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FEMA will spend $8.6M to build flood control basin in Nogales area

Ephraim Canyon Flood Project will protect 'vital infrastructure'

The Federal Emergency Management Agency will allocate more than $8.6 million to mitigate flash flooding in the Nogales area, U.S. Rep. Raúl Grijalva announced.

The effort, known as the Ephraim Canyon Flood Project, will including the development and construction of a detention basin located between Interstate 19 and the Mariposa border crossing in Nogales.

During monsoon storms, water rushes downhill from Mexico and runs east along the border past the Mariposa Port of Entry into Ephraim Canyon. Water then floods into the Western Avenue wash, which eventually links to the Nogales Wash further north, and during major storms, runoff can overwhelm narrow channels and pour into the surrounding neighborhoods, swamping people's homes and buildings.

"This project is one of many that will protect and reduce the impact of flooding events on the (International Outfall Interceptor) sewer line and communities in Nogales and Southern Arizona. As we continue to build out critical infrastructure, we must ensure these projects are built in a resilient and sustainable way that mitigate the effects of the climate crisis," said Grijalva in a news release Friday.

The Ephraim Canyon project will work to protect "vital infrastructure" in the Nogales area, including a vast sewer line known as the International Outfall Interceptor, as well as state and railroad lines, a major local natural gas and water line, as well as several critical infrastructure locations such as gas stations, fire stations, the Arizona Department of Public Safety buildings, public and private schools. 

The project will also protect a considerable section of the produce sector in Nogales, Ariz., Grijalva's office said.

The project will help decrease the flow of water, and reduce erosion in the Nogales Wash and Potrero Creek.

During rainstorms, vast amounts of water moves through the Nogales Wash and Potrero Creek, and in recent years, such flooding has compromised the structural integrity of the International Outfall Interceptor—a 30-inch-wide sewer trunk line carries 12-14 million gallons of raw sewage and runoff each day from Nogales, Sonora, and Nogales, Ariz., to a treatment plant near Rio Rico, as part of an international water treatment plan regulated by the International Boundary and Water Commission under a 1953 agreement.

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In July 2017, flooding undermined the IOI causing a leak near a manhole, allowing untreated wastewater to bubble up into the north-flowing Potrero Creek, which connects with the Santa Cruz River. Following the discovery of the breach, Grijalva pushed on the governor's office to declare an emergency. Arizona Gov. Doug Ducey agreed, and declared a state of emergency and called for the U.S. Army Corps of Engineers to provide technical assistance, and allocated $200,000 to the Department of Emergency and Military Affairs for the work, along with other assets included under the state's emergency response plan.

Late last year, the federal government agreed to spend another $2.8 million to upgrade the IOI as part of the Border Water Infrastructure Grant Program managed by the Environmental Protection Agency. Along with Grijalva, U.S. Sens. Krysten Sinema and Mark Kelly sought to get funding for the IOI in Nogales, as well as $500,000 for a project for Patagonia

The Ephraim Canyon project will include a 48-foot high earthern berm, with a pipe to allow water to escape and an emergency spillway to release flows that could come during extraordinary 500-year flood events, FEMA said in a public notice about the project published in November. Along with the construction of the berm, the project will include regrading of the wash and canyon sides, revamping about 17 acres of the canyon. This will include removing vegetation, FEMA said, however some native vegetation will be restored after the construction by hydroseeding—a process that sprays fertilizer, seeds and additives to stabilize the slope.

The Ephraim Canyon project will be one of three basins developed inside the city of Nogales to reduce flooding and potential damage to property and infrastructure, said Grijalva. And, the project would seek to solve recurring flood damage to more than 250 individual structures including residential, businesses and a local elementary downstream of the project area.

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Jonathan Clark/Nogales International

Flooding in Nogales.

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