Optimum design of gravity stormwater detention tanks for managing peak runoff rates from small developments

Abstract

With the current trend of urbanization, necessity of runoff management is increasing and stormwater detention tank can always play as an efficient tool to prevent flooding happen. Undoubtedly, design modelling software like SWMM has widely been introduced into the industry and provided practical solution to the user. However, the characteristics of complex manipulations and large amount of field data required have caused difficulties for user to handle this kind of modelling. Therefore, the development of a user-friendly model for preliminary design of detention tank is always welcome. Researches and studies are carried out to find an efficient and simple method that could provide an optimized detention tank size with the function of managing peak runoff rates. For the ease of user, the methodology will be formulated into an Excel spreadsheet embedded with VBA program. The background of this model is set at Singapore. Therefore, the allowable discharge rate from the tank will be based on Public Utilities Board, Singapore’s National Water Agency (PUB) requirement as standard. Other factors for example rainfall intensity are also based on Singapore conditions. The model includes two methods, first one as suggested by PUB and the second based on level pool routing. A comparison between the required storages by both methods from several perspectives will be made to compare their efficiency. Lastly, experiments are carried out using the model to develop the relationship between characteristics of site, especially tc with the required storage.