There are two uses for drainage system as part of existing and developing urban systems or cities. Drainage systems are in place to remove the excess water in a development. This could be floodwater and rainwater and different kinds of runoff. Drainage systems are also in place to remove wastewater effectively, and this is referred to as sewer system.
Not having a proper drainage system in place will result in flooding of low-lying areas, thereby causing property damage and health risks. An effective drainage system is the one that removes all excess water without causing inconveniences in terms of design. For example, in an area which has a lot of buildings like residences and shops, there cannot be open drains that flow through the areas.
Drainage systems can be separate for stormwater and sewers but sometimes both these inputs drain into the same underground drainage system. The advantage of having separate drainage systems is that stormwater runoff is not so dangerous that it has to be treated. This can be drained directly into water bodies. Water containing sewage and industrial wastes, on the other hand, can be extremely toxic. Therefore, they have to undergo at least a primary treatment before they can be let into water bodies.
Closed drain system and and Open drain system
There are both closed and open drains in different areas. Closed drain form a complex network underground. The primary refuse from individual areas are collected and transported to a main network which finally goes to a treatment plant. Open drain are mostly used to collect wastewater that is not sewage. Use of open drains to dispose sanitary waste is extremely unhygienic and unsafe. Use of open drains to certain degree can be acceptable. However, any place with collection of water breeds various disease-carrying pathogens.
Use of open drains is not a good option to carry wastewater even if the solids have been removed by use of septic or interceptor tanks because people can easily come into contact with it. Moreover, since they are open any excess water can result in flooding. The only advantages of using open drains is in its convenience of construction and maintenance as it is easily accessible. This is why you can still see the use of open drains in rural areas. However, in densely populated urban areas, such a system will fail in its effectiveness.
For more information on wastewater systems and treatment of wastewater check out BYJU’s – The Learning App.