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.
Unfortunately, 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 land for the purpose of reducing the flood risk and improving water quality in the lower Ōpāwaho/ Heathcote River.
e2Environmental 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. e2Environmental then designed and provided construction drawings for earthworks, including basins, pipework, culverts, siphon structures and spillways for the pond system. Challenges included high groundwater and siphons under existing streams.
The basins which are some of the largest in New Zealand, have now been constructed and 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, 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.
Project manager(s)
Andrew Tisch
Services involved:
