Daily Potomac flow and demand update (Saturday, 2023-10-28)
Situational Awareness (Saturday, 2023-10-28)
Overall, Potomac River flows continue to slowly decline. But yesterday, National Park Service contractors temporarily adjusted operations at Dam 4 in order to collect more bathymetric data, causing a sharp increase and then decrease in river flow. This intra-daily fluctuation of almost 1000 cfs can be viewed at the Shepherdstown gage: https://waterdata.usgs.gov/monitoring-location/01618000/#parameterCode=00060&period=P30D&showMedian=true. The temporary rise in flow is now visible at the Point of Rocks gage.
According to Middle Atlantic River Forecast Center predictions, rainfall in the watershed above the Little Falls gage will average approximately 0.2 inches 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: 0.02 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.02 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.09 (inches)
Daily flows:
Little Falls gage flow 2023-10-27: 750 MGD (1160 cfs)
Little Falls gage flow 2023-10-28: 737 MGD (est., based on recently available real-time data) (1140 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-10-27: 821 MGD (1270 cfs)
Point of Rocks flow 2023-10-28: 1047 MGD (est., based on recently available real-time data) (1620 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2023-10-27: 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 (2023-10-27):
Fairfax Water Corbalis withdrawal - Potomac: 97 MGD
WSSC Water Potomac withdrawal: 134 MGD
Washington Aqueduct withdrawal - Great Falls: 62 MGD
Washington Aqueduct withdrawal - Little Falls: 64 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 362 MGD
Total net Potomac withdrawal: 356 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-10-27):
FW Occoquan withdrawal: 70 MGD
WSSC Patuxent withdrawal: 32 MGD
Yesterday's total system withdrawal (2023-10-27): 459 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1270 cfs
QPR, obs: 1270 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.