- Review of existing design alternatives
- Review of existing BCA documents
- Update cost estimates
- Perform independent analyses
Challenge
Per the Town’s record, approximately 3,000 structures are mapped within the Town’s floodplain, including many Town buildings and historical sites, five (5) churches, three (3) schools, and roughly 15 percent of the town's residential housing. In 2019, the U.S. Army Corp of Engineers (USACE) conducted a town-wide study that resulted in a multi-section proposed plan to protect the Fairfield shoreline. USACE concluded that hundreds of millions of dollars in total estimated damages and potential loss of life were at risk during a 1% Annual Exceedance Probability (AEP) flood. The USACE’s plan intends to protect most of the Town’s infrastructure and residences from such flooding and has a projected cost of $546 million. While it had a benefit-cost ratio (BCR) of 1.7, it does not meet the benefit cost thresholds to be approved for federal funding. The estimated cost was considered too high for the Town to proceed on its own. The Town has assessed the USACE plan and identified “critical” sections that, if implemented, have the potential to mitigate the majority of the damages and impact from major floods. The Town was interested in applying for individual grants for each of these sections as grant funding becomes available and requested benefit-cost analysis (BCA) for individual segments of the town-wide design.
Solution
The Town received funding from Connecticut Institute for Resilience and Climate Adaptation (CIRCA) to perform BCA for 3 selected priority projects. GZA performed a site walk-through and documented key site features. GZA also performed an independent desktop review of the existing topographic data around the project area based and closely evaluated flood pathways for coasting flooding in Fairfield. GZA determined that the selected high priority projects (i.e., discrete segments of the town-wide coastal flood barrier project) do not provide flood mitigation benefits. GZA performed a BCA for a tide gate/stormwater outfall project using Federal Emergency Management Agency (FEMA) BCA Toolkit (v.6.0), including environmental ecosystem benefits.
Benefit
GZA's BCA study results provided useful information for the Town to advance to the next phase of flood resiliency planning.