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 July 7, 2014 through July 13, 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 by an increase in salinity throughout the basin. Salinity in Lake Pontchartrain increased from 1.5 ppt at the eastern edge to 3 ppt. Salinity in Chandeleur Sound increased from 13-20 ppt to 18-29 ppt. Salinity also increased significantly in the Cat Island Channel and Mississippi Sound. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 5,785 to 3,440 cfs
- Tangipahoa = 1,077 to 702 cfs
- Tickfaw = 359 to 235 cfs
- Amite = 1,114 to 5,419 cfs
- Caernarvon Diversion = 140 to 139 cfs
- Mardi Gras Pass = 2,240 to 1,904 cfs
- Violet Siphon = 260 to N/A cfs
- Bohemia Spillway = 0 to 0 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 2,056 to 1,497 cfs
- Fort St. Philip = 28,891 to 21,753 cfs
- Baptiste Collete = 65,466 to 51,539 cfs
- Grand and Tiger Pass = 48,900 to 44,918 cfs
- Main Pass = 49,000 to 44,067 cfs
- West Bay = 41,100 to 37,228 cfs
- Pass A Loutre = 31,300 to 29,770 cfs
- Southwest Pass = 200,000 to 180,316 cfs
- South Pass = 84,400 to 76,605 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 some rainfall across the almost the entire basin, ranging from 0 to 3 inches. Resultant winds were variable ranging from northwest, southwest, south and southeast but were predominantly from the southwest. 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 Bogue Falaya. High fecal coliform counts were found at Amite at Hwy 16/42, Amite at Idle Road and Bayou Manchac at Amite. 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.