Three-Dimensional Flow Characteristics in Slit-Type Permeable Spur Dike Fields: Efficacy in Riverbank Protection

Shampa Shampa,Yuji Hasegawa,Hiroshi Takebayashi,Kenji Kawaike,Hajime Nakagawa

doi:10.3390/w12040964

Shampa Shampa, Yuji Hasegawa + Show 3 more

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https://doi.org/10.3390/w12040964

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Abstract

This paper focuses on finding efficient solutions for the design of a highly permeable pile spur (or slit type) dike field used in morphologically dynamic alluvial rivers. To test the suitability of different arrangements of this type of permeable pile spur dike field, laboratory experiments were conducted, and a three-dimensional multiphase numerical model was developed and applied, based on the experimental conditions. Three different angles to the approach flow and two types of individual pile position arrangements were tested. The results show that by using a series of slit-type spurs, the approach velocity of the flow can be considerably reduced within the spur dike zone. Using different sets of angles and installation positions, this type of permeable spur dike can be used more efficiently than traditional dikes. Notably, this type of spur dike can reduce the longitudinal velocity, turbulence intensity, and bed shear stress in the near-bank area. Additionally, the deflection of the permeable spur produces more transverse flow to the opposite bank. Arranging the piles in staggered grid positions among different spurs in a spur dike field improves functionality in terms of creating a quasi-uniform turbulence zone while simultaneously reducing the bed shear stress. Finally, the efficacy of the slit-type permeable spur dike field as a solution to the riverbank erosion problem is numerically tested in a reach of a braided river, the Brahmaputra–Jamuna River, and a comparison is made with a conventional spur dike field. The results indicate that the proposed structure ensures the smooth passing of flow compared with that for the conventional impermeable spur structure by producing a lower level of scouring (low bed shear stress) and flow intensification.

Highlights

Riverbank erosion is considered one of the major issues in the deltaic regions of the world, especially in the Ganges–Brahmaputra–Meghna (GBM) delta region, from which more than sixty thousand people migrate each year due to riverbank erosion [1,2]
The three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations were coupled with the k-ω SST turbulence use
RANS equations werewith coupled with k-ω SST model turbulence model and the volume of fluid (VOF) method to capture the free water surface, and we found the hydrodynamic model the VOF

Summary

Introduction

Riverbank erosion is considered one of the major issues in the deltaic regions of the world, especially in the Ganges–Brahmaputra–Meghna (GBM) delta region, from which more than sixty thousand people migrate each year due to riverbank erosion [1,2]. The rapid change in braided channel geometry triggers variations in the flow boundary conditions and the hydraulic structures, and changes are considered the key management issues for dynamic alluvial rivers worldwide, the Brahmaputra–Jamuna River [3,4]. Bedform movement, and rapid siltation or erosion downstream create favorable conditions for local scouring [7,8,16,17,18,19,20,21,22,23] a detailed understanding of the flow around such structures is crucial for the optimum design of spur dikes to manage this type of dynamic river

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