July 25, 2016--Snow, runoff and the Colorado River Basin (Mountain Town News)

From his office in Glenwood Springs overlooking the Colorado River, Eric Kuhn has become one of the West’s most prominent thinkers about the intersection of water, climate change, and allocations for farms, factories and cities, including ski towns. He joined the Colorado River Water Conservation District as an engineer after working in the private sector as a nuclear engineer. He has been manager of the water district since 1996. The district encompasses all of the Colorado River drainage in Colorado upstream from Fruita. As such, the district is a primary source of water not just for the bulk of Colorado ski towns and Front Range cities but also downstream farms and cities, including Phoenix, Los Angeles, and San Diego. Mountain Town News collaborated with Kuhn on a reader-friendly Q&A to probe the growing evidence that warming temperatures have started upsetting the apple cart of Colorado River operations.

Was it a good snow year in the upper Colorado River Basin? It varied, of course, but generally it was average to a little above average in the Gunnison, Yampa, Green and other basins of the upper Colorado River.

Does that mean the reservoirs in the Colorado River Basin are filling? We’ve been hearing a lot about declining levels of Lake Powell and Lake Mead, the two giant reservoirs on the Colorado River. Water runoff is a more complicated story than snowpack. This year, for example, the runoff reached about 94 percent of average. So, average or above-average snowpack but below-average runoff. The best way to understand snowmelt is to study the inflow into Lake Powell. You can call this reservoir the savings account for the Upper Colorado River Basin. It is this savings account that allows the upper division states of Colorado, Utah, Wyoming and New Mexico to consistently meet water supply obligations to the Lower Basin at Lake Mead as spelled out by the Colorado River Compact of 1922. The lower division states are California, Nevada, and Arizona. There is no such thing as an average snow year—nowhere, no place. Snowpack varies wildly from year to year. That said, in an average water year, about 10.7 million acre-feet flows into Powell. Three-fourths of that occurs during April through July.

Average snowpack but below-average runoff? That poses an obvious question. But first, would you explain this savings account more? The 1922 compact requires the upper division states to not deplete the flows downstream to Lake Mead below a certain volume. Powell most often releases 8.23 to 9 million acre-feet, as required by the 2007 interim agreement among the seven basin states and the federal government, a side agreement to the compact. But ordinarily, because of evaporation, that means the effective demand on Powell is 8.6 to 9.4 million acre-feet. What this means is that in any year with an 85 percent of average runoff, Lake Powell just about breaks even. In other words, water levels are not gaining but neither are they declining. For local supply reservoirs in most of Colorado, we can get by with an 85 percent or better inflow year without too many concerns.

So nothing to worry about in the upper basin? We’re meeting our obligations, end of story? We are OK for now and probably for the immediate future, but if the current conditions transition into a drought over the next several years, as happened after the 1998 El Niño event, we could be in serious trouble because unlike in 1998-99 when system reservoirs were plumb full, today they’re only about half full.

How much of the water in Lake Powell and Lake Mead comes from upstream of Grand Junction (or Moab)? And how much of that originates as snow in places like Steamboat Springs, the Eagle Valley, and the San Juan Mountains? Most of the run-off in the upper basin originates from about 20 percent of the land: those watersheds above about 9,000 feet in elevation, where snowpack accumulates and sticks through the snow season. The Green River drainage contributes 36 percent of the flow into Lake Powell, the Colorado mainstream 36 percent, the San Juan 24 percent, and the others 4 percent, according to the U.S. Bureau of Reclamation. This is the long-term average.

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