Final Public Notice: Collier Canyon Creek Silt Basin (Phase 2)

FINAL PUBLIC NOTICE

COLLIER CANYON CREEK SILT BASIN (PHASE 2)
ALAMEDA COUNTY, CALIFORNIA
HMGP-4344-132-040R

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 City of Livermore (Subapplicant) in Alameda County, California, to mitigate impacts from flooding by constructing an emergency bypass of the existing culverts via overflow piping under Collier Canyon Road (proposed action). Pursuant to Executive Order 11988 (Floodplain Management), Executive Order 11990 (Wetlands 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. The proposed action consists of the following: 1) site preparation, including vegetation removal; 2) construction of two concrete weir structures in front of the existing culvert headwalls; 3) trenching and installation of an overflow pipe connected to the weirs under Collier Canyon Road; 4) construction of a concrete floodwall along the northern roadway shoulder; and 5) ancillary post‑construction improvements, including repaving a section of Collier Canyon Road, tree planting, and hydroseeding impacted areas. 

The project area is depicted on the FEMA Flood Insurance Rate Map (FIRM), Map Number 06001C0333G, effective date August 3, 2009. The FIRM shows that the proposed action lies within Zone AE, an area that has a 1-percent probability of flooding every year and where predicted floodwater elevations have been established. The U.S. Fish and Wildlife Service National Wetlands Inventory map shows freshwater emergent wetlands associated with Collier Canyon Creek near the project area. 

A map of the project area and its location within the floodplain and wetlands is available for public inspection. 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: Alternative 1: No Action; and Alternative 2: Trash Racks and Wing Wall Realignment. Alternative 1 would take no action and leave conditions as they currently exist. This Alternative is not recommended because it would result in ongoing flood risk and damage to private property and public facilities, increase flood hazards downstream, and threaten riparian areas, fish and wildlife species and their habitat. Alternative 2 included construction of a trash rack at the upper and lower headwall and realigning the wing walls to increase velocities through the culverts to better carry sediment and debris. This Alternative is not recommended as this would only mitigate some flood hazards for smaller storm events, and there would be no flood mitigation for larger storm events. 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 benefit the area by reducing the risk of flooding and flood damage. Therefore, measures to minimize impacts on the floodplain are not necessary. The City of Livermore 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. 

The project area is adjacent to potential wetlands associated with Collier Creek. The City of Livermore would implement best management practices to prevent erosion and sedimentation to nearby wetlands.

Additional information about FEMA’s proposed action may be requested by writing 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.