2019 Annual WMA Drought Exercise, Morning Potomac flow and demand update (Wednesday 2019-11-20)

This is Day 1 of the annual Washington metropolitan area (WMA) drought exercise, which will be conducted on Wednesday, Nov 20 and Thursday, Nov 21. 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 Wednesday, August 26, 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 11.5 BG (simulated), or 68% of combined capacity. The drought stage, per the MWCOG regional plan, is “Watch”.

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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: 0.01 (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 2019-11-19: 1790 MGD (2770 cfs)

Little Falls gage flow 2019-11-20: 1745 MGD (est., based on recently available real time data) (2700 cfs)

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

Point of Rocks flow 2019-11-19: 1616 MGD (2500 cfs)

Point of Rocks flow 2019-11-20: 1461 MGD (est., based on recently available real time data) (2260 cfs)

Yesterday's Net Potomac withdrawal (2019-11-19):

FW Corbalis withdrawal (Potomac): 91 MGD

WSSC Potomac withdrawal: 114 MGD

Aqueduct withdrawal: 112 MGD

Loudoun withdrawal: 10 MGD

Total Potomac withdrawal: 327 MGD

Yesterday's Patuxent, Occoquan, and Net Total System Withdrawal (2019-11-19):

FW Occoquan withdrawal: 67 MGD

WSSC Patuxent withdrawal: 39 MGD

Total system withdrawal: 422 MGD

Loudoun Water Broad Run discharge:

Yesterday's (2019-11-19): 5 MGD

Today's (2019-11-20): 5 MGD

Tomorrow's (2019-11-21): 5 MGD

Today's estimated production* (2019-11-20):

FW estimated production: 159 MGD

WSSC estimated production: 141 MGD

Aqueduct estimated production: 135 MGD

Total estimated production: 435 MGD

*Based on CO-OP daily demand forecasting models

Tomorrow's estimated production* (2019-11-21):

FW estimated production: 155 MGD

WSSC estimated production: 141 MGD

Aqueduct estimated production: 135 MGD

Total estimated production: 431 MGD

*Based on CO-OP daily demand forecasting models

Reservoirs - Usable storage (actual on 2019-11-20 A.M., BG):

Facility, %Full, Current, Capacity*

WSSC’s Patuxent reservoirs, 46%, 4.69, 10.2

Fairfax Water’s Occoquan reservoir, 96%, 8.12, 8.5

Little Seneca Reservoir, 99%, 3.88, 3.9

Jennings Randolph Total Reservoir, 65%, 19.0, 29.4

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

Jennings Randolph water quality**, 36%, 5.9, 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 (2019-11-20 A.M.):

Fairfax Water:

Occoquan/Griffith - increase production (simulated) by 30 MGD from yesterday's rate

Potomac/Corbalis - per operational preference, but keeping Potomac withdrawal rate as steady as possible

WSSC:

Keep Potomac withdrawal rate (simulated) as steady as possible.

Seneca (release date, time, amount in MGD):

Initiate release from Little Seneca Reservoir of 12 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 223 cfs (144 MGD)