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 October 6, 2014 through October 12, 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.). This Hydrocoast period is characterized by a slight decrease in salinity across the basin. Salinity in the eastern end of Lake Pontchartrain decreased from 12 ppt to 5 ppt while the rest of the lake was similar to the last Hydrocoast period. Salinity remained similar in Lake Borgne, and decreased in Chandeleur Sound and Breton Sound. Discharge from all northshore rivers increased except in the Tangipahoa and decreased in all river passes. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 2,233 to 2,332 cfs
- Tangipahoa = 459 to 429 cfs
- Tickfaw = 128 to 133 cfs
- Amite = 556 to 562 cfs
- Caernarvon Diversion = 96 to 104 cfs
- Mardi Gras Pass = 1,707 to 504 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 696 to 585 cfs
- Fort St. Philip = 15,130 to 7,585 cfs
- Baptiste Collete = 37,500 to 19,944 cfs
- Grand and Tiger Pass = 33,920 to 23,516 cfs
- Main Pass = 34,307 to 24,868 cfs
- West Bay = 29,028 to 20,804 cfs
- Pass A Loutre = 22,494 to 15,750 cfs
- Southwest Pass = 141,984 to 101,986 cfs
- South Pass = 57,290 to 36,675 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 spotty light rainfall across the basin, ranging from 0 to 2 inches. Resultant winds were mostly from the southeast and also the south. Wind speeds ranged from 0 to 8.8 m/s (2 to 20 miles/hr).
The fourth "Water Quality" shows the results of LPBF's water quality sampling around Lake Pontchartrain, reporting the water quality parameters of fecal coliform counts, water visibility, salinity and dissolved oxygen. During this Hydrocoast period high fecal coliform counts were found at Bogue Falaya. Water Quality data were not available at all the usual sites this period. 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 map also shows an area of hypoxia in the Chandeleur Sound which was detected on September 9th, 2014.
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 October 8th at 7 am. There were 156 shrimp boats, mostly in the Biloxi Marshes and along the Mississippi River. There were nine oyster boats counted, mostly in the Biloxi Marshes. 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.