Approaches to delivery modelling in LOIS

A catchment-scale distributed water quality model has been developed and applied to rivers in the east of England and southern Scotland. The model uses a catchment discretisation based on hydrological response units, or HRUs, which are hydrologically independent as defined by topography and drain to an identified location on a stream network. Within each HRU there is no further explicit spatial discretisation, flow and contaminant fluxes being simulated according to the internal statistical distribution of spatial properties. The complete model simulates the daily flux of water and a range of contaminants from each HRU to the distributed river network, and routes within the river network to the catchment outlet, taking account of point sources. The model is under test at a sample of representative catchments.