Excavation in Gwandalan
All of Gwandalan's residential land lies inside the Swansea North Entrance mine subsidence district, and much of it carries Subsidence Advisory NSW's Guideline 2, for properties at risk of trough subsidence over old coal workings. Before a dig is designed in Gwandalan, check the guideline for your lot: under Guideline 2, basements, stepped slabs and retaining walls that hold up the house are not permitted.
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Excavation around Gwandalan
Guideline 2 says trough subsidence forms over underlying, unstable historical coal mine workings. It prohibits integral retaining walls supporting a building, basements, including partial basements where a wall retains the ground, and suspended, drop-edge or stepped slabs, while in-ground concrete pools and retaining walls that don't support a structure are permitted. Other Gwandalan lots carry Guideline 3, which allows a single-level basement, and a few carry Guideline 7, which Subsidence Advisory NSW must assess itself.
So the same house plan can suit one lot and need rethinking on the next, and the difference shows up at the dig: a flat pad and a pool are one kind of job, a house stepped down the slope over a basement is another. Subsidence Advisory NSW says different guidelines may apply to neighbouring properties within a district, which is why a neighbour's result is no guide to yours.
Permits and Central Coast Council rules
Subsidence Advisory NSW says anyone planning to build within a district must get its approval before starting work, though applications that comply with Guidelines 2, 3, 3A, 6 or 8 can be approved by Council or a certifier. Gwandalan's mapped flood planning land comes from Council's Lake Macquarie catchments overland flood study of 2021, and there filling in flood planning precinct 2 needs a qualified engineer's report approved by Council.
Source: Subsidence Advisory NSW, Surface Development Guidelines 2, 3 and 7; Central Coast DCP 2022 Chapter 3.1 Part B — confirm current requirements with Central Coast Council.
Our Gwandalan service area
Enquiries from Gwandalan are referred on to an independent provider, who gets in touch to see the site.
See all Excavation on the Central Coast. We also work in Lake Munmorah, a short drive south, where some lots carry the same guideline.
Call (02) 4326 8289Last reviewed · Updated · First published