Creating Open Watercourses in the Peat Fields: The Challenges

Installing open channels through peat land has been successfully employed by farmers for hundreds of years. The implementation of open channels in an urban planning environment in similar geotechnical conditions is quite different. The design and consenting of 1.7 km of open channel in Takanini to accommodate proposed future urban development has identified a number of challenges, both as part of the design, and in the greater planning context.

The Takanini east urban intensification area is currently unserviced by stormwater infrastructure, located in peat fields and is predominantly flat. The urban area is currently within a predicted 1% AEP (annual exceedance probability) floodplain and is unable to be comprehensively developed until a stormwater solution is implemented.

Traditional piped systems, open channels and hybrid systems including attenuation were considered and evaluated. An open watercourse was selected as the most resilient solution and one that would also provide amenity and ecological benefits. However, the design of such is not without its challenges.

This paper outlines the key issues that have been identified as part of the design process and how these have been resolved during the planning and design.