应用流量历时曲线分析黄土高原水利水保措施对河川径流的影响

流量历时曲线（Flow Duration Curve，FDC）是用于分析流域径流特征及其变化的有效方法之一。以长序列日流量为基础，采用FDC方法并结合各流域的径流量时间变化趋势分析方法，研究了黄土高原佳芦河、秃尾河、延河和湫水河等4条流域流量变化的基本特征；通过临界年份前后两个时段序列及不同年代序列的流量历时曲线变化的比较，分析了流域径流过程对大面积水土保持措施的响应。结果表明：随水土保持措施累积面积的不断增大，佳芦河、湫水河、秃尾河的径流量逐年减少，且水土保持措施对高流量部分径流减少的程度较低流量部分大，尤以工程措施为主的湫水河流量减少最明显。在延河流域，与临界年份前的时段相比，后期的高流量部分的径流量减小，而常水和低流量部分的径流量相对增大。尽管流域水土流失综合治理并未使河川径流量增加，但由于高流量部分流量的减少程度较低流量部分径流量减少程度大，从而使流域年内日径流量变化过程趋于均匀化。

Estimating the Impact of Conservation Measures on Stream-flow Regime in Catchments of the Loess Plateau, China

Catchments in the Loess Plateau have been under the influence of human activities for centuries, especially in the last several decades when soil conservation measures were accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchments management plans in the region. This study evaluated changes in stream flow regime for four selected catchments in the Loess Plateau following large scale soil conservation measures. Parametric and non parametric Mann Kendall tests were used to identify trends in annual stream flow and results showed significant downward trends in three out of the four catchments. The Pettitt's test indicated that a change point occurred in 1978 in these three catchments. Comparison of daily flow duration curves for two 20 years periods starting and ending in the mid 1970's (i.e., mid 1950s to mid 1970s and mid 1970s to mid 1990s) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 to 45 %, while reduction in low flows was much greater. Overall the reductions in daily flow are increasing as a function of time, with significant changes occurred in the 1990's. However, it is not clear if these catchments have seen the full effects of the soil conservation measures.