PROJECT
Alleviating flooding within the Ōpāwaho / Heathcote River catchment
As development has increased in the Ōpāwaho / Heathcote River catchment, the proportion of hardstanding area from roofs, sealed roads and driveways has increased. This has caused additional stormwater runoff which contributed to flooding in the lower river catchment and compromised the stormwater runoff quality. Flood storage systems could not readily be added to the already built-up catchment. Luckily the Christchurch City Council owned land in the upper catchment which was earmarked for stormwater management.
The Council proposed a series of ponds and wetlands on the allocated land for the purpose of reducing the flood risk and improving water quality in the lower Ōpāwaho / Heathcote River. Groundwater was high and existing stream paths had to be navigated.
Fox Environmental was commissioned to provide a hydraulic model of a first flush basin and wetland for water quality treatment, as well as an attenuation basin for flood control. We then designed and provided construction drawings for:
The basins, which are some of the largest in NZ, have now been constructed. The result is a significant reduction in peak storm flow in the lower Ōpāwaho / Heathcote River and an improvement in stormwater quality from runoff in the upper catchment.
The basins are designed to temporarily store stormwater during heavy rainfall events, reducing downstream peak flows. Once the storm has passed, the stored water is released slowly back into the system, helping to reduce downstream flooding and protect surrounding properties.
Like all stormwater treatment devices, the basins require regular inspection and maintenance to ensure they continue to perform effectively. They are designed to minimise maintenance requirements by separating cleaner flows from sediment-laden runoff during storm events, which helps maintain treatment efficiency and storage capacity over time.
The most suitable stormwater treatment solution depends on your site's specific requirements, including runoff volumes, flow rates, available space, treatment objectives, and budget. Contact us to discuss your project and we can help identify the most appropriate solution.
Talk to one of our specialists about your catchment, your modelling requirements and the best way forward.
