Sedimental Journey

A Grim Prospect for Lake Powell

by Richard J. Ingebretsen, M.D., Ph.D.,  
President, Glen Canyon Institute

August 1998

In his power to alter the face of the only earth he has to live on, man has become a geologic force. Unless this power is tempered with responsibility, how is it better than storm, earthquake, drought and flood? Humans can do better.

- David Brower

The Colorado River was once, "too thick to drink and too thin to plow." Now the Bureau of Reclamation boasts of creating a sparkling blue reservoir and a clear trout stream in the middle of a desert. However, before we get too ecstatic, we must ask: what happened to all of the sediment and sand that gave the Colorado its milk chocolate color? The Colorado River and its tributaries, one of the siltiest river systems in the world, still erode just as much land as ever and send it down toward the Gulf of California. The relentless accumulation of sediment behind Glen Canyon Dam has for too long been ignored.

We have spent seventy-five years allocating Colorado River water, while not considering the sediment that flows with the water. That is a big mistake. Three years ago at the first annual conference of the Glen Canyon Institute, we held a debate between former Sierra Club Executive Director, David Brower, and Floyd Dominy, the powerful former Commissioner of Reclamation. Mr. Dominy was asked what the Bureau's plans were once Glen Canyon reservoir was filled with sediment. Mr. Dominy laughed out loud and said, "We will let people in the future worry about it." No one laughed with him.

Why didn't the Bureau consider the sediment load delivered into the reservoir? Well, for one reason, no one really knew how important the sediment was to the heath of the ecosystem. And no one really knew that its accumulation would be so bio-toxic. But we know better now.

Grand Canyon's ecosystem will not survive unless we let the river deliver the sediment that created that system. The delicate Colorado River Delta thirsts for water and sediment, essential ingredients to its thriving past. And then there is Powell reservoir itself. The Bureau's beloved "Jewel of the Colorado" is also doomed as it fills in with sediment laced with mercury, arsenic, and selenium.

When will it fill with sediment? The Bureau of Reclamation claims the reservoir will fill in seven hundred years. This optimistic figure came from a study that measured actual siltation during the first decades of the reservoir. Other studies conducted by the government estimate the reservoir could fill with silt in 200 or 300 years. In any case, a single 500-year flood down the powerful and unpredictable Colorado would obliterate these optimistic estimates.

However, how long it would take the reservoir to silt in is moot. More significant to note is that the upper 100 feet of the reservoir holds 48% of its capacity. As the dam is 560 feet high, silt could fill the reservoir to the 460 foot level much sooner than the Bureau is willing to admit. Enough sediment flows into the reservoir, under current hydrologic conditions, to fill the reservoir to the generator intake level within 105 years. The power station penstocks and the river outlet work "safety valves," all lie below this level. Think of it: when silt reaches the river outlet work valves that allow the reservoir to be drawn down, for safety or other reasons, the dam will become unsafe. In less than 105 years, the dam could be rendered useless for power generation or flood control.

Aggradation is another problem that has been ignored. The sediment accumulates where the river flow dwindles, at the narrow head of the 186-mile-long reservoir. Although much sediment continues to ooze downstream, it also, through aggradation, begins to accumulate further and further upstream, forming a classic sloping delta. This aggraded delta will eventually rise hundreds of feet above the current reservoir level. Say good-bye to the few remaining rapids of Cataract Canyon, the lazy river through the Goosenecks of the San Juan, and in the end, the towns of Moab and Green River, Utah as well - not a happy thought.

As sediment continues to fill the reservoir, the storage capacity of the reservoir will diminish, increasing the probability of catastrophic releases. As the sediment rises at the dam, it and the higher average water level will create new problems in cavitation at the dam's outlets and increased acidification of the concrete and Navajo sandstone foundation. The loss of water through the sandstone, already enormous, will be exacerbated.

All of these scenarios are complex and hypothetical, but none of them bode well for the future of the dam. However, more to the point, should laws that were made 700 years ago govern the way water is distributed today? It is ludicrous to think that water laws made in 1956 will govern people 100 years from now, not to mention 700 years from now.

Big dams are already outmoded technology, relics of a time when humanity preferred to deny the existence of problems or our own limitations. The next fifty years cannot accommodate the current frightening growth of the Desert Southwest. As we develop less damaging technologies, water laws as we know them will become obsolete.

Glen Canyon Dam is one of the most destructive objects man has built. The few, short-term benefits touted by its proponents are overshadowed by what it will, in the long term, destroy ecosystems of the Colorado River, Grand Canyon, and the Colorado Delta, local communities, and finally the reservoir itself. At enormous costs, Lake Powell will fulfill its destiny.

One day, in the not too distant future, a smarter generation may stand at the edge of a toxic wasteland that was once Glen Canyon and wonder what on earth this generation was thinking when we destroyed such a unique place. They could wonder why we didn't consider impacts to Grand Canyon, just downstream, through which the run-off from this wasteland must inevitably flow.

Perhaps we could suggest another future. This generation could reassess decisions that were made in a less enlightened time, insisting that man's genius and vision be used instead of his inertia. Glen Canyon is a place to restore for future generations, and with it a river to inspire - many, many hundreds of miles of it, all vitally alive.

The Citizens Environmental Assessment