FAQs

The Moulamein Flood Study Review (2025) supersedes the Moulamein Flood Study (2019) and provides up to date information to support town planning, guide future development and assist emergency response in future riverine floods and local storms (overland flow). The models produced in this study will be used to investigate potential flood mitigation options for the Moulamein community in a ‘Floodplain Risk Management Study and Plan’, which is the next stage of the project.

The previous flood study, completed in 2019, is being updated to incorporate new data and modelling techniques in line with current industry practice. In particular, the new study uses newer topographic data (from 2022), and takes advantage of the data collected in the 2022 flood event to calibrate the flood model, i.e., checking the model can reproduce a real flood event and match observed levels and extents. This gives us more confidence in using the models to simulate theoretical events (e.g. The 1% AEP event), which we use for planning.

Overland flooding describes flooding that occurs during and following local storms, where rainfall runoff is making its way to a piped network or creek/river system.   Overland flooding is different to riverine flooding, which occurs when a river or creek overflows its banks and the water spills over onto nearby land, often affecting areas close to the river.

Overland flow flooding generally occurs in streets, yards, or low-lying areas where water builds up and can’t drain away quickly enough. Riverine flooding can vary in scale depending on the catchment size and characteristics of the watercourse, and often has far greater impacts on communities and properties.

While Council regularly maintains and cleans drains, this alone cannot prevent all flooding. During extreme rainfall events, the capacity of even perfectly clean drains can be exceeded by the sheer volume of water. Most stormwater drains are designed to capture the run off in a storm with an Annual Exceedance Probability of about 20%, whereas this study is investigating the flooding caused by storm events 20 times this magnitude (i.e. the 1% AEP event). Storms of this size require other management measures, such as retarding basins, open channels and pumps, and will be investigated in the Floodplain Risk Management Study and Plan, which will follow this Flood Study Review.

Flood modelling creates digital maps showing how and where water moves through Moulamein during various sized flood events and local storm events. These maps use colours to indicate water depths, levels, hazard and velocities. User friendly maps can be accessed here: Moulamein Flood Study Review - Draft Flood Modelling Results

A flood study and a flood risk management study and plan are 2 separate types of projects:

Flood study – A flood study is a technical engineering report that identifies how flooding behaves within a catchment area. Using models, the study simulates how floodwaters move through the region. The results of the flood study show how, when and where flooding will affect the community.

Floodplain risk management study and plan – The floodplain risk management study and plan come after the flood study. It uses the results from the flood study (the how, when and where of flooding) to identify and assess different management measures to reduce the impact of flooding on the community.

This study has followed the NSW Government Flood Prone Land Policy, which outlines a staged process involving data collection, a flood study, a floodplain risk management study and plan and the implementation of the plan.

The stages of the project were:

• Collect and review all available flood-related information and data for the area.
• Develop and calibrate a computer flood model using historic flood events to simulate flood behaviour within the local catchment for overland flow, and for riverine flooding from the Edward River and Billabong Creek in and around Moulamein.
• Simulate a range of hypothetical flood events, from common storms to the worst-case flood scenario.
• Produce a range of outputs for use by Council, Emergency Services and the Community

Council does not set or influence insurance premiums. These are determined by your provider based on many factors. If your insurer requires evidence of your property’s flood risk, you can supply data such as your floor level compared to the 1% AEP flood level, available within this strategy. 

Shopping around may also help, as many insurers offer competitive rates or offer varying inclusions and exclusions to suit your situation. There is more information available on the Insurance Council of Australia website: 

The strategy provides valuable technical data to inform future development in Moulamein. It has provided Council with an Interim Flood Planning Area (FPA) that provides information about areas that need to consider flood risk when submitting a development application. The Interim FPA will be finalised in the subsequent FRMS&P.

Annual Exceedance Probability (AEP) refers to the likelihood of a rainfall or flood event of a certain size occurring in any given year. AEP is expressed as a percentage. It describes how probable it is that a particular storm or flood event will be equalled or exceeded in any one year. For example a 1-in-100 year event has a 1% AEP, or a 1% chance of this event happening in any given year.