This presentation on aquifer properties by ACWADAM deals with the storage and transmission properties of aquifers. The two functions of an aquifer, accumulation of water (storage) and flow of water (transmission) are discussed. The permeability or hydraulic conductivity of the aquifer which allows water to flow towards the well is described. 

Groundwater related work in a watershed requires at least a broad understanding of the relationship between watershed and the underlying aquifers and an idea about the aquifer properties. In order to understand what happens in the well and the aquifer during pumping, the presentation deals with an understanding of some common terms related to aquifer properties –

• The permeability or hydraulic conductivity of the aquifer allows water to flow towards the well.
• The storage of groundwater in the aquifer due to the porosity of the rocks/rock material provides storage of water to feed the well through permeable zones.
• The storage capacity of the aquifer depends on the porosity of the rock formation.
• The scale of an aquifer may be quite local or may extend regionally (under a large area).
• The storage function of the aquifer is related to two processes.
  • Addition to aquifer storage (recharge)
  • Reduction in the aquifer storage (discharge)
• Changes in the aquifer storage (due to recharge and discharge) results in a change in the water table or potentiometric surfaces.
• Storativity is the capacity of the aquifer in terms of the quantity of water that it can take in or release. In other words, it is the quantity of water in aquifer storage per unit surface area per unit change in head. It is expressed in percentage or fraction.
• The change in head is either the change in the water table or the potentiometric surface with respect to datum.
• The specific quantity of water released by saturated rock under the influence of gravity is specific yield (Sy) of the rock.
• In unconfined aquifers the storativity is equivalent to the specific yield of the rock formation.
• Specific yield can be used to calculate the changes in aquifer storage of an unconfined aquifer and is most important in developing water balances.

This presentation is part of the training modules on planning, development and management of groundwater with special reference to watershed management programmes by ACWADAM. Please write to ACWADAM at acwadam@vsnl.net for sourcing these presentations.