Surrogate root system modeling — A hybrid dune reinforcement

Coastal dunes are a critical natural defense against storm surges and sea level rise, yet their stability is increasingly compromised by intensified hydrodynamic forces. To withstand stronger and more frequent storm surges as a result of climate change, engineered natural coastal barriers play an important role. This study systematically investigates the potential of artificial root system surrogates based on the root structure of Ammophila arenaria to augment dune stability under simulated storm surge conditions. Laboratory experiments were conducted in a 1.0 m wide and 90.0 m long wave flume, replicating the geomorphological characteristics of a dune profile from Sankt Peter-Ording, Germany, at a scale of 1:7. Three surrogate materials (i) coir grid, (ii) basalt grid, and (iii) coir mat were evaluated across three distinct placement configurations (Crest-only, Crest-Slope and Crest-Slope-Foot) under hydrodynamic regimes corresponding to collision, minor overwash, and heavy overwash. High-resolution 3D-lidar scanning provided quantitative, continuous assessments of erosion volumes and dune profile changes. The experimental results indicate that the flexibility of the materials, particularly coir grid and coir mat, substantially mitigates erosion through attenuation of incoming waves and sediment retention, while the relatively stiffer basalt grid exhibits inferior performance. Comparative analyses of small-scale experiments demonstrate that strategically designed artificial root systems can reduce erosion by 13.3 % to 47.6 %, thereby matching or surpassing the 23 % to 40 % reductions documented for natural vegetation. These findings provide critical insights for advancing nature-based coastal defense strategies and highlight the necessity for further large-scale investigations to refine material properties and deployment configurations.