2.9 Flooding and Foreshore Risk Management

A Flood Impact and Risk Assessment Report (FIRA) is required for developments on Flood Liable Land (Figure 2.9.1) where:

• a)The property is identified as a Flood Control Lot (Figure 2.9.2), or
• b)The development includes sensitive or hazardous development (as defined in the Inner West IWLEP 2022). This includes emergency service facilities, early education and care, boarding houses, group homes and, seniors housing, or
• c)The works are likely to substantially increase the flood risk to the subject or nearby sites.

For single dwelling houses, dual occupancies, secondary dwellings and semi-detached dwellings, with a value of works greater than $50,000, the FIRA is to be certified by qualified practicing Civil Engineer and address:

• a)Outline existing flood behaviour around the site, including flood extent, depth, and hazard
• b)Determine the Flood Planning Level(s) across the site in accordance with Control C3.

Outline the adopted strategies to minimise risk to occupants and property during all possible flood events, including:

• a)Proposed floor levels
• b)Building materials that maintain integrity under immersion
• c)Waterproofing methods for inundated areas, electrical equipment, wiring and utility connections.
• d)A proposed evacuation strategy to flood free land
• e)A response plan to minimise flood damage and provide storage for hazardous materials and valuable goods above the flood level
• f)The report is to be informed by a Flood Certificate for the subject property, obtained by application to Council. The Certificate provides relevant flood information for the subject site and surrounds, including the 1% Annual Exceedance Probability (AEP) flood level, Flood Planning Level, Probable Maximum Flood (PMF) level and the Flood Hazard Category.

For all other developments, the Flood Impact and Risk Assessment Report is to be prepared by a qualified practicing Civil Engineer with demonstrated relevant experience in flood management and address:

• a)Site Analysis & Climate:
• i.Detail the flood extent, depth, and hazard levels relative to the development.
• ii.Determine the Flood Planning Level(s) across the site in accordance with Control C3.
• iii.Assess future climate impacts on flood behaviour.
• iv.Assess likely cumulative impacts of similar development in the surrounding area
• b)Site Modification: Assessment of new structures and earthworks, demonstrating:
• i.Flood levels increased by no more than 10mm
• ii.Downstream velocities increased by no more than 10%.
• iii.No redirection of flows onto adjacent properties or creation of local drainage issues
• iv.No adverse effect on the development potential or risk to surrounding properties and public infrastructure
• c)Safety, Risk Mitigation and Response Strategies: Outline how the following measures are implemented:
• i.Provision for flood-free access for emergency services during a flood event
• ii.On-site storage for valuables/hazardous materials above flood levels.
• iii.A flood evacuation strategy must be provided for all occupants to reach flood free land
• iv.Strategies to minimise damage and risk to occupants during 1% AEP and Probable Maximum Flood (PMF) events, including:
• •Structural integrity under immersion, velocity, and debris impact.
• •Protection of electrical, fuel, and service connections.

The Report is to be informed by a Flood Certificate for the subject property, obtained by application to Council. The Certificate provides relevant flood information for the subject site and surrounds, including the 1% AEP flood level, Flood Planning Level, PMF level and the Flood Hazard Category.

The FPL is to be determined in accordance with Table 2.9.1:

Garage, carport, parking spaces, and any associated accesses are to be located outside any High Hazard flooding area.

Any above-ground parking space is to be at or above the 1% AEP flood level plus 200mm freeboard.

To prevent severe flooding of underground areas and ensure occupant safety, basements are to comply with the following:

• a)Water Entry Points (Low Hazard): In areas subject to Low Hazard flooding, all potential water entry points—including driveway crests, air vents, and lift shafts—are to be raised to or above the Flood Planning Level (FPL).
• b)Water Entry Points (High Hazard): In areas subject to High Hazard flooding, all potential water entry points are to be raised to or above the PMF level or the FPL, whichever is higher.
• c)Pedestrian Evacuation: Provide a clearly signposted, dedicated pedestrian evacuation route that is:
• i.Completely separate from vehicular access ramps; and
• ii.Provides a continuous path of travel from the lowest basement level to flood free land above the PMF level.
• d)Shielding & Waterproofing: Any structural elements of the basement below the flood level are to be designed to withstand hydrostatic and hydrodynamic pressures.

Single dwelling houses, dual occupancies, secondary dwellings and semi-detached housing are to provide for reliable access for evacuation to flood free land, or to a flood free area of the site above the PMF level, where off-site evacuation cannot be achieved.

All other development is to provide a flood-free evacuation route for all occupants from the site to flood-free land.

Any sensitive or hazardous development, or development for vulnerable people is to provide flood-free access for emergency vehicles to the site to support emergency response and evacuation.

Any proposed works to modify the stormwater drainage system or flood behaviour within a property must not increase the consequence of flooding to the subject or surrounding properties.

