15-17 Unwins Bridge Road St Peters NSW September 2013

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1 Marrickville Council j:\jobs\112010\propertytagging\letter docx Unwins Bridge Road St Peters NSW September 2013 Review of Marrickville Council s Property Flood Tagging INTRODUCTION Marrickville Council has undertaken to address flood liability within the Marrickville local government area (LGA) by engaging in the NSW Government s floodplain risk management process and undertaking flood studies to determine the extent of inundation in design flood events. It is seeking to develop and apply a uniform policy for the identification of properties that would be subject to flood related development controls as indicated on the Section 149 (2) planning certificate (termed property tagging) in the context of existing and climate change scenarios. Tagging is undertaken to comply with the planning legislation regarding Section 149 certificates to ensure that appropriate flood related development controls are applied to: Minimise future flood damages; Minimise risk to life; Ensure future development does not worsen the existing flood problem. Without tagging Council officers would have no mechanism to identify properties which are at risk and prospective purchasers would not know the development constraints on the property they were about to purchase. SCOPE OF THIS REVIEW The scope of this review undertaken by WMAwater is summarised as follows: o provide a brief review of the history of property tagging in NSW; o summarise the background to property tagging undertaken by Marrickville Council to date; o provide a review of issues between overland and mainstream flooding; o provide a comparison of the two approaches suggested for Marrickville LGA. It should be noted that this scope does not conclude with any recommendation as Marrickville Council wishes to seek the opinion of the Department of Planning. BRIEF HISTORY OF PROPERTY TAGGING IN NSW The identification of flood liable properties has been undertaken by some NSW Councils for over 20 years, although there are still some Sydney Councils that have not undertaken this process, Prior to the year 2000 properties that were identified were largely derived as a result of mainstream flooding (i.e overtopping of the banks of a river or creek such as the Hunter River or Cooks River, though much smaller creeks were also included in areas that had experienced flooding in the past and were under development pressures), There is no consensus of opinion among NSW Councils regarding the approach to tagging of flood liable properties. Some Councils tag to the 100 year ARI, some to the 100 year ARI + 0.5m freeboard and some tag for both categories using different words. In the past some Councils Webb, McKeown & Associates Pty Ltd (trading as WMAwater) ABN DIRECTORS ASSOCIATES Level 2, 160 Clarence St, SYDNEY NSW 2000 M K Babister BE(Hons), MEngSc GradDipMgt, FIEAust R Hardwick Jones BE(Hons), MEngSc, MIEAust Phone: Fax: R W Dewar BSc(Hons), MEngSc, MAIG, MIEAust enquiry@wmawater.com.au E J Askew BE(Hons), MIEAust Website: wmawater.com.au S D Gray BE, MEng

2 tagged to lower levels (say the 50 year ARI) but this is now not current practice and the consensus is the 100 year ARI. Tagging to above the 100 year ARI + 0.5m is now prohibited for residential properties unless there are special circumstances but it can be applied for non residential properties, The 2001 and subsequent 2005 Floodplain Development Manual introduced the need for Councils to consider overland flooding in addition to mainstream flooding and thus the need to tag properties in these areas, The climate change induced sea level rise (and consequent rise in flood level) has been adopted by some Councils and is under discussion by others. Few Councils have adopted a climate change induced rainfall increase in their planning controls, In the last few years the availability of residential flood insurance and recent floods in urban areas (Newcastle in 2007 and Brisbane in 2011) has increased public awareness of flooding and particularly the potential implications of property tagging and information on the Section 149 certificates resulting in higher insurance premiums, Over the last 10 years significant technological advances (use of Geographic Information Systems (GIS) and 2 Dimensional (2D) hydraulic models employing Airborne Laser Scanning (ALS)) have enabled more accurate and sophisticated property tagging approaches to be employed, Section 149 (2) only requires the Council to include "whether or not the Council has by resolution adopted a policy to restrict the development of the land because of the likelihood of land slip, bushfire, flooding, tidal inundation and subsidence or any other risks. Section 149 (5) provides that a Council may include advice on such other relevant matter affecting the land of which it may be aware. There is no consistent approach between Councils regarding the wording or the details provided or not, in the Section 149 (2) or (5) certificate, The correct definition of flood liable lands is to the Probable Maximum Flood (PMF). However this event has an average recurrence interval of something rarer than 100,000 years. Other natural disasters of similar rarity may be tsunami or a major earthquake in Sydney. It is generally agreed placing building controls on residential housing to negate the impact in these rare events is unreasonable. Several Councils have received adverse publicity when exhibiting their approach to tagging as residents consider it may: lower property values, make construction more expensive, limit some types of development, influence insurance premiums, elicit such comments as this is ridiculous - I have lived here for 50 years and flood waters have never reached my house. This comment may be correct but it can be difficult to explain to residents. The following are some key principles that might be considered in applying a tagging approach: defensible in the Land & Environment Court, in accordance with best practice, simple to apply by Council (e.g to nearest 0.1m), approach should be understood by the public, quantitative rather than qualitative approach to eliminate errors and is able to be replicated on all catchments in the LGA, able to be modified if the need arises due to more accurate survey becoming available or where there is some justifiable complaint, 2

