Miles Street & Grant Street Sebastopol FIA & SWMS

WMS was engaged by Beveridge Williams to conduct a flood impact assessment for a proposed residential subdivision at Miles & Grant Streets, Sebastopol. The assessment focused on defining pre- and post-development flood conditions for the 1% and 10% Annual Exceedance Probability (AEP) storm events, ensuring compliance with flood management guidelines and safeguarding the development against flood risk.

The study involved repurposing existing RORB and TUFLOW models to assess the site’s flood and stormwater conditions under both current and proposed development scenarios. Key updates included refining impervious area fractions and maintaining critical storm duration patterns consistent with the Ballarat West PSP drainage strategy. Results confirmed the proposed drainage network and swale system could effectively manage flows for up to the 1% AEP storm event. The internal roads achieved H1 flood hazard safety, and the flood risk along Miles Street improved from H5 to H1, with no adverse downstream impacts observed.

The results demonstrated that the proposed development met the Guidelines for Development in Flood Affected Areas. No increases in flood depths or downstream flows were identified, and adequate egress is ensured during significant storm events. The modeling assumptions, such as the direct use of the Ballarat West PSP Review Drainage Strategy model and representation of planned infrastructure upgrades, provided a reliable basis for decision-making, which ensured flood-safe residential expansion in Sebastopol.