West Coast Stopbank Upgrades

West Coast Regional Council is working hard to enhance flood protection infrastructure along the Hokitika, Orowaiti, and Buller Rivers in New Zealand’s South Island. WGA is working with Davis Ogilvie to support Council to upgrade the existing stopbanks at Hokitika, and to construct new stopbank structures at McKenna Road, Avery’s, and Floating Lagoon in Westport.

WGA has undertaken transient finite element groundwater seepage modelling to facilitate the stopbank upgrades. Using the Slide2 modelling package, seepage and pore water pressure assessments were undertaken to model the effectiveness of stopbanks in Hokitika and Westport during flood events.

The modelling scenarios assessed seepage against the Bay of Plenty Regional Council stability criteria by calculating seepage velocities, total hydraulic exit gradients, and pore pressure. Iterative modelling was used to guide the design of site-specific features like toe drains and fill overlays to prevent seepage and heave.

The finite-element transient groundwater seepage modelling guided the detailed design for West Coast Regional Council’s stopbank upgrades, demonstrating non-erosive seepage and compliance with hydraulic criteria and stability standards. The models tested tailored designs to prevent erosive seepage and enhance flood resilience for the region.