Water Quality in Lake Pontchartrain and western Mississippi Sound during openings of Bonnet Carré Spillway

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The Bonnet Carré Spillway, located about 28 miles northwest of New Orleans, Louisiana, was constructed in the early 1930s as part of an integrated flood-control structure for the lower Mississippi River Plain. The spillway is designed to divert water from the Mississippi River into Lake Pontchartrain, thus relieving pressure on levees downstream. Opening of the spillway occurs when measured streamflow in the Mississippi River at New Orleans exceeds 1.25 million cubic feet per second, which normally occurs late in the spring season.  Over the approximately 90 years since its construction, the spillway has been opened only twelve times; however, in 2019, it was opened twice. Monitoring the quality of surface waters receiving diverted Mississippi River water including Lake(s) Pontchartrain and Borgne and the Mississippi Sound is of vital importance to public- and natural resource managers in Louisiana and Mississippi. These bodies of water provide crucial habitat for fish, crabs and other shellfish, seagrasses, and marine mammals, such as dolphins and manatees.  Coastal waters are also used for recreation and commercial fishing.

The U.S. Geological Survey (USGS), Lower Mississippi-Gulf Water Science Center (LMG), in cooperation with the U.S. Army Corp of Engineers (USACE) New Orleans District, has sampled water from Lake Pontchartrain, Lake Borgne, and the western Mississippi Sound prior, during, and after each spillway opening from 2008 to present. In 2020, discrete water-quality samples are being collected at all stations in Lake(s) Pontchartrain and Borgne and the western Mississippi Sound (map thumbnail) except at Rigolets at Hwy 90 near Slidell, LA (RIG) and East Pearl River at CSX Railroad near Claiborne, MS (EPR). Samples are analyzed for major ions, nutrients, inorganic plus organic particulate carbon, total suspended solids, chlorophyll a, phytoplankton composition, and algal toxins. Euphotic depths are determined from Secchi depth readings and then used to guide the sample collection depths for chlorophyll, phytoplankton, and algal toxins. Currently, the USGS-LMG also measures continuous water quality (stage, salinity, and temperature) at five stations in the western Mississippi Sound (Table 1).

A multi-parameter data sonde is used at each of the sites at the time of sample collection to measure water temperature, specific conductance, salinity, dissolved oxygen, and pH typically at 0.5 meters above the bottom depth, mid-depth, and 0.5 meters below the water surface to document any salinity or dissolved-oxygen stratifications within the water column. These field data are useful in monitoring changes in salinity and stratification that influence biological processes in the lake and sound waters.

 

US Army Corps of Engineers

 

 

 

USACE Spillway Operation Information 

 

 

BonnetCarre2020_StillMap_20200521

Table 1 - U.S. Geological Survey routine and synoptic water-quality sampling stations in

Lakes Pontchartrain/Borgne and the western Mississippi Sound.

[click on station type for a link to the data from the USGS National Water Information System web interface (waterdata.usgs.gov); 2020 field parameters are shown in Tables 2.1-2.3] 

