This is Day 2 of the annual Washington metropolitan area (WMA) drought exercise. The exercise scenario appears below. During the exercise, WMA water suppliers are sending data on withdrawals and reservoir levels twice daily, and ICPRB CO-OP staff are communicating via phone with supplier operations staff regarding requested operational changes.
EXERCISE SCENARIO
The day is Thursday, August 27, 2020 and the basin is in moderate drought. The region experienced a “flash drought” during September of last year, and precipitation continued to be low throughout the past fall and winter. CO-OP began daily drought monitoring in mid-June, when Potomac River flow at Point of Rocks, Maryland fell below 2000 cubic feet per second. Enhanced drought monitoring began on Friday, July 24, when daily flow in the Potomac River above the Washington metropolitan area intakes, less the amount required for the flow-by over Little Falls Dam, fell to a level less than twice the total daily withdrawals. Releases from upstream reservoirs, Jennings Randolph and Little Seneca, began in early August. Combined upstream storage is currently 11.4 billion gallons (BG) (simulated), or 67% of combined capacity. The drought stage, per the MWCOG regional plan, is “Watch”.
This morning, simulated hourly flow at Little Falls has dipped below 100 MGD. We believe this to be due to a temporary elevation in the previous night's withdrawals on the Potomac. But as a precautionary measure, a WSSC load shift to the Patuxent is being implemented to ensure that average daily flow is above 100 MGD at Little Falls. We have also increased the Little Seneca release to 100 MGD based on today's 1-day flow forecast for Little Falls. There is a high probability of substantial rain in the next three days, which should alleviate dry conditions.
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ACTUAL CONDITIONS REPORTED BELOW
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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 precip: 0.00 (inches)
Past 3-day cumulative area-weighted average basin precip: 0.01 (inches)
Past 7-day cumulative area-weighted average basin precip: 0.01 (inches)
Daily Flows:
Little Falls gage flow 2019-11-20: 1790 MGD (2770 cfs)
Little Falls gage flow 2019-11-21: 1680 MGD (est., based on recently available real time data) (2600 cfs)
Note: Gage flow at Little Falls is measured after water supply withdrawals.
Point of Rocks flow 2019-11-20: 1551 MGD (2400 cfs)
Point of Rocks flow 2019-11-21: 1428 MGD (est., based on recently available real time data) (2210 cfs)
Yesterday's Net Potomac withdrawal (2019-11-20):
FW Corbalis withdrawal (Potomac): 86 MGD
WSSC Potomac withdrawal: 110 MGD
Aqueduct withdrawal: 110 MGD
Loudoun withdrawal: 10 MGD
Total Potomac withdrawal: 316 MGD
Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2019-11-20):
FW Occoquan withdrawal: 65 MGD
WSSC Patuxent withdrawal: 39 MGD
Total system withdrawal: 410 MGD
Loudoun Water Broad Run discharge:
Yesterday's (2019-11-20): 5 MGD
Today's (2019-11-21): 5 MGD
Tomorrow's (2019-11-22): 5 MGD
Today's estimated production* (2019-11-21):
FW estimated production: 160 MGD
WSSC estimated production: 142 MGD
Aqueduct estimated production: 137 MGD
Total estimated production: 439 MGD
*Based on CO-OP daily demand forecasting models
Tomorrow's estimated production* (2019-11-22):
FW estimated production: 159 MGD
WSSC estimated production: 143 MGD
Aqueduct estimated production: 136 MGD
Total estimated production: 438 MGD
*Based on CO-OP daily demand forecasting models
Reservoirs - Usable storage (2019-11-21 A.M., BG):
Facility, %Full, Current, Capacity*
WSSC’s Patuxent reservoirs, 46%, 4.67, 10.2
Fairfax Water’s Occoquan reservoir, 95%, 8.05, 8.5
Little Seneca Reservoir, 99%, 3.87, 3.9
Jennings Randolph Total Reservoir, 64%,18.9, 29.4
Jennings Randolph water supply**, 100%, 13.1, 13.1
Jennings Randolph water quality**, 36%, 5.8, 16.3
Savage Reservoir, 41%, 2.6, 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.
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SIMULATED CONDITIONS AND DROUGHT OPERATIONS APPEAR BELOW
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Recommended operations (simulated) for today (2019-11-21 A.M.):
Fairfax Water:
Occoquan/Griffith - maintain maximum production at plant (simulated)
Potomac/Corbalis - per operational preference, but keeping Potomac withdrawal rate as steady as possible
WSSC:
Patuxent - immediate load shift to maximum 65 MGD production (simulated, assuming no maintenance constraints; due to dam maintenance, 40 MGD is current actual Patuxent plant max)
Potomac - per operational preference, but keeping Potomac withdrawal rate as steady as possible
Seneca (release date, time, amount in MGD):
Immediate increase release from Little Seneca Reservoir to 100 MGD (simulated)
Aqueduct:
No change in operations requested. Continue making entire withdrawal from Little Falls (simulated)
North Branch Reservoirs A.M. Summary:
Jennings Randolph water supply release (simulated): Luke target of 255 cfs (165 MGD)