Long Profile Evolution of a Mountain Stream in Relation to Gravel Load Management: Example of the Middle Giffre River (French Alps)

Abstract

/ 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-order high-energy river draining an intramountain plain in the northern French Alps, leads us to qualify this general opinion. Although the Giffre underwent considerable incision as early as the 1960s (-1.16 m between 1912 and 1988, for a total sediment loss of 2 x 10(6) m3) following extensive gravel extraction from the channel, this evolution appears to be reversed today, showing that this river is capable of rehabilitating itself. The watershed supplies the river with 50,000 m3/yr of material and part of this load (30,000 m3/yr) is extracted. Although it is theoretically possible to reverse this phenomenon, it is unacceptable for the local economy as man-made installations unadapted to flooding were developed along the river during the period of incision. Today, the development policy is in conflict with the maintenance and the preservation of natural sediment transport and deposition.KEY WORDS: Bed incision; Gravel load management; Giffre River; France