Fingered flow occurred in the unsaturated soil

当在细粗纹理剖面中的积水入渗过程中发生指状流时，在纹理界面(感应区)正下方形成一个薄的湿区。在湿润锋不稳定开始时，形成了一个薄的感应区，许多小手指最初就是从这个感应区长出来的。随后，这些手指中的一小部分变得占优势；它们继续生长，而其余的手指则停滞不前。两种可能的机制支配着这一过程：(1)从土壤表面的任何位置向最近的手指横向输送水分所需的压头梯度，使得干燥土壤的水分入射值在距离手指某一距离处被超过，从而导致另一根手指在该点处充分发育，以及(2)通量密度强烈放大了湿润锋或压力头的扰动波长。在前一种情况下，指间距由诱导区的性质决定，在后一种情况下，由单个手指传导的流量和供水率决定。为了研究诱导区内的流动，以及诱导区和手指之间相互作用的性质和程度，我们使用玻璃微珠多孔介质进行了二维实验。用微张力计监测感应区和手指的压头。我们在纹理界面上以不同的间隔进行小干扰(凹槽)，以触发手指的形成，并改变最初出现的手指的数量。

When fingered flow occurs during ponding infiltration in a fine-coarse-textured profile, a thin wet zone forms directly below the textural interface (induction zone). During the onset of wetting front instability, a thin induction zone develops from which many small fingers grow initially. Subsequently, a few of these fingers become dominant; they continue to grow at the expense of the remaining fingers which stagnate. Two possible mechanisms govern this process: (1) the pressure head gradient required to laterally transport water from any location at the soil surface to the nearest finger is such that the water entry value of the dry soil is exceeded at some distance from a finger, thus causing another finger to fully develop at that point, and (2) the flux density strongly amplified wavelength of perturbations of the wetting front or the pressure head. Finger spacing in the former case is determined by the properties of the induction zone, and in the latter case by the flux conducted by an individual finger as well as the water supply rate.In order to investigate flow in the induction zone, and nature and extent of the interaction between the induction zone and the fingers, we performed two-dimensional experiments using a glass-bead porous medium. Pressure heads in the induction zone and the fingers were monitored by microtensiometers. We made small disturbances (notches) at various intervals in the textural interface to trigger finger formation and change the number of fingers occurring at first.