Filterra® Case Study - Rotorua School
Project Overview
A school in Rotorua required a stormwater treatment solution to manage runoff from a new road layout and carpark upgrade, ensuring stormwater discharge met water quality requirements before entering the council network.
As a retrofit project within an established school environment, the solution needed to deliver effective treatment while working within existing site constraints, maintaining safety, and minimising disruption.
Solution
Filterra® was selected as the preferred stormwater treatment solution due to its high treatment performance, compact footprint, and simple maintenance requirements.
The engineered biofiltration system provided an ideal solution for the constrained site, allowing stormwater treatment to be integrated into landscaped areas without requiring significant additional space.
Filterra® combines engineered media with natural biological processes to remove pollutants from stormwater runoff, providing a reliable and sustainable alternative to traditional larger-footprint treatment systems.
Design Features
The site presented several hydraulic challenges, including ring road sag points that made the original curb and channel sheet flow design unsuitable.
To overcome these constraints, the design incorporated:
- Two Filterra® units integrated within landscaped areas
- Dedicated conveyance channels directing runoff into the treatment systems
- A central peak flow bypass between the units to manage higher flows once ponding depth was reached
- Precise level control to ensure effective hydraulic performance
Successful delivery required close collaboration between the design team and installation contractor to ensure the system was installed accurately and operated as intended.
Target Pollutants
The Filterra® system was designed to target key stormwater pollutants, including:
- 75% Total Suspended Solids (TSS) removal
- Hydrocarbons
- Heavy metals
Through physical filtration, adsorption, and biological treatment processes, Filterra® helps reduce pollutant loads entering the wider stormwater network and receiving environment.
Maintenance
To support long-term performance, Stormwater360 will complete the first 12 months of maintenance before handing the system over to the school.
The maintenance programme includes:
- Regular system inspections
- Six-monthly mulch replacement
- On-site and online training for ongoing asset management
Filterra® is designed for straightforward maintenance, helping asset owners maintain consistent treatment performance while reducing operational complexity.
Overview
The Rotorua School project demonstrates how engineered bioretention systems can be successfully integrated into retrofit environments where traditional stormwater solutions may not be practical.
By combining compact design, reliable treatment performance, and simple maintenance requirements, Filterra® delivered an effective stormwater solution that protects water quality while fitting seamlessly into the school environment.
