Mississippi Valley Division U.S. Army Corps of Engineers, New Orleans District

Southwest Pass Outlets 

Bathymetry and Flow 

Distribution Assessment

MRG&P Report No. 5 • July 2015
Mississippi River Geomorphology & 

Potamology Program 

MRG&P Report No. 5 

July 2015 

Southwest Pass Outlets Bathymetry 

and Flow Distribution Assessment

Data Collection Summary and Analysis

Steven K. Ayres

Hydraulics & Hydrologic Branch

U.S. Army Corps of Engineers, New Orleans District 

7400 Leake Avenue

New Orleans, LA 70118

Final report 

Approved for public release; distribution is unlimited. 
MRG&P Report No. 5 ii

Abstract

The Southwest Pass distributary of the Mississippi River is the primary 

navigable channel connecting the Gulf of Mexico and the Mississippi 

River. The average expenditure of the U. S. Government on Southwest 

Pass and the lower Mississippi River dredging has averaged approximately 

$55 million/year for the previous 5 years. Numerical modeling tools 

covering this important navigational route are being developed to provide 

a better understanding of the impact of proposed Mississippi River system 

changes. Understanding the flow exchange between the Southwest Pass 

distributary and the surrounding Gulf of Mexico under various river and 

tide conditions is essential to the development of these analytic modeling 

tools to be used to predict system response to proposed upriver diversions 

and dredging templates resulting from navigable channel deepening 

proposals. The ongoing development of these numerical modeling tools 

has revealed a data need for bathymetry and velocity information for the 

four major lateral outlets of the Southwest Pass. Multi-beam channel bed 

surveys and Acoustic Doppler Current Profiler data were collected over 

3 days. The collected data will be used to calibrate the flow exchange and 

improve the predictive ability of the multidimensional numerical models 

and the resulting water/sediment ratios at the four lateral outlets.

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. 5 iii

Contents

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

Figures and Tables.................................................................................................................................iv

Preface....................................................................................................................................................vi

Unit Conversion Factors......................................................................................................................viii

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

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

Data collection overview.......................................................................................................... 6

2 Multi-Beam and Single-Beam Surveys......................................................................................... 7

Data collection methodology ................................................................................................... 7

Survey results ........................................................................................................................... 9

3 ADCP Data.....................................................................................................................................17

Data collection methodology ................................................................................................. 17

ADCP flow measurement summaries ...................................................................................18

Southwest Pass flow distribution ..........................................................................................24

Velocity profiles.......................................................................................................................27

4 Summary .......................................................................................................................................32

Report Documentation Page
MRG&P Report No. 5 iv

Figures and Tables

Figures

Figure 1. Regional map.............................................................................................................................. 1

Figure 2. Southwest Pass lateral outlets.................................................................................................. 2

Figure 3. Outlet W-1 entrance detail. ....................................................................................................... 3

Figure 4. Joseph Bayou entrance detail................................................................................................... 4

Figure 5. Outlet W-2 entrance detail. ....................................................................................................... 5

Figure 6. Burrwood Bayou......................................................................................................................... 6

Figure 7. Outlet W-1 survey samples........................................................................................................ 7

Figure 8. Joseph Bayou survey samples.................................................................................................. 7

Figure 9. Outlet W-2 survey samples........................................................................................................ 8

Figure 10. Burrwood Bayou survey samples. .......................................................................................... 8

Figure 11. Outlet W-1 bathymetry............................................................................................................. 9

Figure 12. Outlet W-1 scour hole detail. ................................................................................................10

Figure 13. Joseph Bayou bathymetry.....................................................................................................11

Figure 14. Joseph Bayou scour hole detail............................................................................................12

Figure 15. Outlet W-2 bathymetry...........................................................................................................13

Figure 16. Outlet W-2 scour hole detail..................................................................................................14

Figure 17. Burrwood Bayou bathymetry. ................................................................................................15

Figure 18. Burrwood Bayou scour hole on the Gulf side of the emergency closure 

structure....................................................................................................................................................16

Figure 19. Mississippi River discharge conditions during ADCP data collection period. .................. 17

Figure 20. Tide conditions during ADCP measurement periods. ........................................................18

Figure 21. Tide conditions during 13 May 2014 data collection period.............................................25

Figure 22. Tide conditions during 14 May 2014 data collection period.............................................26

Figure 23. Tide conditions during 15 May 2014 data collection period............................................. 27

Figure 24. Southwest Pass Upstream of Outlet W-1, 13 May 2014 cross-section plot. ................... 27

Figure 25. Southwest Pass Upstream of Outlet W-1, 13 May 2014 velocity profile..........................28

Figure 26. Southwest Pass Upstream of Joseph Bayou, 13 May 2014 cross-section plot...............28

Figure 27. Southwest Pass Upstream of Joseph Bayou, 13 May 2014 velocity profile.....................29

Figure 28. Southwest Pass Downstream of Joseph Bayou, 13 May 2014 cross-section plot...............29

Figure 29. Southwest Pass Downstream of Joseph Bayou, 13 May 2014 velocity profile. ...................30

Figure 30. Southwest Pass Upstream of Burrwood Bayou, 15 May 2014 cross-section plot...............30

Figure 31. Southwest Pass Upstream of Burrwood Bayou, 15 May 2014 velocity profile................ 31

