ABSTRACT Natural Flood Management (NFM) is increasingly adopted as a sustainable strategy for mitigating flood risk. Among these measures, the installation of leaky wooden dams (LWDs) at catchment scale is a widely used intervention aimed at slowing flow and desynchronising runoff peaks between sub‐catchments, thereby reducing flood magnitude. Despite their popularity, the long‐term effectiveness of LWDs and particularly their influence on sediment transport and catchment‐scale hydro‐geomorphic connectivity remains poorly understood. To address this knowledge gap, we used a modified version of the CAESAR‐Lisflood landscape evolution model to simulate the hydrological and geomorphic impacts of LWDs within a proxy of a catchment in North Yorkshire, UK. We ran a suite of 20‐year numerical experiments driven by a spatially variable, convection‐permitting rainfall timeseries to explore how the spatial configuration, stream order placement, and density of LWDs affect flood peak attenuation. All LWDs simulated were representative of channel‐spanning structures within the catchment, with a uniform starting gap size of 0.2 m and height of 1 m. Results show that LWDs installed on first‐order streams were most effective, reducing flood peaks by up to 44% and increasing both water and sediment retention. LWDs placed on higher‐order streams had a limited overall impact, though they could reduce individual peaks by up to 35% in some instances, whilst in other cases, flood peaks were amplified by as much as 77%. Importantly, the introduction of LWDs increased geomorphic variability across the catchment. This included both enhanced erosion and deposition along channel segments, with first‐order LWD placements generating the greatest geomorphic response. Furthermore, interactions between LWD in different stream orders and sub‐catchments led to unexpected and non‐linear effects, altering sediment transport regimes and morphodynamic feedbacks throughout the network and changing the efficacy of flood peak attenuation over time. These findings highlight the critical importance of spatial placement and stream network interactions in determining the long‐term hydrological and geomorphic efficacy of LWDs, with notable implications for the design and installation of future catchment‐scale natural flood management strategies.
Wolstenholme et al. (Sun,) studied this question.