Two-dimensional 2-phase modeling of controlled sediment deposition during floods: the case study of the Bevieux off-stream settling basin.

Marina Launay, Pedro Manso, Gérard De Montmollin, Rui ML Ferreira, Marcelo Leite Ribeiro, Daniel Conde

Tuesday 30 june 2015

17:36 - 17:39h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: Poster pitches: 7A. Sediment - Erosion

Sediment transport in the fluvial environment is responsible for significant morphological variations of the river system which may lead to the amplification of inundation hazards (Hausmann et al. 2012). Monitoring and controlling sediment transport are mandatory for the achievement and maintenance of given security and ecological standards. The SEDITRANS project aims to advance knowledge in the broad area of sediment transport characterization and modelling. It includes developing models for fluvial problems involving complex morphologies and sediment transport, and validating them in real engineering problems. In this context, the objective of this work is to test a novel flow-morphology simulation tool with data from a river reach at Bevieux, Switzerland. The numerical model, STAV2D, is a two-dimensional depth-averaged deterministic model for highly unsteady discontinuous flows over complex time-evolving geometries (Canelas et al. 2013, Conde et al. 2013). The river reach belongs to the Avançon river, a right bank tributary of the Rhône River upstream of Lake Geneva. An off-stream sediment settling basin has recently been built, aiming at sponsoring sediment deposition on a selected low-vulnerability location. The basin allows sediment deposition mainly for flood events with return periods above 20 years, above which the hydraulic capacity of the river reach downstream and through the town of Bex is insufficient. The sediment deposition zone is located in the inner floodplain of a river bend. Flood water and sediment are diverted laterally to the deposition area once a given water level is reached. Sediments settle as a consequence of the mild slope and section widening. Local head losses at the river control structure and lateral weir are critical to trigger lateral flow diversion. The river bed evolution near the lateral overflow varies considerably and plays a key role in flow repartition. Such phenomena are yet not object of reliable numerical representation. Validation of the numerical tool involves assessing its ability in describing the physical processes associated to the transit of high sediment-laden flood events through a steep river reach equipped with an off-stream deposit area. For this purpose, physical modeling results and 2-years of prototype behavior observation are available.