A Section 88B notation under the Conveyancing Act 1919 will be required on the land title, informing future landowners of the location, type and any ongoing upkeep requirements associated with the installed flood mitigation measures.

Set all floor levels for any Sensitive or Hazardous Development at or above the PMF level.

Provide a flood-free evacuation route for safe evacuation of occupants of the site to flood-free land.

Provide flood-free access for emergency vehicles to support evacuation and response to hazards.

Ensure the floor level for any new or altered floor area is at or above the Flood Planning Level.

Provide sufficient floodproofing (wet or dry) up to the Flood Planning Level for any existing ground floor area that is retained unchanged.

Design any first storey alterations and additions with sufficient floor to ceiling clearance above unchanged ground floor areas to allow for ground floor levels to be raised to the Flood Planning Level in the future.

Maintain existing boundary setbacks to preserve overland flow paths without adverse impacts on adjoining properties.

Provide reliable access for evacuation to a safe haven above the Probable Maximum Flood level.

Ensure all floor levels are at or above the Flood Planning Level.

Set back all structures from the property boundaries to maintain existing overland flow paths without adverse impacts on adjoining land.

Provide reliable access for evacuation to a safe location above the PMF level.

Ensure all floor levels are at or above the Flood Planning Level.

Provide a flood evacuation route for safe evacuation from the site to flood-free land.

Provide all floor levels at or above the Flood Planning Level.

Where ground floor entrances are to be level with the footpath under Section 3.6, internal floor levels are to transition from the footpath entry to the Flood Planning Level.

Design and construct alterations and additions above any retained floor levels to allow future raising to the Flood Planning Level.

Ensure all entrances and evacuation routes servicing residential components are above the Flood Planning Level.

Ensure that all building materials and structures, including street-fronting glazing, maintain structural integrity under immersion, water velocity, and buoyant debris.

Demonstrate that any change of use within an existing building retained below the Flood Planning Level does not increase flood risk or consequence, considering:

• a)The nature of the proposed use
• b)Provision of adequate evacuation
• c)Number of occupants
• d)Storage and housing of materials
• e)Foreseeable risk of pollution during a flood event

Demonstrate that the proposed subdivision and anticipated future development:

• a)Building Envelopes: Provides adequate building platforms/developable areas at or above the Flood Planning Level and not affected by High Hazard (H5-H6) flooding
• b)Hydraulic Impact: Does not redirect flows onto neighbouring properties or result in an increase in flood levels or velocities off-site
• c)Consequence Management: Does not increase the "consequence" of flooding within the subject or surrounding properties, that is, to place more people in a position that is dependent on emergency services in a flood event
• d)Safety and Continuity: Subdivision of an existing building or land subject to a current development consent is to maintain adequate flood management measures for all lots created by the subdivision, including provision for safe evacuation from each lot

A Foreshore Risk Management Report is required for all development on a Foreshore Flood Control Lot (Figure 2.9.3), except where all the following apply:

• a)The value of works is under $50,000
• b)There are no existing habitable structures or buildings below RL 3.5m AHD
• c)No new works are proposed below RL 3.5m AHD
• d)Any proposed jetties, bridging ramps or pontoons are located on the seaward side of the foreshore edge

The Foreshore Risk Management Report is to:

• a)Establish the Foreshore Planning Level for the site, accounting for:
• i.Mean tide level
• ii.Wave run-up
• iii.Climate change and Sea Level Rise
• b)Assess the long-term stability of structures below the Foreshore Planning Level
• c)Assess the impact of the development on surrounding properties and structures

The Foreshore Risk Management Report is to be prepared by a qualified practicing Civil Engineer with relevant foreshore engineering experience.

Ensure the floor level for any new or altered habitable floor area is at or above the Foreshore Planning Level.

Provide sufficient floodproofing (wet or dry) up to the Foreshore Planning Level for any floor areas that are retained unchanged below the Foreshore Planning Level.

Provide sufficient floor to ceiling clearance above any existing and unchanged areas retained below the Foreshore Planning Level to accommodate future raising of the floor to the Foreshore Planning Level.

Ensure the floor level of all garages, carports and car park areas is at or above the Foreshore Planning Level.

Raise all access and potential water entry points for any basement above the Foreshore Planning Level and provide a clearly signposted pedestrian evacuation route separate from vehicular access.

Demonstrate that proposed subdivision provides adequate building platforms or developable areas, including car parking and access, above the Foreshore Planning Level.

Demonstrate that any proposed works to modify wave action or tidal inundation behaviour (such as land filling, retaining structures, or wave protection walls) do not increase wave action, tidal inundation or erosion to the subject property or surrounding lands.

A Section 88B notation under the Conveyancing Act 1919 will be required on the land title, informing future landowners of the location, type and any ongoing upkeep requirements of any such mitigation works or structures.