A double rainbow arches over the Painted Wall in Black Canyon at Gunnison National Park.
Photo Credit: Dave Showalter
From email from Reclamation (Erik Knight):
Releases from the Aspinall Unit will be decreased from 1500 cfs to 1450 cfs in the afternoon of Monday, August 26th. Releases are being decreased as flows on the lower Gunnison River are well above the baseflow target of 1050 cfs.
Flows in the lower Gunnison River are currently above the baseflow target of 1050 cfs. River flows are expected to remain above the baseflow target for the foreseeable future.
Pursuant to the Aspinall Unit Operations Record of Decision (ROD), the baseflow target in the lower Gunnison River, as measured at the Whitewater gage, is 1050 cfs for August through December.
Currently, Gunnison Tunnel diversions are 1050 cfs and flows in the Gunnison River through the Black Canyon are around 450 cfs. After this release change Gunnison Tunnel diversions will still be 1050 cfs and flows in the Gunnison River through the Black Canyon will be around 400 cfs. Current flow information is obtained from provisional data that may undergo revision subsequent to review.
“New plot using the nClimGrid data, which is a better source than PRISM for long-term trends. Of course, the combined reservoir contents increase from last year, but the increase is less than 2011 and looks puny compared to the ‘hole’ in the reservoirs. The blue Loess lines subtly change. Last year those lines ended pointing downwards. This year they end flat-ish. 2023 temps were still above the 20th century average, although close. Another interesting aspect is that the 20C Mean and 21C Mean lines on the individual plots really don’t change much. Finally, the 2023 Natural Flows are almost exactly equal to 2019. (17.678 maf vs 17.672 maf). For all the hoopla about how this was record-setting year, the fact is that this year was significantly less than 2011 (20.159 maf) and no different than 2019” — Brad Udall
Hydrological drought is a pervasive and reoccurring challenge in managing water resources. Reservoirs are critical for lessening the impacts of drought on water available for many uses. We use a novel and generalized approach to identify periods of unusually low reservoir storage—via comparisons to operational rule curves and historical patterns—to investigate how droughts affect storage in 250 reservoirs across the conterminous U.S. (CONUS). We find that the maximum amount of water stored in reservoirs is decreasing, and that periods of unusually low storage are becoming longer, more severe, and more variable in (a) western and central CONUS reservoirs, and (b) reservoirs with primarily over-year storage. Results suggest that reservoir storage has become less reliable and more vulnerable to larger deviations from desired storage patterns. These changes have coincided with ongoing shifts to the hydroclimate of CONUS, and with sedimentation further reducing available reservoir storage.
Key Points
Low-storage periods are longer, more severe, and more variable in over-year storage reservoirs and in the western and central CONUS
Longer periods of low storage for some regions in recent years suggests decreased reservoir reliability in a changing hydroclimate
Maximum annual storage is also declining across CONUS, furthered by storage losses from sedimentation
Plain Language Summary
Drought in water systems is a major challenge in managing water resources. Reservoirs are important as they can lessen the impacts of drought on water availability for many users. However, they are impacted by drought as well. We use a novel and generally applicable method to identify when reservoir storage is unusually low, potentially from drought, at 250 reservoirs across the conterminous U.S. We find that the maximum amount of water stored in reservoirs is decreasing across the U.S. We also find that periods of unusually low storage are becoming longer and more severe in western and central U.S. regions as well as for certain types of reservoirs. This suggests that reservoir storage may be less reliable and more vulnerable to extreme conditions and may be further impacted by changing climate and hydrology across the U.S. and by sediment building up behind reservoirs.
