Drainage is the disposal of excess water on land (either used or in form of storm water). It must be suited from flood operate which is the arresting of damage as a corollary of overflow from river. There are two type of system adopted for waste water collection. Cut off hygienic and combined system. In Cut off hygienic system, there is a Cut off sewer that collects the household, market and market waste water and disposes them while a Cut off sewer collects the storm water and disposes it separately. In the combined system, both the storm water and domestic water are conveyed through the same pipe network.
Sanitary sewers should have a self cleansing velocity of (.6-1
m/s). This self cleansing velocity is achieved by laying the drain on a steep slope. Manholes should be settled at interval of 100-120m for the purpose of maintaining and servicing of the sewer. It should be noted that waste water in the sewer are ordinarily portable by gravitational force rather than mechanical means (pumping) for suitable sake. This is why in laying sewer pipes; the topography of the area should be well understood.
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The storm water flow can be estimated by .278Cia where C is the coefficient of runoff, I is the rainfall intensity and A is the catchment area. C is ordinarily got from table which is a function of factors that influence infiltration. From rainfall data I can be estimated.
A can be estimated by using planimeter or superimposing scaled grid paper on the map and note the grid that fall within the boundary of the map . The waste water from industry, market centers and domestic uses are ordinarily estimated by knowing the quantity of waste water the users' discharges through the use of questionnaire and personal interview. The citizen of citizen and whole of industries should be noted for this estimation.
The whole steps in layout sewers include:
Establish whole map of the area including road contour, topography and utilities
Drains are shown with a single line with arrows for direction
Manholes are shown with a dot at all its principal locations as the junctions and its intermediate point of 100-120m interval
Sewers are form to corollary natural topography
Sewers are mostly branch network
Sewers or drains are ordinarily settled along the road
form advent for sewers is as follows;
estimate manning constant and opt slope
Compute the section factor
Get the best hydraulic section whether rectangle or trapezoid
Check the pleasure of minimum velocity
addition of enough freeboard to avoid overflowing
The disposal of the waste water could be treated or not treated. However, the treatment is ordinarily by biological method. The disposal of waste water is of immerse prominent for economic growth. The treated or untreated waste could be used as a source of irrigation, supplement stream or river flow and could be used as a source of recharge for ground water.
It is certain in the cities of the developing countries that the most of building industries do not take note of all the above mentioned process. As a corollary storm water follows drains that are not specified for them or overflows the drains there by causing erosions. On the other hand, some of the storm water are stagnant in the drains there by becoming a breeding place for mosquitoes and toads. This could corollary in growth of malaria and water linked disease in the vicinity. All this is because; most government in such cities have not yet understand the prominent of drainage systems and the role it plays in social- economic development.
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