Council — Ku-ring-gai Council
Development — Residential, New Dwelling
Services — Flood Modelling, Flood Risk Assessment, Hydrology Assessment
Year — 2026
Outcome — Approved
Background
The owner planned a new two-storey house with a pool in Pymble, approved as a complying development (CDC).
The problem
The site is low-lying and the rear of the lot backs onto a watercourse. When the Section 68 application went in, Council's engineers asked for a flood study to understand how the development might change flood behaviour. Without it, the project couldn't move forward, and there was a real risk council would impose flood controls such as raised floor levels that would add significant cost to the design and build.
Our solution
We were engaged to carry out a flood impact and risk assessment. We delineated the upstream catchment and ran a DRAINS hydrology analysis to find how much water reaches the site. That fed into a 2D TUFLOW model of the site and surrounds, built from LiDAR terrain, roughness values, existing building footprints and boundary conditions, which we used to map the 1% AEP flood extent, levels, depths, velocities, hazard (H1–H6) and hydraulic categories.
We then added the proposed house to the model and compared before and after results. The development caused no adverse flood impacts and the flood controls didn’t apply, so there was no redesign and no added flood measures, saving the client a large amount in design and construction costs.
Was it approved? yes.
Flood Model