ABSTRACT
The key parameter for designing channels in storm and combined sewer systems is the maximum flow. Its values can be obtained using advanced computational models (mechanistic models requiring a large amount of detailed data, taking into account the variability of rainfall over time) and simplified methods (catchment runoff complexity is reduced to assess concentration time, and flow in pipes is calculated assuming steady-state traffic conditions). This chapter discusses the theoretical principles of simplified models for maximum flow calculations. The key parameters describing the transformation of rainfall into surface runoff (flow reduction factor) and how it is affected by the variability of the slope of the land, as well as the type of development, are presented. The theoretical basis of methods for determining the authoritative rainfall for designing storm sewers, assuming constant rainfall intensity during rainfall episodes, is given.
