Flushing Manholes

Where it is not possible to achieve self-cleansing velocities due to the flatness of the gradient especially at the top ends of the branch sewers, which receive very little flow, it is essential that some form of flushing device be incorporated in the system. This can be done by providing an overhead water tank from which connections are made through pipes and flushing hydrants to rush water to the sewers. Flushing can also be accomplished by the use of a fire hydrant or tanker and hose. Approximate quantities of water needed for flushing are as given in Table 8 below.

                 Table 8: Approximate Quantities of Water Needed for Flushing (CPHEEO, 1993)