Overland flow path

An overland flow path is the route stormwater naturally takes across the surface of a site in heavy rain once the piped drainage system is full, typically following the lowest points of the land toward a stream, reserve or road.

Why councils protect them

Every site's stormwater system is designed for a certain storm intensity. Beyond that, water has to go somewhere on the surface — the overland flow path is where it's meant to go, by design, so it doesn't pond against buildings or flood a neighbour's property instead. Councils identify and protect these routes on their planning maps because building over or diverting one just moves the flooding problem, it doesn't remove it.

Why it's one of the most common reasons a development is declined

Building platforms, garages, decks and retaining walls placed across an identified flow path routinely get declined or heavily conditioned, because the council has to be satisfied the redirected water won't damage the applicant's own property or a neighbour's. Minor dwellings and subdivisions on sloping or low-lying sites are affected particularly often.

How to find out whether a site has one

Most councils publish overland flow path and stormwater hazard layers on their online GIS/property information viewer — search the address before assuming a site is clear. A LIM or PIM will also generally disclose it if the council holds the information. Where a flow path crosses a site, an engineer can advise whether it can be accommodated, piped, or must be left open.

Common misunderstanding

A dry-looking gully or shallow swale is not evidence there's no flow path — it may simply not have rained hard enough recently to show it. Treat the council's mapped layer, not the visible ground, as the source of truth, and check it before committing to a building platform.

Related terms

Last reviewed: 1 August 2026 · General information only, not legal advice.

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