Fingered flow occurred in the unsaturated soil

当指状流发生在细-粗纹理剖面的积水入渗过程中时，在纹理界面（诱导区）正下方形成一个薄的湿区。在润湿锋不稳定的发病过程中，一个薄的感应区的发展，许多小手指最初生长。随后，这些手指中的一些变得占主导地位;它们继续增长，而其余的手指则停滞不前。两种可能的机制支配这一过程：（1）将水从土壤表面的任何位置横向输送到最近的指状物所需的压头梯度使得在距指状物一定距离处超过干燥土壤的水进入值，从而导致另一个指状物在该点处完全形成，以及（2）通量密度强烈放大了润湿锋或压头扰动的波长。前一种情况下的指间距由感应区的特性决定，后一种情况下的指间距由单个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，我们使用玻璃珠多孔介质进行了二维实验。通过微张力计监测感应区和手指中的压头。我们在纹理界面的不同间隔处进行小扰动（缺口），以触发手指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.