Glen Canyon Dam was constructed to protect the Upper Basin States water supply from being used prematurely by the Lower Basin States. The dam was constructed with three primary means of releasing water.

1. Primary water release is through the eight generators that make electricity. The penstocks are at an elevation of 3470, approximately 333 feet above the bottom of the reservoir. The Bureau of Reclamation makes it a goal to release all of the monthly volume of water required for downstream use through the penstocks.
   
2. River Outlet Works. The secondary release point is from the four hollow jet tubes that are located at elevation 3374, about 96 feet below the elevation of the penstocks and 237 above the bottom of the reservoir. The four hollow jet tubes have no electrical generators and are used primarily to release excess water from the reservoir.
   
3. Spillways. Two spillways were constructed at Glen Canyon Dam, one on each side. They can function only when the reservoir reaches within 50 feet of being full. They are the last line of defense when the Bureau of Reclamation is trying to control the level of water in the reservoir and what is released downstream.

Two river outlets diverted water around the damsite during construction. Both are river level and were cemented closed in 1963 following completion of the dam. The lower end of both spillways became the bottom section of the two spillways.

All Dams are Temporary

Because dams are built to store water, they also store the sediment that all rivers carry. This sediment builds and steadily decreases the storage capacity of the reservoir. Ultimately all dams fill with sediment or are destroyed by natural floods.

Built in 1963, Glen Canyon Dam is 563 feet high and has steadily been filling with the equivalent of 30,000 dump truck loads of sediment every single day—100 million tons of sediment annually.

The 200-foot high Matilija Dam (left, photo courtesy of Matilija Coalition), has completely filled in with sediment in only thirty years. It has been decommissioned and the process of removing the dam and restoring the river has begun. Because the reservoir behind Matilija Dam has filled with sediment, the costs of decommissioning this dam are very high. If the decision to decommission the Matilija Dam had been made earlier, the restoration costs would have been greatly minimized.

Glen Canyon Dam will share the same fate as the Matilija Dam. It too is temporary, and the longer we wait to address the temporary nature and ultimate risk of Glen Canyon Dam, the more expensive it will become. The true and staggering costs of sedimentation will ultimately be born by the next generation unless practical solutions are developed now.

Glen Canyon Can Be Restored

As one of the most damaging side effects of the reservoir in Glen Canyon, skeptics claimed that Glen Canyon was buried under the sediment and would take a century or more to restore. The dropping water levels since 1999 have proven this to be false. In reality, restoration of the side and main channel canyons is remarkably rapid, as seasonal monsoonal and spring floods clean the canyons of the huge sediment deposits.

In the 1980s, high water silted up this side canyon on the lower Escalante (far left, 1983). As the reservoir dropped over the next few years, summer rainstorms caused flash floods that moved out the sediment (left, 1993), returning the canyon to its original state. Riparian habitat quickly returned to the canyon and the reservoir deposited mineral "bathtub ring" fades within several years.

In 1999, this beach (photo) at Imperial Rapids, in Cataract Canyon, was covered with 50 feet of sediment from Lake Powell. The river's natural flows have since restored the canyon.

Scientific studies predict that without the reservoir, sediment deposits in the main channel upstream of the dam could be flushed out in as little as five years (CEA). The actual time is dependent on the future hydrologic events occurring in the Colorado River Basin.

Music Temple Bar, photo by Bruce Berger

As sediment builds up in Lake Powell reservoir, water storage capacity steadily decreases, ultimately filling the reservoir completely. If you'd like to help restore the Colorado River and help save future generations from a truly unjust and extremely expensive burden, please join Glen Canyon Institute. Thank you for your support.

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