Environmental Issues: Glen Canyon Dam

The upper Colorado River and it’s tributaries run mostly in remote country. The land is arid and wild with many spectacular canyons that are often inaccessible.

Glen Canyon Dam

It’s all about the silt. The upper Colorado and it’s tributaries cut through sandstone and limestone through much of their length and produce thousands of tons of silt every year. Glen Canyon Dam at Page, Arizona stops much of this silt, the water flows out clean and green. Which isn’t as good as you might think.

Glen Canyon is thought to trap 45 million tons of silt EVERY YEAR. The Sierra Club estimates the total useable life span of the Dam to be less than 100 years-The Bureau of Reclamation estimate is 500 to 700 years.

It’s quite simple: As the volume of silt increases the volume of Lake Powell decreases by a like amount. The silt falls out in the slow water behind the dam, so the degradation of the reservoir is running from the north end to the Dam at the south. When the silt reaches the base of the dam there will be trouble. If the Dam lasts that long.

There are engineering problems with the siting of the Dam itself. The sandstone cliffs are just barely enough to stand up to the normal pressure exerted by the dam. There was a huge flood event in 1983 that very nearly overtopped Glen Canyon Dam and actually caused the footings for the dam to shift. In other words, the dam very nearly failed.

Which would be catastrophic for the river and the 40 million people that rely on it for drinking water. Glen Canyon is built in a sandstone canyon and has actually moved a teeny amount. That is a bad thing for the engineers that designed it and for the dam itself. There are now problems with the spillway gates which are essential in flood control. Not big problems, yet.

Should Glen Canyon fail it might be disastrous for Hoover Dam at the other end of the Grand Canyon. The reservoir behind Glen Canyon is significantly larger than the reservoir behind Hoover Dam.

What can be done? Dredging silt from somewhere behind Glen Canyon is a last ditch option. Where do you put 45 million cubic yards of silt? Every year? It would be a monumental dredging project and an ecological disaster to the river that provides water to the entire South West United States.

You may remember from earlier issues that Glen Canyon was a compromise location, and the real start of the American environmental movement. Typically of most compromises it isn’t an ideal location from any perspective and represents one of the largest potential ecological catastrophes that I know of.

The Likelyhood

The chances of Glen Canyon Dam being the biggest ecological disaster in this century is quite good in my mind. Like maybe 2% per year. It’s almost certainly when something really bad happens there, not if something bad will happen there.

Glen Canyon will hopefully fail slower rather than faster. The exception being the one in 100 year snow melt in the watershed. The last time it happened (1983) the reservoir wasn’t full from the original construction and it still very nearly overtopped. With 45 million tons of silt making the reservoir smaller by the same volume. It’s an explosive combination.

Conclusion

What can be done? Not much. I can’t see dredging as a viable option, the quantity is just too big. If you could get it out of the basin, where do you put it? Remember that it may be significantly contaminated soil from all the upstream mining.

Glen Canyon Dam is going to fail. Whether it fails very slowly by just filling the resivoir with silt of at a more explosive rate by over topping or shifting position is the question at this point. Either way it's going to be a horrible mess for the next generations to deal with.

If you are moved to action by what you’ve read and need to do something you can support the Grand Canyon Trust and tell your congressman to support the Grand Canyon Centennial Protection Act.

I’m going to stick with the Colorado River (and it’s tributaries) as we look at the environmental concerns that dog the whole drainage basin in my next post. Thanks for following along!

All words in this post are mine. The photographs are either sourced properly or taken by me and used courtesy of the author. Some have been published previously

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