干热河谷区耕作侵蚀作用下坡面水力侵蚀特性

为了研究耕作侵蚀对坡面水动力学特性的影响,选择金沙江干热河谷地区的坡耕地作为研究对象,采用放水冲刷的试验方法,探讨耕作侵蚀影响侵蚀区土层厚度和作为侵蚀物源传输纽带这2种耕作侵蚀形式作用下坡面水动力参数的变化与分布规律,并分析坡面水动力参数与坡面产流和土壤剥离速率之间的关系。结果表明:耕作侵蚀区不同耕作侵蚀强度处理中,随着耕作侵蚀强度的增大,坡面产流速率和土壤剥离速率均呈现增大趋势;0~35年耕作侵蚀强度处理下坡面水流流态主要表现为紊状缓流,耕作侵蚀强度达到40年时则为紊状急流;阻力系数呈现随耕作侵蚀强度增大而减小的趋势,剪切力则呈增大的趋势。在耕作沉积区不同耕作位移处理中,随着耕作位移量的增大,坡面产流速率呈减小趋势,而土壤剥离速率呈增大趋势;0,12 kg/m的耕作位移处理下坡面水流流态主要表现为紊状急流,当耕作位移量达到21 kg/m,即下坡部位的细沟因土壤耕作位移被完全填充时,水流流态则为紊状缓流;随着耕作位移量的增大,阻力系数表现为增大趋势,剪切力则呈减小趋势。将坡面产流速率、土壤剥离速率与水动力参数进行相关性分析后,发现雷诺数能够较好的描述耕作侵蚀作用下坡面水力侵蚀状态。研究结果为干热河谷区坡耕地土壤侵蚀机理及治理方法提供了科学依据。

Effect of Tillage Erosion on Characteristics of Hydraulic Erosion in the Dry-hot Valley Region

This study aimed to quantitatively evaluate the effect of tillage erosion on runoff yield, sediment yield as well as hydraulic characteristics in the hilly croplands in the Dry-hot Valley Region by the simulated tillage and scouring experiments. Two forms of tillage erosion were adopted that one was the simulated tillage duration (10-, 20-, 30-, 35-, 40-year tillage) which caused the attenuation of soil thickness at the upper slope positions, and the other was the simulated soil flux (0, 12, 21 kg/m) which occurred in rills at the lower slope positions. Results showed that under the influence of tillage duration, both runoff yield and soil detachment rate displayed an increasing trend with the increase of tillage duration. Runoff stayed in the pattern of rapid laminar-flow for the treatment of 40-year tillage, while the slow laminar-flow for the other treatments. The drag coefficient and shear stress exhibited a decreasing and increasing trend as the tillage duration increased, respectively. Under the influence of soil flux, runoff yield rate was in a decreasing trend with the increase of soil flux while soil detachment rate was in an increasing trend. Runoff changed from the pattern of rapid laminar-flow to slow laminar-flow when the soil flux reached 21 kg/m. As the soil flux increased, drag coefficient presented an increasing trend and shear stress was in a decreasing trend. Reynolds number was the best hydrodynamic parameter which could explain the characteristics of hydraulic erosion under the influence of tillage erosion by correlation analysis. These results could provide scientific guidance for the exploration of soil erosion mechanism and treatment methods in the hilly croplands of Dry-hot Valley Region.