Three-dimensional numerical modelling of water flow in a river with large bed roughness

# Three-dimensional numerical modelling of water flow in a river with large bed roughness

## Abstract

A numerical model for three-dimensional simulation of water flow in rivers with large
roughness elements is developed. The bed roughness elements are large stones and rocks
in the rivers. The model uses a finite volume method to solve the Navier-Stokes equations
for three dimensions on a general non-orthogonal grid. The k-e turbulence model is used
to solve the Reynolds-stress term. A porosity model is developed to model the bed
roughness elements. The porosity model is used in combination with the solution of
the Navier-Stokes equations to calculate interactions between porous and non-porous
areas. To test the model, a reach of the Norwegian river Sokna is modelled. Velocity
measurements from the river are taken at a number of locations and at several discharges.
The measured velocities compare well with the results from the numerical model.