黄土高原丘陵沟壑区坡面-沟道系统中的高含沙水流(Ⅱ)--泥沙存储-释放及降雨、径流特征的影响

以黄河中游多沙粗沙区子洲径流站和离石王家沟试验站的径流场观测资料为基础，对黄土高原丘陵沟壑区坡沟系统中高含沙水流特征进行了研究。研究表明，在坡面-沟道系统中，存在着泥沙的存贮-释放机制，这一机制与非高含沙水流和高含沙水流不同的输沙行为有关。当水流为非高含沙水流时，来自坡面和悬移质泥沙中的粗粒部分可在沟道中发生沉积；当为高含沙水流时，前期沉积的粗粒泥沙将因沟道高含沙水流强烈的侵蚀搬运作用而发生释放。降雨对坡沟系统高含沙水流的形成关系密切。在冲沟次降雨最大含沙量与雨强的关系中，表现出两个临界值。超过第一个临界值以后，含沙量急剧增大；超过第二个临界值之后，则出现极限含沙量，即含沙量不再随雨强的增大而增大。

Hyperconcentrated flows in slope-channel systems of gullied hilly area in the Loess Plateau (Ⅱ) :influences of sediment storage-release rainfall and runoff

Based on the data from Zizhou and Wangjiagou Experimental stations in the coarse sediment-producing area of the middle Yellow River drainage basin, this study deals with characteristics of hyperconcentrated flows in slope-channel systems in the gullied hilly areas. The results show that there exists a sediment storing-releasing mechanism in the systems, which is related to the different behaviors of sediment transport by non-hyperconcentrated and hyperconcentrated flows. For the non-hyperconcentrated flows, the relatively coarse fractions of sediment from the slopes are deposited in the channel,and for the hyperconcentrated flows, the previously deposited coarse sediment may be eroded and released from the channel. There is a close relationship between rainfall and the formation of hyperconcentrated flows. Two thresholds are observed from the plot of event maximum suspended sediment concentration versus rainfall intensity. When the first threshold is exceeded, the sediment concentration increases sharply and when the second is exceeded, there is a extreme concentration, i.e., the sediment concentration remain unchanged with the increase in rainfall intensity.