.3 

Brownlie 

Equations 

on 2002 

Falling 

Limb 

Increase 

Roughness 

on 2002 

Falling 

Limb 

Increase 

Roughness 

for Entire 

Simulation 

Reduce Hydropower 

Diversion Ratio 50% 

Reduce Low 

Sill and 

Auxiliary 

Diversion 

Ratio 50% 

437.28 -.02 2.65

436.0 2.53 6.40

435.37 4.82 10.09

434.60 1.98 7.52

433.00 .82 3.60

326.6 -1.65 -1.20 -2.26 -2.19 -1.37 -1.69 -1.65

324.6 2.60 3.25 1.87 2.90 2.91 2.63 2.66

323.0 0.36 0.77 -1.85 0.53 0.64 0.38 0.43

321.0 -2.83 -2.30 -2.36 -3.27 -2.68 -2.91 -2.83

320.1 2.76 3.25 5.15 2.39 2.88 2.71 2.77

317.3 -2.11 -1.73 -2.03 -1.99 -1.94 -2.22 -2.09

315.4 11.13 11.58 10.92 10.53 11.20 11.28 11.10

315 9.86 10.32 11.92 9.87 10.02 9.95 9.86

314.2 6.42 6.75 6.51 6.72 6.47 6.53 6.64

313.7 6.40 6.70 6.39 6.58 6.91 6.51 6.57

313.2 5.47 5.85 5.08 5.46 5.47 5.59 5.60

311.6 15.04 15.46 17.36 15.27 15.19 15.14 15.38

310.1 4.98 4.99 5.93 4.54 4.65 4.60 4.84

308.4 3.35 3.82 2.83 3.29 3.42 3.49 3.73

306.3 -0.89 -0.58 -2.81 -0.86 -0.83 -0.87 -0.69
MRG&P Report No. 30 177 

Table 46. Roughness coefficients, falling limb of 2002 hydrograph, RM 267–306.3. 

Discharge, cfs 1991 Average, n Falling Limb, n 1992–2002 Average, n 

250,000 0.029 0.030 0.030

650,000 0.024 0.034 0.027

850,000 0.022 0.033 0.025

1,000,000 0.021 0.026 0.023

1,500,000 0.020 0.025 0.020

Degradation at Smithland Crossing 

Channel constriction works were constructed in the Mississippi River at 

Smithland Crossing between September 1990 and June 1996. The 

constriction works are located between RMs 297.45 and 300.3 in the HEC6T model. A navigation map of Smithland Crossing prior to construction 

of the constriction works is shown in Figure 120. Note that the navigation 

channel is on the right side of the river and that an island separates the 

navigation channel from what is labeled Raccourci Cutoff, which is the 

new navigation channel.

Figure 120. Navigation map of Smithland Crossing before construction of contraction works. 
MRG&P Report No. 30 178 

The construction sequence at Smithland Crossing started in September 

1990 with a trench-fill revetment through the middle of the island. The 

trench-fill revetment was finished in July 1992. This revetment is the new 

right bank of the navigation channel. The constriction dikes were 

constructed on the left bank of the river between August 1991 and 

December 1991. The 1991–1992 hydrographic survey through this reach 

was surveyed between 26 November and 6 December 1991. A 1998 

navigation map of Smithland Crossing is shown in Figure 121. A postconstruction photograph of Smithland Crossing looking upstream is 

shown in Figure 122. Note that in Figure 122, the navigation is still 

occurring in the old channel and that the trench fill revetment has not yet 

been reached. Sedimentation has begun in the dike field.

Figure 121. Navigation map of Smithland Crossing after construction. 

Hog Point 1998
MRG&P Report No. 30 179 

Figure 122. Looking upstream at Smithland Crossing after construction of dikes. The 

chute closure structure has not been completed, the river has not eroded to the 

trench fill revetment, and sediment has begun to deposit in the dike field. 

A recent photograph of Smithland Crossing (looking downstream) is 

shown in Figure 123. In this picture, the navigation channel has moved to 

the left side of the island, the river has eroded to the trench fill revetment, 

and significant sediment has deposited in the dike field. 

Figure 123. Smithland Crossing after completion of chute closure structure. Looking 

downstream — the river has eroded back to the trench fill revetment, and sediment 

has deposited in dike field.
MRG&P Report No. 30 180 

The HEC-6T numerical model was verified using data from Smithland 

Crossing. This verification study was conducted chronologically before the 

final calibration of initial bed material gradation and sediment inflow was 

completed. Therefore, the magnitude of calculated results may be different 

than those calculated with the final calibrated model. However, the 

calculated trends will be identical.

The initial geometry outside of the dike field came from the 1991–1992 

hydrographic survey. The geometry at Smithland Crossing was modified to 

account for the closure structure and projection of dikes in the dike field. 

Bed elevations in the chute were raised to account for the closure structure 

so that conveyance in the chute was equal to the flow that occurs over the 

closure weir. Erosion limits in the model were set at the toe of the dikes and 

at the toe of the trench-fill revetment. Deposition limits were initially set at 

the right and left bank of the river. However, these limits were changed to 

match the erosion limits when excessive deposition was calculated in the 

dike field. This occurs in the numerical simulation when only deposition is 

allowed to occur in the dike field. Erosion cannot be allowed in the dike field 

because in the HEC-6T model all the bed elevation points within the erosion 

and deposition limits are moved an equal distance in the solution of the 

sediment continuity equation during each time-step. The 1D model does not 

allow for lateral variation of erosion rates, so it is an all-or-nothing choice. 

The consequence is that deposition in the dike field and on the island is not 

accounted for in the numerical model. The channel banks in the numerical 

model were set at the top of the trench fill revetment and at the end of the 

projection of the dikes. This designation is significant because it is the 

channel hydraulic parameters that are used in the sediment transport 

equations. Roughness coefficients in the dike field and in the chute were set 

at 0.035. Roughness coefficients in the channel were varied with discharge.

The HEC-6T cross sections through Smithland Crossing are shown in 

Figure 124 through Figure 128. The original cross sections from the 1991–

1992 hydrographic survey are shown on these figures for reference, but 

they were not used in the HEC-6T simulations. The dike field was added to 

the 1991–1992 geometry and is indicated by the shaded green area in the 

figures. Blockage of the cross-sectional area in the chute for conveyance 

calculations is indicated by the shaded blue area in the figures. This 

modified geometry was then used as the initial conditions in the model. 

The cross sections labeled “2004” shown in the figures are from the 2004 

hydrographic survey. Aggradation and degradation calculated by HEC-6T 
MRG&P Report No. 30 181 

between 2 November 1991 and 10 December 2002 is shown on the figures. 

These are close to the actual dates of the hydrographic surveys at 

Smithland Crossing. The simulation covered 4,057 days, which is a little 

more than 11 years. 

Calculated bed changes in the HEC-6T model occur equally at each crosssection point within the movable bed. Thus, the model is not able to 

reproduce the change in cross-section shape that occurred as a result of 

the construction of the constriction works. However, the model can be 

used to estimate the volume of erosion that occurs as a result of channel 

constriction.

Calculated and measured erosion at RM 300.3 are shown in Figure 124. 

This figure demonstrates that that the channel shape changed between 1992 

and 2004. However, the change in measured and calculated cross-sectional 

area is similar. Figure 125 and Figure 126, which show the calculated and 

measured erosion at RMs 299.5 and 298.9, also demonstrate the differences 

between calculated and measured cross-section shapes, but a similarity in 

change in cross-sectional areas. The success of the model to produce a 

reasonable channel shape at RMs 299.5 and 298.9 is especially encouraging 

considering the extreme changes in the cross sections that were introduced 

by the dikes and the closure of the chute.

