Background
1This appeal is against council's refusal of a development application for the construction of a split-level dwelling at 265 Seventh Avenue, Llandilo. The site is situated within the South Creek floodplain and is liable to flooding.
2In summary the contentions are:
The proposed development should not be approved because it is located within the floodway and any obstruction caused by the new dwelling could restrict flows and cause adverse impacts on other properties in the area.
The site is within a high hazard area where the risk to persons and property is unacceptable and likely to place additional demand on emergency services.
[2]
The proposal
3The proposal involves the construction of a flood free mound, which is about 900 mm above natural ground level (NGL), which is typically RL 16.1 m AHD upon which the dwelling is to be constructed. The proposed twostorey split level dwelling comprises:
a. The ground floor plan contains a double garage, store - room, laundry and washroom (RL 17.278m AHD).
b. The mid level on the ground floor plan shows a family room, dining room, kitchen, study and lounge (RL 18.64m AHD).
c. The first floor plan shows four bedrooms, a TV area, a bathroom and an ensuite (RL 20.15m AHD).
4The site plan indicates the dwelling would be located 20 m from the front northern boundary (Seventh Avenue), 25 m from the eastern boundary, 59.145 m from the western boundary and 157.85 m from the southern boundary.
[3]
The site
5The subject site is currently vacant and is situated at the eastern end of Seventh Avenue approximately 400 m west of South Creek. It has a frontage of 100.58 m and a depth of 201.25m. The site has an area of 2.026 ha
6The subject site is orientated in a northerly direction and is relatively flat with less than 500 mm fall overall. It is generally clear of vegetation although there are some trees along the eastern boundary.
7The subject site is situated within the South Creek floodplain. Major flood events in South Creek have occurred in 1956 and 1988. The 1% Annual Exceedance Probability (AEP) flood level for the site is estimated to be RL18.1m AHD. The flood modelling predicts that the area around the mound would in the 100 year flood event be subject to depths and velocities of water of approximately 1.7m - 2.0m and 0.5m/s - 0.6 m/s respectively. The site is completely submerged by floodwater during the 1% AEP.
8The surrounding area is characterised by rural and rural-residential development with intensive horticulture in the form of market gardens to the south and further north of the site.
[4]
Planning controls
9The site is subject to the following controls. Firstly, the Penrith LEP 2010 applies, under which the site is in the RU4 Primary Production Small Lots zone. The objectives of the zone are:
To enable sustainable primary industry and other compatible land uses.
To encourage and promote diversity and employment opportunities in relation to primary industry enterprises, particularly those that require smaller lots or that are more intensive in nature.
To minimise conflict between land uses within this zone and land uses within adjoining zones.
To ensure land uses are of a scale and nature that is compatible with the environmental capabilities of the land.
To preserve and improve natural resources through appropriate land management practices.
10Clause 6.3 of LEP 2010, "Flood planning" applies to the subject land. The objectives of clause 6.3 are as follows:
a. to minimise the flood risk associated with the use of the land,
b. to limit uses to those compatible with flow conveyance function and flood hazard,
c. to manage uses to be compatible with flood risks,
d. to enable safe and effective evacuation of land,
e. to ensure the existing flood regime and flow conveyance capacity is not compromised,
f. to avoid detrimental effects on the environment that would cause avoidable erosion, siltation, destruction of riparian vegetation or a reduction in the stability of river banks or waterways.
11Clause 6.3(4) states that development consent must not be granted for development on land that is flood planning area or other land at or below the flood planning level unless the consent authority is satisfied that the development:
a. is compatible with the flood hazard of the land, and
b. if located in a floodway, is compatible with the flow conveyance function of the floodway and the flood hazard within the floodway, and
c. is not likely to adversely affect flood behaviour resulting in detrimental increases in the potential flood affectation of other development or properties, and
d. is not likely to significantly alter flow distributions and velocities to the detriment of other properties or the environment, and
e. is not likely to adversely affect the safe and effective evacuation of the land and the surrounding area, and
f. is not likely to significantly detrimentally affect the environment or cause avoidable erosion, destruction of riparian vegetation or a reduction in the stability of river banks or waterways, and
g. is not likely to result in unsustainable social and economic costs to the community as a consequence of flooding, and
h. is consistent with any relevant floodplain risk management plan.
12Penrith Development Control Plan 2010 (the DCP) applies to the site. Chapter C3 cl 3.5(C)(2)(a) of the DCP states that Council will consider development on flood liable land but will not grant consent to development in floodways or in high hazard areas.
13The New South Wales Flood Prone Land Policy as contained in the 2005 Floodplain Development Manual (FDM) are relevant to the proposed development. The Floodplain Development Manual seeks to reduce the impact of flooding and flood liability on owners and occupiers of flood prone land and to reduce private and public losses resulting from floods. The manual seeks a balanced approach to risk management taking into account existing flood risk, future flood risk and continued flood risk based on flood data.
[5]
The evidence
14Detailed evidence was presented by:
Mr C Thomas; Council's consulting engineer
Mr D Bewsher; Applicant's consulting engineer
Mr A Wilkinson; Council's Engineering Services Manager,
Mr P Wood; Council's D. A. Coordinator
Mr P Grech; Applicant's consulting planner.
A number of local residents gave their opinions on past flooding events in Seventh Avenue.
15The threshold issue in this matter concerns the degree of flooding and associated risk to persons and property. Mr Thomas explained that since 2005 his company Worley Parsons has been engaged with Penrith, Liverpool, Blacktown and Fairfield City Councils to develop an updated flood model of the South Creek system. This model is based on an extensive array of topographic data that has been shown to be more reliable than the data that was available at the time the previous flood studies were completed. The new flood model is considered to be the most up-to-date and reliable tool for flood estimation and has been used as the basis for the Draft Updated South Creek Flood Study that is currently before all Councils for adoption.
