Seepage, Rock Stability & Bank Stabilization, Abiquiu Dam and Reservoir, New Mexico

Abiquiu Dam and Reservoir is located on the Rio Chama, approximately 35 miles northwest of Española, New Mexico. The dam consists of low permeability rolled earth fill with downstream drainage layers, controlled outlet works and an uncontrolled rockcut spillway. The dam was authorized for flood control and sediment retention and was designed as a dry dam, holding flood pools for relatively short durations. The dam is founded on the highly fractured sedimentary mudstone, sandstone and conglomerate of the Abo Formation and the Poleo Sandstone Lense of the Chinle Formation. Construction was completed in 1963 and the first pool was impounded in 1964. Due to water resource issues in the desert southwest, use of the dam has changed and it has been utilized to store water year round and for downstream power production. Seepage along both the right and left abutments has also been a concern historically. Seepage and rock stability along the left abutment continues to be a persistent problem presenting hazards to personnel, outlet works structures and the County of Los Alamos hydroelectric plant. In 2004, the Albuquerque District initiated a study into the kinematics of rock failure along the left abutment as well as developing Factors of Safety (F.O.S.) using 2-d limiting equilibrium analysis. Results of this study will be presented as well as recommendations for left abutment bank stabilization. 22 pp., 9 figures, 2 tables, 17 references.