Runoff news: Hot and dry weather causes streamflows to drop in the San Luis Valley

A picture named riogranderiver

From the Valley Courier (Ruth Heide):

Colorado Division of Water Resources Division III Engineer Craig Cotten announced a zero curtailment for irrigators on both Rio Grande and Conejos River systems beginning Wednesday, primarily because no water is flowing and the state’s obligation to downstream states has been adjusted accordingly. He said he has lowered the projected annual index for the Rio Grande to 530,000 acre feet, 5,000 less than the projection at the beginning of this month and considerably less than the 575,000-acre-foot June 1 forecast. Of the new 530,000-acre-foot projection, the Rio Grande must deliver 137,200 acre feet or about 27 percent to downstream states through the Rio Grande Compact. The Rio Grande has already delivered nearly 100,000 acre feet to downstream states, and the additional required delivery will likely be met through current return flows, Closed Basin Project water and winter flows in November and December, Cotten said. “So we won’t need much at all during the irrigation season,” he said.

Cotten also decreased by 5,000 acre feet the projected annual index on the Conejos River system, which is now forecast at 290,000 acre feet. At the beginning of June the forecast was 315,000 acre feet. Of the 290,000 acre feet projected annual index, the Conejos River system must deliver 102,200 acre feet downstream, or about 35 percent. The river will have no problem meeting that requirement. In fact, it will likely over deliver this year, Cotten said. “We don’t need anything through the rest of the irrigation season to the bottom end of the Conejos,” he said. “However, that is also anticipating we are going to get 2,800 acre feet out of the Closed Basin Project.”[…]

Cotten explained that stream flows on the Rio Grande and Conejos were tracking average until about June 10, when they dropped significantly. “It just cratered, dropped real hard and we are continuing to drop,” he said. On the Conejos River system, he said, “We are significantly below our average stream flows on almost all of our gauging stations right now.” He said the low river levels are an indication of the lack of precipitation the Valley has received so far this summer.

From the Summit County Citizens Voice (Bob Berwyn):

As of July 19, about 375 cubic feet per second were being diverted under the Continental Divide to the South Platte drainage. “It’s been really hot in Denver,” said water resource project manager Dave Bennett, “Demand is up.” Bennett said about 800 acre feet of water so far have been withdrawn from Dillon Reservoir, leaving it a few inches shy of its highest elevation…

Little said about 109 cfs is flowing out through the dam and into the Lower Blue, still well above the minimum 50 cfs level set by state rules to protect trout. The total combined inflow for all the Blue River and all its tributaries flowing into the reservoir was only 177 cfs on July 19. Blue River water commissioner Scott Hummer said most local streams, notably the Snake River, are flowing near historic lows after the snowpack quickly vanished in June. Making an educated guess, Hummer said some local streams could drop to the levels of the historic drought in 2002, when some streams reached all-time record low flows.

The good news is that all the reservoirs in the state are full or nearly full, giving water managers a buffer to work with…

Summer rains in the Denver area could reduce the demand for water from Dillon Reservoir, Bennett said, explaining that operations of the Roberts Tunnel are weather-dependent. Cool, wet weather in Denver could lead to a reduction in diversions through the tunnel.

Leave a Reply