Situational Awareness (Saturday, 2024-09-21)
Today, CO-OP is suspending its daily drought monitoring and reporting. This phase of CO-OP’s drought response is triggered when daily Potomac River flow at the USGS’s Point of Rocks gage falls below 2000 cubic feet per second (cfs). Yesterday’s flow rose above that threshold and is expected to continue rising due to storms throughout the weekend. The Middle Atlantic River Forecast Center predicts that precipitation in the portion of the Potomac basin upstream of the USGS’s Little Falls gage will average 0.2 inches over the next day, 0.4 inches over the next 3 days, and 1 inch over the next week. Although forecasted rain might not materialize, current information indicates that drought conditions in the Potomac basin are likely to improve, at least through early next week.
We want to express our appreciation to all of the people who provide us with the data we use in our reports: Washington metropolitan area water suppliers at Fairfax Water, Washington Aqueduct, WSSC Water, and Loudoun Water, and also our partner organizations, the US Geological Survey and the Middle Atlantic River Forecast Center.
Special Conditions
At least part of the increase in flow observed at the Point of Rocks gage is likely due to dam operations, which may be artificially elevating the readings.
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: 0.51 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.59 (inches)
Daily flows:
Little Falls gage flow 2024-09-20: 959 MGD ( 1485 cfs)
Little Falls gage flow 2024-09-21: 1008 MGD (est., based on recently available real-time data) (1560 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2024-09-20: 1377 MGD (2130 cfs)
Point of Rocks flow 2024-09-21: 2010 MGD (est., based on recently available real-time data) (3110 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2024-09-20: 1047 MGD (1573 cfs)
Note: Estimated flow below Great Falls intake is flow at Little Falls plus Little Falls water supply withdrawal.
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2024-09-20):
Fairfax Water Corbalis withdrawal - Potomac: 104 MGD
WSSC Water Potomac withdrawal: 114 MGD
Washington Aqueduct withdrawal - Great Falls: 94 MGD
Washington Aqueduct withdrawal - Little Falls: 88 MGD
Loudoun Water withdrawal: 13 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 413 MGD
Total net Potomac withdrawal: 406 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 2130 cfs
QPR, obs: 2130 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 – https://www.weather.gov/erh/mmefs_marfc?id=PORM2&model=NAEFS. See US Army Corps of Engineers Potomac River Basin page for observed releases from Savage and Jennings Randolph reservoirs - https://www.nab-wc.usace.army.mil/nab/poto.html; See US Army Corps of Engineers North Branch Potomac River and Savage River page for scheduled releases - https://www.nab-wc.usace.army.mil/nab/northBranch.html.
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.