The aquifer under the Indus basin of Pakistan is of marine origin and the native groundwater is saline which is overlain by a freshwater layer. The upper freshwater layer is formed as a result of seepage from rivers, canals, field irrigation losses and precipitation. About 6.42 million ha area has freshwater layer of variable thickness. The exploitation of upper freshwater layer is hindered by saline water intrusion and saline upconing under pumping wells. To extract this freshwater for agricultural, domestic and industrial purposes, different techniques are being practiced in the Indus basin to minimize the saline water intrusion. These include; shallow tubewells, skimming tubewells, scavenger wells, dug wells, and radial collector wells. The adoptability of these techniques depends upon the thickness of the freshwater layer, availability of local material, availability of technical personnel for installation and maintenance, local customs and traditions, and the affordability. The present paper reviews the skimming well technologies used for extracting freshwater in various parts of the Indus basin of Pakistan, their feasibility in different part of the basin, the present status of these techniques and associated constraints.

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The fluid flow through a rough w alled rock fracture has a big influence on advection, diffusion and dispersion of solvent. On groundwater simulation, Darcy's law is basically used as a dominant equation. But in a rock fracture, the velocity of fluid flow sometimes becomes very large and there is a possibility that non-linear/non-Darcy flow occurs. In this paper, many epoxy replicas of rock fracture are prepared and some experiments of single-phase flow are carried out in order to define the specific parameters of non-linear flow behavior. The topographical shape and three-dimensional spatial distribution of aperture in a fracture are measured in detail. Water or air is injected into the fracture in order to investigate the relationship between the flux and the pressure drop gradient in the steady state condition. As a result, it is confirmed that the pressure gradient could be well approximated to a quadratic function of the flux, and that the non-linear character becomes prominent in the case where the order of Reynolds number of the flux becomes more than 1. In addition, a relatively good relationship between the specific parameter of the non-linear flow and the geometrical parameter of the fracture surface is found. The authors also newly propose a non-linear equation regressed from all the experimental results in this study and confirm the difference between this equation and some other equations that had already been suggested in past studies with regard to non-linear flow in porous media. The equation proposed in this study would be useful for a simulation study adapted to underground water since the effect of non-linearity can be estimated if the permeability in the region of a flow is defined from the experimental results of hydraulic tests.

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The theory of poroelasticity whi c h describes the coupled behavior between mechanical deformation and fluid flow is overviewed. We summarized that the responses of pore pressure and water level in wells to atmospheric loading and earth tides were formulated with this theory. In order to estimate hydraulic properties of the formations from field data, the effects of the unsaturated zone process and wellbore storage on the amplitude attenuation and phase lag of the measured data relative to the loading were discussed. Finally, we tried to show the possibilities of new methods to determine hydraulic properties through the responses of pore pressure or water level to atmospheric loading and earth tides.

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