Council has received a number of questions about development at the Vanderville Estate, particularly in relation to the requirement for On Site Detention (OSD) on private allotments. Click on the Frequently Asked Questions to find out more information.
Acoustic treatment requirements have been imposed for the seven lots fronting Montpellier Drive. The requirements are detailed in the 88B Instrument for Stage 1 of the Vanderville Estate (see Restriction No 13).
The restrictions which relate to total glazed areas, glass thickness, acoustic seals and sound transmission ratings apply to the western elevation of the dwelling only. It is understood that some building companies have provided Council with certification from an Acoustic consultant demonstrating compliance with these requirements.
It is also understood that some property owners have provided Council with a full Acoustic Report. Council has undertaken to refund any owner for the cost of preparing a full Acoustic Report.
In relation to the requirements under the Infrastructure SEPP to consider road noise impacts, it is Council’s position that those provisions are satisfied if the dwelling incorporates the measures outlined in the 88B Instrument. If the property owner does not wish to incorporate these acoustic measures into their house design, Council requires an Acoustic Report demonstrating compliance with the noise intrusion criteria contained in Clause 102 of the Infrastructure SEPP.
Do I need approval under Section 68 of the Local Government Act to construct a private on-site detention system (OSD)?
Council considers the construction of an OSD system on private allotments to be ancillary development to the principal dwelling. Consequently the appropriate approval pathway for the construction of a private OSD is via the Development Application or Complying Development Certificate process. Please note there is a requirement in the 88B Instrument to include details of the OSD system on any building plans for approval.
Separate approval under Section 68 of the Local Government Act is not required from Council for a private OSD system.
The central basin is designed to treat stormwater in terms of the quality and quantity of water leaving the development site.
Under the terms of the Consent issued by Council, it is the developer’s responsibility to maintain the basin for the first 5 years following practical completion of the subdivision. Beyond the 5 years period, the maintenance obligation will pass to Council.
Any concerns about the condition of the central stormwater basin should be logged on Council’s Customer Request Management System by phoning 4677 1100. Council will co-ordinate any necessary maintenance works.
Vanderville Estate has been provided with barrier and roll top kerbs. A footpath has been provided to one side of the street.
The engineering specifications in terms of concrete thickness are the same for footpaths and driveway crossings. Consequently the existing footpath can remain and the driveway can join up on either side. The footway crossing should be plain concrete with no colour to match the footpath. Internal driveways can be coloured.
A Property Entrance Application is required for any work undertaken within the road reserve. Details of proposed driveway construction should be provided for Council’s consideration and approval prior to commencement of any work.
Who is responsible for maintenance of the front fence erected by the developer along Montpellier Drive?
The fence erected along the front of the Estate will be maintained by the developer during the 12 month maintenance liability period. Beyond the 12 month period, the maintenance obligation will pass to the relevant land owner.
In this regard the 88B Instrument restricts the type of fencing that can be erected along the western boundary of those lots fronting Montpellier Drive. The permitted fencing is essentially consistent with that already erected by the developer (see Restriction No 11 for Stage 1).
The table below summarises the requirement for internal fencing at Vanderville Estate.
Construction details for fences that cross overland flowpaths.
No solid or metal fencing is permitted along the western boundary of those lots fronting Montpelier Drive. Open style fencing must comply child proof fencing standards.
No solid or metal fencing is permitted along the southern boundary of the Estate.
Consent required from Rhodes and/or Wintle for erection of fencing along the common boundary of their land.
Fencing must comply with Council’s DCP. Fences erected behind the building line must be constructed of ‘hardwood’ lapped and capped.
Construction details for fences that cross overland flowpaths.
No solid or metal fencing permitted along the southern boundary of the Estate.
No solid or metal fencing permitted along the eastern boundary of the Estate.
Fencing must comply with Council’s DCP. Fences erected behind the building line must be constructed of ‘timber’ lapped and capped.
Consent required from Rhodes and/or Wintle for erection of fencing along the common boundary of their land.
*Denotes restrictions that benefit every other lot.
open style/palisade fencing
It is acknowledged that there is an inconsistency in the 88B Instrument for Stages 1 and 2 in terms of the lapped and capped fencing requirement. Stage 1 requires “hardwood” panels whilst Stage 2 requires “timber” panels.
