On-site detention methods & the cumulative effect

Over the past few decades there has been a significant push to at the very least limit flooding caused by new developments to pre-development conditions. Previously little regards was given to the increased run-off that new developments produced. On-site detention (OSD) has been employed by many local governments seeking to return the runoff flows to near existing conditions. On-site detention is the creation of stormwater storage devices to attenuate the peak flow rates generally to pre-developed state (or less). Detention devices are designed to store runoff for longer storm events and gradually release water between storm peaks thus reducing the peak flow rates. Depending on the OSD method used to calculate the storage volume this volume can vary drastically between methods. As these calculations are carried out on an individual basis (i.e. one allotment/dwelling) the cumulative effects of all the on-site detention storage devices within a particular catchment may not be taken into consideration. This dissertation investigates the numerous Onsite Detention techniques and strategies for typical urban catchments within Australia. With the aid of DRAINS software the primary goal of the dissertation is to compare the common OSD techniques for adequacy and efficiency and to determine the cumulative effects these have within typical urban development scenarios. Reducing runoff from developments is of growing importance, especially in a world increasingly focused on environmental impacts. 'DRAINS' modelling has found that regardless of the OSD method used that it generally reduces the peak flows. However the effectiveness & efficiency varies between each method. Reducing runoff from developments is of growing importance, especially in a world increasingly focused on environmental impacts. 'DRAINS' modelling has found that regardless of the OSD method used that it generally reduces the peak flows. However the effectiveness & efficiency varies between each method. It is hoped that the findings in this dissertation may assist the reader in selecting an appropriate process for calculating OSD to provide adequate reductions in stormwater runoff