Sediment management measures for river restoration and flood protection in alpine valleys

Sediment transport plays a key role in the morphological and ecological value of river ecosystems. The present study explores the design of sediment management measures for a flood control and revitalization project in an alpine valley of the Swiss Alps. The project was initiated after the October 2000 flood and it stands out for its extent, with reach of a 1 km long. The expected outcomes are the restoration of the river bed dynamics with the formation of alternate bars and an improvement of the longitudinal and lateral connectivity. The effects of the channel modification on the bedload transport capacity have been simulated with the 1D hydraulic and sediment transport model DuPiro. The project design has undergone several iterations to address both environmental and flood protection constraints. It results in the implementation of several sediment control measures that stabilize the morphological regime and allow the fish migration in the river, while ensuring the flood protection. It involves to extract gravel in some key locations, to replace weirs by rock ramps and to use lateral deflectors to protect and structure the river banks. The developed methods and concepts can apply generally to design restoration projects in alpine valleys. The advantages and limitations of the modeling approach are examined in the discussion of the results.