When the ground surface is below the potentiometric surface this is the result?
If the potentiometric surface lies above ground surface, a flowing well will result. It should be noted that a confined aquifer becomes an unconfined aquifer when the potentiometric surface falls below the bottom of the upper confining bed (Todd, 1959). At this point, compression of the aquifer may occur.
What does it mean if the potentiometric surface does not reach above the ground surface?
What does it mean if the potentiometric surface does NOT reach above the ground surface? The aquifer does not have any recharge into it and thus is dry. There will never be any artesian wells or springs associated with the aquifer. It will not be possible to pull water out of the aquifer from any type of well.
How do confining layers affect groundwater movement?
Material that slows down the flow is called a semi-confining layer, while material that stops any flow from passing through is a confining layer. An aquifer’s porosity and permeability determine how good a source of water it is and the direction and speed of water flow.
Does water flow from higher head to lower head or lower head to higher head?
The pressure head represents the energy due to pore fluid pressure, and the elevation head represents the gravitational energy arising from elevation. Water flows from high to low hydraulic heads.
Which condition may exist when the potentiometric surface is above ground level?
For groundwater “potentiometric surface” is a synonym of “piezometric surface” which is an imaginary surface that defines the level to which water in a confined aquifer would rise were it completely pierced with wells. If the potentiometric surface lies above the ground surface, a flowing artesian well results.
Why are unconfined aquifers more likely to be contaminated than confined aquifers?
water from unconfined aquifers is much more likely to be contaminated with chemicals released by human activities, since it has a direct connection with surface. areas where soil has been baked hard by drought cannot soak up water from heavy rainfall- instead it runs off into storm swears or nearby streams.
What is confined aquifer and unconfined aquifer?
A confined aquifer is an aquifer below the land surface that is saturated with water. A water-table–or unconfined–aquifer is an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.
Is a confining layer beneath the earth’s surface that restricts groundwater flow?
Large amounts of water are stored beneath the earth’s surface in aquifers. Confined aquifers have non-porous layers above and below the aquifer zone. The non-porous layers hold water and restrict water movement. Such layers are referred to as aquitards or aquicludes.
Do unconfined aquifers interact with surface water?
Unconfined aquifers occur near the Earth’s surface so they may interact better to the processes that occur near or above land surface. Because unconfined aquifers are exposed to the atmosphere, they may interact with surface water features, such as rivers and lakes.
What controls the direction that water and pollutants move below the water table?
What factors affect the flow direction of the water below the water table? Groundwater flows from regions of recharge to those of discharge, driven by gravity and water pressure. Groundwater flow is very slow compared to currents in surface water, generally moving at less then one and one-half meters per day.
Does water flow from high elevation to low elevation?
Stream and River Erosion As a stream moves water from high elevations, like mountains, towards low elevations, like the ocean, which is at sea level, the work of the stream changes.
What are confined and unconfined aquifers?
Confined aquifers with upper impermeable layers where recharge only occurs from precipitation where the water-bearing formations outcrop at land surface. 2. Unconfined (phreatic) aquifers in wet regions where rainfall is high and evapotranspiration is low.
How do you withdraw water from a confined aquifer?
Pumping can withdraw water not only from a confined aquifer but also from an adjoining confining unit, either through vertical leakage from overlying aquifers or from storage within the confining unit, when the hydraulic head in the pumped aquifer becomes less than that in the confining unit.
What is the specific storage of an aquifer?
In turn, the specific storage of the aquifer is defined as: where b is the aquifer thickness, β P is the matrix compressibility, and βW is the compressibility of water. In an unconfined aquifer, water is primarily yielded by desaturation.
How do you find the specific discharge from an aquifer?
Imagine that this boundary is a cylinder of radius r centered on the well. The height of the aquifer is b, so the surface area that flow goes through on this cylinder is 2πrb. The specific discharge in the negative r direction (towards the well) anywhere on this cylindrical surface is − qr = K lpar dh / dr).