LONG PROFILE EVOLUTION OF A MOUNTAIN STREAM IN RELATION TO GRAVEL LOAD MANAGEMENT - EXAMPLE OF THE MIDDLE GIFFRE RIVER (FRENCH ALPS)

Since the 1970s, many French riverbeds have been incised by more than 1 m. This generalized phenomenon, apparently irreversible, is rightly considered as alarming. However, our study of the Giffre, a sixth-orde r high-energy river draining an intramountain plain in the northern Fr ench Alps, leads us to qualify this general opinion. Although the Giff re underwent considerable incision as early as the 1960s (-1.16 m betw een 1912 and 1988, for a total sediment loss of 2 x 10(6) m(3)) follow ing extensive gravel extraction from the channel, this evolution appea rs to be reversed today, showing that this river is capable of rehabil itating itself. The watershed supplies the river with 50,000 m(3)/yr o f material and part oi this load (30,000 m(3)/yr) is extracted. Althou gh it is theoretically possible to reverse this phenomenon, it is unac ceptable for the local economy as man-made installations unadapted to flooding were developed along the river during the period oi incision. Today, the development policy is in conflict with the maintenance and the preservation of natural sediment transport and deposition.