In the case of a drought, there are several upstream reservoirs which are used as storage if we need to supplement the river’s flow to provide sufficient water to downstream communities. ICPRB’s Section for Cooperative Water Supply Operations on the Potomac (CO-OP) provides a monthly Water Supply Outlook which explores precipitation data, flows and other data to provide the possibility of water supply releases from these reservoirs. The report is an analysis of where the Potomac watershed stands with regards to water supply and drought preparation.
The August report found an above-normal probability of releases from the Washington metropolitan area’s backup water supply reservoirs for the 2023 summer and fall seasons. These releases are typically prompted by low flows resulting from a combination of insufficient summer precipitation and low groundwater levels. July’s average precipitation in the Potomac Basin was 0.4 inches below normal. Although recent rainfall improved conditions reported in the U.S. Seasonal Outlook and the U.S. Drought Monitor, on July 28th, CO-OP resumed daily drought monitoring. Presently, the Potomac River flow at the U.S. Geological Survey’s gage in Point of Rocks, Maryland, remains below CO-OP’s daily monitoring trigger of 2,000 cubic feet per second (cfs). The basin is also experiencing a long-term cumulative precipitation deficit of approximately 6.4 inches below normal (11 to 12 percent below normal). As a result, the adjusted stream flow at Little Falls remains below normal but remains above the 10th percentile, while groundwater monitoring wells used in the outlook indicate below-normal levels.
Despite the current conditions, the Potomac River’s flow is adequate to meet the water demands of the Washington metropolitan area without requiring releases from upstream reservoirs. Thanks to well-designed drought-contingency plans, the area is well-prepared to handle further reductions in flow.