Re-meandering attenuates frequent high-flows and diversifies physical habitat in a gravel-bed river

Channel re-meandering is commonly used in river restoration. However, few investigations have combined multi-temporal, reach-scale data from hydrological and topographic monitoring, and hydraulic numerical modelling to evaluate this restoration approach, particularly for low to medium energy gravel-bed rivers in low sediment supply settings. The Eddleston Water project focuses on the application and evaluation of Natural Flood Management measures to reduce flood risk to downstream communities and improve riverine physical habitat; providing a natural laboratory to examine re-meandering. A 1.6 km section of river was re-meandered between 2013 and 2016, increasing river length by 18 %. Assessment of the impact on flood attenuation was made using analysis of hydrological time series (2011-2020), comparing repeat (2018 and 2020) reach-scale topographic surveys of the channels to map geomorphic change, and numerically modelling two-dimensional flood extents and dynamics for flood events of different magnitude. Hydrological analysis showed enhanced flow attenuation was only statistically significant for in-channel events. Numerical hydraulic modelling showed a small impact on flood attenuation for a Q5 event (<15 min peak travel time delay, <1.2 % peak attenuation); effects were just discernible for a Q20 event. Repeat topographic surveys and sediment budgets identified overall bed degradation but showed physical habitat diversity was maintained. Whilst hydraulic effects were relatively small, they should be considered in the context of re-meandering being only undertaken on a small proportion of the river network. However, insights from hydraulic modelling show re-meandering design must consider interactions between channel and floodplain topography to maximise connectivity and thus attenuation.