SUSPENDING DAILY MONITORING - Daily Potomac flow and demand update (Monday, 2023-09-25)

Submitted by admin1 on Mon, 09/25/2023 - 12:39

Situational Awareness (Monday, 2023-09-25)

CO-OP is suspending drought operations because flow at the US Geological Survey’s gage at Point of Rocks, Maryland, has risen above the daily monitoring threshold of 2000 cfs. We will resume monitoring should flows fall below the 2000 cfs threshold. The basin received close to 2 inches of rain over the past 7 days.  According to the Middle Atlantic River Forecast Center predictions, the basin may receive 0.1 inches over the coming week. Thank you for your continued support and cooperation.


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: 0.89 (inches)

Past 3-day cumulative area-weighted average basin precipitation: 1.82 (inches)

Past 7-day cumulative area-weighted average basin precipitation: 1.95 (inches)


Daily flows:

Little Falls gage flow 2023-09-24: 3581 MGD (5540 cfs)

Little Falls gage flow 2023-09-25: 3206 MGD (est., based on recently available real-time data) (4960 cfs)

Note: Gage flow at Little Falls is measured after water supply withdrawals.

Point of Rocks flow 2023-09-24: 1338 MGD (2070 cfs)

Point of Rocks flow 2023-09-25: 1687 MGD (est., based on recently available real-time data) (2610 cfs)


Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-09-24):

Fairfax Water Corbalis withdrawal - Potomac: 84 MGD

WSSC Water Potomac withdrawal: 113 MGD

Washington Aqueduct withdrawal - Great Falls: 134 MGD

Washington Aqueduct withdrawal - Little Falls: 0 MGD

Loudoun Water withdrawal: 5 MGD

Loudoun Water Broad Run discharge: 7 MGD

Total Potomac withdrawal: 335 MGD

Total net Potomac withdrawal: 329 MGD


Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):

QPR: 2070 cfs

QPR, obs: 2070 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 – see


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 Reports formatted in approved templates should be submitted by email to by 8:00 am for automated processing. Published monitoring reports are at

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