Predicting Riverbed Deformation During Floods for a Sustainable Design of Headworks Structures

Understanding and predicting riverbed deformation during floods is important for the proper and sustainable design of headworks structures. Field-scale study of floods is challenging, and existing literature shows that mainly qualitative data (Photographic and Videographic) have been used in riverbed deformation studies. On the other hand, laboratory experiments allow studying floods in more detail and under a controlled environment. In this research, bed deformation of river channel during floods was investigated by conducting experiments in a curved flume. Parameters of the experiments were chosen with respect to gravel-cobbled River in Nepal. Four different floods with different magnitudes and durations were investigated in the experiments. Riverbed deformation was quantified by differencing pre and post-flood DEMs obtained using Structure from Motion (SfM) technology. The maximum scour during the floods was measured by scour chains made with light beads in a thread. The results showed that the magnitude and duration of floods are both important factors for riverbed deformation. The volume of channel bed erosion increased with the increase in flood magnitude. However, the total volume of sediment reworked was higher in the case of floods which are of lower magnitude but occur frequently in multiple cycles. The depth of maximum bed scour during the floods was observed much higher than the channel bed resulted at the end of the floods. The difference was more prominent along the bends where the secondary currents are stronger. The understanding could be used to better validate sediment transport models, and thus predict riverbed deformation more accurately for sustainable design of headworks structures.