Daily Potomac flow and demand update (Thursday, 2023-09-21)

Submitted by snummer on Thu, 09/21/2023 - 12:50

Situational Awareness (Thursday, 2023-09-21)
River flows at Little Falls continue to hold relatively steady after the impacts of last weeks' rainfall have receded. Flows at Point of Rocks have risen to over 2000 cfs over the past 24 hours. We are still making daily morning email updates on conditions and will continue to do so until we see conditions remain stable above that threshold.

No appreciable rainfall is expected over the next 24 hours according to the Middle Atlantic River Forecast Center predictions. The next 3 days can expect to see about 0.8 inches of rainfall in the basin.

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: 0.15 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.91 (inches)

Daily flows:
Little Falls gage flow 2023-09-20: 801 MGD (1240 cfs)
Little Falls gage flow 2023-09-21: 808 MGD (est., based on recently available real-time data) (1250 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-20: 1306 MGD (2020 cfs)
Point of Rocks flow 2023-09-21: 1370 MGD (est., based on recently available real-time data) (2120 cfs)

Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-09-20):
Fairfax Water Corbalis withdrawal - Potomac: 121 MGD
WSSC Water Potomac withdrawal: 138 MGD
Washington Aqueduct withdrawal - Great Falls: 143 MGD
Washington Aqueduct withdrawal - Little Falls: 0 MGD
Loudoun Water withdrawal: 6 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 407 MGD
Total net Potomac withdrawal: 401 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 – 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