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 8, 2014 through September 14, 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 a decrease in salinity in Rigolets and Chef Menteur Passes and Lake Borgne but an increase in salinity in Chandeleur Sound. Therefore, the salinity gradient across the basin is steeper (contours are closer together). However, salinity increased in eastern and middle Lake Pontchartrain. Discharge in all northshore rivers and Mississippi River passes and diversions except at Mardi Gras Pass, Fort St. Philip and Baptiste Collette. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 2,288 to 3,276 cfs
- Tangipahoa = 485 to 683 cfs
- Tickfaw = 149 to 269 cfs
- Amite = 868 to 954 cfs
- Caernarvon Diversion = 90 to 111 cfs
- Mardi Gras Pass = 1,480 to 1,393 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 646 to 696 cfs
- Fort St. Philip = 10,564 to 10,367 cfs
- Baptiste Collete = 27,088 to 26,592 cfs
- Grand and Tiger Pass = 23,756 to 43,992 cfs
- Main Pass = 25,091 to 43,254 cfs
- West Bay = 21,005 to 36,558 cfs
- Pass A Loutre = 15,903 to 29,151 cfs
- Southwest Pass = 102,997 to 177,250 cfs
- South Pass = 37,200 to 75,064 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 rainfall across the basin, ranging from 0.5 to 4 inches. Resultant winds were variable ranging from the northeast, east, southeast and the west. 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 Bayou Manchac at Amite, Abita River and Bayou Lacombe. High fecal coliform counts were found at Bogue Falaya, Amite River at Hwy 16/42 and the Little Tchefuncte 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 9, 2014. The Hypoxic area has shrunk slightly from that observed in June 23, 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 9th at 7 am. There were 94 shrimp boats scattered throughout the basin. There were 18 oyster boats counted. 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.