Graduation Semester and Year
Fall 2025
Language
English
Document Type
Thesis
Degree Name
Master of Science in Civil Engineering
Department
Civil Engineering
First Advisor
Dr. Michelle Hummel
Second Advisor
Dr. Adnan Rajib
Third Advisor
Dr. Jessica A Eisma
Abstract
Nature and Nature-based Features (NNBF), such as salt marshes, offer a promising complement to traditional hard infrastructure as a means to build resiliency against flood impacts due to sea-level rise (SLR). When used as part of hybrid protection approaches, marshes can reduce wave loading and overtopping of shoreline infrastructure such as levees and seawalls, allowing coastal communities to achieve high levels of flood protection while still enjoying the benefits of natural ecosystems. However, the fate of marshes in response to accelerating SLR is not clear, leading to questions of how long marsh systems can continue to provide protective benefits. Past studies of the performance of marsh-fronted levees and seawalls have assumed ideal conditions of a healthy marsh located within the intertidal zone without considering how the marsh’s long-term ecological response to SLR alters its protective benefits. This study investigates the performance of a marsh-fronted levee in Humboldt Bay, CA, to evaluate whether it can continue to provide flood risk reduction benefits in response to projected SLR through 2100. Unlike previous studies, we explicitly account for the ecological response of the marsh to SLR when quantifying its protective benefits over time. We use the Marsh Equilibrium Model (MEM) in conjunction with a hydrodynamic model to simulate the feedback between hydrodynamic and marsh accretion processes on a decadal timescale and to assess whether the marsh can accrete at a rate sufficient to keep pace with SLR. Based on the predicted marsh platform elevation and vegetation density/coverage from the MEM model, we then calculate the wave attenuation capacity of the marsh and the resulting overtopping rate at the levee for a range of storm intensities in each decade. By comparing across decades, we identify how the protective benefits of the marsh-fronted levee change and when additional measures may be needed to satisfy risk-reduction requirements. Our findings highlight the importance of accounting for the dynamic nature of NNBF when evaluating their flood risk reduction benefits, particularly over long timescales. Results from this work can inform the design, implementation, and adaptive management of nature-based and hybrid shoreline protection strategies to advance their application in coastal regions.
Keywords
Hybrid nature based coastal defenses, salt marsh restoration, marsh fronted levees, sea level rise impacts, wave attenuation, overtopping reduction, marsh equilibrium model, Delft3D SWAN modeling, thin layer placement, coastal resilience
Disciplines
Civil Engineering
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Rahman, Azizur, "Evaluating a Hybrid Nature-Based Solution to Improve Resilience against Sea-Level Rise in Humboldt Bay, CA" (2025). Civil Engineering Theses. 466.
https://mavmatrix.uta.edu/civilengineering_theses/466