Rehabilitation of the Piedra Liza Dam near Bernalillo, NM

Abstract Only - This presentation provides a case study in designing improvements to rehabilitate an aging dam located just north of Albuquerque, near Bernalillo, New Mexico. The project is being conducted under the USDA-Natural Resource Conservation Service (NRCS) Watershed Rehabilitation Program. The U.S. Department of Agriculture was first authorized by Congress to help local communities with flood control and watershed protection more than 50 years ago. Since 1948, local communities have constructed more than 11,000 flood control dams in 47 states under various authorities. New Mexico has 32 small watershed projects with 78 flood control dams. Many were constructed between 1955 and 1965 and are reaching the end of their service life; and need rehabilitation to address structural deterioration, sediment accumulation, and to comply with current dam safety design criteria. In 2000, Congress amended the Watershed Protection and Flood Prevention Act (PL-566) and authorized the NRCS to work with project sponsors to address public health and safety concerns and potential environmental impacts of aging dams. The NRCS provides technical and financial assistance in planning, designing, and implementing watershed rehabilitation projects. Piedra Liza Dam near Bernalillo, New Mexico is one such structure. It was constructed in 1955 by Santa Fe-Sandoval Soil Conservation District with financial and technical assistance from the Soil Conservation Service. The dam is a 1030-foot-long, 39-foot-high, earthen embankment located on an ephemeral watercourse that drains a 4.15-square-mile watershed. It currently provides protection against flood damages from storms up to the 100-year, 24-hour event. The affected area includes 600 structures and 1600 residents in the City of Bernalillo, as well as Interstate Highway 25, the Burlington Northern-Santa Fe Railroad, and other public facilities. The dam has been well maintained by the Coronado Soil and Water Conservation District, but has reached the end of its 50 year design life. In 2003, the SWCD applied for assistance from the NRCS to rehabilitate Piedra Liza Dam. Planning Studies were initiated in October 2003 and the Final Supplemental Watershed Plan and Environmental Assessment (Plan/EA) was completed by the NRCS and Tetra Tech, Inc. in March 2005. The Plan/EA determined that there was a federal interest (i.e., benefit cost ratio greater than 1.0) in rehabilitating the dam to operate for an additional 100 years. The recommended plan includes raising the crest of the dam by roughly one-foot, enlarging the auxiliary spillway to convey floodwater from the probable maximum precipitation storm, installing roller-compacted-concrete revetment on the auxiliary spillway to provide integrity, and improving the inlet and outlet for the principal spillway. In July 2005, The NRCS contracted with Tetra Tech to complete design studies for the recommended improvements and to prepare the plans and specifications for construction. The final submittal is scheduled for completion in January 2006 and construction is scheduled to begin in the summer of 2006.