Fundamental Investigation of Saturated Flow Through Porous Media with Macropores

Abstract

Among the foremost issues in the area of hydrological sciences is the estimation of infiltration fluxes and the associated contaminant exchange from the near-surface to the ground water table. While the simplest and traditional conceptualization of infiltration is that of a uniform, downward-advancing wetting front in a homogeneous medium, field observations indicate that it is highly nonuniform. Macropores are ubiquitously found in the subsurface and have a significant impact on hydrological processes. The presence of macropores leads to preferential water flow through both unsaturated and saturated soils, which are difficult to predict. In the first part, the effect of macropore density and connectivity on water flow in porous media was studied by comparing the hydraulic conductivity of different distributions of artificial macropores. The effective hydraulic conductivity was measured by constant head method, and the artificial macropores are prepared with stainless steel mesh reinforcements used in co-axial cables. The result shows that as macropores become increasingly discontinuous, the hydraulic conductivity approaches the value of no-macropore media. Also, the extent of effects of macropore connectivity on the hydraulic conductivity decreases with coarser media. Since the velocity in macropores could be large in certain cases, we have also investigated the validity of Darcy’s Law under high Reynolds number conditions. Ergun equation is one of the most common empirical formulations that used to model porous media flow in high Reynolds number systems. In this study, we have formulated a new form of Ergun equation, identified as the inverted Ergun (IE) equation, which is more appropriate for modeling hydrological problems. The validity of the IE equation has been tested by using various forms of error analyses and also by using experimental datasets. The results show that IE equation is a useful alternative for modeling high velocity flows in porous media systems.