|Operation and Maintenance of Water and Sewerage Systems (Ministry of Water - Tanzania - Rwegarulila Water Resources Institute, 1999, 90 p.)|
|C. General Guide Lines in Construction of Water Structure|
1.1 Outline of Intake Structures
Intake is a well type masonry or concrete structure, whose function is provide clam and still water, free from floating matter for water supply schemes. Its main purpose is to provide cals and still water conditions so that comparatively pure water may be conveniently collected from the source. While selecting site for locating the intake, the below mentioned points should be carefully attended to:-
(i) Intake work should provide purer water so that its treatment may become less exhaustive.
(ii) Heavy water currents should not strike the intake directly. This aspect can be achieved by suitably shifting the proposed intake.
(iii) Intake should be located at such a situation where sufficient quantity of water remains available under all the circumstances.
(iv) Site should be well connected by good type of roads.
(v) Site should be such that intake should be in a position to provide more water if required to do so.
(vi) It should not be located in navigation channels, because water of such channels is generally polluted.
(vii) During floods in rivers, flood waters should not be concentrated towards the intake.
(viii) It should not be located on the curve of the river. If there is no alternative then intake should be located on the outer bank and not on the inner bank.
(ix) Intake should be located on up stream side of the town. Water will not be contaminated on this side due to sewage disposal of the city.
In spite of all the effort and precautions, problems may still be there due to natural causes. Temperature, seasonal variations in quantity and quality, wind currents etc. may affect the stability and safety of the intake works.
1.2 Design of Intake
Intake should be designed on the basis of the following considerations:-
(i) Intake should be sufficiently heavy so that it may not start floating due to upthrust of water. Also a heavy intake will not be washed away by heavy water currents.
(ii) All the forces which are expected to work on intake should be carefully analysed and intake should be designed to withstand all these forces.
(iii) The foundation of the intake should be taken sufficiently deep. This will avoid overturning of the structure.
(iv) Intake should not be constructed in a navigation channel as possible. If it has to be constructed it should be protected by cluster of piles all round from forces caused by moving ships and steamers.
(v) Strainers in the form of wire mesh should be provided on all the intake inlets. This will avoid entry of large floating objects and fishes into the intake.
(vi) Intake should be of such size and so located that sufficient quantity of water can be obtained from the intake in all circumstances.
1.3 Types of Intake
(i) River intake
(ii) Canal intake
(iii) Reservoir intake
(iv) Lake intake
Intake work = inlet (+pump for suction and transport)
Requirements inlet constructions:
* protection inlet against damages (navigation, floods)
* raw water quality considerations
- avoid coarse floating materials and fish
- quality at various depth
(swing pipe, closeable openings etc.)
Some intake works
Intake from a river:
Unprotected river intake
Pumped river water intake
River intake station
Intake from a impounded reservoir or lake
Water intake from reservoirs through hinged tubes.
Dam and intake tower for an impounded surface-water supply.
Intake by means of river bed infiltration:
Erosion of the embankment damaging the suction pipes.
Bank river intake using infiltration drains.
Pumping station in embankment water abstraction in the river bed.