Percy v Wollongong City Council

Case •

[2014] NSWLEC 1102

•

28 May 2014

Land and Environment Court


New South Wales

Medium Neutral Citation: Percy & anor v Wollongong City Council [2014] NSWLEC 1102
Hearing dates:20 March 2014
Decision date: 28 May 2014
Jurisdiction:Class 1
Before: Fakes C
Decision:

The appeal is dismissed

Catchwords: DEVELOPMENT APPLICATION: Alterations and additions; use of existing structures; flooding; design flood levels; adopted council policy;
Legislation Cited: Environmental Planning and Assessment Act 1979
Wollongong Local Environmental Plan 2009
Cases Cited: Stockland Development Pty Ltd v Manly Council [2004] NSWLEC 472
Category:Principal judgment
Parties: Alisa Jane Percy (First Applicant)
John McKenzie Pirrie (Second Applicant)
Wollongong City Council (Respondent)
Representation: Applicants: Mr P Moggach (Solicitor)
Respondent: Mr J Reilly (Solicitor)
Applicants: RMB Lawyers
Respondent: Wollongong City Council
File Number(s):10693 of 2013

Judgment

  1. COMMISSIONER: In August 1998, Wollongong experienced a significant rain event that resulted in extensive flooding and much damage to property. Immediately after the flood, Wollongong City Council collected considerable and detailed data on the nature of the flooding, in particular the type and extent of blockages of stormwater culverts. The data collected resulted in a review of council's blockage criteria to be applied to structures across all watercourses when calculating design flood levels in the many floodplains throughout the City. These design flood levels are integral to determining whether certain developments are permissible or not.

  1. The applicants appeal Wollongong City Council's refusal of Development Application DA-2013/601. The applicants seek development consent for alterations and additions to an existing dwelling house, including the use of an existing structure as a dwelling addition and the use of an existing structure as a storage shed.

  1. The appeal is made pursuant to s 97(1) of the Environmental Planning and Assessment Act 1979 (the Act).

The site and locality

  1. The site is an irregularly shaped lot on the north-eastern side of Hewitts Avenue, Thirroul. It has an area of approximately 3745m2.

  1. Vehicular access is from Hewitts Avenue. The site is bounded to the east by the southern railway line, to the south by residential development, and to the west by vacant land. Hewitts Creek runs across the northern portion of the site. The northern boundary adjoins the rear yards of a residential development.

  1. The site currently contains a single-storey weatherboard cottage, a larger, more recently constructed fibro-clad building on brick piers used for residential purposes, a large metal-clad shed used for storage, and several other minor structures/outbuildings.

  1. Adjacent to the north-western boundary is a Fig tree (Ficus obliqua) listed as an item of local heritage in Wollongong Local Environmental Plan 2009.

  1. Further to the east, beyond the railway line, are a large stormwater channel and a new residential development. Woodlands Creek is further to the south.

  1. The surrounding and nearby residential development comprises detached dwellings.

The catchment

  1. The site is located in the Hewitts Creek Floodplain. Hewitts Creek traverses the northern portion of the site and flows to the east beneath the Hewitts Creek Railway Bridge. This bridge is only metres from the north-eastern corner of the site. As stated above, the railway line and its embankment are on the southern boundary. Hewitts Creek is one of several creeks in the Hewitts Creek Floodplain that collect water from the escarpment to the west. There is a culvert below Lawrence Hargrave Drive to the west of the site.

  1. Upstream of the Hewitts Creek Railway Bridge are the backyards of large lots backing onto a roughly paved track that leads to the concrete apron of the underpass beneath the bridge. This track adjoins a drainage channel between Lawrence Hargrave Drive and the Railway Bridge culvert. The banks of the channel are vegetated with weedy trees and shrubs. There is a large low-lying paddock to the immediate northwest of the site between Hewitts Creek and the drainage channel.

  1. The other relevant Creek is Woodlands Creek, about 300m to the south of the site and which also flows east through a culvert beneath the railway line. The Floodplain also incorporates Slacky, Tramway, and Thomas Gibson Creeks.

The proposal and relevant background

  1. The proposal seeks approval for:

  • Internal alterations to the existing weatherboard cottage as well as the addition of a first floor storage room/refuge.
  • Use of the existing, more recently constructed, residential structure as an addition to the cottage, to be connected by a covered walkway.
  • The use of the existing shed for domestic storage purposes.

  1. Neither the residential structure, nor the shed have council approval.

  1. According to the Statement of Environmental Effects that accompanied the development application, the residential structure occupies the site of a number of original structures. The shed replaces a previous shed deemed to be structurally unsound and which crossed the boundary with the adjoining property.

