A rock with good porosity can hold a lot of groundwater. For groundwater to be able to get into a rock with good porosity it must also have good permeability. For a rock to be permeable and for water to move through it, the pore spaces between the grains in the rock must be connected.
How does porosity and permeability affect the rate of groundwater flow?
Porosity is a description of how much space there could be to hold water under the ground, and permeability describes how those pores are shaped and interconnected. This determines how easy it is for water to flow from one pore to the next.
How does porosity affect groundwater?
The total volume of open space in which the groundwater can reside is porosity. Porosity determines the amount of water that a rock or sediment can contain. In sediments or sedimentary rocks the porosity depends on grain size, the shapes of the grains, and the degree of sorting, and the degree of cementation.
How does permeability and porosity of soil affect the formation of groundwater?
Porosity ultimately affects the amount of water a particular rock type can hold and depends on a couple of different factors. The ability of the ground water to pass through the pore spaces in the rock is described as the rock's permeability. Permeable layers of rock that store and transport water are called aquifers.
What is meant by porosity and permeability and how do they affect the groundwater storage?
While porosity is the percent of open spaces or voids within a volume of soil or rock, permeability is the rate of water movement through interconnected pores within soil or rock. Porosity of rocks describes the rocks' capacity to hold water. Soil porosity is affected by soil composition, such as particle size.
Why is porosity and permeability important?
The porosity and permeability of rocks is important in determining which rocks will make a good reservoir. A rock that is both porous and permeable would make a good reservoir rock as it allows oil and gas to move up through the pores in the rock closer to the surface where it can be extracted.
Does porosity affect speed at which groundwater flows?
For example, oil has a higher viscosity than water and therefore flows more slowly through a medium. The porosity and permeability of the media also affects water speed. The more permeable the medium, the faster water will flow through it. In such cases, engineers say that water has high hydraulic conductivity.
What is the relationship between porosity permeability and good aquifers?
Permeability is a measure of the interconnectedness of pores. The connection between pore spaces allows groundwater to flow through the sediment or rock. The combination of water storage (porosity) and flow (permeability) makes a good aquifer—a rock unit or sediment that contains usable groundwater.
What is the relationship between porosity and permeability?
More specifically, porosity of a rock is a measure of its ability to hold a fluid. Mathematically, it is the open space in a rock divided by the total rock volume (solid and space). Permeability is a measure of the ease of flow of a fluid through a porous solid.
How does porosity affect the movement of water?
Well, the more porous the sediment, the more water it can hold. The more water it can hold, the more water can move down into the ground!
What porosity makes a good aquifer?
10-30%"Good aquifers" tend to have values of effective porosity in the range of 10-30%, although examples of higher and lower values can be found. Figure 1 illustrates the relationship among the types of porosity and the volume of water in storage.
Why is permeability of soil important?
Soil permeability is the property of the soil to transmit water and air and is one of the most important qualities to consider for fish culture. A pond built in impermeable soil will lose little water through seepage. The more permeable the soil, the greater the seepage.
What is the permeability of water?
Water permeability is a key feature of the cell plasma membranes and it has seminal importance for a number of cell functions such as cell volume regulation, cell proliferation, cell migration, and angiogenesis to name a few.
How does porosity relate to aquifer?
The porosity of the aquifer is the volume of void space to the total volume, typically expressed as a percentage. Effective porosity is the space available for fluid to flow, and is calculated as the volume of interconnected void space to the total volume, typically given as a percentage.
What is the relationship between aquifers and porosity?
The combination of water storage (porosity) and flow (permeability) makes a good aquifer—a rock unit or sediment that contains usable groundwater. Well-sorted sediments (i.e., uniform grain size) have higher porosity, because smaller sediment particles do not fill in the spaces between the larger particles.
What porosity makes a good aquifer?
10-30%"Good aquifers" tend to have values of effective porosity in the range of 10-30%, although examples of higher and lower values can be found. Figure 1 illustrates the relationship among the types of porosity and the volume of water in storage.
