Morphological Changes induced by River Training Structures: Bandal-like structures and Groins

Abstract

本論文ではバンダル水制がもたらす流れおよび河床形成について着目し、移動床実験と数値解析によってバンダル水制周辺の複雑な流砂メカニズムを明らかにした。移動床実験では片側に2基の水制を設置した直線水路を用い、流れおよび局所洗掘された水制周辺の河床高計測をおこなった。数値計算で用いた河床変動モデルは非構造格子を用いており、流れは3次元のRANS(Reynolds-averaged Navier Stokes)方程式と標準k-ε;モデルを解き、掃流砂の連続方程式により河床高変化を計算している。水制周辺の河床形状と流速分布の実験および計算結果を解析し、従来の水制構造物に比べて安価なバンダル水制の適用性について考察を行った。

This paper is focused on the investigation of the characteristics of flow patterns and bed deformation around river training structures like groins with emphasis on the so-called bandal-like structures. Through laboratory experiments and numerical simulations, the complex sediment transport mechanism influenced by bandal-like structures is clarified. The experimental studies were conducted in a straight flume with two structures positioned on one side of channel for the measurements of the velocity field and deformed bed level near the structures under lived-bed scour condition. A morphological model based on unstructured meshes was developed to simulate the flow patterns and bed variation around the structures, which solves the RANS (Reynolds-averaged Navier Stokes) equations for 3D flow calculation with the standard k-ε model for turbulence closure, and the sediment transport calculation considering the bed load transport rate through the mass-balance equation. The experimental and numerical results for flow velocity distributions and deformed bed level around the structures field were analyzed and the applicability of bandal-like structures as a low cost alternative method compared to the conventional structures as groins is discussed.