At RMs 299.5, 298.9, and 298.1 (Figure 125, Figure 126, and Figure 127), 

the 2004 hydrographic survey shows that deposition occurred above the 

top elevation of the dikes and at RM 298.9 on the island. This deposition 

was not simulated in the numerical model because cross-section changes 

were restricted to the channel. In one test with the numerical model, 

deposition was allowed in the dike field. Under these conditions, between 

12 and 15 ft of deposition above the dike crest elevation was calculated. 

This result highlights a dilemma with the modeling approach. To achieve 

appropriate conveyance in the main channel, it is necessary to assume that 

the dike field is filled to the top of the dikes for initial conditions. This 

means that the area between the dikes is available to accumulate sediment 

in the prototype but not in the model. Thus, if the model is allowed to 

deposit sediment in the dike field, the accumulation of sediment above the 

dike crest elevation begins at the start of the hydrograph simulation. 

Figure 123 shows that the area between the dikes has essentially been 

filled with sediment so that future projections based on the assumption of 

fill between the dikes will not have this problem.
MRG&P Report No. 30 182 

Figure 124. Calculated and measured degradation at Smithland Crossing, RM 300.3. 

Figure 125. Calculated and measured degradation at Smithland Crossing, RM 299.5. 

-40.00

-20.00

0.00

20.00

40.00

60.00

80.00

0 2000 4000 6000 8000

Distance ft Elevation ft

1992

2004

CALC
MRG&P Report No. 30 183 

Figure 126. Calculated and measured degradation at Smithland Crossing, RM 298.9. 

Figure 127. Calculated and measured degradation at Smithland Crossing, RM 298.1. 
MRG&P Report No. 30 184

Figure 128. Calculated and measured degradation at Smithland Crossing, RM 297.45. 

It is important to consider that calculated deposition in the dike field is a 

function of the sediment inflow and sediment transport capacity in the 

channel. The model deposits excess sediment uniformly across both the 

dike field and the channel if the movable bed includes the dike field. The 

flow parameters across the dike field are not considered in the model. 

Thus, at higher flows when erosion may actually occur across the dike field 

in the prototype, no erosion occurs in the model. 

There are two options for modeling a dike field:

1. Allow sediment deposition in dike field. The Smithland Crossing results 

indicate that this approach will significantly overestimate the deposition in 

the dike field, at least for the first 11 years.

2. Restrict the movable bed to the main channel. The Smithland Crossing 

results indicate that this approach will not account for the deposition that 

occurs above the crest of the dikes. Over many years, the dike field may 

increase in elevation as the channel adjusts its shape to conform to 

upstream channel geometry.

The model verification results are based on the approach where channel 

erosion and deposition is limited to the channel. Calculated channel 
MRG&P Report No. 30 185 

erosion in the Smithland Crossing reach is compared to measured erosion 

over the 11-year period between hydrographic surveys in Table 47. The 

tabulation does not include the deposition in the dike field or on the 

island. The calculated results are based on the assumption that the 

constriction works were in place at the beginning of the simulation in 

November 1991. This was true for the dikes, but the chute closure 

structure was not completed until June 1996. Therefore, modeled erosion 

is expected to be greater than prototype erosion. The calculated erosion in 

this reach was within 10 percent of the measured for the 11-year period.

Table 47. Calculated and measured erosion at Smithland Crossing, 1991–2002. 

Cross Section 

Calculated with HEC-6T 

cubic yards 

Measured 

cubic yards 

297.45

4,370,000 4,176,000

298.1

12,778,000 12,692,000

298.9

8,695,000 7,300,000

299.5

9,309,000 7,854,000

300.3

Total 35,152,000 32,022,000 

The designation of the movable bed limits will not only affect the shape of 

the cross sections in the dike field itself, it will also affect the sediment 

load downstream. A test was made to compare cross-section shape and 

downstream sediment transport load with the 1991–2002 hydrograph for 

the case where deposition was allowed in the Smithland Crossing dike field 

and for the case where it was not.

Calculated cross-section shape changes at Cross Section 298.1, for the case 

where deposition was allowed in the dike field and for the case where it 

was not, are shown in Figure 129. Note that there is less scour in the main 

channel for the case where deposition was not allowed in the dike field. 

Allowing deposition in the dike field resulted in less cross-sectional area at 

all Smithland Crossing cross sections. 
MRG&P Report No. 30 186 

Figure 129. Calculated bed changes at cross section 298.1 for 1991–2002. 

Calculated accumulated sediment transport downstream from Smithland 

Crossing, for the case where deposition was allowed in the dike field and 

for the case where it was not, is shown in Figure 130. Note that the dike 

field increased the sediment load downstream for both cases. The net 

effect of deposition in the dike field and more scour in the channel results 

in more sediment load downstream. The maximum increase in sediment 

load due to allowing deposition in the dike field is approximately 

6 percent. The increased sediment load continues for approximately 

100 miles downstream. 

This appears to be a matter of approximating a 3D process with a 1D 

computation. It is possible that there may be long-term results in which 

the deposits exceed the height of the dikes if vegetation can get started. 

Two options that may allow the 1D model to approximate that condition 

are the following: 

1. Include the dike field in the deposition zone for the best estimate of longterm future results and accept the fact that initial deposits build too 

quickly.

2. Put a loop through the dike field to determine if program will make a 

better estimate of the entire process. 

-40

-20

0

20

40

60

80

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Station FT Elevation FT NGVD

1992 Initial Contition

2002 No deposition in Dike Field

2002 Deposition in Dike Field
MRG&P Report No. 30 187 

Figure 130. Calculated accumulated sediment load for 1991–2002. 

320,000,000

340,000,000

360,000,000

380,000,000

400,000,000

420,000,000

440,000,000

460,000,000

480,000,000

500,000,000

520,000,000

540,000,000

0 50 100 150 200 250 300 350

River Mile Accumulated Tons Passing

No Deposition in Dike Field

Depostion in Dike Field
MRG&P Report No. 30 188 

4 Model Results

Sediment yield 

The accumulated sediment load at each model cross section is calculated 

by the HEC-6T numerical model. A profile of the total sediment delivery, 

the sand sediment delivery, and the sediment delivery for each size class 

can be displayed at any time during the numerical simulation. This profile 

provides insight into sedimentation trends along the river. Sand delivery 

profiles after 1 year of simulation and after 12 years (1991–2002) of 

simulation are shown in Figure 131. Moving downstream (right to left on 

the figure), an increase in sediment delivery along the profile indicates a 

degrading reach while a decreasing sediment delivery indicates an 

aggrading reach. For example, Figure 131 indicates significant degradation 

trends between RMs 900 and 840, 750 and 650, and 580 and 470. 

Aggradation trends are indicated between RMs 650 and 580, 470 and 410, 

and 230 and 0. The sharp decline in sediment delivery near RM 311 is due 

to diversions at the Old River Control Complex. Significant sediment 

diversion also occurs through several distributaries downstream from 

RM 15. A general conclusion is that the Lower Mississippi River is 

generally degrading upstream from RM 650 and aggrading downstream 

from RM 470. The degradation trend can be attributed to the low 

sediment concentrations being supplied by the Ohio River and the 

corresponding response of sediment entrainment from the bed of the 

Mississippi River to meet the increased sediment transport capacity. 

Downstream from RM 470, the aggradation trend can be attributed to the 

normal decrease in sediment transport capacity due to decreasing slope in 

the downstream reaches of natural rivers. 
MRG&P Report No. 30 189 

Figure 131. Calculated cumulative sand delivery for 1 year and 12 years. 

