What are different types of intakes?
Depending on the source of water the intake works are classified as follows:
1. Lake intake
2. River intake
3. Reservoir intake
4. Canal intake
1. Lake intake: For obtaining water from lakes mostly submersible intakes are used. These intakes are constructed in the bed of the lake below the low water level so as to draw water in the dry season also.
It consists of a pipe laid in the bed of the river. One end which is in the middle of the lake is fitted with a bell mouth opening covered with a mesh and protected by a timber or concrete crib.
The water enters the pipe through the bell mouth opening and flows under gravity to the bank where it is collected in a sump well and then pumped to the De treatment plants for necessary treatment.
The advantages of this intake is De there is no obstruction to navigation, no danger from floating bodies, and no trouble due to ice.
2. River intake: Water from the river is always drawn from the upstream side because it is free from the contamination caused by the disposal of sewage in it.
These intakes are circular masonry towers of 4 to 7 m in diameter constructed along the bank of the river at such a place from where the required quantity of water can be obtained even in the dry period.
The water enters in the lower portion of the intake known as the sump well from penstocks. The penstocks are fitted with screens to check the entry of floating solids and are placed on the downstream side so that water free from suspended solids only enters the well.
The water from the sump well is pumped to the waterworks by pumps installed in the upstream portion of the intake.
3. Reservoir intake: There is a large variation in the discharge of all the rivers during monsoon and summer. Water in some rivers remains sufficient to meet up the demand, but some rivers dry up partly or fully and cannot meet the hot weather demand.
In such cases, reservoirs are constructed by constructing weirs or dams across the rivers. These are mostly used to draw water from the earthen dam reservoir.
These consist of an intake tower constructed on the slope of the dam at such a place from where intake can draw a sufficient quantity of water even in the driest period.
Intake pipes are fixed at different levels, so as to draw water near the surface in all variations of water levels. These all inlet pipes are connected to one vertical pipe inside the intake well.
Screens are provided at the mouth of all intake pipes to prevent the entry of suspended matter. The water from the well is taken to the other side of the dam by means of an outlet pipe. At the top of the intake tower, sluice valves are provided to control the flow of water.
4. Canal intake: Canal intake is a very simple structure constructed on the bank. It consists of a pipe placed in a brick masonry chamber constructed partly in the canal bank.
On one side of the chamber, an opening is provided with coarse screens for the entrance of water. The end of the pipe inside the chamber is provided with a bell mouth fitted with a hemispherical fine screen.
The outlet pipe carries the water to the other side of the canal bank from where it is taken to the treatment plants. One sluice valve which is operated by a wheel from the top of the masonry chamber is provided to control the flow of water in the pipe.
What are the factors which governs the final choice of the source of water supply?
The choice of source of water supply to a town or city depends on the following factors:
1. Location: The source of water should be as near to the town as possible. If there are both surface and ground sources available to the town the selection will be decided by considering other factors also.
If there is no river, stream or reservoirs, the city will have to depend on the ground source of water only because there is no other alternative.
2. Quantity of water: The source of water should have a sufficient quantity of water to meet up all the demands of city such as domestic, industrial, fire fighting, public, etc, throughout the year.
There should be sufficient extra quantity of water to be required in future while expansion of the city is done. The Source of water should be able to meet the maximum demand in dry weather also.
What are different types of intakes?
3. Quality of water: The quality of water should be good and can be easily and cheaply treated. It should not contain disease germs or other pathogenic bacteria which may endanger the health of the public.
Therefore as far as possible the water of the source should be wholesome, safe, and free from pollution.
4. Cost: The cost of the water supply scheme depends on many factors as a system of supply, ground levels of the city, the distance between the source and distribution system, etc.
If the water flows under the gravitational force it will be cheap, but if it is to be pumped it will be costly. Similarly, the cost will directly depend on the distance between the source of water and the city, if the distance is more it will be costly.
The selection is done based on the above points and the source which will give good quality and the quantity at less cost will be selected.
What are intakes Mention the points which should be taken into consideration in deciding the location and design of an intake for the water supply?
Intakes are structures that consist of an opening, grating or strainer through which the raw water from a river, canal or reservoir enters and is carried to a sump well by means of conduits.
Water from the sump is pumped through the rising mains to the treatment plant. The main function of intake works is to collect the water from the surface source and then discharge water so collected, by means of pumps or directly to the treatment plants.
Points to be kept in mind while selecting a site for intake works:
1. The best quality of water should be available at the site so that it can be easily and economically purified
2. For the safety of the intake structures there should not be a heavy current of water at the site.
3. The site should be such that intake can draw a sufficient quantity of water even in the worst condition when the discharge of the source is minimum.
4. The site should be easily approachable without any obstruction.
5. As far as possible the site should be near the treatment works, it will reduce the conveyance cost from the source to the waterworks.
6. At the site sufficient quantity should be available for the future expansion of the waterworks.
7. As far as possible the intake should not be located in the vicinity of the point of disposal of sewage.
If at all it becomes necessary due to unavoidable reasons to locate intakes in close proximity of the sewage disposal, a weir should be constructed upstream of the disposal point, and the intake should be located in the upstream side of the weir.
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