Facing flooding from fast-melting snow, Summit County authorities — normally wary of letting water be taken across the Continental Divide — are now urging Denver Water to draw all it can out of an overflowing Dillon Reservoir.
But while the metro area’s water utility was pumping through a transmountain tunnel to accommodate the request, water managers warned that reservoirs on the eastern side of the Divide also are full.
The use of Denver’s tunnel as a safety valve technically may violate a river compact that lets Denver divert water only for a “beneficial use.” While water attorneys pondered the point, the withdrawals from Dillon have been happening all week.
Icy torrents of surplus water simultaneously are gushing through the Dillon Reservoir dam’s safety spillway into the Blue River below the dam.
Yet reservoir operators still are struggling to control the water surging in from melting snow on the Rocky Mountains. Before a cooldown Thursday afternoon, temperatures at Keystone had reached the 80s this week.
Denver’s reservoir operators must “keep the level at some safe level,” Summit County Commissioner Bob French said Thursday morning.
“If (Dillon Reservoir) is full and is dumping into the Blue River and threatening flooding down the Blue River, we are happy to have them take water. . . . We’d like them, if they can, to help us prevent flooding.”
The only way to do that now is by diverting more water through the 10-foot-3-inch-diameter Roberts tunnel — which runs from Dillon Reservoir 23.3 miles under mountains to the eastern side of the Continental Divide.
The diversions brought immediate relief. Water levels below the reservoir dam along the Blue River on Thursday decreased slightly to 1,700 cubic feet per second, down from 1,800 cfs earlier this week — the limit above which flooding is likely.
Minor flooding was reported near Frisco and Silverthorne, Summit County sheriff’s spokeswoman Tracy LeClair said. Sandbags have been positioned around the county for property owners who want to set up barriers.
“We’re at the mercy of Mother Nature — how much snow we’ve got, how warm it gets, how much it melts,” LeClair said. Denver Water officials “have been very cooperative. . . . We’ve been in touch with them numerous times throughout the week.”
Diversions to Denver started Sunday. The water is run through the tunnel down the North Fork of the South Platte River to the Strontia Springs and Chatfield reservoirs.
Water lawyers were pondering whether the diversion is allowed under what is known as the Blue River Decree. Denver Water officials argued that it meets the test of “beneficial use” because the water eventually will help meet needs of 1.3 million metro-area customers — with the extra benefit of some flood control.
“It is not a decreed right that we have . . . to take water through the tunnel for flood control. Our right is to take water through the tunnel for use by customers. That’s where we get into a little bit of a rub. We’re certainly willing to do things to help out here,” said David Little, Denver Water’s director of planning.
While temperatures dropped Thursday in the mountains, perhaps slowing snowmelt, the cool weather is accompanied by rain, doing nothing to alleviate flooding concerns.
“If you get a major rainstorm up there, and the snowmelt is the way it is coming right now, we’re going to have a bigger problem,” Little said.
“Best of all worlds: No one gets flooded out this year. We’re doing everything we can to help. But we are running out of options.”
Bruce Finley: 303-954-1700 or bfinley@denverpost.com