16The results of the flood modelling that has been undertaken for the Updated South Creek Flood Study have been referenced to determine the flood affectation of the property that is proposed for development. The results show that the site is located within the 1 % Annual Exceedance Probability (AEP) floodplain of South Creek. The 1% AEP flood level at the site due to flooding from South Creek is 18.1 m AHD. Flooding of the site from the Hawkesbury River can also occur due to floodwaters backing up along South Creek. The 1 % AEP flood level at the site due to flooding of the Hawkesbury River is estimated to be 17.3 m AHD.
17The flood characteristics at the site are summarised in Table 1 for a number of design 1 % AEP flood scenarios.
Table 1 FLOOD CHARACTERISCS AT THE SITE FOR DESIGN 1% AEP SCENARIOS
SCENARIO DESCRIPTION 1% AEP FLOOD MODELLING RESULTS
Minimum Level (mAHD) Maximum Level (mAHD) Minimum Velocity (m/s) Maximum Velocity (m/s) Minimum V x D Product (m2/s) Maximum V x D Product (m2/s)
1 Local catchment 1% AEP flood + Hawkesbury River 1% AEP floor (Refer Figure 1) 17.95 18.10 0.5 0.8 1.0 1.6
2 Local catchment 1% AEP flood (Refer Figure 2) 17.45 17.70 0.6 1.0 0.85 1.6
3 Hawkesbury River 1% AEP Flood 17.3 17.3 N/A N/A N/A N/A
[6]
18From these scenarios, Mr Thomas says that based on available topographic data for the site, the occurrence of a 1 % AEP flood in South Creek with a concurrent 1% AEP flood in the Hawkesbury River (Scenario 1 in Table 1) would result in flooding to a depth of 2.1 m in the vicinity of the area proposed for the new dwelling. Peak floodwater velocities of between 0.5 and 0.8 m/s would be experienced during the course of a flood of this magnitude.
19In Scenario 2, the occurrence of a 1% AEP flood in South Creek only (with no concurrent flooding in the Hawkesbury River) would lead to flooding at the site to a depth of 1.7 m. Peak floodwater velocities of between 0.6 and 1 m/s are predicted in the vicinity of the site.
20In Scenario 3, the occurrence of a 1% AEP flood in the Hawkesbury River only (with no flooding in South Creek) would lead to flooding at the Site to a depth of 1.3 m. However, the likelihood of flooding of the Hawkesbury River without some concurrent flooding of South Creek is likely to be minor.
21Mr Bewsher is also a very experienced hydrological and flooding expert with over 30 years experience in flooding investigations within many LGAs. He disagrees with significant parts of Mr Woods opinion and initially said that from his investigations that there are four potential modes of flooding that can cause inundation of the subject site, as follows:
(a)overflow of floodwaters from South Creek;
(b)backup of floodwaters from the Hawkesbury River at Windsor;
(c)run-off from the local catchment upslope of the site and generally to the west and south-west. This run-off drains towards South Creek along natural drainage lines including various man-made drains3 (see Figure 1); and
(d)combinations of (a), (b) and (c).
22Consequently, he considers that because of its location in the lower reaches of South Creek adjacent to the much larger Hawkesbury River, the highest flooding of the site will occur by backup of the Hawkesbury River from Windsor. Nevertheless very significant flooding can also occur from South Creek and the weather systems may influence the effect of flooding.
23Mr Bewsher says that the 2013 draft South Creek Flood Study and the previous 1990 flood study, both adopted coincident 100 year average recurrence interval (ARI) flooding on the Hawkesbury-Nepean and South Creek catchments. Whilst this is possible, it represents a probability of occurrence rarer than 1%. Both flood studies appear to have acknowledged this problem but nonetheless adopted coincident peak flooding on both systems, (noting that if coincidence was not assumed, the resultant lowering of water level was relatively minor).
24Whilst inundation of the site caused by run-off from the local catchment can occur, he considers this is largely a drainage issue. Consequently, he does not consider the mode of flooding relevant in this matter.
25Mr Wilkinson outlined the planning control framework with particular reference to the provisions of the FDM and the Draft South Creek Flood study. In support of his position that the site is unsuitable for this development due to its high hazard flooding risk category, he says that:
The FDM (Section 1.1.1 page 1) notes that the policy provides for "the protection of councils, government agencies, and their staff against claims for damages resulting from their issuing advice or granting approvals on floodplains, provided such action was taken in accordance with the principles and guidelines in this manual".
It establishes risk management principles that are based on a hierarchy of avoidance, minimisation and mitigation. In this instance, given the flood characteristics of the site, it is considered appropriate not to introduce (where one presently does not exist) a significant and foreseeable risk through the development of a residential dwelling on the existing vacant land.
It prescribes a process for the development and implementation of risk management plans. In relation to the South Creek, Council is presently finalising the "flood study" component. The results from the Draft South Creek Flood Study have provided the relevant flood characteristics of the site and informed the assessment of the application.
The Draft South Creek Flood Study has identified the subject property as being affected by the floodway and is also located with the high/very high hazard area of the floodplain.
The Manual describes provisions for "Voluntary Purchase". The Manual states (J2.2) "In certain high hazard areas of the floodplain it may be impractical or uneconomical to mitigate flooding to existing properties at risk. In such circumstances it may be appropriate to cease occupation of such properties in order to free both residents and potential rescuers from the danger and cost of future floods". The relevance of this to the application is that the high hazard (flood) characteristics of the site would likely result in authorities (where mitigation is uneconomical or impractical) encouraging de-occupation of the floodplain, as opposed to promoting (as the Application seeks) an increased occupation of the high hazard floodway area of the floodplain.
The Manual notes "In determining appropriate hydraulic categories, it is important that the cumulative impact of progressive development be evaluated, particularly with respect to floodway and flood storage areas. Whilst the impact of individual developments maybe small, the cumulative effect of the ultimate development of the area can be significant and may result in unacceptable increases in flood levels and flood velocities elsewhere in the floodplain".
