@USBR: Aspinall Unit Forecast for Spring Operations: Current projected inflow to Blue Mesa Reservoir = 925,000 acre-feet

From email from Reclamation (Erik Knight):

The April 1 forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 925,000 acre-feet. This is 137% of the 30 year average. Snowpack in the upper Gunnison River basin is currently 132% of average. Blue Mesa Reservoir current content is 259,000 acre-feet which is 31% of full. Current elevation is 7440 feet. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 feet.

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 925,000 acre-feet of runoff volume, the peak flow target will be 6,513 cfs for a duration of 24 hours. The shoulder flow target will be 915 cfs, for the period between May 1 and July 25. The point of measurement of flows to satisfy the Black Canyon Water Right is at 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 925,000 acre-feet of runoff volume, the hydrologic year type will be set as Moderately Wet. Under a Moderately Wet year the peak flow target will be 14,350 cfs and the duration target at this flow will be 10 days. The duration target for the half-bankfull flow of 8,070 cfs will be 20 days. The criteria have been met for the drought rule that allows half-bankfull flows to be reduced from 40 days to 20 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 over 7,500 cfs for 10 days in order to achieve the desired peak flow and duration at Whitewater. With this runoff forecast and corresponding downstream targets, Blue Mesa Reservoir is currently projected to fill to an elevation of around 7500 feet with an approximate peak content of 660,000 acre-feet.

Aspinall Unit dams

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