Groundwater is a valuable resource that is more extensively dispersed than any other mineral resource on the planet. It is replenished annually by precipitation, and the world’s total water resources are estimated to be 1.37108 million hectares metres. Only 2.8 percent of the world’s water resources are available as freshwater, with 97.2 percent being salty water-primarily found in oceans. Even though 2.2 percent of surface water is available as surface water and 0.6 percent as groundwater, 2.15 percent of surface water is available as freshwater glaciers and ice caps, which is useless. Only 0.05 percent of the world’s surface water is suitable for human consumption. Only roughly 0.3 percent of the 0.6 percent of stored groundwater can be economically retrieved. The remaining resources are unavailable as they are present at greater depth.
Groundwater hydrology may be defined as the science of occurrence distribution and movement of water below the surface of the earth.
Scopes of groundwater hydrology:
- Groundwater is defined as the water that fills all of the spaces in the geological strata. This saturation zone, which differs from unsaturated or aeration zones in which voids are filled with water and air, is significant for engineering works, geological investigations, and water supply development, and the true occurrence of water in these will be highlighted here.
- Unsaturated zones arise around the saturated zone and extend up to the ground surface, including soil moisture within the root zone of water, which is an important concern in agricultural Botany and soil science.
- Groundwater is significant in petroleum engineering; three fluid systems including gas, oil, and water, as well as two-fluid systems involving soil and water, occur frequently in petroleum production. As a result, groundwater hydrology emphasises the amount of petroleum existing in the earth depends on the type of load system.
- Groundwater is the world’s largest supply of freshwater, excluding freshwater glaciers. The amount of groundwater within 800 metres of the ground surface is 30 times that of streams, hence it is given special attention.
Vertical distribution of groundwater:
The vertical distribution of surface water is divided into the following two zones
1. Aeration Zones
The zone of aeration is located above the zone of saturation and reaches up to the ground surface. This zone contains voids that are partially filled with water and partially filled with air. The water that occurs in this zone is known as vadose water.
The zone of aeration is further divided into three main parts
1.1 Soil water zone:
The water zone in the soil extends from the ground surface to the primary root zone. When the soil in the zone is irrigated or when it rains, the soil gets saturated. Under the pull of gravity, excess water drains through the soil and enters the intermediate zone as gravitational water. After gravitational water drains out, the remaining water is known as capillary water. The water in the soil water zone is gradually depleted by operation and transpiration from vegetal growth on the ground surface, and if it is not replenished, the water content may be reduced to the point where only a thin film of moisture on the surface of the soil particle remains absorbed as hygroscopic water.
1.2 Intermediate zone:
Zone in the middle This zone normally contains non-moving vadose water, also known as pellicular water, which extends from the bottom edge of the soil water to the upper limit of capillaries. In the form of hygroscopic and capillary water, which is kept in place by molecular and surface tension forces. This zone may temporarily retain some extra water, which will flow downwards as gravitational water.
1.3 Capillary zone:
The capillary zone extends from the water table up to the limit of the capillary rise of water. The thickness of this zone is depending on the texture of soil formation.
2. Zone of saturation:
Under hydrostatic pressure, all the voids in the saturation zone are filled with water. At the top, the zone of saturation is confined by either a limiting surface of saturation known as the water table or impermeable strata. If a well penetrates a zone of saturation with the water table, the pressure is equal to atmospheric pressure. The well’s upper surface is formed by the static water level, which is at the same elevation as the water table.
