Relating stream-bank erosion to in-stream transport of suspended sediment

We seek an improved and quantitative understanding of the sources and trans port of sediment and attached phosphorus in upland catchments and downstrea m reaches of the Namoi River in New South Wales, Australia. Study of the so urces of phosphorus and related sediment was motivated by severe problems w ith blooms of blue-green algae and toxic by-products in the Darling and Nam oi Rivers. Using atmospheric fall-out of radionuclides as tracers, Olley et al. (1996) concluded that much of the sediment deposited in the lower reac hes came from subsoil rather than topsoil. With this insight, we focus on q uantifying sediment sources from stream bank erosion, especially in seasona lly erosional reaches of Cox's Creek and the Mooki River. The approach presented here integrates interdecadal aerial photography, int erseasonal field measurements of bank erosion processes, continuous monitor ing of stream flow and turbidity and event sampling of suspended solids and phosphorus, with an analytical model of in-stream suspended sediment trans port. We compare a lateral source term in the calibrated transport model wi th field-based and aerial measurements of stream bank erosion. Calibration of the in-stream model is illustrated for two reaches of the Mooki River, w ith the changes in parameter values being related to aspects of the hydraul ic geometry and particle size. The processes of stream flow and bank erosio n due to undercutting, desiccation, block failure and mass wasting of aggre gated particles interact to produce instream fluxes of suspended sediment t hat are transported and redeposited downstream. The combined approach demon strated here has potential for predictive spatial modelling of sediment con centrations and loads. Copyright (C) 1999 John Wiley & Sons, Ltd.