America’s largest reservoir, Las Vegas’ main water source, and an important indicator for water supplies in the Southwest — will fall this week to its lowest level since 1937 when the manmade lake was first being filled, according to forecasts from the federal Bureau of Reclamation.
The record-setting low water mark — a surface elevation of 1,081.8 feet above sea level — will not trigger any restrictions for the seven states in the Colorado River Basin. Restrictions will most likely come in 2016 when the lake is projected to drop below 1,075 feet, a threshold that forces cuts in water deliveries to Arizona and Nevada, states at the head of the line for rationing.
But the steadily draining lake does signal an era of new risks and urgency for an iconic and ebbing watershed that provides up to 40 million people in the U.S. and Mexico with a portion of their drinking water. The rules governing the river are complex, but the risk equation is straightforward: less supply due to a changing climate, plus increasing demands from new development, leads to greater odds of shortages…
Yet despite a shrinking lake, diminishing supplies, and ardent pleas from tour guides and environmental groups to preserve a canyon-cutting marvel, the four states in the basin upriver from Lake Mead intend to increase the amount of water they take out of the Colorado River. All of the states are updating or developing new state water strategies, most of which involve using more Colorado River water, not less.
“We have mapped out how the remainder of our allocation can be used,” Eric Millis, director of the Utah Division of Water Resources, told Circle of Blue. “It’s going to happen sooner rather than later. We have a place for every drop.”
Utah — like fellow upper basin states Colorado, New Mexico, and Wyoming — is not using all the Colorado River water it was granted by a 1922 interstate compact. The four states have the legal authority to increase their Colorado River diversions.
However, the water they seek may not be available. The calculations of availability stem from wetter hydrological conditions and supply forecasts made nearly a century ago. Under the 1922 compact, the upper basin is entitled to 7.5 million acre-feet. A later agreement apportioned each state a percentage of the available supply. The upper basin’s average annual use between 2007 and 2011, the most recent figures, was 4.6 million acre-feet.
The legal entitlement, granted at a time when the river’s hydrology was poorly understood, is surely too high. All the states acknowledge that fact. “We’re not pegging our hopes or analysis on the full 7.5,” said James Eklund, director of the Colorado Water Conservation Board, the state water planning agency…
The upper basin put forward a plan this spring to keep more water in Powell. The states would do this by paying farmers not to farm and by changing how smaller mountain reservoirs are managed. Three urban water utilities in the lower basin, along with Denver and the federal government, put up $US 11 million to develop a similar basin-wide program…
Though the lower basin is using its entire allocation, the four upper basin states are not. They desire more water from the Colorado, yet exactly how much water is available is uncertain.
The only concrete number to emerge so far is 5.8 million acre-feet of water available for the upper basin, or three-quarters of what was granted. That figure, called the hydrological determination, was developed by New Mexico and the Department of the Interior in 2007 as part of a water supply study.
New Mexico is the only state using 5.8 million acre-feet as a firm number. Millis said Utah is using 6.5 million acre-feet of upper basin supply for its planning, and Colorado and Wyoming are looking at a range of values.
Eklund told Circle of Blue there is “vigorous debate” both within and between states over what number should be used to assess water availability and what the acceptable levels of risk are as water use increases.
“There’s a sliding scale of risk,” Eklund said. “The more water you develop, the more risk you take on. But that doesn’t necessarily counsel against a project.”