Beach Accretion Enhancement by a Recently Developed Nature Assisted Recovery Technique

Abstract:

The development of new nature-based solutions is fundamental for guaranteeing the future of healthy coasts worldwide. Many countries are facing the problem of progressive shoreline retreat due to sand loss during winter storms that is not fully recovered during calm weather periods. Climate change accelerates this process with sea level rising and increasing the strength and frequency of storms.

Recently, a new nature assisted recovery technique was field tested at Laida beach in northern Spain (Gainza et al., 2019, https://doi.org/10.2112/jcoastres-d-18-00033.1). It consists of mechanically ploughing the intertidal area of a beach periodically to enhance natural accretion processes. This innovative technique showed promising results in the field experiment and has been tested at laboratory in this study.

Under controlled conditions, the behavior of five ridges and furrows was compared to a non-ploughed intertidal bar. Both geometries of natural sand were exposed to accreting wave conditions on a real scale experiment. Each test lasted 1 h and was performed for seven different water levels, from 0 to 0.45 m over the sandy bottom. Results indicate that ploughing produces an average increase of 2.9 times the accretionary sediment transport naturally produced on an intertidal area of a beach. Accretion processes were accelerated for all water levels tested.

The integrated effect of ploughing over a full tidal cycle is under study. Longer laboratory experiments, up to 7 h of wave action, are being analyzed in order to determine how long the ridges and furrows last and the attenuation of its effect as they smooth out. Additionally, new reduced scale laboratory experiments are being performed to analyze the combined effect of waves and astronomical tides over a fully ploughed intertidal area. The results of these experiments will be presented in the conference.

Mechanically ploughing the intertidal area of a beach has demonstrated to be a promising nature friendly technique to enhance natural beach accretion.