Essential Infrastructure Repairs
In March this year, a request was submitted to central government to fund emergency repairs to the infrastructure damaged in both the July and February flood events in Buller. This is separate from the Kawatiri Business Case which is seeking co-investment in long-term flood resilience measures for Westport.
Government agreed to fund $17.1 million for emergency infrastructure repairs (100% central government funding). This includes $10.6 million granted to Buller District Council (BDC) for infrastructure repairs that were outside policy for Government funding.
In addition to this, BDC was also granted additional funding for the emergency repairs to the Westport and Carters Beach water supply damaged in the February event which has a total budget of $1.6m.
The essential infrastructure projects are:
• Wharf damage
• Shipping channel dredging
• Reefton stop bank
• Reefton landfill
• Three waters
Wharf Damage (as at December 2022)
Buller District Council is responsible for more than 1.5km of wharf assets. This project focuses on an area of around 300 metres of flood-damaged wharf (at the upstream area of the river wharves). This portion of the overall wharf area is considered critical to current and future Port operations.
Repairs to the Holcim and Kawatiri wharves will enable fishing and bulk shipping vessels to continue to use the port. Among other issues, holes have opened up in the decking of the Ex-Holcim Wharf due to underlying flood induced failure and significant deflection has occurred in wharf piles. Holes and slumping are visible.
A project manager has been appointed to oversee repairs to the Holcim and Kawatiri wharves.
A crucial part of the wharf repair project is understanding ground conditions so that the repair design is appropriate. In September 2022, a specialised drilling rig drilled three 20-metre-deep holes along the length of the damaged wharf and tested ground conditions at regular (1m) intervals.
The foundation design of the repaired structure will be informed by the results of this investigation work. The overall repair strategy, design and approvals are scheduled to be completed in the first half of next year, with physical repair work forecast to commence in Autumn 2023 and take approximately a year to complete.
Shipping Channel Dredging
The floods caused a build-up of debris and gravel/silt in the navigable part of the river and port. Approximately 240,000 m3 of debris, gravel and silt that needs to be removed to return the river to a state that it can be serviceable to the bulk carriers expected to be using the port in the future.
The Kawatiri Dredge was in Nelson for maintenance and to carry out dredging work from October until early December 2022, and has recently returned to Westport. It has now commenced dredging of the shipping channel.
22 December 2022
Contractor appointed for repairs to Westport’s north-eastern tiphead
The contract to repair to the north-east tiphead wall (officially known as the Eastern Westport River Training Wall) has been granted to Rosco Contractors Ltd, following a tender process.
The tiphead is a Buller District Council port asset at the mouth of the Buller River. It sustained damage during both the July 2021 and February 2022 weather events.
Flood waters flowed through the structure and overtopped the inner revetment wall. The overflow undermined the groyne by removing supporting rocks and base infill. Runoff scoured the revetment foundation and ultimately undermined a large section of the revetment wall. Remedial work is required to prevent a major breach of the tiphead.
The repairs are being funded by the National Emergency Management Agency (NEMA) as part of a $17million programme of essential infrastructure repair work in Buller.
Buller District Council Chief Financial Officer Douglas Marshall says the project consists of placing around 3,000m3 of Riprap (rock) on the eastern side of the tiphead road to reinforce the road embankment. The 360m area of embankment will be broken up into four 90m sections.
The trees, bushes and topsoil will be cleared before backfilling with rock. The trees will then be replanted once the rock has been placed.
“In terms of impacts of the work, we recognise that some of the land area required for the work site is used by a local cycle group. They have also recently replanted this area. Unfortunately, the plantings will need to be uplifted, but the area will be replanted and cycle trails reinstated once the tiphead is repaired.
“We also ask local residents to bear with us as there will be about 10 truck trips per day carrying rock to the site for about 25 days. We will try and reduce the impacts on residents as much as possible while we complete these repairs,” says Mr Marshall.
Draft design for the tiphead repairs is complete and Rosco Contractors Ltd will commence work in mid January 2023. Works are expected to be completed by March.
Northern Tiphead repairs will impact on cyclists and pedestrians using paths in the area for about two months from mid January 2023. Roscos will have traffic management in place, but cyclists are warned to be aware of changes to the track layout and large vehicle movements during that time.
The northern bank of the closed Reefton Landfill was scoured away by the Inangahua River during the severe February weather event, causing waste to be swept away.
Major clean-up and enabling works at the historic Reefton Landfill site have been ongoing since February in preparation for the repair of a section of the flood-damaged rock wall that protects the historic landfill site from the river. Buller District Council contractor Rosco’s will continue to maintain the site to ensure it is protected prior to construction getting underway in the coming months.
As at December 2022, a contract to design remedial works required for a section of the flood-damaged rock wall was awarded to WSP NZ.
WSP is working on design work for the rock revetment to re-cap the disturbed landfill and landscape the area.
The plan is for design to be complete by early February with construction starting late February/early March. The work is expected to take about two months.
