assage of the Colorado River Storage Project Act of 1956 authorized construction of Glen Canyon Dam and marked the loss of a long battle by Sierra Club founder David Brower to stop further damming of the Colorado River. Now, 34 years after completion of the dam in 1963, Brower has sounded the second battle cry—let the river flow freely through Glen Canyon Dam but let the dam stand as a reminder to our mistakes.
Decommissioning Glen Canyon Dam may seem inevitable as sediment is expected to fill the reservoir in 700 years and the dam structure and retaining walls slowly erode, but this time frame is considered in centuries, not in years or decades.
Political considerations aside, what then are the ecological consequences of allowing the Colorado River to flow freely through Glen Canyon Dam? At its present volume of 25,000,000 acre-feet—or nearly double the annual flow of the Colorado River—it would take approximately 2 years to drain the reservoir at a constant release of 20,000 cfs and also accommodate an average runoff.

An estimated 868,231 acre-feet of sediment had accumulated on the bottom of Lake Powell as of 1986, mostly in the Colorado River and San Juan River inflows. Maximum depth in 1986 at Dark Canyon was 182 feet with 36 feet at the dam.

At an accumulation rate of 36,946 acre-feet per year, the volume of sediment in the reservoir in 1997 is about 1,237,691 acre-feet. This is enough sediment to fill nearly 200 million dump trucks, or cover an area of about 2,000 square miles to a depth of 1 foot--an area the size of the State of Delaware.
Allowing the Colorado River to flow freely through that large sediment deposit would result in a constant erosion and subsequent downstream relocation of sediment as well as constant turbidity and suspended sediment load for many years. Persistent sediment would virtually eliminate all instream photosynthetic production, reproduction by all fish species, and the blue ribbon tailwater trout fishery. Release of contaminants in sediments could infuse massive and persistent quantities of chlorinated hydrocarbons, petroleum byproducts, and heavy metals for uptake into downstream ecosystems. Draining Lake Powell would release tons of some 15 different species of fish, posing serious predation, competition, and disease pressures on native fishes as well as game fishes through Grand Canyon, Lake Mead, and very likely, the rest of the reservoirs in the system, including Lake Mohave and Lake Havasu.
Draining Lake Powell may sound like a long-term environmental solution, but the short-term impacts may be costly trade-offs that could spell ecological disaster.

Rich Valdez