Assessing Whenuapai’s Watercourse Geomorphology

Whenuapai in northwestern Auckland is an area undergoing rapid development and land use change as agricultural area transitions into a dense urban suburb.

To help guide this transition, Auckland Council undertook a review of their Structure Plan for Whenuapai to cover the next 20 years, and Morphum was asked to conduct a geomorphic assessment of the entire catchment to inform the adjustment potential of the streams.

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Previous watercourse assessments had been completed in the catchment, which led to combining the watercourse assessment resurvey and a geomorphic assessment. This combination meant that our team could provide a holistic view of the geomorphology, ecology and engineering operations in the catchment, providing insights to the interconnected nature of these effects on our taiao.

This was the first time that a River Styles geomorphic assessment was conducted in tandem with a catchment watercourse assessment.

Over six weeks, Morphum’s team conducted extensive fieldwork through the 34.2km of waterways that make up the Whenuapai catchment. Each team was made up of an engineer and an ecologist to assess the full breadth of engineering assets, geomorphic condition, and ecological values in the catchment, recording the data using our mobile GIS tools.

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The Morphum team was able to prepare a comprehensive report and detailed maps that identified numerous recommendations, datasets and opportunities based on the catchment’s current state and the changes assessed since the previous surveys.

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These included:

• Adjustment potential of streams
• Geomorphic stability, erosion scarring and potential hotspots
• Stormwater inlet/outlet asset condition and maintenance requirements
• Riparian vegetation condition
• Native fish species
• In-stream fish passage barriers
• Pest weed infestation spread
• Wetland extents
• Areas vulnerable to development pressures such as altered hydrographs

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With the reported information and data available, Auckland Council are able to make informed decisions for the Structure Plan for Whenuapai that can proactively improve the health of the catchment for the community.

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