Blue Mountains Council Stormwater & Drainage Requirements

A City Inside a World Heritage Area

The Blue Mountains is unlike any other NSW council area: a string of towns along a single ridgeline, surrounded on both sides by the Greater Blue Mountains World Heritage Area. Building activity is steady rather than booming — new dwellings, knock-down rebuilds and dual occupancies in Katoomba, Leura, Wentworth Falls and Blackheath in the upper mountains, and stronger volumes through Springwood, Winmalee, Blaxland and Glenbrook in the lower mountains, where Sydney commuters keep demand healthy.

Because every backyard here ultimately drains into protected bushland or drinking water catchment, Blue Mountains City Council treats stormwater as an environmental issue first and an engineering issue second. Builders should expect closer scrutiny of discharge arrangements than almost anywhere in the Sydney region.

The Planning Framework: Blue Mountains DCP 2015

The governing document is the Blue Mountains Development Control Plan 2015, which contains Council’s water management and water sensitive urban design (WSUD) controls alongside Blue Mountains Local Environmental Plan 2015. The DCP requires stormwater systems to be designed to current WSUD best practice, using a treatment train — a sequence of measures providing retention, filtering, infiltration and safe disposal — rather than a single pipe-to-street solution. Typical elements include rainwater tanks with re-use, detention basins or tanks, raingardens, and sediment and gross pollutant capture.

Parts of the LGA also drain toward Sydney’s drinking water catchment, where development must achieve a neutral or beneficial effect on water quality under the state framework — another layer on top of Council’s own controls.

What Is Typically Required

• Stormwater/WSUD strategy with the DA: showing how roof and surface water is captured, treated, detained and disposed of, sized to current WSUD guidance.
• Detention and controlled discharge: limiting post-development flows so that downhill bushland, neighbours and Council systems are not impacted.
• Rainwater retention and re-use: tanks are a near-universal expectation, doing double duty for BASIX and stormwater.
• Carefully designed disposal: where no street drainage exists — common in the mountains — dispersal trenches or level spreaders must be designed for the soil and slope, and erosion risk is assessed closely.

Targets and sizing should be confirmed against the current DCP and Council’s engineering requirements, as guidance documents are updated periodically.

Local Factors: Ridge-Top Development Above Sensitive Valleys

The defining condition is topography. Towns sit on the ridge; everything else falls away steeply into the Jamison, Grose and Megalong valleys. Stormwater leaving a building site can quickly become an erosion gully in hanging swamps and sandstone bushland below — and those downslope communities, including endangered upland swamps, are exactly what the World Heritage listing protects.

Practical consequences for builders include shallow sandstone making excavation costly, dispersive and erodible soils on slopes, limited formal street drainage in older areas, and bushfire controls interacting with landscape and drainage design. Council’s expectation is simple: water leaves the site at no greater rate, and in no worse condition, than it did before development.

How Builders Should Prepare

• Identify the legal discharge point early — many mountains blocks have no kerb and gutter, making disposal design the critical path.
• Get geotechnical advice on soil dispersal capability before committing to on-site disposal.
• Integrate tanks, raingardens and detention into the site plan at concept stage.
• Check whether the site drains to the drinking water catchment and what that adds to the approval pathway.
• Prepare a genuine erosion and sediment control plan — on steep mountain sites it is enforced.

Stormwater Design in the Blue Mountains

Contrive Consultants prepares WSUD-based stormwater and OSD designs for homes and dual occupancies across the Blue Mountains, from Glenbrook to Blackheath. View our stormwater design services or contact the team — call +61 497 848 111 or email info@contriveconsultants.com.au.