USGS Station ID USGS Station Name Latitude Longitude Station Abbreviation Station Type Field Parameters Laboratory Water Quality
300115090245000 Bonnet Carré Spillway at US Hwy 61 near Norco, LA 30.02083 -90.413889 BC Discrete X X
301853090060700 Lake Pontchartrain at Causeway Bridge near Mandeville 30.31472 -90.101944 C1 Discrete X X
301528090064600 Lake Pontchartrain at Causeway Bridge near Mandeville, LA 30.25778 -90.112778 C2 Discrete X X
301200090072400 Lake Pontchartrain at Crossover 4 near Mandeville, LA 30.19964 -90.12275 C4 Discrete X  
300412090084300 Lake Pontchartrain at Causeway Bridge near Metairie 30.07 -90.145278 C7 Discrete X X
301050089511600 Lake Pontchartrain at Hwy 11 Causeway near Slidell 30.18056 -89.854444 H11 Discrete X X
300218089374500 Lake Borgne 5.5 miles east of   Alligator Point, LA 30.03833 -89.629167 LB Discrete X X
300454089284200 Western Mississippi Sound near Le Petit Pass Island, LA  30.08166 -89.47839 PP Discrete X  
300233089224200 Western Mississippi Sound near Three Mile Bay, LA 30.04236 -89.37823 TM Discrete X  
301001089442600 Rigolets at Hwy 90 near Slidell, LA 30.16694 -89.74056 RIG Continuous    
301141089320300 E. Pearl River at CSX RR near Claiborne, MS 30.19472 -89.53417 EPR Continuous    
301104089253400 Mississippi Sound at St. Joseph Island Light, MS 30.19083 -89.42222 SJ Continuous X X
301429089145600 Mississippi Sound at Merrill Shell Bank Light, MS 30.23806 -89.242778 MB Continuous X X
300722089150100 Mississippi Sound near Grand Pass, LA 30.12278 -89.2502778 GP Continuous X X
301746089143500 MB2, 1 mile south of Pass Christian, MS 30.29608 -89.24317 MB2 Discrete X  
301636089144400 MB1, 2.5 miles north of Merrill Bank, MS 30.27665 -89.24555 MB1 Discrete X  
301252089150400 GP2, 6 miles north of Grand Pass, LA 30.21452 -89.25105 GP2 Discrete X  
301047089150200 GP1, 3 miles north of Grand Pass, LA 30.1796 -89.25063 GP1 Discrete X  

 

 

Table 2.1 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of April 6–10, 2020, spillway week 1*

Station Abbreviation Date Time (CST) Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
BC 4/9/2020 1131 0.27 16.6 315 0.1 7.7 9.2 0.4
    1132 1.19 16.6 315 0.1 7.7 9.2 -
    1133 2.68 16.6 315 0.1 7.7 9.2 -
C1 4/8/2020 1001 0.27 23.9 676 0.3 7.8 8.7 0.55
    1002 2.26 23.6 688 0.3 7.6 8.3 -
    1003 4.60 23.6 728 0.3 7.6 8.2 -
C2 4/8/2020 1101 0.21 23.9 774 0.3 7.7 8.7 0.5
    1102 2.47 23.4 791 0.3 7.4 7.4 -
    1103 4.85 23.5 802 0.3 7.3 7.3 -
C4 4/8/2020 1130 0.06 24.2 898 0.4 7.9 8.9 0.7
    1131 2.62 24.2 976 0.4 7.4 8.2 -
    1132 5.09 23.3 880 0.4 7.3 8.1 -
C7 4/8/2020 1201 0.24 23.5 1,170 0.6 7.7 8.4 1.05
    1202 2.32 23.4 1,170 0.6 7.6 8.2 -
    1203 4.42 23.4 1,180 0.6 7.5   -
H11 4/9/2020 1131 0.27 24.8 1,130 0.6 7.8 8.1 0.4
    1132 1.95 24.8 1,130 0.6 7.8 8.1 -
    1133 3.99 24.8 1,130 0.6 7.6 8.1 -

 

 

Table 2.2 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of April 20–24, 2020, spillway week 3*

