The effectiveness of incorporating storage in storm drainage systems was investigated for a residential subdivision of 100 acres under development in Southern Ontario. The types of storage examined were flat roofs, on-site storage of roof runoff, catch basin storage and holding reservoirs. A runoff model, which computes complete sewer hydrographs from given rainfall intensity-time patterns, was used to determine the storm sewer flow hydrograph at the subdivision outfall for a 2-year design storm. The effects of different storage methods on the outflow hydrograph were tested. Holding reservoirs can be utilized to make peak flows as small as desired, but with corresponding increases in storage volumes. The other local storage methods provided peak flow reductions of about 30 per cent, but the operational reliability of these methods needs to be established.

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