Accumulated sediment inflow/outflow at the model boundaries during the 

numerical simulation are calculated by the HEC-6T model. Calculated 

sediment loads from tributaries into the Lower Mississippi River between 

Cairo and the Old River Control Complex, between 1991and 2002, are 

shown in Table 48. Calculated outflow through distributaries between 1991 

and 2002 are also shown in Table 48. The table includes calculated 

weights of both the total sediment load (clay, silt and sand) and the sand 

load. Only the sand load affects changes in river morphology. 

Table 48. Calculated sediment loads from tributaries and distributaries, 1991–2002. 

Tributary River Mile 

Total 

million tons 

Sand 

million tons 

Percentage of 

Sand Load 

Upstream of 

Old River 

Control 

Complex 

Middle Mississippi 953 1457.02 421.43 66.87

Ohio 953 433.35 60.36 9.58

Obion 819.2 31.21 3.97 0.63

Hatchie 773 7.76 0.99 0.16

St. Francis 672.4 8.53 0.16 0.04

0

100

200

300

400

500

600

700

800

900

1,000

0 100 200 300 400 500 600 700 800 900 1,000 1,100 Sand Delivery - Tons Millions

Mississippi River Mile

1991-2002

1991-1992 Ohio Old River Arkansas St Francis White 
MRG&P Report No. 30 190

Tributary River Mile 

Total 

million tons 

Sand 

million tons 

Percentage of 

Sand Load 

Upstream of 

Old River 

Control 

Complex 

White 599 22.96 2.85 0.45

Arkansas 580.8 74.05 37.16 5.90

Yazoo 437 69.68 1.35 0.21

Total Eroded between Cairo 

and Old River Control 

Complex 103.28 16.37

Distributary

Old River Outflow Channel 312 – 316 -447.70 -84.65 13.43

Bonnet Carré 129 -8.28 -1.94 0.31

Caernarvon 81.4 -10.61 -0.70 0.11

Bohemia Spillway 33 - 45 -7.31 0 0.00

Baptiste Collette 11.5 -147.63 -16.96 2.70

Grand Pass 10.5 -146.18 -22.81 3.62

Cubits Gap 3.0 -193.79 -12.47 1.98

South Pass and Pass a 

Loutre 0.0 -326.98 -30.29 4.81

SWP at Mile 3.0 -3.0 -18.36 -1.27 0.20

Joseph Bayou -4.5 -53.14 -3.79 0.60

Outlet W-2 -9.8 -26.48 -0.82 0.13

Burrwood Bayou -14.4 -43.18 -3.33 0.53

Pilots Station -18.0 -367.57 -73.09 11.59

Total Outflow downstream 

from Coochie 1797.21 -252.12 40.01

Total Dredged/Deposited 

downstream from Coochie 409.47 378.08 59.99

Data From NODR_FINAL_ADJ_MODEL 1990-2011.T6

Modified hydrograph 2003–2011 

The hydrographs used to evaluate conditions after the 30 September 2002 

calibration period were based on data from upstream boundary gages and 

did not include adjustments to tributary inflows to match downstream 

gages. This approach maintains the beneficial effect of simulating the 
MRG&P Report No. 30 191 

correct timing of tributary contributions but does not account for 

differences in measured discharges in upstream and downstream gages. 

The inflow hydrograph for the Middle Mississippi River was developed 

from USGS gages on the Mississippi River at Chester (RM 110, USGS 

07020500) and Thebes (RM 44, USGS 0702200) and from the USGS gage 

on the Big Muddy at Plumfield (RM 87, USGS 05597000). It is expected 

that the combined discharges at Chester and the Big Muddy should equal 

the discharge at Thebes. Since the Plumfield gage is located a considerable 

distance from the Big Muddy confluence with the Mississippi River, it is 

appropriate to take the difference between the Chester and Thebes 

measured data to be the contribution from the Big Muddy. However, there 

were several days when the measured discharge at Chester was greater 

than the measured discharge at Thebes. This apparent discrepancy could 

be due to measurement error or to floodplain/channel storage. The 

measured discharge at Plumfield was compared to the difference between 

the measured discharges at Chester and Thebes and the maximum of the 

two was used in the numerical model hydrograph. This assignment 

eliminates zero and negative flows from the Big Muddy. The measured 

daily discharge at Chester was compared to the sum of the measured daily 

data at Thebes minus the computed Big Muddy daily discharge. The 

maximum of these two values was used as the upstream boundary 

discharge on the Middle Mississippi River. The model hydrograph tends to 

maximize inflow from the measured data. However, the difference in total 

runoff volume between the maximized hydrograph and measured 

discharge at Thebes was calculated to be less than 1 percent. 

The 2003–2011 hydrograph did not include changes to distributary 

outflow percentages that occurred after 2002. Changes in outflow 

percentages have been confirmed by recent measurements. Also excluded 

are new diversions constructed after 2002, including the Davis Pond 

(RM 118.4) and West Bay (RM 4.9) diversions. These updates have been 

incorporated into a separate HEC-6T numerical model developed by 

Mobile Boundary Hydraulics for the State of Louisiana (Thomas 2012) and 

were incorporated into the Flowline Sedimentation Model developed by 

the USACE (Copeland 2018).

Sediment inflow for the Middle Mississippi River 2003–2012 

Measured sediment data at Thebes (USGS 07022000), which is located at 

RM 43.7 above the confluence of the Ohio River, suggest that sediment 
MRG&P Report No. 30 192

concentration is declining. The USGS Water Science Center in Rolla, MO, 

provided the following information about how sediment data are collected 

at Thebes: 

Samples are collected at Thebes by both USGS personnel and 

contract observers. The contract observers collect a daily 

sediment sample at a single vertical using a D-74 depthintegrating sampler. The USGS collects sediment samples at 

5 verticals using the equal-discharge-increment (EDI) 

method. The USGS also collects a sample at the contract 

observer transect. Both the contract observers and the USGS 

collected samples from the railroad bridge at Thebes until 

1997, when both changed to collecting samples from a boat – 

the USGS just upstream from the bridge and the contract 

observers under the bridge at the same location that was 

used from the bridge. The USGS used a P-61 sampler to 

obtain depth- integrated samples until 2009, when they 

switched to a D-96 depth-integrating bag sampler. The daily 

samples collected by contract observers are adjusted to 

account for lateral variability in concentration across the 

cross section. The adjustment coefficient is determined by 

the USGS, each year, using data from their EDI 

measurements and the measurement taken at the contract 

observer sampling transect.1

Data collected by the USGS were obtained from the USGS web site 

http://nwis.waterdata.usgs.gov/il/nwis/. The data are found in the Water Quality - 

Field/Lab Samples data categories. Figure 132 shows plotted measured 

suspended sediment concentrations and power regression curves for the 

1991–2002 and 2003–2012 time periods. Figure 133 shows the same for 

measured suspended sand concentrations. The figures suggest a decline in 

sediment concentrations for discharges greater than 150,000 cfs.

 

1 Personal communication with Miya N. Barr, Hydrologist/QW DBA/ Sediment, Lab Chief USGS-Missouri 

Water Science Center, 10 Oct 2012.
MRG&P Report No. 30 193

Figure 132. Measured total suspended sediment concentration at Thebes. 

Figure 133. Measured suspended sand concentration at Thebes. 

