The effect of hydraulic resistance on the downstream evolution of the water surface profile h in a sloping channel covered by a uniform dense rod canopy following the instantaneous collapse of a dam was examined using flume experiments. Near the head of the advancing wavefront, where h meets the rods, the conventional picture of a turbulent boundary layer was contrasted to a distributed drag force representation. The details of the boundary layer around the rod and any interferences between rods were lumped into a drag coefficient C d . The study demonstrated the following: In the absence of a canopy, the Ritter solution agreed well with the measurements. When the canopy was represented by an equivalent wall friction as common when employing Manning's formula with constant roughness, it was possible to match the measured wavefront speed but not the precise shape of the water surface profile. However, upon adopting a distributed drag force with a constant C d , the agreement between measured and modeled h was quite satisfactory at all positions and times. The measurements and model calculations suggested that the shape of h near the wavefront was quasilinear with longitudinal distance for a constant C d . The computed constant C d (≈0.4) was surprisingly much smaller than the C d (≈1) reported in uniform flow experiments with staggered cylinders for the same element Reynolds number. This finding suggested that drag reduction mechanisms associated with unsteadiness, nonuniformity, transient waves, and other flow disturbances were more likely to play a role when compared to conventional sheltering effects.After a dam break, the flow is generally approximated by the Saint-Venant equation (SVE) derived from the Navier-Stokes equations assuming (i) constant water density, (ii) that the water depth h is small compared with other length scales such as the wave length of the water surface or the channel width, (iii) that the pressure distribution is approximately hydrostatic so that vertical acceleration can be ignored, and (iv) that the bed slope is not too steep (de Saint-Venant, 1871). For these conditions, the continuity equation and SVE for a rectangular prismatic section of width B after a dam break are given by (French, 1985;Lighthill &