L'aménagement intégré d'un grand fleuve : le Rhône – A. Conception générale et effets sur les crues et les nappes phréatiques

Integrated development of a large river : the Rhône – A. General design and effect on floods and subsurface water layers

Directeur des Etudes et Travaux à la Compagnie Nationale du Rhône

Abstract

Responsibility for the development of the 500 km of the French part of the Rhône is in the hands of the National Rhône Corporation (CNR). The operation is virtually completed to-day as 16 of the 19 locations to be harnessed are already in service. This is a multi-purpose development (hydro-electric generation, navigation by wide vessels, agricultural development, protection against floods, port facilities, etc.). The Rhône has promising potential with a semi-permanent flow of 1 460 m3/s., conveying an average 50 billions m3 per year. It produced 16.9 TWh in 1981. The navigable section built as of that date is 350 km long and can handle the passage of 4 000 to 5 000 ton convoys. Given the fact that the valley is populated, the project has been designed to occupy as little space as possible and to reduce the absorption of land to the strict minimum. Consequently, it includes very long lateral dykes and apart from Genissiat upstream, head 70 m, is divided into a continuous series of low heads. As a result, reservoirs are low by comparison with the river's flow. This has a very positive effect on the quality of the water and the transit of solid matter, but necessitates very sophisticated operation to secure correct propagation of floodwaters. It is particularly important to prevent acceleration and overflowing of floodwaters, albeit the floodable surfaces have been significantly reduced by dykes and diversion canals. This type of project also implies very tight control of subsurface water layers, whether on farmable sites or in the urban environment. The report shows the methods used to master the phenamenon in particular using very large-scale drainage devices. The continuity of the work, which was spread over thirty years, and the fact that the CNR is both designer and operator, have made it possible for this development to benefit at all times from the significant technological progress which has occurred in recent decades.