The Sensitivity of a Dike-Marsh System to Sea-Level Rise—A Model-Based Exploration

Richard Marijnissen,Matthijs Kok,Jantsje Van Loon-Steensma,Carolien Kroeze

doi:10.3390/jmse8010042

Abstract

Integrating natural components in flood defence infrastructure can add resilience to sea-level rise. Natural foreshores can keep pace with sea-level rise by accumulating sediment and attenuate waves before reaching the adjacent flood defences. In this study we address how natural foreshores affect the future need for dike heightening. A simplified model of vertical marsh accretion was combined with a wave model and a probabilistic evaluation of dike failure by overtopping. The sensitivity of a marsh-dike system was evaluated in relation to a combination of processes: (1) sea-level rise, (2) changes in sediment concentration, (3) a retreat of the marsh edge, and (4) compaction of the marsh. Results indicate that foreshore processes considerably affect the need for dike heightening in the future. At a low sea-level rise rate, the marshes can accrete such that dike heightening is partially mitigated. But with sea-level rise accelerating, a threshold is reached where dike heightening needs to compensate for the loss of marshes, and for increasing water levels. The level of the threshold depends mostly on the delivery of sediment and degree of compaction on the marsh; with sufficient width of the marsh, lateral erosion only has a minor effect. The study shows how processes and practices that hamper or enhance marsh development today exacerbate or alleviate the challenge of flood protection posed by accelerated sea-level rise.

Highlights

To protect the growing number of people living in deltas against flooding, flood protection measures are required
One would expect that for every millimetre of sea-level rise requires an equivalent amount of dike reinforcement would be necessary
It has been recognized that marsh ecosystems play a role in flood protection, because of their wave- and storm surge attenuation properties

Summary

Introduction

To protect the growing number of people living in deltas against flooding, flood protection measures are required. “grey” solutions such as dikes, levees, and storm surge barriers have been implemented [1,2,3]. These measures are designed to function over long periods, yet are relatively inflexible to unforeseen accelerated sea-level rises [2,4,5,6]. Nature-based solutions, where “green” ecosystems aid in flood protection, have recently garnered a great deal of attention [4,5]. A major benefit of marsh ecosystems in flood protection is their ability to naturally adapt to sea-level rise under the right conditions [13,14]. Hybrid flood defences, incorporating both traditional flood defences structures and natural elements, are an attractive strategy to protect deltas [4,5,6]

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Conclusion