Heavy rain gives rise to heavy concerns

Storm water system through Hikuwai development during heavy rainfall.

 

Queenstown Lakes District Council (QLDC) wants to assure the community that it is investigating a range of stormwater concerns in Wanaka. The substantial rain events last week reminded many residents about the ongoing issue of surface flooding from construction runoff and the resulting pollution of silt and sediment that is deposited into local creeks and rivers.

Despite Otago Regional Council's (ORC) recent court action on alleged storm water contamination from surface flooding from local construction and developments regarding the effect they appear to have had on increased flows of discoloured water into the Clutha Mata-Au River during rain events in August 2017, nearby residents claim to continue to witness brown sediment spreading into the river during heavy rainfall. Many locals have taken to social media as a tool to express their concerns and to gain collective wisdom on how to lodge requests for service and establish a united approach to “put pressure” on ORC and QLDC regulating authorities to hold the land developers accountable for the storm water runoff.

It is claimed that the storm water starts from the Northlake development site, flows through an easement across the Hikuwai development and the Department of Conservation’s Hikuwai Reserve, before dropping down into the river. Otago Fish & Game officer Paul van Klink has told the Wanaka Sun that pre- and post-development runoff and rainfall levels remain the same, yet earthworks and poor on-site management have increased the runoff as it travels through a single discharge point through the Hikuwai Reserve rather than it naturally seeping into the ground and dissipating into a wider area free of sediment.

When asked what is being put into place before the next substantial rainfall to prevent further possible river contamination from Northlake’s site, QLDC planning and development general manager Tony Avery said QLDC continues to work with developers and individual lot owners to install best practice sediment and erosion controls on sites noted as contributing to discoloured storm water.

“Land developers associated with Northlake and Hikuwai have been required to revise their respective site management practices and implement further sediment and erosion controls. These have been closely monitored and have led to an improvement of the quality of storm water discharging beyond the boundaries of the sites.”

He said he expects to see continued improvement to the control of sediment and erosion at these subdivisions.

In addition, Avery said QLDC has developed a best practice sediment fact sheet, which has been distributed to building sites in Northlake, Hikuwai and Meadowstone subdivisions and that Council is also reviewing its land-use earthworks guidelines and expects to have a revised site management best practice guideline in place soon.

Working closely alongside ORC, QLDC has previously addressed these concerns by focusing on the overall design and management of the on-site stormwater systems and design, which require appropriate protections installed in order to remove potential contaminants from the storm water and meet sediment discharge and flow limits. Northlake has an approved consent for its storm water design. "With Northlake, we have not commissioned an independent review, however we are internally reviewing the design of the storm water system on an ongoing basis. We are also continuing to work with the developers to ensure they implement the necessary design improvements," said Avery.

He added that QLDC is reviewing the budgets as part of the upcoming annual plan process and that outcome will decide if whether or not some budget will be allocated to help address these issues.


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