Modelling Connectivity Between Pollutant Source Areas and Streams

The nature of pollutant connectivity between unsealed forest roads and adjacent nearby streams is examined numerically in terms of spatial and temporal patterns of runoff generation, erosion, and sediment transport. In this paper we consider the relative effects of rainfall intensity and duration, surface roughness, infiltration rate, macropore flow and sediment detachment and transport. The objective of the numerical simulation of this hillslope system is to identify the dominant processes and parameters that affect the degree of pollutant connectivity between roads and streams. The St. Venant equations are applied to extract a two-dimensional diffusion wave model with variable conductivity and diffusivity to represent the behaviour of flow dynamics mathematically. The resulting nonlinear partial differential equation was solved with appropriate initial and boundary conditions using the MacCormack finite difference numerical technique. Sediment detachment due to rainfall and flow dynamics is linked to the equations for mass conservation and continuity to represent erosion and was solved numerically using the finite difference method. The current numeric representation involves numerous parameters, many of which are unavailable for practical field application. Therefore, present work deals with the selection and/or development of methods to determine the relative significance of each process or parameter, so as to ultimately reduce the parameter space of this complex hillslope problem, improving our ability to scale-up the impacts of forest roads on catchment water quality in future works.