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.