Tables

Table 1. ADCP transect summaries for Outlet W-1. ..............................................................................18
MRG&P Report No. 5 v

Table 2. ADCP transect summaries for Joseph Bayou..........................................................................20

Table 3. ADCP transect summaries for Outlet W-2. ..............................................................................21

Table 4. ADCP transect summaries for Burrwood Bayou.....................................................................23

Table 5. Southwest Pass flow distribution for an ebb tide condition on 13 March 2014................. 24

Table 6. Southwest Pass flow distribution for an ebb tide condition on 14 March 2014. ................25

Table 7. Southwest Pass flow distribution for a high-tide condition on 15 March 2014...................26
MRG&P Report No. 5 vi

Preface

The research documented in this report was conducted as part of the 

Mississippi River Geomorphology and Potamology (MRG&P) Program. 

The MRG&P is part of the Mississippi River and Tributaries Program 

(MR&T) and is managed by the U.S. Army Corps of Engineers (USACE), 

Mississippi Valley Division (MVD), and Districts. The MRG&P Senior 

Program Manager was Freddie Pinkard and the Technical Director was 

Dr. Barbara Kleiss. The MVD Commander was MG Michael C. Wehr. The 

MVD Director of Programs was Edward Belk. 

Mississippi River engineering direction and policy advice were provided by 

the Mississippi River Commission. The Commission members were 

MG Wehr, USACE; the Honorable Sam E. Angel; the Honorable 

R. D. James; the Honorable Norma Jean Mattei, Ph.D.; RDML Gerd F. 

Glang, National Oceanic and Atmospheric Administration; BG Margaret W. 

Burcham, USACE; and BG John S. Kem, USACE.

This report was prepared by Steven K. Ayres, P.E., of USACE-New Orleans 

District. The report was prepared under the general supervision of 

David A. Ramirez, P.E., Chief, River Engineering Section; Julie Z. LeBlanc, 

P.E., Chief, Hydraulics & Hydrologic Branch; and John C. Bivona, P.E., 

Chief, Engineering Division. COL Richard L. Hansen was Commander of 

New Orleans District. Research in support of the MRG&P was conducted 

by the U.S. Army Engineer Research and Development Center (ERDC) 

under the purview of the Coastal and Hydraulics Laboratory (CHL), 

Vicksburg, MS. 

This report would not have been possible without the help of New Orleans 

District (MVN) and United States Geological Survey (USGS) personnel. In 

particular, thanks are extended to Michael French (MVN), Jonathan 

Flowers (MVN), and Garron Ross (USGS). Thanks are also extended to 

Chustz Surveying Inc. Additionally, thanks are extended to Loren 

Wehmeyer (ERDC) and Ty Wamsley (ERDC) for providing reviews and 

suggestions to help improve the final product. 
MRG&P Report No. 5 vii

This report should be cited as follows:

Ayres, S. K. 2015. Southwest Pass outlets bathymetry and flow 

distribution assessment: Data collection summary and analysis.

MRG&P Report No. 5. Vicksburg, MS: U.S. Army Engineer 

Research and Development Center.
MRG&P Report No. 5 viii

Unit Conversion Factors

Multiply By To Obtain 

cubic feet 0.02831685 cubic meters

feet 0.3048 meters

miles (nautical) 1,852 meters

miles (U.S. statute) 1,609.347 meters

square feet 0.09290304 square meters

square miles 2.589998 E+06 square meters

square yards 0.8361274 square meters
MRG&P Report No. 5 1

1 Introduction

Background

The Southwest Pass distributary is the main navigable channel in the 

modern Mississippi River delta connecting the lower Mississippi River 

channel to the Gulf of Mexico (Figure 1). The U.S. Government expends 

approximately $55 million/year on average for dredging efforts in 

Southwest Pass and the area around Head of Passes in the lower 

Mississippi River. The channel is currently maintained to a navigable 

depth of 45 feet (ft). 

Figure 1. Regional map. 

Numerical modeling tools covering this important stretch of the 

navigation route are being developed to study the impact of proposed 

Mississippi River system changes. An understanding of the flow exchange 

between the Southwest Pass distributary and the surrounding Gulf of 

Mexico under various river and tide conditions is essential to the 

development of these analytic modeling tools that will be used to predict 
MRG&P Report No. 5 2

system response to proposed upriver diversions and dredging templates 

resulting from navigable channel deepening proposals. 

Located along the Southwest Pass channel are four lateral outlets 

connecting Southwest Pass to the Gulf of Mexico and to various Bays in 

the Mississippi Delta. Outlets W-1 and W-2 are located on the West side of 

the channel; Joseph and Burrwood Bayous are located on the East side of 

the channel (Figure 2). 

Figure 2. Southwest Pass lateral outlets. 
MRG&P Report No. 5 3

The flow exchange through these outlets and their entrance1 width is 

controlled by rock structures on the Southwest Pass side of the outlets.

Burrwood Bayou has an additional structure that was added in 2004 at the 

Gulf side of the channel as an emergency measure to prevent avulsion of 

the channel and improve navigation safety in Southwest Pass near the 

entrance to Burrwood Bayou. These rock structures are visible in the 2012 

imagery displayed here as Figures 3–6. 

Figure 3. Outlet W-1 entrance detail. 

