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 24, 2014 through March 2, 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 continued freshening of Lake Pontchartrain and Lake Borgne with increased rainfall and freshwater discharge from local rivers. Salinities in eastern Lake Pontchartrain decreased from 4 ppt to 3 ppt and the 1 ppt line moved further east in the lake. The southern end of Chandeleur Sound and Breton Sound experienced an increase in salinity, most likely due to decreased discharge from river outlets and southeast winds pushing saline water into the basin. Salinities increased in basin where there was no barrier to flow such as the Chandeleur Islands. 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. Average daily discharge difference between last Hydrocoast and the current was:
- Pearl River = 29,657 to 27,939 cfs
- Tangipahoa = 1,751 to 3,530 cfs
- Tickfaw = 797 to 1,722 cfs
- Amite = 5,934 to 11,646 cfs
- Caernarvon Diversion = 2,681 to 782 cfs
- Mardi Gras Pass = 1,176 to 1,120 cfs
- Violet Siphon = 225 to 220 cfs
- Bonnet Carré Spillway = 0 to 0 cfs
- Bayou Lamoque = 548 to 533 cfs
- Fort St. Philip = 14,260 to 13,596 cfs
- Baptiste Collete = 35,358 to 34,074 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 rainfall across the northshore at 3 to 5 inches and light rain around the bird’s foot delta at 0 to 2 inches. The resultant winds for this period were blowing mostly from the southeast but also from the northwest and the south. 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 Pontchartrain Beach, Northshore Beach and the Amite at Riverscape and high fecal coliform counts were found at the Bonnabel Boat Launch, Old Beach, Bogue Falaya, Tchefuncte River, Bayou Castine, Blood River at Warsaw, Amite Diversion at Waterfront East, Amite Diversion at DC Road, the Amite at River Road, Amite at Hwy 18/42, Bayou Manchac at Amite and Liberty Bayou. 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.