Station Abbreviation Date Time (CST) Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
BC 4/16/2020 1000 0.46 16.9 320 0 7.7 8.6 0.7
SJ 4/20/2020 1201 0.09 22.9 2,380 1.2 7.4 8.2 0.25
    1202 1.46 22.7 2,440 1.2 7.3 8.1 -
    1203 0.99 22.4 2,840 1.5 7.3 8 -
MB2 4/20/2020 0945 0.46 22 12,100 6.9 7.8 8.7 0.8
    0946 1.34 21.8 15,700 9.2 7.7 8.2 -
    0947 2.83 20.9 26,000 16 7.3 5.1 -
MB1 4/20/2020 0930 0.27 22.2 10,500 6 8 9.2 0.65
    0932 1.74 21.9 11,900 6.8 7.7 7.8 -
    0932 3.54 21.1 23,400 14 7.4 5.7 -
MB 4/20/2020 1131 0.34 21.9 8,290 4.6 7.7 8.3 0.7
    1132 2.23 21.8 8,270 4.6 7.7 8.1 -
    1133 4.51 21 24,300 15 7.3 6.5 -
GP2 4/20/2020 1015 0.21 22 7,970 4 8 8.9 0.7
    1016 1.74 21.9 7,990 4 7.9 8.4 -
    1017 3.51 20.9 24,900 15 7.4 5.9 -
GP1 4/20/2020 1000 0.40 21.9 7,080 4 7.9 8.6 0.7
    1001 2.04 21.7 7,160 4 8 8.2 -
    1002 3.99 21 34,800 22 7.7 6.4 -
GP 4/20/2020 1031 0.37 22.3 10,900 8.8 7.8 8.8 0.6
    1032 1.10 22.2 10,900 8.6 7.9 8.6 -
    1033 2.83 21.9 11,300 8.2 7.8 8.2 -
LB 4/21/2020 1031 0.21 23.1 1,370 0.7 8.3 9.5 0.25
    1032 1.98 22.2 1,360 0.7 7.8 8.5 -
    1033 3.41 22.2 1,370 0.7 7.9 8.4 -
PP 4/20/2020 1400 0.15 23 2,070 1 7.8 8.9 0.2
    1401 1.71 22.3 2,070 1 7.7 8.6 -
    1402 3.44 22.1 2,070 1 7.7 8.6 -
TM 4/20/2020 1250 0.09 23.4 2,850 1.9 8 9.1 0.2
    1251 0.85 23.1 2,880 2 7.9 8.9 -
    1252 1.80 22.5 3,230 2 7.8 8.6 -

 

Table 2.3 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of April 27 – May 1, 2020, spillway week 4*

Station Abbreviation Date Time (CST) Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
C1 4/28/2020 1001 0.30 22.6 857 0.4 7.5 12.2 0.6
    1002 2.47 22.7 859 0.4 7.4 8.3 -
    1003 4.75 22.7 859 0.4 7.3 8.2 -
C2 4/28/2020 1101 0.30 22.3 860 0.4 7.5 8.5 0.55
    1102 2.77 22.4 853 0.4 7.4 8.4 -
    1103 4.85 22.4 853 0.4 7.3 8 -
C4 4/28/2020 N/A - - - - - - -
C7 4/28/2020 1201 0.58 21.7 343 0.2 7.9 9 0.75
    1202 2.68 21.6 343 0.2 7.9 8.9 -
    1203 4.91 21.6 343 0.2 7.8 8.8 -
H11 4/29/2020 1131 0.46 22.4 437 0.2 8 8.5 0.25
    1132 1.98 22.4 437 0.2 7.9 8.5 -
    1133 3.93 21.4 437 0.2 7.9 8.5 -

 

Table 2.4 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of May 25–29, 2020, week 4 after spillway was closed

Station Abbreviation Date Time Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
C1 5/26/2020 1001 0.64 27 944 0.5 7.5 7.4 0.7
    1002 2.96 26.9 943 0.5 7.5 7.4 -
    1003 4.88 26.9 943 0.5 7.5 7.4 -
C2 5/26/2020 1101 0.21 26.8 686 0.3 7.5 7.7 0.7
    1102 2.47 26.7 683 0.3 7.4 7.5 -
    1103 5.03 26.6 711 0.3 7.3 7.4 -
C4 5/26/2020 1131 0.37 26.9 814 0.4 7.6 7.8 0.55
    1132 2.65 26.7 814 0.4 7.4 7.6 -
    1133 5.43 26.6 814 0.4 7.3 7.5 -
C7 5/26/2020 1201 0.40 27.1 547 0.3 7.5 7.6 0.7
    1202 2.68 26.7 548 0.3 7.5 7.4 -
    1203 5.06 26.7 548 0.3 7.4 7.4 -
H11 5/27/2020 1131 0.58 27.6 438 0.2 7.8 7.9 0.2
    1132 2.62 27.1 619 0.3 7.8 7.8 -
    1133 4.75 26.9 869 0.4 7.7 7.6 -

 

Table 2.5 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of June 1–5, 2020, week 5 after spillway was closed

