CO-OP is suspending drought operations because flow at the US Geological Survey’s gage at Little Falls, Maryland, has risen well above the drought operations threshold and is approaching median flows. We will continue sending daily morning updates on conditions while flow at Point of Rocks remains below 2,000 cfs. According to the Middle Atlantic River Forecast Center predictions, the next 24 hours may see 0.3 inches of rain. Over the next three days, the average basin rainfall may be around 0.6 inches.
The Washington Aqueduct plans to suspend their voluntary load shift (withdrawal) at Little Falls.
Thank you for your continued support and cooperation.
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: 0.22 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 1.18 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 1.43 (inches)
Daily flows:
Little Falls gage flow 2023-09-10: 1493 MGD (2310 cfs)
Little Falls gage flow 2023-09-11: 1474 MGD (est., based on recently available real-time data) (2280 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-10: 821 MGD (1270 cfs)
Point of Rocks flow 2023-09-11: 860 MGD (est., based on recently available real-time data) (1330 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2023-09-10: 1557 MGD (2409 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 (2023-09-10):
Fairfax Water Corbalis withdrawal - Potomac: 90 MGD
WSSC Water Potomac withdrawal: 121 MGD
Washington Aqueduct withdrawal - Great Falls: 64 MGD
Washington Aqueduct withdrawal - Little Falls: 64 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 344 MGD
Total net Potomac withdrawal: 337 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-09-10):
FW Occoquan withdrawal: 72 MGD
WSSC Patuxent withdrawal: 50 MGD
Yesterday's total system withdrawal (2023-09-10): 462 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.
Today's estimated total withdrawal* (2023-09-11):
FW estimated withdrawal: 185 MGD
WSSC estimated withdrawal: 177 MGD
Washington Aqueduct estimated withdrawal: 137 MGD
Total estimated withdrawal: 490 MGD
LW estimated withdrawal + purchase: 28 MGD**
*Based on CO-OP daily demand forecasting models. FW includes the LW purchase and excludes Falls Church. Washington Aqueduct includes Falls Church
**LW's estimate is not included in the total estimated withdrawal
Tomorrow's estimated total withdrawal* (2023-09-12):
FW estimated withdrawal: 185 MGD
WSSC estimated withdrawal: 171 MGD
Washington Aqueduct estimated withdrawal: 139 MGD
Total estimated withdrawal: 481 MGD
LW estimated withdrawal + purchase: 27 MGD**
*Based on CO-OP daily demand forecasting models. FW includes the LW purchase and excludes Falls Church. Washington Aqueduct includes Falls Church
**LW's estimate is not included in the total estimated withdrawal
Recommended operations for today (2023-09-11 A.M.):
Fairfax Water:
Per operational preference.
WSSC:
Per operational preference.
Aqueduct:
Per operational preference.
Reservoirs - Recent usable storage as of 2023-09-11 (BG):
Facility, %Full, Current, Usable Capacity*
WSSC’s Patuxent reservoirs, 44%, 4.67, 10.53
Fairfax Water’s Occoquan reservoir, 99%, 8.1, 8.17
Little Seneca Reservoir, 98%, 3.81, 3.87
Jennings Randolph Total Reservoir, 71%, 20.77, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 47%, 7.67, 16.3
Savage Reservoir, 53%, 3.34, 6.33
*Storage capacities for Occoquan, Patuxent, and Little Seneca reservoirs are provided by Washington metropolitan area water utilities based on available data. Jennings Randolph and Savage reservoir capacities are determined from observed water levels and USACE tables from 2013 and 1998, respectively. A correction was made to USACE storage values, previously sourced from a storage estimate provided on the USGS website.
** ICPRB's initial estimate. Final accounting of Jennings Randolph water supply versus water quality storage will be provided at a later date by the USACE.