Aspinall Unit and Gunnison Tunnel Operations
June 17, 2021 Update from Ryan Christian, – USBR
Gunnison River flows have dropped off quickly over the last few days and there is a need for more water in the Gunnison River to meet the target of 1050 cfs, pursuant to the Aspinall Unit Operations Record of Decision (ROD). Therefore, releases from the Aspinall Unit will be increased by 150 cfs tomorrow afternoon, June 18th at 2pm.
Currently, diversions into the Gunnison Tunnel are 1040 cfs and flows in the Gunnison River through the Black Canyon are around 475 cfs. After these release changes, flows in the Gunnison River through the Black Canyon will be around 625 cfs. Current flow information is obtained from provisional data that may undergo revision subsequent to review.
This scheduled release change is subject to changes in river flows and weather conditions. For questions or concerns regarding these operations contact:
Erik Knight at (970) 248-0629, e-mail: [email protected]
Ryan Christianson at (970) 248-0652, email: [email protected]
Aspinall Unit Operations, January 2021
Erik Knight, US Bureau of Reclamation
Background: A Record of Decision for the Aspinall Unit Operations Environmental Impact Statement was signed on May 3, 2012. The EIS modifies the operations of the Aspinall Unit to provide sufficient releases of water at times, quantities, and durations necessary to avoid jeopardy to endangered fish species and adverse modification of their designated critical habitat while maintaining and continuing to meet authorized purposes of the Aspinall Unit. Meetings regarding the operations of the Aspinall Unit are open to stakeholders, and take place tri-annually, with meetings typically occurring in January, April, and August of each year.
April thru December precipitation has been near record low for many sites within the Gunnison Basin. Soil moisture conditions are drier than they were at this time a year ago. Snow conditions are well below normal as of mid-January. Snowpack in much of the Upper Gunnison Basin is in the 50-70% of normal range.
The mid-January runoff forecast for Blue Mesa Reservoir predicts 470,000 AF of runoff which is 70% of average. Below normal soil moisture, precipitation, and SWE conditions are the primary contributors to the below average water supply outlook.
Blue Mesa Reservoir finished 2020 at an elevation of 7465 ft, which is 25 feet below the winter target of 7490 ft.
Spring Flow Targets: Current runoff forecasts for major streams within the Gunnison Basin range between 50% and 75% of average. The runoff forecast for Blue Mesa Reservoir would put this year into the Moderately Dry category. In the Moderately Dry category the ROD peak target would be 5,000 cfs. This is due to the activation of a drought rule which reduces the peak target to 5,000 cfs (from 6,200 cfs) when a Moderately Dry year (2021 forecast) follows a Moderately Dry year (2020 actual runoff). This rule will come into effect if the content in Blue Mesa Reservoir is under 400,000 AF on either March 31 or April 30, 2021.
In a Moderately Dry year there are no duration days at half bankfull or peak flow. The peak at the Whitewater gage would last for 1 day. The Black Canyon water right 1day peak flow target would be 2,510 cfs if the May 1 forecast is the same as the January 15 forecast.
Future Operations: After the spring peak, operations at Aspinall will continue to meet the baseflow targets at the Whitewater gage. In the Moderately Dry category these targets range between 750 cfs and 1050 cfs from summer into winter. Blue Mesa Reservoir is currently projected to fill to a maximum content of 573,000 AF (69% full).
Weather Outlook – Aldis Strautins (National Weather Service)
Temperatures this water year have been normal to slightly cool, while precipitation remains well below normal. Extreme drought in the upper basin and exceptional drought in the lower basin remain entrenched. ENSO-La Nina conditions are present and are expected to continue this winter and then transition toward neutral during the spring. A more progressive pattern is indicated for the second half of January and into early February which would allow more storms and increased precipitation and snow chances. Spring into early summer longer range forecasts indicate higher chances of below normal precipitation and higher chances of above normal temperatures.
Useful information from previous operational updates:
Downstream Flow Targets
Downstream flow targets are finalized based on the May runoff forecast for unregulated inflow to Blue Mesa Reservoir
Aspinall Unit Operations ROD
Hydrologic Category = Moderately Dry
Peak Flow Target = 3200 cfs
Duration at Peak Flow Target = 1 day
Baseflow Target: May = 890 cfs | June/July/Aug = 1050 cfs
(Point of measurement is the Gunnison River near Grand Junction streamgage, commonly called the Gunnison River at Whitewater)
Black Canyon Water Right
Peak Flow Target = 2200 cfs (24 hour duration)
Shoulder Flow Target = 300 cfs (May 1 – July 25)
(Point of measurement is the Gunnison River below Gunnison Tunnel streamgage at the upstream boundary of Black Canyon of the Gunnison National Park)
Blue Mesa Dam (looking east, upstream)