The water is high, but not like it used to be
June 19, 2011
BASALT – The diversions that syphon water from the Roaring Fork River basin are frequently cursed for robbing the area of a natural asset, but they have also nearly eliminated flooding along rivers and streams engorged by snowmelt.
That’s good for riverside property owners, not so great for the environment, said Sharon Clarke, land and water conservation specialist with the nonprofit Roaring Fork Conservancy. The health of riparian areas depends on high water to flush sediments and replenish wetlands, she said.
It wouldn’t be in good taste to try to educate people about the benefits of high water while flooding remains a risk to some homeowners, Clarke said. However, the conservancy wants to find tactful ways in the future to increase education about the ecological benefits of high water.
Data compiled for the Basalt-based organization in its 2008 State of the Roaring Fork Watershed report shows how drastically the Roaring Fork and Fryingpan rivers have been tamed over the years. The study compares flooding in the decades before and after large-scale water development in the Roaring Fork basin. It shows that flooding used to be relatively frequent along the Roaring Fork River, lower Fryingpan River and even some of the larger creeks. Now, flooding is all but eliminated.
Before diversions started draining a portion of the upper Roaring Fork River, minor flooding occurred about nine of every 20 years, the study showed. After water development, minor flooding occurs only once every 30 years.
Large-flood frequency used to be once every 15 years on the Roaring Fork River near Aspen. Since water development, that has declined to once every 30 years.
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In the midvalley, the small flooding frequency of the Roaring Fork River has declined from about four out of 10 years to roughly three in every 20 years, the report showed.
Large flooding in the midvalley dropped from once every 10 years to about half that rate.
The lower Fryingpan River used to experience one large flood per 10 years before Ruedi Reservoir was constructed in the 1960s. Large flooding is now eliminated and minor flooding occurs about one of every 20 years since the dam was installed, the report showed.
This year is demonstrating the dramatic difference diversions have made on the Fryingpan River. The Fryingpan-Arkansas Project, which collects water from the upper Fryingpan Valley and diverts it to Turquoise Reservoir, is expected to divert about 94,000 acre feet throughout the spring and into the summer. The annual average diversion is about 54,000 acre feet.
Even with the active diversion season, the inflow to Ruedi Reservoir has been consistently at 1,300 cubic feet per second this spring. The snowpack was significantly higher than average this year, so the runoff is high. The U.S. Bureau of Reclamation is releasing about 775 cfs from the Ruedi dam. The lower Fryingpan is flowing at 850 cfs with the water from Rocky Fork added.
In other words, the lower Fryingpan River would be flowing about 50 percent higher without the dam, flooding low-lying lands down into Basalt.
While diversion isn’t as visible on the upper Roaring Fork River, studies have shown up to 38 percent of the water is diverted in the late spring and summer months.
The existing diversions aren’t going to be reduced and, in fact, could increase. The Roaring Fork Conservancy and its partners in the Roaring Fork Watershed Collaborative Water Group want to make sure area residents are aware of the effect increased diversions could have on the environment.