El Vado Dam Middle Rio Grande Project, New Mexico: Issue Evaluation - Service Spillway - Operational Testing & Dynamic Analysis

El Vado Dam located on the Rio Chama about 160 miles north of Albuquerque, was built by the Middle Rio Grande Conservancy District in 1934-1935 and was rehabilitated by the Bureau of Reclamation in 1954-1955. A new outlet works was built by Reclamation in 1965-1966 to accommodate the additional water from the San Juan-Chama Project. The dam embankment is of rolled gravel fill with a steel membrane on the upstream face. The dam is 175 feet high and has a crest length of 1,326 feet. The reservoir has a total capacity of 196,500 acre-feet. The service spillway is a steel-plate-lined channel with inflow controlled by a 36-ft by 24-ft radial gate. The spillway channel is located on the right abutment and is founded on earthen material
that includes Mancos shale.
The service spillway at El Vado Dam is a unique design, unlike any other structure that
Reclamation operates and maintains. Over the years, maintenance activities on the spillway have included weld repairs to cracks and failed welds. These repairs have been only partially successful due to post repair cracking in the heat affected zones of the welds. The floor/invert plates are 5/16-in-thick and the wall plates are ¼-in-thick; both invert and side wall lining plates are attached to a steel channel support system using 13/16-inch-diameter plug welds.
This technical memorandum will serve as the deliverable for the Operational Testing and Dynamic Analysis of the Service Spillway at El Vado Dam, funded by Reclamation’s Dam Safety Office to satisfy SOD recommendation 2006-SOD-A. This report summarizes testing at the dam site during the week of June 23, 2008. The testing included a modal survey of several spillway lining plates and in addition, results from strain and acceleration measurements during an operational test of the spillway. The results of the testing were used to perform a fatigue life analysis and additional structural analyses in order to provide critical input for future risk assessment and associated flood routing decisions.