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 February 9, 2015 through February 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 salinity remained similar in Lakes Pontchartrain and Borgne from the last Hydrocoast period. Salinity decreased slightly in Chandeleur and Breton Sounds. Average discharge in all rivers and outlets decreased from the last Hydrocoast period to this one. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 11,457 to 4,474 cfs
- Tangipahoa = 890 to 521 cfs
- Tickfaw = 419 to 176 cfs
- Amite = 2,253 to 926 cfs
- Caernarvon Diversion = 1,923 to 641 cfs
- Mardi Gras Pass = 514 to 376 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 85 to 0 cfs
- Fort St. Philip = 7,676 to 6,407 cfs
- Baptiste Collete = 20,169 to 17,014 cfs
- Grand and Tiger Pass = 30,813 to 26,673 cfs
- Main Pass = 31,507 to 27,757 cfs
- West Bay = 26,613 to 23,356 cfs
- Pass A Loutre = 20,469 to 17,789 cfs
- Southwest Pass = 130,367 to 114,572 cfs
- South Pass = 51,260 to 43,164 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 almost no rain across the basin. Resultant winds were variable from the south, southwest, northwest and northeast. Wind speeds ranged from 2 to more than 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 Bonnabel Boat Launch and Old Beach and high 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. Also shown are the results of an aerial survey for oyster boats conducted on February 11th at 7 am. Shrimp season has closed and therefore reconnaissance concentrated on the oyster fleet. There were 75 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.