3 the approach must be fully documented, the approach must be uniformly applied across LGA, Council s legal representatives must confirm the proposed policy. BACKGROUND The following provides a brief summary of the approach to date by Marrickville Council for property tagging. Flood liable properties in the 100 year ARI event were first identified (exact date unknown) on Section 149 (2) certificates following completion of the Public Works Department Cooks River Flood Study in Following completion of the Cooks River Floodplain Risk Management Study in 1994 all properties within the 100 year ARI + 0.5m freeboard extent were identified as such on their Section 149 (2) certificate. In 1995 Council added a general notation under the Section 149 (5) to every property in the LGA, stating that the subject property has been or may be likely to be affected by local drainage flooding (this was undertaken as no detailed information was available). In 2007 Council had undertaken drainage studies of 12 of the 19 sub-catchments within the LGA and where appropriate this overland flooding information was included on Section 149 (2) certificates. Currently 884 properties are identified on Section 149 (2) certificates as a result of Cooks River (mainstream) flooding and 1799 properties as a result of local (overland) flooding. According to Council s DCP Flood Management, Section 2.22 floodprone land consists of land which: o is in the flood planning area (Cooks River defined as inundated in the 100 year ARI + 0.5m freeboard), and/or o is in the flood planning area (local overland flooding defined as inundated in the 100 year ARI with no freeboard), or o is flood prone land, but is not in a flood planning area (some land above the Cooks River flood planning area up to the PMF). The 2009 Sydney Water Cooks River Flood Study redefined flood levels along the Cooks River and Council has recently had two Flood Studies undertaken to define flood levels in urban areas away from the Cooks River. These latter studies are termed overland flood studies as opposed to mainstream flooding associated with the Cooks River. A simple definition of mainstream is where flooding occurs due to floodwaters exiting from the main creek or channel and overland is where flooding occurs prior to entry to the main creek or channel. However there is no strict definition and in places the nature of flooding is a mixture of both. ISSUES WITH APPROACHES TO TAGGING IN MAINSTREAM AND OVERLAND FLOODING AREAS For mainstream flooding the tagging is mostly undertaken by NSW Councils to the 100 year ARI + 0.5m freeboard level to ensure that all new buildings are constructed to that level. If the tagging was undertaken just to the 100 year ARI level then the adjoining property (say just 0.1m above the 100 year ARI level) might build a slab on ground house with the floor below the 100 year ARI + 0.5m freeboard level. This approach is commonly used for mainstream flooding throughout NSW for this reason. For overland flooding a different approach is generally adopted due to the relatively flat terrain and/or shallow depths of inundation. The idea of tagging is to ensure that the flood risk on the property is 3

