Modelling the spatial variability in floodplain soil contamination during flood events to improve chemical mass balance estimates

The spatial distribution of pollutants entering floodplain soils during a flood event will be controlled by the interactions between flood hydraulics, floodplain topography, pollutant concentration, soil conditions, suspended sediment size and chemical reactions between the pollutants, water and soil. These interactions produce spatial variations in pollution build-up that are difficult to sample using current field-based techniques. Coupled hydraulic and hydrological models provide an ideal framework in which to explore these interactions and to improve current, reach-scale, chemical budget calculations. This paper presents a distributed model of floodplain pollution transport which for the first time allows a prediction of the spatial distribution of deposited and infiltrated pollutants within river reaches over a range of scales (1-60 km). The model is shown to be able to predict many of the features of floodplain pollutant build-up that are observed in the field. Using data from hypothetical examples it is suggested that the model can be used in the development of site-specific field sampling strategies. (C) 1998 John Wiley Sons, Ltd.