Last updated on August 27th, 2023 at 11:05 pm
Classification of wells Depending on the method of construction, wells are classified as follows:
1. Dug wells or percolation wells
2. Tube wells
3. Driven well or percussion wells
1. Dug wells or percolation wells: Sometimes these are also known as ‘Draw Wells’ or ‘Open Wells’. These are shallow wells which are usually confined to soft ground, sand and gravel. The diameter of these wells may be between 1m to 4m and depth may be up to 20m depending on the requirement and geological structure of the earth.
These wells are suitable for the small discharge of about 20 cu.m/hr. The walls of these wells may be constructed with precast RCC blocks, bricks or stone masonry.
Dug wells are very cheap in construction and very popular in rural areas and small towns. Wells should be disinfected frequently to avoid the risk of contamination because these wells generally are in poor sanitary conditions.
2. Tube wells: The maximum discharge which is available from the ordinary open wells, is between 4 to 6 liters/sec. due to their low-yield open wells are useful for small locality or private dwellings.
For small localities or private estates, there may be their own source of water supply.
It is not economical to install pumps in these wells, due to their low yield. For obtaining more yield tube wells are commonly used.
These wells essentially consist of blind pipes and strainer pipes, and their supply of water is from a large number of aquifers.
The depth of the tube welis may o vary from 50 to 500m. and the maximum yield from the tube well maybe about DE 200liters/sec.
The yield of the average tube well is about 50 liters/sec.
3. Driven wells or percussion well: This is a shallow well constructed by driving a casing pipe of 2.5 cm to 15cm in diameter. The lower portion of the casing pipe which is driven in the water-bearing stratum is perforated. The bottom end of the casing pipe is pointed known as drive paint or well point.
The perforated portion of the pipe is covered with a fine wire gauge to prevent the passage of soil and sand particles Ho inside the well.
The discharge of these wells is very small and these are suitable for De domestic purposes only. These pipes may be up to 12m deep; after this depth, the od water can be taken out by means of pumps.
Explain the development of wells
In the case of rocks, the capacity of the well can be increased by an explosion in the wells which will increase the cracks and passages through which water enters in the wells. In the case of the sandy stratum, the yield can be increased by packing gravel around the well.
classification of wells
In the beginning when the new well has been constructed the water which is drawn contains a large quantity of fine sand.
These sand particles will stick on the mesh of the strainer pipe and will decrease the capacity of the well.
This choking strainer can be removed by the following methods.
1. Backwashing or back blows. In this method, the water is forced in the reverse direction by means of compressed air pressure. All the sand, clay material which is sticked around the strainer pipe and choked it is agitated and removed. These are then removed by means of pumping and bailing.
2. Surging. In this method, the sand particles are removed from the filter mesh by lowering a plunger in the well and giving severe agitation of the water inside the strainer pipe.
3. Gravel packing. In this method, the gravel is packed around the strainer pipe. First, the gravel is filled between the strainer pipe and the outer casing of the tube well. Then casing is lifted upward to the top of the screen and gravel remains around the strainer pipe.
Discuss the suitability of surface water with regard to quantity and quality
Rainfall directly affects the quantity of surface water. As the rainfall is not uniform throughout the year, the quantity of surface water also has large variations.
The discharge in rivers and streams remains maximum in the rainy season and minimum in summer.
If the quantity of water in summer is not sufficient to meet the demand, it should be stored in impounded reservoirs.
In hilly areas having large lakes, the construction of artificial reservoirs is not necessary.
Surface waters mostly contain a large amounts of impurities in both suspended and dissolved forms. Surface water is contaminated by impurities while traveling on the ground.
The suspended impurities contain disease-producing bacteria, therefore, surface water should not be used before treatment.
In lakes and reservoirs, the suspended impurities settle down in the bottom, but in their bed algae, weeds, vegetables, and organic growth take place, which produces a bad smell, taste, and color in water.
Therefore this water should also be used after purification.
The sewage of towns and cities situated near the rivers is also discharged in the rivers, which pollute the river water up to a certain length.
Therefore while taking water for water supply purposes, intakes should always be installed in the upstream side, which is free from contamination due to sewage.
When water is stored for a long time in reservoirs it should be aerated and chlorinated to kill the microscopic organisms which are born in water.
Discuss the suitability of groundwater sources with regard to quantity and quality.
Groundwater is the water that percolates in the ground after rainfall. Therefore the quantity of groundwater directly depends on the rainfall.
As the rainfall is not uniformly spread throughout the year, the quantity of groundwater varies throughout the year.
In the monsoon or rainy season, the yield will be maximum and in summer it will be minimum.
The quantity of groundwater also depends on the Billunderground storage and geological formation of pervious and impervious Clostratums and the type of source of water. The yield from springs will be minimum.
The yield of water from shallow wells will depend on the depth of the water-bearing stratum and its catchment area, but it is usually less and temporary which decreases in dry weather.
The quantity of water from deep wells and tube wells is much more because water is trapped from several aquifers into these wells.
Therefore supplies of tube wells and deep wells are constant and more reliable than shallow wells and springs.
If we compare the quantity of groundwater with surface water, the more quantity is available from surface sources.
The quality of groundwater is much better than surface water, because surface water contains a large amount of suspended impurities, whereas groundwater is free from it.
But sometimes ground water dissolves minerals, salts, etc which come in its contact while in movement. The strainer action of soil also removes a large quantity of bacteria.
Therefore ground water is mostly free from bacteria but may be soft or hard depending on the dissolved impurities.
Overall ground water is good in quality but requires some treatment to remove dissolved impurities and to improve its chemical characteristics.