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.
To receive Hydrocoast maps by email click the sign up button below:
Click on link below map for larger image.
The Hydrocoast maps for the week of September 21, 2015 through September 27, 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 salinity increased on across the basin. Salinity in the Rigolets and eastern end of Lake Pontchartrain increased from 9.0 ppt to 12.0 ppt an increased to 4.0 ppt in the middle of the lake. Around Half Moon Island, salinity increased from 19.0 ppt to 24.0 ppt. Salinity also increased in Breton Sound. Discharge decreased at all nothshore rivers and river outlets around the Bird’s Foot Delta and increased at all other river outlets. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 1,751 to 1,550 cfs
- Tangipahoa = 424 to 373 cfs
- Tickfaw = 150 to 111 cfs
- Amite = 889 to 336 cfs
- Caernarvon Diversion = 275 to 504 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 = 317 to 472 cfs
- Fort St. Philip = 9,332 to 11,792 cfs
- Baptiste Collete = 24,158 to 29,949 cfs
- Grand and Tiger Pass = 24,026 to 21,965 cfs
- Main Pass = 25,339 to 23,445 cfs
- West Bay = 21,225 to 19,544 cfs
- Pass A Loutre = 16,076 to 14,754 cfs
- Southwest Pass = 104,086 to 95,753 cfs
- South Pass = 37,762 to 33,460 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 entire basin. Rainfall ranged from 0 to 4 inches. Resultant winds were mostly from the northeast. 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 Harrell Lane Public Launch and Jefferson Hwy. 73 and high counts at Old Beach, Pontchartrain Beach, Bayou St. John, Bogue Falaya, Abita River, 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.
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 a survey flight conducted on September 23 at 7am are shown. There were 47 shrimp boats counted across the basin mostly by the Bird’s Foot Delta. There were 11 oyster boats counted, all north of the MRGO. 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.