 

1 Henceforth, the entrance to the outlet is defined as the Southwest Pass end of the outlet.
MRG&P Report No. 5 4

Figure 4. Joseph Bayou entrance detail. 
MRG&P Report No. 5 5

Figure 5. Outlet W-2 entrance detail. 
MRG&P Report No. 5 6

Figure 6. Burrwood Bayou. 

Data collection overview

Multi-beam and single-beam surveys were collected at each of the four 

outlets during June and July 2014. Surveys were concentrated on what 

was thought to be the main flow paths determined from aerial imagery. 

Determination of the predominant flow path is complicated by the 

multiple small channels branching off from the outlet channels as seen in 

the imagery. Single-beam surveys were collected in areas too shallow for 

the multi-beam instrumentation to get a more complete coverage of the 

predominant flow path. 

Acoustic Doppler Current Profiler (ADCP) data was collected over a 3-day 

period from 13–15 May 2014. Cross-section locations were selected 

upstream and downstream of each outlet in Southwest Pass and in the 

outlet channel to give a flow budget of the Southwest Pass flow and outlet 

flow for three different data sets representing various tide conditions.
MRG&P Report No. 5 7

2 Multi-Beam and Single-Beam Surveys

Data collection methodology

All survey data were collected between 30 June and 17 July 2014 by Chustz 

Surveying Inc. Topographic data were collected using a Trimble TSC 3, 

Trimble R8, and a Samsung Galaxy Rugby. The hydrographic data were 

collected using an Odom Hydrotrac Echo Sounder and a Teledyne RESON 

SeaBat 7101 multi-beam system. Figures 7–10 show the location of the 

survey sample points at the four data collection sites.

Figure 7. Outlet W-1 survey samples. 

Figure 8. Joseph Bayou survey 

samples. 
MRG&P Report No. 5 8

Figure 9. Outlet W-2 survey samples. 

Figure 10. Burrwood Bayou survey samples. 

Vertical control for the surveys was established through observation of 

water level as recorded by the three water level gages in the area located at 

Head of Passes (gage ID no. 01545), Southwest Pass at River Mile (RM) 7.5 

Below Head of Passes (BHP) (gage ID no. 01575), and Southwest Pass at 

East Jetty (gage ID no. 01670) referenced to NAVD88 (2009.55). Nails 

were set at each survey site (RM 3.0 BHP, RM 4.5 BHP, RM 9.8 BHP, and 

RM14.3 BHP) and at the three automatic gage sites. Using a Virtual 

Reference System (VRS) tied to GULFNet, the nails were surveyed at RM 

3.0 BHP and RM 4.5 BHP. Poor cell phone coverage prevented collection 

of VRS data at the RM 9.8 BHP and RM 14.3 BHP sites. At these sites, the 

water level was calculated by prorating the water levels at RM 3.0 BHP 

and RM 4.5 BHP. This information was compared to the water level as 
MRG&P Report No. 5 9

recorded by the automatic gages to establish elevation reference at the two 

sites without VRS coverage.

Survey results

All of the outlets displayed scour holes of varying degree in size and depth 

just downstream of their entrances at Southwest Pass. Burrwood Bayou is 

unique in that it has two scour holes, the largest of which is on the Gulf 

side of the emergency closure structure which would indicate that the flow 

through Burrwood Bayou is controlled by the emergency closure structure 

as intended. Figures 11–18 present survey elevation and scour hole detail 

for each of the four outlets.

Figure 11. Outlet W-1 bathymetry. 
MRG&P Report No. 5 10

Figure 12. Outlet W-1 scour hole detail. 
MRG&P Report No. 5 11

Figure 13. Joseph Bayou bathymetry. 
MRG&P Report No. 5 12

Figure 14. Joseph Bayou scour hole detail. 
MRG&P Report No. 5 13

Figure 15. Outlet W-2 bathymetry. 
MRG&P Report No. 5 14

Figure 16. Outlet W-2 scour hole detail. 
MRG&P Report No. 5 15

Figure 17. Burrwood Bayou bathymetry. 
MRG&P Report No. 5 16

Figure 18. Burrwood Bayou scour hole on the Gulf side of the emergency closure structure. 
MRG&P Report No. 5 17

3 ADCP Data

Data collection methodology

ADCP measurements were taken at each site, including measurements in 

the outflow channels, and upstream and downstream of the outflow 

channel in Southwest Pass. Each location included measurements 

conducted under a variety of tide conditions. The measurements were 

conducted on 13–15 May 2014 using two RDI 600 MHz WorkHorse Rio 

Grande Broadband ADCP. The Mississippi River flow conditions for the 

data collection period are shown in Figure 19. Tide conditions at the 

mouth of Southwest Pass are shown in Figure 20.

Figure 19. Mississippi River discharge conditions during ADCP data collection period. 
MRG&P Report No. 5 18

Figure 20. Tide conditions during ADCP measurement periods. 

ADCP flow measurement summaries

The ADCP raw data were postprocessed by the Teledyne WinRiver II 

software. The ADCP data contained samples of stratified flow; therefore, 

the total flow computed by WinRiver II may represent less flow than the 

absolute sum of the positive and negative flow. Summary Tables 1–4

present postprocessing results for each data collection site. The total flux 

column represents the sum of the measured portion of the cross section 

and the estimates for the unmeasured portions. The delta flux column 

represents the deviation of the transects’ computed flux from the average 

of all transects at that location and tide condition.

