Retrofitting stormwater infrastructure in a constrained neighbourhood to reduce chronic flooding

We are increasingly aware of the limited capacity of municipal stormwater infrastructure as witnessed by the rising number of flood events which in turn cause varying degrees of damage to private and public property. The results of a recent infrastructure assessment of the Stormwater network of a local municipality indicated that all of the 334 storm sewers experienced a high degree of surcharge under the current 2-year and 5-year design storm conditions. The pipe sizes were recommended to be increased, on average, by 32% with values ranging from 13% to 80%. Implementing recommendations from such reports is challenging as simply replacing pipe is neither cost effective nor practical. An opportunity recently arose with the City of Kitchener during a road reconstruction project where chronic flooding has been occurring within the project limits. A number of challenges were overcome to model the existing conditions including resolving storm sewer network data accuracy, interconnectivity between adjoining sewer catchments and altered topography of the overland flow routes. Developing viable solutions to alleviate flooding was even more challenging and required the use of the dual-drainage design methods. Significant design constraints included the presence of a large “berm” that effectively bisected the major system of the study area, historical retrofits to the storm sewer network to presumably accommodate the “berm” and the timing of the peak flow at the outlets of the study area that interfered with the performance of the proposed storm sewer network within the study area. The solution included the use of storage within the conveyance system as well as detention storage at one of the outlets of the study area.