Concern at subdivision flood risk

19:00, Nov 20 2012

The chairman of a hearing panel considering whether to approve a 160-section housing subdivision south of Blenheim yesterday asked the applicant to show plans that would cope with a one-in-200 years flood.

The hearing is for a plan change to develop 160 sections ranging between 2000 and 4000 square metres on 50 hectares of rural-zoned land near the intersection of Taylor Pass and Maxwell Pass roads, south of Blenheim.

The proposed subdivision is called Maxwell Heights, and the land is owned by Marlborough businessman John Marris' Kapiti Views Trust.

The applicant's specialists, including geotechnical expert Edwyn Ladley, stormwater expert Jason Budd, wastewater and effluent expert Grant Fleming and planner Janice Carter gave their evidence in support of the plan change on the second day of the hearing at the Marlborough Convention Centre yesterday.

However, hearing chairman John Maassen said he was concerned about standards their risk management solutions was based on.

"This is a dynamic, geotechnical flooding environment.


"We're all conscious of hazards given what the country's been through and need to think very intelligently about the information, planning and what level of protection the community is seeking," he said.

He asked for Kapiti Views to provide written policies identifying flood and erosion hazards and the specific designs of house foundations, wastewater, stormwater and floodwater systems required to mitigate the risks in the area.

These policies would become part of the consent process if the project was to go ahead, so those involved with planning and construction of the subdivision would have a clear idea of the intended standards.

"If we got to the point of deciding to approve the application, we'd need to spell out what would need to occur on every level of planning."

Mr Budd talked about his proposed methods for flood management, including five stormwater treatment ponds rated to deal with a one-in-100 year flood.

These measures were based on the New Zealand Standard 4404 and the Marlborough District Council's engineering code of practice, which required a stormwater management plan for only a one-in-50 year flood.

However, Mr Maassen asked for the plan to be revised to one-in-200 year flood.

He also requested landscape architect Christopher Glasson to provide a montage of what the subdivision might look like after all 160 sections were built within 10 years and 20 years, to gauge the visual impact from the road.

Mr Glasson had only supplied a plan of what the subdivision might look like with less than 60 houses built within seven years.

Mr Ladley presented his proposal for managing erosion hazards, including vegetation, chemical stabilisation to make the soils "non-erodible" and construction of a surface water cut-off drain and sub-surface drain uphill of the development.

The Maxwell Heights plans include an estimated 2.5 kilometres of roads, of which 80 to 90 per cent will sit alongside retaining walls up to three metres high, he said.

Mr Maassen said it sounded like quite a high level of infrastructure for a subdivision.

But Mr Ladley said he was "comfortable" with the extent of the works given the proposed erosion mitigation work.


The Marlborough Express