  1. The Class 1 Application includes a Structural Engineer's Report which considers proposed modifications to the cottage and the residential structure to render them capable of withstanding dead, live and wind loads and be able to resist calculated net flowing water, debris impact forces and buoyancy forces up to RL 17.7m AHD. Another Structural Engineer's report considers modifications to the shed.

The issues

  1. The council contends that the proposal should be refused for the following reasons:

  • The proposal is prohibited under cl 7.3 Wollongong Local Environmental Plan 2009 Wollongong Local Environmental Plan 2009 (WLEP) as the entirety of the site and the habitable floor levels of the existing cottage and residential structure are below the flood planning level, being the applicable level during the 1% Annual Exceedence Probability (AEP) flood event plus 0.5m freeboard.
  • Consent for use of the dwelling addition and storage shed would increase the flood risk to persons and property on the site. Apart from the habitable floor levels being below the flood planning level, the building components and structural integrity are inadequate to withstand forces associated with floods, and no reliable evacuation path has been demonstrated.
  • The proposal fails to comply with relevant sections of Wollongong Development Control Plan 2009 (WDCP), particularly in regards to flood risk.

  1. The applicants' position is that because of the parameters used in the Hewitts Creek Flood Study, it does not provide a true estimate of the 1% AEP flood at that site. The applicants contend that the proposed development has habitable floors above the flood planning level when based on the revised estimate of the 1% AEP flood level and therefore complies with cl 7.3 WLEP. This revised level changes the flood risk from high to medium. They also contend that the proposal complies with relevant performance criteria in WDCP.

Background to council's floodplain controls

  1. Some background to council's floodplain controls is useful in understanding the parties' differences in regards to the applicable flood planning level and thus the permissibility of the proposed development.

  1. The comprehensive report of council's Policy Strategy & Review Committee dated 18.11.2002 provides the background and rationale supporting council's adoption of a conduit blockage procedure as an amendment to its Drainage Design Code. The report includes a conference paper given by E.H Rigby and P Silveri "The Impact of Blockages on Flood Behaviour in the Wollongong Storm of August 1998" at the Conference on Hydraulics in Civil Engineering in Hobart, 2001. This paper describes the data collection and analysis that lead to the formulation of the new procedure.

  1. As stated in the introduction, in August 1998, the northern suburbs of Wollongong received very heavy rainfall, which resulted in flooding, widespread scouring of streams, deposition, blockage of drainage structures, and widespread damage to property including the destruction of dwellings. From the extent of the damage associated with many blockages and flow diversions it was apparent that earlier flood studies failed to reflect the actual flood behaviour. As a result, Wollongong City Council initiated an investigation into flood behaviour during the event in order to assess the appropriateness of its existing flood policies. In October 1999 there was another flood.

  1. A substantial amount of data was collected. According to an undated paper by A.J. Bathelmess and E.H. Rigby, some 162 culvert structures were surveyed, measured and levels of debris accumulation and blockages were recorded on data sheets. Relevantly, the data sheet for the Hewitts Creek Railway Bridge records a blockage of 20%. In addition, people were interviewed and photographs taken.

  1. The 1998 storm event demonstrated that council's practice of considering culvert structures, as 'clear' in the preparation of flood studies did not reflect reality. During that event, blocked culverts elevated flood levels and caused flow diversions that resulted considerable damage.

  1. Analysis of this data formed the basis of council's blockage criteria to be applied to structures across all watercourses when calculating design flood levels. Relevantly, these criteria are:

(i) 100% blockage for structures with a major diagonal opening width of <6m
(ii) 25% bottom up blockage for structures with a major diagonal opening width of >6m.

  1. The conduit blockage procedure was developed in consultation with three engineering consulting firms (including Forbes Rigby Pty Ltd), officers from the (then) Department of Land and Water Conservation (DLWC), and relevant flood plain management committees, including Hewitts Creek. The participants endorsed the new conduit blockage policy.

  1. Council's Blockage Procedure was adopted in 2002. It was incorporated by amendment into council's Drainage Design Code as cl 7.3.1(b). Clause 7.3.1 of the Drainage Design Code considers - Hydraulic Design - Estimation of Design Flood Level. The blockage procedure was used in the modelling undertaken in the Hewitts Creek Flood Study. Hydraulic Design, including council's blockage procedure is incorporated into Chapter E14: Stormwater Management in WDCP 2009.