10

100

1000

10000

10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

1991-2002

2002-2012

Power (1991-2002)

Power (2002-2012)

1

10

100

1000

10,000 100,000 1,000,000

Concentration mg/l

Discharge cfs

1991-2002

2003-2011

Power (1991-2002)

Power (2003-2011)
MRG&P Report No. 30 194

There is considerable uncertainty associated with approximations obtained 

from power regression curves at the extremes of the data range. A more 

accurate approximation of average sediment concentration at the upper and 

lower ends of the discharge range can be obtained if additional data points 

are used. Thebes is one of the few sediment gages where a long-term daily 

sediment record is available. The mean daily sediment measurements at 

Thebes provide additional data for the total suspended sediment load but 

not for the sand load. There are 7,670 adjusted mean daily sediment 

concentrations at Thebes, for water years 1991 through 2011, reported in the 

USGS web site at http://nwis.waterdata.usgs.gov/il/nwis/ . The data are found in the 

Surface Water – Daily Data data categories. Figure 134 shows plotted 

mean daily suspended sediment concentrations and power regression 

curves for the entire 21-year period, between 1991 to 2011, and for the 1991–

2002 and 2003–2011 time periods. The results suggest that the average 

sediment concentrations at all discharges were lower for 2003–2011 than 

for 1991–2002. The results also suggest that average sediment 

concentrations at discharges less than 100,000 cfs are essentially the same 

for 1991–2002 and 2003–2011. Figure 134 also highlights the considerable 

uncertainty at discharges greater than 400,000 cfs. 

Figure 134. Mean daily measured total suspended sediment concentration at Thebes. 

10

100

1000

10000

10,000 100,000 1,000,000 Concentration MG/L

Discharge CFS

1991-2002

2003-2011

Power (1991-2011)

Power (1991-2002)

Power (2003-2011)
MRG&P Report No. 30 195

A significant portion of the sediment in the Middle Mississippi River at 

Chester and Thebes is provided by the Missouri River. Meade (1995) 

estimated that currently, nearly fifty percent of the sediment delivered to 

the Gulf of Mexico comes from the Missouri River. To check the 

conclusion that sediment concentrations at Thebes have declined since 

2002, sediment data from the Missouri River were evaluated. 

The first long-term sediment gage on the Missouri River, upstream from 

its confluence with the Mississippi River, is at Hermann (USGS 0693450). 

Hermann is located at RM 98. The USGS, in cooperation with the USACE 

Kansas City District, reported 220 sediment measurements at Hermann 

between 1991 and 2002 and 199 sediment measurements between 2003 

and 2012. Sediment concentration data for the period 1991–2008 is 

available in Heimann et al. (2010). Data for 2009–2012 is available from 

the USGS web site http://nwis.waterdata.usgs.gov/mo/nwis/. According to Heimann 

et al. (2010), the sediment data were collected using either the equalwidth-increment method or the equal-discharge-increment method during 

the 1991–2008 study period. Between 1991 and 2004, depth-integrated 

and point samples were collected with either the US-P61 or US-P63 

sampler. In 2005, the sampling equipment was changed to a US-D96, 

which collects only depth-integrated samples. 

Measured suspended sediment and suspended sand concentrations 

between 1991 and 2002 at the Hermann gage were compared to measured 

sand concentrations between 2003 and 2012. As shown in Figure 135 and 

Figure 136, a comparison of power regression curves, through the measured 

data, indicates a decline in suspended sediment and suspended sand 

concentrations after 2002. This result supports the conclusion that the 

suspended sediment concentrations at Thebes have declined after 2002. 
MRG&P Report No. 30 196

Figure 135. Measured total suspended sediment concentration, at Hermann. 

Figure 136. Measured suspended sand concentration for the Missouri River at Hermann. 

10

100

1,000

10,000

10,000 100,000 1,000,000 Concentation MG/L

Discharge CFS

1991-2002 Total

2003-2012 Total

Power (1991-2002 Total)

Power (2003-2012 Total)

1

10

100

1,000

10,000 100,000 1,000,000 Concentration MG/L

Discharge CFS

1991-2002 Sand

2003-2012 Sand

Power (1991-2002 Sand)

Power (2003-2012 Sand)
MRG&P Report No. 30 197 

Effect of declining sediment inflow at Thebes 

The numerical model was used to test the effect of a declining sediment 

inflow at Thebes on sediment delivery in the Mississippi River between 

Cairo and the Gulf of Mexico. The model hydrograph was extended to 

30 September 2011. Sediment delivery for the 1991–2011 time period was 

then calculated using the same boundary conditions used for the 1991–

2002 calibration period. Another calculation was made for the 1991–2011 

time period with a reduced sediment inflow curve at Chester starting on 

1 October 2002. All other boundary conditions were left unchanged. The 

calculated cumulative sand deliveries are shown in Figure 137. The 

numerical model results indicate that the change in sediment inflow from 

the Middle Mississippi River has a very small effect on sediment delivery 

after the first 50 miles. 

Figure 137. Calculated cumulative sand delivery 1991–2011. 

Calculated 2003–2011 sand delivery, at several Mississippi River gage 

locations, is shown in Table 49. The difference in sand transport for the 

9-year period due to declining sediment inflow at Thebes is 43.8 million 

tons at Cairo, 42.7 million tons at Wickliffe, 25.9 million tons at Hickman, 

and 17.5 million tons at New Madrid. At Memphis, the decrease in sand 

delivery is 5.2 million tons, and the decrease in sand delivery is less at each 

downstream gage. 

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

0 100 200 300 400 500 600 700 800 900 1,000 1,100 Sand Delivery - Tons Millions

Mississippi River Mile

1991-2002

1991-2011

Change QS in 2003 Ohio Old River Arkansas St Francis White 
MRG&P Report No. 30 198

Table 49. 2003–2011 calculated sediment delivery. 

Station River Mile 

1991–2002 Inflow 2003–2011 Inflow Difference 

Million Tons 

Coochie 317 422.0 421.8 -0.2

Natchez 363 451.4 449.0 -2.4

Vicksburg 435 489.6 486.6 -3.0

Greenville 531 498.6 496.4 -2.3

Rosedale 592 475.9 473.0 -3.0

Helena 663 538.2 534.5 -3.7

Memphis 736 518.9 513.7 -5.2

New Madrid 889 370.0 352.5 -17.5

Hickman 922 347.9 322.1 -25.9

Wickliffe 952 352.5 309.8 -42.7

Cairo 953 361.1 317.2 -43.8

Effect of hard points on degradation 

The river bed was assigned a fixed bed at RMs 917.6, 921, and 922 in the 

calibrated numerical model. This assignment reflects the existence of a 

known hard point in the Mississippi River bed at Hickman. Numerical 

model results indicate that this reach of the Mississippi River is 

degradational, which suggests that the Hickman hard point could have a 

significant influence on river morphology. The significance of this hard 

point was evaluated by removing the hard points at the three cross 

sections in the model and running the 1991–2012 simulated hydrograph. 

The 1991–2002 sediment inflow curves at Thebes were used in the 

comparison study. Figure 138 shows the 21-year difference in sand 

delivery, and Figure 139 shows the 21-year difference in calculated average 

bed change with the hard points removed. 

Removing the hard points results in almost 10 ft of degradation at 

Hickman over the 21-year period. Figure 138 shows that the increase in 

downstream cumulative sand delivery due to the degradation at Hickman 

and the subsequent increase in sediment transport potential upstream is 

relatively small. The calculations indicate that the eroded sediment at 

Hickman does not result in any significant increase in downstream 

aggradation until RM 600, and then the increase in average bed elevation 

is on the order of tenths of a foot. The reason for the 300-mile lag before 
MRG&P Report No. 30 199

the deposition pattern begins is that the 300-mile reach below Hickman is 

generally a degradation reach. 

Figure 138. Effect of hard points at Hickman on calculated cumulative sand delivery. 

Figure 139. Calculated difference in average bed with hard points at Hickman removed. 

