Potomac River flows at Little Falls have increased slightly, we believe due to last weekend’s Jennings Randolph Reservoir whitewater recreational releases along with the past week’s modest precipitation in the upper basin. According to National Weather Service, no rainfall is expected in the Potomac basin over the next three days. The week-long outlook points to an approximate total of 0.1 inches across the basin.
Based on yesterday's daily flow and withdrawals, flows increased above the numerical threshold for the Alert Stage of the Low Flow Allocation Agreement (LFAA).
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: 0.09 (inches)
Past 7-day cumulative area-weighted average basin precipitation: 0.33 (inches)
Daily flows:
Little Falls gage flow 2023-09-01: 457 MGD (707 cfs)
Little Falls gage flow 2023-09-02: 519 MGD (est., based on recently available real-time data) (803 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2023-09-01: 821 MGD (1270 cfs)
Point of Rocks flow 2023-09-02: 724 MGD (est., based on recently available real-time data) (1120 cfs)
Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-09-01):
Fairfax Water Corbalis withdrawal - Potomac: 133 MGD
WSSC Water Potomac withdrawal: 142 MGD
Washington Aqueduct withdrawal - Great Falls: 67 MGD
Washington Aqueduct withdrawal - Little Falls: 83 MGD
Loudoun Water withdrawal: 4 MGD
Loudoun Water Broad Run discharge: 6 MGD
Total Potomac withdrawal: 429 MGD
Total net Potomac withdrawal: 423 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-09-01):
FW Occoquan withdrawal: 70 MGD
WSSC Patuxent withdrawal: 48 MGD
Yesterday's total system withdrawal (2023-09-01): 543 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.
Recommended operations for today (2023-09-02 A.M.):
Fairfax Water:
Per operational preference.
WSSC:
Per operational preference.
Aqueduct:
Per operational preference.
Reservoirs - Usable storage for yesterday (2023-09-01, BG):
Facility, %Full, Current, Usable Capacity*
WSSC’s Patuxent reservoirs, 49%, 5.17, 10.53
Fairfax Water’s Occoquan reservoir, 96%, 7.85, 8.17
Little Seneca Reservoir, 97%, 3.77, 3.87
Jennings Randolph Total Reservoir, 78%, 23.01, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 61%, 9.91, 16.3
Savage Reservoir, 59%, 3.71, 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.