For Developers

Screen sites for overland flow before you settle.

Most council flood maps stop at major rivers. Buying land for subdivision or multi-unit residential? You want to know whether overland flow paths cross the site before settlement — not after the engineer flags it at design stage. The map is free.

When to use it

Three points in the deal where the OFP layer matters.

Pre-purchase DD

Before you go unconditional

Open the map, search the address, see whether overland flow paths cross the site. Identify problem sites in your shortlist before you commit to the formal due-diligence spend.

Feasibility

Lot yield modelling

Flow paths constrain building platforms and reserve setbacks. Knowing where they run shapes the realistic lot yield before you commission concept layouts.

Design hand-off

Brief your civil engineer

Send the engineer a screenshot or share the FloodMap link with the address. They have a free check on overland flow before they start the consent design — fewer clarifying-question loops.

A worked example

Why a 30-second check is the cheapest line item in your DD.

Scenario

4-lot rural-residential subdivision, pre-settlement DD

Site looks clean on the council viewer — no mapped flood overlay. Vendor and agent both confirm "no flooding". You're 7 days from going unconditional on a $1.4M rural block.

Open FloodMap. The map shows a Tier 4 flow path crossing the proposed building envelope, with a 6.2 ha upstream catchment. Council mapping missed it because their layer was built from 2016 LiDAR; the 2024 LiDAR shows the gully has scoured deeper.

Outcome: you renegotiate the price to absorb the redesign and detention pond, or walk away. Cost of finding out via the free map: zero. Cost of finding out at the engineering stage: a late variation, a delayed consent, and a settlement extension you didn't budget for.

Illustrative — actual outcomes depend on the site and council requirements. For a formal site-specific flood assessment with HEC-RAS depth and velocity outputs, that's an engineering job; SAE Ltd can scope and quote.