Author(s): Mikayla Ward; Monique Retallick; Mark Babister

Linked Author(s): Mikayla Ward, Mark Babister

Keywords: Decision Support; Data; Flood; Uncertainty

Abstract: The floods on the Hawkesbury-Nepean River pose arguably the most severe risk to life of any floodplain in Australia. Flood behaviour in the Hawkesbury-Nepean is driven by outflows from Warragamba Dam which on average controls 70% of flood flows in the system. Downstream of the dam is an at-risk population of 70,000. Upstream of Warragamba Dam is World Heritage listed National Park. In order to capture the many aspects of variability and evacuation uncertainty, the modelling used a Monte Carlo process where each option was assessed using an ensemble of 20,000 synthetic flood events. Each simulation involved running a hydrologic model of the catchment, dam operations and a quasi-2D hydraulic model of 200km of the river. One of the challenges of the project is condensing and communicating this enormous data set of flood risk to experts in other fields including emergency managers, government officials and the community. The task involved the creation of an online portal with a series of applications that could flexibly display data and more importantly act as decision support tool. The uses to date have included: -real-time consequence and evacuation assessment during floods, -evacuation modelling and planning, -land use planning, -ecological assessment, and -infrastructure performance assessment. Using the R-Shiny package, web applications were developed where 20,000 flood events could be interrogated at locations over 200km of river traversing major population centres. Beyond the normal parameters including flow rate and level; warning time for evacuation trigger levels, duration of inundation above a threshold, rate of rise, fall and time to rise to a threshold could be interactively changed by the user. This is a particularly important tool going forward when assessing mitigation options, and the performance of these measures under future scenarios such as climate change. The comparative ability of this tool is a powerful mechanism for the communication of improvement to flood risk. During recent floods in March 2021, this tool was used by emergency services to predict a range of plausible outcomes in locations across the floodplain as the flood progressed. This impacted the evacuation of thousands of people. This paper discusses the challenges and benefits of giving different organisations access to large data sets to help them understand the variability of significant flood events. Central to the future capability of this tool is improving the broader communities understanding of flood risk and resilience to flood disasters.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221018

Year: 2022