人类活动对黄河中游高含沙水流的影响

以黄河中游干流和渭河、无定河的资料研究了人类活动对黄土高原河流高含沙水流的发生频率的影响。人类破坏森林植被，大量拦截黄河上游清水来源区的清水基流，使得高含沙水流发生频率增大，大规模水土保持措施的实施则使高含沙水流发生频率迅速减小。近50年来黄河干流和一些支流的高含沙水流随时间的变化可以用一个三阶段模式来概括，即20世纪50-60年代，由于人类破坏植被，使高含水流频率增大；20世纪60年代末至80年代中期，大规模水土保持措施的实施使高含沙水流发生的频率减小；20世纪80年代末期以来，人类大量拦截利用清水资源，使高含沙水流的发生频率又复增大。

Influence of Human Activities on Hyperconcentrated Flows in the Middle Yellow River

Hyperconcentrated flow is a hazardous streamflow, which is typical in the Loess Plateau of China. Strong human activities such as deforestation and steep land cultivation in this area can be traced back to 2000 years ago. Since the 1960s, large scale soil conservation measures have been put into practice. All these have far reaching effects on the hyperconcentrated flows. The middle Yellow River mainstream, the Wudinghe River and the Weihe River have been selected for a study on the influence of human activities on the hyperconcentrated flows. To quantify the occurrence of hyperconcentrated flows, the concept of the frequency of hyperconcentrated flows is proposed, which is defined as the number of days with daily suspended sediment concentration >300 kg/m 3 in a given period, usually in a year. Then, this index is correlated with those indices that quantified the human activities. The results show that the frequency of hyperconcentrated flows is negatively correlated with forest cover, implying that the deforestation by humans in history may lead to a higher frequency of hyperconcentrated flows. The data from the Wudinghe River and the Weihe River show that the frequency of hyperconcentrated flows declines with the increase of the area with soil control measures and with the sediment reduction by soil conservation measures. However, the interception of clear water from the upper Yellow River by the Longyangxia and Liujiaxia reservoirs significantly increases the frequency of hyperconcentrated flows in the middle Yellow River mainstream. The temporal variation of hyperconcentrated flows in the past 50 years can be generalized as a three stage model. In the 1950s to 1960s, the frequency of hyperconcentrated flows increased due to the destruction of natural vegetation by humans. From the late 1960s to the mid 1980s, the practice of large scale soil conservation measures resulted in a decline in the frequency of hyperconcentrated flows. However, the frequency of hyperconcentrated flows has increased again since the late 1980s, because large quantitis of clear water are intercepted by reservoirs in the upper Yellow River for hydro power generation.