Modelling the influence of beach building pole heights on aeolian morphology and downwind sediment transport

Abstract

Buildings on beaches either sit directly on the sediment surface or are placed on poles. These structures alter near-bed airflow around them. To quantify the influence of pole height on airflow, resulting bed morphology around these buildings and sediment fluxes passing these buildings towards the dunes, three-dimensional simulations were performed. To compute airflow, we used the open-source computational fluid dynamics software OpenFOAM. For sand transport and bed level changes, we used the Exner equation combined with Bagnold's sediment transport flux formulation, and a newly-developed model that couples the airflow model with the sediment transport model AeoLiS. In the simulations, we modelled a row of ten full-scale beach buildings on a flat/smooth sandy bed, with a constant gap size between neighbouring buildings, varying the pole heights between simulations. Our findings showed that elevated buildings affect the wind speed in a larger region, both upwind and downwind, compared to buildings without poles. The model simulations showed that airflow accelerated both underneath the elevated buildings and through the gaps between the buildings. Moreover, besides flow acceleration underneath the buildings, the elevated buildings induced slightly higher flow acceleration through the gaps between buildings. Depending on pole height to building width ratio, elevated buildings could both decrease and increase the downwind sediment flux compared to an undisturbed situation. For ratios between 0 and 0.5, downwind fluxes were reduced in a zone between 5 and 40 m behind the buildings, while for ratios above 1.3, downwind fluxes were observed to increase in a zone up to 20 m behind the buildings. Also, this study emphasizes the importance of selecting an optimal pole height to maximize the benefits of beach buildings in terms of passing on sediment transport towards the dunes.