On the coast, rainfall mixes with seawater from the Gulf, resulting in a coastal system called an estuary. Many of the external influences on an estuary are the same influences that affect the weather, like rainfall or winds; but the estuary is also impacted by an additional set of factors, including tides or river diversions. This daily interaction of freshwater and seawater is as complex as our local weather, and it is almost as important.
Lake Pontchartrain Basin Foundation (LPBF) sees a parallel between water monitoring and weather forecasting. Just as weather networks and websites use maps to forecast the weather, LPBF will use a map to show water movement and the most recent distribution of salinity across the basin. LPBF has developed a map to display hydrology for the Pontchartrain Basin. We call our map the “Hydrocoast Map.” Please see below to view LPBF's latest Hydrocoast Maps. You can also view our archived maps and methodology.
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Click on link below map for larger image.
The Hydrocoast maps for the week of April 4 through April 10, 2016 were produced using field data, MODIS, satellite imagery, precipitation data, wind data and permanent monitoring stations in the basin (USGS buoys, Coastwide Reference Monitoring System (CRMS), etc.). During this Hydrocoast period the salinity remained similar to the last period across most of the basin with Lake Pontchartrain below 2 ppt, Lake Borgne below 3 ppt and Chandeleur Sound staying in between 15 ppt to 26 ppt. There was a plume of freshwater reaching out into Breton Sound most likely due to high flow out of Ft. St. Philip and sustained west and southwest winds. Discharge decreased at all rivers and outlets. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 56,107 to 22,899 cfs
- Tangipahoa = 1,394 to 1,036 cfs
- Tickfaw = 584 to 429 cfs
- Amite = 2,186 to 2,152 cfs
- Caernarvon Diversion = 71 to 89 cfs
- Mardi Gras Pass = 8,500 to 8,100 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 22,278 to 7,423 cfs
- Bonnet Carré Spillway = 4,040 to 300 cfs
- Bayou Lamoque = 2,537 to 2,361 cfs
- Fort St. Philip = 161,846 to 122,976 cfs
- Baptiste Collete = 108,120 to 88,816 cfs
- Grand and Tiger Pass = 91,620 to 73,934 cfs
- Main Pass = 83,298 to 68,830 cfs
- West Bay = 52,000 to 42,716 cfs
- Pass A Loutre = 67,720 to 57,374 cfs
- Southwest Pass = 321,689 to 272,545 cfs
- South Pass = 94,327 to 79,917 cfs
The first map (Hydrocoast map without precipitation) shows the salinity contours and freshwater discharge across the Pontchartrain Basin. The solid line salinity contours are at 1 ppt salinity increments. The salinity is highest out past the Chandeleur Islands (red lines, 32 ppt) and decreases to fresh conditions (dark blue lines) in the basin. Sea water generally has a salinity of 32 ppt. Green asterisks represent salinity leak points, usually in the form of gates in storm surge protection features but also in passes, portions of roads that are raised, canals, and bayous that are holes in the salinity barriers (pink lines) in the form of levees, roads, natural ridges and canals (with associated spoil banks). Salinity contours that are close together represent an area where salinity changes quickly over a short distance, which is seen slightly offshore throughout the basin during this Hydrocoast period. Contours that are farther apart represent a more gradual change over longer distances which can be seen in throughout the interior of the basin, in Lake Pontchartrain and Lake Maurepas.
The second map shows the salinity contours laid on top of a habitat/land -use map, showing where fresh to salt marsh and swamps are found in the basin. This map also shows soil water salinity contours across the land masses. The third map shows the salinity contours in conjunction with weekly rainfall and wind roses in the Pontchartrain basin. During this Hydrocoast period there was no rainfall across the basin. Resultant winds were variable from the northwest, west, southwest, south and southeast. Wind speeds ranged from 2 to 11.2 m/s (2 to 25 miles/hr).
The fourth "Water Quality" shows the results of LPBF's water quality sampling around Lake Pontchartrain, reporting the fecal coliform counts. Elevated fecal coliform counts were found at Bayou Castine and Natalbany River/LA22. High counts were found at Bonnabel Boat Launch, Bayou St. John, Bogue Falaya, Abita River, Little Tchefuncte River, Liberty Bayou, Bayou Bonfouca, Ponchatoula Creek/LA22, and Yellow River/LA22. The water quality map also shows the impaired water bodies for Primary Contact (swimming, immersion likely) and Secondary Contact (boating wading, immersion unlikely) in the basin as prepared by the Louisiana Department of Environmental Quality under the EPA 305(b)/303(d) guidelines.
The fifth “Biological Map” shows oyster harvest area closure, as determined by the Louisiana Department of Health and Hospitals and the location of the public oyster seed grounds. During this Hydrocoast period, oyster harvest area 8 was closed. The biological map also shows the impaired water bodies for fishing and oyster propagation in the basin as prepared by the Louisiana Department of Environmental Quality under the EPA 305(b)/303(d) guidelines. Impairments due to metal contamination and fecal coliform are shown.