Main MenuAspinall Unit and Gunnison Tunnel Operations
May 11, 2021 Update from Erik Knight – USBR
Highlights:
The spring peak from the Aspinall Unit will occur on Saturday, May 15th
Flows in the Gunnison River through the Black Canyon will increase to 1,000 cfs for 24 hours
After the spring peak ramp down flows in the Gunnison River through the Black Canyon will drop to 500 cfs
Details of current status and future operations:
Upper Gunnison Basin Snowpack
Current = 52% of median
Total Accumulation = 73% of average
April – July unregulated inflow volume to Blue Mesa Reservoir
Current Forecast (May 1) = 340,000 AF (50% of average)
Blue Mesa Reservoir current conditions
Content = 354,000 AF
Elevation = 7458 ft
Inflow = 1000 cfs
Crystal Release = 1700 cfs
Gunnison Tunnel diversion = 1050 cfs
Gunnison River flow = 700 cfs
Downstream Flow Targets
Downstream flow targets have been finalized based on the May runoff forecast for unregulated inflow to Blue Mesa Reservoir.
Aspinall Unit Operations ROD
Hydrologic Category = Dry
Peak Flow Target = 900 cfs
Duration at Peak Flow Target = 1 day
Baseflow Target: May = 890 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 = 973 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)
Projected Spring Operations Highlights
1 day peak flow ~ 1000 cfs in Gunnison River through the Black Canyon & Gunnison Gorge
Peak flow of ~ 1900 cfs in Gunnison River at Delta
Peak flow ~ 2200 cfs in lower Gunnison River (measured at Whitewater gage)
Projected Blue Mesa Reservoir maximum fill = 443,000 AF at 7472 ft elevation
Projected Blue Mesa Reservoir conditions on Dec 31 = 309,000 AF at 7450 ft elevation
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.
January 2021 Aspinall Meeting Presentation
Water Supply Outlook – Cody Moser (Colorado Basin River Forecast Center)
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)