A rocky road, but solution sought

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The stream bed is building up with rubble from a landslip – and when the stream rises, it can cut off residents on the far side of the Peel Forest waterway.

Now there are plans to fix the problem.

A range of access options are being considered for isolated Blandswood residents on the western side of the wild Kowhai Stream, Peel Forest.

The options are provided by the Timaru District Council and before the Geraldine Community Board for comment.

But any option supported or decided upon is not likely to be built for several years.

Options range from a low-cost ($20,000) improved rock weir for the existing stream crossing to single-lane vehicle bridge with an indicative cost of $780,000.

The existing crossing at Kowhai Stream is an at-grade ford next to the Blandswood Settlement – the sole road to nine properties and a tourist lodge on the western side of the waterway.

Because of its large catchment, the water level in Kowhai Stream can rise rapidly, particularly when the catchment is saturated after heavy rain.

The high water prevents vehicles crossing the stream, and there is no alternative access.

The Timaru council said the stream bed was “very dynamic” with a high level of aggradation – a build-up of gravel lifting the stream bed.

The gravel is washed down from a large landslip and “expected to continue”.

Residents have long been concerned about the access and the risk of isolation.

Council is working with Environment Canterbury, the Department of Conservation and the residents.

The council has considered five options:

Enhanced status quo (rock weir), a multi-cell box culvert, a single lane bridge, a concrete ford, or a pedestrian bridge.

The multi-cell box culvert would be suitable for vehicles to drive over and cost around $440,000.

A single-lane bridge could cope with changes to the river bed but cost around $780,000.

A concrete ford in the stream bed would cost around $120,000 but would be sensitive to changes in river bed levels.

A pedestrian bridge would cost around $120,000 and would give some increase in service.

The council said the single lane bridge would provide the greatest benefit with a structure set well above the level of the stop banks, so flood risk would be low. But that option was expensive.

A multi-cell box culvert would improve access and resilience for residents, but it might be vulnerable to blockage.

The recommendation to the community board is to provide comment for the council’s 2021-2031 Long Term Plan.