Permeability and seepage

As a result of the hydrological cycle (rainfall, infiltration) it is inevitable that the pores between soil particles will fill with water until they become fully saturated. There then exists a zone of saturation below ground level the upper surface of which is called the water table. The water table generally follows the shape of the ground surface topography but in a subdued manner. A sloping water table surface is an indication of the flow of groundwater or seepage in the direction of the fall. Water tables change with varying rates of infiltration so that with high winter rainfall they can be expected at high levels and at lower levels in drier summers. The pores of permeable deposits such as sands will fill up easily and also allow this water to flow out easily. Such permeable deposits are called aquifers (bearing water). The pore spaces in a clay will also contain water but these pore spaces are so small that flow of water is significantly impeded making a clay impermeable. Clay deposits will then act as aquicludes (confining water). The location and state of groundwater in soil deposits is often determined by the stratification of sand–clay or permeable–impermeable sequences.