200

400

600

800

1,000

1,200

1,400

1,600

1,800

800 820 840 860 880 900 920 940 960 980 1,000 Sand Delivery - Tons Millions

Mississippi River Mile

1991-2002

1991-2010

1991-2011

No Hard Pts 91-02

No Hard Pts 91-10

No Hard Pts 91-11 Ohio Hickman

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

0 100 200 300 400 500 600 700 800 900 1000 Difference in Average Bed Change FEET

River Mile

1991-2011
MRG&P Report No. 30 200

Effects of dike construction 

The numerical model was used to determine the effect of dike construction 

on sediment delivery and average bed change. The 1991–2011 hydrograph 

was used for the evaluation. Dike construction between RMs 427.4 and 

453 were added to the numerical model geometry at the time in the 

hydrograph that construction occurred. A new dike constructed in the 

Below Racetrack Dike field (RM 427.4) was added in August 1997. 

Increased dike heights in the Below Racetrack Dike Field (RM 429.2 and 

RM 431) were added in January 1996. New dikes in the Racetrack 

Towhead Dike Field (RM 432 and RM 433) were added in January 1995 

and January 1996, respectively. Dike elevations in the Forest Home 

Towhead Dike Field (RM 448.8, RM 451.2 and RM 453) were raised in 

August 1997, September 1994, and July 1997, respectively. The 1991–2002 

sediment inflow curves at Thebes were used in the comparison study.

As shown in Figure 140, the dike construction had only a small effect on 

the cumulative sediment delivery. Sediment delivery was increased 

upstream and downstream from the dike fields.

As expected, the dike construction resulted in significant degradation in 

the dike fields — approximately 4.5 ft in the Racetrack Dike Fields and 

approximately 8.5 ft in the Forest Home Dike Field (Figure 141). Average 

bed elevations increased by approximately 1 ft immediately downstream 

from the Racetrack Dike Field, decreasing to zero in approximately 

60 miles. Slight increases in average bed elevations (on the order of tenths 

of a foot) were calculated upstream from the Forest Home Dike Field for 

approximately 200 miles. 

These tests demonstrate the numerical model’s capability to determine the 

effective degradation induced in the vicinity of new dike construction and 

to determine the effect of the dike construction on river morphology 

upstream and downstream. 
MRG&P Report No. 30 201 

Figure 140. Effect of dike construction on calculated cumulative sand delivery. 

Figure 141. Calculated difference in average bed change with dike construction. 

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

300 350 400 450 500 550 600 Sand Delivery - Tons Millions

Mississippi River Mile

1991-2002

Add Dikes 91-02

Add Dikes 91-11

1991-2011

Racetrack

Forest Home Old RiverArkansas White 

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

0 100 200 300 400 500 600 700 800 900 1000 Difference in Average Bed Change FEET

River Mile

1991-2011 
MRG&P Report No. 30 202

5 Summary and Recommendations

The purpose of this study was to develop a numerical sedimentation model 

that could identify and predict the effects of planned Mississippi River and 

Tributaries Project features and dredging strategies on long-term 

sediment trends in the Lower Mississippi River. The model is constructed 

so that specific design features can be evaluated by adding more 

refinement to the numerical model. 

The study approach was to develop a 1D numerical model using the 

computer program HEC-6T. This program has been applied successfully to 

evaluate long-term sedimentation responses to various engineering 

projects along the Lower Mississippi River. These applications have 

included river response to dredging, river response to flow diversions 

through distributaries, stability of a low-flow sediment sill, and the effect 

of contraction works on navigation depth. Calculations in the HEC-6T 

numerical model are governed by physical properties that maintain 

sediment continuity throughout the study reach. Sediment continuity is 

maintained by bed aggradation/degradation and sediment transport. This 

characteristic of numerical modeling provides a distinct advantage over 

using reported sediment measurements at specific locations along the 

river to define sediment conditions where satisfaction of sediment 

continuity with upstream or downstream reaches is not required.

The New Orleans, Vicksburg, Memphis, and St. Louis Districts were 

responsible for developing the numerical model in their respective reaches 

of responsibility along the Mississippi River. The numerical model’s 

downstream boundary was at Pilots Station, LA, which is just inside the 

jetties at the end of Southwest Pass (RM -18). The upstream boundaries 

were at Chester, IL, at Middle Mississippi RM 109.0, and Metropolis on 

the Ohio River, which is approximately 37 miles upstream from the 

confluence with the Mississippi River. The numerical model includes 

reaches along three major tributaries: the Arkansas River (28.2 miles), the 

White River (100 miles), and the St. Francis River (17.2 miles). Shorter 

reaches are included for minor tributaries. The numerical model simulates 

over 1000 miles of the Mississippi River.

The cross-section geometry in the HEC-6T model was developed from 

hydrographic survey data taken between 1987 and 1992. The hydrographic 

surveys were conducted at different times in the different districts. There 
MRG&P Report No. 30 203

is even a time discontinuity in the cross sections surveyed in individual 

districts as the hydrographic surveys in each district were conducted over 

a period of a year or more. One of the consequences of this anomaly is that 

direct comparisons between historical surveys at individual cross sections 

or even reaches may be misleading. This factor makes model calibration to 

changes in surveyed bed volumes difficult and most likely unreliable. 

The model geometry includes dike fields that were present in 1992. Cross 

sections where dikes were present were modified to reflect the projections 

of upstream and downstream dikes in the vicinity of the cross section. This 

is equivalent to assuming that cross sections in the dike field are filled to 

the dike crest elevations. Recent enhancement of the HEC-6T model 

allows for changing cross-section geometry during the course of the 

historical simulation so that dikes can be added as they were constructed. 

Future studies should take advantage of this option.

HEC-6T approximates unsteady flow by stepping through a time-sequence 

of steady-state discharges. Mean daily flow data are entered at the 

upstream boundaries, and a backwater computation is made for the 1-day 

time step for the entire model length. This computational approach does 

not take into account flow routing or backwater storage effects, which 

introduces the potential for timing issues in flow propagation through the 

model. Thus, HEC-6T may not be appropriate for predicting flood 

hydrographs and stages, but experience has shown that it is successful in 

predicting long-term sedimentation processes. In this study, 1991–2002 

historical mean-daily flows were used to define the hydrograph in the 

numerical model.

The calibration and verification procedure adopted for this study is the 

accepted USACE methodology described in Guidelines for Calibration and 

Application of HEC-6 (HEC 1982) and Chapter 14 of ASCE Manual 110 

(ASCE 2006). It is recommended that future numerical sediment studies 

adopt these standardized guidelines for numerical model calibration and 

verification. 

The study process reveled discrepancies associated with the reported 

discharge data. Continuity of the Lower Mississippi River discharge record 

is inconsistent in time and distance. During the 1991–2002 calibration 

period, there was approximately a 4 percent loss in annual flow volume at

Helena when compared to the sum of Memphis and St. Francis River 
MRG&P Report No. 30 204

annual flows. The 12-year volume of water passing Arkansas City is 

consistent with the sum of the flow volumes from the Mississippi River at 

Helena and the White and Arkansas Rivers. There is approximately a 

2 percent increase in annual flow volume at Vicksburg when compared to 

the sum of Arkansas City and Yazoo River annual flows. Annual flow past 

Vicksburg and Natchez is relatively consistent. The largest discrepancy is 

at the Old River Control Complex where the sum of reported discharges in 

the Old River Outflow Channel and in the Mississippi River at Tarbert 

Landing is approximately 8 percent higher than the reported discharge 

upstream at Natchez and Vicksburg. The discrepancies between reported 

discharges are not consistent annually. There is an annual variation in the 

discrepancies between Natchez and Old River and Vicksburg and Natchez. 

