Stormwater detention and bioretention basin design.
Case study: civil design of stormwater detention and bioretention systems for a commercial industrial estate in Western Sydney — to AS 3500.3, MUSIC modelling and Sydney Water requirements.
Project overview
ASTCAD designed the on-site stormwater detention basin and a 1,200 m² bioretention basin for a new 4.8 ha commercial industrial estate in Western Sydney. Design included MUSIC modelling for water quality targets and detailed civil documentation for council submission and Sydney Water approval.
The challenge
The estate’s runoff coefficient post-development jumped from 0.35 to 0.85. Council required on-site detention to pre-development discharge plus 90% TSS and 60% TP load reduction. The available basin footprint was constrained by setback requirements and an underground sewer easement.
Our approach
- DRAINS modelling for storm event design (Q5, Q20, Q100)
- Basin sizing optimised for available footprint with multi-stage outlet structure
- MUSIC modelling targeting 90% TSS / 60% TP load reduction
- Bioretention media specification per FAWB guidelines
- Outlet structure detailing for low-flow and overflow events
Deliverables
- Civil drawings — basin, outlet structure, pipework
- DRAINS model and stormwater report
- MUSIC model and water quality compliance report
- Sydney Water approval documentation
- Vegetation specification and maintenance plan
Outcome
Both council and Sydney Water approvals issued without revision request. The basin was constructed during dry-weather and operational at handover. Monitoring after first 12 months of operation confirmed the bioretention is meeting water quality targets.