Non-uniform water and solute flow in uniform soil media

在窄柱（9 mm I.D.）中观察到不同的含水量分布，在润湿前沿和紧接着润湿前沿之后具有饱和θ-隆起。均匀的空气干燥玻璃珠在向下的一维渗透。在低于饱和导水率的情况下施加水通量。根据理查兹方程，采用独立测量的排水过程的水力传导系数K（θ）和持水特性θ（h），并在移动湿润锋处施加接近大气压的压力边界条件h，计算了入渗含水率剖面和湿润锋位置随时间<we>的变化。计算结果与实测值吻合较好，证实了风干玻璃微珠确实存在动态入水压力（θ（h_<we>）为饱和水含量），尽管它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润湿前沿后面产生向上的负压分布，如果柱直径较大，则将不可避免地产生指状流。在湿润锋处，含水量和压力在孔径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.