Estimation of Flow Resistance Due to Embankments and Spur Dikes during Floods

Flow resistance is a key factor in predicting the river conveyance capacity and associated water levels. In addition to bed resistance, the obstacles (embankments, spur dikes etc.) in the flood plain of a river contribute to the flow resistance. In particular the elevated parts are expected to play an important role. The objective of this study is to develop and parameterize an analytical model for the form drag due to such obstacles. An experimental study was carried out for validation purposes of the developed analytical model. The prototype weir-like structure (in the form of an embankment) was modeled as a weir with various leeside slopes. Measurements for energy head losses were carried out for a range of discharges and downstream water levels covering submerged flow conditions. The energy head loss due to submerged dikes was modeled as an expansion loss form drag. The analytical form drag model was estimated using a one-dimensional momentum conservation equation which accounts for the energy loss associated with a deceleration of the flow in the leeside region of the sudden expansion. The predicted losses from the analytical model agreed well with the experimental results. The minor deviations observed could be attributed to downstream slope effects and non- uniform velocity distribution in expansion zone (recirculation region) of an embankment