Albuquerque Area Office

Water Operations Group

Annual Operations Plan - Calendar Year 2001

Elephant Butte Dam and Reservoir: The reservoir operations are based on average historic reservoir losses and evaporation rates for Elephant Butte and Caballo Reservoirs. Scheduled outflow from Elephant Butte and Caballo are based on average irrigation demands for years with a full water supply.

Inflow Forecast: The projected 2001 reservoir operating plans are based on the expected March through July runoff flows at the Rio Grande at the Otowi Bridge and at San Marcial, using the coordinated National Weather Service/Natural Resources Conservation Service May 1, 2001 forecast.

The most probable runoff predicts a 50 percent chance of exceeding 785,000 af at the Otowi Bridge Station, 114 percent of the 30-year average of 686,000 and 500,000 af at the San Marcial Station, 100 percent of the 30-year average of 501,000 af.

The reasonable minimum forecast predicts a 90 percent chance of exceeding 322,000 af at the Otowi Bridge Station and 161,000 af at the San Marcial Station. The reasonable maximum forecast predicts a 10 percent chance of exceeding 1,108,000 af at the Otowi Bridge Station and 839,000 af at the San Marcial Station.

Elephant Butte Dam and Reservoir: Inflow into Elephant Butte Reservoir during 2001 is projected to total 626,000 af, measured at San Marcial, New Mexico. The inflow into Elephant Butte will be approximately 71% of the 87-year average annual inflow at San Marcial of 881,517 af. The water supply March through July runoff on the Rio Grande is projected to be 542,000 af, or 79 % of the 30-year average of 686,000 af at the Otowi Bridge Station, and 317,000 af, or 63.3% of the 30-year average of 501,000 af at the Rio Grande at San Marcial Station; this is a regulated water supply based on upstream reservoir operations.

The storage content for Elephant Butte Reservoir at the beginning of the year, on December 31, 2000, was 1,266,840 af at an elevation of 4,381.68 feet. The storage content at the end of year, on December 31, 2001, is projected to be 986,830 af at an elevation of 4,369.39 feet. Project storage for Elephant Butte and Caballo Reservoirs, based on the May 1 forecast, has already peaked on February 22, 2001, at a combined storage of 1,360,290 af, or 61.8% of combined conservation capacity of 2,200,030 af (Combined reservoir conservation capacity = 2,023,358 af (Elephant Butte Reservoir) - 50,000 af ( EB flood control space) + 326,672 af (Caballo Reservoir) - 100,000 af (Caballo flood control space)).

The peak storage for Elephant Butte Reservoir of 1,306,100 af at an elevation of 4,383.24 feet has already occurred on January 31, 2001. The highest storage ever recorded at Elephant Butte Reservoir was 2,302,800 af at an elevation of 4,409.19 feet, 2.19 feet above the spillway crest elevation of 4,407.00 feet. This high storage occurred June 16, 1942. The lowest storage at Elephant Butte Reservoir during 2001 is projected to occur on October 15 at 907,300 af at an elevation of 4,365.42 feet. The average storage at Elephant Butte Reservoir during 2001 will be 1,077,790 af at an elevation of 4,373.64 feet. Elephant Butte releases for 2001 are estimated to be 794,000 af.

A reservation of a certain portion of conservation storage for prudent flood operating space in Elephant Butte Reservoir was implemented in 1990. This space was provided to operate the dam in a prudent and safe manner to ensure that releases from the dam would not exceed 5,000 ft³/s in the river channel below Elephant Butte Dam during a 100-year flood event above Elephant Butte Reservoir. The summer operating space for the flood pool is 50,000 af (elev. 4,405.60 feet to elev. 4407.00 feet) from April 1 to September 30, and the winter operating space for the flood pool is 25,000 af (elev. 4,406.30 feet to elev. 4,407.00 feet) from October 1 to March 31 each year.

New area and capacity tables for Caballo and Elephant Butte Reservoirs, dated April 1999, came into effect on January 1, 2001.

[Elephant Butte Reservoir]