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 December 1, 2014 through December 7, 2014 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.). There was again a slight freshening in Lake Pontchartrain, Chandeleur Sound and the Breton Sound but overall salinity conditions remained similar to the last Hydrocoast. Discharge from all Northshore rivers and the river outlets decreased except those around the Bird’s Foot Delta which increased. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 2,919 to 2,079 cfs
- Tangipahoa = 486 to 340 cfs
- Tickfaw = 250 to 118 cfs
- Amite = 1,632 to 636 cfs
- Caernarvon Diversion = 84 to 57 cfs
- Mardi Gras Pass = 522 to 467 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 274 to 268 cfs
- Fort St. Philip = 7,752 to 7,235 cfs
- Baptiste Collete = 20,349 to 19,087 cfs
- Grand and Tiger Pass = 23,901 to 24,087 cfs
- Main Pass = 25,225 to 25,395 cfs
- West Bay = 21,123 to 21,273 cfs
- Pass A Loutre = 15,996 to 16,116 cfs
- Southwest Pass = 103,584 to 104,322 cfs
- South Pass = 37,503 to 37,883 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 0.25 to 1 inches of rain in a few isolated areas on the Northshore and the Biloxi Marshes. Resultant winds were mostly from the northeast and east. Wind speeds ranged from 2 to 11.1 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. During this Hydrocoast period there were no high fecal coliform counts. 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. Also shown are the results of an aerial survey for shrimp and oyster boats conducted on December 3rd at 7 am. There were 46 shrimp boats, with the biggest fleets near the Bird’s Foot Delta. There were 49 oyster boats counted, mostly in the Biloxi Marshes and in the public oyster grounds in Breton Sound. 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.