Station Abbreviation Date Time (CST) Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
SJ 6/2/2020 1401 0.30 27.6 10,100 5.7 7.7 7.2 0.5
    1402 1.98 27.6 10,100 5.7 7.7 7.2 -
    1403 3.35 27.6 10,100 5.7 7.7 7.2 -
MB2 6/2/2020 1100 0.37 27.7 17,800 10.5 8.1 7.5 1.1
    1101 1.92 27.7 18,100 10.7 8 7 -
    1102 3.08 27.8 18,800 11.1 7.8 6.3 -
MB1 6/2/2020 1115 0.24 27.7 18,100 10.7 8.2 7.9 1.3
    1116 1.40 27.7 18,200 10.7 8.1 7.6 -
    1117 2.77 27.7 19,100 11.3 8.1 7.1 -
MB 6/2/2020 1131 0.40 27.7 17,800 10.5 8.1 7.4 1.3
    1132 1.31 27.6 17,800 10.5 8 7.1 -
    1133 4.63 27.5 22,700 13.6 7.7 3.3 -
GP2 6/2/2020 1000 0.18 27.8 20,100 11.9 8.2 7.6 1.15
    1001 1.86 27.8 20,300 12.1 8.2 7.3 -
    1002 3.69 27.4 23,500 14.2 7.8 4.2 -
GP1 6/2/2020 1015 0.49 27.7 20,900 12.5 8.3 8 0.95
    1016 1.98 27.6 23,600 14.2 8.3 7.4 -
    1017 4.15 27.6 25,800 15.7 8.2 6.8 -
GP 6/2/2020 1031 0.21 27.6 18,900 11.2 7.8 5 0.65
    1032 1.68 27.6 19,000 11.2 7.9 6 -
    1033 3.38 27.3 20,900 12.5 7.6 2.9 -
LB 6/2/2020 1301 0.34 27.8 3,280 1.7 8 7.5 0.55
    1302 2.07 27.8 3,260 1.7 8 7.5 -
    1303 3.63 27.8 3,260 1.7 8.1 7.5 -
PP 6/2/2020 1245 0.27 27.8 6,520 3.5 8 7.3 0.4
    1246 1.89 27.8 6,520 3.5 7.9 7.2 -
    1247 3.84 27.8 6,550 3.5 7.9 7.2 -
TM 6/2/2020 1230 0.30 27.9 9,030 5 7.8 7.1 0.55
    1231 1.43 27.8 9,110 5.1 7.8 6.8 -
    1232 2.16 27.7 9,410 5.3 7.9 5.4 -

 

 

Table 2.6 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of June 22–26, 2020, week 8 after spillway was closed

Station Abbreviation Date Time Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
C1 6/23/2020 1001 0.55 28.2 597 0.29 7 7.1 0.75
    1002 2.57 28.2 597 0.29 6.9 7.1 -
    1003 4.39 28.2 597 0.29 6.8 7.1 -
C2 6/23/2020 1101 0.69 28 710 0.34 7.2 7.2 0.9
    1102 2.64 28 710 0.34 7.1 7.1 -
    1103 4.63 28 710 0.34 7 7 -
C4 6/23/2020 1130 0.39 27.9 613 0.3 7.2 7.3 1.1
    1131 2.63 27.9 613 0.3 7.2 7.2 -
    1132 5.03 27.9 613 0.3 7.1 7.1 -
C7 6/23/2020 1201 0.36 27.7 643 0.31 7.4 7.2 1
    1202 2.64 27.7 643 0.31 7.3 7.2 -
    1203 4.63 27.7 643 0.31 7.2 7.1 -
H11 6/23/2020 1301 0.45 27.8 1,410 0.7 7.1 6.7 0.55
    1302 2.40 27.7 1,400 0.7 7 6.5 -
    1303 4.15 27.7 1,400 0.7 6.9 6.5 -

 

 

Table 2.7 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of July 20–24, 2020, week 12 after spillway was closed

