Amistad Dam bridge closed for power plant maintenance

Officials with the International Boundary and Water Commission have temporarily closed the international bridge that spans the top of Amistad Dam in order to carry out routine maintenance on a power plant underneath the structure.

The bridge was closed last Friday and will not reopen until Thursday, IBWC officials said.

The closure comes after a three-day long inspection of the power plant by the U.S. Army Corps of Engineers, IBWC Public Affairs Chief Frank Fisher said.

“The generator and turbine … components are important assets of this detailed inspection,” Fisher said.

In order to inspect the machinery, water that traverses the dam must first be removed from the components.

“(The) bulkhead gate was lowered into the penstock intake slot to prevent the flow of water from reservoir pool into power plant. Once the gate is lowered, and sealed, the entire penstock is drained, and personnel can go inside … for inspection,” Fisher further stated.

The maintenance process involves shutting down one of the power plant’s two generators, which gives engineers a rare opportunity to kill two birds with one stone.

“We have also taken advantage of this opportunity by having contractors come out and see the infrastructure for future rehabilitation projects,” Fisher said.

Officials have previously said that Amistad Dam needs substantial overhaul due to the prehistoric limestone bedrock upon which it is built.

That bedrock, known as the karstic Georgetown limestone, is extremely porous and soft. Over time, the weight of billions of tons of water has put pressure on the limestone substrate which has, in turn, led water to seep through downstream at various springs.

USACE engineers have since categorized Amistad Dam as a “Class II” on its five-point rating scale, meaning it is at high risk of failure.

However, the IBWC has developed a complex plan to rehabilitate the structure, but is currently awaiting the funding to do so.

Meanwhile, IBWC staff are in the process of removing the bulkhead that was placed in the dam to carry out the power plant inspection.

“IBWC staff will remove the bulkhead gate utilizing our 100 ton mobile crane which occupies the entire roadway,” Fisher said.

The removal process will take several more days to complete. The bridge is expected to reopen on Thursday.