放水冲刷条件下紫色土细沟侵蚀特征

Rill erosion characteristics of purple soil by flume flushing method

细沟侵蚀对于坡面侵蚀量的贡献很大。以长江中上游典型侵蚀性土壤紫色土为研究对象,采用变坡限定性细沟径流土槽放水冲刷试验,研究不同流量、坡度和坡长情况下,紫色土细沟侵蚀特征。结果表明:相同坡度和流量情况下,清水流速大于浑水流速,坡度和流量影响流速的变化;不同流量情况下,5°坡面流速随坡长增大变化幅度很小,基本稳定。15°和23°坡面流速呈现随坡长增加而减小的趋势,并趋于稳定。在给定的坡度和流量条件下,产沙量随着坡长的增加而增加,但增加的幅度越来越小,且趋近一个稳定值。5°坡面含沙量稳定所需的坡长在5、15和25 L/min情况下,分别为7、5和5 m。15°和23°坡面在5和15 L/min情况下,含沙量稳定所需的坡长分别为7和6 m,25 L/min情况下坡长到试验坡长10 m时,含沙量还没稳定,含沙量与坡长成对数函数关系。其研究结果为紫色土坡面侵蚀物理模型的建立提供参数支持。

[Background]The rill erosion is the main source of the total erosion amount,and it is the greatest contribution to the slope erosion. Rill flow velocity changes with the slope gradient changing. The sediment load changes not only by the impact of soil properties but also by the hydraulic characteristics and slope characteristics. At present,soil erosion study for purple soil was relatively shortened and the data that could be used is very little. [Methods] A series of flume experiments of restrictive rills were conducted to understand erosion characteristics of rills under the condition of different slope gradients and slope lengths. Quantitative study of the rill erosion is the basis for best understanding the slope erosion mechanism. The soil used was purple soil,a clay soil. The test sediment was air dried and sieved through a 5 mm sieve. Three slope gradients： 5°,15°,and 23°,as well as three flow discharges： 5 L/min,15 L/min,and 25 L/min were adopted in the experiments. Flow discharge was controlled by a series of valves installed on a flow diversion box and measured directly by a calibrated flow meter. The elevation of the upper flume end was adjusted by a stepping motor,allowing adjustment of the bed gradient up to 45%. The rills were 10 cm wide. Rill length was 0. 5 m,1 m,2 m,3 m,4 m,5 m,6 m,7 m,8 m,9 m,and 10 m respectively. [Results]The velocity of clean water in rill was larger than that of muddy water under the same slope gradient and runoff. Both slope gradient and runoff dischargeimpacted the flow velocity. Under different runoff discharge,the flow velocity of slope 5° had little variation and was stable. The flow velocity of 15° and 23° decreased with the slope length increasing,and the situation tended towards stability. Under a given slope gradient and runoff discharge,the sediment load increased as the slope length increasing,but the rate of increasing was getting smaller and smaller till it approached a stable value. On the slope gradient of 5°,the slope length value while sediment load reached stable became shorter along with the increase of flow discharge,and the values were 7 m,5 m,and 5 m respectively at the flow discharge of 5 L/min,15 L/min,and 25 L/min. On the slope gradient of 15° and 23°,the slope length values while sediment load became stable were 7 m and 6m under the flow discharge of 5 L/min and 15 L/min. The sediment load did not become stable when the slope length was 10 m that was the largest length of the experiment under the flow discharge of 25 L/min.The yield of sediment and slope length presented a relationship of logarithmic function. [Conclusions]The results are conducive to the comprehensive understanding rill erosion of purple soil and provide basic data for physical erosion model＇s establishment.