Hikurangi FEWS page. The map shows the Hikurangi catchment including Wairoa River and its surrounding wetland (pastureland) area

Project Scope and Objectives

Ewaters has recently completed a mostly one-dimensional (1D) model to describe the existing flood scheme and provide a tool for testing various options. The project scope encompasses an area of approximately 700 km2, extending from the upper reaches to the Wairoa Falls.

The project's primary objective is to evaluate options that can enhance the management and operations of this vital area. The project's key objectives are to analyze the options provided by WDC and understand the changes that can be made to improve the flood scheme. The study will evaluate options for modifying the scheme, including:

·         Adjustments to stop banks.

·         Removal of stop banks.

·         Addition of weirs for storm overflows

·         Installation of gates

·         Land retirement.

Methodology

In evaluating proposed options, we will consider their feasibility in both short and long-term scenarios, encompassing 10-year and 100-year projections, as well as their hydraulic and hydrologic viability. Additionally, we will closely examine the potential impacts of each option, including changes in water levels, residence time, and storage volumes. Functionality aspects such as flood impacts, riparian health, and implications for land use will also be thoroughly assessed. This comprehensive evaluation will ensure we make informed decisions about the management and enhancement of the Hikurangi wetlands and the Wairoa River catchment.

A structured approach was designed to ensure thorough evaluation and informed decision-making, aiming to enhance the flood scheme's efficiency and effectiveness while addressing stakeholder concerns. This approach includes the following steps:

·         Extending the model to Wairoa Falls.

·         Running simulations for current conditions to set a baseline.

·         Analyzing the baseline to understand current conditions.

·         Running design options for the Junction culvert.

·         Discussing each option and planning necessary model modifications.

·         Modifying the model appropriately for 1D and 2D areas and running simulations.

·         Processing simulation results for comprehensive analysis.

·         Compiling findings into detailed reports.

·         Providing clear recommendations and outlining the next steps.

Immediate and Long-term Goals

This ongoing project has its immediate and long-term goals. The immediate goals include evaluating the Junction pocket culvert location and sizing and assessing the feasibility of various proposed options. The long-term aim is to provide a comprehensive analysis and recommendations that will facilitate improved management decisions for the Hikurangi wetlands and the Wairoa River catchment.

Hikurangi FEWS. This page shows observed rainfall and water level at selected locations from the map of Hikurangi area

Conclusion

Ewaters is committed to enhancing the flood management scheme for the Hikurangi wetlands, ensuring sustainable and efficient operations that benefit all stakeholders. Through detailed modeling, simulations, and thorough analysis, we aim to provide actionable insights and recommendations that will significantly improve the management of this critical sub-tropical wetland area.