The Manual describes High Hazard as "possible danger to personal safety; evacuation by trucks difficult; able-bodied adults would have difficulty in wading to safety; potential for significant structural damage to buildings".
26Mr Wilkinson acknowledged that whilst he is not an expert in emergency response, nevertheless the following matters in the FDM are relevant for consideration:
At L5 the Manual notes "that evacuation measures proposed in private or site specific flood plans for individual developments, outside the development types considered appropriate in the management plan, is not an appropriate measure to rectify adverse impacts, to manage the consequences of inappropriate decisions or to override the management plan. Therefore private or site specific flood plans should not form the basis for development consent
[7]
Conclusion
60For the determination of this matter I have carefully considered the evidence, the matters expressed on-site, the submissions, and observations at the view. My determination is based on the provisions of the current planning controls and associated policies.
61Firstly, I note that the site is subject to the provisions of the PLEP 2010 under which it is zoned RU4 Primary Production Small Lots and a dwelling house is permitted with consent. There are a number of objectives for this zone including:
To enable sustainable primary industry and other compatible land uses...
To ensure land uses are of a scale and nature that is compatible with the environmental capabilities of the land...
62However the land is situated within the South Creek floodplain and liable to flooding whereby cl 6.3 of the PLEP relevantly contains the flood planning controls, including a number of specific objectives as follows:
a) to minimise the flood risk associated with the use of the land,
b) to limit uses to those compatible with flood risks,
c) to manage uses to be compatible with flood risks...
63Clause 6.3(4) is also particularly relevant to this application because development consent must not be granted for development on land that is in a flood planning area or other land at or below the flood planning level unless the consent authority is satisfied with a number of designated factors. Subclause (6) provides a reference to the Floodplain Development Manual.
64Insofar as the provisions of the relevant development control plan - PDCP section C3.6 - Flood Liable Land require consideration, there was some argument about cl 3.5C(2)(a), which states:
(a) Council will consider development on flood liable land but will not grant consent to development in floodways or high hazard areas.
65On the basis of the evidence presented to the Court, I initially set this particular control aside in order to assess the merits of the proposal, particularly in the context of cl 6.3(4) of the PLEP. In any case, I note that the DCP contains a number of qualitative objectives, which are similar to those in the PLEP, which endeavour to ensure floodplain risk management minimises the potential impact of development on floodway behaviour and risks to persons and property. I have considered the general DCP objectives on the basis that some discretion and flexibility can be exercised when considering the DCP provisions depending on the circumstances of the matter. I do not give cl 3.5C(2)(a) of the DCP determinative weight.
66In this matter, considerable reference was made to the draft South Creek Flood Study (31 August 2013) (SCFS), which undertook a comprehensive investigation and flood modelling exercise for this catchment covering a number of other local government areas. I note Mr Wilkinson's evidence that the draft SCFS is the initial stage in the development of council's Flood Risk Management Plan, prepared in accordance with the FDM procedure. Its adoption will enable completion of a risk management study and development of a risk management plan.
67Taking into consideration the level of external consultation, extensive peer review and the experience of the flooding engineers in this matter, who agree that that the SCFS modelling represents current best practice and the most up to date information available, I think it should be given determinative weight, notwithstanding its draft status.
68Accordingly, the SCFS model shows that at the proposed building platform the following levels occur and the engineers agree on the associated flooding matters:
The NGL (natural ground level) is in the order of RL 16.1m AHD
Building platform is 1.1m above NGL
Garage FFL (finished floor level) is RL 17.28m AHD
Habitable first floor FFL is RL 18.84 AHD
Flood level estimates:
20 year ARI is RL 17.1 m AHD
50 year ARI is RL 17.5m AHD
100 year ARI is RL 18.1m AHD
PMF (probable maximum flood) is RL 26.5m AHD
Flood velocities
100 year ARI is 0.5 - 0.6 m/s
20 year ARI is 0.6m/s
Flood depth in 100 year ARI: in the order of 2m.
Flood risk: high hazard area.
69Reference then to the various maps in the SCFS includes the delineation of the extent of the floodway as shown in Figure 1. This is a threshold consideration according to the requirement of cl 6.3(4) of PLEP. As noted in the aforementioned evidence there was total disagreement by the engineers on the delineation of the floodway based on the interpretation of the definition in the FDM.
70Mr Thomas relies on the SCFS delineation that the site, particularly the building platform area is totally within the floodway, except for a small area in the southwestern corner. Against this, Mr Bewsher says that when the second part of the definition is taken into account, the effect of partial blockage on the site means that the site is not in a floodway.
71In order to understand this proposition, Mr Bewsher was taken to three cross sections (CS1, CS2 and CS3), which are in the vicinity of the site. He agreed that there was a floodway component at each of these cross sections, presumably occurring because of the redistributed flood waters from the natural creek to the east of the site. However he considers the extent of the floodway would be somewhere to the east of the site and not affecting the building mound.
72The reason for this difference is because of Mr Bewsher's definitional interpretation that the site is not in a floodway "because partial blockage of the flowpath across the subject site through the construction of the proposed dwelling would not cause a significant flow restriction."
73However, in this regard engineers agreed that if the building was allowed to proceed, then it alone would have an insignificant effect in the floodway. I then note Mr Thomas' rejection of Mr Bewsher's assertion about 'blockage effect' on the basis that consideration of a fill pad with dimensions of 28m x 38m is nonsense and that in any case floodways are primarily areas, which carry a significant volume of water in floods. Based on the depth and velocity of the floodwaters at the site, it appears to me that the approach of Mr Thomas' seems the most realistic in the subject circumstances.
