Grandview Estate – Wetland and Retarding Basin

Aerial view of Grand View Estate wetlands and retarding basin

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Recently, we assisted with the development the Grandview Estate wetland and retarding basin. Engaged by Stockland, DPM Consulting Group was tasked with preparing a functional and detailed design package for the wetland and retarding basin as outlined in the Dry Creek Upper Development Services Scheme (DSS).

A key component of the Dry Creek Upper DSS

The wetland/retarding basin, designated as WI09 in alignment with the PSP naming convention or RBWL6 in accordance with the DSS naming convention, forms an integral part of the Dry Creek Upper DSS. Covering a drainage reserve of 3.12 hectares on the south-west corner of the Grandview Estate, it sits east of the future Outer Metropolitan Ring (OMR). The primary purpose of this water quality asset is to attenuate post-developed flows to a target outflow of 4.18 m3/s during a 100-year Average Recurrence Interval (ARI) event and providing stormwater quality treatment to the upstream catchment in order to achieve Best Practice Environmental Management Guidelines (BPEMG).

Approval and adaptation to changing project needs

Following the approval of the Stormwater Management Strategy (SWMS) for the Grandview Estate, DPM Consulting Group conducted additional investigations due to amendments in the planning permit for the overall estate and advancements in the design of the residential development. This meticulous approach underscores our commitment to adapting to evolving project requirements and ensuring the asset’s efficacy.

Working collaboratively with stakeholders

Collaborating closely with Melbourne Water, our team facilitated the inclusion of a dedicated bypass line to convey bypass flows directly to the twin-chamber pit. This design feature involved twin 1050 pipes leading from the weir pit to the junction pit WQ/3 and a 1500 mm diameter pipe from WQ/3 to the weir pit. The bypass line, strategically connected to the downstream side of the twin-chamber outfall pit, ensures efficient management of flows, considering the maximum allowable downstream flow and results obtained through RORB analysis.

Furthermore, we actively engaged in discussions with Melbourne Water to enhance the drainage system’s efficiency. They advocated for replacing the originally proposed constructed waterway with a 1% AEP drainage pipeline, directing flows to the weir pit upstream of the northern sediment pond. This modification, endorsed by Melbourne Water, reflects our commitment to optimising the system for superior performance.

Review and risk assessment

The comprehensive drainage scheme asset underwent thorough review and risk assessment, with an ANCOLD consequence assessment prepared to identify and mitigate potential risks associated with the wetland and retarding basin. The project is anticipated to reach completion by the end of 2024, showcasing our dedication to delivering effective and resilient water management infrastructure. DPM Consulting Group’s involvement in the Grandview wetland and retarding basin underscores our expertise in hydraulic design, stormwater management, and collaborative problem-solving to meet evolving project needs and regulatory standards.

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