Which one of the following is INCORRECT about design consideration of sewers system?
1
The quantity of sanitary sewage and industrial waste is proportional to the water supplied by public supply
2
A deep of about 12 mm is given in a manhole where only direction changes
3
Sanitary sewers should be designed for self-creating velocity of at least 60 cm/sec and combined sewers for a velocity of 75 to 90 cm/sec
4
Sewers in the combined system should be capable of carrying at least two times the Dry Weather Flow (D.W.F.) in addition to stormwater