Flow Resistance of Vegetated Weirlike Obstacles during High Water Stages

The objective of this study is to estimate, model, and parameterize the form drag due to vegetated weirlike obstacles. An experimental study has been carried out for validation purposes. The prototype weirlike structure (in the form of a dike or groyne) has been modeled as a weir with various downstream slopes (1:4, 1:7, 1:15), and vegetation has been represented in various shapes placed on top of the crest of the weir with 25% blockage area inside the vegetated region. Measurements for energy head losses are carried out for a range of discharges and downstream water levels covering submerged and subcritical flow conditions. The energy head loss attributable to submerged vegetated dikes and groynes can be modeled well by an expansion loss form drag model, which is based on a one-dimensional energy and momentum conservation equations.