SOME IMPORTANT TERMS
Following are some important terms which are frequently use in the exploitation of ground water reservoir.
1. Aquifer.
- The permeable formations which permit appreciable water to move through them under ordinary field conditions are know as aquifers.
- These are geological formations made of gravel or sand, which possess lot of ground water.
2. Aquicludes.
- These are such formations which contain water in them but are not capable of transmitting.
- Clay formations are the examples of such formations.
3. Aquifuge.
- These are such formations which neither contain any water nor allow any transmission of water through them.
- Rock formations are the examples of such formations.
4. Porosity.
- Porosity is defined as the percentage of the voids present in a given volume of aggregate.
- Mathematically it can be expressed
Porosity \[= \frac{Total- volume -of -voids }{Total -volume -of-the-soil}\]
\[= \frac{V}{V}\times 100\]
- The porosity of rock and unconsolidated material may vary considerably.
- Generally porosity does not exceed 40% except in very poorly compacted materials.
- For uniform loose sand and dense sand it is 45% and 35% respectively. For clays, it may vary from 20% to as much as 75%. Porosity as worked out for soils
5. Specific Yield.
- The amount of ground water that can be extract by gravity drainage from a saturat water bearing material is know the yield.
- When it is expresse ratio of the volume of the total material drain, then it is know specific yield.
∴ Specific yield \[= \frac{Volume -of -water- obtain- by- gravity- drainage}{Total- volume -of -the -material -drain}\times 100\]
6. Specific Retention.
- The quantity of water retain by the material against the pull of the gravity is term as specific retention or field capacity.
- Specific yield or field capacity
\[= \frac{Volume -of- water- held -against -gravity -drainage}{Total -volume- of- the -material -draine}\times 100\]