TABLE OF CONTENTS One of the most useful pieces of information to solve urban drainage problems is knowing the flow carrying capacity of the channel or sewer. There are actually various kinds of capacities. There is the capacity for a single sewer. There is the capacity of the sewer net- work as a system which usually is different from the capacity of individual sewers. For an open channel, often the maximum steady uniform flow that the channel can carry without spilling over bank is quoted as its capacity. For a sewer, the just about full gravity (open-channel) steady uniform flow is usually quoted.
In fact, for a subcritical open-channel flow, the discharge that the channel can carry depends on the downstream water level. For a channel with a range of possible exit water levels, this would require repeated backwater profile computations. For a channel or sewer network that has a number of connected channels, the number of backwater computations can easily become very large making it nearly impossible, if not impractical, for the network capacity determination. Yen and Gonz lez (1994) developed a method to summarize the backwater information of a channel into a hydraulic performance graph from which the network capacity can be determined. Knowing the channel or sewer capacities allows a new approach to solve flood drainage problems by separating them into two parts: The demand part of how much water needs to be drained, which is essentially a hydrology problem. The supply part of how much...
