South Branch Arroyo Conejo Deficiency Study

In 2010, the Federal Emergency Management Agency (FEMA) revised flood maps in the Newbury Park area that included over 300 homes within City limits and unincorporated County area. The revisions to the maps adversely impacted residents with a flood designation, requiring homeowners to obtain flood insurance. In 2014, the United States Army Corp of Engineers (USACE) funded and conducted a Federal Interested Determination (FID) that pre-qualified the South Branch Arroyo Conejo (SBAC) under Section 205 for investigating and implementing solutions that could authorize up to $10 million in federal funds to analyze, study and construct water flow solutions. In 2015, the FID designation was deemed “qualified” for Section 205, which was finalized by the USACE in 2016 and in 2017 was executed by the Los Angeles District Commander, prompting the initiation of a Phase II Feasibility Study, which included an analysis of the area to determine justifiable financing of possible mitigation improvements. In 2018, the City and the Ventura County Public Works Watershed Protection (VCPWA - PD) created a project management plan and cost sharing agreement that was approved by the Los Angeles District Commander in 2019 and the Phase II Feasibility Study was initiated. A USACE project team along with City and VCWPA representatives tour the area and completed modeling and hydrology studies and analytics of the SBAC. In 2020, USACE’s preliminary conclusions recommended against the completion of a full Feasibility Study of the SBAC due to substantially lower cost-benefit ratios than previously estimated in the FID. It was also noted that flooding in the SBAC may occur because of a low capacity in the existing culverts as opposed to the floodplain channel, which would not result in significant damage more than $1 million from a 100-year flood incident, disqualifying the City and area from additional federal support. Since the FID evaluation did not match the Feasibility Study assumptions, the USACE recommended that the City and VCPWPA-WP pursue local versus federal solutions to mitigate area flooding issues. City staff have since requested modifications to the hydraulic modeling, hydrology inputs and economic reports to accurately depict properties potentially impacted by flooding.