Flow Resistance and Velocity Structure in Shallow Lakes with Flexible Vegetation under Surface Shear Action

AbstractThis study was conducted to investigate the flow restructure and resistance in vegetal flow under wind shear action in shallow lakes. A special racetrack-style flume with two sets of driving devices installed on the top was designed to simulate the wind-driven current. Two typical types of live vegetation, Vallisneria natans and Acorus calamus of Taihu Lake in China, were planted in the system. The results revealed that the velocity distribution of vegetal flow under wind action differed from that in open channels. The velocity distribution can be described as logarithmic-curve shaped and contained a compensation current in the lower layer. The area within the effective height of vegetation in which the velocity was obviously affected comprised an effective friction region. When compared with V. natans, A. calamus displayed better resisting capacity. Based on measured data, a new empirical relationship between drag coefficient and wind speed was presented, which indicated the resistance ability of vegetation under different intensities of wind action. Variations in the equivalent roughness coefficient were also discussed.