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 April 6, 2015 through April 12, 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 Lake Borgne, Chandeleur Sound, and Breton Sound were all slightly fresher while Lake Pontchartrain remained similar to the previous period. Discharge increased at all northshore rivers except the Pearl River. Discharge also increased at upper river passes but decreased at all the Bird’s Foot Delta Passes. There was also some leakage from Bonnet Carré Spillway. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 19,920 to 7,473 cfs
- Tangipahoa = 1,268 to 1,467 cfs
- Tickfaw = 556 to 847 cfs
- Amite = 2,001 to 2,689 cfs
- Caernarvon Diversion = 564 to 51 cfs
- Mardi Gras Pass = 365 to 1,937 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 20,000 cfs
- Bonnet Carré Spillway = 1,000 to 1,120 cfs
- Bayou Lamoque = 2,688 to 2,816 cfs
- Fort St. Philip = 44,853 to 46,667 cfs
- Baptiste Collete = 93,838 to 96,813 cfs
- Grand and Tiger Pass = 90,936 to 83,282 cfs
- Main Pass = 82,739 to 76,523 cfs
- West Bay = 66,683 to 62,271 cfs
- Pass A Loutre = 61,642 to 53,196 cfs
- Southwest Pass = 301,790 to 285,492 cfs
- South Pass = 135,248 to 127,758 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 light to medium rainfall across the basin accumulating from 0.25 to greater than 8 inches. Resultant winds were from the southeast. Wind speeds ranged from 2 to more than 8.8 m/s (2 to more than 20 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 Fontainebleau Beach, Amite at Idle Road, Bayou Manchac at Amite, Bayou Bonfouca, and Alligator Bayou. There were high counts at Bogue Falaya, Northshore Beach, Amite Diversion at DC Road, Amite at Highway 16/42, Abita River, Liberty Bayou, Harrell Lane Public Launch, Jefferson Highway 73, and Horseshoe Bend. 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.