The New Mexico Office of the State Engineer has lowered the safety ratings of the two reservoirs in the Santa Fe Municipal Watershed to “poor” and alerted city officials earlier this week that pipe problems could lead to leaks or erosion of dam embankments.
The city said it is already addressing the problems with the outlet pipes of the McClure and Nichols dams, discovered in May during separate city and state evaluations. Those reviews followed a 2018 report by the U.S. Army Corps of Engineers that had rated the dams “satisfactory.”
City spokeswoman Lilia Chacon said crews have completed about 30 percent of the engineering upgrades at the Nichols Dam, and the city hopes to finish the project in winter 2020-21. Then the city will begin to address problems at McClure Dam, which could take another two years, she said.
Charles Thompson, chief of the Dam Safety Bureau for the State Engineer’s Office, told Santa Fe Public Utilities Director Shannon Jones in a letter Monday that the dams’ outlet conduits “are in need of mitigation or rehabilitation measures without which the safety of the dams may be compromised.”
He also announced the dams’ safety ratings had been downgraded, and noted the need for routine maintenance measures, such as rodent abatement, vegetation management and more consistent monitoring of the conduits.
“The city is working on a problem that is likely a low risk at this point, but it’s a problem that could grow,” Thompson said in an interview Thursday, “… so we have to be wary.”
City officials responded quickly to the concerns and began working on the problems almost immediately, he added.
Chacon downplayed the lower safety rating, saying the dams are not in danger of failing.
“Just because they have been downgraded to poor does not mean a dam is going to break and all hell will come down the hill,” she said. “The downgrading is a result of the uncertainty of what may be there, not because there is something imminent that will happen.”
An inspection report provided by the State Engineer’s Office said there was a “significant amount of leaks/seeps through cracks and joints in concrete” at the McClure Reservoir’s dam. “The walls, ceiling and floor were wet at many areas.”
The two nearly century-old earthen dams have the capacity to hold a total of 1.2 billion gallons of water, providing between 40 percent and 50 percent of the city’s annual supply.
With the new rating, the two Santa Fe dams join some 200 others around the state that were rated in poor condition in the 2018 Army Corps of Engineers report. Another eight dams were rated unsatisfactory.
Earlier this year, State Engineer John D’Antonio told a legislative committee a wet winter and heavy spring runoff had increased risks for many state-regulated dams, possibly causing them to overflow or burst under the weight of heavy flows.
New Mexico has not experienced a serious dam break in many years. But in 2013, heavy rains did cause a breach in an earthen dam upstream from La Union in Doña Ana County. That dam received an unsatisfactory rating in the 2018 report.
The state regulates about 300 of the state’s 400 dams, including many it does not own, while the federal and tribal governments regulate the remaining 100.
The American Society of Civil Engineers also rates dams around the nation. In 2017, it gave New Mexico a D for the condition of its dams and said 219 of them are high-hazard structures, meaning lives would be threatened downstream if there were a breach or overflow.
The Army Corps of Engineers has classified Nichols and McClure as high-hazard dams.