Station Abbreviation Date Time (CST) Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
SJ 7/21/2020 1401 0.18 29.9 32,100 19.9 7.9 6.6 0.5
    1402 0.91 29.8 32,100 19.9 7.9 6.6 -
    1403 2.99 29.8 32,100 19.9 7.9 6.4 -
MB2 7/20/2020 1100 0.12 30.6 34,400 21.4 8.0 7.1 0.8
    1101 1.37 30.6 34,400 21.4 8.0 7.1 -
    1102 2.77 30.6 34,400 21.4 8.0 7 -
MB1 7/20/2020 1115 0.15 30.4 35,900 22.5 8.0 7.2 0.9
    1116 1.83 30.3 36,000 22.6 8.0 7.1 -
    1117 3.93 30.3 36,100 22.6 8.0 7 -
MB 7/20/2020 1131 0.30 30 40,400 25.65 8.1 7 0.8
    1132 2.74 29.9 40,400 25.65 8.1 6.9 -
    1133 4.66 29.9 40,400 25.65 8.1 6.9 -
GP2 7/21/2020 1015 0.40 29.6 37,300 23.5 8.1 6.5 0.9
    1016 1.89 29.5 38,000 24 8.1 6 -
    1017 3.47 29.5 38,500 24.4 8.1 5.8 -
GP1 7/21/2020 1000 0.24 29.6 39,800 25.3 8.1 5.4 0.65
    1001 2.16 29.6 39,800 25.3 8.1 5.4 -
    1002 4.30 29.6 39,800 25.3 8.1 5.3 -
GP 7/21/2020 1031 0.24 29.4 36,200 22.8 7.9 5.8 0.45
    1032 1.58 29.3 36,200 22.8 7.9 5.7 -
    1033 3.23 29.3 36,200 22.8 7.9 5.6 -
LB 7/21/2020 1301 0.34 29.7 15,600 9 7.9 7.3 0.5
    1302 1.65 29.7 15,600 9 7.9 7.3 -
    1303 3.38 29.7 15,600 9 7.9 7.2 -
PP 7/21/2020 1200 0.37 29.2 22,600 13.6 7.8 6.6 0.45
    1201 2.19 29.2 22,700 13.6 7.8 6.5 -
    1202 4.08 29.2 22,900 13.7 7.7 5.9 -
TM 7/21/2020 1130 0.24 29.8 18,500 10.9 8 7.8 0.35
    1131 0.98 29.7 19,000 11.2 8 7.4 -
    1132 1.65 29.2 23,700 14.3 7.6 4.4 -

 

 

Table 2.8 - U.S. Geological Survey field water-quality data from selected sampling stations in Lakes Pontchartrain/Borgne and western Mississippi Sound, 2020. 

Field data for week of July 27–31, 2020, week 13 after spillway was closed

Station Abbreviation Date Time Sample Depth (m) Water Temperature (°C) Specfic Conductance (µS/cm) Salinity (ppt) pH (units) Dissolved Oxygen (mg/L) Secchi Depth (m)
C1 7/27/2020 1001 0.46 27.7 361 0.17 8.1 7.7 1
    1002 2.67 27.7 361 0.17 8.1 7.6 -
    1003 4.88 27.7 361 0.17 8.2 7.6 -
C2 7/27/2020 1101 0.43 27.7 1,770 0.89 7.7 7.3 1.1
    1102 2.68 27.7 1,930 0.97 7.7 7.1 -
    1103 5.00 28 4,360 2.31 7.5 6 -
C4 7/27/2020 1115 0.50 27.6 3430 1.79 7.8 7.4 1.1
    1116 2.13 27.6 3440 1.8 7.8 7.3 -
    1117 5.36 28.1 4610 2.45 7.3 4.9 -
C7 7/27/2020 1201 0.48 27.7 559 0.27 7.8 7.2 1.1
    1202 2.67 27.7 559 0.27 7.8 7.2 -
    1203 5.06 27.7 558 0.27 7.9 7.4 -
H11 7/27/2020 1301 0.21 27.1 6,520 3.55 7.7 7.2 1
    1302 2.59 27.1 6,520 3.55 7.7 7.2 -
    1303 4.75 27.1 6,530 3.55 7.7 7.2 -

 

 

BonnetCarre2020_SamplingSchedule_20200522

Bonnet Carré sampling schedule as of 5/22/2020.

(Credit: Robinson, Angela L. Public domain.)

*USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.