Groundwater Occurrence

Groundwater Occurrence

Groundwater accounts for nearly 95 percent of the nation’s fresh water resources. It can stay underground for hundreds of thousands of years, or it c come to the surface and help fill rivers, streams, lakes, ponds, and
wetlands. Groundwater is stored in the tiny open spaces between rock and sand, soil, and gravel. Groundwater is found in two zones. The unsaturated zone, immediately below the land surface, contains water and air in the open spaces, or pores. The saturated zone, a zone in which all the pores and rock fractures are filled with water, underlies the unsaturated zone. The top of the saturated zone is called the water table.

 Hydrological Cycle

Hydrology can not be without water and so can never be hydrogeology without water and geology. Hydrologists use the term groundwater to represent water in the zone of saturation. Practically, all groundwater constitutes as a part of the hydrological cycle. However, a little amount of water may enter the cycle from other sources (e.g., magmatic water). The hydrological cycle is the series of transformations that occur in the circulation of water from the atmosphere to the surface and into the subsurface regions of the earth, and then back from the surface to the atmosphere. Precipitation becomes surface water, soil moisture, and groundwater. Groundwater circulates back to the surface, and from the surface all water returns to the atmosphere through evaporation and transpiration. The main source of groundwater is precipitation. when rain falls, some of the water will move as runoff whereas the other part will move downwards via infiltration and percolation processes. The infiltrated water, upon meeting the soil moisture deficiency percolates deeply and becomes groundwater. This process is called recharge. The formation below the earth’s surface is divided into two zones by an irregular surface called the water table. At all points on the water table, the pressure is atmospheric. The zone between the ground surface and the water table is called the unsaturated zone or the vadose zone. In the zone below the water table all the soil pores are completely filled with water, hence referred to as the zone of saturation or the phreatic
zone.

                                                                      Hydrological Cycle




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