INTERACTION OF BED TOPOGRAPHY, FLOW TURBULENCE AND SEDIMENT TRANSPORT: HARNESSING THE POWER OF LABORATORY EXPERIMENTS FOR IMPROVING PREDICTIVE ABILITY IN REAL RIVERS

Over the past three years a series of laboratory experiments in a large-scale experimental flume (55 m long, 2.75 m wide) at SAFL/NCED have been conducted for the purpose of understanding and quantifying the dependence of sediment transport variability on near-bed turbulence, bed topography and particle-size distribution, and derive stochastic transport models which reproduce the observed micro- to macro-scale dynamics. An integrated summary of the main findings of this series of experiments will be presented with special emphasis on the following results: (a) it was demonstrated that bedload sediment transport at very small time scales can be an order of magnitude larger or smaller than the long-time average and this variability was quantified within a multiscaling framework similar to that of fully developed turbulence; (b) bed morphodynamics, and especially characteristic scales of bedforms, can be inferred from measurements of turbulent velocity fluctuations above the bed suggesting that turbulence can serve as a proxy for the prediction of bedform dynamics; and (c) the nature of scaling and the degree of complexity and non-linearity in bed elevation fluctuations and sediment transport rates depends on the bed shear stress, with implications for parameterization of predictive models. The main thrust of this work lies in understanding the complexity of interacting processes (bed topography, turbulence and sediment transport) over a range of scales and enabling the prediction of unresolved or unobserved small scale variability, e.g., important for biologic activity in rivers, from larger scale measurements.