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Abstract
Engineering projects combining protection against floods and reconnection of diked areas to the natural flooding regime are very complex and difficult to design at large scale. By using hydrological and hydraulics modelling, engineer and scientists should be able to assess the effectiveness of strategies based on detention in natural or restored floodplains.
Flood modelling is based on fine topographic data set on the whole floodplain. Digital Elevation Models with very good altimetric accuracy are now available thanks to airborne laser surveys. Two points must be carefully dealt with in the modelling: unsteady flow simulations must be performed in order to take into account the dynamic storage on floodplain, the hydrographs used as input must be designed in order to yield peak flows of given frequency. We used a stochastic model for hourly rainfall, coupled with a conceptual rainfall‐runoff model, to compute many hydrographs for different catchments scales. We built hydrographs which have the same peak flow frequency anywhere along the river.
By comparing different restoration scenarios, we can assess the hydrological effectiveness of re‐entering river waters onto floodplains. For mountain rivers, floodplain reconnection can be advocated to preserve water quality and floodplain biodiversity, but is not a good solution to improve flood mitigation.