Table 1. ADCP transect summaries for Outlet W-1. 

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

UULS000

Southwest Pass 

Upstream of 

Outlet W-1 Ebb 5/13/2014 21:51:05 Right 5985 691 857 72 44 7649 -4

UULS001

Southwest Pass 

Upstream of 

Outlet W-1 Ebb 5/13/2014 21:58:24 Left 6568 768 809 80 43 8268 4

UUSS000

Southwest Pass 

Upstream of 

Outlet W-1 Ebb 5/14/2014 18:31:27 Right 4703 533 568 39 21 5865 -6

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

5/12/14 0:00

5/12/14 12:00

5/13/14 0:00

5/13/14 12:00

5/14/14 0:00

5/14/14 12:00

5/15/14 0:00

5/15/14 12:00

5/16/14 0:00

5/16/14 12:00

5/17/14 0:00

Water Level (meters MSL)

Greenwich Mean Time

Observed Water Levels at 8760922 Pilots Station East, SW Pass, LA

during the data collection period 

13 May 2014 data

collection period

14 May 2014 data

collection period

15 May 2014 data

collection period
MRG&P Report No. 5 19

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

UUSS001

Southwest Pass 

Upstream of 

Outlet W-1 Ebb 5/14/2014 18:39:14 Left 5258 598 643 40 16 6556 6

UUHS000

Southwest Pass 

Upstream of 

Outlet W-1 High 5/15/2014 16:42:08 Right 4148 479 547 69 -4 5239 -7

UUHS001

Southwest Pass 

Upstream of 

Outlet W-1 High 5/15/2014 16:49:44 Left 4682 574 670 54 18 5998 7

UILS000 Outlet W-1 Ebb 5/13/2014 21:19:45 Right 335 40 107 -5 0 478 -1

UILS001 Outlet W-1 Ebb 5/13/2014 21:25:00 Left 394 57 142 39 -4 627 30

UILS003 Outlet W-1 Ebb 5/13/2014 21:28:56 Right 295 45 77 12 -7 423 -12

UILS004 Outlet W-1 Ebb 5/13/2014 21:32:17 Left 335 65 113 14 6 533 10

UILS005 Outlet W-1 Ebb 5/13/2014 21:37:05 Right 214 21 78 -19 -33 261 -46

UILS006 Outlet W-1 Ebb 5/13/2014 21:41:57 Left 406 42 129 1 -3 574 19

UISS000 Outlet W-1 Ebb 5/14/2014 18:04:19 Right 203 37 63 -15 -16 273 -36

UISS001 Outlet W-1 Ebb 5/14/2014 18:07:51 Left 279 65 82 46 -6 466 8

UISS002 Outlet W-1 Ebb 5/14/2014 18:10:57 Right 206 46 62 28 -7 335 -22

UISS003 Outlet W-1 Ebb 5/14/2014 18:13:27 Left 420 53 160 22 -10 646 50

UISS004 Outlet W-1 Ebb 5/14/2014 18:20:08 Right 225 63 83 58 -1 428 0

UISS005 Outlet W-1 Ebb 5/14/2014 18:22:40 Left 246 65 84 32 1 429 0

UIHS000 Outlet W-1 High 5/15/2014 16:20:51 Right 259 60 80 75 -4 470 -6

UIHS001 Outlet W-1 High 5/15/2014 16:22:49 Left 255 61 78 64 -6 453 -9

UIHS002 Outlet W-1 High 5/15/2014 16:25:02 Right 264 76 96 73 43 553 11

UIHS003 Outlet W-1 High 5/15/2014 16:27:17 Left 288 79 87 21 -5 469 -6

UIHS004 Outlet W-1 High 5/15/2014 16:30:16 Right 269 87 94 89 18 558 12

UIHS005 Outlet W-1 High 5/15/2014 16:32:50 Left 268 66 84 69 -4 484 -3

UDLC000

Southwest Pass 

Downstream of 

Outlet W-1 Ebb 5/13/2014 21:12:19 Right 5888 702 723 36 37 7386 2

UDLC001

Southwest Pass 

Downstream of 

Outlet W-1 Ebb 5/13/2014 21:19:57 Left 5649 674 693 43 35 7094 -2

UDSC000

Southwest Pass 

Downstream of 

Outlet W-1 Ebb 5/14/2014 18:19:14 Right 4593 543 537 28 21 5722 2

UDSC001

Southwest Pass 

Downstream of 

Outlet W-1 Ebb 5/14/2014 18:25:22 Left 4393 519 513 25 19 5470 -2
MRG&P Report No. 5 20

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

UDHC000

Southwest Pass 

Downstream of 

Outlet W-1 High 5/15/2014 16:22:16 Right 4224 581 509 38 22 5374 6

UDHC001

Southwest Pass 

Downstream of 

Outlet W-1 High 5/15/2014 16:28:22 Left 3772 510 443 36 27 4788 -6

Table 2. ADCP transect summaries for Joseph Bayou. 

