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Auckland Council’s long-term ecology monitoring of 10 sites in the Ōkura estuary from 1999 to 2018 shows ongoing declines in ecology and increases in sediment at some locations.
Council’s Healthy Waters general manager Craig Mcilroy says similar trends have been seen in other small east coast estuaries.
“The Ōkura estuary and Wēiti River are considered a high priority and, as such, developments in the area have had amongst the highest levels of compliance monitoring in the region – at least fortnightly by Council experts and every other week by an independent expert,” Mr Mcilroy says.
“Additional inspections are undertaken following storm events.”
He says erosion and sediment controls at these locations are achieving high levels of effectiveness.
“We expect these devices to retain a maximum of 90 percent of sediment when operating at their best, and less during storm events.
Mr Mcilroy says Healthy Waters wanted to explore what other aspects needed to be considered for future development.
A report was prepared in order to guide the planning processes around future developments that could affect catchments that drain out to the Ōkura estuary/Wēiti river systems, including the Long Bay Ōkura Marine Reserve.
The objective of the report was to understand the sediment and metal loads on the catchment by examining several scenarios, as a result of development, and to understand where these contaminants will end up in the long term.
The report recognises that development will lead to increases in copper and zinc levels in the Ōkura and Wēiti estuaries generally.
“In some development scenarios, copper and zinc would be expected to exceed levels in certain parts of the estuaries. However, contaminant management strategies (e.g. more stringent controls on roofing material types) will successfully reduce these long term levels,” Mr Mcilroy says.
“Future developments will need to undertake strategies such as stormwater treatment and control of roofing materials to limit sediment and metal discharges, in order to avoid effects.”
The scenarios only evaluated the impact of the catchment when development was completed and not the stages through site development and its concomitant effects during construction.
