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.
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Click on link below map for larger image.
The Hydrocoast maps for the week of March 9, 2015 through March 15, 2015 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 decreased slightly across the basin, most likely due to increased rainfall. Salinity eastern Lake Pontchartrain decreased by half from 6 ppt to 3 ppt. Salinity in Lake Borgne, Breton Sound, Chandeleur Sound and waters around the Bird’s Foot Delta also decreased. Discharge increased in all outlet and rivers except for the Caernarvon Diversion. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 12,556 to 25,174 cfs
- Tangipahoa = 751 to 1,701 cfs
- Tickfaw = 388 to 1,489 cfs
- Amite = 1,769 to 4,544 cfs
- Caernarvon Diversion = 441 to 248 cfs
- Mardi Gras Pass = 365 to 1,937 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 300 to 1,101 cfs
- Fort St. Philip = 6,297 to 22,450 cfs
- Baptiste Collete = 16,744 to 52,823 cfs
- Grand and Tiger Pass = 30,313 to 56,321 cfs
- Main Pass = 31,059 to 53,918 cfs
- West Bay = 26,230 to 45,132 cfs
- Pass A Loutre = 20,142 to 37,489 cfs
- Southwest Pass = 128,540 to 215,260 cfs
- South Pass = 50,329 to 93,943 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 and dashed lines represent 0.5 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 substantial rainfall across the basin with areas over the Biloxi Marsh and Chandeleur Sound receiving 7-8 inches. Resultant winds were from the east and southeast. Wind speeds ranged from 2 to 11.1 m/s (2 to more than 25 miles/hr).
The fourth "Water Quality" shows the results of LPBF's water quality sampling around Lake Pontchartrain, reporting the fecal coliform counts. During this Hydrocoast period there were elevated fecal coliform counts at Bogue Falaya. 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 (spanning the Bird's Foot Delta) was closed while all other areas east of the Mississippi River remained open. 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, fecal coliform and remnants from the BP Oil Spill are shown.