Unsteady roof gutter flow: Development and application of simulation

The flow in a roof gutter during and following a storm is unsteady free surface flow, however design guides concentrate on the determination of safe' flow capacities based on steady state data. The development of partially filled unsteady pipeflow simulations aimed at building drainage design also make possible simulations capable of defining the roof gutter flow response to both time and location dependent lateral inflows by means of a method of characteristics solution of the governing St Venant equations. This paper details the developed simulation and compares its predictions to both historic data and to recently gathered storm data. It concludes that such simulations are advantageous and address a number of important parameters omitted from current design guides, including the need to improve on gutter roughness simulation by means of the Colebrook-White frictional representation and to determine gutter response times to variations in rainfall intensity.