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

JULS001

Southwest Pass 

Upstream of 

Joseph Bayou Ebb 5/13/2014 20:49:56 Left 6313 761 788 37 49 7947 6

JULS002

Southwest Pass 

Upstream of 

Joseph Bayou Ebb 5/13/2014 20:56:09 Right 5564 657 691 41 38 6991 -6

JUSS000

Southwest Pass 

Upstream of 

Joseph Bayou Ebb 5/14/2014 17:39:45 Left 4464 517 583 26 92 5682 8

JUSS001

Southwest Pass 

Upstream of 

Joseph Bayou Ebb 5/14/2014 17:49:22 Right 3822 436 483 37 66 4843 -8

JUHS000

Southwest Pass 

Upstream of 

Joseph Bayou High 5/15/2014 15:58:26 Left 4379 521 541 19 62 5522 7

JUHS001

Southwest Pass 

Upstream of 

Joseph Bayou High 5/15/2014 16:05:57 Right 3797 453 496 18 77 4841 -7

JILC000 Joseph Bayou Ebb 5/13/2014 20:41:26 Right 321 77 75 111 187 772 5

JILC001 Joseph Bayou Ebb 5/13/2014 20:43:16 Left 377 88 77 101 125 769 4

JILC002 Joseph Bayou Ebb 5/13/2014 20:46:06 Right 355 82 73 10 133 653 -12

JILC003 Joseph Bayou Ebb 5/13/2014 20:48:14 Left 306 74 63 79 175 697 -5

JILC004 Joseph Bayou Ebb 5/13/2014 20:51:46 Right 324 77 72 72 196 741 0

JILC005 Joseph Bayou Ebb 5/13/2014 20:54:03 Left 306 77 68 103 241 795 8

JISC000 Joseph Bayou Ebb 5/14/2014 17:50:07 Right 368 86 83 101 78 716 1

JISC001 Joseph Bayou Ebb 5/14/2014 17:52:59 Left 342 77 72 90 120 700 -1

JISC002 Joseph Bayou Ebb 5/14/2014 17:55:12 Right 436 93 92 95 115 831 17

JISC003 Joseph Bayou Ebb 5/14/2014 17:57:44 Left 274 68 59 88 80 568 -20

JISC004 Joseph Bayou Ebb 5/14/2014 18:00:07 Right 421 93 93 76 112 796 12

JISC005 Joseph Bayou Ebb 5/14/2014 18:02:28 Left 327 75 72 79 88 641 -10

JIHC000 Joseph Bayou High 5/15/2014 15:30:57 Right 430 89 88 147 129 882 -1
MRG&P Report No. 5 21

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

JIHC001 Joseph Bayou High 5/15/2014 15:32:48 Left 403 87 80 120 210 900 1

JIHC002 Joseph Bayou High 5/15/2014 15:34:22 Right 357 79 76 107 192 811 -9

JIHC003 Joseph Bayou High 5/15/2014 15:36:20 Left 379 81 76 141 219 896 0

JIHC004 Joseph Bayou High 5/15/2014 15:38:45 Right 452 99 100 115 181 947 6

JIHC005 Joseph Bayou High 5/15/2014 15:41:03 Left 410 84 76 108 249 926 4

JDLC000

Southwest Pass 

Downstream of 

Joseph Bayou Ebb 5/13/2014 20:16:54 Left 4927 567 579 43 2 6118 -3

JDLC001

Southwest Pass 

Downstream of 

Joseph Bayou Ebb 5/13/2014 20:23:28 Right 5257 593 618 51 2 6521 3

JDSC000

Southwest Pass 

Downstream of 

Joseph Bayou Ebb 5/14/2014 17:33:07 Left 3453 391 412 36 10 4302 -5

JDSC001

Southwest Pass 

Downstream of 

Joseph Bayou Ebb 5/14/2014 17:38:40 Right 3816 437 472 37 8 4770 5

JDHC000

Southwest Pass 

Downstream of 

Joseph Bayou High 5/15/2014 15:11:44 Left 3061 395 362 26 -2 3841 -4

JDHC001

Southwest Pass 

Downstream of 

Joseph Bayou High 5/15/2014 15:18:35 Right 3308 428 401 32 -4 4164 4

Table 3. ADCP transect summaries for Outlet W-2. 

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

WULS000

Southwest Pass 

Upstream of 

Outlet W-2 Ebb 5/13/2014 20:10:28 Right 4903 681 282 27 12 5906 -6

WULS001

Southwest Pass 

Upstream of 

Outlet W-2 Ebb 5/13/2014 20:16:27 Left 5448 749 453 32 34 6717 6

WUSS000

Southwest Pass 

Upstream of 

Outlet W-2 Ebb 5/14/2014 17:08:38 Right 3288 421 419 17 8 4153 -10

WUSS001

Southwest Pass 

Upstream of 

Outlet W-2 Ebb 5/14/2014 17:15:09 Left 3986 509 503 21 20 5038 10

WUHS001

Southwest Pass 

Upstream of 

Outlet W-2 High 5/15/2014 15:29:48 Left 3711 479 471 35 52 4748 6
MRG&P Report No. 5 22

Transect 

ID 

Location of 

Transect Tide Date 

Start Time 

(GMT) 