74Furthermore, Mr Thomas said that the effect of blockages was included in the floodway delineation utilising the methodology involving an iterative approach that considers:
section averaged velocity in the planning level flood at both the peak and on the rising limb of the hydrograph
[8]
Court orders
99The Court orders that:
(1)The appeal is dismissed.
(2)Development consent to DA12/0308 for the construction of a split-level dwelling at 265 Seventh Avenue, Llandilo is refused.
(3)The exhibits may be returned except for 1, 4, 5, 8, A, E and F.
R Hussey
Commissioner of the Court
Figure 1
DISCLAIMER - Every effort has been made to comply with suppression orders or statutory provisions prohibiting publication that may apply to this judgment or decision. The onus remains on any person using material in the judgment or decision to ensure that the intended use of that material does not breach any such order or provision. Further enquiries may be directed to the Registry of the Court or Tribunal in which it was generated.
Decision last updated: 29 May 2014
The Manual further recognises (at A5) "that private or site specific flood plans written for individual developments and separate from the overall floodplain risk management plan or local flood plan are ineffectual and should not form the basis of development consent".
At N7 the Manual strongly cautions against the use of private flood plans to support new developments; in particular at N7.2.
27According to Mr Wilkinson, the "Land Use Planning" guideline published in 2006 was one of a suite of three documents prepared for the HawkesburyNepean Floodplain Management Steering Committee. These documents accord with the Government's Flood Prone Land Policy and the NSW Floodplain Development Manual (2005).
28The Land Use Planning guideline notes:
Floodways are primarily defined by their hydraulic function. They are where most conveyance of floodwater along a particular flow path occurs. Typically, adjacent to the main channel and any remnant anabranches, velocity may be relatively high compared to other areas of the floodplain resulting in high hazard areas. However, in some circumstances they may have very low flow velocities. Floodways are best kept free of obstructions such as structures or buildings, as development has the potential to redirect flows, increase danger to personal safety and lead to significant financial losses due to damage potential. Floodways can be utilised for agriculture or recreation to maintain them as open generally undeveloped areas. The extent and behaviour of a floodway may change in rarer floods but obstructions can have a significant impact on upstream flood levels even in the flood selected for planning purposes....
29In terms of best practice, Mr Wilkinson said that council's existing development controls are responsive to the planning guidelines and do not support residential development within the floodway and high hazard areas of the floodplain. This has been a long held adopted policy position through Interim Flood Policies and more recently flood related development controls embedded into statutory planning documents.
30Accordingly, Mr Wilkinson says that the current Draft South Creek Flood Study is the initial stage of the development of Council's Flood Risk Management Plan, in accordance with the Floodplain Risk Management Process detailed in the Manual. Once adopted, the next steps involve the completion of a risk management study and development of a risk management plan. The subsequent process will necessitate a review of risk management options, including Council's flood policies and adopted planning controls, to ensure consistency with Government Policies and best practice floodplain management principles.
31Consequently, Mr Wilkinson does not consider the South Creek flood study procedure diminishes the application of present adopted policies and controls which are considered valid and contemporary. In fact, he thinks that their consistency will ensure that similar principles and controls will be carried forward through into any new floodplain management documents prepared by Council. Apparently several councils that partnered with council in the preparation of the South Creek Flood Study have already undertaken separate risk management process and adopted policies and flood related development controls that are generally consistent with best practice floodplain management principles.
32As part of the appeal process, the drainage experts undertook joint conferencing on the contentions in terms of the assessment of the proposal and agreed on the following matters:
a. the site is in the floodplain of South Creek and its flood characteristics are informed by the draft Flood Study;
b. the 100 year ARI flood level at the site is 18.1m AHD;
c. the 20 year ARI flood level is 17.1 m AHD;
d. the predicted peak level of the Probable Maximum Flood (PMF) is 26.5mAHD;
e. Messrs Wilkinson and Thomas consider the 100 year ARI flow velocities at the location of the fill platform that is to be constructed for the proposed dwelling are 0.6 m/s. Mr Bewsher considers the velocity at the fill pad ranges from 0.5 m/s to 0.6 m/s;
f. Messrs Wilkinson and Thomas advised that in the 20 year ARI event the velocities are 0.6 m/s. (Mr Bewsher considers these to be of the right order as he would expect the velocities to be similar and slightly smaller than the 100 year velocities);
g. Messrs Wilkinson and Thomas advised that in relation to the whole site, peak velocities are in the range 0.6 to 0.9 m/s in both the 20 and 100 year ARI events Mr Bewsher's inspection of the 100 year velocities indicated that they ranged from 0.5 to 0.9 m/s;
h. Messrs Wilkinson and Thomas advised that the ALS survey indicates that ground levels in the vicinity of the fill platform are typically at an elevation of 16.0 mAHD. Based on this level the 100 year ARI floodwater depth at the site is predicted to be 2.1 metres;
i. the Applicant's survey plan shows the ground level at the fill platform to be 16.2 mAHD. This level gives the 100 year ARI flood depth as 1.9 m. At the conference Mr Bewsher gave Messrs Thomas and Wilkinson a copy of this survey plan which is dated 9 March 2010;
j. the site is classified as high hazard based on criteria specified in the NSW Floodplain Development Manual, in both the 100 year and 20 year ARI events;
k. the majority of the site including the proposed fill pad is classified as floodway within the draft Flood Study (refer Fig No 7.27 of draft Flood Study....
I. access from the site to higher ground can occur via Seventh Avenue in a westerly direction. The depth of floodwaters across Seventh Avenue at the frontage to the site is approximately 2 metres in the 100 year ARI event. The flow velocities will be up to 0.6 m/s at the peak of the 100 year ARI flood. In a 20 year ARI flood, the depth and velocity of floodwaters across Seventh Avenue at the frontage to the site are approximately 1 metre and 0.6 m/s. (Mr Bewsher notes that he has not been able to check the velocity). The distance from the site along Seventh Avenue to the extent of flooding, adjacent to Second Avenue, at the peak of the 100 year ARI flood is approximately 500 metres;
m. Mr Bewsher considers that evacuees from the site who travelled along Seventh Ave from the driveway of the proposed dwelling in a westerly direction, would not travel through deeper water as they progressed to the high ground west of Second Avenue;
n. Mr Bewsher notes the draft Flood Study determined that the 36 hour storm was the critical duration rainfall for South Creek in the Llandilo area."
