Nature-Based Coastal Protection by Large Woody Debris as Compared to Seawalls: A Physical Model Study of Beach Morphology and Wave Reflection

Pauline Falkenrich,Andrew Cornett,Ioan Nistor,Nils Goseberg,Abdolmajid Mohammadian,Jessica Wilson

doi:10.3390/w13152020

Abstract

Anchored Large Woody Debris (LWD) is increasingly being used as one of several nature-based coastal protection strategies along the north-western coasts of Canada and the US. As an alternative to conventional hard armoring (e.g., seawalls), its usage is widely considered to be less harmful to the coastal ecosystem while maintaining the ability to protect the beaches against wave attack and erosion. The effects of seawalls on beaches have been extensively studied; however, the performance and efficacy of LWD and its potential as a suitable alternative to seawalls (and other shoreline protection structures) are still understudied in current research. This paper presents and compares the effects of a conventional vertical seawall with two different LWD structures on beach morphology and wave reflection through large-scale physical modeling in a wave flume at a 1:5 scale. An assessment of techniques used to measure beach morphology and an assessment of model effects were included in the study. It was found that the wave reflection could be reduced by using a single log instead of a wall structure, while changes in the beach morphology response largely depended on the type of the LWD structure. A stacked log wall showed near-identical behavior as a conventional seawall. Visible model effects from the experiments, including the effect of the flume sidewalls on the beach morphology, were quantified and analyzed to inform future research.

Highlights

A paradigm shift towards using natural and nature-based coastal protection methods can be observed at a global level [7,8], and conventional “hard“ structures undergo scrutiny as to whether their protective benefits can be achieved through more natural methods of coastal protection [9]
Motivated by the need to better understand the efficacy of anchored Large Woody Debris (LWD) as coastal protection, this study aims to compare the effects of anchored LWD in comparison to conventional seawalls for the case of a gravel beach
As part of an thisanalysis study, an analysis of model effects related to beach morphology w conducted before comparing the main results on beach morphology changes and reflection conducted before comparing the main results on beach morphology changes and refl from LWD structures and a vertical seawall

Summary

Introduction

Concerns about potential adverse environmental effects of conventional shoreline armoring (e.g., seawalls) and its suitability to mitigate the potential effects of climate change (e.g., sea-level rise and increasing storm intensity) are growing in many coastal communities [1,2]. In contrast to unmanaged shorelines, seawall-protected beaches have recently been shown to reduce in coastal biodiversity and abundance of organisms [5]. A paradigm shift towards using natural and nature-based coastal protection methods can be observed at a global level [7,8], and conventional “hard“ structures undergo scrutiny as to whether their protective benefits can be achieved through more natural methods of coastal protection [9]. Following the definition of the US Army Corps of Engineers, nature-based coastal protection is defined as an imitation of natural coastal features intentionally built and designed by humans [10]

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