Reservoirs

Published October 25, 2011

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—decreased by about 951,000 acre-feet during the 2011 water year. Levels in the San Carlos Reservoir decreased substantially during the water year (Table 1). On the Colorado River, combined storage in Lakes Powell and Mead increased by 5.28 million acre-feet (maf; Figure 3a) due to substantial snowpack in the northern part of the Colorado River Basin. In April, based on the projected elevation of Lake Powell at the end of the water year, the U.S. Bureau of Reclamation shifted the coordinated operations of Lakes Powell and Mead to the Equalization Tier in accordance with the Interim Guidelines on managing the Colorado River. The Equalization Tier goes into effect when Lake Powell’s projected January 1 elevation is above a specified elevation and allows more than 8.23 maf of water to be released from Lake Powell during the Water Year until the content of the lakes equalizes or certain elevations. This has resulted in substantial increases in storage in Lake Mead.

New Mexico

Total storage in New Mexico reservoirs was about 351,000 acre-feet less than one year ago, not including changes in the storage for El Vado and Heron reservoirs, which had no report for September 2011. Navajo Reservoir, in the San Juan River Basin, decreased by almost 66,000 acre-feet. Pecos River Reservoir storage decreased by more than 58,000 acre-feet. The 2010–2011 La Niña winter is in part to blame for decreasing water storage. Storage also declined by 195,300 acre-feet in the Rio Grande Basin (Table 2), partially the result of average to below-average snowpack in most of the Rio Grande headwaters. New Mexico’s largest reservoir, Elephant Butte, declined by almost 172,000 acre-feet. Combined storage in Elephant Butte and Caballo reservoirs, used to determine water restrictions set forth in the Rio Grande Compact, approached restriction levels in the spring. Without substantial snowpack in the headwaters of the Rio Grande this winter, restrictions likely will be implemented in 2012.