33From these agreed points, the flooding experts then agreed that the "floodway" is the key concept or element in the consideration of this development application, which is located within the floodplain. Insofar as Mr Bewsher does not consider it necessary to define the floodway, nevertheless he says that it is important to determine whether a development will have an adverse flood impact on adjacent properties. It is his opinion that from a strictly definitional point of view, the site is not a floodway because partial blockage of the site will not cause a significant redistribution of flood flow.
34Both Mr Thomas and Mr Wilkinson disagree with this approach. Instead they say that based their determination of the floodway classification for the site on the rigorous and robust process that has been followed in preparing the draft Flood Study, which established the hydraulic categories for South Creek, including the extent of the floodway corridor, then the site is located within a floodway as shown in Figure 1 annexed to this judgment.
35The floodway consideration is relevant because cl 6.3(4) of the PLEP particularly requires the consent authority to be satisfied on a number of matters concerning the location/proximity to a floodway. Clause 6.3(6) introduces into this the consideration of the words and expressions contained in the FDM. Accordingly, under the FDM 'floodway areas' are defined as:
...those areas of the floodplain where a significant discharge of water occurs during floods. They are often aligned with naturally defined channels. Floodways are areas that, even if only partially blocked, would cause significant redistribution of flood flow, or a significant increase in flood levels.
36The Flood Prone Land Policy (Policy) is contained within the FDM and its stated primary objective is to:
...reduce the impact of flood liability on individual owners and occupiers of flood prone property, and to reduce private and public losses resulting to them or the community.
37Furthermore, the Policy provides for a merit-based approach to be adopted for all development decisions in the floodplain to take into account social, economic and ecological factors, as well as flooding considerations. The Policy states that whilst flood prone land should not be sterilised, nevertheless any development should "not cause undue future distress to individuals nor duly increase potential flood liability to them or the community".
38Considering the relative importance of the floodway and the disparate opinions expressed by the flooding experts, they were subject to lengthy cross- examination. In response to questions on the two main components of the floodway definition i.e. areas of significant discharge and effect of blockages, Mr Thomas says that when one assesses a floodplain for the purposes of establishing where a floodway corridor might exist and the extent of that corridor, one undertakes a rigorous and robust approach that considers a range of characteristics. Those characteristics are many and varied and include the potential for blockage.
39This process does not go to looking at blockage associated with one individual house pad or ten individual house pads. Instead it looks at the capacity for a blockage to occur of a certain scale that would lead to a change in flood levels. There are some long standing rules of thumb that apply to this, which say that once you start to get an impact, it leads to 100-mm increase in flood level extending upstream. This indicates the starting of an approach into the floodway and causes adverse impacts and, therefore, gives confidence around where one's floodway delineation has been determined.
40In summary, Mr Thomas' evidence is that in the flooding assessment of a site, if the blockage from the individual site is found to be insignificant, nevertheless there can still be a floodway through the site. He considers the subject site to be substantially located within the floodway.
41As noted, this is a critical determination in the subject matter. Mr Bewsher's opposing view is that the site is not within a floodway. His opinion is that the floodway delineation (red line) shown in Ex L should be somewhere to the east of the site.
42When examined on this opinion, he was referred to Figure 1, which shows the site, the designated floodway extent and velocity - depth mapping. This figure excludes a minor area in the south-western corner of the site from the floodway, which is flood storage area. However the area of the building site is within the designated floodway. The basis for his opinion was tested by reference to three cross section lines:
CS 1; through the centre of the lot near the building platform
CS 2, a section to the south of the site, and
CS 3; a section to the north of the site.
43Mr Bewsher agreed that there was a floodway within all of these three cross sections, extending westward from the main creek area. However he disagreed with the designated floodway delineation, saying that the floodway would be narrower and to the east of the subject site and would not include the building platform. But he admitted that he had not analysed it in detail and therefore he was unable to provide a rational alternative floodway delineation.
44When questioned on his approach to determine the extent of the floodway across CS 1, he said it would involve an examination of partial blockage of various allotments through the area, including upstream and down stream. Insofar as he previously agreed with the other engineers that any blockage effect at the subject site was insignificant, he nevertheless said that the model was two-dimensional and did not use cross sections. Instead it used topography in a two-dimensional description.
45However, Mr Thomas then clarified this, saying that the model does interpret the cross sectional in the same fashion that a one-dimensional model does. Following extensive questioning on the veracity of the flood modelling in the South Creek Flood Study, Mr Thomas acknowledged that other experts could place the floodway delineation in another location.
46But Mr Thomas then says that whilst there is potential for that to occur, nevertheless most flood studies and floodplain management studies usually involve:
...there is a committee, a subcommittee that is a technical subcommittee that comprises technical experts from within the council, as well as technical experts from within the state government organisations, the flood unit, and concurrently all confer and much time, I can assure you, is spent pouring over the delineation of that line around that map to make sure there is consensus.
47Furthermore he says that:
...that the delineation of the floodway for the South Creek Flood Study is probably the most rigorous process I have been involved in for determination of floodways ever. Just to extend that, commissioner, in relation to the commentary around modelling, it involved extensive encroachment testing or partial blockage testing to establish the veracity of the floodway extent line. It also recognised that, yes, this is a flood study that covers a large area of the South Creek floodplain but by virtue of the nature of the South Creek floodplain, we have a system that is subject to or exposed to hydraulic controls by virtue of the various crossings that occur across the floodplain and across the creek which means that in effect one ends up having to compartmentalise the floodplain as a function of those crossings so that one goes to almost a local scale investigation between those crossings of the floodplain. That is indeed why there has been such a degree of rigour that has been applied to that process.