What factors affect porosity?
The principal factors that control porosity are grain size and shape, the degree of sorting (a well-sorted sediment has a narrow range of grain size), the extent to which cement occupies the pore spaces of grains and the amount of fracturing.
What is the pore space of an aquifer?
The pore space of an aquifer is the spaces or voids between the solid material. The porosity of the aquifer is the volume of void space to the total volume, typically expressed as a percentage.
Does grain size affect porosity?
Porosity is highly dependent upon the arrangement, the shape, and the size of the material. However the diameter of the grain size does not affect porosity, since it is the ratio of open space volume to total volume.
Is primary or secondary porosity?
Porosity can be deemed either primary or secondary. Void spaces in primary porosity formed at the time the geologic material was created. Void spaces in secondary porosity formed after the rock was created. Examples of secondary porosity include fractures, solution-created channel ways, etc.
What is the property of permeability?
Permeability is another intrinsic property of all materials and is closely related to porosity. Permeability refers to how connected pore spaces are to one another. If the material has high permeability than pore spaces are connected to one another allowing water to flow from one to another, however, if there is low permeability then the pore spaces are isolated and water is trapped within them. For example, in a gravel all of the pores well connected one another allowing water to flow through it, however, in a clay most of the pore spaces are blocked, meaning water cannot flow through it easily.
What is the porosity of a material?
Porosity is an intrinsic property of every material. It refers to the amount of empty space within a given material. In a soil or rock the porosity (empty space) exists between the grains of minerals. In a material like gravel the grains are large and there is lots of empty space between them since they don’t fit together very well. However, in a material like a gravel, sand and clay mixture the porosity is much less as the smaller grains fill the spaces. The amount of water a material can hold is directly related to the porosity since water will try and fill the empty spaces in a material. We measure porosity by the percentage of empty space that exists within a particular porous media.
What is the opposite of an aquifer?
The other type is a confined aquifer that has an aquitard above and below it. An aquitard is basically the opposite of an aquifer with one key exception. Aquitards have very low permeability and do not transfer water well at all. In fact, in the ground they often act as a barrier to water flow and separate two aquifers. The one key exception is that aquitards can have high porosity and hold lots of water however, due to the their low permeability they are unable to transmit it from pore to pore and therefore water cannot flow within an aquitard very well. A good example of an aquitard is a layer of clay. Clay often has high porosity but almost no permeability meaning it is essentially a barrier which water cannot flow through and the water within it is trapped. However, there is still limited water flow within aquitards due to other processes that I won’t get into now.
How do aquifers get recharged?
Aquifers are replenished when surface water infiltrates through the ground and refills the pore spaces in the aquifer. This process is called recharge. It is especially important to ensure that recharge is clean and uncontaminated or the entire aquifer could become polluted. There are two main types of aquifer.
What is it called when water is pumped out of a rock?
When a water-bearing rock readily transmits water to wells and springs, it is called an aquifer . Wells can be drilled into the aquifers and water can be pumped out. Precipitation eventually adds water ( recharge) into the porous rock of the aquifer.
What are some examples of aquifers?
Good examples of aquifers are glacial till or sandy soils which have both high porosity and high permeability. Aquifers allows us to recover groundwater by pumping quickly and easily. However, overpumping can easily reduce the amount of water in an aquifer and cause it to dry up.
What is confined aquifer?
Sometimes the porous rock layers become tilted in the earth. There might be a confining layer of less porous rock both above and below the porous layer. This is an example of a confined aquifer. In this case, the rocks surrounding the aquifer confines the pressure in the porous rock and its water. If a well is drilled into this “pressurized” aquifer, the internal pressure might (depending on the ability of the rock to transport water) be enough to push the water up the well and up to the surface without the aid of a pump, sometimes completely out of the well. This type of well is called artesian. The pressure of water from an artesian well can be quite dramatic.
