Conference paper

Unsteady flow in a channel with large scale bank roughness

Systematic investigations on positive and negative surge waves from upstream have been conducted in a 40 m long channel with a mean bed slope of 1.14? and non-prismatic bank geometries. The channel banks included macro-roughness elements, namely various cavities. In total, 41 different geometrical configurations have been investigated. The surge wave experiments confirmed the applicability of the elementary surge wave theory including secondary waves and wave breaking in the prismatic reference configuration. In geometries with channel bank macro-roughness, the absolute surge wave celerity Vw and the celerity surge wave celerity c are reduced. Among other reasons, the observed reduction of the absolute surge wave celerity is due to the increased flow resistance and lays between 5% and 30% for both, positive and negative waves from upstream. Due to the dispersive character, the positive and negative surges from upstream are characterized by a sudden change (front), followed by a progressive change (body) of the water level. Under the influence of bottom slope and friction, the height of the front of a surge wave is reduced exponentially along the channel. This reduction can be described by a simple mathematical model. Its calibration on the surge wave experiments pointed out the extra diffusion due to the macro-scale roughness.

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