48Consequently, Mr Thomas' opinion is that this South Creek flood modelling represents best current practice and helpfully Mr Bewsher agrees that it contains the best information available. Therefore I consider the SCFS should be given determinative weight.
Planning
49Apart from this, the planners separately addressed the following matters. Firstly, they agree that the location of the proposed dwelling is within the extent of the floodway identified in the Draft South Creek Flood Study. Although Mr Grech defers to Mr Bewsher on aspects of the flood mapping.
50With regard to the cumulative impact contention, Mr Grech undertook an investigation of other vacant properties with similar possibilities for development, to assess the cumulative impact contention.
51According to Mr Wood's assessment, the following points are relevant:
The subject property located in a floodway with a high hazard area in relation to flood hazard classifications, Penrith Development Control Plan 2010 (DCP 2010).
The DCP in cl 3.5 Background states, "In order to determine what development may occur in areas subject to partial or full flooding, it is necessary to classify land according to flood hazard." The DCP establishes a clear consistency with Clause 6.3 of LEP 2010 by referring to land to which this clause applies as being the land to which the controls of DCP 2010 Clause 3.5 apply. It provides more detailed objectives and controls for assessment to be read in conjunction with the LEP.
Clause 3.5 C 2(a) of DCP 2010 states, "Council will consider development on flood liable land but will not grant consent to development in floodways or high hazard areas. From this hierarchy of controls there is no merit in considering a flood liable site within a floodway, classified as high hazard, as being suitable for a habitable residential development.
Cumulative impact assessment for the purposes of this contention is relative not only to the locality but the Flood Planning Area throughout the whole Local Government Area identified on the Flood Planning Land (Clause Application) Map pursuant to Clause 6.3(2)(a) of Penrith Local Environmental Plan 2010 (LEP 2010). DCP2010 Clause 3.5 Objective i) is "To deal equitably and consistently (where possible) with applications for development on land affected by potential floods, in accordance with the principles contained in the Floodplain Development Manual, issued by the NSW Government." To fulfil this statutory obligation and prevent an undesirable precedent being set which will lead to unacceptable cumulative impact, the consent authority must not consent to development applications for development contrary to the principles of the Floodplain Development Manual.
52Against this, Mr Grech says that this issue raised by Council relates to the floodway not the high hazard area. The high hazard area relates to a different part of the floodplain and issues, which are either not raised by Council or are dealt with under subsequent contentions.
53His position is that:
The provisions of the LEP or the DCP do not require the assessment of the impact of development on the floodway to include an assessment of cumulative impact.
The cumulative impact assessment required for the purposes of this contention relates to whether the proposed development when considered in conjunction with other development that might be approved by Council could result in the blocking of the floodway such that it will alter flood behaviour (flood flow conveyance and levels) and have an unacceptable impact. This assessment is a matter for the expert flood engineers.
In order to assist in the cumulative assessment impact, he mapped the location of properties showing some past approvals and where consent for additional dwelling houses may likely be sought and other related information.
54From this, Mr Grech says that in this case the application should be assessed on its merits and that there is a legitimate basis to give minimal weight to any precedent from approval of the application because:
the subject site is uniquely positioned amongst a cluster of lots already developed with dwelling houses.
the circumstances of proposed development on other sites elsewhere within the area analysed in the map could be different with respect to such matters as the flood behaviour at the particular site, the design and siting of that proposed development, its relationship with existing surrounding buildings/structures and the possible existence of existing buildings/structures that could be altered in conjunction with proposed development.
as documented, Council has approved development in the floodway inconsistent with its policies dating back to at least 2000. Council's 1991 Policy (clause 3.2).
with regard to the potential devilment of the 451 lots referred to by Mr Woods, this is a general reference to lots that exist within the LGA. There is no information such as where the lots are located, whether these lots are vacant, what they are zoned, their locational context or whether they are subject to a planning strategy. Therefore these 451 lots cannot be given any weight in the consideration of precedent.
55The next contention addressed by the planners concerns whether the development should be approved considering its location within a high hazard area. They identify the relevant planning controls for the merit assessment and Mr Grech says notwithstanding the high hazard flood classification, other council's such as Hawkesbury Council conditionally permit dwellings houses within high flood hazard areas. In this regard, it seems to me that what happens in other LGAs would be given diminished weight, if any.
56Accordingly, Mr Grech says that whilst development may be permitted in a high hazard flood area, it is important to ensure that the risks associated with such development are appropriately managed in accordance with basic flood planning principles, which are consistent with the relevant considerations required by clause 6.3 of LEP 2010 and Section C3 of DCP as follows:
a) design and siting of the dwelling house minimises any unacceptable flood impacts external to the site;
b) building would be structurally sound during a design flood;
c) design of the building meets minimum habitable floor level and flood compatible material standards;
d) available warning time for evacuation exists and that evacuation routes are accessible and with capacity to accommodate the occupants; and
e) satisfying the above criteria does not give rise to any consequential unacceptable environmental or amenity impacts.
57In response to Contention 4 concerning unacceptable risks to person and property, Mr Grech says that there is a coordinated evacuation strategy in place for Hawkesbury Nepean Valley and that as the proposed development will only generate an extra 3 to 4 persons, it is minimal and can covered within this existing evacuation strategy.
58Mr Woods disagrees with this position mainly on the basis that the applicant has not satisfactorily demonstrated that the development will not adversely affect the safe and effective evacuation of the subject site and surrounding area.
