TRANPLAN Sydney - Town Planning & Flood

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 Flooding can cause significant damage to property and risk to life. Councils are required by the NSW Government to undertake studies to determine what land has the potential to be affected by flooding. This is to ensure that new developments are adequately protected and do not make flooding worse.

Each Councils Floodplain Risk Management Studies and Plans are usually prepared in accordance to the NSW Government's  

Flood Risk Management Manual (June 2023) - replacing the Floodplain Development Manual (2005).

Being flood affected means a property has a risk of being impacted by flooding during specific rainfall events. This may result in flood-related development controls being applied to a proposed development, for example raising floor levels or using flood resistant materials.

 Homeowners and property developers should especially be aware that certain categories of flood-affectation / flood risk categories also disqualify (rule out) properties for the CDC approval pathway, per clause 3B.5 of SEPP 2008 – Low Rise Housing Diversity Code. 

Our town planners will be able to review your Council’s Flood Mapping & Studies, and Section 10.7 Certificate (see note below) to advise whether your property is affected by flood, and confirm if Complying Development Certificate / CDC approval is possible (e.g. for dual occupancy / duplex, terrace, manor homes).

Note: Under Schedule 2 of the Environmental Planning and Assessment Regulation 2021, the following clauses for Section 10.7 Certificates issued for land affected by flood-related development controls apply:

1. Clause 9(1) requires Councils to include a notation on S10.7 Certificates if the land or part of the land to which the certificate relates is within the Flood Planning Area (FPA).
2. Clause 9(2) requires Councils to include a notation on S10.7 Certificates if the land or part of the land to which the certificate relates is between the FPA and the Probable Maximum Flood (PMF).

Flood Planning Area  

The Flood Planning Area (FPA) is the area of land below the Flood Planning Level (FPL) and thus subject to flood related development controls. 

Flood Planning Level 

Flood Planning Levels (FPL) are the combinations of flood levels (estimated heights of floodwater from defined flood events) and freeboards selected for floodplain risk management purposes, as determined in management studies and incorporated in management plans.

Freeboard

 Freeboard is a height included in the FPL and provides reasonable certainty that the risk exposure selected in deciding on a particular flood chosen as the basis for the FPL is actually provided. It is a factor of safety typically used in relation to the setting of floor levels, levee crest levels, etc., to account for factors such as wind, waves and any other localised hydraulic effects. Freeboard can vary but is usually 0.5m above a flood level for habitable areas. 

Annual Exceedance Probability

Annual Exceedance Probability (AEP), measured as a percentage) is a term used to describe flood size. It is a means of describing how likely a flood is to occur in a given year. For example, a 1% AEP flood is a flood that has a 1% chance of occurring, or being exceeded, in any one year. 

Average Recurrence Interval

 A 1-in-100 year Average Recurrence Interval (ARI) flood is a flood event that has the probability of occurring on average once every 100 years, i.e. there is a 1% chance of a flood of this size occurring at a particular location in any given year. This does not mean that if a location floods one year that it will not flood for the next 99 years. Nor, if it has not flooded for 99 years that it will necessarily flood the next year. Some parts of Australia have experienced more than one ‘1 in 100 year’ floods within a decade of each other. 

Probable Maximum Flood

 The Probable Maximum Flood (PMF) is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation, and where applicable, snow melt, coupled with the worst flood producing catchment conditions. Generally, it is not physically or economically possible to provide complete protection against this event. The PMF defines the extent of flood prone land, that is, the floodplain. 

We provide a FREE initial flood consultation so that our specialist flood consultant can fully understand how flooding issues may affect the design of your development. Contact TRANPLAN's Planning Consultant now for free initial advice about flood and Council approval of your DA.

My property has never been flooded - why is it in the Flood Planning Area?

Floods do not occur in a regular pattern. There may be a period of no floods and a period of several floods. For example, the last time the Brisbane River flooded was in 1974, before the 2011 disaster. Residents who moved there in more recent times may never considered flooding an issue until the floods in January 2011.

Where do I see flood related development controls?

The flood related development controls are within your Council’s relevant Local Environmental Plans (LEP) and Development Control Plans(DCP). Our town planners will be able to review your Council’s Flood Mapping & Studies, Section 10.7 Certificate, and Council’s flood development controls in the LEP & DCP.

Why does my Section 10.7(5) state ‘PMF’ information?

If the Section 10.7(5) Certificate indicates that your property is within the Probable Maximum Flood (PMF), a Flood Report/Study may be required as part of any development application (DA) to determine if a proposed development could affect flood behaviour and have the potential to negatively impact the flood affectation to the neighbouring properties.

Will I have to do a flood study when I develop my land?

It depends on the type and scale of the development. New developments which affects the flood behaviour and has potential to negatively impact the flood affectation to the neighbouring properties will require a Flood Report/Study with DA lodgement. 

If the above brief summary about flood planning and building design requirements is a bit too much information to process – and all the various acronyms such as FPA, PMF, FPL, AEP, ARI, freeboard etc. are leaving you with a slight headache – feel free to contact our specialist Town Planning consultant for expert guidance on your DA. 

Why not let our Town Planner do all the hard work for you, and research all the planning laws and cross-reference with flood legislation clauses.

We can assist with preparing all the relevant Flood Reports (e.g. Flood Risk Management Plan / Flood Risk Assessment Report / Flood Planning Advice Report / Flood Assessment Report), provide DA project management and navigate the Council approval process on your behalf.