Hydrological controls on the morphogenesis of low-energy meanders (Cher River, France)

- Estimation of morphogenesis conditions of a low-energy fluvial system.
- The morphogenic activity results from high frequency and low intensity floods.
- First control factor: a frequent lateral erosion and bedload mobilization.
- Second control factor: a weak difference of energy between small and large floods.
- High ability of the meanders to self-restore their fluvial dynamics.

SummaryRiver restoration is a key-issue for European hydrosystems that were modified over centuries by human activities. This is particularly true for numerous low energy rivers flowing in the plateaus of Western Europe. Because of this limited energy, their potential in terms of autogenic restoration a priori appears strongly restricted. This study examines the conditions under which the morphogenesis on one of these systems occurs in relation to various hydrologic conditions. Two complementary approaches are combined on three reaches of the meandering Cher River (France). Firstly, we examine at a pluri-decadal scale the control of duration, frequency and intensity of floods on the planimetric erosion (bank retreat mainly). Secondly, we estimate the range of effective discharge for bedload transport. The results show that the morphogenesis is controlled by low magnitude hydrological events. Two major controlling factors are suggested: low differential of energy between small and large floods, peculiar to low energy rivers of mid-latitude, and low critical discharges for lateral erosion and bedload mobilization. For these reasons, the ability of the alluvial Cher River to self-restore its fluvial dynamics seems to be relatively high.