Grahams Creek – Flood Mitigation when Engineering and Environment Combine

Flood mitigation from a pure engineering perspective can often be viewed as simple, in that solutions for flooding problem revolve around improving conveyance of waterways to carry flood volumes from A to B at a defined level. However, when you factor in the economic, social, cultural, ecological, environmental aspects a wicked problem1 emerges. Flood mitigation projects can falter when faced with a wicked problem, conflicting knowledge – technical expert vs community, ability to pay, ownership of the issue, or even the short term nature of our memories – ‘oh the flood wasn’t that bad’, can make finding an agreed solution that delivers, near impossible to find consensus.

Grahams Creek on the Coromandel Peninsulas east coast was one such area. A short sharp catchment that goes from no flood to full flood in 3 hours is further complicated by tidal influence and an undersized causeway bridge.

Decades of discussion, multiple options and conflicting views had left the community and agencies frustrated. In 2014 a Waikato Regional Council lead working party was established with community, stakeholder, political and landowner representation. This group along with key engineering and ecological oversight co-designed a new scheme. Construction of this long awaited flood mitigation scheme has commenced.

So what changed? Challenges became opportunities – Lack of funding, led to partnerships with others, ecological sensitivities led to innovation in design and construction. Collectively leading to regional firsts including; a powerless automatic floodgate and spillway designed to function similarly to coastal wetland (includes saltmarsh translocation).

This paper shares the journey from the engineering, ecological and engagement perspective from design to construction.