Development Control Plan

Minor Additions Exception

This section applies to all development on flood prone land with the exception of minor additions to existing buildings.  Minor additions are allowable without further reference to the provisions of this section, provided that the flood risk is not unreasonably increased.  Minor additions for purposes of this section are total proposed additions that fall below the following limits.

Existing building area	Minor addition limit
< 250 m2	50 m2
250 m2 – 750 m2	20% of the existing building area
>750 m2	150 m2

Minimum Floor Level for Occupiable Rooms

City of Newcastle has adopted the Rhelm model of a 1% Annual Exceedance Probability (AEP) event in 2050 as the Defined Flood Event across the study area.“Council's Throsby, Styx & Cottage Creek Flood Study (Rhelm, 2023) (‘TSCC Flood Study’) was adopted by Council on 12 December 2023 and all DAs lodged after this date are to have regard to the new flood data.”

City of Newcastle (2024), Request for Information DA2024/00650, p.2)

Although a reference has not been sighted, it appears City of Newcastle applies a 0.5 m freeboard to the defined flood level to arrive at the minimum floor level for occupiable rooms.  The Australian Building Code defines freeboard as the height above the defined flood level (DFL) as determined by the appropriate authority, in this case City of Newcastle.  DCP 2023 B1(b) defines freeboard as “a margin applied to the estimation of flood levels to compensate for factors such as wave action, localised hydraulic behaviour, climatic change and modelling confidence”.  Freeboards typically range from 0.3 to 0.6 m.  The “lower freeboard is generally only considered acceptable for use in very shallow water where the potential for other effects is limited” (Australian Disaster Resilience Handbook 7 Managing the Floodplain: A Guide to Best Practice in Flood Risk Management in Australia (AIDR 2017)). Freeboard should not be relied upon to provide protection for flood events larger than the relevant defined flood event of a design flood.The relationships between the defined flood event (Rhelm model for 1% AEP in 2050), freeboard and the minimum floor level for occupiable rooms is shown diagrammatically in the following figure.

Identifying Defined Flood Level (DFL), Flood Hazard Level (FHL) and Freeboard

(Source: Commonwealth of Australia and States and Territories (2019). ABCB Standard: Construction of buildings in flood hazard areas.  Australian Building Codes Board, Canberra.)

 The following map is extracted from the Rhelm flood study; Map G320c Throsby, Styx and Cottage Creek Flood Study - Peak Flood Depth and Elevation 1% AEP in 2050 (0.5% AEP, 0.4m SLR) - Map 3 of 4. You can get an estimate of your minimum floor level for occupiable rooms in a new development by adding 0.5 m of freeboard to the peak flood depth shown in the map.  Your garage floor levels must be no lower than peak flood depth shown in the map below, i.e., no lower than the 1% 2050 AEP event.  However, it is recognised that in some circumstances this may be impractical due to vehicular access constraints. In these cases, garage floor levels are as high as practicable. To get accurate information for your property you will need to apply to City of Newcastle for a Flood Certificate.  The application fee for residential and non-residential properties is $385.00 (2024/25).

Defined Flood Level (DFL) in Wickham (Rhelm (2022), Part of Map G320c)

Risk to Property and Life

The Flood Certificate issued by City of Newcastle also specifies the Highest Property Hazard Category and the Highest Life Hazard Category.  These P1 to P6 and L1 to L6 values are required to apply parts of DCP 2023 B1(b).8.0, Management of Risk to Property, and B1(b).9.0, Management of Risk to Life, respectively.  The following map is extracted from the Rhelm flood study; Map G341c Throsby, Styx and Cottage Creek Flood Study - Peak Flood Hazard PMF - Map 3 of 4.

