Situational Awareness (Friday, 2024-07-19)
Dry conditions persist and Potomac basin stream flows continue to decline. According to the Middle Atlantic River Forecast Center, the Potomac watershed above Little Falls is expected to receive no precipitation over the next day, 0.2 inches over the next 3 days, and 1.1 inches over the next week.
Special Conditions
National Park Service contractor dam inspection work on July 16 and 17 at Dams 4 and 5 are affecting downstream flows. The flow fluctuations are clearly visible at the Point of Rocks gage – see this morning’s hydrograph from the USGS’s NWIS website:
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: 0.32 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.53 (inches)
Daily flows:
Little Falls gage flow 2024-07-18: 937 MGD (1450 cfs)
Little Falls gage flow 2024-07-19: 821 MGD (est., based on recently available real-time data) (1270 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-07-18: 918 MGD (1420 cfs)
Point of Rocks flow 2024-07-19: 905 MGD (est., based on recently available real-time data) (1400 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-07-18: 1066 MGD (1649 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 (2024-07-18):
Fairfax Water Corbalis withdrawal - Potomac: 106 MGD
WSSC Water Potomac withdrawal: 130 MGD
Washington Aqueduct withdrawal - Great Falls: 0 MGD
Washington Aqueduct withdrawal - Little Falls: 129 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 378 MGD
Total net Potomac withdrawal: 371 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1420 cfs
QPR, obs: 1420 cfs
QPR, WS: 0 cfs