Tracer advection in an idealised river bend with groynes

Abstract

This paper presents numerical simulations of particle advection in the bend of an open channel containing groynes, which is an idealised form of a shallow river bend in a wide river. The flow field is computed using a boundary-fitted solver of the non-orthogonal, curvilinear shallow water equations. The computational grid is generated by solving Poisson-type elliptic partial differential equations using an iterative multi-grid scheme for prescribed boundary coordinates. The shallow water equations are discretised with finite differences in space, and 4th order Runge-Kutta integration in time. Tracers introduced at specific initial locations have their trajectories computed using Lagrangian particle tracking. The numerical shallow flow model is verified by comparison to the analytical solution of fully developed flow in an open channel. The combined shallow flow and Lagrangian particle-tracking model is then used to simulate the advection of tracer particles in a rectangular channel containing a pair of parallel groynes, and tracer particles in a curved open channel containing groynes, of dimensions roughly equivalent to a Danube River bend.