The provision of on-site detention (OSD) storage is a common planning condition imposed by Councils on new developments to address flash flooding and existing drainage capacity issues. A common method for OSD sizing in Victoria is the Swinburne Method (Phillips, 1995) calculated using the software package OSD4w. However, OSD4w does not have the latest 2016 IFD data from BOM and does not account for climate change impacts and the resulting increase in rainfall. This means that an OSD storage designed in OSD4w today may not be able to control flash flooding under future climate change scenarios. This poses a large risk for developments considering a typical design life of 50 to 100 years. The most recent update in AR&R (Ball et al., 2019) has provided a way for practitioners to account for climate change when sizing OSD by adjusting the rainfall inputs (IFD data) for future climate scenarios. However, as OSD4w is no longer developed and maintained, users are still not able to consider the new AR&R climate change adjustments in OSD4w calculations and are using outdated IFD datasets.
This project addresses this gap by developing a new tool (OSDs For VIPs) that allows practitioners to consider climate change adjustments when using the Swinburne Method to size OSD. First, the Swinburne Method was implemented in OSDs For VIPs. Results from the new tool were then calibrated against OSD4w using 1987 IFD data. This was to ensure that the methods and calculations in both tools are comparable and therefore acceptable by various Councils (City of Kingston, 2025; City of Melbourne, 2023; Maroondah City Council,2016; Wyndham City Council, 2020) that accept OSD4w results. Once the results have been validated, OSDs For VIPs was developed to automatically obtain latest 2016 IFD data from BOM website. This is the latest dataset recommended by AR&R for the purposes of climate change adjustments. Once the IFD data is obtained for the project location, OSDs For VIPs allows the adjustment of IFD data based on equations provided in AR&R for a range of scenarios and time frames.
Case studies using the new tool showed that under future climate change scenarios, OSD storages designed using 2016 IFD are undersized for future climate change predictions. As a decision making tool, OSDs For VIPs allows authorities and practitioners to make appropriate & informed decisions when it comes to approval and design of OSD storages to ensure our flood protection assets and developments are resilient in the face of climate change.