Irrigation biggest user of water in Louisiana
By Tom Aswell
According to the report filed with the Louisiana Legislature earlier this year by the Louisiana Groundwater Resources Commission, irrigation accounts for 670 million gallons per day (Mgal/d) or 42 percent of groundwater withdrawals in Louisianqa, with public supply a distant second, accounting for 378 Mgal/d, or 24 percent. Other uses of groundwater included industry (243 Mgal/d, 15 percent), aquaculture (191 Mgal/d, 12 percent), power generation (76 Mgal/d, 5 percent) and rural domestic and livestock (45 Mgal/d, 3 percent).
Surface water withdrawals paint a completely different picture with power generation accounting for 4,352 Mgal/d, or 63 percent of the total), industry (1,183 Mgal/d, 26 percent), public supply (368 Mgal/d, 5 percent), irrigation (258 Mgal/d, 4 percent) and livestock and aquaculture (116 Mgal/d, 2 percent).
The combined total for both surface water and groundwater withdrawals showed that power generation accounted for 4,429 Mgal/d, or 52 percent. Others included industry (2,076 Mgal/d, 24 percent), irrigation (928 Mgal/d, 11 percent), public supply (746 Mgal/d, 9 percent), aquaculture (303 Mgal/d, 4 percent) and rural domestic and livestock (49 Mgal/d, 1 percent).
The report listed problems with each of the aquifers. These problems included drops in water tables, shallow saltwater intrusion, the presence of methane, chloride, pesticides, herbicides, fertilizers and metal in the water.
The Chicot Aquifer in southwest Louisiana provides groundwater to 15 parishes, including Acadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline, Iberia, Jefferson Davis, Lafayette, Rapides, St. Landry, St. Martin, St. Mary, Vermilion and Vernon.
The 649.33 million gallons per day drawn from Chicot is by far the biggest single aquifer, exceeding the second biggest, the Mississippi River Alluvia Aquifer by more than 250 million gallons per day, the report shows.
Of the 15 parishes that make up the Chicot Aquifer, Acadia and Jefferson Davis account for almost half of the total consumption with 183.25 Mgal/d and 140.46 Mgal/d, respectively. Vernon Parish, with only 500,000 gallons per day, uses the least amount of water of the 15 parishes.
Predictably, of the 649.33 Mgal/d used in the 15 parishes, 341.9 Mgal/d is used for rice irrigation. Public supply is a distant second at 97.35 Mgal/d.
Southwest Louisiana is home to about 20 percent of the state's population and produces about 65 percent of the rice grown in Louisiana, generates 42 percent of the aquaculture and fisheries and grows 34 percent of the state's sugar cane crop.
The U.S. Environmental Protection Agency (EPA) refers to the Chicot Aquifer system as the "sole-source aquifer" for the area, with no available alternative reliable source of groundwater.
Surface water diversions from both the Toledo Bend Reservoir to the Sabine River and onward to the Sabine River Diversion Canal provide some water supply to industries to the west around the Lake Charles area. Likewise, surface water from the Atchafalaya River to Bayou Teche is available to farmers to the east.
The Sabine River Authority of Louisiana currently diverts about 79 million gallons of Toledo Bend Reservoir water to provide 12 industries and two public utilities with water via the Sabine River Diversion Canal.
The water levels of the Chicot Aquifer, however, have dropped as much as 50 feet or more in Calcasieu, Jefferson Davis and Acadia parishes since major industrial pumping began, the report says.
The rate of decline in these areas is primarily because of industrial use in the Lake Charles area and rice irrigation, it says. The observed decline has been as much as one to two feet per year but because water level declines in the rice-growing areas are seasonal, the water levels fluctuate as much as 20 feet each year but usually recover to their pre-pumping levels.
A bigger problem is saltwater intrusion/migration from deeper sands in wells located in the high water use Lake Charles area. Other areas with saltwater concerns are the areas of Iowa and Opelousas and areas along the eastern edge of the Chicot Aquifer System, which are affected by the presence of salt domes and/or relic saltwater.
It was estimated in 2011 that as many as 80,000 acres of irrigated rice fields in southwest Louisiana, primarily in Vermilion Parish, might be at risk if intrusion of saltwater from the Gulf of Mexico within canals used for irrigation could not be stopped. Saltwater intrusion in coastal Louisiana, always a constant battle, has been worsened by drought that caused decreased freshwater influx, damaged levees and old spoil banks, and damaged water control structures.
Diversion of 138 billion gallons of Atchafalaya River water by the Tech-Vermilion Freshwater District eased the saltwater problem to some degree in eastern Vermilion Parish but the current lack of freshwater influx and/or the presence of saltwater have remained an issue for many rice farmers, the report said.
