密云水库上游流域次降雨坡面产流产沙特征

以北京市密云县石匣小流域为研究区,利用2006-2010年连续5 a的坡面径流试验小区观测资料,运用统计方法,分析了密云水库上游流域的降雨、产流产沙特征以及在不同土地利用和不同坡度条件下,降雨量、降雨强度与产流、产沙之间的关系。结果表明:1)该研究区域水土保持治理措施实施的关键时间为每年的7、8月份,当降雨量大于10 mm时,应注意采取水土保持措施;2)在裸地、耕地和林地条件下,高雨量、中雨强型降雨为导致产流、产沙的主要雨型,在草地条件下,中雨量、高雨强型降雨为导致产流、产沙的主要雨型;3)中雨量高雨强型降雨条件下,林地的减流效益最好,低雨量低雨强型降雨和高雨量中雨强型降雨条件下,耕地的减流效益相对较低,草地和林地的减流效益差异不大;在3种不同雨型条件下,耕地、草地和林地的减沙效益差别不大;4)裸地条件下,降雨量与产流量间的关系更为密切,尤其在14.4°坡面下相关性最高;耕地条件下,产流量与降雨量的相关性较好,产沙量则与降雨强度的相关性较好,11.4°的坡面产流量、产沙量与降雨因子间的相关系数最高;草地条件下,降雨强度与产流量间的关系较为密切;林地条件下,产流量、产沙量与降雨因子间的相关性均不显著。研究结果可为密云水库上游水土保持措施及农业面源污染管理措施的科学实施提供依据。

Characteristics of runoff and sediment during individual rainfall in upper area of Miyun Reservoir

Abstract: Rainfall is the main factor driving surface runoff and soil erosion. In order to clarify the characteristics of individual rainfall runoff and soil erosion in upper area of Miyun Reservoir and the impact of rainfall depth and intensity on surface runoff and soil erosion under different land use types with various slopes, data on rainfall runoff and soil erosion of 213 individual rainfalls in experimental plots of Shixia watershed from 2006 to 2010 were collected and analyzed. Clustering analysis, variance analysis and correlation analysis was conducted, and the results showed that: 1) The critical period to implement soil and water conservation measures was in July and August of each year. When the rainfall depth of 24h was larger than 10 mm, the water and soil conservation measures should be adopted; 2) In upper area of Miyun Reservoir, the rainfall could be divided into 3 different types according to rainfall depth and intensity. The main rainfall type in this region was the low precipitation with low intensity, although it couldn't drive soil loss substantially. Across the land-uses of bare land, arable land and forestland, high depth but medium intensity rainfall is always the major reason that should be responsible for surface runoff and soil erosion. While, in the grass land, medium depth but high intensity rainfall was the main type causing surface runoff and soil erosion; 3) The runoff depth and sediment yield of bare land was always the highest among different land-use patterns. For the medium precipitation with high intensity, forestland can greatly reduce the runoff in comparison with bare land. While, for low precipitation with low intensity and high precipitation but with medium intensity, the runoff reduction efficiency in the arable land was very low, while the efficiency was extremely high in the grassland and forestland. The reduction of sediment had not shown any significant difference across these land-uses; 4) The relationship between runoff depth, sediment amount and rainfall depth, rainfall intensity under different land-uses also were different. For the bare land, the relationships between runoff, sediment amount and precipitation on different slopes were all significant (P<0.05), while the correlation coefficient between runoff and precipitation was higher than that of rainfall intensity and runoff, and the correlation coefficient was the highest, which was 0.607 (P<0.01) when the slope was 14.4°. For arable land, a significant relationship between rainfall depth and runoff was observed while other relationships were not noticeable. Our results also implied that the correlation coefficient could be magnified when the slope was 11.4°, which was 0.625 (P<0.01). For grassland, the correlation between runoff and rainfall intensity was noticeable but noisy when slope was 27° while between runoff and rainfall depth was not significant. For woodland, all of the relationships were not noticed, which indicated that the relationship between runoff, sediment amount and rainfall factors could be weakened to some extent. Our study can provide valuble information for the soil and water conservation and Best Management Practices in the upper watershed of Miyun Reservoir.