The advisers spent five years inspecting the four dams in the United States and Mexico that are supervised by the International Boundary Water Commission. They found that both the 132-MW Amistad and 63-MW Falcon dams could be unsafe.
Declaring the need for action to be urgent, the inspectors classified the 254-foot-tall Amistad to be �potentially unsafe.� They recommended a panel of geotechnical consultants be convened to evaluate further the stability and foundation of Amistad, a multi-purpose dam near Del Rio, Texas, in the U.S., and Ciudad Acuna, in Mexico.
The Amistad finding was based largely on naturally occurring sinkholes that have existed since the dam was completed in 1969 and that could affect stability. The dam has a concrete gravity section and flanking earth embankments. A hydro plant was built on the U.S. side of the dam in 1983; Mexico added a powerhouse in 1987.
The advisers classified Falcon Dam �conditionally unsafe,� saying the need for action is a high priority. They recommended current analytical methods be used to update seepage and stability analyses of the 150-foot-tall, multi-purpose rolled earthfill embankment near Roma, Texas, in the U.S., and Nueva Ciudad Guerrero, in Mexico.
�Based on our observations, review of records, and in consideration of the project experiences with foundation seepage, sulfates in the foundation seepage, and lack of current seepage and stability analysis, we conclude that the dam is conditionally unsafe, and that specific investigations, evaluations, and studies are needed,� the advisers reported.
They said updated analyses of Falcon would help the IBWC confirm, or change, classification of the dam and to make any repairs that might be needed. Power plants on the U.S. and Mexico sides of the dam each house three turbine-generators.
IBWC and technical advisers from the Corps of Engineers and Mexico's National Water Commission and Federal Electricity Commission released the inspection report in August. It also covers two non-hydropower dams, Anzalduas and Retamal.
The inspectors determined all four dams generally are well maintained and capable of operating under normal conditions. Three of the dams also are capable of operating under flood conditions; the inspectors recommended modification of flood operating procedures at Retamal due to gate problems.
IBWC said the commission is committed to complying with the recommendations. The commission plans to use its annual allocation of dam safety program money appropriated by Congress to initiate recommended studies, IBWC spokesman Sally Spener said. Appropriation bills pending in Congress include $550,000 for the dam safety program, she added.