Using ISIS sediment for simulating graded sediment behaviour in rivers

Results of testing the performance of one-dimensional computer model ISIS Sediment for simulating the behaviour of graded sediments are presented. The Ackers and White total transport function derived for uniform sediments and the Parker bedload formula based on graded sediment data were used for sediment transport computations. The model was tested on the detailed non-equilibrium graded sediment transport data collected in an 18 m long and 0.8-1.1 m wide trapezoidal concrete laboratory channel. The test simulations demonstrate that the use of the Ackers and White transport function does not provide an adequate prediction of graded sediment transport and bed evolution, while the use of the Parker formula gives a better agreement with the measured data in terms of the bedload and bed surface composition. It is concluded that an adequate prediction of long-term trends in the behaviour of graded sediment streambeds is only possible if a proper formulation of intergranular effects in sediment mixtures is available and is accounted for in the sediment transport formula used for the simulations.