Following the impacts of Cyclone Gabrielle in February 2023, Council is investigating flood resilience improvements across Tairāwhiti.
Within the Te Ārai catchment the city's main water pipeline was damaged causing supply interruptions for 20 days. To date about $14.1m has been spent repairing watermain bridges as well as $2.25m removing large wood debris and live willow trees from the Te Arai River channel and floodplain.
10 homes in the catchment classified Category 2 under FOSAL (Future of Severely Affected Land) framework, may be raised if feasible. Damage to horticulture and cropping land was extensive and widespread.
This project focuses on identifying and implementing cost effective solutions to reduce the likelihood of repeat damage from similar flood events in this community.
Te Ārai catchment
Manutuke
The catchment covers an area of 3,131 hectares, with around 300 dwellings located within the flood resilience investigation area, as indicated in the red overlay on this map.
This project aims to safeguard lives, protect property, community facilities and evacuation routes.
What's happening now?
We're at Stage 1 and 50% complete
Potential solutions to improve flood resilience include:
- increased channel capacity through stream clearing of vegetation/widening to manage water flow
- developing extra flood storage opportunities to slow the water
- improved evacuation routes
- protection of critical infrastructure
- identification, enhancement and protection of secondary flowpaths to minimise the areas prone to flooding
Construction of stopbanks along the river is not expected to be part of the solution.
Once preferred solutions have been identified, these will be presented for second stage approval.
Option analysis
A hydraulic model of the Te Ārai catchment is requirement to enable options assessments. The model build is underway now. The model needs to investigate the backwater effect from the Waipaoa River with recently increased stopbank flood heights.
Once complete, the model will enable assessment of mitigation options and will identify any secondary flows paths that could be enhanced and protected.
Hazard mapping (both current and future) will allow comparison to assess insurability and any need for future land use constraints.
Preferred objectives
The preferred option/s will be confirmed once Stage 1 works are completed. Identification, enhancement and legal protection (preferably with easements or designations) of secondary flows paths, planning controls to prevent such paths from being compromised or restricted. Community education and awareness is also expected to be in the preferred options.
This is categorised as a complex project - cost benefit analysis will be done prior to Stage 2 approval and before any decision to proceed. Any works would also consider protecting the state highway as well as land and property.
Programme
This is the proposed programme for the resilience improvement project - this may change once investigations are complete.
