Colorado: Green Mountain Reservoir not likely to fill this year

Bureau of Reclamation starts filling the reservoir April 1, the earliest date possible

Recreation could be affected by low water levels at Green Mountain Reservoir this summer.

By Bob Berwyn

SUMMIT COUNTY — Green Mountain Reservoir is unlikely to fill this year, even though the U.S. Bureau of Reclamation is already staking its claim to Blue River water with the earliest “start of fill” on record.

The reservoir at the north end of Summit County is a key piece of the regional water supply puzzle, helping buffer the Upper Blue when senior water rights holders downstream on the Colorado call for water, at Xcel’s Shoshone power plant in Glenwood Canyon and irrigation in the Grand Valley, for example.

Green Mountain Reservoir is currently about 43 feet below its maximum level and BuRec has shut the valve on outflows below Green Mountain Dam. Currently, only about 75 cubic feet per second are flowing past the dam and into the Blue River. Those low flows will likely persist until senior water rights holders down stream call for water from the reservoir.

BuRec spokesperson Kara Lamb said the agency isn’t sure yet whether Green Mountain Reservoir will even have a so-called paper fill this year. As of April 5, water experts were still crunching snowpack numbers and streamflow projections, with at least some preliminary projections for Green Mountain Reservoir due by the end of next week.

Those projections will be of interest to recreational stakeholders at Green Mountain Reservoir, who rely on a short summer boating and fishing season to maintain businesses through the year.

A paper fill is when some the water that’s technically part of  the Green Mountain water right is held back in Dillon Reservoir. Instead of letting that water flow down the Blue to Green Mountain Reservoir, Denver Water, through an exchange, uses water from Williams Fork Reservoir to meet downstream demands for Green Mountain water.

The April 1 start of fill declaration by the BuRec is the earliest date that the agency can start calling for water to fill Green Mountain Reservoir. The timing was triggered by the dismal snowpack and the expectation of an early runoff, said BuRec spokesperson Kara Lamb.

Already, many streams in the headwaters region are running well above average for this time of year, and the snowpack in the Upper Colorado is below 50 percent of average and dropping fast.

Major transmountain diversions in Colorado.

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