What is well development? Explain its various method
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Well development is very necessary to use a tubewell only construction is not make it ready to use in daily purpose. We need to drill the tubewell. In this process, finer particles are removed and improve the permeability.
Well-development improvises the quality of water and gives sand-free water obtained from the screen. It brings the maximum capacity of the well that gives maximum yield at a minimum drawdown level. It prevents bridging of sand grains from surrounding screen to gravel pack and aquifer and makes well more efficient to use. It gives an idea of the available water supply and which capacity pump and power unit need to install.
Various methods of well development are as follows:
This is the most common method used to remove fine sand particles. In this water is pumped out from the well at a higher rate than the discharge. In this case pump with variable speed is used and overpumping is done. Initially, withdrawn speed is low and increased step by step and in between speed is constant until no other sand particles come out.
Pumping should be done until its reaches maximum discharge and no further sand particles are removed. After that water pumping is stopped and allows water comes to its normal level naturally. And the process is repeated until no further particles are coming out. Initially, if speed is higher the chances of sand particles clogging the perforation in pipes are high and failure of tubewell is also high.
Here main components or parts of this process are air pipe with a smaller diameter and drop pipe with a bigger diameter. Drop pipe is also known as discharge pipe because this method is very similar to an airlift pump. Here air compressor is directly connected to the air tank and it is connected to the air pipe and quick valve.
Both the pipe is introduced to the well at the level until they reach the bottom of the first strainer pipe. the Air pipe is adjusted just like its bottom end is about 30cm above the lower end of the drop ( discharge pipe). And this adjustment is known as pumping position.
Now after positioning air compression is started for pumping and continued until sand-free water is gained. After that valve is closed to stop air compression but the compressor is on to bring the tank to full pressure. In meantime, the air pipe is lower down by 30cm below the lower end of the drop pipe.
Now again valve is opened quickly and a heavy sudden rush of air creates a surge of water. Now this situation forces well water in the aquifer to pass through the screen. This surge of water shakes the aquifer and removes unwanted fine sand particles.
Now again positioning of the air pipe is done and reversed the process of water entering in well is done which brings unwanted sand particles with it this vice versa process is done until the well is developed fully and no further sand particles are there.
A plunger is inserted into the well to repetitively create a surge. Water is coming out and moves into the soil with the downward and backward movement. a Plunger is inserted into the casing pipe provided well above the screening portion. Now this repetitive surging forces to draw fine particles in well and leave coarser ones as it is in an aquifer.
In this process sometimes dispersing agent sodium-hexa-meta-phosphate is added. This process is continued to draw sand from an aquifer and add that water to the well until no further sand particle is drawn to the well.
as per the name backwashing, water is pumped is by force to the aquifer passing through the well through the screen. It creates agitation and broke the bridging of sand particles. So backwashing is one of the effective ways to develop well. And various methods and appliances are used for backwashing water.