Hills Shire Stormwater & OSD Requirements: A Builder’s Guide

Stormwater Approval in The Hills: What to Expect

The Hills Shire is at the heart of Sydney’s north-west building boom. Box Hill, North Kellyville, Rouse Hill, The Gables, Kellyville and Castle Hill are delivering new homes at a pace few councils can match, while established suburbs like Baulkham Hills and Bella Vista see steady duplex and infill activity. Whether you are building a single dwelling on a new Box Hill lot or a multi-dwelling project in Castle Hill, stormwater is one of the first things Council’s engineers will assess – and one of the most common reasons applications are held up.

The Planning Controls That Apply

The principal document is The Hills Development Control Plan 2012 (The Hills DCP 2012), which contains general and residential controls including stormwater and drainage requirements. Release areas have their own site-specific sections within the DCP – for example, dedicated parts covering Box Hill and Box Hill North – which carry precinct drainage strategies prepared for those growth fronts.

Sitting under the DCP, Council publishes engineering guidelines, including its flood modelling and stormwater design guidance, which govern the technical detail of drainage and flood assessment. Your engineer should design to both layers: the DCP controls and the current engineering specifications.

Typical Requirements for Homes, Duplexes and Townhouses

• On-site detention (OSD): most development that increases impervious area requires OSD to limit post-development discharge. The Hills has a well-known preference for above-ground storage (landscaped depressions, driveways) where possible, with underground tanks accepted subject to capture and access criteria. Confirm the current permissible site discharge and storage criteria for your catchment before design – do not rely on figures from older approvals.
• Stormwater drainage plans: a full drainage layout by a civil engineer showing the lawful point of discharge, pipe sizes, pit locations and overland flow paths is expected with the DA or CDC.
• Inter-allotment easements: many Hills lots fall away from the street. If your site cannot drain by gravity to the kerb or a Council pit, an easement to drain water over downstream properties is generally required – pump-out systems are only accepted in limited circumstances.
• WSUD and water quality: larger residential projects and subdivisions need water quality treatment consistent with Council’s controls, typically demonstrated with MUSIC modelling.

Building in Box Hill and The Gables

Box Hill and The Gables sit on the rural-urban fringe where trunk drainage is still being delivered. Lots here often rely on staged precinct infrastructure, and Council will check that your connection point actually exists and has capacity. In some cases interim detention or temporary discharge arrangements are needed until downstream works are complete – a detail best resolved before lodgement, not after.

Local Factors in The Hills

• Topography: the Shire is genuinely hilly. Steep blocks in Castle Hill and Glenhaven create high-velocity runoff and difficult overland flow paths that must be managed within the site.
• Clay soils: Cumberland Plain and shale-derived clays across much of the LGA limit infiltration, so absorption systems rarely satisfy Council as a primary disposal method.
• Creek catchments: Cattai Creek and Smalls Creek receive runoff from the growth precincts, and development affecting them attracts closer water quality scrutiny.

How to Prepare a Smooth Application

Order a detail survey early, identify the lawful point of discharge before you finalise the floor plan, and have your stormwater concept resolved alongside the architectural design – not after it. If an easement is required, allow time for negotiation and registration. A compliant OSD and drainage package lodged with the application is the single best way to avoid a months-long request-for-information cycle.

Contrive Consultants is based in Bella Vista, in the heart of The Hills, and prepares stormwater drainage and OSD designs accepted by The Hills Shire Council. See our civil and stormwater services or contact us today – call +61 497 848 111 or email info@contriveconsultants.com.au to discuss your project.