Watercare Services Limited (Watercare) operates the Omaha wastewater treatment plant (WWTP) in the Rodney District. This WWTP receives raw wastewater from Omaha, Matakana, and Point Wells and irrigates treated wastewater to the Omaha Golf Course and a forestry block next to the WWTP. The end receiving environment for the discharges to land is the Waikokopu Creek, south of the Broadlands Drive Causeway in the Whangateau Harbour.
In 2022, the Watercare’s discharge consents granted by Auckland Council triggered review of the marine receiving environment in Waikokopu Creek. Tonkin + Taylor undertook a comprehensive review of water quality data and benthic ecology for the area.
To assess changes in benthic habitats, we developed an approach based on aerial imagery collected from a helicopter using a multispectral camera in August 2022. This generated high resolution imagery and multispectral data that could be used to categorise habitat types within the estuary, and importantly enabled a repeatable and efficient method to assess changes over time.
Aerial imagery was classified using ArcGIS to five key categories, sand, mangroves, seagrass, salt marsh, and channel. The classification methodology was also run over available aerial imagery from 2017, which was around the time consents were granted. The collection of real time aerial imagery allowed us to detect changes to benthic habitats over time. The results from this analysis were then used alongside analysis of long-term water quality groundwater and surface water datasets to identify any correlations between water quality changes and benthic habitat changes. This allowed the team to draw any conclusions on the influence of discharges from the Omaha WWTP on the Waikokopu Creek.