Morning Potomac flow and demand update (Friday, 2023-09-01)

Submitted by admin1 on Fri, 09/08/2023 - 13:12

According to Middle Atlantic River Forecast Center predictions, no precipitation is anticipated over the next 72 hours. The whitewater releases on August 26th and 27th from Jennings Randolph Reservoir are expected to arrive at Little Falls over the weekend. 


Based on yesterday's daily flow and withdrawals, the numerical trigger for the Alert stage of the Low Flow Allocation Agreement (LFAA) has been met. At this time Washington Aqueduct, in consultation with WSSC Water and Fairfax Water, may declare the LFAA Alert stage because the numerical trigger has been met. 


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: 0.19 (inches)

Past 7-day cumulative area-weighted average basin precipitation: 0.58 (inches)


Daily flows:

Little Falls gage flow 2023-08-31: 388 MGD (600 cfs)

Little Falls gage flow 2023-09-01: 455 MGD (est., based on recently available real-time data) (704 cfs)

Note: Gage flow at Little Falls is measured after water supply withdrawals.

Point of Rocks flow 2023-08-31: 860 MGD (1330 cfs)

Point of Rocks flow 2023-09-01: 847 MGD (est., based on recently available real-time data) (1310 cfs)


Yesterday's Washington metropolitan area Potomac River withdrawals and discharges (2023-08-31):

Fairfax Water Corbalis withdrawal (Potomac): 126 MGD

WSSC Water Potomac withdrawal: 139 MGD

Washington Aqueduct withdrawal - Great Falls: 74 MGD

Washington Aqueduct withdrawal - Little Falls: 73 MGD

Loudoun Water withdrawal: 4 MGD

Loudoun Water Broad Run discharge: 6 MGD

Total Potomac withdrawal: 417 MGD

Total net Potomac withdrawal: 410 MGD


Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2023-08-31):

FW Occoquan withdrawal: 70 MGD

WSSC Patuxent withdrawal: 53 MGD


Yesterday's total system withdrawal (2023-08-31): 535 MGD


Loudoun Water Potomac River (PR) flow values for drought operations protocol (based on yesterday's flows):

QPR: 1330 cfs

QPR, obs: 1330 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


Recommended operations for today (2023-09-01 A.M.):

Fairfax Water:

Per operational preference.



Per operational preference.



Per operational preference.


Reservoirs - Usable storage for yesterday (2023-08-31, BG):

Facility, %Full, Current, Usable Capacity*

WSSC’s Patuxent reservoirs, 50%, 5.21, 10.5

Fairfax Water’s Occoquan reservoir, 96%, 7.89, 8.2

Little Seneca Reservoir, 97%, 3.77, 3.9

Jennings Randolph Total Reservoir, 79%, 23.12, 29.4

Jennings Randolph water supply**, 100%, 13.1, 13.1

Jennings Randolph water quality**, 61%, 10.02, 16.3

Savage Reservoir, 60%, 3.77, 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, by email to, or by telephone by leaving a message with the CO-OP operations number at 301-274-8132. Monitoring emails can be viewed at Thank you for your contribution to the monitoring efforts.


AM Report
Enhanced Operations