It may be better to use power law relationships between suspended sediment concentration and 'erosive rainfall', soil water flow, or some other flow path (or several flow paths). Rather than using the reach discharge. This would take sediment source and transport pathways into account more, but perhaps (or perhaps not?) at the expense of increased complexity. Something to look into! See e.g. https://www.hydrol-earth-syst-sci-discuss.net/hess-2017-419/hess-2017-419.pdf
It may be better to use power law relationships between suspended sediment concentration and 'erosive rainfall', soil water flow, or some other flow path (or several flow paths). Rather than using the reach discharge. This would take sediment source and transport pathways into account more, but perhaps (or perhaps not?) at the expense of increased complexity. Something to look into! See e.g. https://www.hydrol-earth-syst-sci-discuss.net/hess-2017-419/hess-2017-419.pdf