Monitoring Braided River Morphodynamics with an Acoustic Doppler Current Profiler

Monitoring the spatial distribution of gravel bedload transport in complex braided morphologies is hampered by high spatial variability of sediment flux pathways, which respond to both local measures of flow competence and upstream sediment supply. Coupling observed morphodynamics with distributed measurements of sediment transport in braided rivers remains a key empirical research goal. For the ReesScan project on the Rees River, New Zealand, calibrated aDcp measurements of apparent bed velocity (va) will be used to: a) close a reach-scale morphological sediment budget, by monitoring bedload transport at a fixed cross-section; and b) study the coupled evolution of sediment transport pathways and short-term morphological evolution of distinct braidunits. The calibration of va has been based on concurrent va measurements and Helley-Smith bedload samples. In this paper we use calibrated va to map the spatial distribution of gravel-sand bedload transport through across a full channel section and along a braid-unit during the falling limb of a flood.