SIMULATION EXPERIMENT OF ANASTOMOSING MULTIPLE CHANNEL FORMATION

摘要

The anastomosing river is a fluvial river pattern that recently gets more and more attention from researchers. The hydrological, geomorphologic and sedimentological characteristics of some anastomosing rivers have been revealed. But the experiment simulation of anastomosing rivers is vacant hitherto. The flume simulation experiments are the reappearance of natural rivers under the condition of decreasing time and space. This work reports the formation and evolution of an anastomosing river simulated in the flume. The experimental beginning condition is: an artificial meandering channel in the assistant area of flume; a rectangle floodplain (4.5 m x 16.5 m) with concave cross sections is in the objective area and its stratum has a structure of double layers. The upper layer with a thickness of 1.5 cm consisted of Gaoling which median grain size is 0.013,2 mm; the under layer, consisted of fine sands which median grain size is 0.188 mm, has a thickness of 0.5 m. The mean longitudinal gradient of the floodplain is 0.005,8 from 5.5 m to 17 m and 0.007,7 from 17 m to 22 m along the ordinate. Adoptive constant discharge is 3 L · s~(-1). Suspended sediment discharge is 4.5 g · min~(-1) in the primary 3 h and 1.2 g · s~(-1) thereafter. The total time span of flume experiment is 50 h. In the initial stage of simulation sedimentation mainly occurred in the upper reach, random erosion occurred in the middle reach and the backward erosion mainly occurred in the lower reach of the objective area. A rudimental anastomosing river with multiple channels connected each other basically appears about 13.5 h. Hereafter, up to 25.5 h the evolution fashion of the anastomosing river changed from downcutting erosion to faint lateral erosion and the fall back of channel banks is not evident, it indicates that the anastomosing channels changes into its autumn. From 25.5 h to 50 h the abandonment or avulsion of an individual channel are the new evolution characteristics of the simulated anastomosing river. The whole flume experiment simulates successfully the formation and evolution of natural anastomosing rivers and proves that the anastomosing river is a new river pattern, which is different from anabranched river. This is a useful attempt to reveal the formation of anastomosing rivers via flume simulation and helpful to understand the characteristics of anastomosing rivers.