Horizons approves work programme to improve Feilding flood resilience

Horizons Regional Council has approved upgrades to key river management infrastructure to improve Feilding’s resilience to flooding, in a collaborative effort with Manawatū District Council.

At Horizons’ Integrated Catchment Committee meeting on Tuesday 10 February, councillors voted to proceed with detailed design to improve the Reid Line Spillway to a 0.2% Annual Exceedance Probability (AEP), which is equivalent to a 1 in 500 year ARI (Annual Return Interval) flood level.
 
Councillors also voted to investigate options to upgrade the Kiwitea and Oroua stopbanks to the same AEP, and investigate a suite of other works related to Feilding flood resilience.
 
Horizons group manager catchment operations Dr Jon Roygard says upgrading the Reid Line Spillway is a key part of the project.
 
“When the Makino Floodgates are activated during a flood event, the spillway diverts water from the Makino Stream into the Kiwitea Stream, reducing pressure on the Makino Stream.
 
“The project will look to increase the height and width of the stopbanks which line the spillway, increasing the capacity of the channel. This will result in less flooding pressure in the urban Feilding area.”
 
Dr Roygard says the spillway upgrades are in addition to ongoing gravel extraction of the Makino Stream at Duke Street Bridge, which began in early 2025.
 
“In March last year we extracted 360 cubic metres of gravel from the Makino Stream under the Duke Street Bridge, increasing the capacity of the stream from 40 cubic metres of water per second to 60 cubic metres per second.
 
“While it is an effective measure to quickly increase stream capacity, the regular gravel extraction is a short-term maintenance solution to a long-term issue.
 
“The longer-term approach is to address the issue at the source, by diverting more water away from the Makino Stream in the first place.”
 
Manawatū District Council Mayor and chair of the Feilding Flood Resilience Governance Group Michael Ford says there is unanimous support for the work among the group.
 
“The governance group, which includes councillors and staff from Manawatū District Council and Horizons, landowners representative, and iwi and hapū representatives, are very supportive of the project.  
 
“Receiving Council approval for the project is great news for the Feilding community. Many longtime residents will recall the severe impacts of flood events such as 1976, 2004 and 2015, as well as several smaller events,” says Mayor Ford.
 
“This collaborative approach between Horizons and Manawatū District Council, as well as iwi, hapū, landowners and others in the community, aims to address Feilding’s flooding issues by looking at both the catchment and stormwater network together to deliver workable solutions.”
 
Dr Roygard says Horizons has applied for central government co-funding for the project to lessen the impact on ratepayers.
 
“Along with several other regional councils across the country, we applied for funding from central government for four infrastructure projects to address flood resilience issues in several areas across the region.
 
“Of the 27 total projects put forward in the application, the Reid Line Spillway upgrade project ranked highly on the list.”

Image caption: Feilding Flood Resilience Governance Group members at the Pharazyn Rd floodgates, while on a tour of various river management sites in Feilding.

Explanation of ARI and AEP
Horizons uses ARI (Annual Return Interval) and AEP (Annual Exceedance Probability) ratings to measure and determine the level of service our river management assets will provide in a given area.
 
A 1 in 100 year ARI means there’s a 1 in 100 chance of a flood of that size occurring in any one year period. The AEP level is the percentage version of ARI – a 1 in 100 level flood means it has a 1% AEP, meaning in any given year, there’s a 1% chance of that level of flooding to occur in the area.
 
The Reid Line Spillway upgrade work is aimed at increasing Feilding’s overall flood resilience from the current 1 in 100 ARI level of service to 1 in 500 ARI.
 
Through robust analysis of historic flood records and modelling of potential future events when accounting for climate change impacts, the decision was made to design for a 1 in 500 ARI level of service to provide Feilding with greater flood resilience for decades to come.