About the stormwater study

A flood study is a technical investigation of flooding behaviour, based on records of rainfall, catchment impacts and physical terrain. It determines how far and high flood waters are expected to reach for floods of various magnitudes. It also identifies the nature of a range of flood risks and flooding behaviour that require special consideration. It investigates ways to reduce and manage flood risks and makes recommendations for potential further action.

It helps us all to understand flooding in this area better. The investigation will provide clarity to landowners on their risk of being flooded during significant flood events. Information produced by the investigation will help avoid making flooding worse with inappropriate development. It provides planners and response agencies with better information to help residents before, during and after flood events. It also provides developers and investors with a tool to assist in planning new buildings.

The information will be used to identify flood risk and flood hazards in and around the study catchment area, which includes the suburbs of North Geelong, Norlane, Bell Post Hill, Bell Park, Lovely Banks and Moorabool.

It will provide a better understanding and a base from which to develop greater awareness of the risks of flooding within the community. This better understanding will lead to improved planning and development decisions that minimise the impact of flooding.

The information will also be used to help plan and prioritise infrastructure improvements, flood mitigation and flood emergency management procedures.

The information from the study will be used to inform future capital works projects within the study catchment area, including key decisions about flood mitigation works and infrastructure improvements. It may be used to declare land liable to flooding and update the City of Greater Geelong Planning Scheme.

The City of Greater Geelong will consult with the community as part of any Planning Scheme Amendment process and for the duration of the flood investigation project. But it does not end there. Over time, as flood events occur and communities grow – we will continually improve and update our knowledge of flooding and how we plan for and respond to it. We must work closely with the community over the long term to best manage future flood events.


You can call or email us to give your feedback.

All feedback needs to be received before the engagement close date to be included.

Flood risk is determined based on a detailed scientific modelling process that combines current and historical data, survey work and flood modelling.

Flood modelling simulates a real-world system by identifying how flood water will travel across the land; how wide it will extend; how deep it will be; and how fast it will travel.

It is important to note that designating areas liable to flooding does not cause or change the likelihood of flooding, but recognises the existing risk.

The designation will not be described on property titles but will be acknowledged in Property Information Certificates issued under the Building Regulations 2018.

The value of a property is determined by many different factors and it is not possible to specify what, if any, effect, the identification of land as liable to flooding may have on the market value.

The City of Greater Geelong can use flood information to develop objectives and strategies for flood management in their Local Planning Policy Framework (LPPF). Appropriate planning provisions can then be applied to control land use and development in flood prone areas.

The planning provisions that may apply to flood prone land include: Floodway Overlays (FO), Urban Floodway Zones (UFZ), Land Subject to Inundation Overlays (LSIO) and Special Building Overlays (SBO). These are derived according to the type of flooding and the level of risk to life and property.

The level of planning control is proportionate with the flood risk. For example, in Floodway areas, most land use types and developments are prohibited due to high flood hazard. Often, only low intensity uses such as open recreation areas are suitable. In areas covered by a Land Subject to Inundation Overlay, a high risk of flooding has been identified, and the type of development is strictly controlled in order to minimise the risk to life and property. Where a proposed development does not expose people to an unacceptable hazard or make flooding worse elsewhere, it may be permitted subject to conditions.

The City is responsible for the management of the stormwater drainage system downstream of private properties (public drains).

A network of pits, underground pipes, open channels and constructed waterways are managed by the City to help convey runoff away from urban areas.

Drainage improvement work is based on known flood problems where houses, commercial or industrial buildings are flooded repeatedly. The key criteria are the potential risk to life from flooding, and the cost per property for flood protection works.

Due to the complexity and high cost to mitigate flooding in established areas works are undertaken incrementally over a period of many years.

It is not feasible for all stormwater to be collected in underground drainage systems. The drains required would have to be enormous!

Drainage systems are generally designed to accommodate stormwater runoff in a piped system to cope with a 20% AEP (1-in-5 year) event.

In a 1% AEP event (1-in-100 year), the piped system quickly fills, and the additional runoff flows along the natural drainage paths towards a larger waterway, across properties, roads and reserves.

Land liable to flood

Areas designated as ‘liable to flooding’ indicate that the land is likely to flood during an event with an Annual Exceedance Probability (AEP) of 1%. A 1% AEP means that a flood of this size has a 1% chance of occurring in any year.

Annual Exceedance Probability is a commonly used international drainage and flood management standard. This standard has been applied in Victoria since the early 1980s and was previously called a ‘1-in-100 year’ flood event. This phrase is misleading as it wrongly implies that the flood event can only occur once every 100 years.

Annual Exceedance Probability is used to define the extent of the overland flow along the drainage system and where flooding from waterways may occur. A 1% AEP means there is a 1%, or 1 in 100, chance of the flood event occurring or being exceeded in any year.

We understand your concern. As part of the project, after this engagement, both the consultant and the City will further analyse the flood results based on the 1% Annual Exceedance Probability (AEP) threshold. The aim is to ensure that properties with isolated water puddles, such as those caused by isolated topographic low points, are not mistakenly tagged as flood-prone. Some of the larger puddles that indicate significant overland flow paths are important to inform the flood risk in 1% AEP event and therefore should form part of the flood map. This analysis will be conducted in the next phase of the project to ensure a fair and accurate designation.