Start 

Bank 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

WUHS002

Southwest Pass 

Upstream of 

Outlet W-2 High 5/15/2014 15:36:49 Right 3200 438 420 16 135 4210 -6

WILS000 Outlet W-2 Ebb 5/13/2014 19:36:50 Left 361 251 144 49 84 889 1

WILS002 Outlet W-2 Ebb 5/13/2014 19:48:02 Right 388 225 96 71 57 837 -5

WILS003 Outlet W-2 Ebb 5/13/2014 19:51:12 Left 421 261 119 52 97 950 8

WILS004 Outlet W-2 Ebb 5/13/2014 19:54:48 Right 367 236 98 70 80 851 -3

WISS000 Outlet W-2 Ebb 5/14/2014 16:44:39 Right 366 199 137 39 73 814 -6

WISS001 Outlet W-2 Ebb 5/14/2014 16:49:14 Left 378 207 144 35 124 889 2

WISS002 Outlet W-2 Ebb 5/14/2014 16:53:52 Right 353 194 128 42 141 858 -1

WISS003 Outlet W-2 Ebb 5/14/2014 16:57:03 Left 447 228 148 29 66 918 6

WIHS000 Outlet W-2 High 5/15/2014 14:25:47 Right 375 169 105 8 129 787 -1

WIHS001 Outlet W-2 High 5/15/2014 14:31:28 Left 394 213 139 9 70 825 4

WIHS002 Outlet W-2 High 5/15/2014 14:35:55 Right 363 190 118 18 65 754 -5

WIHS003 Outlet W-2 High 5/15/2014 14:38:45 Left 389 187 123 18 88 805 2

WDLC000

Southwest Pass 

Downstream of 

Outlet W-2 Ebb 5/13/2014 19:43:52 Right 4349 586 611 13 16 5575 2

WDLC001

Southwest Pass 

Downstream of 

Outlet W-2 Ebb 5/13/2014 19:51:17 Left 4236 564 549 8 14 5371 -2

WDSC000

Southwest Pass 

Downstream of 

Outlet W-2 Ebb 5/14/2014 17:05:00 Right 2961 387 389 -3 18 3751 6

WDSC001

Southwest Pass 

Downstream of 

Outlet W-2 Ebb 5/14/2014 17:11:11 Left 2630 343 337 -2 16 3323 -6

WDHC000

Southwest Pass 

Downstream of 

Outlet W-2 High 5/15/2014 14:27:48 Right 2939 386 392 24 34 3776 8

WDHC001

Southwest Pass 

Downstream of 

Outlet W-2 High 5/15/2014 14:33:04 Left 2538 328 313 25 0 3204 -8
MRG&P Report No. 5 23

Table 4. ADCP transect summaries for Burrwood Bayou. 

Transect 

ID Location of Transect Tide Date 

Start 

Time 

(GMT) 

Start 

Bank 

 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

BULS000

Southwest Pass 

Upstream of 

Burrwood Bayou Ebb 5/13/2014 18:50:49 Left 4021 801 191 65 -9 5070 7

BULS001

Southwest Pass 

Upstream of 

Burrwood Bayou Ebb 5/13/2014 18:57:48 Right 3478 738 87 82 4 4389 -7

BUSS000

Southwest Pass 

Upstream of 

Burrwood Bayou Ebb 5/14/2014 16:00:51 Left 2442 379 356 73 -5 3244 11

BUSS002

Southwest Pass 

Upstream of 

Burrwood Bayou Ebb 5/14/2014 16:09:08 Right 1822 317 302 102 37 2579 -11

BUHS000

Southwest Pass 

Upstream of 

Burrwood Bayou High 5/15/2014 13:35:22 Left 2797 438 452 72 90 3849 11

BUHS002

Southwest Pass 

Upstream of 

Burrwood Bayou High 5/15/2014 14:02:41 Right 2302 361 343 72 38 3116 -11

BILC000 Burrwood Bayou Ebb 5/13/2014 19:12:33 Right 163 67 47 66 44 387 9

BILC001 Burrwood Bayou Ebb 5/13/2014 19:16:36 Left 115 50 34 28 37 263 -26

BILC002 Burrwood Bayou Ebb 5/13/2014 19:22:13 Right 209 116 69 27 10 431 21

BILC003 Burrwood Bayou Ebb 5/13/2014 19:25:30 Left 168 92 54 19 10 343 -4

BISC000 Burrwood Bayou Ebb 5/14/2014 16:36:07 Right 228 110 72 6 7 422 11

BISC001 Burrwood Bayou Ebb 5/14/2014 16:40:49 Left 173 76 49 15 8 322 -15

BISC002 Burrwood Bayou Ebb 5/14/2014 16:43:33 Right 224 103 67 23 9 426 12

BISC003 Burrwood Bayou Ebb 5/14/2014 16:47:20 Left 188 84 56 14 6 349 -8

BIHC000 Burrwood Bayou High 5/15/2014 13:42:46 Right 264 144 85 49 14 555 10

BIHC001 Burrwood Bayou High 5/15/2014 13:46:00 Left 217 115 67 36 13 447 -11

BIHC002 Burrwood Bayou High 5/15/2014 13:47:51 Right 264 142 83 49 14 553 9

BIHC003 Burrwood Bayou High 5/15/2014 13:50:56 Left 216 116 69 48 15 464 -8

BDLC000

Southwest Pass 

Downstream of 

Burrwood Bayou Ebb 5/13/2014 18:45:15 Left 3085 502 456 42 30 4114 -8

BDLC001

Southwest Pass 

Downstream of 

Burrwood Bayou Ebb 5/13/2014 18:53:48 Right 3597 583 560 19 28 4787 8

BDSC001

Southwest Pass 

Downstream of 

Burrwood Bayou Ebb 5/14/2014 16:08:17 Left 1744 310 257 28 7 2345 -10
MRG&P Report No. 5 24

