On the first day of spring, Southern Nevada Water Authority board members heard promising news about what proved to be a very wet winter at the headwaters of the Colorado River.
The latest projections call for a 50-foot rise in Lake Powell and a 10-foot rise in Lake Mead as a result of an unusually heavy snowpack along the western slope of the Rocky Mountains.
The snow is so deep in some places that floods could be triggered when the melt arrives in parts of Colorado.
As of last week, the snowpack stood at 121 percent of average throughout the Colorado River basin. The runoff from all that snow is predicted to be about 117 percent of average.
But Thursday’s monthly drought report came with a warning from Kay Brothers, deputy general manager for the authority: “It’s still too early,” she said. “Next month we will have a good idea of where we’re at and what the runoff will be.”
The Las Vegas Valley gets about 90 percent of its water from the Colorado River by way of Lake Mead.
Water use and precipitation in Southern Nevada have little measurable effect on the water level at the lake. The rise and fall of the reservoir is almost entirely a function of Rocky Mountain snow, the amount of water released from Lake Powell upstream, and the amount of water delivered downstream to Arizona, California and Mexico.
As recently as last month it looked as if Mead might not benefit from this year’s above-average snowpack because operational rules require Powell to partially refill first.
Brothers said it now looks as if Powell will recover much more quickly than expected.
Between December and March, the U.S. Bureau of Reclamation doubled its projected gains for the reservoir on the Utah-Arizona border. The bureau now expects Powell to gain 50 vertical feet of water by midyear.
Brothers said that will allow for a 15 percent increase in the amount of water released downstream to Lake Mead, which would change the decline the bureau had been projecting into a 10-foot gain.
The rules governing the increased release were finalized in December, as part of a sweeping new accord among the seven states that share the Colorado River.
Part of that agreement allows the joint operation of Lake Mead and Lake Powell to protect water supplies in Colorado, New Mexico, Utah and Wyoming.
Right now, Lake Powell is at 44 percent of capacity and Lake Mead is at 51 percent.
The surface of Lake Mead has plunged more than 90 feet since the current drought clamped down in 2000, reducing the river system to about half its normal runoff.
In 2002, the driest year on record, runoff fell to 30 percent of average.
If the current projections hold, 2008 will go down as the best year on the river in more than a decade.
That’s good news to be sure, Brothers said, but it’s also worthy of another warning: “This is just one year.”
Contact reporter Henry Brean at firstname.lastname@example.org or (702) 383-0350.