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An unconfined aquifer has no impermeable barrier immediately above it, such that the water level can rise in response to recharge. A confined aquifer has an overlying impermeable barrier that prevents the water level in the aquifer from rising any higher. An aquifer in the same geologic unit may be confined in one area and unconfined in another.
For a confined aquifer or aquitard, storativity is the vertically integrated specific storage value. Specific storage is the volume of water released from one unit volume of the aquifer under one unit decline in head. This is related to both the compressibility of the aquifer and the compressibility of the water itself.
In a confined aquifer, the upper surface of water is overlain by a layer of impervious rock, so the groundwater is stored under pressure. [2] Aquifers receive water through two ways, one from precipitation that flows through the unsaturated zone of the soil profile, and two from lakes and rivers. [2]
Download as PDF; Printable version; In other projects ... The following is a partial list of aquifers around the world. A category-based list of aquifers is also ...
The above figures simulate possible coastal aquifers. In reality, it is complex. Due to complex geology - non-uniform rock layers and weathering, both confined and unconfined aquifers can be found within a coast. It is possible to have multiple confined aquifers at the bottom and an unconfined aquifers at the top of a coast.
When trapped water in an aquifer is surrounded by layers of impermeable rock or clay, which apply positive pressure to the water, it is known as an artesian aquifer. [1] If a well were to be sunk into an artesian aquifer, water in the well-pipe would rise to a height corresponding to the point where hydrostatic equilibrium is reached.
Hence the actual amount of water that can be extracted from the unit volume of aquifer by pumping or under the action of gravity is called as specific yield. The fraction of water held back in the aquifer is known as specific retention. Thus it can be said that porosity is the sum of specific yield and specific retention.
The gif shows how fault, induced by seismic events, propagates into a confined aquifer. [31] And fluid of the confined aquifer fills the fault zone and precipitates minerals. [31] Mineralization blocks further fluid movement. Repeated seismic events can deposit economically vulnerable vein structured ore deposit.