Velocity distributions in channels partially covered with vegetation have b
een computed using a three dimensional model. The Navier-Stokes equations w
ere solved, using the SIMPLE method and the k-epsilon turbulence model. The
vegetation was modeled as vertical cylinders. A formula for the drag force
on the vegetation was included as a sink term in the Navier-Stokes equatio
ns. The advantage with this method compared with using large roughness is t
hat effects of the vegetation over the whole water depth can be taken into
account, instead of only affecting the velocity near the bed. The numerical
model was tested against three laboratory experiments from straight flumes
with uniform flow, where vegetation partially covered the cross-section. T
he velocity and vegetation density varied in both vertical and horizontal d
irections in the different cases. The experiments also included varying cro
ss-sectional shapes. All tests gave fairly good correspondence between comp
uted and measured velocity profiles.