Contemporary fine‐grained bed sediment sources across the River Wensum Demonstration Test Catchment, UK

Because the sources of fine-grained sediment problems in river systems are diffuse, it is essential to assemble catchment scale information for informing management strategies. Sediment source-tracing procedures have increasingly been adopted in this respect. Accordingly, a recently refined composite tracing procedure was used to investigate contemporary sources of fine-grained channel bed sediment in 11 sub-catchments (364km2) of the River Wensum Demonstration Test Catchment, in the eastern UK. The procedure incorporated a combination of statistical tests for discriminating source end members, plus numerical mass balance modelling incorporating weightings for within-source tracer variations and tracer-specific discriminatory power, as well as a combination of local and genetic algorithm optimisation coupled with Monte Carlo uncertainty analysis. Replicate Monte Carlo runs demonstrated the convergence of the modelling outputs within +/- 1% of the average medians. Relative frequency-weighted average median source type contributions were estimated to range between 27%69% (agricultural topsoils; predicted deviate median inputs 0%98% and 9%100%), 0%38% (damaged road verges; predicted deviate median inputs 0%58% and 0%100%) and 21%48% (channel banks/subsurface sources; predicted deviate median inputs 0%50% and 4%50%). The study provides further evidence of the importance of channel banks and damaged road verges as sediment sources and the need to include such areas in catchment sediment management strategies. Copyright (c) 2012 John Wiley & Sons, Ltd.