The Wattle Farm Reserve stormwater pond is situated in a large wetland between suburbs and the harbour. The pond had been a sanctuary environment to a diverse population of birds, insects, and aquatic species but was also subject to illegal rubbish dumping. An adjacent pond is used for model boat racing, and waka ama and canoeing.
The stormwater pond required restoration to remediate sediment that had accumulated during the past 60 years from a 407ha catchment area (Manurewa), reducing the pond capacity by more than 80%.
RILEY investigated the sediment for contamination and found it contained elevated lead and zinc associated with the catchment’s long-term residential land use. Subsequent contamination reporting included detailed site investigation, a site management plan, and an assessment of potential effects for consent. During construction, monitoring and observations for geotechnical and contamination aspects of the project were undertaken.
Phase 1: sediment from the stormwater forebay was disposed of at licensed landfill facility.
Phase 2: sediment in the larger part of the pond was mainly encapsulated and placed on the northern side of the pond, increasing the stormwater capacity by more than approximately 60%, and significantly reducing off-site disposal costs. The encapsulated sludge was compacted, sealed, and planted to improve the former bird habitat.
Outcomes from the pond improvements included:
A significant visual amenity improvement for the community outdoor space.
Healthy Water way – Improved water quality and increased vegetation that has provided a safer wildlife habitat for birds and aquatic species, both within the pond and downstream.