Trajectoire d’évolution d’un cours d’eau à faible énergie au cours du second Holocène : la Charente entre Angoulême et Saintes

Improving Grain Size Analysis to Characterize Sedimentary Processes in a Low-Energy River: A Case Study of the Charente River (Southwest France)

“…The channel is confined within a narrower alluvial plain with a width ranging from 0.5 to 1.5 km, and evidence of side channel changes is relatively scarce [34]. The channel width in this single-channel section ranges from 30 to 70 m, with a mean width-depth ratio of approximately 10 [35]. The mean stream power in this segment is estimated to be around 7 W.m −2 , and the average low-gradient is approximately Above the Chaniers gauging station, the Charente River exhibits very low stream power, which is estimated to be around 5 W.m −2 .…”

“…The fluvial pattern of the Charente River undergoes changes along its course. It starts as an irregular incised single channel from its source to Civray, transitions to a highly anastomosed pattern with 2-13 channels between Civray and Angoulême, becomes discontinuous and weakly anastomosed with 3-5 channels from Angoulême to Cognac, and finally takes on a meandering-to-sinuous single-channel form from Cognac to the estuary [34][35][36][37].…”

“…Field observations within the study area indicate a predominant fine suspended load and a limited bedload consisting mainly of sandy sediments, particularly upstream from Cognac. Duquesne et al [34,35] have shown that fluvial forms have very limited mobility in the medium term (around 150 years) due to the natural characteristics of the river such as its very low slope and flood flows with minimal morphogenic effects. Additionally, there is minimal change in the number of islands, except for those influenced by human activities [36].…”

“…The width of the alluvial plain ranges from 1 to 2 km. The channels have a low sinuosity (approximately 1.05) and moderate width-depth ratios (around 15) and are bordered by natural low levees [34,35].…”

“…The mean stream power in this segment is estimated to be around 7 W.m −2 , and the average low-gradient is approximately Above the Chaniers gauging station, the Charente River exhibits very low stream power, which is estimated to be around 5 W.m −2 . This is primarily due to the presence of a moderate bankfull discharge, approximately 200 m 3 .s −1 , and a gentle slope of around 0.0002 m.m −1 [35]. According to the classification by Nanson and Croke [42], the Charente River falls under the category of low-or very-low-energy rivers, with stream powers greater than 10 W.m −2 .…”