Water Use and Quality of Fresh Surface-Water Resources in the Barataria-Terrebonne Basins, Louisiana

Abstract

Approximately 170 Mgal/d (million gallons per day) of ground- and surface-water was withdrawn from the Barataria-Terrebonne Basins in 1995. Of this amount, surface water accounted for 64 percent ( 110 Mgal/ d) of the total withdrawal rates in the basins. The largest surface-water withdrawal rates were from Bayou Lafourche ( 40 Mgal/d), Bayou Boeuf ( 14 Mgal/d), and the Gulf Intracoastal Waterway (4.2 Mgal/d). The largest ground-water withdrawal rates were from the Mississippi River alluvial aquifer (29 Mgal/d), the Gonzales-New Orleans aquifer (9.5 Mgal/d), and the Norco aquifer (3.6 Mgal/d).

The amounts of water withdrawn in the basins in 1995 differed by category of use. Public water suppliers within the basins withdrew 41 Mgal/d of water. The five largest public water suppliers in the basins withdrew 30 Mgal/d of surface water: Terrebonne Waterworks District 1 withdrew the largest amount, almost 15 Mgal/d. Industrial facilities withdrew 88 Mgal/d, fossil-fuel plants withdrew 4.7 Mgal/d, and commercial facilities withdrew 0.67 Mgal/d. Aggregate water-withdrawal rates, compiled by parish for aquaculture (37 Mgal/d), livestock (0.56 Mgal/d), rural domestic (0.44 Mgal/d), and irrigation uses (0.54 Mgal/d), totaled about 38 Mgal/d in the basins. Ninety-five percent of aquaculture withdrawal rates, primarily for crawfish and alligator farming, were from surface-water sources.

Total water-withdrawal rates increased 221 percent from 1960-95. Surface-water withdrawal rates have increased by 310 percent, and ground-water withdrawal rates have increased by 133 percent. The projection for the total water-withdrawal rates in 2020 is 220 Mgal/d, an increase of 30 percent from 1995. Surface- water withdrawal rates would account for 59 percent of the total, or 130 Mgal/d. Surface-water withdrawal rates are projected to increase by 20 percent from 1995 to 2020.

Analysis of water-quality data from the Mississippi River indicates that the main threats to surface water resources are from the herbicide atrazine and excessive nutrients. Atrazine concentrations in the Mississippi River at Baton Rouge briefly exceed the U.S. Environmental Protection Agency maximum contaminant level of 3.0 micrograms per liter during periods in the late spring and early summer. Trace metals in bottom material collected from Bayou Lafourche indicate that the reach of Bayou Lafourche from Donaldsonville to Golden Meadow is adversely affected by low-level contamination. Dissolved nitrate had a mean concentration of 1.4 milligrams per liter in the Mississippi River near Bayou Lafourche and can contribute to excessive plant growth.

Long-term salinity records near Bayou Lafourche indicate no pronounced trends, with the exception of the Gulf Intracoastal Waterway at Houma. At this site, salinities remained low until 1961, when the Gulf Intracoastal Waterway was connected to the Gulf of Mexico by the Houma Navigation Canal. The sources of saltwater are variable. Some saltwater has entered Bayou Lafourche south of the Gulf Intracoastal Waterway; at other times saltwater has moved up the Houma Navigation Canal and has flowed east in the Gulf Intracoastal Waterway, north into Company Canal, and southeast in Bayou Lafourche towards Larose, Louisiana.

First posted March 11, 2014