Flow Through Rigid Streambank Vegetation

An analytical model is presented for predicting how rigid streambank vegetation effects the depth-averaged velocity at any point in a channel. The model was developed in conjunction with a study on the influence of black willow (Salix nigra) cuttings that were planted in 1994 along Harland Creek in Holmes County, MS, as part of an experimental bank stabilization project. A physical model study was performed in a 1.5-m-wide flume with a half-trapezoid shaped test section. Simulated willow cuttings (6.4-mm-diameter dowels) were arranged in four configurations and tests were performed for flow depths ranging from 23 to 38 cm, and discharges ranging from 22 to 113 1/s. Results from the physical model study were used to calibrate and verify the analytical model. Depth averaged velocities amid the simulated willow posts (6.4-mm-diameter dowels) were reduced by more than 50%. Predicted depth-averaged velocities amid the simulated willow posts were within 2%, on average, of the measured velocities when no model assumptions were violated. Insight gained from this study is used to make recommendations for improving the effective use of planted vegetation for bank stabilization, or bioengineering.