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The EU Water Framework Directive includes specific requirements to control diffuse pollution. Given the pivotal role phosphorous, nitrate and sediment play in influencing water quality and biodiversity, and that agriculture is thought to be responsible for 50% of the inputs to surface waters, predicting the movement of these diffuse pollutants from land to water is becoming increasingly important. The transport of eroded agricultural soil and associated pollutants from farmlands, results in the eutrophication of surface waters, damage to freshwater ecosystems,  the microbial contamination of surface water sources and is a major pollutant source responsible for the reduction of water quality in UK beaches and coastal environments. Pollutants are either carried in dissolved form in the runoff water, or through attachment to the soil particles. Since pollutants bind preferentially to different sized soil particles, determining the pollutant loading to waterways requires predicting or calculating the sediment size distribution of the eroded sediment. No model exists which explicitly describes the transport of contaminants in the solid and solution phase in overland flow nor is there a dataset which can be used to test such a model.

This project will fill this knowledge gap by solving the multi-particle size class, multi-dimensional soil erosion model of Hairsine and Rose in conjunction with a transport equation for the dissolved pollutants. Validation and calibration of the model will be done through a hierarchical programme, moving from well controlled laboratory experiments, to natural hillslopes and finally a small catchment. At each scale we will determine model performance both at the outlet and spatially. For the flume, measured outflow data will include time varying particle size and pollutant distributions as a function of soil type, surface geometry, rainfall rate and initial soil moisture conditions. High resolution spatial data will be obtained through the use of digital photogrammetry where local aspect and local slope measurements of the surface topography in the flume can be measured for comparison against predictions from the erosion model. At the hillslope scale we will link with the Defra funded Mitigation of Phosphorus and Sediment Project, using a supplementing data collection from 52 instrumented hillsides on three contrasting soil types. We will also utilise rare earth element oxides as tracers at this scale to determine where the sources of sediment are and compare this spatial data with our model predictions. At the catchment scale we will use existing rare earth catchment data obtained from Coschocton, Ohio to test the spatial predictions of the model.


Mathematical Modelling, Experiments & Field Evaluation

Multi-dimensional Soil Erosion & Associated Chemical Transport