In this study the effect of the cross sectional blockage factor (the fraction of the cross section blocked by vegetation) on vegetated channel resistance is investigated numerically. Three dimensional computations, based on the Reynolds Averaged Navier Stokes (RANS) equations and two turbulence models of the k-ε type, based on vegetation dynamics and on a porous media approach respectively, are used. In addition, the effect of the location of the blocked area on channel resistance is investigated. Detailed computed results within the channel cross-section are presented and bulk quantities (discharge, velocity, Manning’s coefficient) are compared with semi-empirical relations.