Uncertainty in design and management of sewer systems

Loads acting on urban drainage systems are intrinsically uncertain, and often known with limited details given their physical complexity. External loads include climate variables, which have a naturally mutable behavior, exacerbated by climate change. Other system variables, such as roughness of surfaces and soil permeability, are normally unknown and only partially measurable. Additional sources of uncertainty derive from the transposition of the physical system into numerical models, routinely used to make predictions about real systems and their design and management. We discuss uncertainty in design and management of sewer systems, and how to cope with it.