Evacuation
59Mr Bewsher presented the main evidence on Contention 4 concerning the risk to persons and property as a consequence of the proposed development being unacceptable. His response to the contention is:
"There is flood risk to property in this development proposal due to inundation from extreme flood events. This risk is acceptable and can be managed by requiring appropriate floor level heights, which are in accordance with normal practice.
There is also a risk to personal safety. In his view this is the key consideration, which the Court has to assess.
The personal safety risks are proposed to be managed in accordance with the same procedures used for existing floodplain developments in Llandilo (and generally in accordance with the majority of the Hawkesbury-Nepean Valley). These procedures require occupants to leave the site ahead of major flooding and seek shelter outside the floodplain with family or friends, or in evacuation centres.
In the event of a major flood, many tens of thousands of people in the Valley are proposed to be evacuated in this manner. Whilst recognising that, for whatever reason, in some circumstances people will not always evacuate, it is his opinion that there are adequate safeguards in place and that the risk to personal safety at the subject site is acceptable
the variation in velocity-depth product for the planning level flood
topographic and geomorphic features along the floodplain
hydraulic controls such as structures that cause backwater effects
flow conveyance and the distribution of flow - specifically the extent of floodplain required to carry approximately 80% of the total flow
the results of hydraulic analysis and / or flood modelling that incorporates encroachment or blockage scenarios.
75In the circumstances where Mr Bewsher offered no compelling evidence to set aside the SCFS delineation of the floodway and agreed that there could be a floodway where there is no obstruction/blockage at a site, I regard his opinion on the floodway as speculative and give it little weight, preferring instead the more realistic opinion of Mr Thomas that is based on best practice flood modelling.
76Accordingly, I rely on the SCF delineation that locates the site within the floodway. Applying this to the cl 6.3(4) (a) - (h) provisions, which deal with location of the development and compatibility with the flood hazard, the applicant relies on Mr Bewsher's opinion that these matters are satisfied because:
Any development risks can be managed satisfactorily through the proposed floor levels and those risks to persons, being his major concern, can be managed by effective evacuation generally in accordance with existing procedures in place by the SES.
The development will not cause detrimental increase in flood behaviour on adjacent properties.
77Whilst I accept that the approval of the development, considered alone, is unlikely to cause detrimental increase in flood behaviour on adjacent properties, nevertheless the various planning controls require detailed assessment of the implications of the high hazard risk and floodway location of the site.
78The evidence shows that there are number of factors that determine the flood hazard and they include effective warning time, flood readiness, depth/velocity effects and evacuation arrangements. At the house site in the 100 year ARI storm, the predicted velocity is in the order of 0.6m/s and the depth is in the order of 2 m resulting in a V x D product of 1.2 sqm/s, which is a High Hazard classification. High hazard is defined as:
...possible danger to personal safety; evacuation by trucks difficult; able bodied adults would have difficulty in wading to safety; potential for significant damage to buildings.
79As a check on this potential outcome, I note that in engineering and planning assessments a common reference to flood safety is contained in Australian Rainfall and Runoff - "A Guide to Flood Estimation" published by the Institution of Engineers. On safety in s 14.10.4 it states:
To prevent pedestrians being swept along streets and other drainage paths during major storm events, the product of velocities and depths in streets and major flow paths generally should not exceed 0.4 m2/s. This limit is based on experimental studies of stability of children in flowing water by Foster and Cox (1973). Where vehicles alone are affected, a higher depth-velocity product, 0.6 or 0.7 m2/s depending on vehicle size, is appropriate. The stability of vehicles in lateral and longitudinal flows has been investigated by Bonham and Hattersley (1967) and Gordon and Stone (1973).
80My concerns about flood safety are increased because a similar level of high hazard flooding would be created in lesser flood events such as the 1:20 year ARI storm event meaning more flood safety risk exposure and likely evacuation requirement. I do not think this is consistent with the flood planning objectives to minimise the flood risk associated with the land.
81In the circumstances, I think that the combination of the high velocities and depths in the order of 1m - 2m depending on the flood event, are significant and dangerous considering that occupants of the dwelling would have to travel some 450 m to the west to reach flood free land. Therefore, I am not satisfied to rely on Mr Bewsher's opinion that by raising the floor levels, then an acceptable safety outcome is achieved. Instead I rely on the opinion of Mr Thomas for my assessment that as the site is located within the floodway and subject to high hazard risk, I am not satisfied that requirements cl 6.3(4) (a) and (b) have been satisfied.
82Apart from the velocity/depth and associated hazard concerns, the respective experts discussed the issue of evacuation, which is Mr Bewsher's associated point in support of the application. As noted, in the 100 year ARI event the area surrounding the dwelling will be subject to approximately 2m depth of water with a velocity in the order of 0.6 m/s. Accordingly, evacuees would have to leave the elevated building platform to reach the road where the water depth would be in the order of 1m. Following this they would have travel some 450m to the west of the site to reach high ground and travelling through water depths in the order of 1m with velocities up to 0.6 m/s.
83In my assessment this would be a hazardous procedure, particularly if it had to be undertaken in the night time when visibility would be reduced.
84According to Mr Bewsher's evidence, this risk to people is the key issue, which he considers can be addressed by evacuation based on his experience in the Hawkesbury - Nepean Valley. His evacuation strategy is:
That in major flooding events all residents should leave the dwelling ahead of the onset of dangerous flow conditions and to seek shelter in suitable facilities above the reach of the floodwaters. He prefers this course rather than remaining in the dwelling;
As Llandilo is not subject to flash flooding, then there will be "some hours of notice available of the need to evacuate people" before Seventh Avenue is inundated.
In the absence of any formal evacuation plan for this area, the residents should have their own evacuation plan that is in accord with FloodSafe guidelines.
