Using hydrodynamic modelling as an input to a cost benefit analysis of climate change adaptation measures

As sea levels are expected to rise throughout the 21st century, low-lying coastal and tidally influenced areas require assistance adapting to the challenges of a warming climate. One way of testing the effectiveness of these adaptation strategies is by undertaking a cost benefit analysis. This requires data on current and expected levels of inundation. A linked one- and two-dimensional model was developed for the catchment running through Southbank, Victoria, with the aim of producing this data. This modelling required input data including topography and drainage infrastructure, as well as an understanding of how the expected changes in climate are predicted to impact boundary conditions. Drainage infrastructure data were collated from the two city Councils responsible for drainage within the study area (i.e. the City of Melbourne and the City of Port Phillip), as well as from Melbourne Water. This was collated to form a comprehensive GIS dataset of the drainage infrastructure in the study area, including location, size and invert levels. Boundary conditions were developed using Melbourne Water standards, which specify climate change conditions in 2100 and the base case conditions. These were used to interpolate climate change conditions for 2040 and 2070. The 10 year Average Recurrence Interval (ARI) flood level in the Yarra River was used as the downstream boundary condition for the model. By combining flood depths, floor levels and land use, an estimate of the Annual Average Damages (AAD) for the site was computed for each time period (2010, 2040, 2070 and 2100). A range of adaptation measures, from education and awareness through to engineering solutions, were developed in conjunction with stakeholders for the study area. The effectiveness of these adaptation measures in reducing the impacts of climate change was then assessed and used to produce an alternative AAD for each option. Annual benefits could then be assessed and used in a cost benefit analysis. The final outcomes of the study include a ranking of adaptation options based on this analysis, as well as optimal timeframes for their implementation, assessed by comparing the present values of the costs and benefits for each option.