Changes in discharge rise and fall rates applied to impact assessment of catchment land use

Despite substantial evidence that land use and management can enhance flood runoff at a local scale, evidence of increased flood risk based on peak discharges is lacking in catchments greater than 10 km². This analysis is instead based on assessing changes in short-term rates of change in discharge. The influence of land use is demonstrated first on the small Coalburn catchment where changes in rates of rise are closely related to drainage and afforestation. For the larger Axe catchment (288 km²), changes in rates of rise are investigated by comparing annual maximum and peaks over a threshold flows for different periods, by comparing rates of rise associated with given daily rainfall and by adapting the method of flow variability analysis for use of rates of change rather than flow itself. All these methods demonstrate significant changes in river flow dynamics which seem to be in parallel with land use changes even when the influence of climate variability from year to year has been taken into account. Rates of change in discharge appear to respond to land use changes and thus provide a potential basis for application to land use management policies.