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, with Application Forms available online. 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.
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
G) Storage of Goods
- 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 location of the development, 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
Planning Requirements for Development on 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 Flooding 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.
Information on some specific controls is presented below.
Flood Emergency Response Planning Requirements (Controls E1, E2, E3)
Flood emergency response planning is about minimising flood risk to occupants within the floodplain.
If a Flood Management Report is required and the property is affected by a Flood Life Hazard Category of H3 or higher in the Probable Maximum Flood (PMF) event, then a Flood Emergency Response Assessment must be included in the report. However it is not required for a Class 10 building or structure (as defined in the Building Codes of Australia), which is a non-habitable building or structure such as a shed, carport, garage or pool.
There are two main forms of flood emergency response:
- Evacuation: Movement out of the floodplain before the property becomes flood affected; and
- Shelter-in-Place Refuge: Occupation in a safe refuge on the property during a flood.
For evacuation to be considered an acceptable flood emergency response, occupants must be able to evacuate safely via a route that is:
- Flood free in the Probable Maximum Flood (PMF) event; and
- Not through private property that is not part of the subject site.
The Flood Emergency Response Assessment should demonstrate that:
- There is sufficient time to evacuate safely before flooding. The proposed flood free evacuation route should be mapped and the mode of transport identified;
- There is an appropriate evacuation destination, with adequate medical, food, water and communication services available;
- The evacuation route is suitable for the likely occupants, taking into account the number of occupants and whether they may need assistance to evacuate;
- An evacuation plan has been prepared outlining the intended flood warning mechanism and flood evacuation response triggers, taking into account flooding at all times of the day. Some examples include water level sensors, alarm stations, panic buttons, flood depth indicators, evacuation depth triggers; and
- The evacuation plan is easily accessible by current and future occupants. If the evacuation route is not obvious, then signage should be installed, particularly for business and industrial land uses.
Note that in the event of a flood, occupants would be required to evacuate if ordered by Emergency Services personnel, regardless of the availability of a shelter-in-place refuge.
2. Shelter-in-Place Refuge
Council, NSW State Emergency Services, and other agencies are unlikely to be able to respond to individual calls for assistance at the onset of major flooding. If safe evacuation cannot be achieved within a sufficient response time then a shelter-in-place refuge is required, together with a plan for self sufficiency.
The Flood Emergency Response Assessment should demonstrate that the shelter-in-place refuge meets the following requirements:
- Floor level is at or above the PMF level;
- Structural integrity is up to the PMF level (verified by a suitably qualified structural engineer);
- Floor space is at least 2m2 per person where the flood duration is long (6 or more hours) in the PMF event, or 1m2 per person for less than 6 hours duration. In the Northern Beaches LGA, long duration flooding environments are typically those affected by lagoon flooding;
- Access is available to all people on the site, plainly evident and self-directing, with sufficient capacity of access routes for all occupants without reliance on an electrical means; and
- Items for self-sufficiency are available during a flood, including as a minimum: sufficient clean water for all occupants; radio with spare batteries; torch with spare batteries and a first aid kit. For Vulnerable or Critical Development, it must also include emergency power and a practical means of medical evacuation. For shorter duration flooding, less than 6 hours, justification by a suitably qualified engineer for non-compliance with certain self-sufficiency requirements may be submitted for consideration.
For further information please contact Council’s Flood Team on 1300 434 434 or by email at email@example.com