Numerical modelling of bed load sediment traps in sewer systems by density currents

A model with density currents has been developed and tested to simulate bed load sediment traps. In this model, the bed load layer over the pipe invert is considered as a continuous layer characterised by a density and a viscosity which depends on the solid concentration. A set of equations has been established that describes the trapping of the bed load material as the dynamics of two non-miscible fluids over and in the bed load sediment trap. The Fluent package has been used and adapted to solve the equations of the model. The VOF method (Volume Of Fluid) has been chosen to solve the two phase approach according to a Euler-Euler scheme. Several series of simulations have been carried out in order to assess the influence of the slot position and trap design on efficiency. The results obtained agree with previous empirical findings, and allow confirmation (in a more reliable manner than before) that the best sediment trap design involves a centrally-placed slot with the two plates covering the trap reservoir placed at the same height as one another.