Sixty years after its creation, Lake Powell faces an uncertain future due to increasing drought and decreased water runoff. As part of Utah State University’s Center for Colorado River Studies lecture series, Science Moab spoke with professor Jack Schmidt and Eric Kuhn, an engineer who was the general manager for the Colorado River District for 37 years. We discuss the policies and politics of Colorado River reservoirs, including the role of Lake Powell and its future in the face of changing climate and politics.
Science Moab: Can you explain the history of Lake Powell and how its policies may soon change?
Schmidt: Keep in mind that Lake Powell and Lake Mead are the two largest reservoirs in the United States, on a river that has a pretty dinky amount of water in it. Essentially, you've got one enormous reservoir (Lake Powell), a ditch through bedrock (the Grand Canyon), and then another enormous reservoir (Lake Mead). So we might have to get over the political mindset about upper and lower basin, and figure out the best way to manage this whole thing, because it really is one integrated system.
Kuhn: The basic reason we have Lake Powell for water storage above Lee’s Ferry [in Coconino County, Arizona] is the 1922 Colorado River Compact, a contract among seven states. The compact gave no water to any individual state, but divided water among basins: those states above Lee’s Ferry, and those below. The upper-basin folks agreed to deliver 75 million acre-feet of water downstream over 10 years, which they thought was about a third of the Colorado River. Today, we think this is about 60% of the river, or more. Nature won't provide that year in and year out. So Lake Powell served as the bank account: in wet years, we put water in that bank. In those drier years, we would draw on that bank. With climate change, there are going to be many discussions about whether we can actually make our obligations under the compact, and what to do if we can't.
Science Moab: Are we bound by the policies enacted years ago? If nature can't sustain those, what then?
Kuhn: One hundred years ago, we had some flexibility because the river was not very well-used. Today, not a drop of the Colorado River reaches the Gulf of California, so we don't have that luxury. The way I look at it is that we legally allocated water based on an assumption that this river system had about 20 million acre-feet. Today, we think it’s more like 13, and it might be less in the future with climate change. Predictions and models show that increasing temperatures are going to reduce flows to the Colorado River. The drama is not how much water we're going to have in the future — we know it's going to be less. The drama is how we’re going to decide who gets less water, and when.
Science Moab: What about the environmental impacts of low water flows, climate change, and the dam itself?
Schmidt: There’s been this decades-long imagination in the minds of some that the mistake of Glen Canyon Dam could be easily reversed by just letting the river run free. But there are messy little details about the science. We have learned that when Lake Powell is low, the water released into the Grand Canyon is much warmer. The Grand Canyon has a unique fish ecosystem, and it's a refuge for the largest population of endangered humpback chub on Earth. If you change that temperature, you might shift that ecosystem. At the same time, many fish biologists view the far western Grand Canyon as the most favorable place for native fish fauna anywhere in the Colorado River Basin. Why? The river is warm down there, but with Lake Mead low, there’s a hair-raising rapid at Pierce Ferry which blocks undesirable non-native reservoir fish coming from Lake Mead. So if you kept Lake Mead relatively full, and you inundated that rapid, you would eliminate the barrier and non-native fish would swamp the Grand Canyon.
As scientists, we can’t say this is unacceptably bad; what we can say is that it would be very different. It's not so simple as saying, “let the river run free, and it'll all be wonderful downstream.” It'll be really different downstream.
This interview has been edited for length and clarity. To learn more and listen to the rest of Jack Schmidt and Eric Kuhn’s interview, visit https://sciencemoab.org/lake_powell_2020/