河道の変動に関する研究(2) ―安定流路の形状と形成過程―

Abstract

As described in the previous paper, '~ a stable or a zero-bed load state is established in the upstream reachof an alluvial channel under conditions of the absence of sediment feeding and a given discharge. This paperdeals with the stable channel profile and process on the basis of several results obtained from experimentsconducted in a large alluvial channel and theoretical consideration based on the fluvial hydraulics.As a degradation of a channel bed and a flow stage in the upstream reach, the channel shape is stabilizedfrom the upper part of the side wall to the central part of the bed in a cross section, and different self-armoringstates by the coarser sediment are observed along the flow perimeter. The stable cross sectional shape ob-served at the final stage is appreciably flatter than Lane's expression for a stable channel in the threshold con-dition, and relations of a cross sectional area and bed slope to channel width according to Lane differ fromthose observed here and by other investigators in alluvial channels with uniform sands. From this fact, itmay be concluded that the self-formed stable channel profiles are affected by the channel process withbank erosion and a stabilized condition.In connection with the channel process, one-dimensional analysis based on the fluvial hydraulic model wasdeveloped for longitudinally uniform and nonuniform channel processes and compared with several experi-mental results. In addition to usual fundamental equations of fiuvial hydraulics, an expression of sedimentsupply due to bank erosion were assumed on the basis of the phenomenological consideration and experimentalresults in several kinds of laboratory flumes. The analytical results are in good agreement with the observedones at the initial stage of channel process.Further study on the effects of sediment mixture and stream meandering on the channel process will beneeded in order to predict the criteria of stable profile in the upstream and the prominent bank erosion in thedownstream reach.