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.
Why has a 1% Annual Exceedance Probability (AEP) been used to determine if land is liable to flooding?
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.
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.
Will a 'land liable to flood' designation stop building works, development or re-development of my property?
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.
About the study
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.
The accuracy of the Cowies Creek Flood Study will be validated against flood impact photos of recorded impact areas.
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 Council 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 Council to help convey runoff away from urban areas.
Drainage standards applied to urban development throughout Victoria changed in the early 1980s. In suburbs established prior to the 1980s, the underground drainage systems were designed to cope with a 20% AEP rainfall, i.e. drains were designed to convey the runoff resulting from a rainfall event of an intensity which occurs on average once every 5 years.
Today the more frequent minor flows are still catered for using underground drains, but current design standards also consider severe storms and the major overland flow which occurs when pipes are full and water travels down roads and along overland flow paths usually above the underground drains in a safe manner.
The City is applying the 1% AEP flooding standard to all new developments. This will ensure that any development on known flood prone land recognises the risk to public health and safety and is planned accordingly including setting of appropriate finished floor level to minimise the flood risk. Provision must now also be made for severe storm event flows to pass safely overland through any new development.
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.
To reduce overland flows in established areas it would cost the community millions of dollars. These works can only be 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 and expensive. 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, the piped system quickly fills, and the additional runoff flows along the natural drainage paths towards a larger waterway across properties, roads and reserves.
About our community engagement
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 and we'll put it on the online system for you. Alternatively, we can send you a hard copy form of our online tool which we'll also transfer online.
All feedback needs to be received before the engagement close date for us to include it as the project progresses.