60-Modelling Effects of Rural Land Management on Flood Risk.

Abstract

Around the world, rural land use and land management are changing. Effects are often subtle, and not possible to detect from catchment-scale data analysis. There is a need for new methodologies that can represent the local scale response and the aggregated effect at catchment scale. In the UK, recent floods have renewed speculation about the linkage between agricultural land management and flooding. Available data to quantify effects of agricultural intensification have been limited, small scale, and mainly focused on the lowlands and arable agriculture. There is a need to quantify impacts for upland areas, which are source areas for runoff generation, and to develop methods to extrapolate from small scale observations to predict catchment-scale response. With assistance from a cooperative of Welsh farmers, and support from the EPSRC Flood Risk Management Research Consortium, a multi-scale experimental programme has been established at Pontbren, in mid-Wales, an area of intensive sheep production. The data have been used to support development of a multi-scale modelling methodology to assess impacts of agricultural intensification and the potential for mitigation of flood risk through land use management. Data are available from statistically-replicated experimental plots under different land management treatments, from instrumented field and hillslope sites, including tree shelter belts, and from first and second order catchments. Measurements include rainfall and climate variables, soil moisture, soil water pressure and soil hydraulic properties at multiple depths and locations, tree interception, overland flow and drainflow, groundwater levels, and streamflow from multiple locations. Detailed, fine resolution, physics-based models have been developed to represent soil and runoff processes, and conditioned using experimental data. The response of these detailed models is used to develop and calibrate simpler 'meta-models' to represent individual hydrological elements—in this case mainly individual fields, with their associated field drainage. These meta-model elements are then combined in a distributed catchment-scale model. The paper presents results of detailed field-scale simulations to demonstrate the dominant runoff processes under intensive sheep production, and impacts of the use of tree shelter belts in improving soil structure and reducing peak runoff intensities. Catchment-scale simulations show the effects of improved and unimproved grassland, and the potential effects of land management interventions, including farm ponds, and tree shelter belts and buffer strips. It is concluded that the methodology developed has the potential to represent and quantify catchment-scale effects of upland management; continuing research is extending the work to a wider range of upland environments and land use types, with the aim of providing generic simulation tools that can be used to provide strategic policy guidance.