Given this is a private restriction (i.e a restriction that benefits every other lot) it is not Council’s intention to enforce these requirements. Under the 88B Instrument, every other lot owner may seek to enforce the requirement as a private matter between land owners.
What resources have Council allocated to assist with the processing of Development Applications for dwellings at Vanderville Estate?
At the March 2016 Ordinary Meeting, Council considered a Notice of Motion dealing with this issue. Council resolved to allocate funds to increase the staff resources for the processing of applications lodged by Vanderville Estate residents.
Council currently has 30 outstanding applications for dwellings proposed within the Estate.
The Assessing Officer’s details for any application lodged with Council will be contained in the acknowledgement letter. For compete applications, the process time is generally between 4 and 6 weeks.
Alternatively land owners may wish to investigate whether the plans for their dwelling can be approved as Complying Development. A Complying Development Certificate can be issued by Council or a Private Certifier subject to compliance with the 88B Instrument requirements for OSD and other restrictions.
Does Council intend to amend its Development Control Plan and detail the OSD requirements for Vanderville?
Provisions were incorporated into Council’s DCP when the land was rezoned in March 2012. The DCP provisions stated:
“Details of individual lot on-site stormwater detention and drainage design and ongoing maintenance for such shall be detailed in Section 88B and 88E Instruments submitted with subdivision plans and then registered on the title of each lot”.
The above provision was removed from Council’s DCP upon registration of the 88B Instrument containing the OSD requirements. It is not intended to insert these provisions into the general engineering section of Council’s DCP.
Why are the requirements for the private OSD system based upon the Upper Parramatta Catchment Authority Trust Handbook?
Council has not adopted the Upper Parramatta River Catchment Trust Handbook.
The Handbook does however contain a calculation procedure used to determine OSD details for development located outside the Parramatta River Cathchment. Relying upon this calculation procedure, data relevant to the Vanderville proposal was entered into a calculation sheet to determine the individual OSD storage volumes and discharge control details.
The detailed OSD design for individual systems must meet predetermined storage volumes and discharge rates in accordance with the Estate’s Engineering Design.
Will Council permit the OSD to be completed by the land owner separate to construction of the dwelling following issue of an Interim Occupation Certificate (OC)?
It is recommended that land owners engage their builder to construct the required OSD system.
It is understood however that some builders are only providing the stormwater pipes, surface collection pits and connection to the stormwater system. Under these arrangements completion of the OSD system is being left to the land owner to co-ordinate. In which case, Council recommends that you negotiate access to the site in the final stages of the dwelling construction to complete these works.
The construction of walls must be checked and certified by an Engineer as part of the overall certification for the OSD.
Because the OSD is an integral part of the dwelling approval, Council will not issue an Interim OC to permit dwelling occupancy whilst these works are being undertaken. All OSD works must be completed and certified prior to the release of any OC by Council.
Would Council consider removing the Asset Protection Zone (APZ) restriction that applies to some lots?
The APZ needs to remain in place due to the unmanaged land on the road reserve at the eastern side of the estate.
A request under the Government Information (Public Access) Act 2009 (GIPAA) may be made to Council to request copies of information on the Stormwater Management Strategy for the Vanderville Estate development.
All lots within the Vanderville Estate are burdened by the OSD requirement. However the requirement is triggered by the construction of a new dwelling.
Are there any Council endorsed alternative methods to satisfy the private On Site Detention requirements?
Wollondilly Shire Council does not have strict design specifications for OSD and as such there is some flexibility in the design of a system. Proposed OSD systems will be assessed individually based upon the site characteristics and building design, site discharge outcomes of the Engineers calculations and compliance with the normal Design Specifications for the particular development type.
A Civil / Hydraulics Engineer or Registered Surveyor must be engaged to prepare the calculations and design of the OSD system. To achieve the best outcome for your particular development it is critical that your Engineer and Architect / Draftsperson work closely to achieve the most appropriate outcome for your development.
Why isn’t the BASIX requirement to provide a 10,000 litre water tank sufficient for private On Site Detention?
