Quelques travaux de correction sur le cours de l'Isère

Examples of river training work along the Isère

¹ Ingénieur en Chef des Ponts et Chaussées
² Ingénieur SOGREAH

Abstract

The river Isère winds its way down the Grésivaudan valley to Grenoble and intersects a cross-valley at Voreppe just after leaving the city. A number of river training schemes have been implemented since the mid-nineteenth century (e.g. canalisation and bank protection works), which were governed by "liberal" policies along the river above the city and a more "directorial" outlook downstream, in accordance with prevailing tendencies at the various times they were put into effect. Major bend-cutting and dyke reinforcement work has been carried out since the middle of the twentieth century, including correction of the river's longitudinal profile, some sections of which were tending to build up by sediment deposition, whilst gravel extraction from others was unduly increasing their depth. Work has just started on irnplementation of a new river flood protection programme for Grenoble. Because of considerable past and predicted river bed level variations, this programme has required more detailed research and testing than earlier schemes, which has involved fresh determination of water levels associated with the predicted rates of river flow, up to and including for the hundred-year peak flood discharge. For the necessary tests, a 1:100 scale model of an 8 km stretch of the river Isère through Grenoble was designed and run in accordance with Froude similarity laws. In addition, a mathematical model of the part of the Isère from its confluence with the river Arc to the sill at Saint Gervais, i.e. about 80 km in length, was subsequently designed and operated. In designing this model, several very complicated computer calculations had to be carried out. In addition to dyke protection and provision of a channel down the middle of the river bed, a number of sub-river sills are to be installed as a means of stabilising the river and its aquifers. Preservation of present flood areas to attenuate major flood peaks above Grenoble is also being envisaged. In view of the highly complex problems involved on both horizontal and longitudinal scales, the physical and mathematical models in use for the study are invaluable assets as regards accurate prediction of data for present and future river engineering projects.