不同降雨强度下土壤结皮强度对侵蚀的影响

Effect of soil crust strength on erosion under different rainfall intensity

为定量分析土壤结皮对坡面侵蚀的影响,该文选择塿土、黄绵土、黑垆土和黄墡土4类土壤,分析其在3种雨强(60、90、120 mm/h)下的结皮强度变化规律。结果表明,当土壤含水率高于30%时,不同降雨强度下结皮强度差异不显著(P>0.05),当含水率小于30%时,结皮强度随降雨强度增大而增强。以杨凌塿土10°坡面为例,进行坡面人工模拟降雨试验,分析计算不同强度结皮坡面的侵蚀产沙、径流剪切力、阻力系数以及流速,结果表明:结皮对坡面产流的影响并不显著,但其存在有效地减少坡面的侵蚀产沙量。结皮存在能有效地减少坡面产沙量,无结皮坡面的产沙量是结皮坡面产沙量的1.24~8.72倍。相同降雨条件下,结皮强度越大,其产沙量越小。进一步通过灰色关联分析得出:随着坡面结皮强度增加,水流功率对坡面侵蚀的作用效益不断减小,而阻力系数的作用效益增加,即水流增加产沙的正效应不断减弱;另一方面,结皮强度增大使得坡面土壤抗蚀性增强,因此,结皮强度越大,坡面侵蚀量将大幅度减少。研究可为准确有效预报坡面土壤侵蚀提供重要依据。

Soil crust plays an important role in rainfall,runoff and erosion process.When it comes to the present situation,most studies analyze the impact mechanism of soil erosion on the existence of soil surface crust,through comparison analysis of sediment yield,runoff producing and characteristic of hydrodynamic under the crust and no crust slope.However,limited studies report on the characteristic of soil sediment yield,runoff produced and the rule of feature variation for hydrodynamic,also,no quantitative evaluation about the hydraulics parameter＇s influence on sediment yield.Therefore,in our research,according to crust strength variation and hydrodynamic characteristic under different crust strength,we conducted quantitative analysis on the impact of crust on slope erosion,and through comparison analysis for characteristic of slope sediment yield,under different crust intensities.We further analyzed the change features of hydraulics parameter under slope erosion,and described strength of effect quantitatively under influence factor,for providing important material to predicate accurately and effectively slope soil erosion.In this paper,the impact mechanism of soil crust on slope erosion was reported using quantitative analysis method.The strength of soil crust change of 4 soil types（Lou soil,Loess soil,Heilu soils and Huangshan soil）under 3 rainfall intensities（60,90,120 mm/h）was analyzed.Our results showed that the relationship between the crust strength and rainfall intensity was complex when soil water content was more than 30%.However,when soil water content was less than 30%,crust strength increased with the increase of rainfall intensity.Taking the 10°slope of Lou soil as an example,sediment yield,shear stress,resistance coefficient and flow velocity of different crust strength under artificial rainfall experiments were determined and analyzed.The existence of crust could reduce slope sediment yield effectively,and the sediment yield of no crust slope was 1.24-8.72 times more than crust slope＇s.The crust on slope effectively reduced the erosion and sediment yield.The greater the crust strength was,the stronger the reduction was.The flow shear stress,stream power,resistance coefficient of no crust slope were all larger than the crust slope,but for crust slope,flow shear stress of various crust strength was not significant different（P〈0.05）.Stream power and flow shear stress were enhanced with increase of crust strength.The larger crust strength was,the smoother surface was,the larger flow velocity was,the smaller resistance was,which improved the stream power.The stream power of high strength crust was larger than low strength crust,but with the smaller sediment yield,its resistance of slope was large.Therefore,the formation of soil erosion was synthetic result of erosion dynamic,slope resistance and soil anti-erodibility.The grey correlation analysis showed that with the increase of the soil crust strength,the influence of the stream power on the erosion of the soil was decreased,and the effect of the resistance coefficient was increased.Therefore,there was a positive effect of water flow on sediment reduction,and the soil erosion resistance of the soil was enhanced with the increase of crust strength,so the erosion amount of soil would decrease greatly.