Quantification of the morphodynamics and ecological functionality of a Mediterranean river

Abstract

The Var River (South-East France) was extensively modified (channelization, dams...) on the 21th century and is currently undergoing an ambitious restoration project to restore its 'natural' active braiding pattern on the downstream reach of the river. As part of the feedback evaluation of the project, this study aims at: (1) quantifying the morphological evolution of the bed that is recovering from sediment discontinuity; (2) identifying and/or developing hydromorphological and ecological indicators which quantify improvement in the river system from hydrosedimentary and ecological points of view. We used LiDAR and orthophoto datasets and performed analyses for unchannelized braiding rivers [1, 2]. Active width (Wrestored = 242 ± 19 m vs. values ranging from 103 ± 53 to 163 ± 53 m for 'unrestored' reaches) and normalized bed relief index values (BRI∗restored = 0,003 ± 0,001 vs. 0,003 ± 0,003 to 0,007 ± 0,004 for 'unrestored' reaches) indicate a combination of low roughness and wide active width. Thus the 'restored' reach shows a different set of indices compared to nearby 'unrestored' reaches, suggesting these tools are promising in discriminating 'restored' vs. 'unrestored' reaches. Adapting existing methods from 'natural' to 'channelized' braiding rivers widened the potential application of the tools developed by Lallias-Tacon [2] to modified braiding river systems.