Diversion strategy could ease Aspen-area flooding | AspenTimes.com

Diversion strategy could ease Aspen-area flooding

Standup paddleboarding
Lauren Glendenning/The Aspen Times |

wet but no aspen record

Aspen had nearly double its usual amount of precipitation during a wet, dreary May, but it didn’t come close to setting a record.

Aspen recorded 3.57 inches of precipitation for the month compared with an average of 2.08 inches between 1981 and 2014, according to the National Weather Service. May 1995 produced 5.41 inches of precipitation, according to records tracked at the Aspen Water Plant.

Record or not, it was rainy enough to give many Roaring Fork Valley residents cabin fever. June also is forecast to be wetter than usual.

The silver lining is that the recent weather dug Colorado out of trouble with its water supply for the summer, according to the U.S. Natural Resources Conservation Service.

The statewide snowpack was 212 percent of median across all mountains as of June 1 and was higher in some of the state’s mountain ranges, the conservation service reported.

The average reservoir storage across the state was 107 percent of average, the agency said.

Ruedi Reservoir east of Basalt is 85.3 percent full. The amount of water flowing in from the upper Fryingpan River is currently at 621 cubic feet per second, while the outflow from the reservoir’s dam is 471 cfs.

“While the exceptionally wet May was great news for many parts of Colorado from a water-supply standpoint, there is a flip side, particularly in areas with the most snow remaining,” the conservation service said in a statement. “Having a substantial amount of snow in the mountains as temperatures continue to rise, and the probability of rain-on-snow events, increases the risk of flooding resulting from accelerated snowmelt.”

The transmountain water diversions that typically make western Colorado residents bristle could be a godsend for the Roaring Fork Valley this spring.

The Twin Lakes Reservoir and Canal Co., based in Ordway, is voluntarily forgoing diversion from the Roaring Fork’s headwaters to save its remaining storage space in Twin Lakes Reservoir on the east side of Independence Pass. The company’s intent is to resume diversions when peak snowmelt runoff is occurring on the river later this month.

That will reduce the flow and potentially prevent flooding of low-lying areas in and around Aspen and farther downvalley.

“This seems like the thing to do,” said Scott Campbell, general manager of the Twin Lakes Reservoir and Canal Co. “I hope we have it timed right.”

The company had the legal right to keep diverting this spring until its allocated storage space in Twin Lakes Reservoir was full and then letting the Roaring Fork Valley worry about handling the entire peak runoff. But the water-diversion organization volunteered to help last week during an annual spring conference call among officials with the city of Aspen, the Colorado River Water Conservation District, the Bureau of Reclamation and the canal company’s shareholders. Coincidentally, the purpose of that conference call is to plan how to ease low flows on the Roaring Fork River later in the summer. This year, the high spring flows were a more immediate concern. The Twin Lakes Reservoir and Canal Co. proposed a course of action that “seems to make sense,” according to Campbell.

“We are a neighbor,” he said. “We do business up in that neck of the woods.”

Phil Overeynder, utility engineer for special projects for the Aspen Water Department, said the canal company’s plan could have tremendous benefits for the Roaring Fork River. Rivers and streams in the upper Roaring Fork Valley still must absorb a lot of water from runoff, according to historical records for when there is a similar snowpack.

“They’re probably only at 60 percent of where they typically peak,” Overeynder said.

The stream flow on the Roaring Fork River east of Aspen has been running between 900 and 1,000 cubic feet per second in recent days, he said. If Twin Lakes Reservoir and Canal Co. can divert water throughout the peak runoff period, it could potentially hold the flow around the 900- to 1,000-cfs level, Overeynder said.

The flows surged above 12,000 cfs during flooding in the 1980s and 1990s, according to Overeynder.

He noted that when the company decided to bypass flows, the water flow spiked from 400 to about 800 cfs. It has continued to rise since then.

“It’s been 16 years since the Roaring Fork flooded like this,” Overeynder said. The last time was July 1999.

The current water level poses little threat of destroying property and provides high ecological value. The high water level has flooded the North Star Nature Preserve east of Aspen. It replenishes groundwater levels and recharges wetlands, Overeynder said. If you think of the ground as a big sponge, he said, this high water level is moistening the sponge. The high, sustained flow in the river for a couple of weeks also will flush the channel of gravel, sand and debris.

A final benefit from the plan of action by the Twin Lakes Reservoir and Canal Co. will be easing peak runoff in the river at the time when Castle and Maroon Creeks are peaking. When the creeks have peaked in the past, it has led to flooding.

The two creeks typically peak at about 600 cfs. They are currently at 300 cfs. Forecasting peak runoff is an inexact science. Right now, it is anticipated to be seven to 10 days away, putting it in mid-June, Overeynder said.

In April, few people if any foresaw a problem with too much water during runoff. As recently as May 1, the federal government forecast lower-than-average stream flows in Colorado and throughout much of the West.

“All the rainfall on the (Front Range) has changed the picture on the (Western) Slope because they’re not diverting as much,” Overeynder said.

Campbell said conditions on both sides of the Continental Divide have created unusual circumstances, such as his company forgoing diversions until later in the season.

“This is a rare event,” he said.

An extremely wet May has filled reservoirs close to capacity on both sides of the Continental Divide, with a lot of snow yet to melt.

Twin Lakes Reservoir and Canal Co. diverts water via the Independence Pass Transmountain Diversion System. Diversion structures move water from the Roaring Fork River as well as Lincoln Creek, Lost Man Creek, Brooklyn Creek, Tabor Creek, New York Creek and Grizzly Creek. Water is diverted to Grizzly Reservoir, up Lincoln Creek and then by tunnel to Lake Creek on the east side of the Continental Divide. The creek feeds Twin Lakes. The Twin Lakes Reservoir and Canal Co. gets its water via releases into the Arkansas River Basin.

Campbell said the company is managing flows at Grizzly Reservoir by mimicking nature. High daytime temperatures create runoff that often peaks at night, and then water levels drop during the day as nighttime temperatures slow the snowmelt.

Twin Lakes Reservoir and Canal Co. will monitor runoff with its partners and will resume diversions during peak runoff for as long as it has storage space available, Campbell said.

“Every year is a normal year, but things are always different and present different challenges,” he said.

scondon@aspentimes.com


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