The Hewitts Creek Floodplain Study

  1. The development of the Hewitts Creek Flood Study and Floodplain Risk Management Study and Plan were overseen by the Hewitts Creek Floodplain Management Committee, which comprised representatives from the community, Wollongong City Council, DLWC, RTA, SES, BHP Billiton and Stocklands.

  1. The study involved collection of historical rainfall and flood data, catchment modelling, calibration, and public consultation. This produced design flow estimates, flood level profiles and flow velocities for a range of storm events ranging from the 50% AEP to the Probable Maximum Flood. The council used the HEC-RAS model [Hydrologic Engineering Centres River Analysis System]. Following feedback and revision, the Plan was put to council and subsequently adopted in February 2003. The modelling for peak flow considered various blockage scenarios including 'clear', 'blocked' and 'critical blockage pattern'. This methodology was used in order to inadvertently neglect a combination of blockages that could lead to the maximised flood level.

  1. The Hewitts Creek Flood Study and Floodplain Risk Management Study and Plan are incorporated into Schedule 2, Chapter E13: Floodplain Management in WDCP 2009. The Hewitts Creek Study and Plan define the flood extents and levels throughout the catchment and recommend flood mitigation options to alleviate the existing hazards. They also define prescriptive planning controls for future development in the catchment.

Council's assessment of the proposal

  1. Council's stormwater engineer assessed the development application against the Hewitts Creek Flood Study and Plan, WLEP 2009, Chapters E13 and E14 of WDCP 2009 and the Australian Rainfall and Runoff Project 11 - Stage 2 Report dated February 2013. The assessment was based on a 'concessional development' land use category in a High Flood Risk Precinct.

  1. The 100 year flood levels/ 1% ARI (AHD) extracted from the Hewitts Creek Flood Study for the site at the location of the dwellings/ shed are noted as 16.0m.

  1. The assessing officer noted:

"A review of the flood study report by Cardno dated May 2013 has revealed that Cardno's determination of the 'alternative' 100 year flood level of RL 13.0 AHD for the site is based on a subjective analysis of conduit blockage, whilst using a draft guideline published by Australian Rainfall and Runoff. In this respect the 'alternative' 100 year flood level presented cannot be relied upon to establish an alternative flood planning level for the site".

Revised level

  1. After council's assessment, during joint conferencing between the parties' flooding experts, the applicants' expert Mr Nichols advised council's independent expert Dr Webb, that the Hewitts Creek Railway Bridge culvert, a critical element in the immediate catchment, was larger in size than modelled in the flood study.

  1. The culvert was resurveyed and the new dimensions were entered into the hydraulic model used to produce the levels within the Flood Study. The revised 1% ARI for the land was determined to be 14.69m AHD. With the addition of 0.5m freeboard, council's revised flood planning level is 15.19m AHD.

  1. The lowest habitable floor level of the development 13.76m AHD. The site ranges from RL 9.39m AHD to 13.8m AHD.

Planning controls

  1. The site is zoned Zone R2 Low Density Residential in WLEP. The proposed development is permitted with consent.

  1. Relevantly, cl 7.3 applies. This states:

7.3 Flood planning area
(1) The [relevant] objectives of this clause are as follows:
(a) to maintain the existing flood regime and flow conveyance capacity,
(b) to enable evacuation from land to which this clause applies,
(c) to avoid adverse impacts on flood behaviour,
(e) to limit uses to those compatible with flow conveyance function and flood hazard
(2) This clause applies to land at or below the flood planning level.
(3) Development consent must not [emphasis added] be granted for development on land to which this clause applies unless the consent authority is satisfied in relation to all the following matters:
(a) all habitable floor levels of the development will be above the flood planning level,
(b) the development will not adversely affect flood behaviour resulting in detrimental increases in the potential flood affectation of other development or properties,
(c) the development will not significantly alter flow distributions and velocities to the detriment of other properties or the environment of the floodplain,
(d) the development will not affect evacuation from the land,
(e) the development will not significantly detrimentally affect the floodplain environment or cause avoidable erosion, siltation, destruction of riparian vegetation or a reduction in the stability of river banks or watercourses,
(f) the development will not result in unsustainable social and economic costs to the community as a consequence of flooding,
(g) if located in a floodway area - the development will not be incompatible with the flow conveyance function of, or increase a flood hazard in, the floodway area.

  1. The parties agree that clause 7.3(3)(a) prohibits the development in its current form if the flood planning level is above 13.76m AHD, which is the lowest habitable floor level of the development.

