Water Resources of Concordia Parish, Louisiana

Knowing how much water Concordia Parish, Louisiana, has, how it is used and how good it is matters for managing its supply. This U.S. Geological Survey fact sheet, prepared with the Louisiana Department of Transportation and Development, draws on earlier reports and the USGS National Water Information System to give water managers, residents and others that picture.

How much water is used

In 2010 the parish withdrew over 50 million gallons a day (Mgal/d): about 28.7 Mgal/d from groundwater and 22.3 Mgal/d from surface water. Farming — rice and general irrigation, aquaculture and livestock — took about 77 percent (39.2 Mgal/d). Records kept every five years since 1960 show withdrawals at their highest in 2010.

Groundwater and surface-water withdrawals in Concordia Parish, 1960–2010. USGS.

Groundwater

The parish's main freshwater aquifer is the Mississippi River alluvial aquifer; fresh water is also found in the Jasper aquifer system and the Catahoula aquifer. Fresh groundwater here means water with no more than 250 milligrams per litre (mg/L) of chloride. In the west of the parish, its base lies in the alluvial aquifer, about 50 to 200 feet below the National Geodetic Vertical Datum of 1929 (NGVD 29); in the east, it lies in the Jasper or Catahoula, from less than 200 to 1,000 feet below. In some places saltwater sits above the base of fresh water.

Concordia Parish: depth to the base of fresh groundwater, river subbasins, and the wells and river sites described here. USGS.

The Mississippi River alluvial aquifer

This aquifer underlies the whole parish. It is the coarser part of sediments laid down mainly by the Mississippi River, grading from clay and silt at the surface to coarse sand and gravel at the base, and is from less than 140 to more than 200 feet thick. Its base lies less than 80 feet below NGVD 29 in the north and more than 160 feet below near the parish's southern tip.

It is recharged mostly by rain soaking in, and also by streams and rivers at high water. Water moves generally south, and leaves naturally into streams and rivers and by evapotranspiration, and artificially through wells. In 1990, water levels ranged from less than 50 feet above NGVD 29 in the north to about 30 feet above in the south. At well Co-215, in the middle of the parish, levels have varied by less than about 10 feet a year and stayed fairly stable from 1989 to 2015; at well Co-45, near Lake St. John, they have changed little overall since 1968.

In 2015 the state listed 383 active wells in the aquifer — 309 for irrigation, 64 domestic and 10 public supply — from 45 to 235 feet deep, with reported yields of 8 to 3,400 gallons a minute. In 2010 about 26.2 Mgal/d came from it, mostly for general irrigation (13.80) and rice (10.38), with smaller amounts for aquaculture (1.70), public supply (0.15), livestock (0.09) and rural homes (0.05).

The Jasper aquifer system and the Catahoula aquifer

The Jasper system comprises the Williamson Creek aquifer, the Dough Hills confining unit and the Carnahan Bayou aquifer. In Concordia Parish these hold fresh water only in a band less than 10 miles wide along the Mississippi River, recharged by rain in southwestern Mississippi.

The Catahoula aquifer underlies the whole parish but holds fresh water only in the northeast and northwest. It is made of white to light grey sands, very coarse to very fine, seldom widespread and interbedded with silts and clays, and is recharged by rain and by flow from aquifers below. In 2013, water levels in two Catahoula wells, near Jonesville and at the south end of Lake St. John, were about zero and 40 feet above NGVD 29; at well Co-50 the level fell about 50 feet from 1972 to 2015.

In 2015 there were 28 active wells in these aquifers — 16 public supply, 6 domestic, 3 industrial and 3 irrigation — 275 to 765 feet deep, yielding 15 to 1,070 gallons a minute. In 2010 they supplied about 2.58 Mgal/d, mostly for public supply (1.85).

Groundwater quality

Samples from the alluvial, Carnahan Bayou and Catahoula aquifers were within the Environmental Protection Agency's secondary maximum contaminant levels (SMCLs) — non-enforceable guidelines on cosmetic, taste and odour, and technical effects — for pH and sulfate. Median hardness was very hard in the alluvial aquifer and soft in the Carnahan Bayou and Catahoula. Iron and manganese exceeded their SMCLs in more than 90 percent of samples from the alluvial and Carnahan Bayou aquifers.

Surface water

The parish's streams flow generally south through three regional basins, much modified by canals, control structures and levees:

• Lower Mississippi–Natchez, the land beside the Mississippi River;
• Boeuf–Tensas, a small area along the Tensas River in the north;
• Lower Red, which drains most of the parish through the Bayou Cocodrie, Black and Lower Red subbasins.

The Mississippi River drains more than 40 percent of the conterminous United States, but because of its levees it drains little of the parish. Near Red River Landing, at the parish's southern tip, it averaged about 460,000 cubic feet per second in 1928–76. The Old River Control Structure, in the south of the parish, sends about 30 percent of the combined flow of the Mississippi and Red Rivers above it into the Atchafalaya River. In 2010, 8.26 Mgal/d was taken from the Mississippi for power generation and 1.50 Mgal/d from the Marengo Bend oxbow lake for public supply.

The Tensas River forms the parish's northwestern border and ends near Jonesville, where it joins the Ouachita and Little Rivers to form the Black River, which runs along the southwestern border into the Red River.

Bayou Cocodrie, which drains most of the parish, rises near Ferriday and joins the Red River near the parish's southern tip. In 2010, 9.14 Mgal/d was taken from it, mostly for rice, and 2.95 Mgal/d from Cross Bayou. The Red River, which forms part of the southern boundary and eventually joins Mississippi water diverted at Old River to form the Atchafalaya, averaged 30,770 cubic feet per second upstream at Alexandria in 1928–82. Cocodrie Lake, Black River Lake, Lake Concordia and Lake St. John are popular for water sports, fishing and swimming.

Surface-water quality

Samples from the Mississippi River near St. Francisville (1954–2013), the Tensas River at Clayton (1968–91) and the Red River near Simmesport (1977–86) were generally within SMCLs for pH, chloride, sulfate, iron and dissolved solids. Median hardness was hard in the Mississippi and moderately hard in the Tensas and Red. Median dissolved oxygen was above 7 mg/L; 5 mg/L is considered the minimum for a diverse community of warm-water life, including sport fish.

What happens upstream affects the Mississippi water reaching the parish. Farm pesticides and nutrients are generally highest in late spring and early summer — the "spring flush" of runoff from upstream fields — and suspended sediment is highest in late winter and early spring and lowest in late summer and autumn.

Sources

• U.S. Geological Survey, in cooperation with the Louisiana Department of Transportation and Development, Water Resources of Concordia Parish, Louisiana, Fact Sheet 2016–3099, February 2017. https://doi.org/10.3133/fs20163099
• USGS Lower Mississippi-Gulf Water Science Center: http://la.water.usgs.gov