EXPERIMENTAL DETERMINATION OF THRESHOLD OF RIVER MEANDERING AND BRAIDING

摘要

A series of experiments was performed in a laboratory flume to determine the threshold of meandering and braiding of river patterns. For the purpose, of modeling, an alluvial reach of Ghezel Ozan (a meandering river in central north of Iran) was selected and using reasonable values of geometric, hydraulic and bed material properties of this river, a physical model with horizontal scale of 1:400 and vertical scale of 1:40 was constructed. After performing several laboratory tests, it was found that discharge and slope were closely related to the threshold values of channel patterns. Also based on regression analysis of experimental results a number of analytical relationships were obtained for determining the threshold of meandering and braiding patterns. The proposed relationships are between the channel longitudinal slope and discharge and between the "Non-dimensional Unit Stream Power (NUSP) and Shields parameter". The later is a new and interesting relationship in river morphology. Several diagrams were made to show that under what initial conditions the meandering and braiding patterns are established. The laboratory observations of this research have indicated that at very low NUSP, the channel remains straight, but at NUSP of 5.5 to 6.5 a meandering channel is formed and as NUSP increases to 12-22 a braided channel is formed.