4 adequately addressed (i.e to implement minimum floor levels) and the problem is not worsened as a result of the development. Thus if there is only a minor amount of flooding on a small part of the property it probably cannot be justified that the property should be subject to flood related development controls. All properties in urban areas are inundated by overland flooding in a major storm event and thus some minimum criteria must be adopted. Different Councils approach this in different ways and certainly some LGAs exhibit different topography which requires a different approach. For example, a steep terrain requires a different approach to the relatively flat terrain and shallow depths of inundation which are typical of Marrickville. In a large rainfall event runoff will occur on every street to above kerb level (150mm) in a flat terrain area and if the 100 year ARI + 0.5m freeboard level was adopted it may extend tens of metres each side of the main flow path. This is unrealistic and the 100 year ARI + 0.5m freeboard level would likely exceed the Probable Maximum Flood (PMF) level at this location. An approach to resolve this issue is to combine a minimum depth and minimum % of property inundation criteria on each property. This has been suggested for the overland flow areas in Marrickville and comprises: all new houses in the LGA must be built with their habitable floor and garage a minimum of 0.3m above the surrounding ground. This assumes a maximum 0.15m water depth and 0.15m freeboard (it is unrealistic to assume a 0.5m freeboard if the water depth is only 0.15m). This should be certified as part of the building approval process and is greater than the Building Code of Australia requirement. a property is tagged if it is inundated by a depth greater than 0.15m and greater than 10% of the property is inundated by floodwaters (both conditions must be satisfied): o by adopting the 300mm rule a minimum depth of inundation in the 100 year ARI event of 0.15m can be adopted, o a minimum 10% inundation (regardless of depth) ensures that the majority of the property is above the flood level. One suggestion is to vary the % based on the lot size, however this adds another layer of complexity. tagging is only to the 100 year ARI extent and not to the 100 year ARI +0.5m freeboard extent. This approach is therefore inconsistent with the generally held mainstream flooding approach. It is considered acceptable as in overland flooding areas in Marrickville there is little difference between the 100 year ARI and PMF levels (say less than 0.5m), thus tagging to the 100 year ARI +0.5m freeboard extent might include properties not inundated in the PMF. With this approach and assuming a minimum floor level of the 100 year ARI +0.5m freeboard, at worst new building floors will be only 0.2m below the standard (as all have to obey the 300mm rule ). This approach could be refined to identify areas where there is a significant increase in level between the 100 year ARI and the PMF but this must be balanced against the adoption of a simplified approach. 4

5 COMPARISON OF TWO POSSIBLE APPROACHES SUGGESTED FOR MARRICKVILLE LGA The two approaches are described as follows. Approach 1: For Mainstream flooding residential properties are tagged based on whether any part of the property is inundated in the 100 year ARI + 0.5m freeboard extent. For Overland flooding the approach is as indicated by the dot points in the preceding section. This approach has already been assessed with associated reports prepared, a Councillor briefing held, public exhibition and workshops undertaken and information letters provided to all ratepayers. A map identifying these properties was recommended to be incorporated into the LEP/DCP next amendment. Approach 2: This approach assumes there is a map in the LEP with a line (termed the Flood Planning Area) which extends to the Cooks River PMF and Overland flooding PMF extent. Thus all the properties with any part of their land within this extent would be tagged as flood liable. However flood related development controls would be applied according to a map provided in the DCP. The map in the DCP would define the same Mainstream flood extent as Approach 1 (100 year ARI + 0.5m freeboard extent) and for Overland flooding the extent would be defined where the land in a property is inundated by greater than 10% inundated in the 100 year ARI + 0.5m freeboard extent. The key features of each approach can be summarised as follows. 1. Approach 2 would involve tagging a much greater number of properties than Approach1. 2. Approach 2 would mean those properties tagged in the LEP and not identified on the DCP map would have no flood related development controls imposed. These residential property owners may consider their property attributes have been adversely affected for no reason. 3. Adoption of Approach 2 would require reworking of the community consultation process. 4. Approach 1 does not address the issue of how new developments on non residential land above the nominated criteria and below the PMF, such as hospitals, SES HQs or other essential services, are advised of the flood risk. This could be addressed by extending the mapping to the PMF on all non residential land. 5. Approach 1 does not identify the possible evacuation issues in the PMF. Though it is unclear whether property tagging should identify such issues and particularly beyond the 100 year ARI. 6. Approach 2 adopts the term Flood Planning Area (FPA) on the LEP map. This is misleading as the FPA is generally assumed to relate to the 100 year ARI + 0.5m freeboard extent yet the Approach 2 mapping extends to the PMF extent. The FPA is determined based on balancing the social, cultural, economic and environmental costs and benefits of restricting usage on flood liable lands. WMAwater R W Dewar Director 5