Summit County Citizens Voice

Cold-season operations vary depending on water, maintenance needs

Ice flowers grow in early December on the surface of Dillon Reservoir while the ice is still thin. PHOTO BY BOB BERWYN.

By Bob Berwyn

SUMMIT COUNTY — During the summer, water watchers keep a close eye on Dillon Reservoir. The water level in the impoundment is critical to the area’s recreation economy and also to downstream fisheries.

But what happens during the cold winter season, when the reservoir rests under a layer of ice? Does the level go up or down? Is water being diverted to the Front Range from under the ice?

To answer those questions, I spoke with Bob Steger, Denver Water’s manager of raw water supplies. Steger is point person for Denver Water in the spring, when Silverthorne wants to know if there’s going to be flooding, and as local marina operators gear up for the boating season.

“We try to keep it as full as our water rights allow,” Steger said, explaining that winter operation of the reservoir depends on a number of factors.

Right now, the reservoir is about three feet below full, a level that enables Denver Water to place a big steel and wood cap on the glory hole.

In late November, the inflow from the tributaries that feed the reservoir was at about 93 cfs, while the outflow into the Blue River was about 88 cfs. Those flows are expected to fluctuate between a minimum required flow of 50 cfs and 105 cfs, sometimes dependent on downstream calls.

This year, the Roberts Tunnel, which transports water from the Blue River Basin under the Continental Divide to the South Platte River, was turned off in late November and will likely remain shut off until well into spring.

Steger said Denver Water is doing some maintenance on the  valves at the eastern end of the conduit. But the tunnel itself will remain filled of water during the winter. It holds about 220 acre feet of water. Keeping it full enables Keystone to draw water from the Montezuma Shaft to augment Snake River flows during snowmaking season and also prevents the inside of the tunnel from icing up.

Some years, Denver Water operates the tunnel during the winter, with diversions aimed at balancing storage throughout the system, with an eye on the relative water levels in Dillon Reservoir and Cheesman Reservoir.

“In years when we do operate it, it runs at about 75 cubic feet per second,” he said. In other years, winter operation of the tunnel is dependent on maintenance requirements.

Filed under: Colorado, Dillon Reservoir, Environment, Summit County Colorado, Summit County news, water Tagged: | Blue River Basin, Denver Water, Dillon Reservoir, Frost flower, Roberts Tunnel, South Platte River, Summit County Colorado