Reza A. Nazari

This graphical abstract illustrates the evaluation of gabion water barrier structures in a mountainous catchment area. The upper section details the study's workflow, which includes site investigations, construction activities, and two-dimensional hydraulic modeling. The central illustration contrasts debris-flow conditions with and without the gabion water barrier. In the absence of the structure, high-velocity flows result in erosion and sediment transport towards rural infrastructure and agricultural lands. However, with the barrier, the flow is intercepted upstream. The lower section summarizes the primary outcomes: a reduction in peak flood discharge, the use of locally sourced construction materials, a decrease in flow velocity, the creation of temporary upstream storage, and the protection of agricultural lands and rural infrastructure. Small mountainous catchments located in semi-arid areas are particularly vulnerable to flash floods and debris-laden flows, which present considerable threats to rural infrastructure and agricultural lands. In these environments, low-cost and easily constructible structural measures are typically favored over more intricate engineering solutions. This study presents a field-based case study on the design, implementation, and performance evaluation of a gabion water barrier (GWB) developed as a viable mitigation strategy in a rural mountainous catchment. The research emphasizes design considerations that are specific to the site, which encompass hydrological conditions, geotechnical characteristics, properties of debris, and structural configuration. Special focus is placed on construction methods, including excavation, foundation preparation, gabion assembly, stone filling, and anchoring, utilizing materials and labor that are locally sourced. Hydraulic modeling was utilized as an additional tool, employing a two-dimensional unsteady flow model in HEC-RAS (version 6.6) to qualitatively evaluate flow behavior during design flood conditions and to compare scenarios both with and without the barrier. The findings reveal significant flow reduction, temporary storage upstream, and decreased velocity; however, the results are still influenced by the magnitude of inflow and the representation of the terrain. In addition to hydraulic performance, the research underscores practical construction difficulties, field limitations, and maintenance factors that affect long-term functionality. The results offer practical engineering insights regarding the viability and efficiency of small-scale gabion barriers as economical and flexible mitigation solutions in mountainous regions with limited data.