BASIX is a water quality and conservation requirement where OSD is a water quantity requirement.
The 10,000 litre rainwater tanks are required to comply with BASIX and NorBE. NorBE is a neutral or beneficial water quality outcome required for all development (e.g. new dwellings or subdivision) within the Sydney Water Catchment area. Compliance with the BASIX and NorBE requirements relies upon the rainwater tank having a particular volume of water available for reuse.
The OSD requirements rely upon a “free” storage volume for stormwater retention during a rain event. The calculations to determine the storage volume must assume that all other available storage is full (i.e. the 10,000 litre is full and not available if a large storm event occurs in the catchment).
Why wasn’t sufficient provision incorporated into the Estate to control the flow of stormwater to avoid the need for private On Site Detention systems?
The Stormwater Management Strategy adopted by the Developer (through design and calculations from their Engineer) considered many site and development factors including site slope, existing drainage capacity, property protection and public safety around storage areas etc. The detailed engineering design work for the Estate determined that the OSD on private allotments was required to avoid downstream flooding.
Did Council take into account the compliance costs associated with homeowners maintaining the stormwater system?
Regardless of whether Council accepts the hand over and maintenance of an asset (eg detention basin on Council land/reserve) or undertakes compliance action in relation to private OSD systems there will be a cost implication.
As a general principle any development of land must not negatively impact on existing downstream drainage infrastructure and properties. Developers must ensure the flooding potential is not made any worse than it was before the development of their land. Several factors have to be considered when looking at how this can be achieved including site slope, flood levels in the existing creek, existing drainage capacity, public safety around storage areas, construction costs and the lot layout for the subdivision.
In August 2012, the Developer submitted a Concept Stormwater Management Plan along with other documentation with their Development Application for land subdivision. The stormwater management proposal included storage basins located in Council owned reserves and individual OSD systems for private allotments. The development was also required to meet water quality targets specified by Water NSW. These water quality targets where achieved by proposing that each dwelling incorporate rainwater tanks for reuse and on road bio filtration ponds that use soil filters and plants to reduce the amount of nutrients and silts finding their way into the downstream creeks.
In May 2013, Council granted consent for the land subdivision including the Concept Stormwater Management Plan. The Developer then started to prepare engineering plans for all the roads and drainage infrastructure. The detailed engineering design work determined that additional OSD on private allotments was required to avoid downstream flooding. These plans included calculations and a design example for an OSD system to demonstrate that such a system could be incorporated on the private allotments.
In July 2014, Council issued construction approval for the subdivision works. Construction commenced in late 2014 and was mostly completed by August 2015.
In order to have the land registered at the Land and Property Information, the Developer had to apply to Council for a Subdivision Certificate. The Developer provided Council with a copy of the Deposited Plan (plan showing the lots) and the 88B Instrument (that creates the easements and restrictions placed on each lot) in August 2015. Minor amendments where requested to the Deposited Plan and 88B instrument to ensure the conditions set out in the Development Consent where complied with. The Subdivision Certificate was issued for Stage 1 in September 2015 and Stage 2 in October 2015. Registration of the land occurred shortly after that in November 2015.
Initial feedback from building companies suggest that the construction of OSD systems on private allotments will cost approximately $20,000 to $25,000.
Did the Development Application contemplate On Site Detention System on private allotments in addition to BASIX Requirements?
Yes. In August 2012 the Developer submitted a Concept Stormwater Management Plan which included stormwater storage on private allotments in addition to that required to satisfy BASIX requirements.
Did Council consider this arrangement to have more merit than increasing the road and storage basin capacity?
The concept put forward by the proponent is a legitimate option to address stormwater detention requirements. Increasing the capacity of the storage basins in Council’s Reserve was not an option given the site topography and risk of downstream flooding.
For further information about the plan contact Council's Development Engineer
Did Wollondilly planning department consider the impact of the On Site Detention requirement on future land owners?
Council considered whether the individual lots could physically accommodate the required OSD system. The cost implication would normally affect the purchase price for individual lots. This issue highlights the pitfalls of buying property off the plan. If you feel that you have been misinformed during the acquisition process you should discuss the matter with your solicitor / conveyancer.
