Land and Environment Court of New South Wales CITATION : Whealey v Warringah Council [2009] NSWLEC 1194 APPLICANT Lisa Whealey PARTIES : RESPONDENT Warringah Council FILE NUMBER(S) : 10050 of 2009 CORAM: Hussey C KEY ISSUES: DEVELOPMENT APPLICATION :- Stormwater/On-site detention LEGISLATION CITED: Environmental Planning and Assessment Act 1979 DATES OF HEARING: 21 April 2009 EX TEMPORE JUDGMENT DATE : 21 April 2009 APPLICANT Ms S Duggan (Barrister) LEGAL REPRESENTATIVES: RESPONDENT Mr D Thomas (Solicitor) SOLICITOR Wellings Lawyers JUDGMENT: THE LAND AND ENVIRONMENT COURT OF NEW SOUTH WALES Hussey C 24 APRIL 2009 10050 of 2009 LISA WHEALEY v WARRINGAH COUNCIL This decision was given extemporaneously. It has been revised and edited prior to publication. JUDGMENT Background 1 This appeal is against conditions of consent imposed on a development consent for the demolition of an existing dwelling, the construction of a new dwelling and swimming pool at 37 Gardere Avenue, Curl Curl. The property is situated on the lower side of the road and the particular conditions appealed relate to the following deferred commencement conditions regarding stormwater control and discharge from the development as follows: 1. Stormwater Drainage Easement As the natural fall of the land is towards the rear of the site the disposal of stormwater drainage is to be in accordance with the drainage plan submitted by Rafeletos Zanuttini Pty Ltd, drawing No. 30063CP dated 25/09/2008. The easement is to be created under s 88B and/or 88K of the Conveyancing Act 1919. The applicant must provide Council with evidence of the creation of the easement in order to activate the consent. 2. Stormwater drainage design Plans indicating all engineering details relevant to the site regarding the collection and disposal of stormwater from the site, buildings, and adjacent areas, shall be submitted to Council for written approval. Stormwater shall be conveyed by gravity from the site to the kerb in Curl Curl Parade. All proposals shall be in accordance with Warringah Council's Stormwater Drainage Design Guidelines for Minor Developments. Reason: To ensure adequate provision is made for stormwater drainage from the site in a proper manner that protects adjoining properties. Evidence required to satisfy these conditions must be submitted to Council within five (5) years of the date of this consent, or the consent will lapse in accordance with s 95 of the Environmental Planning and Assessment Regulation 2000. 2 Following conferencing between the parties agreement has been reached to consent orders in this matter and the conditions be varied. The site. 3 The subject site is No. 37 Gardere Avenue, Curl Curl (Lot 147 in DP 5539). The allotment is a rectangular allotment having front and rear boundaries of 10.6 m, a length of 45.265, and a total site area of 455.36 m sq. The site is within the F5 Curl Curl locality under the Warringah Local Environmental Plan 2000 (LEP). 4 The site has a north-south orientation and slopes gradually from the front boundary (RL 37.3) at the south to the rear boundary (RL 35.2) at the north. However a related approval for swimming pool and landscaping approved in January 2009, will result in a finished rear lawn level of RL 36.5 and swimming pool coping level at RL36. As such, the current fall of the land is now approximately 2.1 m over a distance of 45.265 m. Under the swimming pool approval, this will become a varied slope of 0.8 m to 1.3 m, over a distance of 45.265 m. The proposal 5 The proposal with regard to the stormwater issue is to have a split drainage system for the new dwelling comprising (a) a charged system to convey excess roof runoff to Gardere Avenue, and (b) an infiltration system in the rear yard adjacent to the swimming pool to accept and dispose of the stormwater runoff from the front yard and driveway. This involves the construction of a pit area with Atlantis cells over which grass is to be planted and it is to be designed to accommodate the volume of runoff from a 50 year ARI storm. Planning controls 6 The relevant stormwater controls are contained the council's Stormwater Drainage: From Low Level Property Policy. The evidence 7 The drainage issue has been assessed by Mr S Khoo, council's drainage engineer, and Dr S Perrens, the applicant's consulting engineer. 8 The proposed roof runoff collection and disposal by the charged system is acceptable to Council. However, concerns were raised by Mr Khoo about the filtration systems. These concerns relate to the underlying subsurface conditions and the ability of the infiltration system to dispose of the water without causing nuisance flooding downstream. Another concern is about controlling stormwater ingress into council's drainage system in Curl Curl Street, which is under capacity. 9 Based on the provisions of council's Stormwater Disposal Policy, he preferred that the water from the infiltration bed be conveyed via a pipe system through the downstream private properties. 10 The applicant has discussed this option with the downstream property owners but the potentially affected neighbours at No's 24, 26 and 28 are unwilling to grant any easement for a number of reasons. This includes their experience that their properties have not been subject to any undue flooding under the existing conditions. As they understand the proposal will reduce the rate of runoff, they do not consider the burden of an easement is now reasonable or necessary. Conclusions 11 Having inspected the site, the surrounding area and considered the joint engineer's reports/addendum, I am satisfied that the intent of the stormwater disposal policy will be achieved by allowing the consent orders to be granted. 12 The main purpose of the policy is to "minimise overland flow, nuisance flooding and groundwater related damage caused by low lever properties to adjacent downstream properties". 13 It identifies a number of options to achieve this, including option 3 for on site absorption systems. Reference to the amended conditions indicates that the required subsurface investigations are to be undertaken to check the infiltration rates. 