Aspinall Unit Forecast for Spring Operations – May 10, 2019
From Erik Knight, Bureau of Reclamation
The May 1st forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 970,000 acre-feet. This is 144% of the 30 year average. Snowpack in the Upper Gunnison Basin peaked at 143% of average. Blue Mesa Reservoir current content is 384,000 acre-feet which is 46% of full. Current elevation is 7462 ft. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 ft.
Based on the May 1st forecast, the Black Canyon Water Right and Aspinall Unit ROD peak flow targets are listed below:
Black Canyon Water Right
The peak flow target is equal to 7,158 cfs for a duration of 24 hours.
The shoulder flow target is 966 cfs, for the period between May 1 and July 25.
Aspinall Unit Operations ROD
The year type is currently classified as Moderately Wet.
The peak flow target will be 14,350 cfs and the duration target at this flow will be 10 days.
The half bankfull target will be 8,070 cfs and the duration target at this flow 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 8,000 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 7515.5 feet with an approximate peak content of 795,000 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.