延河流域极端暴雨下侵蚀产沙特征野外观测分析

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

针对黄土高原目前侵蚀环境明显改善条件下能否经受得住极端暴雨事件的考验及可能出现的问题,该文依据在延河6个典型小流域的植被调查及土壤侵蚀监测结果,分析了2013年极端暴雨条件下延河流域不同尺度的侵蚀产沙特征。结果表明,天然乔木(辽东栎和三角槭)植被的平均侵蚀强度<1 000 t/km^2,自然灌木植被在1 118.1~1 161.2 t/km^2之间,演替中后期的草本植被在1 245.2~1 827.8 t/km^2之间,而演替中前期的草本植被在3 087.6~4 408.4 t/km^2之间;人工灌木林(2 119.7~2 183.9 t/km^2)比人工乔木林(2 625.7~5 149.6 t/km^2)具有较强的减蚀能力。坡面良好的植被覆盖能有效抵御暴雨侵蚀,小流域坡面平均侵蚀强度基本<2 500 t/km^2;但滑坡侵蚀占主导地位,占各小流域侵蚀总量的49.0%~88.5%,特别是距暴雨中心较近流域的南部2个小流域的滑坡侵蚀可达7 290.3和7 424.9 t/km^2左右。不同小流域内有6.4%~18.3%的侵蚀量淤积在沟道里;延河甘谷驿以上不同河段的淤积量为13.2~145.2万t,平均占总侵蚀产沙量的15%。延河甘谷驿控制区的侵蚀产沙强度变化在2 326.7~7 774.4 t/km^2之间,其中强度为5 000~8 000 t/km^2的面积占59.3%。因此,加强沟间地径流蓄排措施,减轻坡面径流下沟对沟坡重力侵蚀的影响,是土壤侵蚀研究与防治中值得重视的问题。

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 0.228×10^8t, while the measured sediment discharge was 0.243×10st. By comparison, the calculated value was 0.015×10^8t 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.