The recent rainfall in the Potomac basin, averaging ¼ inch, has not significantly changed streamflows. Operation of hydroelectric dams on the Potomac River, Dams 4 and 5, are resulting in high peaks and low troughs in flow, which are visible at the USGS Potomac River streamflow gages at Shepherdstown, Point of Rocks, and Little Falls. A flow peak is currently at Little Falls, but we expect a trough to arrive at water supply intakes and at Little Falls late tomorrow. CO-OP staff will be reaching out to Maryland Department of Environment and to the dam owner in the coming week concerning 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: 0.25 (inches)
Past 3-day cumulative area-weighted average basin precipitation: 0.3 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.3 (inches)
Daily flows:
Little Falls gage flow 2023-08-25: 582 MGD (900 cfs)
Little Falls gage flow 2023-08-26: 898 MGD (est., based on recently available real-time data) (1390 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-08-25: 636 MGD (984 cfs)
Point of Rocks flow 2023-08-26: 957 MGD (est., based on recently available real-time data) (1480 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-08-25):
Fairfax Water Corbalis withdrawal (Potomac): 128 MGD
WSSC Water Potomac withdrawal: 144 MGD
Washington Aqueduct withdrawal: 142 MGD
Loudoun Water withdrawal: 5 MGD
Loudoun Water Broad Run discharge: 5 MGD
Total Potomac withdrawal: 419 MGD
Total net Potomac withdrawal: 414 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-08-25):
FW Occoquan withdrawal: 72 MGD
WSSC Patuxent withdrawal: NA MGD
Yesterday's total system withdrawal (2023-08-25): 502 MGD
Not sufficient data.
Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):
QPR: 984 cfs
QPR, obs: 984 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 (2023-08-26 A.M.):
None at this time.
Reservoirs - Usable storage (1969-12-31 A.M., BG):
Facility, %Full, Current, Capacity*
WSSC’s Patuxent reservoirs, 54%, 5.5, 10.2
Fairfax Water’s Occoquan reservoir, 102%, 8.2, 8.05
Little Seneca Reservoir, 97%, 3.8, 3.9
Jennings Randolph Total Reservoir, 82%, 24.1, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 67%, 11.0, 16.3
Savage Reservoir, 63%, 3.94, 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.