Author(s): Amina Fakhar; Norio Tanaka; Fakhar Muhammad Abbas

Linked Author(s): Norio Tanaka

Keywords: Debris Morphology; Vegetation Patch Orientation; Scouring; Dike Breaching; 3D Reynolds Stress Model

Abstract: Woody debris, often carried by floods and accumulating around riparian vegetation, poses a significant threat to river systems. These debris can obstruct flow, leading to increased backwater effects and eventually dike breaching occurred. In view of this, physical experiments in controlled flume settings (under mobile bed conditions) and numerical simulations using a threedimensional Reynolds-averaged Navier–Stokes (RANS) turbulence model in ANSYS FLUENT were conducted. The varying configurations of Vegetation patch Models (VPM) and Debris Models (DM) was utilized that influence flow hydrodynamics along the dike of an open channel. The scouring patterns were observed by considering six angles of VPM i.e., angle of the VPM to the dike or flume wall: Ø= 0°,30°,60°,90°,120°,150°, VPM distance i.e., gap between VM and the dike or flume: L and initial Froude number Fr=0.7; sub critical flow. The results showed that, when VPM was closed to the near wall i.e., (N_nd≤0.25) and angle orientation was 30°,90°,120° with DM, I-type debris as compared to U-type debris, maximum scour, turbulences, and pressure distribution were observed near the wall posing a risk of dike breaching during floods. These factors were found to contribute significantly to the risk of dike breach during flood events, highlighting the importance of carefully considering vegetation arrangements and their spatial relationships to dike in flood-prone areas. Therefore, as a result, it is suggested to orient the vegetation patches meeting the (N_nd≤0.25) criterion, while refraining from utilizing patch orientations at 30°, 90°, and 120°.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024