The greater metropolitan Washington area’s water supply could face “considerable stress” by 2035, requiring mandatory water-use restrictions, if the region were to experience a drought, according to a new study of the Potomac River.
What’s more, water storage at Little Seneca Reservoir in Montgomery County, Maryland, could become “exhausted” by 2040 under those conditions, according to the study by the Interstate Commission on the Potomac River Basin.
“In both 2035 and 2040, there is a small probability that flow in the Potomac River would drop below the minimum environmental flow level of 100 MGD [million gallons per day] at Little Falls dam, though the predicted flow deficit is less than 1 MGD,” says the commission’s “2015 Washington Metropolitan Area Water Supply Study,” released last week.
Rainfall in the Potomac River basin averaged about 2 inches below normal in August, prompting daily monitoring of the river by the metropolitan area’s water suppliers — the U.S. Army Corps of Engineers, the Fairfax County Water Authority and the Washington Suburban Sanitary Commission, the commission says on its website.
These agencies “will continue to prepare for the possibility that more serious drought conditions could develop in the upcoming weeks,” the commission says. “At present, there is sufficient flow in the Potomac River to meet the Washington metropolitan area’s water demands without augmentation from upstream reservoirs.”
In its new study, the commission recommends that the area’s water suppliers continue to seek out new water storage facilities, such as reservoirs, and to develop tools to forecast the Potomac’s flow in real time. It also recommends improving its database and modeling tools to better plan for water use.
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Founded by Congress in 1940, the Interstate Commission on the Potomac River Basin is a non-regulatory, interstate advisory agency that monitors the 383-mile-long Potomac — the primary source of water for the metropolitan Washington area.
According to the commission’s study, the area’s water use has remained steady since the 1990s, even though the area’s population has increased by 18 percent during that period, from 3.9 million people in 1990 to 4.6 million people this year. Washington-area residents have used an average of 466 million gallons of water per day since 2009. An average of 7 billion gallons flows per day in the Potomac, according to the commission.
The study’s forecast models predict 5.7 million people in the metropolitan area by 2040 (a 23 percent increase over 2015’s population), with each household using the current amount of water — about 25.3 gallons per day indoors.
The study was prepared by S.N. Ahmed, K.R. Bencala and C.L. Schultz.
The commission comprises the federal government and the Potomac basin jurisdictions of Maryland, Virginia, the District, West Virginia and Pennsylvania.