Home Managing Natural Resources Nature-Based Solutions Investigation - Ōroua and Pohangina Rivers Project Details

Project Details

Background

The Horizons Region has been facing increased flood activity during recent years, with substantial changes to the Ōroua and Pohangina rivers observed as a result. The damage caused during recent events has raised questions about the financial and environmental sustainability of the current flood protection schemes. Recent flood events have resulted in significant damage to flood infrastructure along the lengths of the Ōroua and Pohangina rivers, including damage to soft and hard engineered protection (e.g. tied trees and rock work). Much of this damage has arisen as a result of the floodwaters not being able to be contained in the designed current active channel and instead connecting back with previous floodplains and/or historical flow paths. Many of these flooded areas have been developed for rural and/or urban land use.

Sediment deposition caused by the Pohangina (left) and Ōroua (right) rivers escaping their designed channels during Cyclone Gabrielle in 2023.

In order to inform future flood protection interventions, the complexity of the Pohangina and Ōroua river corridors and floodplains need to be better understood. This will ensure future flood mitigations and action plans can be drawn up and implemented to allow for more resilient flood protection, and also enable the river to undertake and complete natural processes.

The study's findings will support Horizons' flood resilience planning, allowing Horizons to make informed decisions regarding future flood management. These decisions will safeguard important infrastructure while recognising the innate nature of the Ōroua and Pohangina catchments. Highly restrictive river widths will be unsustainable financially and environmentally in the medium-to-long term. This information will be used to inform changes in river management practices, where development can and cannot occur, and what land use may be appropriate in certain places within the catchments (i.e. rural vs residential).

Purpose:

To develop a holistic and sustainable flood protection model for the Pohangina, Ōroua and Manawatū (between the Pohangina and Oroua confluences) rivers.

Aim:

To work with the natural environment, minimising the need for engineering interventions and ongoing maintenance.

Objectives:

Prioritising the river's room to move to express her natural character;
Restoring the integrity of riparian margins, gravel bar habitats and floodplain connectivity;
Avoiding channelisation of the river corridor, and promoting and enhancing habitat complexity with pools, riffles, runs, meanders and side channels;
Increasing channel size and capacity to provide for flood flows within defined floodplains;
Where possible, prioritising the removal of infrastructure from floodplains that are vulnerable to flooding;
Promoting financial resilience and long-term solutions, minimising maintenance needs over time, and focusing on preventative rather than reactive works;
Maintaining fish passage and fish habitat;
Maintaining access to existing recreational areas, and preserving and enhancing the desirable features of those recreation areas;
Maintaining and promoting access to food gathering, mahinga kai harvesting areas and wāhi tapu, preserving and enhancing the populations of mahinga kai and important characteristics of wāhi tapu; and
Promoting community, social, economic and cultural connection and resilience.

If you have any questions about this project, please contact the project team by emailing NatureBasedSolutions@horizons.govt.nz.