Laboratory evaluation of the effectiveness of nature-assisted beach enhancement techniques

Abstract

Beaches are eroded and accrete under the effect of storms and calm marine conditions, respectively. Normally, beaches reach their narrower state in spring, after the action of winter storms. Accretion processes are slow, and maximum beach recovery doesn't occur until late summer. Sometimes this recovery is not enough to reach the width the beach had the previous year, producing a progressive shoreline retreat and an increased risk of dune erosion and inland flooding during the following winter seasons. The need for wider beaches in early summer for touristic purposes and social support to soft-engineering measures, have increased the interest in Nature-Assisted Beach Enhancement (NABE) techniques. In this study, reduced-scale laboratory experiments on beach ploughing and scraping allowed the comparison of various of these techniques and their effectiveness in controlled conditions for the first time. The beach widening and accretion achieved for five different NABE geometries were analysed and contrasted with natural (control) conditions. Our results show that the best technique is goal-dependent. For dry beach widening, ploughing is recommended as an effective and easy-to-design technique. Scraping the lower intertidal area and placing the sand on an intertidal bar or the beachfront are also effective alternatives if adequately designed. For dune nourishment, the best option is scraping the upper intertidal area and using the borrowed sand for dune regeneration. In general, all the analysed techniques enhance natural beach accretion, in collaboration with natural processes, thus reducing the human action required to achieve the desired objectives from a Building with Nature perspective.