Objectives

The objective of this Study is to define the nature of the existing flood behaviour in the Burradoo BU2 catchment. To achieve the objective, the following tasks were undertaken:

• Collate available flood-related data,
• Define existing catchment condition flood behaviour for mainstream flooding in the catchment,
• Define design flood levels, velocities and flow distributions for the catchment,
• Define the extent of flooding the 5 year, 20 year, 50 year, and 100 year ARI and PMF events for the catchment,
• Define provisional flood hazard for the flood-affected areas,
• Define the hydraulic categories for the flood-affected areas,
• Assess impacts of climate change,
• Preliminary assessment of flood damages for the flood-affected areas,
• Identify preliminary remedial options.

Methodology

This Study was carried out using computer-based hydrologic and hydraulic modelling. Two numerical modelling tools were developed:

• A hydrologic model was utilised to convert rainfall on the catchment to runoff. The hydrologic model RAFTS was used, which combines rainfall information with local catchment characteristics to estimate runoff hydrographs.
• A hydraulic model was utilised to convert runoff hydrographs into water levels and velocities in the study area. The model simulates the hydraulic behaviour of the water within the study area by accounting for flow in the major channels as well as potential overland flowpaths, which develop when the capacity of the channels is exceeded. It relies on boundary conditions, which were the runoff hydrographs produced by the hydrologic model and downstream boundary conditions from the creek into which it discharges. The TUFLOW modelling system was used for this purpose.

The Study details are grouped together under the following sections of the report:

• Section 3 provides a general description of the catchment
• __ Section 4__ discusses the content and sources of relevant data, which were utilised for the study. Historical rainfall and flood data used in the calibration of the established hydrologic and hydraulic models and survey data used are detailed.
• Section 5 discusses the catchment characteristics and describes the hydrologic model setup for the study.
• Section 6 describes the hydraulic model utilised for the study, its verification and subsequent use for design rainfall events.
• Section 7 details results for the design flood events.
• Section 8 reviews the sensitivity of the model to the data used.
• Section 9 identifies the provisional flood hazard.
• Section 10 identifies the hydraulic categorisation.
• Section 11 reviews the impacts of climate change.