Stormwater

Stormwater design establishes how rainwater falling on the development site is collected, conveyed, treated, and discharged. It includes pipe networks, inlet structures, manholes, attenuation devices, and treatment systems. The design must manage both the quantity and quality of stormwater to meet the council's requirements and protect the downstream environment.

New developments create impermeable surfaces (roofs, driveways, roads) that increase stormwater runoff rates and volumes compared to the pre-development site. Without management, this increases the risk of flooding, erosion, and water quality problems downstream. Council standards require developers to address these effects as part of the development.

A stormwater management plan (SWMP) is a technical document that describes how the development's stormwater will be managed in accordance with the council's requirements. It typically includes a description of the catchment and receiving environment, the proposed infrastructure, modelling results, and the management and maintenance arrangements. Orogen prepares SWMPs for council approval.

Yes. We use industry-standard hydrological modelling software to model stormwater flows for the design storms required by the council. Modelling results demonstrate that the proposed infrastructure manages runoff to within the accepted limits, which supports both the design and the resource consent application.

Raingarden devices, proprietary gross pollutant traps, bioretention areas, sediment forebays, and wetland treatment systems. Treatment device selection depends on the site constraints, the volume of stormwater to be treated, and the council's specific requirements. Orogen recommends the most cost-effective solution that meets the consent requirements.

We engage with the council's engineers early in the design process to understand their specific requirements and to get early feedback on our proposed approach. For complex catchments or large developments, we arrange technical meetings with the council before finalising the design. This avoids late-stage redesign driven by council feedback.

Pipe sizes and gradients to convey the design storm without surcharging, inlet capacity to handle peak inflows, attenuation storage volumes to limit peak discharge rates, and treatment device sizing to meet water quality standards. Orogen designs to the council's specific storm return periods and level of service requirements.

If there's no council stormwater system to connect to, options include on-site soakage (if the ground allows infiltration), discharge to an open watercourse (if permitted), or detaining water and releasing it at a controlled rate once a connection is established. We assess each site's options and recommend the most practical and compliant approach.

A detention tank stores rainwater temporarily during a storm and releases it slowly afterwards — preventing increased flooding downstream. Councils commonly require them in new developments that significantly increase impervious area. We can model your site's runoff to determine whether one is needed and what size it should be.

Yes. We regularly prepare Stormwater Management Plans and Stormwater Impact Assessments — covering pre- and post-development runoff analysis, drainage design, green infrastructure, water quality treatment, and consent requirements. We can also present the plan to council if needed.