Laboratory Experiment on One-dimenisonal Unsteady Groundwater Flow in Phreatic Aquifer and on Darcy's Law in Unsteady State

One of the basic equations governing the flow motions through porous media is the equation of motion which is known universally as Darcy's law. This law states that the rate of flow q (water volume per unit time per unit cross sectional area) is proportional to the hydraulic gradient, this coefficient of proportionality K which is called hydraulic conductivity of porous media is said to be constant depending on both the various properties of solid matrix and fluid properties, although this law is widely applicable to the various field of ground water hydrology, however, in theoretical consideration, it seems that there are limits of applicability of the law, for example, the flow at high Reynold number, in unsaturated porous media, and also in unsteady flow this law is expected to be invalid. In this paper, the authors considered unsteady flows occurring in phreatic aquifers due to tide in littoral zone and have made laboratory experiment, in these experiment, homogeneous sand of different grain size was used as a model of porous media (d=0.35mm, d=1mm) and oscillate the water level sinusoidally at the end of sand model at a various period T, various amplitude ζ_0,and examined the variations of water level in porous media, experimental results suggests that, as the period of oscillation decrease, as grain size decrease, phreatic surface deviate from theoretical surface calculated with the hydraulic conductivity in steady state and the water permeate into the porous media to almost same degree in both sand models. Although this experimental result is, at present, not yet ready for theoretical explanation. It is expected that ground water flow through porous media, in some cases, have to be treated from reological point of view.