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maintain Lake Mead’s elevation, adding an element of uncertainty to the goal of maintaining approximately equivalent volumes in the two reservoirs as part of the 2007 Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead. Observers say the unprecedented

dryness has pushed water management into another realm. “Te folks in the Upper Basin are

very nervous about whether the Lower Basin can stabilize Lake Mead,” said Doug Kenney, director of the Western Water Policy Program at the University of Colorado, Boulder’s law school. “If Mead gets in a lot of trouble, there is this concern that the status of Lake Powell is out of their control.” Lake Mead receives about 9 million

acre-feet of water each year from Lake Powell. When evaporative losses are accounted for, the demand on Lake Mead is about 10.2 million acre-feet each year. Tat shortfall between inflow and outflow has come to be known as the structural deficit. Furthermore, it’s widely accepted that the 1922 Colorado River Compact’s allocation of 7.5 mil- lion acre-feet annually for each basin was based on an overestimation of how much water the river could provide. “It’s long been known that the 7.5 million acre-feet of beneficial consump- tive use promised to the Upper Basin in the 1922 Compact is not as reliable of a supply as they thought back then,” Ostler said. “We have looked at the yield of the river and what the Upper Basin has considered to be an acceptable short- age risk, and determined on several occa- sions that there is a little over 6 million acre-feet, including shared evaporation

“If we start with less than 15 or 16 million acre-feet of water in Lake Powell and we were to go through another 2001- 2004-type drought, we essentially drain Lake Powell without action.”

– Don Ostler, Upper Colorado River Commission

losses, of consumptive use that is avail- able at a reasonable risk.” Te Lower Basin states use their full allocation of 7.5 million acre-feet, with California leading the way at 4.4 million acre-feet annually. (Under terms of a 1944 international treaty Mexico receives 1.5 million acre-feet a year.) Allocation in the Upper Basin states is determined on a percentage basis and the Colorado River Compact requires that they not deplete the river below an aggregate of 75 million acre-feet for any period of 10 years. “Tis has allowed the Upper Basin

states to recognize long-term changes in hydrology and study what the reliable safe yield of the river is before natural growth has exceeded the supply,” Ostler said, adding that several hydrologic determination studies show a safe yield with a tolerable risk of shortage of about 6 million acre-feet of use per year. Some of this water is captured and

stored in reservoirs above Lake Powell. For the most part, there is not enough water to meet all the needs. “Te Upper Basin lives with shortage

every year,” Ostler said. “Somewhere in the Basin there is a lack of snowfall and the water stops running down a creek before the irrigation season ends and

farmers are shorted. We call it hydro- logic shortage as opposed to compact shortage or regulated shortages.”

Managing Risk In the Upper Basin, the state of Colorado is entitled to the largest share of the river – 51 percent (or approximately 3.8 million acre-feet annually based on the 7.5 million acre-feet allocation.) Te state, however, is nearing its limit of what it can take from the river – especially if one considers 6 million acre-feet the amount of available water – according to its Water Plan released in 2015. “As is the case with other Western states, Colorado does not have enough water to meet historic and future uses in a balanced manner without a collaborative plan of action,” the Plan said.

Colorado’s situation is an example

of the West’s hydrological divide. As much as 80 percent of its water is west of the Continental Divide with about 90 percent of the population living east of it in communities and cities that include Denver, Boulder and Colorado Springs. Teir water is delivered via 24 tunnels and ditches carrying an annual average of 500,000 acre-feet. Tere is the belief that Colorado has

to proceed carefully in its water supply management. “Tere is risk associated with where

we are today,” said Aaron Derwingson, agricultural coordinator for Te Nature Conservancy’s Colorado River Program. “Tere may be water to develop in any given year, but that’s going to vary a lot with hydrology. Any further amount we develop is going to increase the risk.” Te Nature Conservancy and its

partners are working on solutions that can be implemented, such as water banking, before a crisis hits, Derwingson said.

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Winter 2016-2017 • River Report • Colorado River Project • 3

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