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 May 4, 2015 through May 10, 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 salinities across the basin remained similar to the salinities during the last Hydrocoast period. Discharge decreased at all northshore rivers and increased at all other outlets. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 18,673 to 4,093 cfs
- Tangipahoa = 1,101 to 553 cfs
- Tickfaw = 498 to 178 cfs
- Amite = 2,179 to 1,210 cfs
- Caernarvon Diversion = 152 to 210 cfs
- Mardi Gras Pass = 4,322 to 4,518 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 9,509 to 10,337 cfs
- Bonnet Carré Spillway = 510 to 1,120 cfs
- Bayou Lamoque = 2,756 to 3,127 cfs
- Fort St. Philip = 45,456 to 47,929 cfs
- Baptiste Collete = 94,860 to 98,887 cfs
- Grand and Tiger Pass = 76,848 to 77,892 cfs
- Main Pass = 71,242 to 72,099 cfs
- West Bay = 58,436 to 59,060 cfs
- Pass A Loutre = 51,657 to 56,392 cfs
- Southwest Pass = 270,770 to 273,174 cfs
- South Pass = 120,869 to 121,996 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. 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 and very scattered rainfall at 0.25 to 1 inch. Resultant winds were from the southeast. 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 elevated fecal coliform counts at Muddy C. Road and high counts at Bogue Falaya, Yellow River/LA22, Natalbany River/LA22, Jefferson Hwy. 73, Horseshoe Bend, and the Amite Diversion at DC Road . 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.