The Form drag due to vegetated weir-like obstacles interpreted as expansion losses

The Objective of this study is to estimate the form drag due to vegetated weirlike obstacles. Head loss due to submerged vegetated dikes and groins has been modeled by expansion loss form drag model (Energy and momentum balance principles) and it has been compared with experimental data. An experimental study has been carried out on a scaled physical model in the Laboratory of Environmental Fluid Mechanics of Delft University of Technology. The prototype dike and groin has been modeled as a weir and vegetation has been represented as cylinders on the crest of the weir with varying blockage area. Different cases have been studied for emerged and submerged cylinders. Measurements for energy head losses were carried out for a range of discharges and down stream water levels covering submerged and subcritical flow conditions. Agreement of theoretical results predicted by an expansion loss form drag model is good with experimental data for the case of a weir with cylinders. So the expansion loss model is of practical use for the prediction of head losses of a vegetated groin or dike.