Catchment-Scale Changes in Runoff Dynamics Following Natural Flood Management Interventions

Natural Flood Management (NFM) interventions and nature-based solutions are increasingly advocated as sustainable flood-mitigation strategies, yet empirical evidence of their hydrological impact at the catchment scale remains limited. This study uses an ensemble approach to characterise runoff-response distributions, drawing on long-term observed data (2011–2023) from the Eddleston catchment in Scotland. Unlike event-focused approaches, this method synthesises system behaviour across diverse hydrometeorological conditions to identify “typical” responses under pre- and post-intervention states.

Results from a small headwater catchment (2.3 km²) reveal statistically significant changes in runoff dynamics, including a delay in peak timing and a reduction in peak height after the installation of a series of leaky barriers. Comparable patterns in a larger catchment (34 km²), within which this smaller headwater catchment is nested, indicate that NFM effects extend beyond headwater sub-catchments. Ensemble-based summaries further highlight the dominant role of antecedent wetness in runoff generation, while also indicating increased infiltration and reduced runoff coefficients under high-flow conditions post-NFM installation.

By integrating ensemble hydrograph separation and impulse-response analysis, this framework provides a transferable tool for assessing NFM effectiveness across multiple scales. Findings strengthen the evidence base for NFM design optimisation and policy integration, supporting long-term strategies for flood resilience.