Denver Water raises outflow from Dillon Reservoir, cuts diversions through Roberts Tunnel, expects reservoir to fill in about 2 weeks
By Summit Voice
SUMMIT COUNTY — The Lower Blue River is flowing perilously close to its banks, as Denver Water increased the flow to 1,750 cfs Thursday. Flooding issues along the Lower Blue start to become more serious at a flow of about 1,800 cfs, but Denver Water’s Bob Steger said he’s hoping the inflow will soon begin to decrease, as predicted by the Colorado Basin River Forecast Center.
Denver Water is also reducing its diversions via the Roberts Tunnel from 250 down to 100 cubic feet per second, as the Front Range reservoirs in the system are nearly full.
Thursday morning, the reservoir was at 9014.17, which is 2.83 feet below the spillway and 0.17 feet higher than Wednesday morning. The average inflow during the last 24 hours was 2,205 cfs. If the inflow stays steady, the reservoir would fill in about 13 days.
Once the reservoir is completely full, water spills through an overflow system into the Blue River below. At that point, Denver Water doesn’t have much control over how much water flows down the valley, as it depends on the inflow. The utility can influence the water level to some degree by changing the diversion amount in the Roberts Tunnel, but that part of the system is not used for flood control. Use of water going through the Roberts Tunnel is subject to very specific conditions under various water decrees.
The wild card in the equation is the rainfall. Strong and persistent thunderstorms could keep the inflow higher than predicted, filling the reservoir more quickly. Thunderstorms are in the forecast through the middle of next week.
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