Modelling turbidity currents in reservoirs

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Abstract

A two-layer mathematical model is presented for sedimentation in reservoirs where turbidity currents are to be expected. As the model is two-dimensional in plan, the suspended-sediment concentration of the turbulent underflow is described by a depth-integrated form of the convection-diffusion equation originally proposed by Galappatti in 1983. The bed-level variations governing this model are described by a depth-integrated sediment balance. For closure of the model various closure relations are required based on the vertical distribution of flow and sediment of the turbidity current. A semi-empirical model, presented to describe these distributions, is used to quantify boundary shear stresses, suspended-sediment transport rate, and the adaptation scales in Galappatti's equation. Additionally a discussion is given on the applicability of various existing relations for interfacial mixing, as well as on relations for the near-bed sediment concentration. The presented model, and the proposed simplified models deduced from it, can be used for various types of reservoirs and to more conventional computations such as for saline underflows.

Acknowledgment

This report has been written during my employment as a research assistant (AlO) in the Hydraulic and Geotechnical Engineering Division of the faculty of Civil Engineering of the Delft University of Technology. This study is carried out as part of a research project to sedimentation in reservoirs, a joint cooperation between Delft University of Technology and Delft Hydraulics, under supervision of Prof. Dr. M. de Vries (Delft University of Technology).

Pro£ Dr. M. de Vries is gratefully acknowledged for his encouraging support and critical reading during the writing of this report. Also Dr. Z.B. Wang is acknowledged for his critical screening of this report and for his valuable suggestions.

I would also like to express my appreciation to Prof. Dr. M.H. Garcia for sending me his comprehensive works on turbidity currents, and to A. Sieben for his fruitful discussions.

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