85Insofar as Mr Bewsher relies totally on the Hawkesbury - Nepean Flood Evacuation Plan (HNFESP) and the SES involvement, it appears that these procedures cover the broader evacuation strategy for this large flood catchment area. However, no specific evacuation procedures were identified for this part of Llandilo. In particular I am interested in how the average person would be come aware of the 'some hours notice' to evacuate. There was no compelling evidence presented regarding an effective early warning system that would enable residents to prepare for evacuation. Whilst there may be general radio broadcasts, I do not consider this provides adequate reliability in the predicted flooding scenarios at the subject site.
86I accept the evidence of Mr Crameri who has been involved with the local Llandilo RFS for many years and that this organisation undertakes to inform and assist residents in flood situations. This consistent with the evidence of the other neighbouring residents who have developed a flood awareness and assist each other when evacuations are required.
87However the evidence before the Court shows that this is all undertaken on an informal or ad hoc basis without any formal delegation from SES authorities. When questioned Mr Crameri admitted that his group had not conducted door knocks for evacuations in the past 3 floods. Also, there is no organised regime to appropriately trigger (evacuation) action at a critical stage of the flooding event.
88Considering that the safety of residents is predicated on their safe evacuation according to Mr Bewsher's opinion, I am not satisfied that there are fail-safe systems in place to achieve safe and effective evacuation of this site, particularly for new residents to the area that may not be aware of the need to regularly evacuate the property in view of the high hazard category of 20 year storm events, let alone the rarer 100 year flood events.
89Part of my concern is that observations at the view indicated that the character of the surrounding rural/residential lots attracts ancillary buildings such as machinery sheds, stables and animal sheds. If the proposal follows this character it is likely such structures would be located towards the south of the dwelling thereby increasing risks to persons and property if items require shifting to higher ground in advance of up to 2m depth of floodwater in the designated 100 year ARI flood. Importantly, this applies to safely shifting animals such as the horses to higher ground when considerably longer warning times should be adopted, if they are to be relocated to higher, safe ground.
90Notwithstanding this, I have considered the applicant's submissions regarding the merits of the proposal, which requires balancing the social, economic and ecological factors. I initially accept that there are social and economic benefits to the applicant's family with the erection of the proposed dwelling in close proximity to family. Also that this family has local knowledge about regular flood evacuation measures.
91But I think overriding weight should be given to safety of all residents, including future residents who may not be well informed of or experienced with the significant flooding risks associated with residing in this high hazard floodway. In the ultimate, any consent applies to the use of the land rather than any particular person(s). On balance then, my assessment is that the overall public interest is well served by the refusal of this application and this outweighs the private interests involved.
92In this regard it seems unfortunate that the s 149 Certificate obtained by the applicant pre-purchase apparently did not specifically identify the flooding risk. However I give this little weight and any dispute on this should be dealt with elsewhere. In my opinion the overriding public interest is well serviced by carefully applying the recently completed flood modelling results contained in the SCFS.
93With regard to precedent, I think that this issue is not determinative in the subject application. Even though a number of other properties were identified where dwellings have in past years been approved, the individual facts and circumstances were not established. I accept that some of these properties are exposed to safety risks being located within the floodway identified in the SCFS. However I do not consider those approvals support approval of the subject application because I do not consider the public interest would be well served by the approval of the new dwelling in this high hazard floodway, especially where there is no formal safety and evacuation arrangements.
94Insofar as submissions were made to a number of other matters involving decisions concerning development within the floodplain, I do not consider they impose any binding requirement on this Court, considering that the merits of this proposal have been considered based on the facts and circumstances applying at present. Importantly the SCFS is the threshold flood authority I rely upon, which was not previously available.
95I have considered the submissions for the applicant regarding the independence of Mr Thomas and Mr Wilkinson because of their roles in the preparation of the SCFS. I do not accept this submission of the basis of Biscoe J finding in Pittwater Council v A1 Professional Tree Recycling Pty Ltd [2008] NSWLEC 325 as follows:
11 The authorities support the following propositions, in my view. First, a mere family, personal or business relationship (including that of a retainer as an investigator), even of a kind that might reasonably cause an expectation of lack of impartiality, is insufficient of itself to lead to rejection of expert evidence. Secondly, and exceptionally, there may be additional factors which justify rejection on the ground of clear lack of capacity to bring the requisite degree of impartiality to the expert's reasons, either because the evidence is then inadmissible or in the exercise of the court's discretion. In my opinion, that an expert witness is or was an employee of the party retaining the expert, has investigated the matter prior to commencement of proceedings, and has recommended that proceedings be taken, are insufficient factors, of themselves, to lead to rejection of the expert's evidence. That is the present case.
96In summary then, I am satisfied from the evidence that the subject site is located within a high hazard floodway section of the South Creek environs as determined by the South Creek Flood Study on which I consider should be given determinative weight. It was agreed by Mr Thomas that this flood study accords with best practice and Mr Bewsher says that it represents the best current information on flooding to rely upon.
97The results from the modelling show that at the proposed dwelling site in the designated 100 year flood event, it will be subject to approximately 2 m depth of floodwaters travelling at and estimated velocity of 0.6m/s. This confirms the high hazard risk categorisation and presents significant safety risks to persons and property. The risks are such that Mr Bewsher says evacuation must take place at "some hours notice". However no compelling details were provided for an effective early warning system to facilitate the safe evacuation of the site in the fairly regular flooding events affecting this site.
98Therefore, I do not consider consent should be granted because the provisions of cl 6.3 (4) of PLEP have not been satisfied in terms of the proposed dwelling being compatible with the high hazard floodway context. Furthermore, in the absence of any formal evacuation plan for the subject area, I think the approval of the development would adversely affect the safe and effective evacuation of the land within the surrounding context. Accordingly, I do not consider this proposal satisfies the flood planning objectives in cl 6.1 of the PLEP, particularly (a) 'to minimise the flood risk associated with the use of the land". To the contrary, the approval of this proposal to intensifying its use, would increase the flood risk associated with the use of the land.