Abstract: With growing attention to ecological environment, the hydraulics research of vegetated flows has achieved a rapid progress in recent years. For submerged vegetation, previous studies generally suggest flow velocity in the surface layer above the vegetation follows a logarithmic distribution, but in shallow water cases the velocity profile of this layer deviates from the logarithmic law significantly. In this paper, variations in the mixing length for shallow vegetated flows are examined by applying Prandtl’s theory, and a new formula is derived to describe the velocity defect distribution. Velocity profiles have been measured experimentally for different surface layer thicknesses, different vegetation densities, and different vegetation stem diameters. Our new formula proves in good agreement with the experimental data.

Key words: vegetation hydraulics, open channel flow, turbulence, submerged vegetation, velocity profile