  1. WLEP Dictionary defines 'flood planning level' as ' the level of a 1:100 ARI (average recurrent interval) flood event plus 0.5 metres freeboard. [1:100 ARI = 1% AEP (Annual Exceedence Probability = The probability that a given rainfall total accumulation over a given duration will be exceeded in any one year)].

  1. Chapter E13: Floodplain Management is the relevant part of Wollongong Development Control Plan 2009. This chapter provides council's controls for development on flood liable land and should be read in conjunction with the NSW Government Flood Prone Lands Policy and the NSW Floodplain Development Manual (FDM) and other relevant parts of WDCP.

  1. The relevant key objectives in cl. 3.1 are:

e) Reduce the risk to human life and damage to property caused by flooding through controlling development on land affected by potential floods.
f) Provide detailed controls for the assessment of applications lodged in accordance with the Environmental Planning and Assessment Act 1979 on land affected by potential floods.
g) Provide different guidelines, for the use and development of land subject to all potential floods in the floodplain, which reflect the probability of the flood occurring and the potential hazard within different areas.
h) Apply a "merit-based approach" to all decisions relating to flood affected development which take account of social, economic and ecological as well as flooding considerations.
i) To control development and activity within each of the individual floodplains within the LGA having regard to the characteristics and level of information available for each of the floodplains, in particular the availability of FRMSs [Floodplain Risk Management Studies] and FRMPs [Floodplain Risk Management Plans] prepared in accordance with the FDM [Floodplain Development Manual - NSW Government 2005] and its predecessor, the FMM [Floodplain Management Manual - NSW Government 2001].
j) Deal equitably and consistently with applications for development on land affected by potential floods, in accordance with the principles contained within the FMM, issued by the NSW Government.

  1. Other relevant definitions from WDCP are:

  • Average Recurrence Interval (ARI) means the long-term average number of years between the occurrence of a flood as big as, or larger than, the selected event. For example, floods with a discharge as great as, or greater than, the 20 year ARI flood event will occur on the average once every 20 years. ARI is another way of expressing the likelihood of occurrence of a flood event.
  • Floodplain (being synonymous with flood liable and flood prone land) is the area of land which is subject to inundation by the probable maximum flood (PMF).
  • Freeboard is a factor of safety expressed as the height above the design flood level. Freeboard provides a factor of safety to compensate for uncertainties in the estimation of flood levels across the floodplain, such as wave action, localised hydraulic behaviour and impacts that are specific event related, such as levee and embankment settlement, and other effects such as "greenhouse" and climate change.
  • Habitable floor area means: In a residential situation: a living or working area, such as a lounge room, dining room, rumpus room, kitchen, bedroom or workroom.
  • Probable maximum flood (PMF) is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation.
  • Reliable access during a flood means the reliability for people to safely evacuate an area subject to imminent flooding within effective warning time, having regard to the depth and velocity of flood waters, the suitability of the evacuation route, and without a need to travel through areas where water depths increase.

  1. Clause 6 explains the key criteria for determining applications. This requires identifying the land use category, the relevant floodplain/ part of that floodplain, and then applying the controls in cl. 6.4.

  1. The relevant land use category as assessed is 'concessional'. The site is located in the Hewitts Creek Floodplain. Schedule 2: Prescriptive Controls - Hewitts Creek Floodplain identifies 'Residential' development as an unsuitable land use in areas of High Flood Risk however, various prescriptive controls apply to 'Concessional Development' (see [50] below).

  1. Clause 6.3.1.a)i. describes a High Flood Risk Precinct (council's position) as the area within envelope of land subject to a high hydraulic hazard in a 100 year flood event plus all land within a corridor 10m from the top of the creek bank. The high flood risk precinct is where high flood damages, potential risk to life, evacuation problems would be anticipated. Most development should be restricted in this precinct. There would be a significant risk of flood damages without compliance with flood related building and planning controls.

  1. A Medium Flood Risk Precinct (the applicants position) is defined as land below the 100 year flood level (plus 0.5m freeboard) that is not within the High Flood Risk Precinct. It is land subject to low hydraulic hazard. There would still be significant risk of flood damage but these damages can be minimised by the application of appropriate development standards (cl.6.3.1.b)i.).

  1. Clause 6.4.1 Objectives (d) and (f) are pressed by council; these are:

(d) To prevent any intensification of the use of High Flood Risk Precinct [FRP] or floodways, and wherever appropriate and possible, allow for their conversion to natural waterway corridors;
(f) To minimise the risk to life by ensuring the provision of appropriate access from areas affected by flooding up to extreme events.

