Reservoirs

Published October 27, 2010

Arizona

Total reservoir storage in the three large reservoir systems within Arizona’s borders, San Carlos Reservoir on the Gila River and the Salt and Verde river reservoir systems, increased by about 340,000 acre-feet during the 2010 water year. Levels in the San Carlos Reservoir increased substantially during the water year (Table 2). Salt and Verde river system storage rose to completely full in the spring, getting a major pulse of runoff during the winter months. On the Colorado River, combined total storage in Lake Powell and Lake Mead decreased by 1.04 million acre-feet, with Lake Mead dropping in September to an elevation of less than 1,084 feet above sea level (ASL)—a level not experienced since 1956 (Figure 3a). Implementation of the Colorado River Interim Guidelines for lower basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead will keep Mead from triggering shortage in the Lower Basin. However, if Mead drops below 1,075 feet ASL, a substantial release of water from Lake Powell will be required.

New Mexico

New Mexico total reservoir storage decreased by approximately 11,000 acre-feet during the 2010 water year. Total Pecos River reservoir storage increased by more than 32,000 acre-feet. However, storage in these reservoirs remains below historic averages. Storage declined by 126,000 acre-feet in the Rio Grande Basin (Table 3) during a winter characterized by average to below-average snowpack in most Rio Grande headwater sub-basins. Consequently, the level in New Mexico’s largest reservoir, Elephant Butte, declined by almost 83,000 acre-feet. Combined storage in Elephant Butte and Caballo Reservoirs—a trigger for Rio Grande Compact Article VII restrictions—declined to within about 10,000 acre-feet of levels that will cause water rationing (Figure 3b). Article VII restrictions were last implemented in December 2007. Navajo Reservoir, in the San Juan River Basin, gained about 98,000 acre-feet. The 2009–2010 El Niño winter delivered plentiful precipitation to the Mimbres and Gila river basins in southern New Mexico, and these streams had well above-average flows during the spring months.