Influence of Sand Trapping Fences on Dune Toe Growth and Its Relation with Potential Aeolian Sediment Transport

Abstract

This study provides insights into dune toe growth around and between individual brushwood lines of sand trapping fences at the dune toe of coastal dunes using digital elevation models obtained from repeated unmanned aerial vehicle surveys. Prevailing boundary conditions, especially sediment supply, as well as the porosity and arrangement of the installed sand trapping fences significantly influence the effectiveness of different configurations of sand trapping fences. The dune toe growth is significant immediately after constructing a new sand trapping fence and decreases over time. According to the results presented in this study, for sand trapping fences that have been in place longer, the protruding branch height and the porosity of the remaining branches play a minor role in trapping sand. Sand trapping fences with lower permeability favour localized coastal dune toe growth directly at their brushwood lines, whereas fences with higher porosity allow for more sediment deposition further downwind. The trend in dune toe changes can be roughly predicted by integrating potential sediment transport rates calculated with hourly meteorological data.

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

“…Overall, the high fence tended to show higher sand-trapping effectiveness than the medium and low fences. However, above a certain fence height, the efficiency to trap sand decreases [22,29]. Figure 6 Similar developments were observed on fences studied by Hotta and Horikawa (1990) [22] and Eichmanns and Schüttrumpf (2021) [29].…”

“…Moreover, the investigations of Ning et al (2020) [26] showed that sand-trapping is highest at the beginning of the first phase, drops significantly until the end of the first phase, and continues to drop slowly until the end of the second phase. The dune grows only horizontally during the second phase until a streamlined equilibrium is reached [29,60,61]. Overall, the high fence tended to show higher sand-trapping effectiveness than the medium and low fences.…”

“…Overall, the high fence tended to show higher sand-trapping effectiveness than the medium and low fences. However, above a certain fence height, the efficiency to trap sand decreases [22,29]. Figure 6 where x [m] is the horizontal distance from the fence, z [m] is the height above the ground, ux,z [m/s] is the horizontal wind velocity with an installed fence in the wind tunnel, and u0x,z [m/s] is the horizontal wind velocity at the same position without any fence [31,35].…”

“…Thus, wind fences can protect infrastructure from damage by sediment load or heavy wind [18,[20][21][22][23][24]. By contrast, in coastal regions, sand trapping fences can support the rehabilitation of eroded areas in coastal dunes, strengthen coastal dune toes, prevent sand drifting, limit human access to (protected) coastal areas in recreational areas, or initiate coastal dune formation by selective sand deposition [17,[25][26][27][28][29]. The positive effect of sand trapping fences results from the local reduction of wind velocity, leading to downwind sediment accumulation at the fences; thus, they function as a coastal protection tool by using aeolian sediment transport to initiate and advance dune stability [15,16].…”

“…However, these studies primarily considered vertical holedplank fences [26,32], perforated plastic or metallic fences [18,[33][34][35], and wire and griddled fences [20]. In particular, the purpose of installing sand trapping fences in coastal areas, e.g., for dune toe growth, is only considered in a few detailed studies [13,29,30,36,37]. Therefore, research on sand trapping fences in coastal areas is generally needed for initiating dune toe growth, so that coastal managers can find adequate locations for the fences along sandy coastlines and within the beach profile.…”