Empowering Communities to Take Charge of Flood Resilience

The Federal Emergency Management Agency (FEMA) is known for its administration of the National Flood Insurance Program and associated Flood Insurance Rate Maps. While they identify areas where flood insurance is required and help keep new development from exacerbating flood problems, they do little to solve existing flood risk before a disaster occurs.   

It makes sense. Mapping a flood hazard is only the first step in understanding and mitigating the associated risk. A community wanting to become more flood resilient faces numerous hurdles: funding, politics, technical expertise, stakeholder support—to name a few. What if we could remove barriers, empower communities and give them the tools to solve flooding issues on their own? 

In Region 9, which includes Hawaii, California, Nevada and Arizona, FEMA conducted a new pilot project using resilience planning support funds. The goal was determining what data and processes could be leveraged as communities engage in resilience planning in the face of sea level rise and existing flood risk. This would be accomplished by partnering with a local community impacted by flooding and working together to develop and prioritize an actionable area drainage plan to address flooding issues. For the action plan to be useful to the community, it needed to:

• Provide a detailed understanding of the location, cause, and extent of flooding
• Identify actionable flood resilience opportunities
• Include a detailed Benefit-Cost Analysis
• Use stakeholder-driven scoring criteria to prioritize alternatives

For Region 9, the City and County of Honolulu (CCH) was a perfect partner. The low-lying Mapunapuna Industrial Area, built on top of old fishponds, has been plagued by flooding for years. The nearby Moanalua and Kalihi Streams run through economically critical areas and have a recent history of overtopping their banks. Other areas are prone to localized flooding due to a lack of storm drain infrastructure, and rising sea levels represent another threat, not just for the Mapunapuna area, but for other coastal areas around Hawaii. 

In June 2021, Region 9 contracted with Strategic Alliance for Risk Reduction (STARR II) to deliver the project. FEMA and CCH made their objectives clear from the beginning. For FEMA, it was engaging local stakeholders. For CCH, it was ensuring the plan was “actionable” and not just an informative report.

The first step was better understanding existing flood risk. A holistic watershed approach was used to analyze flooding from all possible sources including storm drain, riverine, tidal and pluvial. Hydrologic models were then developed to determine hypothetical flowrates. A coupled 1D/2D hydraulic model was developed incorporating storm drains, river hydraulics, tidal boundary conditions including sea level rise and localized flooding using a rain-on-grid approach. The result was a comprehensive issues map enabling CCH to see their flood risk in a way they never could before.

The next step was identifying actionable resilience opportunities. Knowing options would be prioritized and scored based on stakeholder-driven criteria, it was important to develop and understand the criteria before recommending ideas for selection. Conceptual alternatives were created based on a comprehensive list of possible scoring criteria, including environmental benefits, impact to underrepresented communities, protecting against largest losses, minimizing permit requirements and more. These criteria were presented in a day-long workshop with technical stakeholders to gather feedback on which criteria mattered most to them. This feedback helped narrow down the list of alternatives to those the community would most likely accept.

Once mitigation alternatives were developed, cost-benefit analyses were performed. To make the study as “actionable” as possible, BCAs were developed in compliance with FEMA grant applications. This enhancement enabled the study to be used as a turnkey grant application, should CCH wish to pursue grant funding for the mitigation projects in the future. In addition, the community was equally interested in learning about scenarios that were not viable from a cost-benefit perspective as they were about alternatives where the cost benefit was high.

Mitigation alternatives were further prioritized by evaluating and scoring their alignment with finalized stakeholder-driven criteria. A prioritization tool was developed to allow CCH to adjust the weights and scoring of different criteria in response to future community engagement and feedback. Current Honolulu floodplain ordinances were also reviewed and recommendations made to limit future development from exacerbating flood risk in the project area.

By the time the study was completed in May 2024, it had empowered the community in several ways because they now had:

• A comprehensive understanding of the cause, location and extent of flooding
• A prioritized list of actionable flood mitigation options that aligned with stakeholder preferences
• A FEMA-compliant BCA for each alternative that could be used to apply for further grant funding
• A list of recommended changes to local floodplain ordinances that would improve resiliency against flooding

The response from FEMA and the community was positive, and requests to perform similar studies came almost immediately. The path to resilience is still long, with project funding, detailed analysis, aerial topography, geotechnical analysis, permitting, right-of-way, plan development, constructability, utility conflicts and construction of a mitigation project needing to be completed. While the hope is the community implements recommended mitigation projects, the empowerment they feel to solve flooding issues may be the most important benefit of all.

This article was originally published in the November 2024 issue of the Floodplain Management Association's quarterly newsletter, "The High Water Mark."