According to Middle Atlantic River Forecast Center forecasts, small amounts of rain are expected in the basin tomorrow, and accumulations of approximately ½ inch are expected over the next three days. The longer-term forecasts are currently very promising, with accumulations of 1 to 2 inches expected. Tropical Storm Lee is expected to become a major hurricane, with potential impacts on the eastern US.
ICPRB staff met with Chesapeake & Ohio (C&O) Canal National Historical Park and Eagle Creek Renewable staff regarding the large intra-daily fluctuations in river flows caused by upstream operations at Dam 4 and 5.
National Park Service is performing hi-definition LIDAR scans of Potomac Dam No. 4, near Sharpsburg, MD to develop measured drawings and document/assess the dam conditions. A LIDAR scan is planned on September 6 or 7. They plan to adjust their operations to minimize the amount of disruption to downstream river flows.
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 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.09 (inches)
Daily flows:
Little Falls gage flow 2023-09-05: 364 MGD (563 cfs)
Little Falls gage flow 2023-09-06: 351 MGD (est., based on recently available real-time data) (543 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-05: 685 MGD (1060 cfs)
Point of Rocks flow 2023-09-06: 679 MGD (est., based on recently available real-time data) (1050 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-09-05):
Fairfax Water Corbalis withdrawal - Potomac: 144 MGD
WSSC Water Potomac withdrawal: 142 MGD
Washington Aqueduct withdrawal - Great Falls: 73 MGD
Washington Aqueduct withdrawal - Little Falls: 78 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 3 MGD
Total Potomac withdrawal: 443 MGD
Total net Potomac withdrawal: 439 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-09-05):
FW Occoquan withdrawal: 95 MGD
WSSC Patuxent withdrawal: 64 MGD
Yesterday's total system withdrawal (2023-09-05): 597 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1060 cfs
QPR, obs: 1060 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* (2023-09-06):
FW estimated withdrawal: 186 MGD
WSSC estimated withdrawal: 180 MGD
Washington Aqueduct estimated withdrawal: 145 MGD
Total estimated withdrawal: 510 MGD
LW estimated withdrawal + purchase: 30 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* (2023-09-07):
FW estimated withdrawal: 180 MGD
WSSC estimated withdrawal: 178 MGD
Washington Aqueduct estimated withdrawal: 146 MGD
Total estimated withdrawal: 504 MGD
LW estimated withdrawal + purchase: 29 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 (2023-09-06 A.M.):
Fairfax Water:
Keep Potomac withdrawals as steady as possible.
WSSC:
Keep Potomac withdrawals as steady as possible.
Aqueduct:
Keep Little Falls withdrawals as steady as possible. Great Falls per operational preference.
Reservoirs - Usable storage for yesterday (2023-09-05, BG):
Facility, %Full, Current, Usable Capacity*
WSSC’s Patuxent reservoirs, 47%, 4.98, 10.53
Fairfax Water’s Occoquan reservoir, 94%, 7.7, 8.17
Little Seneca Reservoir, 97%, 3.76, 3.87
Jennings Randolph Total Reservoir, 76%, 22.47, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 57%, 9.37, 16.3
Savage Reservoir, 57%, 3.59, 6.33
*Storage and capacities for Occoquan, Patuxent and Little Seneca reservoirs are provided by Washington metropolitan area water utilities, and based on best available information. Storage and capacities for Jennings Randolph and Savage reservoirs are based on observed water levels and available US ACE water level/storage tables from 1998. ICPRB estimates that sedimentation has resulted in a loss of total available storage in Jennings Randolph Reservoir of 1.6 BG in recent years, and this loss is not reflected in the numbers above.
** ICPRB's initial estimate. Final accounting of Jennings Randolph water supply versus water quality storage will be provided at a later date by the US ACE.
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.