Unexpected water content profiles under flux‐limited one‐dimensional downward infiltration in initially dry granular media
Unexpected water content profiles under flux‐limited one‐dimensional downward infiltration in initially dry granular media
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DOI：
10.1029/2003wr002197
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发表时间：
2004-07
影响因子：
5.4
通讯作者：
S. Shiozawa;H. Fujimaki
中科院分区：
文献类型：
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作者：
S. Shiozawa;H. Fujimaki
在向下一维渗透条件下，在低于饱和渗透系数的条件下，在均匀风干玻璃微珠的窄柱(9 mm直径)中观察到不同的含水率剖面，在湿润锋面及其后面有饱和的θ凸起。根据Richards方程，利用独立测量的排水过程的水力传导函数K(θ)和水分保持特性θ(H)，并在移动的湿润锋处施加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。计算值与观测值的良好一致性证实，风干玻璃微珠确实存在动态入水压力HWE(其中θ(HWE)为饱和含水率)，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形成向上的负压分布，如果柱直径较大，则不可避免地会产生指状流。在润湿前沿，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 wetting fronts, were observed in narrow columns (9 mm ID) of homogeneous air‐dried glass beads under downward one‐dimensional 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, hwe, 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 hwe (where θ(hwe) is the saturated water content), does exist for air‐dried glass beads, although it is in contradiction to the modern theory of unsaturated water flow in porous media. This physical property of 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‐dried and saturated media.