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

Abstract

Abstract:We seek an improved and quantitative understanding of the sources and transport of sediment and attached phosphorus in upland catchments and downstream reaches of the Namoi River in New South Wales, Australia. Study of the sources of phosphorus and related sediment was motivated by severe problems with blooms of blue-green algae and toxic by-products in the Darling and Namoi Rivers. Using atmospheric fall-out of radionuclides as tracers, Olley et al. (1996) concluded that much of the sediment deposited in the lower reaches came from subsoil rather than topsoil. With this insight, we focus on quantifying sediment sources from stream bank erosion, especially in seasonally erosional reaches of Cox's Creek and the Mooki River.The approach presented here integrates interdecadal aerial photography, interseasonal ®eld measurements of bank erosion processes, continuous monitoring of stream¯ow and turbidity and event sampling of suspended solids and phosphorus, with an analytical model of in-stream suspended sediment transport. We compare a lateral source term in the calibrated transport model with ®eld-based and aerial measurements of stream bank erosion. Calibration of the in-stream model is illustrated for two reaches of the Mooki River, with the changes in parameter values being related to aspects of the hydraulic geometry and particle size. The processes of stream ow and bank erosion due to undercutting, desiccation, block failure and mass wasting of aggregated particles interact to produce instream¯uxes of suspended sediment that are transported and redeposited downstream. The combined approach demonstrated here has potential for predictive spatial modelling of sediment concentrations and loads.

Bank erosion of legacy sediment at the transition from vertical to lateral stream incision

“…Erosion was greatest in summer months along the Richland Creek streambank. This is contrary to other studies (Wolman, 1959;Hooke, 1979;Wynn et al, 2008) where streambank erosion was most severe in winter owing to more frequent freeze-thaw cycles; although processes at the Richland Creek site follow Green et al (1999) who described mass wastingdominated streambank erosion due to desiccation cracking. The volume that eroded in the summer would decrease if desiccation was not an important process along Richland Creek.…”

Assessing ecosystem functioning in streams affected by forest management: increased leaf decomposition occurs without changes to the composition of benthic assemblages

“…Similar channel narrowing has been observed previously following forest clearance, and was associated with increased current velocities (Sweeney et al. , 2004), while bank undercutting indicates increased erosion and sediment loads (Green et al. , 1999).…”

“…obs.). Similar channel narrowing has been observed previously following forest clearance, and was associated with increased current velocities (Sweeney et al, 2004), while bank undercutting indicates increased erosion and sediment loads (Green et al, 1999). Any increases in flow and ⁄ or suspended sediment have potential to increase physical abrasion of the leaves, particularly during spates Lepori, Palm & Malmqvist, 2005).…”

Sediment Matters

“…For example; sediment-turbidity relationship is used to convert a time-series of turbidity to suspended sediment concentration. If turbidity is missing for a period but flow has been measured at that period, the suspended sediment-flow relationship can be used to fill the gaps in the data (Green et al 1999).…”