Feds promise $8.6 million for Ephraim Canyon retention basin

The federal government has earmarked $8.6 million for a long-desired project to prevent flash flooding in western Nogales, the office of U.S. Rep. Raul Grijalva announced on Friday.

Still, the goal of building a retention basin in Ephraim Canyon to prevent rainwater from rushing down and overwhelming the Western Avenue wash is several years away from completion, according to John Hays, Santa Cruz County’s flood control coordinator.

During rain events, water runs downhill from Mexico and east along the border, under the Mariposa Port of Entry into Ephraim Canyon behind Holy Cross Hospital. From there, the runoff passes under Interstate 19 and into the Western Avenue wash, which eventually connects with the Nogales Wash.

During especially heavy downpours, the runoff can overwhelm the narrow channel at Leyva Bridge, near Western Avenue’s intersection with I-19, and pour into the street and surrounding neighborhood. One of the worst floods in recent memory came in late July 2014, when a wall of runoff toppled a section of border wall near the Mariposa port and brought a torrent of debris-filled floodwater into yards and homes along Western Avenue – a number of which suffered significant damage.

The idea of a flood control project in the area has been bandied about for decades. Then, about 15 years ago, Hays said, the county began to look seriously at building a retention basin in the area and commissioned a preliminary engineering design.

“The result of that preliminary engineering indicates it is possible to build a basin large enough that the vast majority of the Western Avenue area downstream of I-19 could be protected from flooding, from not only the one-percent flood (aka 100-year flood), but protected up to almost the 0.2-percent flood (aka the 500-year flood),” Hays wrote in an email last Friday.

Feds promise .6 million for Ephraim Canyon retention basin

“Since then, we have been working on trying to figure out how to acquire funding for the project,” he wrote, noting that the estimated price tag was in the vicinity of $10 million.

A couple of years ago, he said, the Federal Emergency Management Agency (FEMA) announced a new grant of up to $10 million for pre-disaster mitigation projects. Each state could only submit one or two projects, Hays said, and Arizona choose the Ephraim Canyon basin as its priority submission.

On Friday, Grijalva’s office announced that FEMA had allocated a little more than $8.6 million for the Ephraim Canyon retention basin, and touted the project for its potential to reduce scour and erosion in the Nogales Wash and Potrero Creek, and better protect the international sewer line that coincides with those two channels.

According to Hays, the FEMA contribution will cover 75 percent of the cost; the county will need to come up with the rest.

“We have had conversations in the past with other entities about providing funds or in kind donations, but we have not, and cannot, formalize anything until we are officially awarded the grant by FEMA,” he wrote in his email. “Once the official award has happened, we can begin to line things up in earnest.”

In addition, Hays said, the plans are approximately 25 percent complete, so those will need to be finalized. Then comes the state and federal permitting process.

“Once the award is granted, we will have three years to get the construction done, once all the permits are in place,” he wrote. “The permitting could take one to two years, so completing the project would be approximately five years after the official award occurs.”

The Ephraim Canyon project is one of three retention bases the county is hoping to construct around Nogales, Hays said.