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 July 21, 2014 through July 27, 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 by a slight freshening in eastern Lake Pontchartrain, Mississippi Sound and Chandeleur Sound. The rest of the basin had similar salinity condition to the last Hydrocoast. Discharge increased in the northshore rivers and decreased in most of the Mississippi River outlets. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 3,440 to 3,669 cfs
- Tangipahoa = 702 to 892 cfs
- Tickfaw = 169 to 643 cfs
- Amite = 1,543 to 2,903 cfs
- Caernarvon Diversion = 139 to 117 cfs
- Mardi Gras Pass = 1,904 to 2,006 cfs
- Violet Siphon = 287 to 285 cfs
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 1,497 to 1,177 cfs
- Fort St. Philip = 21,753 to 22,069 cfs
- Baptiste Collete = 51,539 to 52,103 cfs
- Grand and Tiger Pass = 44,918 to 43,993 cfs
- Main Pass = 44,067 to 43,254 cfs
- West Bay = 37,228 to 36,559 cfs
- Pass A Loutre = 29,770 to 29,152 cfs
- Southwest Pass = 180,316 to 177,251 cfs
- South Pass = 76,605 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 spotty rainfall on the northshore and rain over most of the southern part of the basin, ranging from 1 to 3 inches. Resultant winds were mostly from the southwest. Wind speeds ranged from 0 to 8.8 m/s (2 to 20 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, an elevated fecal coliform count was found at the Tchefuncte River. High fecal coliform counts were found at Old Beach, Bogue Falaya, Abita River, Little Tchefuncte River, Cane Bayou and Liberty Bayou. 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 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 July 22 at 7 am. There were 44 shrimp boats in the Biloxi Marshes and along the Mississippi River. There were 24 oyster boats found mostly in the Biloxi Marshes. Also shown on the map are the market prices for shrimp, hamper of crab, half sack of oysters and a pound of crawfish.