非均质条件下河流包气带水分运移的原位试验

围绕非均质条件下河流包气带水分运移,选择渭河河漫滩开展原位试验。在渭河原位试验点开挖7 m×1 m×2.8 m的探坑,以一侧剖面为研究面,刨光成垂直平面并对剖面做保护工作,方便观测。在不同层位按不同深度、在不同岩性的层位上打孔,分别安装MP-917时域反射仪与水银压力计,监测含水率及地下水压力势,并采用自制Bauwer渗水仪做持续5 d的有压入渗试验,研究非均质条件下河流包气带水分运移规律及入渗速度与水头高度的关系。结果表明,包气带介质含水率分布与包气带结构有关,受岩性渗透系数制约,其中弱透水层的存在阻滞了水分的运移,包气带很难达到饱和,在弱透水层以上形成上层滞水并以非饱和流形式入渗。入渗速度随水层的厚度增大而增大,且入渗速度与水头高度呈对数关系。

Field test of moisture migration in vadose zone under heterogeneity

The paper is engaged in a field test of moisture migration in vadose zone under the heterogeneous condition in the Weihe(Shaanxi) flood-plain.The reason why we have chosen the topic is that the evolution of a river may exert serious consequential effects on the groundwater change,the water quality and even the ecological environment along the entire river reach.It is for such purposes,we have dug up some measuring pits as large as 7 m×1 m×2.8 m and taken them as our study profile.For the convenience of observation,we have installed a MP-917 Time Domain Reflectometry(TDR) and a mercury manometer to observe the potential pressure and the moisture content in correspondence with the different properties of lithology and depth respectively.And,then,we have done a five-day infiltration test by using our own-made Bauwer Ooze water meter.Though it is difficult to understand the infiltration mechanism for its complexity with the unsaturated zone being heterogeneous with compacted sandwich structure,the field test is comparatively simple about the moisture migration in vadose zone under heterogeneity.In addition,we have also tested the moisture migration regularity under the heterogeneous condition and the relationship between the infiltration speed and water head height by using the above said Ooze water meter.The results of our study show that,the distribution of moisture content is restricted by the lithology permeability in relation to the vadose zone medium and aeration zone structure.The vadose zone doesn’t prove to be easy to get saturated due to the presence of aquitard blocked moisture migration.The infiltration speed,which extends with the thickness of the layer,may help to show its the relation with the height of the water head,because the water infiltrated as unsaturated flow above semipervious layer contributes to the formation of the upper sluggish water volume.And,therefore,in the process of evaluating the water resources formerly,it is not easy to judge exactly the recharge of the river water to the groundwater,for it is necessary to emphasize the role of semipervious layer as the head boundary or the rain type flowing boundary.Thus,it can be seen that the results of our field test can be taken as an exponential support for the problem of disconnection between the river and the groundwater,thus providing a scientific basis for the recoverable resource evaluation and sustainable maintenance of the ecological function of the river water and the surrounding groundwater sources.