Modelling reservoir sediment flushing through a bottom tunnel with an initially covered intake

Sediment flushing through a bottom tunnel is one of the most effective methods to alleviate reservoir sedimentation. However, the multi-physical hydro-sediment-morphological processes of reservoir sediment flushing through an initially covered bottom tunnel intake have remained poorly understood, and a physically enhanced and practically viable mathematical model is required. The present study uses an integrated model to resolve sediment flushing through an initially covered bottom tunnel intake. The proposed model couples a two-dimensional double layer-averaged model for the reservoir with a one-dimensional model for the bottom tunnel by means of numerical fluxes calculations at the inner boundary. The governing equations are solved synchronously using a well-balanced finite volume method. Several parameters related to boundary resistances and sediment exchange flux need to be determined for model closure. The model is tested against data from a series of physical experiments on reservoir sediment flushing, with sound agreement achieved between computed and measured scour hole geometries. Moreover, the present model successfully predicts the occurrence of tunnel blockage. The results prove that reservoir sediment flushing is best accomplished for high reservoir water level, small cover layer thickness, short tunnel length and steep tunnel slope. The present model facilitates reservoir design and operation to help preserve reservoir capacity.