Non-uniform water and solute flow in uniform soil media

在狭窄的柱子(直径9 mm)中，观察到了不同的含水率剖面，在湿润锋面及其后面有饱和的θ凸起。均匀的风干玻璃微珠在向下一维渗透下。当施加的水通量低于饱和导水率时。根据理查兹方程，利用排水过程的水力传导函数K(θ)和保水特性θ(H)，并在移动的湿润锋上应用几乎为大气压的压力边界条件，计算了渗透含水率分布和湿润锋位置随时间的变化。结果表明，风干玻璃微珠的动态入水压力(θ(h&lt；we&gt；)为饱和含水率)确实存在，但与现代多孔介质中非饱和水流动理论相矛盾。干燥介质的这种物理性质在湿润前沿后面产生向上的负压分布，如果柱直径较大，将不可避免地产生指状流。在湿润前沿，水的含量和压力在孔隙大小的水平上应该是完全不连续的，因此达西方程不能应用于风干和饱和介质之间的界面。

Distinct water-content profiles, having saturated θ-bumps at and immediately behind the wetting front, were observed in narrow columns (9 mm I.D.) of homogeneous air-dry glass beads under downward 1D-infiltration. with applied water fluxes at lower than the saturated hydraulic conductivity. The infiltrating water content profiles and the position of the wetting front as a function of time were also calculated based on Richards' equation using an independently-measured hydraulic conductivity function, K(θ), and water retention characteristic, θ(h), of the drainage process, and by applying a pressure boundary condition, h_<we>, which is almost atmospheric pressure, at the moving wetting front. The good agreement between the calculated profiles and the observed confirms that the dynamic water entry pressure (where θ(h_<we>) is the saturated water content), does exist for air-dried glass beads, although it is in contradiction with the modern theory of unsaturated water flow in porous media. This physical property of the dry media creates an upward negative pressure profile behind the wetting front that would inevitably produce finger flow if the column diameter were larger. At the wetting front, the water content and pressure should be completely discontinuous at the level of pore size, and hence Darcy's equation cannot be applied across the interface between the air-dry and saturated media.