Prediction of alluvial river bed variation by SDAR model

Abstract

In this research, a mathematical model is developed to predict bed elevation variation of alluvial rivers. Scour and Deposition model of Alluvial Rivers (SDAR) is a newly developed model with two principal modules of hydraulics and sediment transport. SDAR is a semi-two-dimensional (S-2D) model in which lateral variation of velocity, flow stresses and sediment transport rate are achieved by subdividing the main channel into several stream tubes, each carrying equal discharges. In order to overcome the existing limitations, a new idea of reachwise stream tube concept is introduced. This enhancement allows to link branch connections and withdrawal points with stream tubes for lateral mass exchanges. Sediment routing and bed variation calculations are accomplished separately along each tube strip designated by virtual interfaces. A new method, based on the advection–dispersion (A–D) principles, is also developed for distributing inflowing sediment from branches among stream tubes. Furthermore, in SDAR model a controlling parameter Ωis included to distinguish between scour and deposition phases. The range of Ωis found to vary between ±1 depending on whether deposition or scouring prevails.A new formula for calculating active layer thickness is also introduced in the model. To test the model behavior, comprehensive calibration scenarios were conducted. During calibration runs, the ability of the model in longitudinal and transversal bed profile simulation and armor layer development prediction were especially detected. Results of simulation are also compared with the outcomes of well-known models, e.g. HEC-6, GSTARS-2, and FLUVIAL-12. It was found that the model's ability in simulating bed variation is noticeably increased when the S-2D concept is introduced. Indeed, the comparative validity tests confirm SDARS's promising role in facing with complex real engineering cases