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 June 15, 2015 through June 21, 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 salinities in Lake Pontchartrain, Lake Borgne and Breton Sound remained similar to the last Hydrocoast period. Chandeleur Sound decreased in salinity from a range of 15 ppt to 29 ppt during the last Hydrocoast period to a range of 15 ppt to 19 ppt during this period. Salinity also increased in Mississippi Sound. Discharge decreased at all northshore rivers and Bayou Lamoque and increased at all other all other outlets. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 10,302 to 5,739 cfs
- Tangipahoa = 1,336 to 635 cfs
- Tickfaw = 600 to 340 cfs
- Amite = 4,459 to 1,909 cfs
- Caernarvon Diversion = 178 to 190 cfs
- Mardi Gras Pass = 3,989 to 4,223 cfs
- Violet Siphon = Closed
- Bohemia Spillway = 1,693 to 2,165 cfs
- Bonnet Carré Spillway = 20 to 110 cfs
- Bayou Lamoque = 2,712 to 2,706 cfs
- Fort St. Philip = 41,380 to 44,240 cfs
- Baptiste Collete = 88,024 to 92,824 cfs
- Grand and Tiger Pass = 64,097 to 65,046 cfs
- Main Pass = 60,584 to 61,386 cfs
- West Bay = 50,404 to 51,023 cfs
- Pass A Loutre = 42,788 to 43,442 cfs
- Southwest Pass = 238,148 to 240,732 cfs
- South Pass = 105,221 to 106,476 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 light rainfall across most of the basin at 0.25 to 2 inches. Resultant winds were mostly from the southeast but also the southwest and south. Wind speeds ranged from 2 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 fecal coliform counts. During this Hydrocoast period there were elevated fecal coliform counts at Cane Bayou and Tickfaw River/LA22. There were high counts at Bogue Falaya, Abita River, Ponchatoula Creek/LA22, Yellow River/LA22 and Muddy C. Road.. 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. A 295 square mile area of hypoxia was detected in Chandeleur Sound during a survey conducted on May 20th. We have seen Hypoxia develop on a yearly basis in this area (http://saveourlake.org/PDF-documents/our-coast/Chandeleur-2013-Hypoxia-July2013.pdf).
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 of aerial reconnaissance of the oyster and shrimp fleet was conducted on June 16th, at 7 am are shown. There were 16 Oyster boats counted in the Biloxi Marshes. There were 96 shrimp boats counted across the basin. 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.