The link between river planform confinement and an altered energy gradient: pathways to revitalisation for the Waikanae River, Aotearoa New Zealand

Imposed straightening of river course necessarily entails alteration of river gradient. As the amplitude of sinuosity is reduced, the bed slope over the shorter course is steepened. The Waikanae River on New Zealand's North Island was a meandering-to-wandering coastal river that has been subjected to a variety of disturbances, at a range of intensities over time, including gravel extraction and channel re-alignment. This has led to a change in longitudinal bed profile, and therefore a change in stream power profile. In its current configuration, the river experiences persistent aggradation in the lower reaches and there is reduced diversity of river form. Local Māori iwi and catchment community are looking at ways to re-establish sediment transport equilibrium, habitat complexity, and cultural connectivity while maintaining a suitable level of flood protection. In this presentation, we review the trajectory of the system over time and some potential options for restoration, leveraging 2D numerical sediment transport models to provide insights into a potential new morphodynamic and ecological equilibrium regime.