PDM - Ephraim Canyon Flood Project Public Notice 002

FINAL PUBLIC NOTICE: Ephraim Canyon Flood Project, Santa Cruz County, Arizona │ PDMC-PJ-09-AZ-2019-001

The U.S. Department of Homeland Security’s Federal Emergency Management Agency (FEMA) intends to provide federal financial assistance under the Pre-Disaster Mitigation Grant Program to the Santa Cruz County Flood Control District in Santa Cruz County, Arizona to construct a detention basin on undeveloped land in a deep canyon section of the Ephraim Canyon Wash. The proposed action would resolve recurring and historic flood damage to more than 250 individual structures downstream of the project area and reduce the overall peak discharge by up to 3,000 cubic feet per second (cfs). Pursuant to Executive Order 11988 (Floodplain Management) and FEMA’s implementing regulations at Title 44 of the Code of Federal Regulations Part 9, FEMA hereby provides interested parties with a notice of its final decision and an explanation of the alternatives that were considered.

The purpose of the proposed action is to reduce flood hazards in areas downstream of Ephraim Canyon affected by flooding from Ephraim Canyon Wash. The proposed action would consist of constructing a 48-foot-high aboveground earthen berm impoundment structure, with a basal bleeder pipe to outlet water and an emergency spillway designed to release flows greater than 500-year flood events. The basin floor and canyon sides, including the wash, would be regraded to achieve a uniform elevation on the bottom. Approximately 17 acres of the canyon would be affected by the grading and the earthen berm. This grading would remove all vegetation beneath the planned structure; some native vegetation would be restored after construction by hydroseeding the basin area. Permanent perimeter fencing would be installed.

The project area is in the 100-year floodplain as depicted on the FEMA Flood Insurance Rate Map (FIRM) Numbers 04023C0629C, effective date December 2, 2011. The FIRM shows that the project area lies within Zone AE, an area that has a 1-percent probability of flooding every year and where predicted floodwater elevations have been established and is in a regulatory floodway.

Three alternatives to the proposed action were considered: Alternative 1 (No Action Alternative), Alternative 2 (Pumping Alternative), and Alternative 3 (Multiple Basins). Alternative 1 would not construct any flood control measures and properties would remain at risk to repetitive flooding events. This Alternative is not recommended because residents would continue to experience flooding and associated property damage and safety risks. Alternative 1 would not meet the purpose and need for the project. Alternative 2 proposed a below-ground basin with pump stations to drain the basin. This alternative is not recommended because the construction cost would be nearly double the cost of a traditional above ground impoundment system and would have a significant higher cost for annual maintenance to ensure the pumps work than the proposed alternative. Alternative 3 would install multiple smaller basins. However, Alternative 3 would require more storage area than is available within the system in the United States and would require construction expenditures in Mexico, where Santa Cruz County has no jurisdiction.  

FEMA has determined that the proposed project is the only practicable alternative available; therefore, the proposed action must be in the floodplain. The proposed action would have no significant adverse impact on the floodplain and would reduce or eliminate the impacts of flooding on public and private structures, public infrastructure, increasing the ability of emergency services to access areas during a flood event, and decreasing the time of travel to the local hospital for emergency medical needs during a flood event. Therefore, measures to minimize impacts on the floodplain are not necessary. This is a floodplain reduction project sponsored by the local Flood Control District. All activities are in compliance with FEMA regulations regarding floodplains.

Additional information about FEMA’s proposed action, including a map of the project area and its location within the floodplain, may be requested by writing the FEMA Region IX Environmental Officer at FEMA, 1111 Broadway, Suite 1200, Oakland, California 94607, or fema-rix-ehp-documents@fema.dhs.gov, or calling (510) 627-7027. All requests should be received no later than 15 days after publication of this notice. No action will be taken before this date.