Numerical algorithms are presented for predicting sediment slides in reservoirs during drawdown of the water levels. The methods are a part of a simulation model to compute flushing of sediments from water reservoirs. The slide computation is based on a visco-elastic Bingham model for the soil with a depth averaged limit equilibrium approach to find the location of the slide. The groundwater level and its effect on the slide are also computed. A differential equation is solved to find the horizontal location of the slide area. The vertical location of the slide is also computed from a differential equation together with an empirical formula for the maximum slide depth. After computing the slide plane, the Navier-Stokes equations for a very viscous fluid are solved to compute the movement of the material. Stopping the movement is also computed based on classical force considerations similar to Bishops simplified method with Coulomb’s friction law. The numerical model is tested on a 1g physical model test of a 3.8 meter high slope in a water tank where the water level is drawn down. The computed and measured slides start at the same time and follow the same formation pattern and size. The final computed geometry of the slide also fits well with a part of the measurements.

Keywords: Sediments, reservoir, limit equilibrium model, slide movement, Navier-Stokes equations

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