Drainage is the removal of excess water from the land (either used or in the form of rainwater). It must be distinguished from flood control, which is the prevention of damage as a result of the river overflowing. There are two types of systems adopted for the collection of sewage. Separate sanitary and combined system. In the separate sanitary system, there is a separate sewer that collects the domestic, commercial and industrial wastewater and discharges it, while a separate sewer collects the rainwater and discharges it separately. In the combined system, both rainwater and domestic water are transported through the same network of pipes.
Sanitary sewers should have a self-cleaning rate of (.6-1
millisecond). This self-cleaning speed is achieved by placing the drain on a steep slope. Manholes should be placed at 100-120 m intervals in order to maintain and repair the sewer. It should be noted that sewage in the sewer is generally transported by gravitational force rather than by mechanical means (pumping) for convenience. That is why in the installation of sewer pipes; the topography of the area must be well understood.
Rainwater flow can be estimated using .278CIA, where C is the runoff coefficient, I is the intensity of rainfall, and A is the catchment area. C is usually obtained from the table, which is a function of the factors that affect infiltration. From the rainfall data, I can estimate it.
A can be estimated using a planimeter or by overlaying graph paper to scale on the map and look at the grid that is within the boundaries of the map. Wastewater from industry, shopping centers and domestic uses is usually estimated knowing the amount of wastewater discharged by users through the use of a questionnaire and personal interview. The population of people and the number of industries must be taken into account for this estimate.
General steps in culvert design include:
- Establish a complete map of the area that includes the outline of the road, topography and public services.
- Drains are shown with a single line with arrows to indicate direction.
- Culverts are shown with a point at all their required locations such as joints and their midpoint of 100-120 m range
- The culverts are designed to follow the natural topography.
- Sewers are mostly branch networks
- Sewers or drains are usually found along the road.
- The design approach for culverts is as follows;
- Estimate the endowment constant and select the slope
- Calculate the section factor
- Get the best hydraulic section whether rectangular or trapezoidal
- Check the satisfaction of the minimum speed.
- Addition of adequate freeboard to prevent overflow
The wastewater disposal may or may not be treated. However, treatment is usually by biological method. Sewage disposal is of great importance for economic growth. The treated or untreated waste could be used as a source of irrigation, supplement the flow of a stream or river, and could be used as a source of groundwater recharge.
It is obvious in the cities of developing countries that most construction industries do not take notice of the entire process mentioned above. As a result, rainwater follows the drains that are not specified for them or overflows the drains there causing erosion. On the other hand, some of the rainwater stagnates in the drains there, becoming a breeding ground for mosquitoes and toads. This could result in an increase in malaria and water-related diseases in the vicinity. All this is because; Most of the governments of these cities have not yet understood the importance of drainage systems and the role they play in socio-economic development.