During 2022, river training work was carried out to reinstate the flood stopbank that protects the Reefton campsite and reserve from flooding from the Inangahua River. That work is complete for the year.
Council is now monitoring the river and some additional river training may be required early next year (2023).
The Reefton Campground is a community asset. The stop bank protects the reserve and Reefton town.
3 Waters flood recovery work programme
Floodwaters from the July 2021 and February 2022 ‘red’ weather events deposited silts and debris through 60% of the stormwater and wastewater networks in Westport. The efficiency of the networks was severely compromised.
Three Waters – Remaining repairs (less than 10% to complete as at September 2022)
- Work is due to start (in early October) on final CCTV inspections of underground pipes. Contractors will be returning to areas that CCTV couldn’t previously access due to suspected pipe blockages.
- Westport Waste Treatment Plant silt/grit clean out of the plant. The third clean out is complete and the fourth is planned for February next year.
- A small number of open drains still require cleaning, these will be completed as the ground dries out into summer.
- Reefton’s drinking water reservoir access track requires further repairs which are currently being planned (to be completed by November 2022).
- Buller District Council (BDC) can complete the Waimangaroa drinking water trunk main replacement once Department of Conservation (DOC) has completed the culvert replacements on Conns Creek Road.
- A repair strategy is being worked out for repair of the historic Brick Arch section of the stormwater network running under Brougham/Palmerston Streets.
- Replacement of the final electrical components on two of Westport’s Wastewater pump stations is complete.
3 Waters – Progress since July 2021 (90% complete as of 31/08/22)
It has taken a full year of flushing, cleaning, and CCTV works to return the stormwater and wastewater networks to pre-flood condition.
Flood silts within the wastewater network also worked their way through the underground network and pump stations to the Westport waste treatment plant. To remain operational, the treatment plant has needed several cleanouts.
Several of Westport’s wastewater pump stations were inundated by flood waters, damaging several critical electrical components. Replacement of parts has been ongoing since July 2021.
Council’s maintenance contractor (Westreef) has been clearing open drains across the region, repairing underground pipes and tomo’s (sinkholes) in the roads arising from damaged pipes.
Waimangaroa water supply’s main trunk line was destroyed in three places along a 1.5km section of access track when culverts were washed out by extremely flooded tributaries. Inangahua and Reefton also required repairs to main trunk lines and access tracks, in the case of Reefton, the work is still ongoing.
What is betterment?
‘Betterment’ projects are those that would benefit from improvement/upgrading/updating whilst carrying out the overall repair programme. Whilst assessing the repair package for 3 Waters, several projects were identified that largely relate to Westport stormwater and wastewater improvements.
Summary of projects to be delivered:
- Upgrading backflow prevention in critical stormwater outfall pipes that drain into both the Buller and Orowaiti Rivers. This will assist in keeping river water out of the stormwater pipes as rivers rise.
- Lifting flood-prone pump station electrics.
- Upgrades to the Westport Waste Treatment Plant to allow it to better manage grit in any future flooding events Westport may face.
- Upgrades to some existing (and addition of some new) critical stormwater assets to better cope with surface flooding and severe weather events in Westport.
The aim is to help provide ongoing resilience. For example, as well as repairing a flooded pump station electrical cabinet, flood-prone cabinets will be lifted above a 100-year flood level.
These projects are being finalised (as at early October 2022), with considerable design input required to ensure the best value for money. The first of these projects is looking to get underway in October, the rest following through the summer months.
Westport Water Repairs
During the February 2022 severe weather events, significant damage was sustained to the Westport Water Supply, placing the town at high risk of running out of water.
Emergency works commenced during the response phase and continued with $1.685 million in Emergency Works funding from Central Government.
Primary Intake (Giles Creek) and Catchment works included:
• Stabilising and repairing the access road to the intake including slips, culverts and crossings.
• Initial intake repairs and maintenance including weir, gates, screens and associated infrastructure.
• Carrying out ongoing intake repairs and maintenance following heavy rainfall events.
• Ensuring ongoing raw water supply including temporary pumping and piping from usable sources.
Repairs were required due to a slip at the Tunnel Pipeline between the third and fourth water tunnels (T3-T4), leaving the 600mm diameter pipe unsupported over a 50-metre span.
• Temporary repairs and interim pipe support to enable water flow and serviceability.
• New, engineered pipe suspension bridge to permanently restore asset integrity and water flow.
The Primary Intake & Catchment work was undertaken by WestReef Services Ltd.
The Tunnel Pipeline T3-T4 was led by Hadlee & Brunton Ltd, with Abseil Access Ltd constructing the pipe suspension bridge.
Buller District Council Programme Sponsor Westport Water Mike Duff says the quick response from all contractors under civil defence emergency works and extremely challenging weather and site conditions was outstanding. The work was completed in August, on time and under budget, at no cost to ratepayers.
The Tunnel Pipeline following the installation of a new, engineered pipe suspension bridge to support the pipeline.