Fingered flow occurred in the unsaturated soil

在细-粗织构剖面中，当池渗过程中发生指状流动时，在织构界面的正下方形成一个薄的湿区（感应区）。在湿锋不稳定的开始，一个薄的感应区发展，许多小手指开始生长。随后，这些手指中的一些成为主要手指；它们继续生长，而剩下的手指则停滞不前。控制这一过程的两种可能机制：(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力头梯度使得干燥土壤在距离手指一定距离处超过水进入值，从而导致另一个手指在该点充分发育；(2)通量密度强烈放大了润湿锋或压力头的扰动波长。在前一种情况下，手指间距由感应区的性质决定，在后一种情况下，由单个手指传导的通量以及供水速率决定。为了研究感应区的流动，以及感应区与手指之间相互作用的性质和程度，我们使用玻璃球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制造小的扰动（缺口）来触发手指的形成，并改变最初发生的手指数量。

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.