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The influence of naturally occurring in‐channel large wood (LW) on the hydraulics, hydrology and geomorphology of rivers is well documented. To inform management and better understand naturally occurring or artificially placed LW, hydraulic and hydrological models are applied to predict the possible benefits and drawbacks for habitat, sediment management and flood risk mitigation. However, knowledge and guidance on appropriate representation in models, needed to underpin realistic predictions, is lacking. This could lead to unrealistic expectations of the effectiveness of LW for different river management goals. To date, seven types of LW representation in hydraulic and hydrological models have been applied, the range partly reflecting the variety of LW, model types, scales and purposes. The most common approach is by altering channel roughness to represent flow resistance. Although qualitatively the effects of LW have been captured using models, to date quantitative validation, as well as transferable knowledge to help a priori parameterization of LW representations, remain limited. Therefore, additional empirical investigations and robust model validation are required to inform defensible LW representations for specific purposes and scales in numerical models coupled with better accounting of input uncertainty to improve confidence in predictions. Future studies should also consider a greater range of artificial and natural LW features, settings, larger spatial scales and better account for temporal variability of flow, morphology and LW configuration. This article is categorized under: Water and Life > Methods Science of Water > Methods Water and Life > Nature of Freshwater Ecosystems

Engineered log jams (ELJs) are employed to address river restoration goals and a range of river management problems including coarse sediment movement. In the Bowmont Water, a dynamic wandering gravel-bed river in the Scottish Borders, 33 previously untested ELJs primarily designed to capture and store coarse sediment, were installed on a trial basis. Using repeated topographical surveys and field observations, the performance of the ELJs in response to a 5-10 year recurrence interval flood that occurred on the 25 September 2012 was evaluated at two reaches with catchment areas of 28 km 2 and 57 km 2 . Three of the structures were damaged due to scour of surrounding material that exposed the pile anchors and all the timbers of one structure were completely displaced downstream. Sixteen structures induced geomorphic responses and only four induced significant deposition (>0.3 m) above that which would occur naturally within the adjacent active gravel bar deposition zones. The placement in gravel bars, minor channel blockage ratio created by the structures and their porous nature limited the hydraulic interference and in turn geomorphic responses. Therefore the ELJ placement goal of increasing sediment storage was not fully met. This study contributes to the empirical evidence base for ELJ performance evaluation of different designs in a range of physiographic settings needed to validate performance and refine design. Using these initial findings and knowledge gained from other studies, recommendations for improving the design and placement strategy are proposed.

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