Aspinall Unit operations update: Crystal Reservoir spill forecasted for May 27, 2019

Aspinall Unit

From email from Reclamation (Erik Knight):

The May 15th forecast for the April – July unregulated inflow volume to Blue Mesa Reservoir is 990,000 acre-feet. This is 147% of the 30 year average. Snowpack in the Upper Gunnison Basin peaked at 143% of average. Blue Mesa Reservoir current content is 457,000 acre-feet which is 55% of full. Current elevation is 7473.2 ft. Maximum content at Blue Mesa Reservoir is 829,500 acre-feet at an elevation of 7519.4 ft.

Based on the May forecasts, 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.)

Pursuant to the Aspinall Unit Operations ROD, 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 latest forecast for flows on the North Fork of the Gunnison River keeps river flows below their projected peak flow level for most of the 10 day forecast period. Warmer weather and higher flows are forecast to return by the first days of June.

Therefore ramp up for the spring peak operation will begin on Wednesday, May 22nd, with the intent of timing releases with this potential higher flow period on the North Fork of the Gunnison River. Releases from Crystal Dam will be ramped up according to the guidelines specified in the EIS, with 2 release changes per day, until Crystal begins to spill. The release schedule for Crystal Dam is:

Crystal Dam will be at full powerplant and bypass release on May 26th. Crystal Reservoir will begin spilling by May 27th and the peak release from Crystal Dam should be reached on May 30th or 31st. The flows in the Gunnison River after that date will be dependent on the timing of the spill and the level of tributary flow contribution. Estimates of those numbers will be determined in the upcoming days.

The current projection for spring peak operations shows flows in the Gunnison River through the Black Canyon between 7,000 cfs and 8,000 cfs for 10 days in order to achieve the desired peak flow and duration at Whitewater. Actual flows will be dependent on the downstream contribution of the North Fork of the Gunnison River and other tributaries. Higher tributary flows will lead to lower releases from the Aspinall Unit and vice versa.

Crystal dam spilling May 2009

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