ABSTRACT
In the previous chapter we looked in detail at methods to design piped storm sewers to operate effectively under defined hydrological conditions. The concept of the design storm was introduced, the choice of which determines the degree of protection afforded against sewer surcharging and flooding. What should be the engineer’s approach to the situation when design flows are exceeded to the extent that flow either emerges on to the urban surface from the underground system or can no longer enter the already full pipes? Historically, in UK and European practice, little account has been taken of this phenomenon because the system was considered to ‘have failed’. It is instructive to revisit the limited advice on this topic given in the first edition of this book (2000): ‘Generally, when piped systems are being designed, care should be taken to “define” overland flow flood routes to minimise damage to properties.’