Each insurance company has their own process for calculating their premiums, so it is best to speak directly with your insurance provider.

Individual insurers decide what criteria they use to determine flood risk and calculate premiums. This may include historical flood information, claims history and building type.

If your property is identified as liable to flooding it does not mean that building permits and building works will not be approved.

The flood information is used to ensure that any building works are carried out in a manner that recognises the areas liable to flooding. Requirements for any proposed building works depend on the flooding characteristics of the land such as water depth, flow velocity, and the nature of the proposal. The City and Corangamite Catchment Management Authority can both provide advice on the requirements for works in these areas.

Depending on the nature of the works you may also need to request a Council Consent. More information can be found on geelongcity.vic.gov.au – search ‘Council Consent’.

We cannot assume a property that has never flooded is safe from flood risk, without investigating the catchment through flood studies. The resulting flood extents identified are the basis for determining if a flood risk exists.

When the new study is completed a flood hazard evaluation based on the depth and velocity of floodwaters will determine whether flood prone properties may be developed. The information provided by this study will be used to ensure that any development addresses all public health and safety issues related to flooding. The flood study will provide information to assist in determining appropriate building locations, floor levels and access requirements for new buildings as part of permits.

Yes. During the exhibition period of a planning scheme amendment, the community has the opportunity to appeal the amendment by submitting any concerns to the Council. All submissions will then considered by the Council.

Key words and phrases explained

Annual Exceedance Probability (measured as a percentage) is a term used to describe the magnitude (size) of a flood.

It is a way of describing the probability of a flood of a particular size being equalled or exceeded in any given year.

For example, a 1% AEP flood is a flood that has a 1% chance of occurring in any one year.

A catchment is an area of land that collects precipitation (rainfall) from the natural landscape.

Vegetation and soils intercept or absorb some of this rainfall. The remaining rainfall evaporates or runs off from natural or manufactured surfaces to the nearest waterway.

These waterways merge into larger water bodies, which ultimately drain into a sea or ocean, known as the catchment outfall.

Flood hazard refers to the danger posed by deep or fast flowing floodwater.

Fast flowing floodwater poses danger to life, health and safety and should always be avoided.

Deep floodwater can conceal many dangers such as trip hazards and open pits and the force of the water can readily sweep people and objects away.

A floodplain is the low lying land typically adjacent to a river or creek channel that is periodically flooded. When the flow of the river is larger than the capacity of the channel, water will flow into the floodplains.

Built up urban land can also be affected by floods that occur during severe storms, when drainage systems exceed capacity.

Floodplains provide routes for natural overland flows and flood storage areas. Floodplains can be parts of a river’s natural domain or located within dense urban areas.

Integrated Water Management (IWM) is a collaborative approach to the way we plan for and manage all elements of the water cycle. The typical water cycle includes potable (drinking) water, wastewater, recycled water, and stormwater.

IWM considers

  • the health of our waterways and bays
  • potable (drinking) water supply
  • alternative water supply options
  • stormwater management
  • water treatment, and
  • wastewater management.

An overland flow path is an above ground component of the drainage system.

Overland flows occur when underground drainage pipes reach their capacity and the excess runoff then flows overland, following low lying, natural drainage paths.

Stormwater refers to rainwater that falls on hard surfaces and runs off to the nearest low point in the landscape.

Runoff occurs when the ground cannot absorb rainwater or if basins, ponds, wetlands, or other storages overflow.

The stormwater then runs off into the nearest pit, pipe, creek or river, and is ultimately emptied into a bay.

Stormwater can wash away mud, dirt, gravel, organic materials, and chemicals (such as pesticides, heavy metals, and oils) into our waterways, wetlands, and bays.

These pollutants, contaminants, or sediments can impact sensitive ecological habitats by causing

  • littering
  • algal blooms
  • loss of vegetation
  • loss of native species, and
  • reduced oxygen levels and food supply.

A stormwater treatment system eliminates or reduces stormwater quality impacts. Some common treatment systems include

  • wetlands
  • sediment basins
  • raingardens
  • biofiltration
  • sand filters
  • swales, and
  • litter traps (also known as gross pollutant traps).

Each system has different capabilities in cleaning or removing pollutants, contaminants, or sediments from stormwater runoff.

The right stormwater treatment system can enhance a natural landscape by improving

  • amenity
  • community access and enjoyment
  • social inclusion and connection
  • urban cooling and passive greening, and
  • use of recreational areas such as a reserve or park.

Urban flooding is the flooding of land or property in our built-up environment.

As there is little open soil that can soak in and be used for water storage, nearly all the rainfall runs off the surfaces and into our roads and drainage systems, which can become quickly overwhelmed during intense storm events.

A wetland (or swamp) is a type of stormwater treatment system that collects, filters, and removes pollutants from runoff in the environment. You could say it's the ‘kidneys of a catchment’.

A wetland can be natural or constructed (manmade).

Constructed wetlands have become popular in urban areas over the last 30 years as they are good at filtering pollutants from runoff and help protect our creeks, rivers, and bays.