不同因素影响下层状土壤水分入渗特征及水力学参数估计

Water Infiltration Characteristics of Layered Soil under Influences of Different Factors and Estimation of Hydraulic Parameters

层状土壤是自然界常见的土体结构,其水分运移规律不同于均质土;大气降水、灌溉水等水分的入渗是土壤水文过程的一个重要环节,同时它也与地下水补给、污染物运移等过程紧密相关。土壤初始含水量、土体构型及供水强度等因素均会影响水分的入渗过程。为探究积水深度、土体构型、初始含水量三种因素对层状土壤水分运移的影响,通过室内积水入渗试验对湿润锋、累积入渗量、土壤剖面压力水头进行观测,并利用Hydrus-1D模型反演水力参数并对相应条件下的水分运移规律进行模拟和分析。结果表明,层状土壤中湿润锋随时间的推进方式由非线性过渡至线性,入渗率逐渐减小。三种因素作用下,层状土壤水分运移特征有明显差异:积水深度、土壤初始含水量增加时,湿润锋运移速率和入渗率均增大,且各观测点压力水头升高加快,土壤不饱和程度降低;上砂壤下粉砂壤构型较上粉砂壤下砂壤构型而言,整体湿润锋推进速率和入渗率较大,出流快,且入渗后期界面处的压力水头高于其他观测点。且结果表明,反演的水力学参数较拟合实测的参数更适用于层状土壤入渗的模拟和预测。该研究旨在揭示和掌握层状土壤水分运移规律和影响因素的作用机制,并进一步为农田灌溉措施的合理制定提供科学依据。

【Objective】Layered soil is more often encountered than homogeneous soil in nature,and its water movement follows a law different from the latter’s.And infiltration of water,such as atmospheric precipitation and irrigation water,is an important part of the hydrological process in soil,and is also closely related to groundwater replenishment and pollutant transport.Soil initial water content,soil texture and structure and water supply intensity are all factors affecting the process of water infiltration.The purpose of this study is to explore and grasp law of the water infiltration in layered soil and mechanisms of the influencing factors,and provide a theoretical basis for further rationalization of farmland irrigation measures.【Method】The layered soil used in this research,was constructed in line with the soil profile in the field,i.e.a silt loam layer(18cm thick)and a sandy loam layer(24 cm),and out of the consideration of the mechanisms of ponding water relative to depth,soil configuration and initial soil moisture content affecting water transport.In the indoor ponding infiltration experiment of layered soil,wetting front,cumulative infiltration and soil profile pressure head,relative to depth of standing water,was observed.Moreover,hydraulic parameters of the layered soil were determined with a Ku-pF device and the Hydrus-1D software inversion module,separately.Based on these parameters,the Hydrus-1D model was used to simulate and predict water transport under various set conditions.Applicabilities of the soil hydraulic parameters were verified by comparing the simulated data of the two sets of parameters.【Result】Results show that the wetting front turned from nonlinear advance to linear advance and the cumulative infiltration increased with time,while the infiltration rate decreased rapidly in the early stage of the infiltration and then slowly as the infiltration going on,which is mainly due to the change in soil matrix potential gradient.The soil was relatively dry and high in water suction at the initial stage of the infiltration;as the soil increased in water content,the water suction decreased.As affected by the three factors,water transport varied sharply in characteristics in the layered soil.When the ponding water increased in depth and the initial soil water increased in content,both the wetting front advancing rate and the infiltration rate increased,and the pressure water head increased quicklyat each observation point and the soil water unsaturation degree decreased,which indicates that the change in depth of ponding depth has some impact on pressure potential,and the change in initial water content is related to matrix potential and disintegration and compression of soil aggregates.Compared with the soil configuration of silt loam overlying sandy loam,the one of the reverse order was higher in overall wetting front advancing rate,infiltration rate and pressure head variation.(The infiltration rate at the interface of the wetting front in the layered soil was 0.20 and 0.021 cm·min–1,respectively.)In addition,the two types of layered soils differed significantly in variation of the pressure water head in the soil water redistribution process【Conclusion】All the findings in this study not only help illustrate that appropriate adjustment of the three influencing factors can reduce soil leakage and optimize soil water management in the field,but also further demonstrate that the parameters of the inversions are more adoptable to simulation and prediction of water infiltration characteristics of layered soils under ponding water in indoor experiments.