Daily Potomac flow and demand update (Friday, 2023-09-15)

Submitted by admin1 on Fri, 09/15/2023 - 13:00

Potomac River flows at Little Falls are still elevated due to the recent precipitation. According to the Middle Atlantic River Forecast Center predictions, rainfall averaging about ½ inches is expected in the basin over the next 3 days.

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 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.19 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 1.6 (inches)

Daily flows:
Little Falls gage flow 2023-09-14: 1506 MGD (2330 cfs)
Little Falls gage flow 2023-09-15: 1079 MGD (est., based on recently available real-time data) (1670 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-14: 1053 MGD (1630 cfs)
Point of Rocks flow 2023-09-15: 873 MGD (est., based on recently available real-time data) (1350 cfs)

Yesterday's estimated daily flows:
Great Falls estimated flow 2023-09-14: 1506 MGD (2330 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 (2023-09-14):
Fairfax Water Corbalis withdrawal - Potomac: 107 MGD
WSSC Water Potomac withdrawal: 131 MGD
Washington Aqueduct withdrawal - Great Falls: 154 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 396 MGD
Total net Potomac withdrawal: 390 MGD

Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1630 cfs
QPR, obs: 1630 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.

Daily Monitoring