PROPERTIES OF AQUIFERS
In addition to porosity and permeability, there are several parameters related to water flow through aquifers and layers. The key parameters are transmissivity and storage coefficient, which are known as aquatic parameters.
Transmissivity
Transmissivity is defined as the rate of water flow per unit square meter per day per unit width (unit width) of the aquifer and the total saturated thickness of the aquifer under the unit hydraulic gradient.
Transmissivity has dimensions of t m 2 / day. Values of T 2 range from <12.4 to 12,400 m / day. Previously, the co-efficient term of transmission was in use. The concept of diffusion is best in confined aquifers but in uncontaminated aquifers, the saturated thickness of aquifers varies with time, The dispersion varies accordingly.
Propagation is expressed as a measure of the communication ability of aquifers Groundwater is closely related to and through its full saturated thickness Potential yield of wells. Transmissivity is defined as the product of hydraulic Conductivity and saturated thickness of aquifers.
This is a highlight Property to understand because a given area has a high value of hydraulic conductivity but a small saturated thickness, resulting in limited yields of Groundwater (Figure 13.9).
Coefficient of storage/storage (S)
The ability of aquifers to collect water is expressed as a designated coefficient S. When the water is collected or released the head in the aquifer indicates a change in the volume of storage in the aquifer.
Storativity is defined as the volume of water aquifer releases or consumes per unit of storage
The surface area of aquifers per unit of the area changes the head component normal to that surface.
Thus, the storativity is equal to the amount of water taken from each vertical column of elevated aquifers hand the area of the base of the unit when the head collapses from one unit (Fig. 13.10).
Storativity
S = water volume / (unit area) (unit head change) 32 = m / (m) (m) Storativity is a dimensionless parameter.
In compressed aquifers, storativity is a result of the compaction of the aquifer and the expansion of the water involved, resulting in reduced pressure due to pumping. The value of
S 0.00001–5–3 (10) to 0.001 (10) for limited aquifers.
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Specific Yield (Sy)
When water is drained from a saturated material by the force of gravity, only a fraction of the total volume stored in its pores is released. In aquifers, some water is held by molecular attraction and cannot be excreted freely under gravity.
This retention water is designated as specific retention. However, water that can be drained under a force of gravity is called a specific yield. The specific yield can be defined as the ratio of the volume of water that the rock gives to its own volume (Figure 13.11).
Specific Yield =
The amount of water drained by gravity
The total volume of aquifers
Specific retention = Amount of retained water Total volume of aquifers
Specific yield + specific retention = porosity
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