Application of URBS-Monte Carlo simulation technique to large catchments for design flood estimation : a case study for the Johnstone River Catchment in Queensland

In recent years, there have been significant researches on holistic approaches to design flood estimation in Australia. Joint Probability Approach and Continuous Simulation are the methods that have received considerable attention. Monte Carlo Simulation Technique, an approximate form of the Joint Probability Approach, has already been developed and tested to small gauged catchments in Australia. This paper presents the extension of the Monte Carlo Simulation Technique to large catchment using runoff routing model URBS. The Monte Carlo Simulation Technique incorporates the probabilistic nature of the key input variables such as rainfall intensity, duration, temporal pattern and initial loss in the design flood estimation. URBS is a semi distributed non-linear runoff routing model, and one of several industry models used for design flood estimation for small to very large catchments. The integrated Monte Carlo Simulation and URBS run-off routing model, here named as the URBS-Monte Carlo Simulation Technique (UMCST), has been applied to the Johnstone River catchment in Queensland. The key assumptions and methodology to apply the UMCST to large catchment are discussed. It has been found that it is quite feasible to apply the Monte Carlo Simulation to large catchments.