Abstract
Abstract. At high water stages, obstacles (submerged and particularly emerged vegetation) in the flood plains of a river contribute to the flow resistance and hamper the conveyance capacity. In particular the elevated vegetated parts are expected to play an important role. The objective of this research work is to determine the form drag due to vegetated oblique weir-like obstacles. Experiments have been performed to measure the energy head losses for a range of subcritical flow conditions, varying discharges and downstream water levels. The energy head loss caused by the submerged vegetated weir-like obstacle has been modeled using an expansion loss form drag model that has been derived from the one-dimensional momentum conservation equation and accounts for the energy loss associated with a deceleration of the flow downstream of a sudden expansion. The results have been compared with the experimental data and showed an overall good agreement.
Highlights
Water level predictions for extreme events are very important for the design of dykes and embankments and the safety of the area behind them
Ali and Uijttewaal (2009, 2010) studied the vegetated weir-like structures oriented perpendicular to the flow direction and quantified the energy head loss caused by such types of obstacles
With a simple expansion loss form drag model which is based on principle of energy and momentum conservation, reasonably accurate (15 % error) results related to the energy head loss and the flow direction over the weir crest have been obtained
Summary
Water level predictions for extreme events (flood waves) are very important for the design of dykes and embankments and the safety of the area behind them. De Vries (1959) did many experiments to examine the energy loss of the flow over dike-form weirs under different oblique angles and flow conditions. Wols et al (2006) investigated that the model could reproduce the bulk parameters like discharge coefficients and the energy head losses due to the trapezoidal weir, the flow field in the recirculation zone of the weir was represented incorrectly. Tuyen (2006, 2007) measured the energy head loss and discharge coefficients for different trapezoidal weir configurations (for 0, 30, 45 and 60◦ angle of obliqueness) and flow conditions. Ali and Uijttewaal (2009, 2010) studied the vegetated weir-like structures oriented perpendicular to the flow direction and quantified the energy head loss caused by such types of obstacles. – Submerged-flow (imperfect weir) conditions: submerged weir flow exists when the downstream water surface is above the crest of the weir (Froude number above the crest < 1)
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