Contenu du sommaire

Vegetation, climatical maps and meteorological centres give data used to realize a synthetical map which shows, in each river drainage-basin : — Annual rainfall (mean) ; — Seasonal rainfall (mean ) ; — Snow pack (Thickness and life) ; — Freezing (Number of day) ; — Temperature of the cold season (October to April). This document allows to estimate annual water-volume brought to the drainage basin of the Upper-french Rhône (above Lyon). Exceptional spells of flood, high or low water are shown by an analysis of data from meteorological stations located in the river drainage basin of each affluent.

In the frame of a multi-purpose research project, this paper describes the hydrologic units of a little region of the upper Rhône basin : that of Morestel, Le Bouchage, Brégnier-Cordon. Here, seven units, very well individualised by their types of water movement both on the surface, in the soils, in the phreatic sheets, and in the vegetation... are described, with a qualitative approach. In the next five years a quantitative approach will be attempted in the same framework.

A study of two reaches of the French Upper Rhône marks out several geomorphological patterns with minor forms, each having its own dynamic evolution. The speed of renewal and disappearance of these units explains the dynamic evolution of the biocoenoses linked to these environments. The reserves set up along the rivers must allow the rejuvenation of fluvial land forms.

The upper Rhone hydrosystem has been partitioned into sub-systems, on the basis of ecological criteria. Every sub-systems, named « functional set », represents a stage of a chronosequence from the river ecosystem, towards the semi-aquatic ecosystems, and ending with the terrestrial system. Each chronosequence depends on geomorphological conditions. Man's activities may change the direction of these evolutionary processes and/or their rate of speed. The cartography of the functional sets will represent both their ecological characteristics, the geomorphohgical conditions giving rise to them and initiating their evolution, and the impact of the man's activities. Such documents may provide assistance to the ecological management of the water supply of the alluvial plain.

Until the XIXth century humain interventions did not modify the hydrological balances in the plains of the French Upper-Rhône. Since, embankments and drainage works have assisted land biocoenoses and impoverished wet environment potentiality. Therefore it is urgent to plan protection of these areas.