The system put forward by the Developer is an industry wide accepted solution to stormwater management. Many Western Sydney Councils require OSD for all new developments that are located in critical catchment areas.
If this is the ideal strategy for stormwater management then surely it will be utilised elsewhere in Wollondilly?
The most appropriate stormwater management system to control water quantity is different for every development. Site characteristics such as land slope, catchment type, previous land use, proposed land use and existing drainage systems must be considered when determining the most appropriate stormwater management system.
A consequence of increasing urbanisation and intensification of development is an increase in stormwater runoff. Without proper safeguards, this increase can overload existing drainage systems, both major and minor, with resulting nuisance and potential damage to existing properties.
One of the methods adopted by Council to alleviate the problem is to require developers to include detention storage in developments, also known as On-Site Detention or OSD.
Detention storage is the provision of depressed areas or specific storages in paved or landscaped areas that are provided with relatively small stormwater outlets, to detain a volume of water for a short duration, during more intense storms. This prevents or mitigates any increase in peak stormwater flow rates from development and delays the peak volume of runoff.
What is the purpose of OSD?
The purpose of OSD is to help offset the effect that developing land has on the existing drainage systems and creeks. When there is a change from a rural to urban land use, there is generally a decrease in natural, pervious areas and an increase in the amount of hard impervious surfaces such as roadways, driveways, pavers and roofs. Rain falling on hard surfaces creates more stormwater runoff than rain falling on the same area of grass or garden. The increased stormwater runoff has to be carried by the existing road drainage or by nearby creeks and rivers. Sometimes these systems don’t have enough capacity to carry the extra stormwater. When this happens there can be flooding of downstream properties.
The introduction of OSD into development helps to offset the increased stormwater runoff by storing some of the stormwater and letting it drain out into the road drainage over a controlled, longer period of time. This slow release of stormwater helps prevent adverse impacts of flooding issues to properties downstream.
What does an OSD look like?
There are many designs for an OSD system. Some systems consist of underground storage tanks or pits or aboveground ponds, tanks and basins. Generally residential OSD take the form of a control pit that regulates the flow of stormwater into the road drainage system and a storage area that can be a pit or walled area and basin.
Other systems may consist of an aboveground rainwater tank that stays empty until it rains and then fills and empties as a storm passes. The design of an OSD system is flexible and can consist of a combination of storage types. In residential areas it is possible to design an OSD to use aboveground storage in the front or rear yard so that the area can be used by the family when not storing stormwater.
Some developments propose large centralised basins to act as the sole OSD provision for the development, while others propose to incorporate smaller provisions into individual lots for the purchaser of the lot to construct with the construction of a house.
The type of OSD provision is a decision of the Developer but must comply with Councils Design Specification to achieve the required performance outcome.
What does OSD mean for property owners?
If OSD is required, the costs associated with design and construction of the system will be the responsibility of the property owner. A Development Application for building a dwelling will be required to include a detailed design for an OSD system. Once built the area used for OSD must not be filled or used to store materials or to erect buildings such as garden sheds. If the design uses aboveground storage areas it can be turfed and used for open space activities.
Maintenance of the OSD components (pits and pipes etc) is critical to ensuring proper operation of the system. The property owner is required to undertake regular maintenance to ensure the system is operating at its best. Generally, well designed systems will need very little maintenance that may only require a check and clean out of leaves every few months. Council may conduct inspections to ensure the systems are operating correctly and could offer advice on any maintenance that may be required.
Owners of OSD systems must ensure that the facilities are adequately maintained so that they continue to function. A Positive Covenant and a Restriction on Use are imposed on the title of the property to bind all current and future owners.
How much stormwater do I need to store?
The OSD system is only used during larger storms during which an amount of stormwater will be stored on the property for a short period of time. After a large storm passes, any stored stormwater will slowly drain away leaving the storage area dry. In residential OSD, the maximum depth of stored stormwater in aboveground depressions is only shallow even during the largest storm.
The calculations required for the design of OSD are critical, it is essential that an experienced Engineer or Surveyor prepare the calculations and design for the OSD system. It is important for the Engineer or Surveyor to work closely with your building designer to ensure you get the best OSD design outcome. Innovative design can create low cost and low impact OSD systems.
