Monte Carlo Modelling using a 1D Hydraulic Model for Assessing Dam Operation

Mark Babister, Monique Retallick, Melanie Loveridge, Ivan Varga, Peter Stensmyr

Wednesday 1 july 2015

11:45 - 12:00h at South America (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flood risk assessment

Parallel session: 9J. Floodrisk - Assessment

The Hawkesbury Nepean River passes through some of the most populated western suburbs of Sydney, Australia. Warragamba Dam is located on the Hawkesbury Nepean and supplies around 80 % of Sydney’s water. Downstream of the dam are a large number of flood prone properties and lives at risk from flooding. The Hawkesbury Nepean has a very large flood range. In 1867 flood waters rose over 19m above their normal tidal level at the town of Windsor. Australian flood estimation practice is also evolving where design inputs are often characterized as an ensemble or probabilistically, instead of as a single input. This is often described as a Monte Carlo approach. Using this type of approach is very important when studying dam operations as an ensemble of temporal patterns will much better test the performance of gate operations then a single pattern for which the gate could be optimized. A Monte Carlo framework was developed to allow a more robust assessment of the short term operational changes proposed for Warragamba Dam. For each scenario the equivalent of a 200,000 year flood record is developed and run through hydrologic and hydraulic models. The Monte Carlo model allowed the impact on downstream flooding to be assessed for a range of flood events. Information was extracted and analysed from the model results to inform the assessment of options and emergency management planning.