According to Middle Atlantic River Forecast Center predictions, the next three days may see approximately 1.5 inches of rainfall.
ICPRB continues to work to improve projected demands and incorporate supplier projections. In an effort to provide the most robust projections possible, we will be contacting suppliers and asking them to begin sending a supplemental email each morning with predicted total and off Potomac withdrawals (in MGD) for today and tomorrow.
The proactive voluntary load shift from Great Falls to Little Falls by Washington Aqueduct is still ongoing.
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: 0.23 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.25 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.25 (inches)
Daily flows:
Little Falls gage flow 2023-09-07: 293 MGD (453 cfs)
Little Falls gage flow 2023-09-08: 337 MGD (est., based on recently available real-time data) (522 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-07: 821 MGD (1270 cfs)
Point of Rocks flow 2023-09-08: 593 MGD (est., based on recently available real-time data) (917 cfs)
Yesterday's estimated daily flows:
Great Falls estimated flow 2023-09-07: 364 MGD (563 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 (2023-09-07):
Fairfax Water Corbalis withdrawal - Potomac: 147 MGD
WSSC Water Potomac withdrawal: 142 MGD
Washington Aqueduct withdrawal - Great Falls: 97 MGD
Washington Aqueduct withdrawal - Little Falls: 71 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 5 MGD
Total Potomac withdrawal: 461 MGD
Total net Potomac withdrawal: 456 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-09-07):
FW Occoquan withdrawal: 83 MGD
WSSC Patuxent withdrawal: 55 MGD
Yesterday's total system withdrawal (2023-09-07): 594 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* (2023-09-08):
FW estimated withdrawal: 173 MGD
WSSC estimated withdrawal: 172 MGD
Washington Aqueduct estimated withdrawal: 144 MGD
Total estimated withdrawal: 489 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* (2023-09-09):
FW estimated withdrawal: 172 MGD
WSSC estimated withdrawal: 170 MGD
Washington Aqueduct estimated withdrawal: 132 MGD
Total estimated withdrawal: 475 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 (2023-09-08 A.M.):
Fairfax Water:
Keep Potomac withdrawals as steady as possible.
WSSC:
Keep Potomac withdrawals as steady as possible.
Aqueduct:
Keep withdrawals as steady as possible. Gradual changes are preferred to sharp changes.
Reservoirs - Recent usable storage as of 2023-09-08 (BG):
Facility, %Full, Current, Usable Capacity*
WSSC’s Patuxent reservoirs, 45%, 4.74, 10.53
Fairfax Water’s Occoquan reservoir, 93%, 7.62, 8.17
Little Seneca Reservoir, 97%, 3.76, 3.87
Jennings Randolph Total Reservoir, 72%, 21.06, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 49%, 7.96, 16.3
Savage Reservoir, 53%, 3.37, 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.
Note: Flow levels have dropped to a level that has triggered enhanced monitoring, per the drought operations manual of the Water Supply Coordination Agreement. When adjusted flow at Little Falls (adjusted flow is gage flow plus upstream withdrawals) less the environmental flow is less than twice the Washington metropolitan area withdrawals, the water suppliers will begin reporting yesterday's and today's withdrawals and this morning's reservoir storage volumes. ICPRB asks that communications be sent by 7:30 am and updates sent by 1:00 pm. Reporting can be submitted through www.icprbcoop.org, by email to coop@icprb.org, or by telephone by leaving a message with the CO-OP operations number at 301-274-8132. Monitoring emails can be viewed at http://icprbcoop.org/products/monitoring-reports. Thank you for your contribution to the monitoring efforts.