The influence of soil surface gradient on rainfall infiltration and related surface runoff generation are not well understood for representation in hydrologic modeling because of conflicting theoretical formulations and experimental results available in the scientific literature. The main objective of this study is to integrate and extend previous laboratory experiments using artificial rainfall over a laboratory setup with adjustable slope angle (α) and consisting of two adjacent natural bare soils that according to the USDA soil classification were of loam (Soil 1) and sandy loam (Soil 2) type, respectively. Soil 2, placed downstream, was subjected to the run-on process due to the overland flow produced over Soil 1. The slope effects are discussed on the basis of measurements of runoff surface (Q_S) and deep flow (Q_d), both strictly linked to the infiltration rate, supported by a simplified rainfall-runoff model. Our results indicate that at a time close to the end of rainfall period (t_re=8 h), for α increasing from 1° to 10°, Q_d decreased by about 25% while Q_S exhibited a corresponding increase in magnitude. In the same slope range, at t → t_re the total volume of water collected as deep flow decreased by about 40% for heavy rainfall and up to about 50% for light rainfall. On the other hand, a growth of the total surface water volume occurred such that the total outflow volume was nearly independent of α. The run-on effect is seen to modulate the differences in steady deep flows for different slopes. The above variations became of minor interest between 10° and 15°. The significant differences in the variations of surface and deep flow to changes of slope angle were analyzed and placed in context with those from earlier experiments. The differences are attributed to a different level of interaction between capillary and gravitational effects that should be represented in existing infiltration models, because appreciable values of α characterize most watershed areas and the decrease of infiltration with increasing α over bare soils can imply a greater contribution to the direct runoff and a significant reduction of the groundwater recharge with respect to a flat surface.

由于科学文献中的理论公式和实验结果相互矛盾，土壤表面梯度对降雨入渗和相关地表径流产生的影响在水文模型中的表现还没有得到很好的理解。本研究的主要目的是整合和扩展先前使用人工降雨的实验室实验，该实验在具有可调坡角 ( α ) 的实验室装置上进行，并由两个相邻的天然裸土组成，根据美国农业部的土壤分类为壤土（土壤 1）和沙壤土（土壤2）类型，分别。由于土壤 1 上产生的地表溢流，位于下游的土壤 2 经受了径流过程。坡度效应在径流表面测量的基础上进行了讨论（Q _S ) 和深水流 ( Q _d )，两者都与入渗率密切相关，由简化的降雨径流模型支持。我们的结果表明，在接近降雨期结束的时间（t _re =8 h），对于α从 1° 增加到 10°，Q _d下降了约 25%，而Q _S表现出相应的幅度增加。在相同的斜率范围内，在t  →  t _re 大雨时深流收集的总水量减少约 40%，小雨时减少约 50%。另一方面，地表水总量的增长使得总流出量几乎与α无关。可以看出，连续效应调节了不同坡度的稳定深水流的差异。上述变化在 10° 和 15° 之间变得无关紧要。分析了地表和深层水流变化对坡角变化的显着差异，并将其与早期实验的结果联系起来。这些差异归因于毛细效应和重力效应之间的不同水平的相互作用，这应该在现有的渗透模型中表示，因为α的可观值大多数流域区域的特征，并且在裸土上随着α的增加入渗减少可能意味着对直接径流的更大贡献以及相对于平坦表面的地下水补给量的显着减少。