生态恢复对流域水沙演变趋势的影响及其程度分析——以北洛河上游为例

Abstract

The Loess Plateau in China is characterized by a heavily dissected landscape and severe soil erosion. To fully understand the impacts of soil conservation measures and vegetation restoration on streamflow,sediment load and runoffsediment behaviors,hydrologic data over 47 years(1963 to 2009) in the upper reaches of the Beiluo River( drainage area of 3408 km2) are assessed. The Beiluo is a secondary tributary of the Yellow River,and has had substantial vegetation restorative effects on the Loess Plateau. Based on the Mann-Kendall trend test,Pettit statistical test and flow duration curve(FDC),the daily streamflow and sediment load at Wuqi hydrological station,which is the maximum control station in theupper reaches of the Beiluo River,was chosen to investigate temporal change and evolution characteristics. Precipitation data and rainfall erosion force were interpolated using tessellation polygons from five representative meteorological stations on the Loess Plateau. A dual mass curve and empirically- based hydrological modeling method were also used to estimate the response of streamflow and sediment load to climate change and human activities. The results indicate that:(1) In the past50 years,under a background of precipitation with no significant trend,both streamflow and sediment load had significant negative trends( P 0. 01),with average annual rates of- 0. 28 mm km- 2a- 1and- 180 t km- 2a- 1,respectively. Under the influence of soil conservation measures that have been applied on the Loess Plateau since the 1960 s,there were change points in 1979 and 2002. Thus,the entire study period was divided into a period 1 of base(1963—1979),period 2 of comprehensive harness of soil and water conservation(1980—2002),and period 3 of the Grain for Green project(2003—2009).(2) The FDC showed that,compared with period 1,streamflow in period 2 for 5% and 50% decreased by 17. 0%and 5. 2%,respectively,while it increased by 94. 2% for 95%. Suspended sediment load decreased more significantly,with 34. 6% and 40. 1% for 5% and 50%,respectively,and no suspended sediment days remained almost constant for95%. Period 3 saw more remarkable changes in both streamflow and suspended sediment load. For 5% and 50%,streamflow decreased by 40. 2% and 26. 8%,respectively,while suspended sediment load decreased by 95. 7% and 96.8%,respectively. For 95%,streamflow rose by 128. 1%,and no sediment days increased. The reduction of sediment load was greater than that of streamflow,with the periods altered and negative changes of sediment load.( 3) Compared with period 1,streamflow and sediment load decreased by 0. 10 × 108m3(3 mm) and 0. 04 × 108t(1408 t km- 2a- 1) in period2. It was estimated that human activities accounted for 38. 2% and 51. 4% of the changes of streamflow and sediment load,respectively. In period 3,there was a greater reduction in both streamflow and sediment load,with 0. 52 × 108m3(15. 2mm) and 0. 33 × 108t(9683. 1t km- 2a- 1),respectively,with effects reaching 74. 7% and 86. 7%. Great improvement in the ecological environment of the Loess Plateau has already demonstrated the advantages of biological treatments on a regional scale in reducing flood volumes,and compensating streamflow.