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Flow over egetated Weir-like obstacles (Groynes,Embankments)

For an accurate prediction of the water levels during flood events, it is important to account for the important processes that contribute to the flow resistance. A significant portion of the energy loss is found in the flow over weir-like obstacles which get submerged at high water stages. In addition to the bed friction that is found everywhere, the rapidly varying flow over, for examples groynes, access roads, and summer embankments complicates the proper estimation of the conveyance capacity. It becomes even more complicated when the elevated parts of the bed are covered with high vegetation in the form of bushes or trees. The flow that is already accelerated above the crest of the groyne or dyke experience a further acceleration passing between the vegetation. In case of high water the resistance of a river reach is for an important part governed by the bed forms and obstacles in the floodplain. The obstacles can consist of groynes, summer dykes, bridge piers, ditches, bushes etc.