Sand Trapping Fences as a Nature-Based Solution for Coastal Protection: An International Review with a Focus on Installations in Germany

Abstract

Sand trapping fences are a widely used nature-based solution to initiate dune toe growth along sandy shorelines for coastal protection. At present, the construction of sand trapping fences is based on empirical knowledge, since only a few scientific studies investigating their efficiency exist. However, the restoration and maintenance of beach-dune systems along the coast requires knowledge of the interaction between the beach-dune system and the sand trapping fences to provide guidance for coastal managers on how and where to install the fences. First, this review gives an overview of the typical aerodynamic and morphodynamic conditions around a single porous fence and the influence of various fence height and porosity values to understand the physical processes during dune establishment. Second, different approaches for evaluating the efficiency of sand trapping fences to trap sediment are described. This review then highlights significant differences between sand trapping fence configurations, nationally as well as internationally, regarding the arrangement, the materials used, and the height and porosity. In summary, it is crucial to enable an intensive exchange among the respective coastal authorities in order to create uniform or transferable guidelines taking local conditions into account, and thus work collaboratively on the idea of sand trapping fences as a nature-based solution in coastal areas worldwide.

Foredune growth and storm surge protection potential at the Eiderstedt Peninsula, Germany

“…In contrast to conventional methods based on fixed vertical elevations (e.g. applied by Hofstede, 1997;De Vries et al, 2012;Donker et al, 2018;Eichmanns et al, 2021;Masselink et al, 2022;Nicolae Lerma et al, 2022), the approach derives a generic toe determination that considers individual dune profile characteristics and adjacent foreshore elevations. As a result, the proposed method omits the problem of defining a fixed geodetic datum, making comparisons between different coastlines and countries accessible, as the detection relies on physically defined criteria.…”

“…Besides the previously highlighted correlation to coastal dune evolution, the approach can be a valuable tool in (i) forecasting vulnerable alongshore dune sections (shallow dune ridges, gaps); (ii) identifying dune sections with a need for reinforcement [e.g. additional sand nourishment (Brand et al, 2022), sand fencing (Eichmanns et al, 2021), hybrid dune core strengthening (Nordstrom, 2019)] and (iii) tracking post-storm related vulnerable sections.…”

“…Furthermore, coastal dunes show a natural capacity for self-repair and post-storm recovery under favorable conditions (Gracia et al, 2018). Several countries apply dune management strategies through sand fences to stimulate dune growth caused by aeolian sand transport (Eichmanns et al, 2021). Therefore, coastal dunes offer multiple adaptive and sustainable benefits compared to traditional hard engineering structures like sea dikes, which require regular maintenance.…”

“…A fact that has been neglected in the past, as the dune toe was commonly defined by a fixed threshold vertical elevation, e.g. at: the Dutch coast at 3 m above the Dutch reference level NAP (De Vries et al, 2012;Donker et al, 2018); the north coast of SW England at 5 m (Masselink et al, 2022); the southwest coast of France at 6 m NGF (official levelling network in mainland France) (Nicolae Lerma et al, 2022); the East Frisian islands in Germany at 3 m above the German reference level NHN (standard elevation zero) (Eichmanns et al, 2021) and the German North Sea at St. Peter-Ording at 2 m + NHN (Hofstede, 1997). Since this definition does not take into account the individual profile of a dune, it is difficult to draw conclusions about long-term dune shifting and ultimately about coastal protection potential.…”

Evaluating the Sand-Trapping Efficiency of Sand Fences Using a Combination of Wind-Blown Sand Measurements and UAV Photogrammetry at Tottori Sand Dunes, Japan

“…Fences with angular openings (e.g., vertical or horizontal slits) exhibit a higher sand-trapping efficiency than those with round edges (e.g., circular holes) [4], and fences in which the porosity increases upward have a higher sand-trapping efficiency than those with decreasing upward porosity [14]. Straight fences have the advantage that they are faster to install and cost less, whereas zig-zag fences exhibit a high sand-trapping efficiency [15]. In addition, the arrangement (e.g., orientation relative to the wind) of a fence also influences the sand-trapping efficiency [4].…”