Collection and distribution system of water
Intakes / Intake Structures
It is the structure built in the body of water to draw water from the source.
Source may be canal, river, dam. It is built as an integral part of the source.
Function of Intakes
- The main function of intakes is to provide highest quality of water from source.
- To protect pipes and pumps from damaging or clogging by wave action, floating bodies and submerged marine.
The intakes consists of opening, strainer or grating through which water enters and conduit conveying the water usually by gravity to a well.
Designing of intake structures
The following points must be considered while designing and locating the intake structures.
- The source of supply must be considered including the wide fluctuation in water level.
- Intake surroundings should be considered. For example depth of water around intake.
- Characteristics of bottom, navigation requirements, the effect of floods and storm to the structure and scouring in the bottom are also considered.
- The location with respect to the sources of pollution is also considered.
- The frequency of floating materials such as ice, vegetation is considered.
- Intake capacity must be large enough to meet the requirement of design discharge.
Types of intakes
Depending upon the source, the intakes may be of the following types
- Reservoir intake
The water of reservoir is likely to vary in quality at different levels. This feature makes it usually desireable to take water from about 1m below the surface.
Due to fluctuations in water level, it is desireable to have ports at various heights with gate valves. These gate valves are used to regulate water supply. When water level goes down, gate valve of lower portion is opened. The access to the ports is made by means of an operating room.
- River Intakes
A river intake consists of a port (conduit) provided with a grating and a sump or gravity well. The conduit is supported on pillars 1-2m above the bottom to prevent entry of silt. Also it is kept 1m below the top surface to avoid entry of floating particles. Velocity should be kept less than 0.15 m/s to prevent entry of small fish.
River intake structure should be constructed above the point of sewage disposal or industrial waste water disposal. River intakes are likely to need screens to exclude large floating matter. The bottom of the river intake must be sufficiently stable.
- Lake intakes
If the lake shore is inhabited, the intake should be constructed so that the danger of pollution is minimized. The intake opening should be 2.5m or more above the bottom so that the entry of silt with water is minimized. Entering velocity must be low to prevent entering of floating matter, sediment, fish or ice. Entering velocity of 0.15 m/s is usually used. Off shore winds tend to stir up sediments which will be carried for long distances. So intakes must be located at a distance not less than 600-900 meter.
The intake conduit
Intakes located at long distances from the pumps usually deliver their water to the pump well at the shore end by gravity. This will required a large pipe or conduit so that the velocity would be low. But velocity should not be low enough to allow sedimentation. The conduit may be a submerged pipe or tunnel. A submerged pipe should be protected
- By burying it in a trench
- By surrounding it with rock or
hold it in place with piling