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Stormwater Drainage & Hydraulic Impact Assessment

SCG Urban delivered the detailed stormwater drainage design and Hydraulic Impact Assessment (HIA) for the 210-lot River Bend residential subdivision located along Mirani–Eton Road, west of Mackay.

The stormwater strategy incorporated a treatment basin on the western boundary of the site, adjacent to the Pioneer River corridor, to achieve both water quality treatment and peak flow attenuation in accordance with Mackay Regional Council requirements.

A key challenge was directing the low-flow drainage system toward the western treatment basin despite the natural surface grading generally falling east toward Mirani–Eton Road. The design required careful regrading, optimisation of underground drainage infrastructure, and strategic management of overland flow paths to capture and convey flows to the basin without worsening downstream discharge conditions.

Hydraulic modelling was undertaken using 12d, DRAINS, and TUFLOW to assess pre- and post-development conditions, confirm no adverse downstream impacts, and ensure compliance with Council standards. The final solution provided a balanced outcome between hydraulic performance, environmental protection, and practical constructability