Protecting estuarine habitat by rehabilitating areas of active bank erosion feeding into Kaipara Harbour

Hōteo River - Bank Erosion Geomorphic Solutions

Kaipara Harbour, at the mouth of the Hōteo River, is New Zealand’s largest estuarine ecosystem and a key habitat for many aquatic species. However, high sediment and nutrient loads from the river and other catchments have reduced water clarity and buried juvenile snapper rearing habitat, threatening the health of the fisheries.

Auckland Council is working with local partners and landowners to protect this valuable ecosystem by identifying and rehabilitating areas of active bank erosion along the catchments feeding into the harbor. They enlisted the help of our team of unstable channel specialists and developers of the bank-stability and toe-erosion model (BSTEM).

Our team developed flow series and channel geometry to model long-term erosion rates at different sites and quantify bank-generated erosion. We also used soil-testing techniques to determine resistance to erosion and analyze root-reinforcement of native plants, integrating this information with modeling outputs.

Based on the modeling results, Auckland Council and their indigenous (iwi) and landowner partners selected three sites to test geomorphically effective management solutions (GEMS)—a toolbox of erosion mitigation options rooted in nature-based solutions. We developed conceptual plans for pilot studies to test the effectiveness and cost-effectiveness of GEMS such as bank battering, riparian planting, and toe protection using fallen trees. We then developed the final design for the sites where GEMS were implemented in 2024.

This new approach to evaluating channel-generated erosion and protecting receiving water bodies is being used by Auckland Council and the community to reduce sediment loading to Kaipara Harbour and protect sea-grass beds and snapper habitat.