Role of Urban Storm‐Flow Volume in Local Drainage Problems

Abstract

At culvert entrances and other drainage obstructions the area upstream of the obstruction acts as a reservoir, holding arriving runoff while earlier arriving waters are still passing through. Urban development in a watershed increases storm‐flow volume and peak rate, increasing the potential accumulation of water and hence rising of stage and overflowing. Storm hydrographs with different flow volumes and peak rates were routed through a computer model of a culvert entrance, with the upstream area functioning as a reservoir. Maximum stage rose with increasing flow volume for more than half of the modeled combinations of conditions. Thus in an urbanizing watershed, for a wide range of conditions, the tendency to overflow at an obstruction increases unless volume of flow is suppressed, whether or not peak rate is suppressed by detention. Storm‐water infiltration, which controls both flow volume and peak rate, would be a more complete solution. Storm‐water management policy that is aimed to prevent overflows at drainage obstructions should consider flow volume control in addition to peak rate control.