  1. Relevant performance criteria in cl. 6.4.2 are:

(a) The proposed development should not result in any increased risk to human life.
(b) The additional economic and social costs which may arise from damage to property from flooding should not be greater than that which can reasonably be managed by the property owner and general community.
(c) The proposal should only be permitted where effective warning time and reliable access is available for the evacuation of an area potentially affected by floods. Evacuation should be consistent with any relevant or flood evacuation strategy where in existence.

  1. Car parking controls in cl 6.5.1-3 include minimising damage to motor vehicles from flooding and ensuring that vehicles do not become moving debris during floods which threaten the integrity of structures or the safety of people, or damage other property. Garages are not permitted within a High FRP. It is noted that there is no easy vehicle access to the applicants' shed.

  1. Additional prescriptive controls for Hewitts Creek Floodplain for a Concessional Development in a High Flood Risk area:

  • Habitable floor levels to be equal to or greater than the 100 year flood level plus freeboard.
  • All structures to have flood compatible building components below or at the 100 year flood level plus freeboard.
  • Engineer's report to certify that any structure can withstand the forces of floodwater, debris and buoyancy up to and including a 100 year flood plus freeboard.
  • An engineer's report is required to certify that the development will not increase flood affectation elsewhere.
  • Reliable access for pedestrians and vehicles during a PMF flood; reliable access for pedestrians or vehicles is required from building, commencing at a minimum level equal to the lowest habitable floor level to an area of refuge above the PMF level or a minimum of 20m2 of the dwelling to be above the PMF level. The applicant is to demonstrate that evacuation of potential development as a consequence of a subdivision proposal can be undertaken in accord with this Plan.

Hearing and evidence

  1. The hearing was held on site and commenced with an inspection of the site and relevant elements of the immediate catchment including the Hewitts Creek Railway Culvert, and the land between the Railway Bridge and the culvert on Lawrence Hargrave Drive to the west. The locations of other flood-affected properties were noted.

  1. The Court heard from Mr Simon Ackerman, a local resident who recalled being able to walk beneath the Hewitts Creek railway bridge the day after the flood. He indicated that a photograph of the culvert showing some mounds of gravel and sediment was essentially as he remembered it.

  1. The applicants rely on the expert report and evidence of Mr Paul Nichols, a Civil Engineer and Senior Principal of Cardno Pty Ltd. Mr Nichols was involved in post-flood insurance inspections, subsequent litigation and the design of flood mitigation works following the 1998 Wollongong flood. Council relies on the expert evidence of Dr Stephen Webb, Civil Engineer (Hydrologist), Stephen N Webb & Associates Pty Ltd, Consulting Engineers. As with Mr Nichols, Dr Webb was involved in post 1998 flood assessments.

  1. The engineers prepared individual reports and participated in joint conferencing. On the critical questions of the applicability of council's blockage policy and ultimately the 1% AEP flood level that applies to the site, there is no agreement. The experts generally agree that the 1998 flood has an ARI of about 30 years.

  1. Annexure A of this judgment shows tables indicating comparative 1% AEP flood levels at the site. Table 1 was supplied to Dr Webb by Wollongong City Council on 16.1.2014 and is taken from p7 Exhibit 5. Table 2 indicates the calculations by Mr Nichols and Dr Webb's HEC-RAS model, being the same model used by council in the 2002 flood study, as well as re-modelling carried out by Cardno at Mr Nichol's request (p 7 Exhibit C).

  1. Table 2 in Annexure A shows that using council's specified 25% bottom-up blockage figure and both 'Policy Blocked' and 'Mixed Mode' scenarios, all models result in a 1% AEP flood level in excess of the 13.73m AHD floor level. However, Mr Nichols fundamentally disagrees with the type and extent of the blockage assumed in council's policy and modelling; in his view this results in a figure that is far too conservative. Dr Webb considers that in the absence of any revised model, this presents a realistic 'best estimate' based on actual data. In his opinion it is not unduly conservative.

  1. The experts' arguments and rationale for their positions are comprehensively and technically detailed in their statements of evidence. The sections below summarise their positions.

Mr Nichols' approach and position

  1. Mr Nichols' view is that while the data collected after the 1998 flood is a good starting point, the assumptions made in regards to the blockage of the railway bridge culvert do not accord with first hand observations he sought from local residents or with photographs taken shortly after the event. He states that many data sheets and other information collected at the time are missing and therefore can't be verified. In his opinion, the relevant culverts, in particular the railway bridge, were considerably less blocked (0 - 5%) than assumed by council, and therefore council's blockage policy results in overly high and conservative design flood levels. In his opinion, any blockage would be more likely to be top-down rather than bottom-up. Similarly, he considers that the historic records of local flooding do not support council's calculated flood levels. He maintains that a 1% AEP flood will be only 28-33% more than the peak discharge in the 1998 flood.

