ABSTRACT
This study focuses on the hydromorphological functioning and the bedload transport characteristics of the Cure river (Morvan Massif, Central France). This small gravel-bed river has undergone two major anthropogenic modifications, one between the mid-16th to the early 20th century for the timber floating industry, and the second one from the 1930’s for hydroelectric production. For almost four centuries, small dams, artificial cut-offs, straightening and water releases have deeply affected the fluvial dynamics and morphology of the rivers. During the 20th century, a complex of three large dams has been built on the Cure river (Crescent complex), impacting the sediment flux on several tens of kilometers in the upper part of the catchment. In order to understand the resulting fluvial forms and the processes at work, two types of influence have to be considered: inherited parameters from former practices (log floating leading to an incision of the bed) and pressures from remaining activities (dams leading to a sediment deficit). The evolution of the river bed as well as former artificial discharges are first reconstructed from historical archives (old maps, engineer plans, documents for dam management, etc.) and the current morphodynamic processes are then studied through the monitoring of bedload transport using PIT tags (RFID technology). More than 500 particles were marked on 5 study sites on the different reaches of the hydro-electric complex. In this way, the diversity of hydrological conditions regarding dam distribution and functioning is taken into account: reaches located upstream/downstream a dam, reaches receiving water releases, by-passed-reach, etc. The comparison between the results of the different study sites, in the light of their hydrological regime (influenced or not by the dams, type of influence), tends to prove the different impacts of the dams on the bedload transport. However, a further geo-historical perspective seems to be needed to fully understand the complexity of fluvial forms and bedload transport characteristics observed on the Cure river course. Indeed, log floating could still be exerting a major influence on current bedload transport processes, notably through the riverbed morphology it contributed to create.
