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 and methodology.
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Click on link below map for larger image.
The Hydrocoast maps for the week of November 16, 2015 through November 22, 2015 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. During this Hydrocoast period the east side of Lake Pontchartrain continued to decrease in salinity, from 8.0 ppt to 6.0 ppt. Salinity continued to decrease in Lake Borgne as well. The rest of the basin remained similar Discharge increased at all rivers and outlets except Tickfaw River, Amite River and the Caernarvon Diversion. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 5,929 to 12,299 cfs
- Tangipahoa = 3,531 to 4,262 cfs
- Tickfaw = 2,343 to 1,839 cfs
- Amite = 10,410 to 10,074 cfs
- Caernarvon Diversion = 856 to 249 cfs
- Mardi Gras Pass = 1,500 - 3,500 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 523 to 568 cfs
- Fort St. Philip = 11,488 to 14,625 cfs
- Baptiste Collete = 29,138 to 36,350 cfs
- Grand and Tiger Pass = 22,916 to 29,661 cfs
- Main Pass = 24,321 to 30,472 cfs
- West Bay = 20,323 to 25,725 cfs
- Pass A Loutre = 15,364 to 19,715 cfs
- Southwest Pass = 99,626 to 126,115 cfs
- South Pass = 35,461 to 49,090 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. 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, up to 4 inches in some areas. Resultant winds were the northeast and heavy winds from the southeast. Wind speeds ranged from 2 to greater than 11.2 m/s (2 to greater than 25 miles/hr).
The fourth "Water Quality" shows the results of LPBF's water quality sampling around Lake Pontchartrain, reporting the fecal coliform counts. During this Hydrocoast period there were elevated fecal coliform counts at Bogue Falaya and Northshore Beach. 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 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. The results on an aerial fleet survey from November 18 at 7 am are shown. There were 15 shrimp boats found, mostly near the Bird’s Foot Delta. There were 93 oyster boats found, mostly near Half Moon Island. 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 and fecal coliform are shown.