Final Public Notice: Sierra Wash Drainage Improvement at Glover Road

SIERRA WASH DRAINAGE IMPROVEMENT AT GLOVER ROAD
PIMA COUNTY, ARIZONA
HMGP-4524-006-004R

The U.S. Department of Homeland Security’s Federal Emergency Management Agency (FEMA) proposes to provide federal financial assistance under the Hazard Mitigation Grant Program to the Town of Oro Valley (Subapplicant) in Pima County, Arizona, to mitigate impacts from flooding by constructing drainage improvement measures downstream of an existing box culvert along the Sierra Wash ephemeral stream (Proposed Action). Pursuant to Executive Order 11988 (Floodplain Management), Executive Order 11990 (Wetlands Management), and FEMA’s implementing regulations at Title 44 Code of Federal Regulations Part 9, FEMA hereby provides interested parties with a notice of its final decision and an explanation of the alternatives considered.

The purpose of the Proposed Action is to reduce flood hazards by addressing existing erosion in the project area. The Proposed Action consists of 1) site preparation, including installation of track-out rock, straw wattle perimeter control, temporary fencing, and concrete washout basins; 2) site clearing, involving vegetation removal; 3) excavation of the stream bed; and 4) installation of a reinforced concrete drop structure, a gabion energy dissipation end sill, and a toe-down.

The project area is depicted on the FEMA Flood Insurance Rate Map (FIRM) Panel 04019C1070L, effective date June 16, 2011. The FIRM shows that the Proposed Action lies within Zone X, an area of minimal flood hazard. However, according to the Oro Valley Floodplain Inquiry Map (accessed on January 2, 2025), the project area is within a locally-mapped floodplain (mapped in 1993). Additionally, the U.S. Fish and Wildlife Service National Wetlands Inventory map (accessed on January 2, 2025) shows seasonally intermittent (contains flowing water only part of the year) streambed riverine habitat within the project area. However, this riverine habitat is an undated “interim scalable map product” that is “preliminary and is a compilation of existing data and limited aerial image interpretation rather than an image-based mapping process.”

A map of the project area and its location within the floodplain and wetland is available for public review. Parties interested in receiving a copy of the map should contact the FEMA Region 9 Environmental Officer using contact information provided in this notice. 

Two alternatives to the Proposed Action were considered: the No Action Alternative; and Alternative 1. Under the No Action Alternative, no construction activity would occur to address existing erosion. This Alternative is not recommended because if no action is taken to protect the culvert’s apron, it may destabilize, putting Glover Road and any existing utilities along the road corridor at risk of flooding. Under Alternative 1, concrete would be installed along the stream bed to dissipate the flowing water’s energy, and baffle block would be installed instead of the gabion mattress included under the Proposed Action. Alternative 1 is not recommended because it would require a deeper foundation (toe-down) and cost more than the Proposed Action to provide the same level of erosion protection.

FEMA has determined that the Proposed Action is the only practicable alternative available; therefore, the Proposed Action must occur within the floodplain and wetland. The Proposed Action would not have a significant adverse impact on the floodplain or wetland and would benefit the area by reducing erosion and sedimentation. During construction, impacts to the floodplain and wetland would be minimized through the use of best management practices (BMPs) to ensure that stormwater runoff does not reach nearby sensitive habitats, including the surrounding wetland and floodplain. All BMPs would be listed in the Stormwater Pollution Prevention Plan. The Town of Oro Valley has stated that the Proposed Action conforms to local floodplain standards, and would be responsible for the management, construction, and maintenance of the Proposed Action.

Additional information about FEMA’s Proposed Action may be requested by writing to the FEMA Region 9 Environmental Officer at FEMA, 1111 Broadway, Suite 1200, Oakland, California 94607, or fema-rix-ehp-documents@fema.dhs.gov. All requests should be received no later than 15 days after publication of this notice. No action will be taken before this date.