Author(s): Induka Werellagama; Harish Painuly; Gregory De Costa
Keywords: Stormwater disposal; Stormwater gratings; Urban flooding; Climate Change induced rain peaks
Abstract: Storm sewers are designed for 1 in 10-year rainfall events, with a design life of 100 years. Rainwater collected on streets travels to storm sewers via catchpits. The street interfaces of a catchpit are the metal grating and the vertical curb opening. Traditional stormwater gratings had horizontal bars, opening parallel to curb line. These openings cause accidents when bicycle wheels fall between them. A new design (cycle-friendly gratings) is now used. The research question was whether cycle-friendly gratings transmit the water efficiently to the storm sewer system. Is the throughflow same if blockage of grating happened from upstream vs downstream end? What is the effect of curb weir opening getting blocked by debris? A full-scale lab experiment was conducted to verify whether the cycle-friendly gratings can drain the storm water even when they are 25%, 50% and 75% blocked by debris. Results show they convey the sewer design flows even when they are partially blocked. The worst case occurs when grating was three quarters blocked from upstream end. Drainage rates were 48% of inflow, (with the curb opening closed). With the curb weir opened, the same grating could transmit 64% of inflow. Results show the value of ensuring the streets are clean of litter and debris, ensuring kerbs and gratings are kept unblocked. The result is useful for city councils to target funds to increase the frequency of street cleaning and solid waste management, educating people to not litter the streets, and selecting which trees to plant by the roadsides.