From The Grand Junction Daily Sentinel (Dave Buchanan):
The peak flows and accompanying shoulder flows are components of the Black Canyon reserved water right. That 2008 settlement includes annual peak flows and shoulder flows — tied to natural inflow — plus a year-round base flow of 300 cubic feet per second. Collectively, these elements were considered to mimic natural flows prior to the construction of the Aspinall Unit dams and deemed critical to the health of the park and the Gunnison River. Once the peak flows are finished, the river will be ramped down by 400 cfs per day to around 800 cfs for the rest of the summer, [Dan Crabtree, lead hydrologist for the Bureau’s Grand Junction office] said. The peak flow and its timing were decided once the May 1 runoff forecast for the Gunnison basin was available, Crabtree said…
The peak flows will be produced by increasing flows from Blue Mesa into Crystal Dam and then opening the outlets on Crystal. That will boost flows to around 4,150 cfs. It take an additional spill of around 800 cfs to make the peak flow target. While it’s not preferable to see water go over the dam instead of through the hydropower generators, there’s little choice when it comes to meeting the Black Canyon water right. “We always want to use the water in the most efficient way possible,” Crabtree said, “whether it’s for hydropower, storage against future drought or for recreational purposes.”
More Aspinall Unit coverage here.