Huit ans de mesures du ravinement des marnes dans les Baronnies méridionales (Préalpes françaises du sud)/Gullying in the South Baronnies (southern French Alps). Results from eight years of monitoring

摘要

Abstract The gullying of marls in the southern Baronnies was monitored over a period of eight years. Annual denudation of unvegetated gullies amounted to 2 cm averaged over three years, on divides as well as on gully channels and side slopes. This average is higher in Oxfordian black marls (3,5 cm/year) than in Gargasian blue marls (2 cm/year) and still higher in the Cenomanian grey marls (1 cm/year). Therefore, gully evolution operated without involving any significant change inform. This suggests that the regional drainage network is going through a phase of active entrenchment. This morphogenic evolution is governed by seasonal factors, which themselves involve interannual variation, accumulation being dominant during the cold season, and erosion during the warm season. Canonical correspondence analysis shows that these seasonal contrasts are site-specific in the gully network, affecting mostly the mid-channel topographic positions. The Gargasian marls are affected by in more "paradoxical" seasonal patterns. These dynamics are above all influenced by water but other climatic agents help in reducing clast sizes, during the cold season. Heavy hot season storm showers remove the debris from the channels. Exceeding time-intensities of 50 mm during б minutes such showers occur from May to October included. Stress release in the bedrock is controlled by the depth of the debris mantle. Since the thinning down of the mantle is essentially controlled by climatic agencies, this depth, easily measurable with a hand-penetwmeter, may constitute an indicator of the erosivity of climate and a proxy for the estimated denudation rate. Clast size may constitute another indicator of marl sensitivity to erosion.