  1. Mr Nichols contends that the calculation of a 'true' 1% AEP should be based on 'likely' blockage factors rather than maximised ones or 'worst-case' scenarios otherwise the probability of the event will be distorted. To this end, in his statement of evidence, November 2013 (Exhibit B) Mr Nichols used a waterway calculation methodology using parameters of partial, top-down blockages for key culverts (including 10% top-down at Hewitts Creek railway bridge), the likely type/mobility/transportability of local debris, and Shellharbour Council's interim blockage policy, which in Mr Nichols' opinion is a more realistic blockage policy for flatter areas. The figure he derived for a 1% AEP flood level was 13.0m AHD, which plus 0.5m freeboard gives a flood planning level of 13.5m AHD and thus achieves compliance with cl 7.3(a) WLEP.

  1. Following joint conferencing with Dr Webb, Mr Nichols refined the his calculated flood levels for the 1% AEP flood to reflect the latest survey of the Hewitts Creek railway bridge using the same waterway calculation methodology as earlier but expanded to include a number of blockage scenarios and combinations. Mr Nichols states that the remodelling by council using the 2002 HEC-RAS model produced levels that concurred with his calculations for the most severe blockages but predicted much higher flood levels for less severe scenarios.

  1. To understand the differences, Mr Nichols reviewed the 2002 HEC-RAS model and determined it was not appropriately schematised for less severe blockages and included, amongst other things, parameters that in his view did not reflect the current channel geometry or appropriate roughness co-efficient. To this end he organised for Cardno's flood modelling team to adjust the HEC-RAS model and calculate the 1% AEP levels to reflect what he maintains is the current situation.

  1. Using the figures from the Cardno HEC-RAS model, and his figures from the Mixed Mode scenarios, Mr Nichols then considered three different overall scenarios of likely blockage using assessments of the probability of the key factors affecting flood flows as a result of blockage (detailed in Exhibit C) to calculate what he contends is the 'true' 1% AEP flood level applicable to the site. In selecting the most conservative of these, that is the scenario that gave the highest level, his revised 'true' 1% AEP flood level is 13.25m AHD giving a flood planning level of 13.73m AHD. This is below the lowest habitable floor level.

  1. The revised 1% AEP flood level results in a 'medium risk' categorisation, however Mr Nichols opines that additional risk management measures are appropriate such as the proposed refuge and adoption of recommendations to ensure structural adequacy.

Dr Webb's position

  1. Dr Webb's position can be summarised as:

  • The 1998 flood had an ARI of no more, and probably less, than 30 years; therefore flooding and potential debris flows, particularly in the lower catchment, could be expected to be much larger in a 100 year ARI (1% AEP) event.
  • The photographs taken some time after the flood do not preclude a greater blockage than the debris indicates.
  • Council's blockage policy is based on unusually good local data from a major flood event in recent times. Council recently reviewed the policy in light of the draft AR&R Project 11 Report. The AR&R report encourages the use of 'local data', which in his view does not include adopted policies from other local government areas such as Shellharbour as used by Mr Nichols. Council concluded there should be no change to their blockage policy.
  • A bottom-up blockage of at least 25% should be assumed for a 100 year ARI flood; council's confirmed normal application of 'mixed-mode' is appropriate and not unduly conservative.
  • Mr Nichol's model use of a nomograph/formula approach, being the waterway calculation, is a less sophisticated approach than the HEC-RAS model in deriving flood levels and is inconsistent with the Hewitts Creek Flood Study methodology and therefore results in artificially low flood levels. The use of Shellharbour City Council's interim blockage policy is not applicable to Wollongong, especially as the Wollongong policy is based on local data. There are similar concerns over inconsistent changes used by Cardno in their reconfigured HEC-RAS modelling.
  • The appropriate, non-conservative, Flood Planning level for the site is 15.19m AHD based on 1% AEP Flood Level of 14.69m AHD (Mixed Mode 25% bottom-up blockage) plus 0.5m freeboard.
  • As a consequence, the revised 1% AEP Design Flood level of 15.19m AHD places the site in a High Flood Risk Precinct and consequential risk to human life. The site is likely to be subject to high velocities, especially during the early stages of a major flood. A PMF would be higher, and would have more flow, velocity and debris than the 1% Design Flood and therefore would be more even more hazardous.
  • Based on reported and analysed rainfall data, the response time in the Illawarra catchments is 30-40 minutes; translated to this site, from the time of a heavy burst of rainfall higher in the catchment, the rising floodwaters would be at the site in about 30 minutes giving anyone on the property little time to evacuate. This would be more serious in a PMF flood.

