Multi-disciplinary approach for sediment dynamics study of active floodplains

Abstract

This study reviews multi-disciplinary approaches developed on active floodplains in order to formulate their evolution model and sediment budget, at different time scales, from historical evolution to hydrological event, and spatial scales (floodplain, active channels and fluvial units). The main objective of the different case studies is to emphasize the need for coupling tools and methods in analysing active floodplain patterns, deposition and erosion rates with regards to hydrological functioning and impact of human activities. The first part of the paper is dedicated to methods that help us to characterize the construction of floodplains at a historical time-scale. The second part examines the functioning of active floodplains at a detailed spatial and time scales. Different case studies selected in European and American floodplains aim at highlighting the contribution and the limits of methods developed at various temporal and spatial scales. Multi-temporal analysis of fluvial planform allows to determine the recycling time of a floodplain (Beni River in Amazonia) or to evaluate the impact of a large flood (Rhone River). Historical sedimentation of floodplain may be estimated on the basis of specific elements present in sediments such as ironwork waste products in Belgian rivers Different methods are used to evaluate sediment remobilization in fluvial beds at different time scales. Bathymetric and topographic surveys, digital elevation models document vertical movements of the fluvial bed (Beni, Moselle and Loire rivers) at pluri-annual and annual scales; they allow the calculation of sediment budgets. At a longer time scale, bedload progression has been evaluated in Ardenne rivers using slag elements.