Water Resources of Grant Parish, Louisiana: Aquifers, Streams and Water Use

Grant Parish and its wells, gages and subbasins. U.S. Geological Survey.

Water use

Knowing how much water Grant Parish, Louisiana, has, uses and how clean it is matters for managing supply. In 2014 the parish withdrew about 5.43 million gallons per day (Mgal/d):

Industry and rural domestic use made up the rest. Withdrawals, tracked every 5 years from 1960 to 2010 and again in 2014, were highest in 1960.

Water withdrawals, 1960–2014. U.S. Geological Survey.

Groundwater

The main freshwater aquifers are the Red River alluvial and terrace aquifers, the Carnahan Bayou aquifer of the Jasper aquifer system, the Catahoula aquifer and the Cockfield aquifer. The base of fresh groundwater (chloride 250 mg/L or less) lies from more than 50 feet above to more than 500 feet below sea level (NGVD 29); the northeast and a small area along the Little River in the southeast have little or none.

An idealized north–south section of Grant Parish's aquifers and confining layers. U.S. Geological Survey.

Water levels have mostly held steady:

• G-338 (Red River alluvial, southeast of Colfax): moved about 10 ft or less in 1973–2018.
• G-314 (terrace, northwest of Dry Prong): less than about 15 ft in 1971–2018; G-127B (terrace, near the southern boundary): less than about 5 ft in 1956–2016.
• G-410 (Carnahan Bayou, near Bentley): fell after its first reading in 1981, then generally rose in 2002–16.
• G-393 (Catahoula, northwest of Colfax): generally stable in 2012–16, and higher than its first reading in 1973.

Water levels in five wells screened in the Red River alluvial, terrace, Carnahan Bayou and Catahoula aquifers. U.S. Geological Survey.

Quality: samples from 107 terrace wells (1939–2015), 26 Carnahan Bayou wells (1939–83) and 65 Catahoula wells (1938–83) had median hardness in the soft range. Sulfate, manganese and dissolved solids were generally below the EPA's Secondary Maximum Contaminant Levels (SMCLs), but chloride exceeded the SMCL in 31 percent of Catahoula samples.

Surface water

The parish drains to three subbasins: Lower Red-Lake Iatt (west), Little (east) and Dugdemona (northeast). In 2014, 3.03 Mgal/d were withdrawn: 1.75 from Big Creek for public supply, 0.66 from Falcon Bayou for irrigation, and 0.62 from other streams, mostly for irrigation.

• Red River: follows the western border into Rapides Parish; downstream at Alexandria, it averaged 30,770 cubic feet per second in 1928–82.
• Lake Iatt: impounded in 1956; about 7,100 acres, 4.5 ft deep on average (19 ft at most), thick with cypress and tupelo; its level often varies 3–4 ft a year, sometimes up to 10 ft.
• Nantachie Lake: created in 1964 on Nantachie Creek for wildlife, fish and recreation; about 1,580 acres, 7 ft deep on average (17 ft at most).
• Big Creek at Pollock: averaged 61.7 cubic feet per second in 1943–2018, highest in February, lowest in August.
• Little River near Rochelle: averaged 2,232 cubic feet per second in 1958–2017, highest in March, lowest in August.
• Dugdemona River: crosses only a short stretch of the parish's far northeast.

Quality: samples from the Red River at Grand Ecore (1987–2000), Big Creek at Pollock (1943–2004) and the Little River near Rochelle (1957–86) were hard for the Red River and soft for the others. Median chloride, sulfate, dissolved solids and pH met the SMCLs, and median dissolved oxygen was at least 7.0 mg/L — above the 5 mg/L generally needed for diverse warmwater life, including sport fish.

Sources

Based on Water Resources of Grant Parish, Louisiana, U.S. Geological Survey Fact Sheet 2020–3064, by Chid J. Murphy (Bureau of Indian Affairs) and Vincent E. White (U.S. Geological Survey), USGS Publications Warehouse; a work of the United States government in the public domain. Figures recovered from the fact sheet's PDF.