Warming temperatures, more high country precipitation fuels runoff
You know it’s runoff when the Colorado River jumps its banks and the Gunnison River below the East Portal gets too deep and swift to wade.
Tuesday morning the Colorado was chewing away at its margins in Grand Junction and hitting 23,700 cubic feet per second at the Utah line.
It’s going to go up, as runoff builds in the face of approaching warm temperatures and after the Grand Valley received an inch of rain over the weekend and more than 3 inches of snow Sunday on top of Grand Mesa.
“I came over the top from Eckert on Sunday and in less than an hour I was in a blizzard, close to a snow slide and observed a flash flood,” wrote Pat Oglesby of Grand Junction in an email Sunday evening. “There was 3-4 inches of snow on Grand Mesa by about 3:30 p.m. and still snowing hard.”
Tuesday the Gunnison below the East Portal was up to 2,400 cubic feet per second and going up by 500 cfs per day, according to the Bureau of Reclamation.
The increases will continue “until Crystal Reservoir begins spilling,” said Erik Knight, hydrologist with the Bureau’s Western Colorado Area Office in Grand Junction.
He said Crystal is expected to start spilling by Thursday in order to get peak flows as required by the Record of Decision for the Aspinall Unit Operations Final Environmental Impact Statement.
“After (spilling), releases will increase until the peak flow level is reached on June 2,” Knight said.
Because Crystal can release only 4,350 cfs with its powerplant and bypass tubes wide open, about 4,000 additional cfs will need to go over the spillway.
To get that unconstrained flow downstream, both Morrow Point and Blue Mesa dams also will need to spill.
Peaks flows will top out close to 9,000 cfs in the Black Canyon of the Gunnison and close to 13,000 to 15,000 cfs at Delta depending on tributary flows from the North Fork of the Gunnison.
Flows in the Black Canyon will remain above 8,000 cfs for 10 days until dropping to 4,000 to 5,000 cfs by mid-June.
Monday, the Gunnison reached 5,800 cfs near Grand Junction, above the Redlands diversion dam.