Experimental Simulation of Anastomosing Multiple Channel Formation

Anastomosing river is a new fluvial river pattern that gets more attention from re- searchers. The hydrological, geomorphological and sedimentological characteristics of some anastomosing rivers have been revealed. But the experiment simulation of anastomosing river is vacant hitherto. The flume simulation experiments are the reappearance of natural rivers under the condition of decreasing time and space. This work reports a formation and evolution of anastomosing river simulated in a flume. The experimental beginning condition is: an artificial meandering channel in the assistant area of flume; a rectangle floodplain (4.5 mx×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 Gaolin whose median grain size is 0.0132 mm;below layer with a thickness of 0.5 m consisted of fine sands whose median grain size is 0.188 mm. The mean longitudinal gradient of the floodplain is 0.0058 from 5.5 m to 17 m and 0,0077 from 17 m to 22 m along the ordinate. Adoptive constant discharge is 3 cm3/s. Suspended sediment load is 4.5 g/min in the first 3 hours and 1.2 g/s thereafter. The total time span of flume experiment is 50 hours. In the initial stage of simulation the sedimentation mainly occurred in the upper reach, the random erosion occurred at 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 hours. Hereafter up to 25.5 hours the evolution fashion of the anastomosing river changed from downcutting erosion to lateral erosion, but the fall back of channel banks is not evident. It indicates that the anastomosing channels change into their autumn. From 25.5 hours to 50 hours the abandonment or avulsion of individual channel is 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 river via flume simulation and helpful to understand the characteristics of anastomosing river.