Abstract The dynamic interaction between erosion, surface morphology and flow hydraulics, causes steeper slopes to develop greater physical and hydraulic roughness, such that the slope can evolve toward a state of equilibrium wherein runoff velocity is independent of slope gradient. This study tests, under controlled condition, the hypothesis that erosion rate may also evolve toward a state wherein erosion rate is uniform across slope gradients after slope-velocity-equilibrium is established. A series of rainfall simulations (intensities of 59 and 178 mm hr−1) were conducted on 2 m by 6.1 m stony soil plot under three slope treatments (5%, 12% and 20%, replicated) with surface elevation, rock cover, flow velocity and sediment measurements. The results showed: 1) rock cover, and both surface physical (random roughness) and hydraulic roughness (Darcy–Weisbach friction) increased as rainfall progressed, leading to reductions in flow velocities and soil loss rates; 2) steeper slopes developed greater surface physical and hydraulic roughness; 3) the final soil loss rates ranged from 0.87 to 1.28 g min−1 m−2, and from 5.36 to 16.01 g min−1 m−2, which were approximately 6% to 15% of the initial maximum values, under low and high rainfall intensity, respectively; 4) soil loss rate was inversely correlated with rock cover while exhibiting no correlation with the random roughness index; 5) the linear coefficient of slope gradient relative to erosion rate measured on the most evolved surface were only 6.5% and 7.3% of those on initial surfaces under low and high rainfall intensity, respectively, implying that erosion rate evolved toward being less sensitive to slope gradient than it would otherwise be; 6) flow velocity and effective shear stress were found to be appropriate predictors for soil loss rate. This study supports the hypothesis of erosion equilibrium, implying that erosion rate decreases as a function of erosion pavement and that influence of slope gradient on soil erosion declines due to the dynamic interactions between soil erosion, surface morphology, and flow hydraulics.

中文翻译：

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模拟降雨条件下岩石覆盖、地表粗糙度的演变及其对土壤侵蚀的影响

摘要 侵蚀、地表形态和流动水力学之间的动态相互作用，导致较陡坡产生更大的物理和水力粗糙度，从而使坡能向平衡状态演化，其中径流速度与坡度无关。本研究检验了在受控条件下，侵蚀率也可能演变为在坡度-速度-平衡建立后侵蚀率在坡度梯度上均匀的状态的假设。一系列降雨模拟（强度为 59 和 178 mm hr-1）在 2 m x 6.1 m 的石质土壤地块上进行了三种坡度处理（5%、12% 和 20%，重复），表面高程、岩石覆盖、流速和沉积物测量。结果表明：1）岩石覆盖，随着降雨的进行，地表物理（随机粗糙度）和水力粗糙度（达西-魏斯巴赫摩擦）均增加，导致流速和土壤流失率降低；2) 坡度越大，地表物理和水力粗糙度越大；3) 最终土壤流失率范围为 0.87 至 1.28 g min-1 m-2 和 5.36 至 16.01 g min-1 m-2，约为初始最大值的 6% 至 15%，在低和分别为高降雨强度；4）土壤流失率与岩石覆盖率呈负相关，与随机粗糙度指数无相关性；5) 在低降雨强度和高降雨强度下，在最进化的表面测得的坡度相对于侵蚀速率的线性系数分别仅为初始表面的 6.5% 和 7.3%，这意味着侵蚀率演变为对坡度梯度不那么敏感；6) 流速和有效剪应力被认为是土壤流失率的合适预测指标。本研究支持侵蚀平衡的假设，这意味着侵蚀速率随着侵蚀路面的变化而降低，并且由于土壤侵蚀、表面形态和流动水力学之间的动态相互作用，坡度对土壤侵蚀的影响下降。