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 September 22, 2014 through September 28, 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 an increase in salinity across the basin. Salinity in the eastern end of Lake Pontchartrain increased from 7 ppt to 12 ppt. Salinity also increased in Lake Borgne, Chandeleur Sound and Breton Sound. Discharge from all rivers and passes, except the Mardi Gras Pass, Bayou Lamoque, Fort St. Philip and Baptiste Collette, decreased from the last Hydrocoast Period to this one. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 3,276 to 2,233 cfs
- Tangipahoa = 683 to 459 cfs
- Tickfaw = 269 to 128 cfs
- Amite = 954 to 556 cfs
- Caernarvon Diversion = 111 to 96 cfs
- Mardi Gras Pass = 1,393 to 1,707 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 696 to 696 cfs
- Fort St. Philip = 10,367 to 15,130 cfs
- Baptiste Collete = 26,592 to 37,500 cfs
- Grand and Tiger Pass = 49,992 to 33,920 cfs
- Main Pass = 43,254 to 34,307 cfs
- West Bay = 36,558 to 29,028 cfs
- Pass A Loutre = 29,151 to 22,494 cfs
- Southwest Pass = 117,250 to 141,984 cfs
- South Pass = 75,064 to 57,290 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 rainfall across the basin, ranging from 0 to 4 inches. Resultant winds were mostly from the southeast and also the northwest. Wind speeds ranged from 0 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 water quality parameters of fecal coliform counts, water visibility, salinity and dissolved oxygen. During this Hydrocoast period elevated fecal coliform counts were found at Laketown and Bogue Falaya and high fecal coliform counts were found at the Abita River. 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 September 22 at 7 am. There were 132 shrimp boats scattered throughout the basin. There were 14 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.