Use of fallout 137Cs measurements for validating and calibrating soil erosion and sediment delivery models

Recent developments in soil erosion and sediment yield modelling have largely focused on the use of distributed models. Such models permit both the spatial heterogeneity of catchment land use, soil properties and topography and the spatial interaction of erosion and sediment delivery processes to be represented. An important constraint on these developments has, however, been the lack of data for validating the spatial distribution of erosion and deposition races within a catchment predicted by the model. The use of fallout Cs-137 affords a means of assembling information on longer-term rates and patterns of erosion and deposition within a catchment which can be used to validate existing erosion and sediment delivery models and to develop and calibrate improved modelling strategies. This paper presents some preliminary results from a detailed investigation or erosion and sediment delivery within a 6.7 ha cultivated field in Devon, UK. Caesium-137 measurements have been used to estimate the rates and spatial patterns of erosion and deposition within this field and this information could be used for model testing and validation. To explore further the potential for using the Cs-137 data to calibrate distributed erosion and sediment delivery models, the spatial distribution of measured Cs-137 inventories within the study area has also been used directly, to calibrate a simple topography-driven soil erosion model superimposed onto a digital elevation model of the study area.