Authors: Can Ding, Heli Yu & Kenji Kawaike
Publication type: A1
Abstract
Embankment failure during extreme flood events can trigger substantial geomorphic change, including sediment deposition in low-lying agricultural areas, with important consequences for paddy field environments. However, the role of drainage trench networks in controlling sediment redistribution during embankment-breach flooding remains insufficiently understood. This study combines physical experiments and numerical modeling to investigate the spatial patterns of sediment deposition in paddy fields influenced by drainage trenches. Laboratory results revealed a distinct central deposition zone along the main flow direction and enhanced sediment accumulation within the trenches due to locally reduced shear stress. To extend this process understanding, a one-dimensional-two-dimensional (1D-2D) coupled numerical model was developed to simulate flow and sediment transport and validated against the experimental results. The model successfully reproduced the observed deposition patterns both on the land surface and within the trench network, demonstrating its ability to capture the key physical effects of trench-induced flow concentration and sediment trapping. Comparison with a fully two-dimensional (2D) model further showed that, although both models performed well under fine mesh conditions, the 1D-2D model remained accurate under coarse mesh resolution, whereas the 2D model failed to resolve narrow trenches and substantially underestimated deposition. These results highlight the value of the experimental model for clarifying the physical role of drainage trenches and the significance of the coupled numerical model for representing sub-grid trench effects efficiently. The study advances understanding of sediment deposition processes induced by embankment-breach flooding in trench-controlled agricultural landscapes and provides a practical framework for flood impact assessment and sediment risk management.