目前 ,黄河中游地区流域的水沙变化主要以水文法和水保法研究为主。由于黄河中游具有明显的自然地带性分布特征 ,流域系统的水沙过程受到环境要素的综合影响。本文根据黄河中游河口镇至龙门区间已控一级支流的测站资料 ,采用地理环境要素法分析水沙变异及成因。研究表明 ,河龙区间流域径流量和输沙量与地理环境因子的影响密切相关。 2 0世纪 70年代以来 ,降雨减水减沙作用不断减小 ,随着水土保持措施的提高 ,人类活动减水减沙所占比重不断增大。 70年代与 80年代气候波动和人类活动影响的平均减水减沙作用分别为5 3 4 %、 2 8 6 %和 4 6 6 %、 71 4 %。

In the last decades, especially since the 1980s, variations in runoff and sediment yield have occurred to the trunk stream and the tributaries of the Yellow River. As a consequence of drastic decline of runoff volume and sediment load, downstream channel shrinkage and dried up as well as disasters induced by a minor flooding event happened. In order to understand these new problems and new situations, a great deal of research work and investigations on impacts of climate and human activities on variations of runoff and sediment yield as well as variation characteristics and causes of changes were carried out in China. At present, runoff and sediment change investigations are mainly focused on studies of hydrologic method and water conservation method in the middle reaches of the Yellow River. Since the middle reaches of the river have distinct natural zonal distribution characteristics, both runoff and sediment processes in the drainage system are synthetically affected by environmental factors. Based on observational data of the controlled primary tributary from Hekou to Longmen at midstream section, this paper analyses the variations and causes of runoff and sediment load by using method of geographic environmental factors. The results indicate that runoff volume and sediment load in the Hekouzhen Longmen section of the drainage basin are closely related to the impact of geographic environmental factors. Runoff and sediment variations are a product of synthetic action of natural environmental factors and human activities. In the 1970s, runoff and sediment reduction is mainly affected by decrease of precipitation as control and management practices then are inadequate. In the 1980s, impact of human activities plays a leading role in reducing runoff and sediment load in the basin as control measures of reservoir and dam projects are effective in reducing water and silt load on the Loess Plateau. Since the 1970s, precipitation has played a less role in reducing runoff and sediment but human activities played an increasing role as a result of improvement in soil and water conservation measures. The average water and silt reduction impacted by climate fluctuation and human activities in the 1970s and 1980s is respectively 53.4%, 28.6% and 46.6% and 71.4%.