14 Importantly I understand that the system has been designed in accordance with point 3 of the design guidelines and that is it is designed for the 50 year ARI storm and there will be an overflow mechanism to minimise overland flow disturbance to the lower properties. 15 I particularly accept Dr Perren's evidence in following paragraphs 23 to 29 of the joint report that this option should satisfy the provisions of the policy. 23. The proposed system is intended to minimise any down-slope seepage by acting as a large version of a self watering planter box. The essential features of the system, as illustrated in the attached longitudinal section running northwards from the proposed new house (Attachment "B") are: a) The system is to be located in an area of the rear yard where it is proposed to provide a significant depth of additional soil to bring the final level of the lawn up to 36.5 m AHD. Attachment "B" (note the exaggerated vertical scale) shows: + The approximate level of the underlying rock based on the geometry of the existing pool (to be removed), data from Sydney Water in relation to the location and depth of the sewer and investigations by the contractor for construction of the new swimming pool to establish the depth of soil; + The level of the existing soil surface based on the site survey; + The level of the proposed lawn with imported soil to fill the void left by the existing swimming pool and filling over the top of the existing soil. b) An impermeable liner will be located underneath and around the sides of a set of "Atlantis" cells. The northern side the liner is 50 mm lower than on the other sides to provide a pathway for excess water to spill in a northerly direction. c) A storage tank will be formed by a series of "Atlantis" cells that are arranged so that there Is soil between the cells to provide a pathway for water retained within the cells to be made available by capillary action to the lawn on top - using the same principle as a self watering planter box. d) The majority of water that drains into the infiltration system will be lost by evapotranspiration from the lawn above. e) In the event of overflow from the infiltration system the water will drain via the northern end of the infiltration system into the soil to the north. f) Any overflow from the infiltration system will percolate into the soil (total depth approximately I m at that point) and gradually drain towards the row of existing trees on the rear boundary (to be retained). These trees provide a further means of absorption of any water as it percolates down slope. 24. The geotechnical report by lack Hodgson Consultants shows that the soil depth in the rear yard of No 37 is about 500 mm deep and comprises: * 100 mm of sandy topsoil, * 100 mm of well sorted sand, * 300 mm of sandy clay. 25. I have been advised that investigations undertaken for construction of the new swimming pool also indicate that soil depth at the rear of the existing pool is about 500 mm. 26. The soil characteristics reported in the geotechnical report are typical of the Lambert soil landscape unit as described and characterised In "Soil Landscapes of the Sydney 1:100000 Sheet" (Chapman & Murphy, 1989) and Appendix C of "Managing Urban Stormwater: Soils and Construction" (Landcom 2004). This soil landscape typically has variable depth shallow sandy loam soils overlying sandstone. 27. In view of the fact that the spaces between the individual cells in the infiltration system will be filled with imported soil and the system will also be surrounded by imported soil, the existing soil will play no role in the functioning of the system infiltration system and will only provide a pathway for any overflow to migrate down-slope along the interface between the soil and the rock in a manner that is characteristic of this landscape. 28. I have obtained rainfall and evaporation data for Sydney Airport from the Bureau of Meteorology for the period 1974 to 2006, That data shows that average annual evapotranspiration exceeds effective rainfall by about 600 mm per year. The proposed infiltration system will be capable of disposing of this depth of water, 29 I acknowledge that there will be occasions on which the infiltration system will overflow and water will percolate into the soil and drain towards the northern boundary of the site. Nevertheless I consider that the proposed system would significantly reduce the volume of water percolating to down-slope properties compared to a conventional infiltration system. Any down-slope seepage of water into adjoining properties will follow the existing seepage pathways that are dictated by the details of the topography of the underlying rock. (In the course of the site inspection of Nos 22 and 24 Curl Curl Parade I observed rock outcrops that will tend to direct any seepage in a north-easterly direction following the general slope of the land.) 16 Consequently, the engineers agree that this system, which collects, contains and then disposes of the run-off from the limited area of the front lawn and drive-way will result in a reduced rate of stormwater discharge from the property. 17 In these circumstances I am satisfied the proposal reasonably satisfies the policy to minimise overland flows. It also seems that in the circumstances of this particular case, taking into account the location of the site infiltration area, which is located towards the upper section of the drainage sub-catchment area, the detention of this stormwater in the proposed system will more likely assist the overloaded downstream pipe drainage systems, rather than increasing discharge rate via pipelines to drainage easement. In the ultimate I accept the engineer's agreement that these agreed revised conditions are reasonable and appropriate to make the consent orders. Court orders 18 The Consent Orders are: 1) The appeal be upheld 2) Development consent be granted to the demolition and construction of a new two (2) storey dwelling and associated landscaping at 37 Gardere Avenue, Curl Curl, subject to conditions in Annexure A 3) The exhibits be returned except 1, 2 and B. ___________________ R Hussey Commissioner of the Court ajl/ljr 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.