As combined sewer systems carry both sanitary sewage and storm water, y overflow when storm water rate is high during rainy season. This causes water pollution. However, se sewer systems are still used by older cities located primarily in Northwest, Norast, and Great Lakes regions.

In separate sewer systems, as two sets of sewers are used, quantity of wastewater flow will also be less in sewers. Hence size of sewers will be small. As two sewers are used, it doesn?t prove to be economical.

Sewer System Management plan is mainly used to maintain and improve condition of collection system infrastructure in order to provide reliable service for future. Reducing size of sewers may lead to overflow conditions during periods of high storm.

As combined systems consist of a single large sewer to carry both sanitary sewage and storm water, it is easy to clean and choking problems are avoided. As size of sewers is large, it becomes difficult to handle and transport sewer pipes.

8 ft/sec is maximum allowable velocity in public water mains. Increasing velocities beyond this limit may lead to hydraulic surges which lead to excessive pressure in water systems.

Combined systems consist of both storm water and sanitary sewage. Hence it becomes costly for as treatment for both are done. In separate systems, required amount of treatment is done for stormwater and sanitary sewage separately.

The bottom of trench is kept at a width of 15 cm and top as 60 cm. This is to facilitate joining of pipes. When ground is not hard enough, it becomes necessary to insert pipes on harder surfaces. Hence sewers are embedded in concrete surfaces.

SSMP is a document used to manage wastewater systems effectively. Hence one of goals of Sewage System Management Plan is to minimize number and impact of sanitary sewer overflows that occur in few regions.

The first formula is used to calculate infiltration area. The third formula is used to calculate load of wastewater. The fourth formula is used to calculate rate of flow. The second formula is used to calculate velocity of flow inside of a pipe (V) where Q stands for flow rate of water inside pipe and D stands for pipe diameter (inside).

The minimum flow velocity is 3 ft/sec to keep foreign particles moving. In certain mains higher velocity is required such as fire hydrants. If velocity is increased higher than limits, foreign particles moving with higher speeds may cause abrasion against inner walls of sewer which leads to wear and tear of sewers.