Experimental investigation of the influence of manhole grates on drainage flows in urban flooding conditions

Abstract

Climate change and urbanization have recently increased the number of flooding events in urban areas. Urban flood modelling tools commonly utilize the weir and orifice equations to quantify the drainage flow from the surface flood flow into a sewer system through a manhole or gully. The calculation of drainage flow exchange is a function of the surface flow depth, the geometrical properties of the manhole/gully opening and the discharge coefficient. This paper presents a series of experimental tests conducted within a unique experimental facility built in the water laboratory at the University of Sheffield that features a model sewer system linked to an urban surface/floodplain via a scaled manhole. Tests to investigate the influence of manhole grates with different geometrical configurations on the drainage flow between surface and sewer flows have been conducted. Head-discharge relationships for six different grates are presented in addition to a fully open (i.e. no grate) condition. Discharge coefficients for each grate type have been derived based on the weir and orifice equations.