Planning applications for the development of land that is prone to inundation by 1 in 100 year ARI flood events, or is likely to be prone to the same in the future as a result of sea-level rise, need to satisfy the provisions of Schedule J of the Battery Point Planning Scheme 1979 or Schedule Q of the City of Hobart Planning Scheme 1982.
These schedules set out ‘acceptable solutions’, which, if met, render the development 'permitted' for the purposes of the Schedule.
As an alternative, there are ‘performance criteria’ which applicants can seek to meet rather than the ‘acceptable solutions’. These applications are 'discretionary' and require public notification.
The Schedules have been introduced by the Council in its capacity as a planning authority, as a prudent response to projected sea level rises arising from global warming.
Storm Surge Prone Land has been defined as all land below 3m on the Australian Height Datum [Tasmania AHD83]. Note that 0.0 metres AHD83 approximates the mean sea level in Tasmania in 1972.
The 3m AHD83 datum is based on a report by Sharples (2006) Indicative Mapping of Tasmanian Coastal Vulnerability to Climate Change and Sea-Level Rise: Explanatory Report (2nd Ed)”. The maximum 1% Annual Exceedance Probability (AEP) for 2100 is 1.943 m above AHD83 in the Hobart Region. A 1.0m freeboard is then added to account for wind and ocean swell generated waves. This totals 2.934m; rounded up to 3m.
#Annual Exceedance Probability (AEP) means the likelihood of occurrence of a flood of a given size or larger in any one year, usually expressed as a percentage. For example, if a peak flood discharge of 100 cubic metres per second has an AEP of 1 percent, there is a 1 percent probability (approximately equivalent to an average recurrence interval of 100 years) of a peak flood discharge of 100 cubic metres per second or larger occurring in any one year. Note however that the AEP of a flood event gives no indication of when a flood of that size will occur next.
Flood Level
The ‘acceptable solution’ for development on flood prone land sets a figure of 300mm above the 1 in 100 year flood level to provide a freeboard above a defined level of risk. It accounts for variations in flood levels due to such events as increases in storm intensity, build up of debris, high tides and storm surge. This is consistent with the Building Act 2000 which states in Clause 159 that:
“A person must not erect or place a building containing habitable rooms on land subject to flooding unless the floor level of each habitable room in the building is 300mm or more above the prescribed designated flood level for that land.”
Indicative plans showing the approximate 3.0m datum and land for those sections of Hobart’s urban watercourse modelled by Council to date as being prone to flooding at the 1% AEP level of risk are available for viewing below.
Storm Surge and Flood Prone Areas
It should be noted that the plans are not a part of the Battery Point Planning Scheme 1979 or the City of Hobart Planning Scheme 1982, but will be referenced by Council in determining whether the Storm Surge and Flood Prone Land Schedule should be invoked. In cases of doubt, surveyed site plans will be required as part of any planning application. Accordingly, having your land surveyed before you commission any design drawings will enable you to plan properly for the development of your property.
If are contemplating the development of land that is close to any watercourse (including one not yet modeled and mapped by Council) and think it may be at risk then you should seek advice from Council officers on (03) 6238 2715.
Note: Some of the land in Map 9 falls within the planning area of the Sullivans Cove Planning Scheme 1997 . That planning scheme has not been subject to an amendment inserting a Storm Surge and Flood Prone Land Schedule.