![]() ![]() The layer above the unconfined aquifer is the water table. ► An unconfined aquifer is a rock or a layer of sand or gravel without a confining layer above it. The confined aquifers are less contaminated because they are protected by impermeable material. It takes a long time for confined aquifers to fill up as its only source is underground tributaries that travel long distances. The cone of depression in confined aquifer grows at a faster pace, but at a rate that diminishes gradually. The water in confined aquifers is under high pressure because of the aquitard. ► A confined aquifer is a rock or a layer of sand or gravel having a confining layer (aquitard or aquiclude) above it because of which the movement of water is restricted to another aquifer. ![]() There are two types of aquifers – confined and unconfined. The surrounding rock or sand layer is then saturated by ground water forming an aquifer. They are created when the water seeps in through the Earth’s surface and permeable rock till the time it reaches the impermeable rock. This is known as ‘induced recharge’.Īquifers are water bodies formed underground, and can occur at various depths. As a result, the water table below the stream or lake gets reduced, and water starts moving towards the groundwater aquifer near the well. It may also happen that the cone of depression stretches to the nearby water bodies such as lakes or streams. The amount of water available to both the wells will be reduced. If two cones of depression intersect or overlap each other, a ‘well interference’ is formed. On the contrary, if the cone comes in contact with any obstacle such as a bedrock, clay body, or edge of the aquifer, then it will decline to much greater depth. In this case, the cone of depression will not expand due to the supply of water from the lake or stream for that matter. The shape of the cone is affected when it intersects a larger water body such as a lake or stream. The farther you go from the well, lesser is the amount of decline. The size and shape of the ‘cone’ depends on various factors such as size of the cone, material and thickness of the aquifer, and amount of water in the storage. Faster the pumping and drawing out of the water, larger will be the cone of depression. The area above the cone of depression is called the ‘area of influence’. The water table surrounding the pump slopes down making a cone shaped pattern around the curved walls. ![]()
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