Bed Deformation Characteristics at Confluence of Rivers Which Have Different Cohesive Characteristics of Sediment

Abstract

カンボジア国・チャトムック地区を対象として，流れの特性，河床変動特性，河床材料の平面分布特性を明らかにするために平面二次元河床変動解析を行った。さらに，河床材料を非粘着性土と粘着性土の両方で取り扱い，粘着性土の平面分布特性が河床変動特性に与える影響を検討した。その結果，トンレサップ河とメコン河の間に形成されている半島は，洪水期の土砂の堆積により，南へ年々延伸していることが明らかとなった。さらに，粘着性土の存在は，流砂量と河床変動を抑制するため，河床変動特性に大きく影響することが明らかとなった。特に，異なる粒度を有する河川が合流するときは，粒度や粘着特性の平面分布の考慮が不可欠であることが示された。

The depth integrated two dimensional bed deformation analysis has been performed to understand the seasonal change of the flow pattern, bed deformation characteristics and horizontal distribution characteristics of bed material size. Furthermore, the bed material is treated as both the cohesive and the non-cohesive sediments and the effect of the horizontal distribution of cohesive material on bed deformation characteristics is discussed. The result shows that the sediment deposited at the south of the peninsula between the Tonle Sap River and the Mekong River during the flood season. The peninsula between the Tonle Sap River and the Mekong River has been extended to south year by year. The sediment deposition during the flood season causes the extension of the peninsula. Furthermore, cohesive characteristics of the sediment affects the bed deformation characteristics because of the suppression of sediment transport rate and bed degradation. Especially, when rivers which have different sediment size characteristics confluents, difference of the cohesive characteristics of the sediment must be considered.