The differences between Vicksburg and Natchez are insignificant, but the 

differences between Natchez and the Old River Control Complex are 

puzzling. These discrepancies at the Old River Control Complex produce a 

conundrum with respect to determining a hydrograph for the HEC-6T 

model. Additional study, which should include evaluation of data at the 

Baton Rouge gage, is recommended to address these issues.

Distributary outflows in the New Orleans District were calculated from 

rating curves developed from limited measured data or as a percentage of 

Mississippi River flow at a station upstream from the distributary. The 

most significant distributary is the Old River Control Complex where 

simple average ratings curves were used rather than actual measured 

discharges to make model application easier for a wide range of projects 

located up and down the 1000-mile study reach. Future studies related to 

a specific diversions on the Mississippi River may require a more detailed 

treatment of the flow through the diversion or diversions of interest. It is 

also critical to continue flow measurement programs to better define the 

outflow from distributaries and possible changes in outflow magnitudes 

with time.

Stages at the downstream end of Southwest Pass showed no stage-discharge 

correlation. Therefore, downstream water-surface elevations at Pilots 

Station were set based on average monthly stages. The simplifying 

assumption of an average monthly stage at the downstream boundary of the 

model is adequate for purposes of the generalized model developed in this 

study. However, studies of specific morphologic changes in the Mississippi 

River below Belle Chasse, especially in response to river diversions, may 

require more a detailed description of the downstream stages.
MRG&P Report No. 30 205

Roughness coefficients in the numerical model were adjusted so that 1991–

2002 calculated stages replicated average reported stage-discharge data at 

several gages. There is significant variability about the average regression 

line of the measured data relating stage to discharge. In the coastal zone, 

some of this variability can be attributed to tidal effects. However, bed 

forms and unsteady flow effects account for most of the variability. Many 

years have an identifiable loop effect in the rating curves. The height and 

distribution of bed forms lag the rise and fall of hydrographs so that there is 

no distinct relationship between bed form shape and discharge. In the 

steady-state 1D sediment model, the objective is to simulate average 

conditions to best replicate the movement of sediment over time. This is 

different from the approach taken to establish flow lines for maximum 

water surface elevations (e.g., for levee design). With the levee design 

approach, roughness coefficients would be chosen to match a regression 

curve through the maximum water surface elevation values rather than the 

average regression curve used in the sediment study. 

A combination of measured and calculated data were used to establish 

sediment inflow boundary conditions for the numerical model. To model 

sedimentation trends in the Mississippi River, it is necessary to account 

for movement and storage of each sediment size class. HEC-6T allows for 

this accounting; however, the required input data are generally lacking. 

Long-term size class sediment data are available in the study reach, at the 

upstream boundary on the Middle Mississippi River at Thebes, located 44 

miles upstream from the Ohio River, and at Chester. Long-term size class 

data are also available at Union Point (RM 326.6) and Coochie (RM 317.3), 

which are located upstream from the Old River Control Complex and at 

Tarbert Landing (RM 306.3), which is located downstream from the Old 

River Control Complex. A shorter record is available at Belle Chasse, 

located 76 miles AHP. Data for the major tributaries, including the Ohio 

River, are generally limited to the sediment concentrations greater and 

less than 0.062 mm. The lack of boundary condition data required that 

size class percentages be estimated by calculation and/or judgment. A 

continuing sediment data collection program is essential to verify and 

enhance future sediment transport predictions.

Cumulative sediment inflows to the Mississippi River from the Middle 

Mississippi and Ohio Rivers and from the tributaries were calculated for 

the 1991–2002 calibration period. These calculations, which were based 

on the historical record, show that the vast majority of the sediment is 
MRG&P Report No. 30 206

supplied by the Middle Mississippi River, even though most of the water is 

supplied by the Ohio River.

Study results highlight the significant discrepancies in the measured 

sediment data for the Mississippi River system. The physical laws that 

govern the numerical model require that sediment continuity be maintained 

throughout the system. However, it is apparent that sediment continuity is 

not maintained in analyses of the measured data at various gages in the 

system. The most probable explanation for the discrepancies in the 

measured data is related to the differences in the sediment collection and 

laboratory methodologies and in the analytical methods used to calculate 

sediment concentrations from the sampled data. It is recommended that a 

comprehensive investigation of the sediment data gathering methods be 

undertaken and that consistent methodologies be incorporated for sediment 

data collection in the Mississippi Valley Division.

Dredging volumes in Southwest Pass and AHP were simulated in the 

numerical model by adjusting the silt and clay deposition coefficients. 

Calculated dredging volumes were calibrated to match reported dredging 

volumes. The reported dredging volumes were taken from New Orleans 

District dredging logs. Estimated volumes of agitation dredging are not 

included in the reported volumes nor are estimated volumes from 

operations where the dredged material was side cast out of the navigation 

channel onto a river bar. In the interim New Orleans District study, the 

1991–2002 calculated dredging was within 0.1 percent of the reported 

dredging in Southwest Pass and within 0.5 percent of the reported 

dredging AHP. Annual calculated and reported dredging volumes do not 

match as well as the overall volumes. This is to be expected because actual 

dredging operations are constrained by budgets, availability of dredges, 

weather, and other factors. 

Calculated dredging AHP and in Southwest Pass did not match the reported 

data as well in the Regional model. The difference is attributed to 

differences in the measured fine sediment data used to develop sediment 

inflow to the two models. The measured data indicate that fine sediment 

concentrations at Union Point and Tarbert Landing, which were used to 

develop sediment inflow for the interim New Orleans District model, are 

significantly greater at the lower discharges than reported at the upstream 

gages that were used to develop fine sediment inflow for the Regional 

model. The consequence of this difference is that calculated dredging 
MRG&P Report No. 30 207 

volumes are approximately 87% of reported volumes in the Regional Model. 

Significant improvement in dredging volumes could not be achieved with 

additional adjustment of the cohesive sediment deposition coefficients. 

Options for improving the dredging simulation in the Regional model 

include decreasing the fine sediment concentrations in the diversions AHP 

and in Southwest Pass and/or arbitrarily increasing fine sediment inflow at 

the upstream boundary or along the reach between Vicksburg and Union 

Point. One could justify the latter by attributing the increase to bank 

erosion. However, these modifications are not systematic and are left to 

future modelers addressing specific issues and objectives in future studies.

Dredging and sediment diversion significantly alter morphologic processes 

in the river system. The numerical model can be used to calculate the 

short-term and long-term effects of proposed dredging activities and the 

effectiveness of a dredging program. The model can calculate the increased 

deposition rates associated with dredging and the length of time required 

to refill the navigation channel back to a critical elevation. The model can 

be used to calculate the effectiveness of in-channel dredge disposal versus 

disposal outside of the channel. The timing of dredging activities with 

respect to annual flood peaks can be evaluated. Similarly, the short-term 

and long-term effects of sediment diversions can be calculated using the 

numerical model. Although, the quantity of sediment diverted must be 

determined external to the numerical model, the morphologic changes 

induced by a specified quantity of sediment diversion can be determined. 

The most useful feature of the numerical model analysis is that systemwide effects of several diversions and dredging activities can be evaluated 

together, so that the effect of each individual feature on the system can be 

determined. These effects can be evaluated using calculated bed elevation 

and corresponding water-surface elevation changes in the river channel, 

sediment yields past designated cross sections, sediment diversion 

quantities through designated diversions, and required dredging 

quantities to maintain project depths.

Dike fields are constructed to hold alignment and increase navigation 

depths. In addition to the intentional bed changes in the dike field, there 

will be additional morphological changes in the upstream and downstream 

river reaches. The numerical model can be used to calculate the short-term 

and long-term bed and water-surface elevation changes in the dike field 

itself and in the river system as a whole. The model also calculates 
MRG&P Report No. 30 208

short-term and long-term changes in sediment yield upstream and 

downstream from proposed dike fields.

