Sumner Dam and Lake Sumner are on the Pecos River about 250 river miles north of Carlsbad and about 16 miles northwest of Fort Sumner, New Mexico. The dam is a zoned earthfill structure 164 feet high with a volume of 2,250,000 cubic yards.
The dam was constructed in 1937 with a major modification in 1956 which raised the dam and increased the spillway capacity. The dam is a zoned earthfill structure 164 feet high with a volume of 2,250,000 cubic yards. It is approximately 3,00 feet long, averages 30 feet wide at the crest, and is 164 feet high at the maximum section. The outlet works consist of a combination pressure tunnel and a 10-foot diameter penstock upstream of the gates and two penstocks, 5.5 feet in diameter, downstream. Releases are controlled by two 48-inch diameter jet flow valves, with a capacity up to 1,740 cubic feet per second at the top of the flood control pool. Irrigation releases, up to 100 cubic feet per second, may be made through a 20-inch jet flow valve. Larger releases are made through a service spillway near the west end of the dam. This service spillway is a tainter-gated chute-type structure with three 45-foot openings and an invert elevation at 4,259 feet mean sea level. An emergency spillway in the left abutment consists of a fuse plug type embankment. A 500-foot concrete sill, with a crest elevation of 4,275 feet mean sea level, is covered with earth and rock fill, and forms four individual sections at elevations 4,282, 4,283, 4,284, and 4,285 feet mean sea level. These sections are 130 feet, 130 feet, 118 feet, and 118 feet respectively.
The reservoir has an estimated active conservation capacity of 43,768 acre-feet in 1999. In addition to storage for irrigation, the dam and reservoir provide flood control and recreation benefits. While there is no storage allocated to recreation, there is a minimum pool of 2,500 acre feet. In 1980, a transfer of irrigation storage rights to Santa Rosa Dam (a Corps of Engineers' dam), and Reservoir in Northern New Mexico provided for more flood control storage in Lake Sumner (under direction of the Corps of Engineers).