Aeolian surface erodibility measured on the Sand Engine
From mobile wind tunnel design towards field expeditions
J.M. van Langeraad (TU Delft - Civil Engineering & Geosciences)
S. de Vries – Mentor (TU Delft - Coastal Engineering)
B Hofland – Graduation committee member (TU Delft - Hydraulic Structures and Flood Risk)
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Abstract
Building with Nature is a sustainable approach to design multifunctional flood defences (e.g., accommodating recreational services, nature development, etc.) that harness natural forces as much as possible. Building with Nature therefore extensively involves coastal dunes. These dynamic sandy barriers naturally grow because of aeolian processes. Building with Nature may harness these aeolian processes to build, maintain and reinforce coastal dunes. In that case, aeolian processes are coupled to the variable flood risk of sandy barriers. To facilitate sustainable coastal management, it is crucial to understand the relation between wind speed and aeolian sand transport. Aeolian sand transport can either be capacity- or supply limited. When sand is abundant and available, the transport rate is generally capacity limited; and is determined by the wind speed. However, if the supply of sand is limited (e.g., due to moisture content, vegetation, etc.), the capacity of the wind cannot be reached. In this supply limiting case, the transport rate is not governed by the wind speed anymore. Many models are still based on capacity limited transport; and therefore, overestimate measured coastal transport rates. Additionally, supply limitations are still not fully quantified. Many supply limitations are posed by the bed’s erodibility, i.e., its ability to supply sand grains to the air flow. Exploring the erodibility of the sand surface can improve this situation. To this end, a specialized mobile wind tunnel system was developed. This system is called Mobi-Gust 2 and also includes a wind gauging system. This research involves the design and performance of Mobi-Gust 2; as well as testing its viability to conduct applied aeolian research. In this process Mobi-Gust 2 experimentally verified some supply limitations. The outcomes demonstrate that Mobi-Gust 2 is able to conduct applied aeolian research. The next step concerns the usage of Mobi-Gust 2, so that coastal aeolian sand exchange can be quantified. In this way Mobi-Gust 2 can improve the predictive power of numerical models (e.g., Aeolis).