Construction of dikes fields between RMs 427.4 and 453 resulted in 

significant degradation in the dike fields as expected. However, the model 

demonstrated that the dike construction had only a small effect on the 

cumulative sediment delivery over a 21-year simulation period. These tests 

demonstrate the numerical model’s capability to determine the effective 

degradation induced in the vicinity of new dike construction and to 

determine the effect of the dike construction on river morphology 

upstream and downstream.

The effects of imposed hydrologic and sedimentation conditions on the 

river system can be evaluated using the numerical model. Changes in the 

sediment supply will affect the aggradation/degradation rates in the river 

system. The numerical model can be used to determine the calculated bed 

changes and the reach lengths affected. The effects of sea-level rise, 

temperature changes, and removal of river-bed hard points can also be 

calculated. The primary calculated metrics are bed elevation change and 

changes in sediment yield.

Measured sediment data at Thebes suggest that sediment concentrations 

in the Middle Mississippi River are declining. The numerical model was 

used to determine the effect of the declining sediment inflow from the 

Middle Mississippi for a 9-year period between 2002 and 2011. The 

numerical model results indicated that the change in sediment inflow has 

a very small effect on sediment delivery after the first 50 miles. 

Removing the hard point at Hickman resulted in almost 10 ft of 

degradation in the immediate vicinity of Hickman over a 21-year period. 

However, significant bed degradation did not occur upstream, at least 

during the 21-year simulation period. The increase in downstream 

cumulative sand delivery due to the degradation at Hickman and the 

subsequent increase in sediment transport potential upstream is relatively 

small. The calculations indicate that the eroded sediment at Hickman does 

not result in any significant increase in downstream aggradation until RM

600, and then the increase in average bed elevation is on the order of 

tenths of a foot. The reason for the 300-mile lag before the deposition 

pattern begins is that the 300-mile reach below Hickman is generally a 

degradation reach. 
MRG&P Report No. 30 209

The HEC-6T model was calibrated to reasonably match measured data 

between 1991 and 2002. Model applications related to the effects of 

sediment diversions and the effects of dredging in the New Orleans 

District were demonstrated. The model’s ability to address the effects of 

new constrictive works on the long-term and short-term river morphology 

was demonstrated. The ability to test the effects of changes in upstream 

sediment inflow was also addressed. The model’s ability to assess the 

effects of natural geomorphic changes, such as erosion of hard points, was 

demonstrated. Future application of this model to specific project sites 

should include the addition of more detailed geometry in the area of 

interest. The HEC-6T numerical sedimentation model developed for this 

study provides the general system-wide model that can be used to address 

the long-term and system effects of specific Mississippi River and 

Tributaries Project features.
MRG&P Report No. 30 210

References

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Measurements with Time –Sequenced Bathymetric Data.” Journal of Hydraulic 

Engineering 137(7): 723–728. 

American Society of Civil Engineers (ASCE). 2006. Sedimentation Engineering. ASCE 

Manuals and Reports on Engineering Practice No. 110. Edited by M. H. Garcia 

Reston, VA. 

Ariathurai, R., and R. B. Krone. 1976. “Finite Element Model for Cohesive Sediment 

Transport.” Journal of the Hydraulics Division, ASCE 102(3): 323–338. 

Barbe, D. E., K. Fagot, and J. A. McCorquodale. 2000. “Effects on Dredging Due to 

Diversions from the Lower Mississippi River.” Journal of Waterway, Port, 

Coastal and Ocean Engineering, ASCE 126(3): 121–129. 

Biendenharn, D. S., and C. R. Thorne. 1994. "Magnitude-Frequency Analysis of Sediment 

Transport in the Lower Mississippi River." Regulated Rivers: Research and 

Management 9: 237–251. 

Catalyst-Old River Hydroelectric. 1999. Lower Mississippi River Sediment Study, Vo. 4 –

HEC-6W Mississippi River Numerical Sedimentation Model Investigation, 

Vicksburg to Donaldsonville. In association with U.S. Army Corps of Engineers 

Waterways Experiment Station, Coastal and Hydraulics Laboratory, Vicksburg 

Mississippi. 

Copeland, R. R., and W. A. Thomas. 1992. Lower Mississippi River Tarbert Landing to 

East Jetty - Sedimentation Study, Numerical Model Investigation. Technical 

Report HL-92-6. Vicksburg, MS: USACE Waterways Experiment Station, 

Hydraulics Laboratory. 

Copeland, R. R. 1991. Dredging Alternatives Study, Lower Mississippi River, Cubits 

Gap, Report 1, TABS-1 Numerical Model Investigation. Technical Report HL-90-

20. Vicksburg, MS: USACE Waterways Experiment Station, Hydraulics 

Laboratory. 

Copeland, R.R. 2018. Mississippi River and Tributaries Flowline Assessment: 

Mississippi River Sedimentation Report. U.S. Army Engineer Mississippi Valley 

Division, Mississippi River Geomorphology and Potamology Program (MRG&P) 

Report No. 24, Vol 4, Vicksburg, MS: U.S. Army Engineer Research and 

Development Center

Demas, C. R., and P. B. Curwick. 1987. Suspended-Sediment, Bottom-Material, and 

Associated Chemical Data from the Lower Mississippi River. Louisiana Water 

Resources Basic Records Report No. 14, U.S. Geological Survey. Baton Rouge, 

LA: Louisiana Department of Transportation and Development. 

Ferguson, R. I. 1986. "River Loads Underestimated by Rating Curves." Water Resources 

Research 22(1): 74–76. 
MRG&P Report No. 30 211 

Heath, R. E., G. L. Brown, C. D. Little, T. C. Pratt, J. J. Ratcliff, D. D. Abraham, D. W.

Perkey, N. B. Ganesh, K. Martin, and D. P. May. 2015. Old River Control 

Complex Sedimentation Investigation. U.S. Army Engineer Mississippi Valley 

Division, Mississippi River Geomorphology and Potamology Program (MRG&P) 

Report No. 6. Vicksburg, MS: U.S. Army Engineer Research and Development 

Center. 

Heimann, D. C., P. P. Rasmussen, T. L. Cline, L. M. Pigue, and H. R. Wagner. 2010. 

Characteristics of Sediment Data and Annual Suspended-Sediment Loads and 

Yields for Selected Lower Missouri River Mainstem and Tributary Stations, 

1976–2008. U.S. Geological Survey Data Series Report 530. Washington, DC: 

U.S. Geological Survey. http://pubs.usgs.gov/ds/530/ 

Hydrologic Engineering Center (HEC). 1982. Guidelines for the Calibration and 

Application of Computer Program HEC-6. Training Document No. 13. Davis, 

CA: USACE Hydrologic Engineering Center. 

Hydrologic Engineering Center (HEC). 2001. HEC-RAS River Analysis System, 

Hydraulics Reference Manual. Davis, CA: USACE Hydrologic Engineering 

Center. 

Kolb, C. R. 1962. Distribution of Soils bordering the Mississippi River From 

Donaldsonville to Head of Passes. TR No. 3-601. Vicksburg, MS: USACE 

Waterways Experiment Station. 

Krone, R. B. 1962. Flume Studies of the Transport of Sediment in Estuarial Shoaling 

Processes. Berkeley, California: Hydraulic Engineering Laboratory, University of 

California. 

Lane, E. W. 1947. “Report of the Subcommittee on Sediment Terminology.” Transactions 

American Geophysical Union 28(6) 936–938. 

Meade, R. H. 1995. Contaminants in the Mississippi River, 1987–92. U.S. Geological 

Survey Circular 1133. Washington, DC: U.S. Geological Survey.

