降雨强度和坡度对细沟形态特征的综合影响

Effects of Rainfall Intensity and Slope Gradient on Rill Morphological Characteristics

细沟的形态特征研究可揭示坡面侵蚀发生机理,且细沟形态对坡面径流和侵蚀有重要影响;而现有研究仅用细沟密度和细沟宽深比等指标来表征细沟形态,不能全面准确地反映细沟的形态特征。为此基于模拟降雨试验,研究降雨强度和坡度对黄土坡面细沟侵蚀和细沟形态特征的综合影响。试验处理包括3种黄土高原有代表性的侵蚀性降雨（50、75、100 mm/h）和3个细沟侵蚀发生最常见的坡度（10°、15°、20°）。试验结果表明,坡面侵蚀速率和细沟侵蚀速率均随着降雨强度和坡度的增加呈幂函数增加。试验条件下,细沟倾斜度介于16°-20°之间,随着降雨强度的增加而增大,随着坡度的增加而减小;细沟密度、细沟割裂度和细沟复杂度分别为0.74-1.95 m/m^2、0.08-0.17和1.09-1.38,三者皆随降雨强度和坡度的增加而增大;细沟宽深比为1.93-2.35,随着降雨强度和坡度的增加而减小。通过相关分析发现,细沟割裂度是评价细沟侵蚀和细沟形态的最优指标;研究降雨强度对细沟形态的影响时,建议优先选用细沟割裂度、细沟复杂度和细沟倾斜度指标;分析坡度对细沟形态的影响时,除选取细沟割裂度外,建议优先选用细沟密度和细沟宽深比指标。细沟横断面主要呈＂V形＂,随着降雨强度和坡度的增加,径流紊动性增强,细沟横断面变化趋于不规则,说明细沟横断面变化可以反映径流的变化特征,从而揭示细沟侵蚀发生机理。

Studies on rill morphological characteristics can reveal soil erosion mechanisms,and rill morphology has important influence on runoff and soil loss of the hill slope. However,the existing studies only use rill density,rill width-depth ratio,etc. to characterize rill morphology,which cannot fully reflect rill morphological characteristics. Effects of rainfall intensity and slope gradient on rill erosion and rill morphology at the loess hill slope were studied based on a rainfall simulation study. The experimental treatments included three rainfall intensities（ 50,75 and 100 mm / h） of representative erosive rainfall on the Loess Plateau and three common slope gradients（ 10°,15° and 20°） of rill erosion occurrence. The results showed that both soil erosion and rill erosion increased with increasing of rainfall intensity and slope gradient, where relationships among them were the power function. Rill inclination angle concentrated between 16° - 20° under the experimental conditions,and it increased with an increase inrainfall intensity and decreased with an increase in slope gradient. Rill density,degree of rill dissection and rill tortuosity complexity were 0. 74 - 1. 95 m / m^2,0. 08 - 0. 17 and 1. 09 - 1. 38,respectively,which all increased as rainfall intensity and slope gradient increased. Rill width-depth ratio was 1. 93 -2. 35,which decreased with increasing rainfall intensity and slope gradient. By analyzing correlations between rill erosion and rill morphological indicators,degree of rill dissection is the best indicator to evaluate rill erosion and rill morphology. When studying the effect of rainfall intensity on rill morphology,indicators of degree of rill dissection,rill tortuosity complexity and rill inclination angle are recommended to preferentially select. When analyzing the effect of slope gradient on rill morphology,indicators of rill density and rill width-depth ratio are recommended to preferentially select,except for degree of rill dissection. Most of rill cross sections presented ＂V＂shapes. Generally,the rill cross section appeared more and more irregular change with increasing rainfall intensity and slope gradient,where the runoff turbulence increased. This indicated that the change of rill cross section can reflect change characteristics of runoff,thereby reveal the rill erosion mechanisms.