Sediment transport over sills at longitudinal training dams with unaligned main flow

Longitudinal training dams (LTDs) are  constructed in the River Waal in the  Netherlands. They are aligned parallel to the  river shore and divide the river into a main and  side channel. The existing groynes are  removed yielding more discharge capacity at  high flows. The side channel creates possibly a  sheltered environment for species compared to  the traditional groyne field (Collas, 2014).  Although the lay-out of the LTDs has been  extensively studied using numerical models  (e.g. Huthoff et al., 2011), the morphodynamic  response is yet unclear and depends strongly  on the dimensions (length and height) of the  openings. The inlet and openings (see Fig. 1)  are sill-type structures which can be changed  relatively easy.  These sills are designed in such a way that  they serve as a barrier for water and bed load  sediment. To make long-term morphological  predictions, it is necessary to understand the  bed load transport processes over these sills.  Suspended sediment transport is not  considered in this study. We developed an  analytical model to predict sediment transport  paths on a slope, using a correction on the  well-known critical Shields parameter.