Situational Awareness (Thursday, 2024-06-27)
Potomac River flows continue to slowly decline due to persistent dry conditions. According to the Middle Atlantic River Forecast Center predictions, a basin-wide average of 0.3 inches of rain is expected over the next 24 hours and 0.5 inches over the next three days. The week-long outlook calls for approximately 0.7 inches of rain in the basin above Little Falls.
Special conditions:
River flow fluctuations from National Park Service bathymetric surveys at Potomac Dams No. 4 and 5 are visible at the USGS’s Shepherdstown and Point of Rocks stream gages. Surveys will continue at these locations, with the dam operator, Eagle Creek, diverting water through the power plant turbines.
The USGS took field measurements yesterday at the Potomac River at Little Falls dam gage (Station No. 01646500). The stage-discharge relationship was updated based on these measurements, resulting in an 11% increase in reported flow.
Recent basin-wide average precipitation (above Little Falls):
(based on CO-OP's Low Flow Forecast System analysis of Middle Atlantic River Forecast Center (MARFC) gridded multisensor precipitation estimates)
Yesterday's area-weighted average basin precipitation: 0.07 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.17 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.23 (inches)
Daily flows:
Little Falls gage flow 2024-06-26: 1041 MGD (1610 cfs)
Little Falls gage flow 2024-06-27: 1254 MGD (est., based on recently available real-time data) (1940 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-06-26: 1306 MGD (2020 cfs)
Point of Rocks flow 2024-06-27: 1112 MGD (est., based on recently available real-time data) (1720 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-06-26: 1198 MGD (1854 cfs)
Note: Estimated flow below Great Falls intake is flow at Little Falls plus Little Falls water supply withdrawal.
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2024-06-26):
Fairfax Water Corbalis withdrawal - Potomac: 144 MGD
WSSC Water Potomac withdrawal: 154 MGD
Washington Aqueduct withdrawal - Great Falls: 0 MGD
Washington Aqueduct withdrawal - Little Falls: 157 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 5 MGD
Total Potomac withdrawal: 469 MGD
Total net Potomac withdrawal: 463 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 2020 cfs
QPR, obs: 2020 cfs
QPR, WS: 0 cfs
Note to Loudoun Water: See NWS ensemble flow forecasts (HEFS, GEFS, NAEFS) for Point of Rocks flow for the next 7 days – https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS. See US Army Corps of Engineers Potomac River Basin page for observed releases from Savage and Jennings Randolph reservoirs - https://www.nab-wc.usace.army.mil/nab/poto.html; See US Army Corps of Engineers North Branch Potomac River and Savage River page for scheduled releases - https://www.nab-wc.usace.army.mil/nab/northBranch.html.
Note: Potomac River flow at Point of Rocks has dropped below the low-flow threshold of 2,000 cfs. When this occurs, per the Water Supply Coordination Agreement of 1982, CO-OP begins daily monitoring and reporting of Potomac flows and withdrawals on behalf of the CO-OP suppliers, Fairfax Water, Washington Aqueduct, and WSSC Water. Suppliers can review data at CO-OP's Data Portal at www.icprbcoop.org. Reports formatted in approved templates should be submitted by email to coop@icprb.org by 8:00 am for automated processing. Published monitoring reports are at http://icprbcoop.org/products/monitoring-reports.