Flows at Little Falls are declining, and a Washington Aqueduct load shift to the Little Falls pumps may be needed today. Based on Middle Atlantic River Forecast Center forecasts, we expect ¼ to 1 inch of rainfall in the basin over the next 72 hours, with a basin-wide average of perhaps ½. The longer term forecast is not promising.
The intra-daily flow fluctuations due to upstream hydropower plant operations, Dams 4 and 5, are still affecting flows at Little Falls. We are communicating with the Maryland Department of Environment, and will be reaching out to dam staff on this issue.
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: 0.13 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.14 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.44 (inches)
Daily flows:
Little Falls gage flow 2023-08-28: 498 MGD (770 cfs)
Little Falls gage flow 2023-08-29: 424 MGD (est., based on recently available real-time data) (656 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-08-28: 743 MGD (1150 cfs)
Point of Rocks flow 2023-08-29: 692 MGD (est., based on recently available real-time data) (1070 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-08-28):
Fairfax Water Corbalis withdrawal (Potomac): 122 MGD
WSSC Water Potomac withdrawal: 142 MGD
Washington Aqueduct withdrawal: 149 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 7 MGD
Total Potomac withdrawal: 418 MGD
Total net Potomac withdrawal: 411 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-08-28):
FW Occoquan withdrawal: 74 MGD
WSSC Patuxent withdrawal: 49 MGD
Yesterday's total system withdrawal (2023-08-28): 536 MGD
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 1150 cfs
QPR, obs: 1150 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.
Recommended operations for today (2023-08-29 A.M.):
Per operational preference.
Reservoirs - Usable storage (1969-12-31 A.M., BG):
Facility, %Full, Current, Capacity*
WSSC’s Patuxent reservoirs, 42%, 4.3, 10.2
Fairfax Water’s Occoquan reservoir, 98%, 8.3, 8.5
Little Seneca Reservoir, 97%, 3.8, 3.9
Jennings Randolph Total Reservoir, 80%, 23.44, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 63%, 10.3, 16.3
Savage Reservoir, 61%, 3.85, 6.3
*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.