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 August 11, 2014 through August 17, 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 2.5 ppt to 8 ppt and from 8 ppt to 12 ppt at the mouth of Lake Borgne. Salinity in Chandeleur Sound increased from a range of 16-30 ppt to 23 to 34 ppt. Salinity also increased in Breton Sound from 14 ppt to 19 ppt. Discharge from all rivers and passes decreased from the last Hydrocoast Period to this one. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 3,669 to 3,558 cfs
- Tangipahoa = 892 to 617 cfs
- Tickfaw = 672 to 264 cfs
- Amite = 2,903 to 1,424 cfs
- Caernarvon Diversion = 117 to 61 cfs
- Mardi Gras Pass = 2,006 to 1,706 cfs
- Violet Siphon = N/A to 50 cfs
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 1,177 to 609 cfs
- Fort St. Philip = 22,069 to 9,571 cfs
- Baptiste Collete = 52,103 to 24,744 cfs
- Grand and Tiger Pass = 43,993 to 26,888 cfs
- Main Pass = 43,254 to 27,951 cfs
- West Bay = 36,559 to 23,522 cfs
- Pass A Loutre = 29,152 to 17,921 cfs
- Southwest Pass = 177,251 to 115,373 cfs
- South Pass = 75,064 to 43,572 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 rainfall across the basin, ranging from 1 to 2 inches. Resultant winds were mostly from the northwest and southwest but also the northeast. 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 Laketown, Old Beach and Abita River. High fecal coliform counts were found at Bogue Falaya, Bayou Castine, Fontainbleau Beach, Amite at Highway 16/42, Amite and Idle Road, Bayou Manchac at Amite and 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 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 August 13 at 7 am. There were 9 shrimp boats in the Biloxi Marshes and Breton Sound, however shrimp fishing was cloased over much of the basin at the time of the survey. There were 27 oyster boats counted, mostly in the Biloxi Marshes but also in the Breton Sound marshes east of Bayou Terre aux Boeufs . Also shown on the map are the market prices for shrimp, hamper of crab, half sack of oysters and a pound of crawfish. 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.