ABSTRACT
Combined sewer systems have already been discussed extensively in Chapter 2. A significant percentage of sewer systems in many countries are combined, which makes them an important topic in urban drainage. Indeed, there are few parts of this book that do not relate in some way to combined sewers. The essential features of combined sewers are that they carry both wastewater and stormwater in the same pipe, that it is not usually feasible for this pipe to be designed to carry the full combined flow at all times to treatment, and that, therefore, at high flow-rates it is necessary for some of the flow to be discharged to a watercourse at a combined sewer overflow (CSO), as illustrated in Fig. 2.2. This chapter deals with the special characteristics of combined sewers, and in particular with combined sewer overflows.
