Daily Potomac flow and demand update (Monday, 2023-09-18)

Submitted by admin1 on Tue, 09/19/2023 - 11:56

Situational Awareness (Monday, 2023-09-18)
River flows have fallen over the past several days as the impact of last week’s rainfall recedes. But the basin received about ¾ of an inch over the weekend, so we expect flows to start rising modestly again. No rain is expected in the basin over the next three days.

The USACE made a whitewater release from Jennings Randolph Reservoir on Saturday, September 16. During this release, flows were increased from approximately 225 cfs to approximately 1000 cfs from 10 AM to 4 PM for the benefit of recreational users.

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: 0.76 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.76 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 1.18 (inches)

Daily flows:
Little Falls gage flow 2023-09-17: 814 MGD (1260 cfs)
Little Falls gage flow 2023-09-18: 782 MGD (est., based on recently available real-time data) (1210 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-17: 905 MGD (1400 cfs)
Point of Rocks flow 2023-09-18: 1021 MGD (est., based on recently available real-time data) (1580 cfs)

Yesterday's estimated daily flows:
Great Falls estimated flow 2023-09-17: 814 MGD (1259 cfs)
Note: Estimated as gage flow at Little Falls plus Little Falls water supply withdrawal.

Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-09-17):
Fairfax Water Corbalis withdrawal - Potomac: 95 MGD
WSSC Water Potomac withdrawal: 136 MGD
Washington Aqueduct withdrawal - Great Falls: 128 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 363 MGD
Total net Potomac withdrawal: 356 MGD

Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1400 cfs
QPR, obs: 1400 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 https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS.

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.


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