关键词: 水沙两相流, 临界现象, 河型, 黄河

Abstract: Through an analysis of the data from some rivers on the Loess Plateau of China, the phenomenon of double thresholds in scour fill process of wide range water sediment two phase flows has been found. The threshold located in non hyperconcentrated flows may be called the lower threshold, and that in hyperconcentrated flows the upper threshold. This double threshold phenomenon plays an important role in sediment transportation of heavily sediment laden rivers. With the increase in sediment concentration, the channel sediment delivery ratio shows an increase first, followed by a decline, intersecting twice with the straight line representing the sediment delivery ratio of 1.0. The two intersection points correspond the lower and upper thresholds, respectively. A new explanation for alluvial channel pattern formation can be reached considering the double thresholds in scour fill process of wide range water sediment two phase flows. Based on the data from nearly 100 alluvial rivers in China, the mean annual sediment transport rate has been plotted against water discharge, with different channel patterns, i.e., meandering at low concentrations, braided and meandering at hyperconcentrations represented by different symbols. The three patterns can be well differentiated by the straight lines represented by suspended sediment concentrations of C=60 kg/m 3 and C=3.3 kg/m 3. The two characteristic concentrations can be regarded as a reflection of the double thresholds in scour fill process of wide range water sediment two phase flows in rivers.

Key words: water sediment, two phase flows, threshold phenomenon, river channel pattern, the Yellow River