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 25, 2014 through August 31, 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 continued increase in salinity across the basin. Salinity in the eastern end of Lake Pontchartrain increased from 8 ppt to 20 ppt and from 12 ppt to 19 ppt at the mouth of Lake Borgne. Salinity in Chandeleur Sound increased from a range of 23-34 ppt to 27-34 ppt. Discharge from all rivers and passes, except the Caernarvon Diversion, 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 = 3,558 to 2,288 cfs
- Tangipahoa = 617 to 485 cfs
- Tickfaw = 264 to 149 cfs
- Amite = 1,424 to 868 cfs
- Caernarvon Diversion = 61 to 90 cfs
- Mardi Gras Pass = 1,706 to 1,480 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 609 to 646 cfs
- Fort St. Philip = 9,571 to 10,564 cfs
- Baptiste Collete = 24,744 to 27,088 cfs
- Grand and Tiger Pass = 26,888 to 23,756 cfs
- Main Pass = 27,951 to 25,091 cfs
- West Bay = 23,522 to 21,005 cfs
- Pass A Loutre = 17,921 to 15,903 cfs
- Southwest Pass = 115,373 to 102,997 cfs
- South Pass = 43,572 to 37,200 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 1 to 4 inches. Resultant winds were mostly from the southwest and 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 high fecal coliform counts were found at Bogue Falaya, Amite at Highway 16/42, Abita River, Cane Bayou and Bayou Bonfouca. 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 27 at 7 am. There were 116 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.