Characteristics of erosion sediment yield with extreme rainstorms in Yanhe Watershed based on field measurement

Abstract: Aiming at whether the present erosion environment could withstand the test and possible problems under the extreme rainstorm events on the Loess Plateau, the characteristics of erosion sediment yield at different scales in 2013 with extreme rainstorm events were analyzed based on the vegetation investigation and soil erosion monitoring in Yanhe River Basin. The average soil erosion intensity was < 1 000 t/km2 for the natural arbor vegetation (Quercus liaotungensis and Acer buergerianum), from 1 118.1 to 1 161.2 t/km2 for the natural shrub vegetation, from 1 245.2 to 1 827.8 t/km2 for the herbaceous vegetation in the middle-late stage of succession, while from 3 087.6 to 4 408.4 t/km2 for the herbaceous vegetation in the early-middle stage of succession. In the artificial vegetation, the ability of reducing soil erosion for artificial shrub vegetation (2 119.7-2 183.9 t/km2) was larger than the artificial arbor vegetation (2 625.7-5 149.6 t/km2). In particular, the average coverage of the 6-8 years of artificial Robinia psendoacacia was only 30% due to the shorter afforestation time, so the soil erosion intensity reached 5 141.6 t/km2. In the condition of the rainstorm in 2013, the average soil erosion intensity of the slopes with good vegetation in all small watersheds was below 2 500 t/km2. The erosion intensity was mainly in the category of slight erosion in the small watersheds of the southern and northern areas, and mainly in the category of mild and moderate erosion in the small watersheds of the middle area. However, the landslide erosion was dominant, accounting for 49.0%-88.5% of the total erosion in small watersheds. The average landslide erosion intensity reached 7 357.7 t/km2 in the southern area near the rainstorm center, 3 706.9 t/km2 in the middle area and 1 678.1 t/km2 in the northern area. There was 6.4%-18.3% of erosion amount deposited in the channels in different small watersheds. The sediment deposition amount was 13.2×104-145.2×104 t in different sections of riverbed in the upstream of Ganguyi Hydrological Station in Yanhe River Basin, accounting for 15% of the total erosion sediment yield on average. The intensity of erosion sediment yield ranged from 2 326.7 to 7 774.4 t/km2 in the controlled area of Ganguyi Hydrological Station, of which the area with erosion sediment intensity of 5000-8000 t/km2 was 59.3%. In 2013, the calculated value of sediment discharge at the Ganguyi Hydrological Station was 0.228×108 t, while the measured sediment discharge was 0.243×108 t. By comparison, the calculated value was 0.015×108 t smaller than the measured value with the relative error of 6.2%. Therefore, the results of this research were reliable. At the present stage, the good vegetation cover of the hill slope could control rainstorm erosion effectively. The erosion type of the sediment source of Yanhe Watershed was dominated by gravitational erosion in the condition of rainstorm. Therefore, in the premise of protecting the achievements of the “Grain for Green” project, it should strengthen the storage and drainage measures in the inter-gully to reduce the slope runoff flowing down the gully and prevent gravitational erosion of the gully slope and the gully erosion. Then, it might effectively prevent soil erosion, and promote the realization of beautiful mountain and river in future.