These guidelines are intended to provide advice to applicants on how to obtain flood information from Council, how to determine what rules apply on flood prone land, and how to prepare a Flood Management Report.
The purpose of a Flood Management Report is to demonstrate how a proposed development will comply with flood related planning requirements.
Flood Hazard Map
Council’s online Flood Hazard Map shows the extent of land identified as flood prone throughout the Northern Beaches. It is divided into three precincts:
- The Medium Flood Risk Precinct is equivalent to the Flood Planning Area (FPA), and covers flood prone land affected by the Flood Planning Level (FPL). The FPL is the 1% Annual Exceedance Probability (AEP) flood level (equivalent to the 1 in 100 year flood level) with a freeboard added.
- The High Flood Risk Precinct lies within the Medium Flood Risk Precinct, and covers flood prone land which is subject to a high hydraulic hazard.
- The Low Flood Risk Precinct covers flood prone land affected by the Probable Maximum Flood (PMF) but which is outside the Medium Flood Risk Precinct. The PMF is equivalent to the largest ever conceivable flood.
Note that none of the online mapped extents include climate change.
Flood Information Report from Council
There are two types of Flood Information Reports which can be provided by Council. Application forms are on Council’s website. It is advisable to check the Flood Hazard Map before applying.
The Basic Report is suitable for flat blocks where the same flood levels apply to the whole block (eg where flooding is back watering from a lagoon). Only the maximum level is provided for the whole block.
The Comprehensive Report is suitable for sloping blocks subject to flooding from creeks or other overland flow such that flood levels vary across the block. Levels are provided at multiple points across the block, and if requested, can be provided at chosen locations.
The type of information available in a Flood Information Report includes the Flood Planning Level, flood levels, depths and velocities, and mapping for flood risk precinct, flood extents, hydraulic category and flood life hazard category. Further details are provided on the application form.
Note that the flood extents shown on the mapping are indicative only. It is recommended that flood levels are compared to registered ground survey to more accurately determine the flood extent.
Additional information is available in the Flood Study Reports.
Planning Requirements for Flood Prone Land
Development must comply with requirements set out in the relevant Local Environment Plan (LEP) and Development Control Plan (DCP). There are separate LEPs and DCPs for each of the former Local Government Areas (LGAs), although preparation of a LGA-wide LEP and DCP is currently under way.
The clauses specific to flooding in the LEPs and DCPs are as follows:
- Manly LEP (2013) – 6.3 Flood Planning
- Warringah LEP (2011) – 6.3 Flood Planning
- Warringah LEP (2000) – 47 Flood Affected Land *
- Pittwater LEP (2014) – 7.3 Flood Planning
- Pittwater LEP (2014) – 7.4 Flood Risk Management
- Warringah DCP (2011) – E11 Flood Prone Land
- Pittwater 21 DCP (2014) – B3.11 Flood Prone Land
- Pittwater 21 DCP (2014) – B3.12 Climate Change
* The Warringah LEP (2000) is relevant only for the “deferred lands” which affects only a very small number of properties, mostly in the Oxford Falls area.
Development on flood prone land must also comply with Council’s Water Management for Development Policy, and if it is in the Warriewood Release Area, with the Warriewood Valley Water Management Specification. Guidelines for Flood Emergency Response Planning are available for addressing emergency response requirements in the DCP. These documents can be found on our Flood page.
Note that if the property is affected by estuarine flooding or other coastal issues, these need to be addressed separately under the relevant DCP clauses.
When is a Flood Management Report required?
A Flood Management Report must be submitted with any Development Application on flood prone land (with exceptions noted below), for Council to consider the potential flood impacts and applicable controls. For Residential or Commercial development, it is required for development on land identified within the Medium or High Flood Risk Precinct. For Vulnerable or Critical development, it is required if it is within any Flood Risk Precinct.
There are some circumstances where a formal Flood Management Report undertaken by a professional engineer may not be required. However the relevant parts of the DCP and LEP would still need to be addressed, so as to demonstrate compliance. Examples where this may apply include:
- If all proposed works are located outside the relevant Flood Risk Precinct extent
- First floor addition only, where the floor level is above the Probable Maximum Flood level
- Internal works only, where habitable floor areas below the FPL are not being increased
Note that development on flood prone land will still be assessed for compliance with the relevant DCP and LEP, and may still be subject to flood related development controls.
What is the purpose of a Flood Management Report?
The purpose of a Flood Management Report is to demonstrate how a proposed development will comply with flood planning requirements, particularly the development controls outlined in the relevant LEP and DCP clauses. The report must detail the design, measures and controls needed to achieve compliance, following the steps outlined below.
A Flood Management Report should reflect the size, type and location of the development, proportionate to the scope of the works proposed, and considering its relationship to surrounding development. The report should also assess the flood risk to life and property.
Preparation of a Flood Management Report
The technical requirements for a Flood Management Report include (where relevant):
1. Description of development
- Outline of the proposed development, with plans if necessary for clarity
- Use of the building, hours of operation, proposed traffic usage or movement
- Type of use, eg vulnerable, critical, residential, business, industrial, subdivision, etc
2. Flood analysis
- 1% AEP flood level
- Flood Planning Level (FPL)
- Probable Maximum Flood (PMF) level
- Flood Risk Precinct, ie High, Medium or Low
- Flood Life Hazard Category
- Mapping of relevant extents
- Flood characteristics for the site, eg depth, velocity, hazard and hydraulic category, and the relevance to the proposed development
If the property is affected by an Estuarine Planning Level (EPL) which is higher than the FPL, then the EPL should be used as the FPL. If the FPL is higher than the PMF level, then the FPL should still be used as the FPL, as it includes freeboard which the PMF does not.
3. Assessment of impacts
- Summary of compliance for each category of the DCP:
- A) Flood effects caused by Development
- B) Building Components & Structural Soundness
- C) Floor Levels
- D) Car parking
- E) Emergency Response
- F) Fencing
- G) Storage of Goods
- H) Pools
- Demonstration of how the development complies with any relevant flood planning requirements from the DCP, LEP, Water Management for Development Policy, and if it is in the Warriewood Valley Urban Land Release Area, with the Warriewood Valley Water Management Specification (2001).
- For any non-compliance, a justification for why the development should still be considered.
- Calculations of available flood storage if compensatory flood storage is proposed.
- Plan of the proposed development site showing the predicted 1% AEP and PMF flood extents, as well as any high hazard or floodway affectation
- Development recommendations and construction methodologies
- Qualifications of author - Council requires that the Flood Management Report be prepared by a suitably qualified Engineer with experience in flood design / management who has, or is eligible for, membership to the Australian Institute of Engineers.
- Any flood advice provided by Council
- Any other details which may be relevant
For further information please contact Council’s Flood Team on 1300 434 434 or by email at email@example.com