Peak Flood Hazard PMF in Wickham (Rhelm (2022), Part of Map G341c)

The Peak Flood Hazard levels H1 to H6 shown on the above map are correlated with the Risk-to-Property categories P1 to P6 and Risk-to-Life categories L1 to L6 in DCP 2023 Table B1(b).05 & Table 1B(b).03 respectively; for easy reference this correlation is tabulated below.  However, caution is advised.  The example flood information provided below for 26 Bishopsgate Street has risk-to-property P2 and risk-to-life L4 which more closely align with the correlations in the now superseded DCP 2012 4.01, Flood Management.  From the above map, 26 Bishopsgate Street is H4 and the DCP 1B(b) correlation gives P4 and L4, not P2 and L4 as advised by City of Newcastle.

Peak Flood Hazard	Risk to Property	Risk to Life
H1	P1	L2
H2	P2	L2
H3	P3	L3
H4	P4	L4
H5	P5	L5
H6	P6	L6

 

Example at 26 Bishopsgate Street

To assist you with developing concept designs, or just for interest, the flood information provided by City of Newcastle for a 2024 development application at 26 Bishopsgate Street may be helpful.  It reads:

“6. Flood Management

Newcastle Development Control Plan 2023 – Flood Management

The following flood information is relevant to the proposed development:

Local Catchment Flooding	Rhelm, 2023
Estimated 1% Annual Exceedance Probability event level: (equivalent to the “Defined Flood Level” in the Building Code of Australia)	2.29m AHD
Estimated Maximum Flow Velocity of floodwaters (in the “Defined Flood Event” as per the Building Code of Australia)	0.1m/s
Highest Property Hazard Category	P2
Estimated Probable Maximum Flood Level	3.15m AHD (Velocity 0.6m/s)
Highest Life Hazard Category	L4
Minimum floor level for occupiable rooms in a new development on this site is: (equivalent to the “Flood Hazard Level” in the Building Code of Australia)	2.79m AHD

In accordance with the updated flood data and Part B Section B1(b) 'Flood Management' of the NDCP 2023, floor levels of any occupiable rooms on the site are not to be lower than the flood planning level (2.79m AHD). Accordingly, the application is required to be amended as follows:

• The ground floor area of the proposed development is to be designed to FPL 2.79m AHD (including all lift structures)
• The Ground Floor parking area is to be designed to a minimum 1% AEP level of 2.29m AHD.”

City of Newcastle (2024), Request for Information DA2024/00650, pp.2-3)

 This Flood Hazard Level of 2.79 AHD has also been used for ground floor finished floor level and for the crest of the basement car park ramp at 10 Dangar Street (Bowline) and 73 Railway Lane (formerly Nuefort).  It is extrapolated that most of Wickham will have a Flood Hazard Level of 2.79 AHD.At 26 Bishopsgate Street, a ground floor level at 2.79 AHD requires six steps up from the footpath as shown on the elevation and street scape view below.  The driveway also ramps up to 2.79 AHD for the rear car parking spaces; 0.5 m higher than the minimum required but probably raised to this height to get the lift structure in the garage up to 2.79 AHD.

26 Bishopsgate Street – Drawing A205_B – North Elevation (Rombus Design)

26 Bishopsgate Street – Drawing A209_B – Street Scape Views with and without Trees (Rombus Design)

This proposed development provides a shop top residence of two storeys above a small ground floor retail space, entry lobby and vehicle entry to 3 car spaces.  Since the ground floor retail space does not have access to the private residence and it has a high risk-to-life of L4, a flood refuge is required.

“7. Flood Refuge

Flood refuge is required to be provided as the site is subject to flooding and has a high risk to life. The proposed commercial floor area must be provided with flood refuge at PMF level of 3.15m AHD.”

City of Newcastle (2024), Request for Information DA2024/00650, p.3)

The following site floor plan shows how the flood refuge is proposed; it is 0.54 m higher than required and 0.9 m above the surrounding floor level.  (Perhaps it doubles as a work bench?)  This development application has been withdrawn so it is not known if the proposed on-site refuge would be acceptable to City of Newcastle.  DCP 2023 1B(b) C-5 requires, among other things, the on-site refuge to cater for the number of people reasonably expected on the development site, be provided with emergency lighting and withstand the effects of flooding. 

26 Bishopsgate Street – Drawing A202_B –Site Ground Floor Plan (Rombus Design)