Planning

  1. Council engaged Mr Mark Adamson, a consultant Town Planner to prepare a statement of evidence. Mr Adamson's evidence is uncontested. Mr Adamson concurs with the council's position in that:

  • The proposal is prohibited as it does not comply with cl 7.3(a) WLEP.
  • The applicants have failed to demonstrate a reliable evacuation path but rely on a refuge within a roof. This is contrary to the objectives and strategy in WDCP E13 that seeks to minimise risk to human life. The structural engineer's report indicates a number of modifications will be required to enable unobstructed flow of flood waters in the roof space and therefore the refuge is a high risk environment.
  • The storage of materials in the shed potentially introduces hazardous substances into the waterway.
  • Increased occupancy of the residential dwellings typically results in an increase in motor vehicles on a site. There are no provisions to minimise damage to vehicles from flooding as required by cl 6.5.1.

Mr Adamson concludes in part:

Given present knowledge of significant flood risk and the particularly low lying nature of the site and locality, it is concluded that the site is not suitable for development of this nature. The works serve only to entrench r residential use in a high risk environment.....To satisfy s 79C(c) the site (and or/surrounding land) may require similar modification [to the recent residential subdivision on the eastern side of the railway] to ensure flood risk is suitably mitigated or an application that demonstrates how an alternative new dwelling could be suitably designed to respond to its high risk environment.

Submissions

  1. Mr Moggach, for the applicants, submits that this matter requires the Court to determine the flood planning level for the site. In this regard he submits that Mr Nichols' evidence should be preferred because Mr Nichols has sought primary evidence of the actual blockage that occurred in 1998 and has undertaken extensive modelling of the likely blockage scenarios. His analysis is detailed and appropriately conservative. The figure he derives is consistent with historical records. Mr Moggach contends that the old cottage, built in the 1940s-mid 1950s and with a floor level of 14.09m AHD, has never flooded.

  1. Mr Reilly for the council maintains that the Hewitts Creek Flood Study and Floodplain Risk Management Study and Plan were prepared in accordance with the relevant NSW Government policy in collaboration with a wide range of stakeholders, subsequently adopted by council and have been applied consistently.

  1. Given the importance of the matter, the council engaged Dr Webb to 'peer-review' council's officer's assessment. Mr Reilly relies on the evidence of Dr Webb and the uncontested evidence of Mr Adamson. In regards to Mr Nichols' approach, Mr Reilly contends that it is inconsistent with the adopted flood study, inconsistent with WDCP, inconsistent with official data collected after the 1998 flood, and is based on subjective evidence and assumptions. In any event, Mr Reilly maintains that the flood planning level figure derived by Mr Nichols is only 40mm lower than the floor level of the residential structure.

Consideration

  1. In essence the determination of this matter rests on whose flood design level I should accept. This begs the greater question of whether an adopted council policy should be abandoned in the particular circumstances of this site and an alternative proposal accepted.

  1. The policy in question is Wollongong City Council's Conduit Blockage Procedure that was incorporated by amendment into council's Drainage Design Code for the purpose of Hydraulic Design - Estimation of Design Flood Level. The procedure was subsequently applied to the Hewitts Creek Flood Study and Floodplain Risk Management Plan, which were then incorporated into WDCP 2009 (see [19]-[29] for a more detailed description of this process).

  1. Dr Webb's evidence includes emails from council's Senior Floodplain Management Engineer confirming council's commitment to leave the blockage policy unchanged.

  1. In Stockland Development Pty Ltd v Manly Council [2004] NSWLEC 472, McClellan J, from [88] to [92], considers the weight to be given to a relevant policy that is not a development control plan. At [91] His Honour states:

91 In my opinion, the weight to be given to a detailed policy will depend upon a number of matters. If the policy has been generated with little, if any, public consultation and was designed to defeat a project which is known to be under consideration by a developer for a particular site, it may be given little weight. Of course, the intrinsic attributes of the policy may be given significant weight, but that weight is not dependent on then being included in a policy. It can be established in other ways. However, the position would be markedly different if the policy is the result of detailed consultation with relevant parties, including the community and the owners of affected land, and reflects outcomes which are within the range of sensible planning options.

