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.
Subscribe: To receive Hydrocoast products by email please email Hydrocoast@saveourlake.org.
Click on link below map for larger image.
The Hydrocoast maps for the week of March 24, 2014 through March 30, 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 similar salinities in Lake Pontchartrain as the last Hydrocoast with the western half of the Lake below 1ppt. Chandeleur Sound increased in salinity. During the last Hydrocoast, salinities ranged from 14 to 20 ppt and increased to 20 to 27 ppt during this Hydrocoast. Salinities in Breton Sound were similar to the Hydrocoast. Average daily discharge for the week increased in the northshore rivers but decreased at all of the Mississippi River outlets. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 7,234 to 12,044 cfs
- Tangipahoa = 815 to 1,784 cfs
- Tickfaw = 230 to 766 cfs
- Amite = 1,523 to 2,251 cfs
- Caernarvon Diversion = 3,130 to 520 cfs
- Mardi Gras Pass = 2,241 to 1,821 cfs
- Violet Siphon = 275 to 248 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 711 to 1,012 cfs
- Fort St. Philip = 25,892 to 21,096 cfs
- Baptiste Collete = 59,810 to 50,164 cfs
- Grand and Tiger Pass = 42,000 cfs
- Main Pass = 43,000 cfs
- West Bay = 36,000 cfs
- Pass A Loutre = 29,000 cfs
- Southwest Pass = 176,000 cfs
- South Pass = 74,000 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 Marepaus.
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. 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 at 3 to 9 inches. The resultant winds for this period were blowing mostly from the southeast but also from the northwest and northeast. Wind speeds ranged from 1 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, elevated fecal coliform counts were found at Laketown, Bonnabel Boat Launch and Bogue Falaya and high fecal coliform counts were found at the Amite at HWY. 18/42, Abita River, Cane Bayou, Bayou Lacombe, Liberty 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 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 Biological Map also includes market prices for the week for hamper of crabs, half sack of oysters, shrimp and crawfish over time since September 13th. Due to low fishing (either effort or catch) during this Hydrocoast period, market prices were not available for oysters and crabs.