Ed Stein

Rocky Mountain News

Jerry Holbert

The Boston Herald

Jeff Stahler

Columbus Dispatch

Robert Ariail

Newspaper Enterprise Association

This spring, for the first time in more than a decade, the U.S. Bureau of Reclamation has an opportunity to provide the Gunnison River with a large flushing flow like those that occurred periodically prior to the construction of Blue Mesa, Morrow Point and Crystal reservoirs.

Thanks to the most significant snowpack in the Gunnison Basin in years, the bureau — the agency that manages the Aspinall Unit, as the three reservoirs are known — should have ample water to release a large flushing flow this spring to re-create more natural conditions downstream in the Gunnison River.

The bureau is hesitant to seize the opportunity. In fact, in anticipation of a sizeable spring snowmelt, since January the bureau has been releasing more water out of the Aspinall Unit than the river has seen for the better part of 10 years.

At 2,000 to 3,000 cubic feet of water per second, the higher-than-usual winter and early spring flows are far smaller than the flush the river requires. But, by releasing more water early in the year, the bureau is limiting the extent to which it will need to make larger releases later this spring and summer that exceed the capacity of the hydropower turbines at Crystal Dam. The Gunnison River may experience a flush in May or June despite the Bureau’s fondness for hydropower, but the unusually high releases this January through April have diminished the amount of water available for the flush.

With current estimates of April through July inflow to the Aspinall Unit of over 1 million acre-feet of water, the Bureau should develop a plan now to provide a flushing flow down the Gunnison River in late May in as large an amount as is possible, perhaps approaching as much as 10,000 cfs.

Prior to the construction of Aspinall, the Gunnison River periodically experienced spring flows well in excess of 10,000 cfs.  But due to drought, low snowpack and the management of the upstream reservoirs, the river has not experienced a flush anywhere near 10,000 cfs for more than a decade.  In fact, aside from the past several months, the Gunnison River downstream of Aspinall has experienced flows above 2,000 cfs only once in the previous 10 years.

The major flushing flows that occurred in the Gunnison under natural conditions served a number of purposes, such as clearing sediment and algae from the river and maintaining the river channel, thus helping to keep the river system in ecological balance. The bureau’s sister agencies, the National Park Service, which manages the Black Canyon National Park just downstream of Aspinall, and the U.S. Fish and Wildlife Service, which has jurisdiction over endangered fish in the lower reaches of the river, have concrete science demonstrating the necessity of periodic high flows for the overall health of the river. In particular, National Park Service science illustrates that a flushing flow on the order of 10,000 cfs is needed about once every 10 years to maintain the Gunnison as a healthy river.

Officials with the Colorado Division of Wildlife have expressed concern that flows above 6,000 cfs in the Black Canyon could damage survival chances for this year’s class of trout fry. While DOW biologists are right to be concerned about the impact of large flows on juvenile trout, on balance the loss of some of this year’s emerging trout may be a necessary trade-off for a healthier river over the long term. Trout populations do not need strong reproduction every year, just as maintaining healthy river habitat does not require a flushing flow each spring. In both cases, the problem is going too long without.

Anglers in the Gunnison already are seeing excessive sediment and vegetation that have resulted from a decade of low flows. If a major flush is not provided and these conditions persist over time, the river’s fishery will suffer, whether or not a large number of trout fry survive in 2008.

Of course, the bureau should do all it can to limit the impact on juvenile fish this year while providing a large flushing flow. As the DOW points out, to minimize the impact on the trout fishery, the bureau should time the flushing flow for late May and should increase and decrease flow rates in the Black Canyon gradually.

There is also concern that high flows in the Gunnison River could cause flooding in Delta. Certainly, the bureau should not operate Aspinall in a way that creates damage to life or property in Delta or anywhere else. The Army Corps of Engineers, however, has established a flood threshold of 15,000 cfs for the town of Delta. The bureau can provide flushing flow for the Gunnison River while remaining below this threshold.

Over the past decade, drought, high air temperatures, diminished snowpack and increased water demand to serve Colorado’s growing population have conspired to produce very low flows in rivers and streams around the state. This year, nature has provided the Bureau of Reclamation an opportunity to help reverse some of the lasting effects of a decade of such low flows of the Gunnison River. The opportunity should not be squandered, especially given that nature may not provide it again for another decade or more.     

Drew Peternell is the director and legal counsel for Trout Unlimited’s Colorado Water Project. He lives in Boulder.