Jefferson Parish, Louisiana: Surrounded by Water, It Draws From One River

Lake Pontchartrain, Lake Cataouatche, Lake Salvador, Little Lake, Barataria Bay and the Gulf of Mexico all lie in or along Jefferson Parish. In 2010 it took no water from any of them. Of about 817 million gallons a day withdrawn in the parish that year, about 810 million came from the Mississippi River and about 7.16 million from wells.

Most of that river water was only borrowed. Power generation accounted for about 91 percent of everything withdrawn, and water taken for power plants is mostly used for cooling and returned to its source.

The parish and the water in and around it. Image from the U.S. Geological Survey's fact sheet.

Where the water went in 2010

In million gallons a day, from the fact sheet's table (after Sargent, 2011):

The surface water is the Mississippi River, apart from the livestock's share, which came from small streams. It was not always this little: counted every five years since 1960, withdrawals peaked at about 1,600 million gallons a day in 1975 and 1980. The jump between 1970 and 1975 came mainly from power generation.

Withdrawals from groundwater and surface water, 1960–2010. Image from the U.S. Geological Survey's fact sheet.

Fresh water underground is scarce

Of the aquifers under the parish, only two are used for supply. The rest — Mississippi River point-bar deposits, the shallow aquifers of the New Orleans area and the Gramercy aquifer — hold very hard water with high iron (more than 300 micrograms per liter) or only saltwater (chloride above 250 milligrams per liter). A clay layer generally separates the two that matter:

Northern Jefferson Parish: fresh water in the Norco aquifer (the narrow band along the lake) and in the Gonzales-New Orleans aquifer (green), with wells Jf-156, Jf-178 and Jf-186. Image from the U.S. Geological Survey's fact sheet.

From Lake Pontchartrain (left) to the Mississippi River (right): blue is fresh water in sand, orange saltwater. Modified from Dial and Tomaszewski, 1988; vertical scale greatly exaggerated. Image from the U.S. Geological Survey's fact sheet.

The parish's two main pumping centers in 2008, about 1 mile southwest and 1 mile northeast of Bridge City, both drew saltwater from the Gonzales-New Orleans aquifer — about 1.8 and an estimated 3.9 million gallons a day in 2007.

The water table is coming back

Pumping from the Gonzales-New Orleans aquifer has fallen, and its water levels have generally risen since the 1970s. At well Jf-156, north of Bridge City, the level has risen about 49 ft since the mid-1970s; at Jf-178, on the lakeshore in the northwest, about 10 ft since 1997. In 2008 levels ranged from about 16 ft below the reference datum (NGVD 29) in the northwest to about 47 ft below near Bridge City, and the water flowed toward the east-southeast. In the Norco aquifer, well Jf-186 has stayed between about 0 and 9 ft below the datum since 1996.

Water levels in the three wells. Image from the U.S. Geological Survey's fact sheet.

The water itself is usable but not pristine. Measured against the EPA's secondary (nuisance) standards, fresh water from the Gonzales-New Orleans aquifer is generally soft, and its median pH, iron and manganese stay within them; dissolved solids are generally under 500 milligrams per liter but locally more, and its yellow color exceeds the limit of 15 platinum-cobalt units. Norco water at Jf-186 is moderately hard, with iron above the 300-microgram limit and color above 15 units, but little manganese.

Fresh water from 28 wells in the Gonzales-New Orleans aquifer, against the secondary standards. Image from the U.S. Geological Survey's fact sheet.

The river that supplies it

The Mississippi at Belle Chasse, sampled from 1977 to 2009, is generally hard but generally within the secondary standards for pH, chloride, sulfate and iron. Its dissolved oxygen is generally above 5 milligrams per liter — the minimum for a varied population of freshwater, warm-water life, sport fish included.

There are no flow records for the river in the parish itself. The nearest stand-in is Red River Landing, about 200 river miles upstream, where the river averaged about 460,000 cubic feet per second — about 298,000 million gallons a day — from 1928 to 1976. With no major tributaries or distributaries between there and the parish, and levees along most of it, the flow arrives much the same. Set beside that, the parish's 810 million gallons a day is a small draw.

Jefferson Parish in Louisiana, and the Red River Landing gauge (07373290) upstream. Image from the U.S. Geological Survey's fact sheet.

The fact sheet as printed

Sources

• U.S. Geological Survey, Water resources of Jefferson Parish, Louisiana, Fact Sheet 2013–3073. Its sources include Sargent (2011), Water use in Louisiana, 2010; Prakken (2009), Groundwater resources in the New Orleans area, 2008; and Dial and Tomaszewski (1988), USGS Water-Resources Investigations Report 88–4097.