Coastal Flooding & Solutions, Workshop Case Studies

Dauphin Island Adaptation Pathway: Navigating sea-level rise uncertainty on barrier islands

Location: Coastal Alabama

Submitted By: Stephanie M. Smallegan - Assistant Professor, University of South Alabama

Project URLs: www.facebook.com/nobreachdi

Project Description

An adaptation pathway is being created for Dauphin Island, AL, a low-lying barrier island vulnerable to storm surge and sea level rise (SLR). The pathway is comprised of several adaptation strategies for barrier island adaptation to future hurricanes and SLR. The strategies are sequentially arranged based on their effectiveness in protecting the island from damage during a hurricane under SLR. Tipping points are identified as the amount of SLR that causes a strategy to no longer meet its original objective of mitigating storm damage, necessitating the implementation of another strategy. The pathway is scientifically-based and community-informed, which means each adaptation strategy is analyzed using computer models and only adaptation strategies of interest to the community are considered. In January 2020, an in-person meeting was held with Dauphin Island leadership. Three vulnerable areas were determined to be of importance for this study and several adaptation strategies were discussed. Although additional in-person community meetings were planned for 2020, the meetings were transitioned to a virtual format due to restrictions imposed during the COVID-19 pandemic. Surveys were sent to residents after a series of live events to inform the pathway. We directly reached over 40 individuals through the virtual events. This presentation will provide lessons learned on hosting virtual community meetings and present recent model results being used to create the adaptation pathway.

Key Successes

Though the project is underway, there have been key successes on the modeling and stakeholder sides. From the modeling perspective, the Brier Skill Score (BSS) indicate close agreement between simulated and surveyed post-storm topography (0.77-0.98; 1 = perfect agreement). Additionally, a combination of data collection methods and comparisons has generated enhanced understanding of how community collected data of conditions post-storm on barrier islands can provide unique insights during model calibration. From the stakeholder side, there were initial challenges by residents about the purpose of the project and suggestions of nefarious attempts to take residents’ land. Through novel engagement approaches, a diversity of stakeholders across age, economics, and education were successfully reached, their questions answered, and all resistance has apparently desisted. Instead there have been expressions of gratitude for the research and for the transparency in our approach. Finally, adaptability has been a key success. The COVID-19 pandemic hit between our focused stakeholder meeting and our resident engagement effort; however, we were able to still pivot our approach to community meetings to reach a broad array of partners. Additionally, we have responded to Cristobal which provided an opportunity to collect additional data that will enhance our understanding of local processes and potential adaptation solutions.

Challenges

The current state-of-the-art numerical modeling is unable to simulate both long-term morphological or evolutionary processes and short-term storm-event driven processes. Ideally, we would be able to accurately simulate morphological change on barrier islands from a storm, through the post-storm recovery process, and over time as sea levels change and additional storms impact the study site. Although individual models exist to simulate each of those scenarios, we are unaware of any model (or coupled models) that can handle all of them. Therefore, we operate under the assumption that the Town will implement adaptation strategies, such as maintenance beach nourishment, over time to maintain present conditions, which enables us to use present-day data to represent a future state (e.g. we use the model grid representative of today’s conditions to evaluate the impacts of future sea level rise assuming the town will take measures to prevent severe island erosion between now and the time it takes for seas to rise to that level). This assumption is a limitation of the research and its impact to the results of the study are mitigated by performing extensive sensitivity analysis which requires significant computational and personnel time. Also, in situ data, including bathymetry, water levels, and waves at specific study sites, is an ongoing limitation and challenges the ability to calibrate and validate numerical models. An economist may be beneficial in quantifying the differences in cost of the different adaptation strategies which could have provided even more guidance for the Town when considering implementation. An economist may also have been able to provide creative strategies for generating those funds as well. Legal expertise would have been helpful as some of the strategies require code/permitting changes and potentially reduced access to homes which has, in some cases, been claimed as an illegal taking.

Any questions regarding this posting, email edl@gatech.edu