Wave transformation across intertidal oyster reefs

Abstract

Coastal protection systems are increasingly expected to provide not only hazard mitigation, but also ecological resilience and adaptability under climate change. This dissertation examines how oyster reef systems function as dynamic coastal infrastructure across biological, hydrodynamic, and human dimensions. Using field observations, wave measurements, ecological surveys, drone surveys, and social–ecological assessment methods, this work investigates how constructed oyster reefs evolve in form and function after deployment, how natural oyster reef morphology influences wave attenuation under elevated water levels, and how people conceptualize and make decisions about living shoreline systems.

Chapter 1 evaluates how oyster recruitment and growth alter the hydrodynamic performance of constructed living breakwaters. Using in situ wave measurements collected before and after two seasons of oyster recruitment on modular breakwaters in North Carolina, this study demonstrates that biological colonization increased wave attenuation by approximately 10–15%. Reductions in wave transmission were associated with oyster-driven increases in surface roughness and reductions in structural porosity. Standard low-crested breakwater transmission models were adapted using ecological parameters, and oyster length emerged as an informative predictor of effective structural diameter. These findings demonstrate that ecological growth measurably alters the engineering performance of living breakwaters through time.

Chapter 2 examines wave attenuation across natural patch and fringing oyster reefs under both baseline and elevated water levels. Using wave gauge deployments and drone-derived reef morphology, this study shows that natural oyster reefs maintained substantial wave attenuation during elevated water levels associated with Tropical Storm Ophelia, which produced water levels comparable to projected mid-century sea-level rise. Wave attenuation ranged from 12–47% under baseline conditions and 16–45% under elevated conditions. Wave transmission scaled nonlinearly with relative freeboard, while reef-scale morphology strongly mediated attenuation efficiency. Fringing reefs consistently attenuated more wave energy than patch reefs, even when submerged, highlighting the importance of elongated, shore-parallel reef configurations for coastal protection.

Chapter 3 investigates how adult learners conceptualize living shorelines as social–ecological systems. Using pre- and post-course surveys and mental model interviews conducted during a Living Shoreline Academy training program, this study demonstrates that educational experiences increased systems-level understanding, confidence, and integration of ecological and engineering concepts among participants. Participants shifted from cost-centered decision-making toward greater emphasis on erosion control, storm resistance, and ecosystem outcomes, while mental models became more interconnected and structurally complex following course participation. Together, these studies demonstrate that oyster reefs are not static coastal structures, but adaptive social–ecological systems whose protective function emerges through interactions among biological growth, physical morphology, hydrodynamic forcing, and human decision-making.