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 November 18 through 24, 2013 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.). In this Hydrocoast period saline waters were found slightly further west in Lake Pontchartrain and Lake Marepaus than the last Hydrocoast with 3.0 ppt water being west of the Causeway Bridge and 1.5 ppt moving into Lake Maurepas. Saline water at 9.0 ppt was found in eastern Lake PontchartrainSalinity in the outer parts of the basin remained similar to the last period. Average daily discharge for the week decreased in Pearl, Tangipahoa and Tickfaw Rivers but increased in the Amite River, Mardi Gras Pass, Bayou Lamoque, Fort St. Philip and Baptiste Collette. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 3,060 to 2,309 cfs
- Tangipahoa = N/A to 227 cfs
- Tickfaw = 100 to 99 cfs
- Amite = 408 to 521 cfs
- Caernarvon Diversion = 0 to 0 cfs
- Mardi Gras Pass = 890 to 897 cfs
- Violet Siphon = Closed
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 490 to 550 cfs
- Fort St. Philip = 8,991 to 9,522 cfs
- Baptiste Collete = 23,302 to 24,586 cfs
- White Ditch Siphon = N/A
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). This time period is characterized by an increase in salinity in Lakes Marepaus and Pontchartrain and similar salinity in the outer basin to the last Hydrocoast period. 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 light to heavy rainfall across the basin ranging from 0.5 to 6 inches of rainfall. The heaviest rainfall in the basin was over the Chandeleur Islands. The resultant winds for this period were mostly from the northeast. Wind speeds ranged from 1 to11.1 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 period, a high fecal coliform counts were found at Abita River Bayou Lacombe.
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 map also shows the results of an aerial survey of the shrimp and oyster fleets conducted from 7:00 am to 8:00 am on November 19. Shrimp boats were found near Half Moon Island, in Eloi Bay, in Breton Sound near the MRGO and east of the Mississippi River at the northern end of the Bird’s Foot delta. In total, there were 26 boats observed in the survey. Oyster boats were observed in the Biloxi Marshes and in the interior marshes in Breton Sound. In total there were 5 oyster boats observed during the survey. Of note, the conditions on the day of the shrimp and oyster survey were very windy, resulting in a smaller fleet. The Biological Map also includes market prices for the week for hamper of crabs, half sack of oysters and shrimp over time since September 13th.