With storms at the end of April, sites in the northern central mountains have reached record-high snowpack, causing water officials to pay special attention to water management at systems like the Dillon Reservoir.
A graph by the Blue River Watershed Group shows that the 2011 snowpack in the Colorado River Basin reached about 165 percent of average at the end of last month, surpassing 1984’s snowpack that hit about 160 percent of average in May. Natural Resources Conservation Service data has the Colorado River Basin at 151 percent of average.
Water content at Copper Mountain, which flows into Ten Mile Creek, is at its highest this year, and the snow survey site on the Snake River above Keystone is at 231 percent of average.
“It’s pretty spectacular,” Denver Water’s Bob Steger said at Tuesday’s State of the River meeting. “It’s right up there with past wet years.”
Other record years include 1995 and 1996 — but up until the end of April, the snowpack hadn't exceeded ’96 amounts. Figures more than double those of last year.
“The last two weeks in April were when we really got pounded with some of the biggest storms of the season — pretty relentless — at some of these locations,” said snow survey supervisor Mike Gillespie, of the Natural Resources Conservation Service.
Snowpack at the Tower SNOTEL site on Buffalo Pass in the Park Range northeast of Steamboat Springs set the all-time state record for total snowpack at a single Colorado site with snow depth of more than 200 inches with 72.6 inches of water content. It exceeds the previous record of 71.1 inches of water equivalent measured in 1978.
The North Platte, Yampa and White river basins have all hit 165 percent of average snowpack, and the South Platte is at 150 percent of average. The Arkansas River is at 112 percent of average.
The high snowpack is causing water officials, like Steger, to take precautions in water management. Steger has a balancing act on his hands — not drawing Dillon Reservoir down so much so it can't fill, but trying to mitigate overfill and downstream flooding.
He estimates there's a 90 percent chance the May through July total inflows would exceed 210,000 acre-feet, and a 10 percent chance inflows could reach 290,000 or more. The 30-year average is about 160,000 acre-feet.
To reduce the risk of flooding below the dam, he plans to leave space in the reservoir before runoff occurs, topping it off after peak inflow. It enables him to better manage the flow out of the dam before and during runoff — benefits not just to flood mitigation, but to rafting, fishing and flat water recreation on the reservoir. However, the fill delay may also delay full operations at the Frisco Marina — which is in shallower water than the Dillon Marina — until mid-June.
“This year, rafting should be great,” Steger said, adding that water levels below the dam will soon be too high for good fishing.
As of Wednesday, the flow below Dillon Dam was 457 cubic feet per second, a draw that's balanced with the 363 cfs through the Roberts Tunnel transmountain
diversion. It'll likely be re-evaluated before the end of the week, Steger said.
“If we continue to get rainy, snowy weather, we're going to have to go up with the outflow,” Steger said.
Steger and others aren't sure how runoff will behave this year — it's entirely dependent on temperature and precipitation in upcoming weeks. The highest snowpack on record was in 1984, but the peak inflow wasn't extremely high because weather was temperate, Steger said. On the other hand, 1995 and 1996 were fast melts, with 1995 being the highest peak inflow rate ever.
Above the reservoir, Denver Water has no control. And Colorado Springs Utilities spokeswoman Kalsoum Abbasi said her company will be skimming a mere 15 cfs off natural Upper Blue River runoff.
“It could be really full this year,” Steger said.
Statewide, snowpack is at 135 percent of average, and at 175 percent of last year. That reflects a less bright situation in southern Colorado, where “it's a totally different story,” Gillespie said.
The Rio Grande and southern Arkansas rivers below Canon City are seeing below average runoff and are already well into the melt season. That trend extends into southwestern Colorado — the San Miguel, Dolores, Animas and San Juan rivers, Gillespie said.