Water Resources of West Baton Rouge Parish, Louisiana

This U.S. Geological Survey summary, prepared with the Louisiana Department of Transportation and Development, gathers what is known about the supply, use and quality of water in West Baton Rouge Parish, across the Mississippi River from Baton Rouge, for water managers and residents.

How much water, and for what

In 2010 the parish withdrew about 10.9 million gallons a day (Mgal/d): about 10.2 from groundwater and 0.73 from surface water. Public supply took about 66 percent (7.21 Mgal/d).

Withdrawals every 5 years since 1960, almost all groundwater. They peaked in 2000. USGS.

Groundwater

The parish's fresh groundwater — water with no more than 250 milligrams per liter of chloride — comes from four sources, shallowest first: the Mississippi River alluvial aquifer and the Chicot, Evangeline and Jasper equivalent aquifer systems. The alluvial aquifer lies nearly flat; the others dip south toward the Gulf of Mexico.

The Baton Rouge Fault crosses the parish, and fresh water reaches far deeper north of it than south of it. North of the fault in the south-central parish, the base of fresh water lies more than 2,500 feet below the National Geodetic Vertical Datum of 1929 (NGVD 29), in the Jasper system; near the southern parish line, south of the fault, it is less than 200 feet down, in the Chicot system.

West Baton Rouge Parish: depth to the base of fresh groundwater, from under 200 feet in the south to 2,500 feet and more, the Tepetate and Baton Rouge Faults, the three wells charted below, and the Mississippi River gaging sites. USGS.

Rain falling in southeastern Louisiana and southwestern Mississippi recharges the three deeper systems. The alluvial aquifer is recharged by rain soaking through the surface clays, by water from the alluvial aquifer to the north and from neighbouring and underlying aquifers, and locally by the Mississippi River. North of the fault, water in the deeper systems flows east toward East Baton Rouge Parish, where the heaviest local pumping from them is reported; water in the alluvial aquifer generally flows south.

West-to-east section through the parish: freshwater sands (blue) of each aquifer system, with saltwater sands (tan) at depth. USGS, modified from Griffith (2003).

• Mississippi River alluvial aquifer. A regional aquifer running through several states along the river, present across the whole parish: fine sand to pea gravel, with gravel at its base. Its base lies less than 200 feet below NGVD 29 in the north and more than 600 feet at the southern border and near the Port Allen Lock, where it is over 550 feet thick (less than 150 feet near Highway 190 at the eastern border). Because it is connected to the river, water levels in its wells rise and fall with the river. It is also connected to the "400-foot" and "600-foot" sands. Its water went mostly to industry (1.23 Mgal/d) and aquaculture (1.07).
• Chicot equivalent system. The shallow sands and the "400-foot" and "600-foot" sands of the Baton Rouge area, fine sand to pea gravel, based less than 350 feet down in the north and more than 950 feet in the south. In well WBR-146 in the "400-foot" sand, levels swing 15 to 20 feet a year but held steady from 1996 to 2015. Its only use in 2010 was rural domestic.
• Evangeline equivalent system. The "800-foot" through "1,700-foot" sands, about 1,000 feet thick, fine to coarse sand. In 2001, levels in the "1,200-foot" sand north of the fault ranged from about NGVD 29 at the parish's western and northern edges to nearly 70 feet below it at Port Allen (well WBR-5); in 2003, levels in the "1,500-foot" and "1,700-foot" sands ranged from about 33 feet below at the western edge to about 91 feet below at Port Allen (well WBR-100A). The two sands have similar levels, a sign they are connected. This system supplies almost all the parish's public water: 7.02 Mgal/d of it in 2010.
• Jasper equivalent system. The "2,000-foot," "2,400-foot" and "2,800-foot" sands, from about 1,300 to at least 2,300 feet deep in the north and 1,900 to more than 2,800 feet in the central parish. North of the fault its lower part, including the "2,800-foot" sand, holds saltwater; south of the fault the whole system generally does.

Water levels in three Port Allen–area wells. WBR-146 ("400-foot" sand) swings seasonally but holds steady; WBR-5 ("1,200-foot" sand) declines; WBR-100A ("1,700-foot" sand) swings seasonally, drops in 2012–13 and recovers slightly by 2015. USGS.

Groundwater quality

Samples from 25 wells in the alluvial aquifer (1942–93) and 62 in the Evangeline system (1942–2011):

Median color, pH and dissolved solids stayed within the EPA's secondary (non-enforceable, cosmetic and aesthetic) limits in both. Median iron and manganese exceeded them in the alluvial aquifer but not in the Evangeline system, where only 54 percent of samples fell within the pH range.

Surface water

Two drainage basins divide the parish: the Lower Mississippi–Baton Rouge Basin, a narrow strip along the river, and the Lower Grand Basin, everything else. Levees mean the Mississippi drains little of the parish itself, but its upstream basin covers more than 40 percent of the conterminous United States; near Red River Landing it averaged about 460,000 cubic feet per second over 1928–76.

The Lower Grand Basin drains roughly south. Its largest waterway is the Gulf Intracoastal Waterway, which meets the Mississippi at the Port Allen Lock and runs west and then south into Iberville Parish, where Choctaw Bayou (fed by Grand and Cholpe Bayous) joins it. Lock and waterway form an important commercial route that greatly shortens shipping between the Gulf of Mexico and river ports near and north of Baton Rouge. In 2010, 0.54 Mgal/d was drawn from the waterway for aquaculture, and 0.19 Mgal/d from other streams for irrigation and livestock.

Surface-water quality

Mississippi River samples near St. Francisville (1978–2010) were generally hard (median 150 mg/L) and stayed within secondary limits for pH, chloride, sulfate and iron. Dissolved oxygen was generally above 5 mg/L, the minimum considered necessary for a diverse population of warm-water freshwater life, sport fish included. Agricultural pesticides and nutrients generally peak in June and July, the "spring flush" of runoff from upstream fields; suspended sediment is highest in late winter and early spring and lowest in late summer and fall. Four samples from Choctaw Bayou near Brusly were hard to very hard (137–222 mg/L), with pH 7.5–8.1 and dissolved solids 194–323 mg/L; chloride, iron, sulfate and manganese were within secondary limits.

Sources

• Vincent E. White and Lawrence B. Prakken, Water Resources of West Baton Rouge Parish, Louisiana, USGS Fact Sheet 2016–3068, prepared in cooperation with the Louisiana Department of Transportation and Development. https://doi.org/10.3133/fs20163068
• USGS National Water Information System: http://waterdata.usgs.gov/nwis