Despite the EPA's contention that the Chicot is the "sole-source aquifer" for southwest Louisiana, there are at least three others that provide at least some water to a few of the parishes that also draw from the Chicot Aquifer. The Evangeline Aquifer, for example, provides groundwater to all or part of eight parishes. They include Allen, Avoyelles, Beauregard, Calcasieu, Evangeline, Rapides, St. Landry and Vernon. Of those eight, only Avoyelles does not get any of its water from Chicot.
Evangeline provides only 24.58 Mgal/d to the eight parishes, 17.66 Mgal/d of which is used for public supply. Evangeline Parish draws 6.99 Mgal/d from the aquifer that bears its name, the most of any of the eight parishes.
Six parishes also get groundwater from the Jasper Aquifer System. They are Avoyelles, Beauregard, Concordia, Grant, Rapides and Vernon. Rapides accounts for 54.52 Mgal/d of the total 76.76 Mgal/d drawn from Jasper sands.
Rapides and Vernon are also among the nine parishes that get at least some of their groundwater from the Catahoula Aquifer. The other parishes are Catahoula, Concordia, Tensas, Grant, LaSalle, Natchitoches and Sabine. Together the nine parishes account for only 4 Mgal/d of water usage from the Catahoula Aquifer.
The Red River Alluvia Aquifer, which extends from the Arkansas border in northwest Louisiana to Rapides Parish in central Louisiana, provides 16.37 Mgal/d to nine parishes. They include Avoyelles (the biggest user at 6.47 Mgal/d), Bossier, Caddo, Catahoula, DeSoto, Grant, Natchitoches, Rapides and Red River.
Geographically, the Mississippi River Alluvia Aquifer is the largest in the state, providing 393.5 Mgal/d groundwater to all or parts of 27 parishes.
The biggest users are Morehouse (67.5 Mgal/d), Madison (38.83 Mgal/d), Franklin (35.18 Mgal/d), Tensas (28.62 Mgal/d), Concordia (26.16 Mgal/d), St. Martin (25.08 Mgal/d), Avoyelles (24.96 Mgal/d), Catahoula (20.49 Mgal/d), Iberville (20.41 Mgal/d), Richland (20.37 Mgal/d), East Carroll (19.91 Mgal/d), St. Landry (19.77 Mgal/d), Pointe Coupee (17.64 Mgal/d) and West Carroll (11.98 Mgal/d).
Water usage by the remaining 13 parishes was in the single digits. They included Ascension, Assumption, Caldwell, East Baton Rouge, Iberia, Lafayette, Lafourche, Ouachita, St. James, St. Mary, Terrebonne, West Baton Rouge and West Feliciana.
The Southern Hills Aquifer System serves 20 southeast Louisiana parishes, including Ascension, Assumption, East and West Baton Rouge, East and West Feliciana, Iberville, Jefferson, Livingston, Orleans, Plaquemines, Pointe Coupee, St. Bernard, St. Charles, St. Helena, St. James, St. John the Baptist, St. Tammany, Tangipahoa and Washington.
East Baton Rouge with 149.81 Mgal/d, accounted for nearly half of the aquifer's 320.76 Mgal/d withdrawal.
Fourteen parishes in north Louisiana are served by the Sparta Aquifer System. They are Bienville, Bossier, Caddo, Caldwell, Claiborne, Jackson, Lincoln, Morehouse, Natchitoches, Ouachita, Sabine, Union, Webster and Winn.
Of the 63.11 Mgal/d drawn from the Sparta sands, 34.61 Mgal/d is for public supply and 25.6 Mgal/d is for industry. Ouachita Parish accounts for more than a third of the total withdrawal with 22.27 Mgal/d.
The Carrizo-Wilcox Aquifer in northwest Louisiana serves Bienville, Bossier, Caddo, DeSoto, Natchitoches, Red River, Sabine and Webster but the eight parishes combined withdraw only 19.31 Mgal/d.
The Cockfield Aquifer likewise provides little water to 16 parishes in central, north central and northeast Louisiana. Only 6.96 Mgal/d from the Cockfield Aquifer is withdrawn from Caldwell, Claiborne, East Carroll, Grant, Jackson, LaSalle, Lincoln, Morehouse, Natchitoches, Ouachita, Richland, Sabine, Union, Vernon, West Carroll and Winn.
The Upland Terrace Aquifer is located in three separate parts of the state-in central, northwest and northeast Louisiana and provides 28.76 Mgal/d of water parts of Avoyelles, Bienville, Bossier, Caddo, DeSoto, Grant, LaSalle, Morehouse, Natchitoches, Ouachita, Rapides, Red River, Sabine, Union, Vernon, Webster and Winn parishes.