TABLE OF CONTENTS Hydraulically, sewers in a network interact, and the mutual flow interaction must be accounted for to achieve realistic results. In designing the sewers in a network, the constraints and assumptions on sizing sewers as discussed in Sec. 14.3.4 should be noted.
The rational method is the most commonly and traditionally used method for the design of sewer sizes. As described in Sec. 14.3.4, each sewer is designed independently without direct, explicit consideration of the flow in other sewers. This can be done because to design a sewer, only the peak discharge, not the entire hydrograph, of the design-storm runoff is required. As previously explained in Sec. 14.3.4, each sewer has its own design storm. The information needed from upstream sewers is only for the alignment and bury depth of the sewer and the flow time to estimate the time of concentration for the determination of the rainfall intensity i for the sewer to be designed.
Contrarily, in simulation of flow in an existing or predetermined sewer network for urban stormwater control and management, often the hydrograph, not merely the peak discharge, is needed, and a higher level of hydraulic analysis that considers the interaction of the sewers in the network is required. This network system analysis involves combining the hydraulics of individual sewers as described in Sec. 14.3, together with the hydraulics of junctions described in Sec. 14.4.
A sewer network can be considered as a number of nodes joined together by a...
