Observations and Preliminary Vulnerability Assessment of a Hybrid Dune-Based Living Shoreline

Maria A Winters,Evyan Borgnis Sloane,Timu W Gallien,Brian Leslie

doi:10.3390/jmse8110920

Maria A Winters, Evyan Borgnis Sloane + Show 2 more

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https://doi.org/10.3390/jmse8110920

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Abstract

A novel hybrid (e.g., vegetation, sand, cobble, rip-rap) nature-based dune structure was constructed at Cardiff State Beach in Encinitas, California, to protect a critical transportation artery from undermining and frequent flooding. A collaboration between regulators, funders, state agencies, professional practice and academia developed a high resolution robust unmanned aerial vehicle (UAV) based monitoring strategy to observe dune construction and evolution. Fifteen construction surveys were conducted to observe each substrate element for future morphodynamic modeling efforts. Six post-construction surveys were conducted to observe seasonal and storm-by-storm dune evolution. Backshore vulnerability was assessed using a sixty-one year time series of tides and hindcast wave forcing fit to a general extreme value distribution. The dune crest is above calculated 100-year water levels; however, the dune remains vulnerable to mass wasting caused by swash interaction at the toe of the dune. Sea-level rise will substantially increase the probability of dune erosion, breaching, and overtopping.

Highlights

Climate change is driving sea-level rise at a rate of around 3–4 mm/yr [1,2] and the global mean sea-level rise is projected to be anywhere from 0.28 to 0.98 m by 2100, depending on modeling methodology and the carbon dioxide emissions scenario [3,4,5]
The unmanned aerial vehicle (UAV) surveys captured about 30% of the completed trench creation, 34% of the completed revetment placement, and 41% of the completed cobble toe placement
Approximately 183 m south from the project start in section 1, the UAV surveys captured all three completed phases: trench, revetment, and cobble

Summary

Introduction

Climate change is driving sea-level rise at a rate of around 3–4 mm/yr [1,2] and the global mean sea-level rise is projected to be anywhere from 0.28 to 0.98 m by 2100, depending on modeling methodology and the carbon dioxide emissions scenario [3,4,5]. Over 30 days of annual flooding will be reached by 2050, and near daily flooding (under RCP 4.5) will occur by 2100 for many areas across the globe [10] This acceleration in coastal flooding will impact increasingly larger coastal populations [11,12]. Implementing coastal protection against increased flooding events outweigh the costs of inaction, and without these protection measures, hundreds of millions of people will be displaced [5,13]

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