Aspinall Unit forecast for spring operations

Aspinall Unit
Aspinall Unit

From email from Reclamation (Erik Knight):

The March 15th forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 590,000 acre-feet. This is 87% of the 30 year average. Snowpack in the Gunnison Basin is currently at 78% of average. Blue Mesa Reservoir current content is 551,800 acre-feet which is 67% of full. Current elevation is 7486.2 ft. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 ft.

Black Canyon Water Right
The peak flow and shoulder flow components of the Black Canyon Water Right will be determined by the May 1 forecast of the April – July unregulated inflow volume to Blue Mesa Reservoir. If the May 1 forecast is equal to the current forecast of 590,000 acre-feet of runoff volume, the peak flow target will be equal to 4,340 cfs for a duration of 24 hours. The shoulder flow target will be 381 cfs, for the period between May 1 and July 25. The point of measurement of flows to satisfy the Black Canyon Water Right is the Gunnison River below Gunnison Tunnel streamgage at the upstream boundary of Black Canyon of the Gunnison National Park.

Aspinall Unit Operations ROD
Pursuant to the Aspinall Unit Operations Record of Decision (ROD), the peak flow and duration flow targets in the lower Gunnison River, as measured at the Whitewater gage, will be determined by the forecast of the April – July unregulated inflow volume to Blue Mesa Reservoir and the hydrologic year type. At the time of the spring operation, if the forecast is equal to the current forecast of 590,000 acre-feet of runoff volume, the hydrologic year type will be set as Average Dry. Under an Average Dry year the peak flow target will be 8,070 cfs and the duration target at this flow will be 10 days.

Projected Spring Operations
During spring operations, releases from the Aspinall Unit will be made in an attempt to match the peak flow of the North Fork of the Gunnison River to maximize the potential of meeting the desired peak at the Whitewater gage, while simultaneously meeting the Black Canyon Water Right peak flow amount. The magnitude of release necessary to meet the desired peak at the Whitewater gage will be dependent on the flow contribution from the North Fork of the Gunnison River and other tributaries downstream from the Aspinall Unit. Current projections for spring peak operations show that flows in the Gunnison River through the Black Canyon could be in the 5,000 to 5,500 cfs range for 10 days in order to achieve the desired peak flow and duration at Whitewater. If actual flows on the North Fork of the Gunnison River are less than currently projected, flows through the Black Canyon could be even higher. With this runoff forecast and corresponding downstream targets, Blue Mesa Reservoir is currently projected to fill to an elevation of around 7508.2 feet with an approximate peak content of 730,000 acre-feet.

Downstream flow targets and the projected spring operations to meet them will change with revisions to the forecast and are highly dependent on tributary flows throughout the Gunnison Basin.

More Aspinall Unite coverage here.

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