Transect 

ID Location of Transect Tide Date 

Start 

Time 

(GMT) 

Start 

Bank 

 

Flux (m3 s-1) 

Meas. Top Bottom Left Right Total Delta 

BDSC002

Southwest Pass 

Downstream of 

Burrwood Bayou Ebb 5/14/2014 16:22:18 Right 2141 362 325 22 7 2857 10

BDHC000

Southwest Pass 

Downstream of 

Burrwood Bayou High 5/15/2014 13:23:52 Left 1799 350 286 23 17 2475 -15

BDHC001

Southwest Pass 

Downstream of 

Burrwood Bayou High 5/15/2014 13:30:42 Right 2451 470 402 30 26 3379 15

Southwest Pass flow distribution

The measured flow distribution in Southwest Pass is summarized in 

Tables 5–7 along with the corresponding tide condition shown in 

Figures 21–23. It was found that the four outlets carry approximately 48% 

of the total Southwest Pass flow for a high-tide condition and 5,619 m3s-1

total discharge. During ebb tide conditions, the outlets carried 31% and 38% 

of the total Southwest Pass discharges of 7,958 m3s-1 and 6,210 m3s-1,

respectively. 

Table 5. Southwest Pass flow distribution for an ebb tide condition on 13 March 2014. 

The ADCP measurements summarized in this table 

were conducted on 13 March 2014 between 1845 

and 2200 GMT. 

Average 

Transect 

Flow 

m3 s-1 

Portion of Total 

Southwest Pass 

Flow 

% 

Portion of Southwest 

Pass Flow at the 

Outlet 

% 

Southwest Pass Upstream of Outlet W-1 7958 100.0

Outlet W-1 483 6.1 6.1

Southwest Pass Downstream of Outlet W-1 7240 91.0

Southwest Pass Upstream of Joseph Bayou 7469 93.8

Joseph Bayou 738 9.3 9.9

Southwest Pass Downstream of Joseph Bayou 6319 79.4

Southwest Pass Upstream of Outlet W-2 6311 79.3

Outlet W-2 882 11.1 14.0

Southwest Pass Downstream of Outlet W-2 5473 68.8

Southwest Pass Upstream of Burrwood Bayou 4729 59.4

Burrwood Bayou 356 4.5 7.5

Southwest Pass Downstream of Burrwood Bayou 4450 55.9

Four Outlets total percentage for this tide 

condition

30.9
MRG&P Report No. 5 25

Figure 21. Tide conditions during 13 May 2014 data collection period. 

Table 6. Southwest Pass flow distribution for an ebb tide condition on 14 March 2014. 

The ADCP measurements summarized in this table 

were conducted on 14 March 2014 between 1600 

and 1845 GMT. 

Average 

Transect 

Flow 

m3 s-1 

Portion of Total 

Southwest Pass 

Flow 

% 

Portion of Southwest 

Pass Flow at the 

Outlet 

% 

Southwest Pass Upstream of Outlet W-1 6210 100.0

Outlet W-1 429 6.9 6.9

Southwest Pass Downstream of Outlet W-1 5596 90.1

Southwest Pass Upstream of Joseph Bayou 5263 84.7

Joseph Bayou 709 11.4 13.5

Southwest Pass Downstream of Joseph Bayou 4536 73.0

Southwest Pass Upstream of Outlet W-2 4596 74.0

Outlet W-2 870 14.0 18.9

Southwest Pass Downstream of Outlet W-2 3537 57.0

Southwest Pass Upstream of Burrwood Bayou 2912 46.9

Burrwood Bayou 380 6.1 13.0

Southwest Pass Downstream of Burrwood Bayou 2601 41.9

Four Outlets total percentage for this tide 

condition

38.4
MRG&P Report No. 5 26

Figure 22. Tide conditions during 14 May 2014 data collection period. 

Table 7. Southwest Pass flow distribution for a high-tide condition on 15 March 2014. 

The ADCP measurements summarized in this table 

were conducted on 15 March 2014 between 1320 

and 1700 GMT. 

Average 

Transect 

Flow 

m3 s-1 

Portion of Total 

Southwest Pass 

Flow 

% 

Portion of Southwest 

Pass Flow at the 

Outlet 

% 

Southwest Pass Upstream of Outlet W-1 5619 100.0

Outlet W-1 498 8.9 8.9

Southwest Pass Downstream of Outlet W-1 5081 90.4

Southwest Pass Upstream of Joseph Bayou 5181 92.2

Joseph Bayou 894 15.9 17.2

Southwest Pass Downstream of Joseph Bayou 4003 71.2

Southwest Pass Upstream of Outlet W-2 4479 79.7

Outlet W-2 793 14.1 17.7

Southwest Pass Downstream of Outlet W-2 3490 62.1

Southwest Pass Upstream of Burrwood Bayou 3482 62.0

Burrwood Bayou 505 9.0 14.5

Southwest Pass Downstream of Burrwood Bayou 2927 52.1

Four Outlets total percentage for this tide 

condition

47.9
MRG&P Report No. 5 27

Figure 23. Tide conditions during 15 May 2014 data collection period. 