  1. I am satisfied on the evidence that council's blockage procedure/ policy is the result of extensive data collection undertaken by a range of appropriately qualified personnel from council and the private sector. It was developed in consultation with engineering consulting firms, State Government departments and six floodplain management committees, all of whom endorsed the procedure. It was a consequence of a significant flooding event that demonstrated the inadequacy of the previous blockage policy. There is no contention from the applicants that council has not consistently applied the policy. To that end, I must give it considerable weight.

  1. The incorporation of the blockage procedure into other codes, plans and eventually WDCP, adds to its weight.

  1. I appreciate Mr Nichols has spent considerable time and effort considering anecdotal and photographic material that suggests the blockage of the Hewitts Creek railway culvert was not as described in council's data sheet. However, I cannot give more weight to recollections, including Mr Ackerman's, some 16 years after the event than to data collected at the time by qualified personnel.

  1. Similarly, I acknowledge Mr Nichols' diligence in applying an alternative model and commissioning Cardno to prepare a revised HEC-RAS model to take account of recent changes in the catchment however, I share Dr Webb's concern that some of the parameters apply to other LGAs. I also have some difficulty in giving more weight to the application of an alternative model that has not been peer-reviewed and which is inconsistent with the model that has been used by council since 2002.

  1. Although I agree that it is inevitable that changes will have occurred in many parts of the catchment over the last 12 years, and a council policy inevitably applies a 'broader brush' that cannot take account of the full range of local variables, I also agree with Dr Webb that until a new model is developed, applied and tested, the only consistent decision making tool is the use of council's model which incorporates the blockage policy. Consistency provides more certainty to planners and developers, which in my view is a sensible planning outcome.

  1. The engineers agree that the 1998 flood was a 30-year ARI event. Therefore it must stand to reason that a 100 year ARI flood event, the benchmark for the relevant prescriptive controls for the site, would be as described by Dr Webb as higher, faster, with more debris. Given the complexity of the catchment, and the potential risk to life and property in any major flood, and the subsequent costs to individuals and communities, it seems reasonable for the council to take a relatively conservative approach in its modelling; a policy position expressed in the Hewitts Creek Flood Study.

  1. I agree with Mr Reilly, Mr Nichols' final figure is just 40mm below the lowest habitable floor level, and given the departures from council's policy and model, there is little room for error.

  1. Therefore I have determined the appropriate flood design level that applies to the site is 15.19m AHD. As this is above 13.76m AHD, which is the lowest habitable floor level of the development, the proposal, in its current form, cannot comply with cl 7.3(a) in WLEP, and consent cannot be granted. It is therefore not necessary to consider the other contentions raised by council. Needless to say, neither does the proposal comply with the prescriptive controls for a Concessional Development in a High Flood Risk area in the Hewitts Creek floodplain as described in WDCP.

  1. At the conclusion of the hearing, Mr Moggach asked that if I found against the applicants I would defer final orders to enable further exploration of an engineering solution to their dilemma. While I empathise with the applicants' position, I must determine the matter on the facts and circumstances that have been presented to me and in accordance with the provisions of s 79C of the Act. To that end, I must refuse the appeal.

  1. However, my refusal of this appeal should not be seen as a deterrent to an appropriately made and further application to council. As previously mentioned, the Class 1 application includes Structural Engineer's reports for the cottage and the residential structure as well as the shed. These reports consider the structural adequacy of the buildings as they are, and make recommendations for any modifications to ensure adequacy in regards to flooding loads as well as dead, live and wind loads. The reports indicate that the buildings can be structurally modified to withstand the relevant loads.

  1. The Class 1 application also includes a BCA Compliance Report, which concludes that subject to required certification and completion of outstanding works, the residential structure could be considered suitable for occupation.

  1. As required, the council has also turned its mind to what works and processes would be required should I have upheld the appeal. The applicant agrees with council's draft without prejudice conditions. Therefore, it would seem to me that there is a way forward but it is contingent, on amongst other things, compliance with all elements of cl 7.3 of WLEP.

Orders

  1. Therefore in conclusion, the Orders of the Court are:

(1)   The appeal is dismissed.

(2)   Development application DA-2013/601 for alterations and additions to an existing dwelling house including the use of an existing structure as a dwelling addition and the use of an existing structure as a storage shed at 32 Hewitts Avenue, Thirroul is refused.

(3)   All exhibits except A, 8 and 9 are returned.

_________________________

Judy Fakes

Commissioner of the Court

Annexure A

Decision last updated: 02 June 2014

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Stockland Development Pty Ltd v Manly Council [2004] NSWLEC 472