Ecoulement et dissipation sur les déversoirs en gradins de gabions

Flows and dissipation of energy on gabion weirs

CEMAGREF, groupement d'Aix-en-Provence, B.P. 31, Le Tholonet, 13612 Aix-en-Provence Cedex 1, Tél. : 42 66 93 10

Abstract

The use of gabions in the small dams in the Sahel regions of Africa is quite common, they are used in flood spillways in which the gabion weirs are usual techniques. Indeed, apart from a good mechanical stability and a high level of resistance to flood flows, gabion weirs enable a large amount of predissipation of water energy before the stilling basin. In the present state of the technique the right dimensions for this type of structure are not well known. To define energy dissipation on the shoulders a systematic study of the standardized wasteways from 3 to 5 m high, for a flow rate of up to 3 m³/s per meter width, has been carried out on scale models on 1/5 scale.

It has enabled the amount of energy dissipation to be quantified and enabled determination of dimensioning parameters for the stilling basin. The results obtained lead to a saving of 10 to 30 % over the length of the stilling basin compared to the lengths obtained with the methods used up to present. Moreover, we also wished to classify the flows on the shoulders and define the phenomena observed during the different hydraulic regimes.