FM-5310-AZ Public Notice 001

FINAL PUBLIC NOTICE: Canada Del Oro Levee Augmentation, Pima County, Arizona | HMGP 5310-01-01

The U.S. Department of Homeland Security’s Federal Emergency Management Agency (FEMA) intends to provide federal financial assistance under the Hazard Mitigation Grant Program (HMGP) to Pima County, Arizona, to increase freeboard capacity along developed portions of the Canada del Oro Wash Levee system in Oro Valley, Arizona (proposed action). Pursuant to Executive Order 11988 (Floodplain Management), Executive Order 11990 (Protection of Wetlands), 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 overall purpose of the proposed action is to reduce flood hazards by constructing six floodwalls and berms on top of the existing levee system. The additional hydraulic capacity in the Canada del Oro Wash is needed to prevent storm water runoff from overtopping the existing soil cement bank protection levee due to the changes in the upstream watershed caused by the Bighorn Fire in the Coronado National Forest. It should be noted that this project does not change regulatory floodplains as the 100-year post fire event is contained. This project will increase freeboard to meet post fire conditions as indicated in the Bighorn Fire: Post-Fire Flood Risk Assessment hydrology study and protect development within FEMA Shaded X Zones, areas with reduced flood risk due to levee.

The project area encompasses multiple flood zones including the X Zone, area of minimal flood hazard, as depicted on the FEMA Flood Insurance Rate Map (FIRM) panel #04019C1090L, effective 6/16/2011; the Shaded X Zone, area with reduced flood risk due to levee, as depicted on FIRM panel #04019C1090L, effective 6/16/2011; the AE Zone, area of Special Flood Hazard Area (100-year floodplain, base floodplain where base flood elevations are provided), as depicted on FIRM panels #04019C1070L, #04019C1095L, effective 6/16/2011; and the AE FLOODWAY Zone, area of Special Flood Hazard Area (100-year floodplain, base floodplain), as depicted on FIRM panels #04019C1089L, #04019C1090L, effective 6/16/2011. A "Regulatory Floodway" means the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height. The U.S. Fish and Wildlife Service National Wetlands Inventory Map shows a riverine wetland within the project area.

Maps of the project area and its location within the floodplain and riverine wetlands are available for public inspection. Parties interested in receiving a copy of either map should contact the FEMA Region IX Environmental Officer using contact information provided in this notice.

Two alternatives to the proposed action were considered: Alternative 1, No Action; and Alternative 2: Debris Management. Alternative 1 would result in no action being taken to mitigate flood hazards. This Alternative is not recommended because the risk of flood hazards, including damage to property and people, would continue. Alternative 2 included dredging sediment from the channel to allow greater capacity for containing flood waters. This Alternative is not recommended because this is a partial solution consisting of monitoring and removing aggraded channels and debris, which addresses sediment buildup but does not address increased flow rates from the denuded fire scar. Under Alternative 2, to recover the current conveyance capacity, 6.3 miles of sediment would need to be removed at a cost of $560,000 per mile, for a total of

$3,528,00 that exceeds the proposed action. Removal of existing sediment would not be a permanent solution to increase capacity to post-fire conditions because greatly increased deposition of debris and sediment eroding from the fire scar above will quickly refill the channel during an event. Therefore, Alternative 2 is not feasible. FEMA has determined that the proposed project is the only practicable alternative available; therefore, the proposed action must be located in the floodplain in order to serve its intended purpose. In addition, the proposed action is economically preferred due to cost, feasibility to provide protection within the shortest period of time and is environmentally preferable to in channel sediment removal as it occurs on top of the existing levee structure rather than within the natural, vegetated channel bottom.

The proposed action, constructing six floodwalls and berms on top of the existing levee system, would have no significant adverse impact on the floodplain and would benefit the area by reducing the risk of flooding and flood damage. The post Bighorn Fire hydrologic study found significant changes to the drainageways and increased risk of flooding and debris flow in areas that were previously low risk. Levee augmentation offers the most cost effective and efficient means of restoring channel capacity by increasing the level of protection to match the post-fire condition and protect developed areas. Therefore, Pima County is proposing to use HMGP Post Fire funds to provide levee augmentation that contains the increased flow rate, including sediment load. Grant funds will help recover the pre-fire flood capacity of impacted drainageways by installing floodwalls at bank protected areas modeled to have freeboard deficiencies during post fire flood events. Pima County has declared 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 the FEMA Region IX 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.