Velocity profiles

Using the WinRiver II postprocessing software, velocity profiles were 

extracted from the raw data, and a few examples are shown here. It is 

evident from the velocity data that a saltwater wedge was present in 

Southwest Pass at the time the ADCP data was collected. The most 

upstream, cross-section velocity plot of data collected in Southwest Pass 

on 13 May displays a uniform velocity profile (Figures 24 and 25). 

However, on the same day, the most upstream advance of the wedge is 

evident in the plots around the Joseph Bayou outlet (Figures 26–29). A 

fully stratified flow situation is evident in the data taken upstream of the 

Burrwood Bayou outlet on 15 May as seen in Figures 30 and 31. 

Figure 24. Southwest Pass Upstream of Outlet W-1, 13 May 2014 cross-section plot. 
MRG&P Report No. 5 28

Figure 25. Southwest Pass Upstream of Outlet W-1, 13 May 2014 velocity profile. 

Figure 26. Southwest Pass Upstream of Joseph Bayou, 13 May 2014 cross-section plot. 
MRG&P Report No. 5 29

Figure 27. Southwest Pass Upstream of Joseph Bayou, 13 May 2014 velocity profile. 

Figure 28. Southwest Pass Downstream of Joseph Bayou, 13 May 2014 cross-section plot. 
MRG&P Report No. 5 30

Figure 29. Southwest Pass Downstream of Joseph Bayou, 13 May 2014 velocity profile. 

Figure 30. Southwest Pass Upstream of Burrwood Bayou, 15 May 2014 cross-section plot. 
MRG&P Report No. 5 31

Figure 31. Southwest Pass Upstream of Burrwood Bayou, 15 May 2014 velocity profile. 
MRG&P Report No. 5 32

4 Summary

The data collected for this study show that given certain tide conditions 

and Mississippi River discharge, the four lateral outlets along Southwest 

Pass are capable of diverting almost half of the flow entering Southwest 

Pass from the lower Mississippi River channel as seen in the ADCP data 

set collected on 15 March 2014. Therefore, the impact of these lateral 

outlets on Southwest Pass flow and sedimentation dynamics must be 

considered in any model study that includes Southwest Pass in its domain. 

The loss of stream power along the channel due to the diversion of water 

through the outlets is likely a primary driver of resulting shoaling patterns 

in Southwest Pass. The flow stratification evident in the velocity profiles 

indicates that flocculation due to salinity would also contribute to the 

sedimentation characteristics observed in Southwest Pass. 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data 

sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other 

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provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE

July 2015

2. REPORT TYPE

MRG&P Report

3. DATES COVERED (From - To)

1927-2014

4. TITLE AND SUBTITLE

Southwest Pass Outlets Bathymetry and Flow Distribution Assessment

5a. CONTRACT NUMBER

N/A

5b. GRANT NUMBER

N/A

5c. PROGRAM ELEMENT NUMBER

N/A

6. AUTHOR(S)

Steven K. Ayres

5d. PROJECT NUMBER

N/A

5e. TASK NUMBER

N/A

5f. WORK UNIT NUMBER

N/A

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Hydraulics & Hydrologic Branch

U.S. Army Corps of Engineers, New Orleans District 

7400 Leake Avenue

New Orleans, LA 70118

8. PERFORMING ORGANIZATION 

REPORT NUMBER

MRG&P Report No. 5

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

US Army Corps of Engineers, Mississippi Valley Division

10. SPONSOR/MONITOR'S ACRONYM(S)

MVD

11. SPONSOR/MONITOR'S REPORT 

NUMBER(S)

1 12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

Report series: MRG&P (Mississippi River Geomorphology & Potamology)

14. ABSTRACT

The Southwest Pass distributary of the Mississippi River is the primary navigable channel connecting the Gulf of Mexico and the 

Mississippi River. The average expenditure of the U.S. Government on Southwest Pass and the lower Mississippi River dredging has 

averaged around $55 million/year for the previous 5 years. Numerical modeling tools covering this important stretch of the navigation 

route are being developed to help gain a better understanding of the impact of proposed Mississippi River system changes. An 

understanding of the flow exchange between Southwest Pass distributary and the surrounding Gulf of Mexico under various river and tide 

conditions is essential to the development of these analytic modeling tools that will be used to predict system response to proposed 

upriver diversions and dredging templates resulting from navigable channel deepening proposals. The ongoing development of these 

numerical modeling tools have revealed a data need for bathymetry and velocity information for the four major lateral outlets of the 

Southwest Pass. Multi-beam channel bed surveys and Acoustic Doppler Current Profiler data was collected over a 3-day period. The 

collected data will be used to calibrate the flow exchange and improve the predictive ability of the multi-dimensional numerical models 

and the resulting water/sediment ratios at the four lateral outlets.

15. SUBJECT TERMS 

Potamology

Mississippi River

River science

River engineering

River morphology

Geomorphology

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT

None

18. NUMBER OF 

PAGES

41

19a. NAME OF RESPONSIBLE PERSON

Jim Lewis

a. REPORT

Unclassified

b. ABSTRACT

Unclassified

c. THIS

PAGE

Unclassified 19b. TELEPHONE NUMBER (Include area code)

601-634-3895