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 February 10, 2014 through February 16, 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 the fresehing of Lake Pontchartrain and Lake Borgne with increased rainfall and freshwater discharge fropm local rivers. Salinities in eastern Lake Pontchartrain decreased from 8 ppt to 4 ppt and in Lake Borgne decreased from 12.0 ppt9 ppt at the mouth. The western side of Chandeleur Sound became more fresh, decreasing from 21 ppt to 17 ppt. Average daily discharge for the week decreased in all the Mississippi River outlets as the river stage decreased and increased in all rivers that are monitored as rainfall in the basin increased. The controlled discharges of Caernarvon Diversion and Violet Siphon both increased. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 4,025 to 29,657 cfs
- Tangipahoa = 436 to 1,751 cfs
- Tickfaw = 107 to 797 cfs
- Amite = 512 to 5,934 cfs
- Caernarvon Diversion = 980 to 2,681 cfs
- Mardi Gras Pass = 1,655 to 1,176 cfs
- Violet Siphon = Closed to 225
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 806 to 548 cfs
- Fort St. Philip = 19,291 to 14,260 cfs
- Baptiste Collete = 46,356 to 35,358 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). 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 rainfall across the southern portion of the basin at 0 to 2 inches of rain. The resultant winds for this period were variable, blowing mostly from the northwest but also from the southwest and the north east. 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 Amite at Idle Road and Little Tchefuncte River and high fecal coliform counts were found at the Bonnabel Boat Launch, Pontchartrain Beach, Bogue Falaya, Amite at Catfish Landing, Amite Diversion at DC Road, the Amite at River Road, Bayou Manchac at Amite, Cane Bayou and Bayou Lacombe. 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. An oyster fleet survey was conducted on January 15th from 7am to 8am. There were a total of 12 oyster boats spotted in the Biloxi Marshes and the Marshes of Breton Sound. 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. Due to low fishing (either effort or catch) during this Hydrocoast period, market prices were not available for crabs or oystersThe 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. A flight to count oyster boats was conducted from 7am to 8am on February 13th. A total of seven boats were counted, six in the Biloxi Marshes and one in the Breton Sound marshes. Low boat counts could be from low fishing effort or very cold temperatures that were present on the survey morning. 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. Due to low fishing (either effort or catch) during this Hydrocoast period, market prices were not available for oysters.