Meyer-Peter, E., and R. Muller. 1948. “Formulas for Bed-Load Transport.” Second 

Meeting of the International Association for Hydraulics Research. Appendix 2. 

Stockholm, Sweden, 39–64. 

Mobile Boundary Hydraulics (MBH). 2002. Sedimentation in Stream Networks (HEC6T). Users Manual, Clinton, MS: Mobile Boundary Hydraulics. 

Nordin, C. F., and B. S. Queen. 1992. Particle Size Distributions of Bed Sediments along 

the Thalweg of the Mississippi River, Cairo, Illinois to Head of Passes, 

September 1989. Potamology Program (P-1) Report 7. Vicksburg, MS: U.S. Army 

Corps of Engineers, Lower Mississippi Valley Division. 

Parthenaides, E. 1965. “Erosion and Deposition of Cohesive Soils.” Journal of the 

Hydraulics Division, ASCE 91(1): 755–771.

Richards, D. R., and M. J. Trawle. 1988. Numerical Model Analysis of Mississippi River 

Passes Navigation Channel Improvements, Report 2, 45-Foot Channel Tests and 

Flow Distribution Schemes. Miscellaneous Paper HL-87-2. Vicksburg, MS: 

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Rouse, H. 1937. “Modern Conceptions of the Mechanics of Fluid Turbulence.” 

Transactions, ASCE 102, Paper no. 1965, 463–505. 

Sharp, J. A., C. D. Little, G. L. Brown, T. C. Pratt, R. E. Heath, L. C. Hubbard, C. F. 

Pinkard, K. Martin, N. D. Clifton, D. W. Perkey, and N. B. Ganesh. 2013. West 

Bay Sediment Diversion Effects. ERDC/CHL TR-13-15. Vicksburg, MS: U.S. 

Army Engineer Research and Development Center. 

Thomas, W. A. 2012. Allocation of Water and Sediment Resources – Myrtle Grove 

Diversion for Land Building. Prepared for Coastal Protection and Restoration 

Authority, Office of Coastal Protection and Restoration, State of Louisiana, by 

Mobile Boundary Hydraulics PLLC. Clinton, MS: Mobile Boundary Hydraulics. 

Thomas, W. A., R. E. Heath, J. P. Stewart, and D. G. Clark. 1989. The Atchafalaya River 

Delta, Report 5, The Atchafalaya River Delta Quasi-Two-Dimensional Model of 

Delta Growth and Impacts on River Stages. Technical Report HL-82-15, Report 

5. Vicksburg, Mississippi: USACE Waterways Experiment Station. 

Toffaleti, F. B. 1968. A Procedure for Computation of the Total River Sand Discharge 

and Detailed Distribution, Bed to Surface. Technical Report No. 5. Vicksburg, 

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Hydrographic Survey 1988-1989, Mouth of White River, Ark. to Black Hawk, 

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Tributaries, Old River Control, LA, Auxiliary Structure, Design Memorandum 

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Hydrographic Survey 1991-1992, Black Hawk, LA to Head of Passes, LA, Mile 0 

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Vicksburg, MS: U.S. Army Waterways Experiment Station. 
MRG&P Report No. 30 213 

Unit Conversion Factors

Multiply By To Obtain 

acres 4,046.873 square meters

acre-feet 1,233.5 cubic meters

cubic feet 0.02831685 cubic meters

cubic inches 1.6387064 E-05 cubic meters

cubic yards 0.7645549 cubic meters

degrees Fahrenheit (F-32)/1.8 degrees Celsius

feet 0.3048 meters

foot-pounds force 1.355818 joules

gallons (U.S. liquid) 3.785412 E-03 cubic meters

hectares 1.0 E+04 square meters

miles (nautical) 1,852 meters

miles (U.S. statute) 1,609.347 meters

miles per hour 0.44704 meters per second

pounds (force) 4.448222 newtons

pounds (force) per foot 14.59390 newtons per meter

pounds (force) per inch 175.1268 newtons per meter

pounds (force) per square foot 47.88026 pascals

pounds (force) per square inch 6.894757 kilopascals

pounds (mass) 0.45359237 kilograms

pounds (mass) per cubic foot 16.01846 kilograms per cubic meter

pounds (mass) per cubic inch 2.757990 E+04 kilograms per cubic meter

pounds (mass) per square foot 4.882428 kilograms per square 

meter

pounds (mass) per square yard 0.542492 kilograms per square 

meter

square miles 2.589998 E+06 square meters

square yards 0.8361274 square meters

tons (force) 8,896.443 newtons

tons (force) per square foot 95.76052 kilopascals

tons (long) per cubic yard 1,328.939 kilograms per cubic meter

tons (2,000 pounds, mass) 907.1847 kilograms
MRG&P Report No. 30 214 

Multiply By To Obtain 

tons (2,000 pounds, mass) per square foot 9,764.856 kilograms per square 

meter

yards 0.9144 meters
MRG&P Report No. 30 215 

Acronyms and Abbreviations

1D one-dimensional

2D two-dimensional

3D three-dimensional

AHP Above Head of Passes

BHP Below Head of Passes

cfs cubic feet per second

EDI equal-discharge increment

ERDC U.S. Army Engineer Research and Development Center

ft foot/feet

in. inch(es)

mm millimeter(s)

MR&T Mississippi River and Tributaries

MSL mean sea level

NGVD National Geodetic Vertical Datum

NOAA National Oceanic and Atmospheric Administration

RM river mile

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey
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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE 

February 2020

2. REPORT TYPE

Final Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Numerical Sedimentation Investigation Mississippi River Cairo to Pilots Station

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Ronald R. Copeland, Leslie Lombard, Roger A. Gaines

5d. PROJECT NUMBER

127672

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) (see reverse) 8. PERFORMING

ORGANIZATION REPORT

NUMBER

MRG&P Report No. 30

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Army Corps of Engineers

Washington, DC 20314-1000

10. SPONSOR/MONITOR'S ACRONYM(S)

USACE

11. SPONSOR/MONITOR'S

REPORT NUMBER(S)

12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

A HEC-6T numerical model of the entire Lower Mississippi River between the end of Southwest Pass and the confluence of the Ohio 

River was developed. The model, which included over 1000 river miles, was calibrated to 1991-2002 measured data. The purpose of the 

numerical sedimentation model was to provide a tool to evaluate the long-term and system –wide effects of specific Mississippi River 

and Tributaries Project features. Model applications related to the effects of sediment diversions and the effects of dredging in the New 

Orleans District were demonstrated. The model demonstrated the effects of new constrictive works on the long-term and short-term river

morphology. The model was used to test the effects of changes in upstream sediment inflow. The model’s ability to assess the effects of 

natural geomorphic changes, such as erosion of hard points, was demonstrated. Future application of this model to specific project sites 

should include the addition of more detailed geometry in the area of interest.

15. SUBJECT TERMS 

Diversion structures (Hydraulic engineering), Dredging, Mississippi River, Sedimentation and deposition—Numerical analysis,

Sediment transport—Numerical analysis

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT

SAR

18. NUMBER 

OF 

PAGES

217

19a. NAME OF RESPONSIBLE PERSON

James. W. Lewis a. REPORT

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified 19b. TELEPHONE NUMBER (Include area code)

601-634-5062

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18 
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) (continued) 

 

U.S. Army Corps of Engineers 

Vicksburg District 

4155 Clay Street 

Vicksburg, Mississippi 39183 

U.S. Army Corps of Engineers 

New Orleans District 

7400 Leake Avenue 

New Orleans, Louisiana 70118 

U.S. Army Corps of Engineers 

Memphis District 

167 N. Main St., Rm B-202

Memphis, Tennessee 38103-1894