Impacts of dams on physical and biological environments

Abstract

Dam settlement in river-beds constitute an obstacle to free-running water and causes a significant transformation to hydrologic regime within the impacted area. This is particularly true for large reservoirs. Such evolutions have great effect on nature and quality of the original biological conditions. It must be mentioned that hydro projects are a response to commercial uses through reservoir capacity and - though - contribute to economical development and social welfare. Unfortunately, they induce also significant trouble to aquatic and semi-aquatic biocenosis. It must be considered of great importance to get from the site and from the project a global knowledge so as to minimise incidences on physical and biological elements, either in normal conditions or during particular events like periodical flush-out of sediments. In the past, such events have induced real ecological catastrophes due to the lack of anticipation on operating schemes. These effects may in fact create considerable prejudice to commercial stakes for which the project was conceived, so as for silt deposits, due to their impacts both on river-beds and outlets of dam conditions. Economical and ecological stakes may in fact tend to a common target, and finally are relevant to a similar operating concept. The present session number 3 is gathering a few history-cases showing geographically changing situations, the diversity of which does yet emphasize some operating principles for multi-uses reservoirs. These situations are of particular interest at the time of transformation for France, of what is called "General regulations for water uses" in our European context.