The design of an OSD will depend on the amount of stormwater that it will need to store. The storage amount depends on several factors including:
- The location of a property to creeks and rivers.
- The capacity of the existing stormwater drainage systems (i.e. how much water it can carry).
- The size of a property.
- The size of house roof and driveway areas on the property (more roof area means more storage required).
What is Wollondilly Shire Council’s OSD Policy?
Generally it will only be required when the existing drainage systems have insufficient capacity for the particular development type or the development will increase the flooding potential for downstream properties.
If required, an OSD system will be assessed on an individual basis and will be approved based the outcomes of the Engineers calculations and the impact on the existing drainage network. Without strict design specifications, a development is given flexibility in the design of a system that provides an opportunity for innovative design.
For larger developments including the creation of new residential lots, a Developer is required to prepare a Stormwater Management Plan. The plan must outline how the Developer proposes to control the increased stormwater runoff and reduce the potential for flooding of the existing drainage systems or downstream properties. There are several methods of controlling the increased volume of stormwater including increasing the capacity of the drainage system, creating areas where rain soaks into the ground, providing on road storage such as large detention ponds and / or OSD.
The OSD must be constructed in accordance with the approved design plans. Generally walls forming any part of the OSD must be constructed of concrete, concrete or clay masonry block with mortar that can withstand the pressure of the stored water. The construction of walls must be checked and certified by an Engineer as part of the overall certification for the OSD. If the design plans are unclear about materials, the builder should contact the design Engineer for clarification.
Significant planting (other than turf) or placement of structures such as planter boxes, sheds, rockeries, or the like within the area designated OSD system is not permitted.
Planting or landscaping around an OSD is allowed. Planter boxes which make up part of the OSD walls will also be considered as long as it does not impact on the available storage. If landscaping is proposed it must be considered as part of the overall design and should be noted on the engineering plans.
If property owners are unsure of what is allowable they should discuss this with the Engineer designing their OSD system or alternatively contact Council’s Development Engineer.
If property owners wish to erect a fence within their OSD area, design details must be submitted with their Development Application. Any such fence must allow unrestricted water flow. Council understands that open style fences may not be practical for privacy reasons, in which case a solid fence may be considered provided the base of the fence is constructed an appropriate distance above the ground level of the OSD basin.
It is Council’s opinion that there is very little scope to increase the capacity of the central OSD basin such that the need for private OSD could be reduced or completely offset.
The investigation, design and engineering work for this option would take considerable time to complete. The uncertainty around the outcome of this process would likely cause further inconvenience to residents.
The approved subdivision had a condition of approval imposed requiring “..provision to be made for the supply of telephone services to all proposed lots in accordance with the requirements of Telstra…”. As per condition 10(2) of the DA approval 516/2012 Council received a “Compliance Certificate - Telecommunications Infrastructure Provisioning Confirmation” for the Vanderville Estate.
In December 2013 the developer of Vanderville Estate had lodged a fibre application with NBN however in line with the, then, Government policy (see link here), this was rejected. The reason being was that the development was for fewer than 100 premises and the area was not at that stage on the approved NBN roll out schedule. The consequence of NBN not accepting the fibre application (in an non NBN ready area) was that Telstra became the service provider.
On behalf of new residents in the Vanderville Estate, Council has now raised concern about the timeframe for provision of the service with Telstra.
Telstra have indicated that:
- The project to provide service will be sent to our contractors who will prepare a design for Telstra approva
- The project will include civil works which requires a notification to Council
- The normal length of time required to complete the work is 8 weeks
- They will request the contractor to fast track this project.
- The Vanderville Estate residents will receive the NBN when the rest of this area is scheduled to be connected. NBN produces a public 3 year construction schedule which is updated one to two times a year (see link here). This indicates that construction for the Oaks region was due to commence last quarter however it can take some 12 or so months to complete construction. The Oaks region will receive a mix of NBN via fibre to the node (FTTN) technology and fixed wireless.
- The NBN website has a section devoted to new developments (see link here), which includes links to Government policy (see link here).