降雨和水保措施对无定河流域径流和产沙量影响

基于无定河流域降雨、泥沙、径流和水土保持措施的历年统计数据,根据M-K-S检验得到径流和侵蚀产沙序列的突变点,将研究期分为基准期(1957—1972年)和措施期(1973—1996年)。采用双累积曲线、经验公式和修正系数法,研究该流域降雨变化和水保措施对径流和产沙量变化的影响,并采用多元回归模型分离了降雨和水保措施对径流和产沙量变化的贡献。结果表明:与基准期相比,水保措施引起径流减少3.16亿～3.42亿m3,占基准期年均径流量的23.0%～24.4%;引起产沙量减少0.71亿～1.07亿t,占基准期年均产沙量的47.1%～57.3%。措施期降雨变化引起径流量减少0.46亿m3,产沙量减少0.13亿t,分别占措施期水、沙实际减少总量的11.6%和11.4%。水土保持措施建设是流域径流和侵蚀产沙减少的主要原因,其对水、沙减少的贡献率分别为80.3%和60.5%。其中,植被措施(林地+草地)对径流影响显著,引起径流量减少2.78亿m3,占径流减少总量的70.2%;工程措施(梯田+坝地)对产沙影响显著,引起产沙量减少0.46亿t,占产沙减少总量的40.3%。降雨变化、植被及工程措施对水沙量变化的影响表现出阶段性变化,主要原因在于降雨的丰枯变化和工程措施对水土流失防治功能的时限性。因此,在水保措施建设过程中,需合理配置工程和植被措施比例,重视对已建梯田、坝地等工程的维护和废弃工程的替换,以增强水土保持措施体系功能的持续性。

Impacts of precipitation variation and soil and water conservation measures on runoff and sediment yield in the Wuding River Basin,middle reaches of the Yellow River

In this study, we analyzed the data of annual precipitation, runoff, sediment yield and soil and water conservation (SWC) measures from 1957 to 1996 in the Wuding River Basin, China. Using Mann-Kendall-Sneyers trend test, we found that runoff and sediment yield changed significantly in 1972. The time series data was in turn divided into two parts: i) a baseline period (BP) (1957--1971) and ii) a period of change (CP) (1972--1996). By using the methods of double mass curve, an empirical formula and a correction coefficient, the impacts of precipitation variation and SWC measures on runoff and sediment yield were analyzed and the contributions of variation in precipitation and SWC measures to runoff and sediment yield were assessed by fitting a multiple regression model. The results showed that during the CP, SWC measures caused the reduction of mean annual runoff by 3.16×108-3.42×108 m³/year, accounting for 23.0%--24.4% of the values obtained during the BP. SWC measures caused the reduction of mean annual sediment yield by 0.71×108-1.07×108 t/year, accounting for 47.1%--57.3% of values during the BP. The variation in precipitation caused the reduction of runoff and sediment yield by 0.46×108 m³/year and 0.13×108 t/year, respectively, which were 11.6% of the total runoff reduction and 11.4% of the total sediment reduction. The reduction of runoff due to the SWC measures via vegetation restoration (planting trees + grass) was 2.78×108 m³/year, which was 70.2% of the total reduction of runoff. The reduction of sediment yield due to the SWC measures via engineering projects (terraces + sediment-trapping dams) was 0.46×108 t/year, which was 40.3% of the total reduction of sediment yield. Because of the variation in precipitation and the limitation of engineering measures, their effects on runoff and sediment yield varied among different periods. Therefore, in the integrated soil and water management of the Wuding River Basin, it is important to apply countermeasures to ensure that the SWC measures are sustainable, i.e. rational allocation of the ratio of the SWC measures via vegetation restoration and engineering projects, paying attention to the maintenance of established terraces and replacing the destroyed SWC engineering in time.