Burrowing rodents caused a century-old irrigation canal to fail and flood a rural Nevada town in January, a team of scientific experts concluded in a report for the U.S. Bureau of Reclamation made public Thursday night.
Muskrats, beavers, gophers and other rodents dug holes as deep as 25 feet into the earthen canal embankment over the years, according to the report.
Water burst through a 50-foot breach in the weakened structure at 4 a.m. on Jan. 5 and flooded hundreds of homes in Fernley, a community of about 20,000 residents about 30 miles east of Reno. As many as 600 homes were damaged by floodwater, which reached 8 feet deep in some places, and the area was declared a federal and state disaster area.
"They believe it was the rodent critters that caused the break of the canal," Jeffrey McCracken, public affairs director of the bureau's Mid-Pacific Region in Sacramento, told The Associated Press.
The bureau owns the 31-mile canal that takes water from the Truckee River south to Fallon-area farmers.
"Obviously, rodents are a problem here. That is what the evaluation team felt was the cause," he said in an interview before the meeting.
Nearly 2 inches of rain fell the day before in the area that averages only about 5 inches of precipitation a year. But the water flow at the time of the breach was at or near the allowable level of 750 cubic square feet per second, the report said.
"This was determined not to be a flooding issue," McCracken said. "The flows were within the capacity of the canal."
Investigators considered and ruled out other possible causes for the canal failure, including erosion, seismic activity, embankment instability and sabotage.
An accompanying evaluation determined that as soon as additional flow measuring gauges are installed, it would be safe to resume diverting a small amount of water from the Truckee River into the canal.
The experts determined nearly half of the maximum water flows can return to the canal, but only if corrective and safety steps are taken.
Returning the canal to its full operation will require "significant repair and/or modification" of the canal, bureau officials said. Federal funding would be needed for the project that would likely carry a price tag of tens of millions if not hundreds of millions of dollars, they said.
Ernie Schank, president of the Truckee-Carson Irrigation District, which operates and maintains the canal under a contract with the bureau, said the findings were expected. He said the district has been working to install new gauges and should be ready for some water to begin flowing Friday.
"We kind of figured there would be some conditions placed on the operations of the canal this year until there was some more permanent things done to bring the canal up to standards," he said.
Request for more testing
A lawyer representing owners of about 80 flooded homes who have filed a class-action lawsuit against the irrigation district in Lyon County District Court in Yerington has asked a federal court to order more testing before reopening the canal.
In addition to filling an unspecified number of rodent holes, the team recommended numerous actions to ensure the safety of the canal, including improving canal facilities and developing emergency response plans.
"Considering the canal has been in operation for 102 years, one would expect that when you evaluate and review it as extensively as we've done that they were going to find this and they are going to have to fix these things," McCracken said.
The investigative team included government and private geophysicists, hydrologists, engineers and geologists.