水蚀风蚀交错区退耕坡面植被利用对产流产沙的影响

Effect of vegetation utilization on runoff and sediment production on grain-for-green slopes in the wind-water erosion crisscross region

为有效利用水蚀风蚀交错区退耕封育坡面植被,确定合理的植被利用强度非常必要.本试验选取黄土高原水蚀风蚀交错区典型小流域——六道沟小流域为试验区,在多年退耕封育坡面布设径流小区,通过人工模拟降雨试验,研究植被地上部分在不同利用强度下各坡度(10°、20°和30°)坡面产流、产沙变化特征,以确定合理的利用强度.结果表明:次降雨过程中径流速率大体可分为两个阶段:初期迅速增长阶段和中后期增长变缓或趋于准稳定阶段.侵蚀速率的变化趋势因坡度的不同而略有差异.利用强度对产流量有显著影响,产流量随利用强度的加强而增加.坡度对侵蚀量影响显著,侵蚀量表现为20°坡面>30°坡面>10°坡面.以植被地上部分未利用小区为对照,相对增水量和相对增沙量均随利用强度加强而增加.结合降雨资料推测,退耕15年左右坡面植被地上部分盖度达到25%时,坡面年土壤侵蚀量基本低于容许土壤流失量.应重视该区20°坡面植被的恢复治理工作.

To effectively utilize the vegetation on grain-for-green slopes in the wind-water erosion crisscross region, it is necessary to determine the reasonable vegetation utilization intensity. We set up runoff plots on slopes which were not cultivated and were closed for many years in the Liudaogou catchment, a typical catchment in wind-water erosion crisscross region of the Loess Plateau. With artificial simulated rainfall experiments, the characteristics of runoff and sediment yield on slopes (10°, 20° and 30°) under different utilization intensity of vegetation were studied to select the reasonable utilization intensity. The results showed that the runoff rate in the process of rainfall simulation could be divided into two periods: rapidly increasing in the initial period and slow increasing or quasi-steady state in the middle and late periods. The variation of erosion rate during the rainfall was dependent on the slope. The utilization intensity had a significant effect on the runoff yield, which increased with the increasing utilization intensities. The slope gradient had a significant effect on the sediment yield, with the variation of sediment yield with slope gradient being: 20°>30°>10°. Compared with the unused (natural) plots, the relative runoff and sediment increased with increasing utilization intensities. Predicted based on the rainfall data, annual soil erosion amount on the slope would be basically lower than the tolerance level of soil loss when the vegetation cover on the slope surface reached 25% in 15 years after abandoning reclamation. More attention should be paid to the restoration and management of vegetation on the slope of 20° in this area.