Flood protection works

Flood protection works following Cyclone Gabrielle

The flood protection network was severely damaged leaving many residents without proper drainage and facing the risk of flooding during future rain events.

Council needs to urgently develop a plan to repair and rebuild the flood protection system to ensure the safety and well-being of its residents, as well as invest in new schemes to prevent further damage to public and private property.

The impacts of the cyclone across the flood protection system are from reduced capacity in the channels due to siltation, woody debris build up at structures and stopbanks that have either failed or are no longer fit for purpose.

The investment needed to restore damaged stopbanks and accelerate known flood bank projects, so the flood protection system is resilient and fit for purpose. Works continues as below:

On this page

Te Arai River - clearing log jams

Updated April 2023

Recovery work has started on removing major log jams in the Te Arai River following Cyclone Gabrielle.

5 priority sites have been identified and in March we completed the clearing of one site at 388 Waingake Road.

Due to silt on the riverbanks and recent rain, we need to wait for the ground to dry out before heavy machinery can get in and start work at the next sites.

Access to the other priority sites can be gained through 453 and 63 Papatu Road, 332 and 300 Waingake Road and 2 sites opposite 77 Whakatere Road.

We have done a number of surveys of the river by drone and kayak following weather events for the last couple of years.

Following Cyclone Gabrielle, staff did a complete inspection by drone and identified blockages in the middle reach of the river. They then did onsite inspections at those identified sites.

Staff have also done a complete inspection upstream of the Te Arai River, upstream of the Waingake Water Treatment Plant.

Recovery work is in progress and our aim is to remove the major log jams before winter, weather permitting.

What’s happening at Te Karaka?

Staff are analysing all the survey data of the middle reaches of the Waipaoa River, upstream of Kaiteretahi Bridge at Te Karaka.

This work involves identifying the reasons for flooding and making long term flood mitigation proposals for Te Karaka.

Flood spread mapping work is also in progress for modelling and then staff will come up with solutions for Te Karaka

Rural land drainage network

Updated April 2023

Work has started clearing silt from Council’s rural land drainage network.

Following Cyclone Gabrielle the drains at Manutuke and Patutahi were fully flooded including some areas in Muriwai.

Contractors have started work at the Whatatuna Drain at Manutuke and from Opou Road on Friday.  Work will also start from Patutahi next week.

One excavator can clear around 200m of drain each day, with some places needing more digging.

It’s estimated to take 25 days to clear 5km of drains, weather permitting.

Our plan is to clear 5km of drains in Patutahi, 4km in Manutuke and 2km in Muriwai initially at critical locations and then continue work in other areas.

We’re thankful for the recent fine weather to be able to start the work. The clearing work will be extended if the weather continues like this.

The high water tables and soggy ground conditions has made it difficult for heavy machinery to get in and do the work until last week and we’re still experiencing difficulties at some sites.

Making the most of the fine weather, at the same time we’re weed spraying the drains as this was missed due to the wet summer and cyclones Hale and Gabrielle.

Usually the drains are dug out and the silt is carted away. But due to the volume of silt, the huge workload and not enough work crews, we’ll dig the drain and leave the silt on the side as we need to use the resources and fine weather while we can.

We’re committed to clearing the rural drainage system before the winter and this is the quickest way to get the work done.

Roadside drains

Updated April 2023

Work on roadside drains and culverts continues.  It’s estimated that there’s over 650,000m3 of silt to be removed from drains, slips and roads.

The silt needs to be carted to disposal sites once we gain landowner agreement and the sites are ready to take the material. Also in some places the silt still needs to dry out before it can be removed.

We know where the worst affected areas are and we’re working as quickly as we can while also prioritizing reopening roads.

For more information on the initial $29M roading recovery work streams

Mangahauini River stopbank repair

31 March 2023

Work on the Mangahauini River stopbank will help protect Tokomaru Bay township from flooding.

The first stage was a 230m section where rock armouring  was installed to help stop erosion and reclaim the section to rebuild the stopbank.

The river mouth opening will also be dug out to relieve the water. This is precautionary for any future heavy rain.

Stage 2 included the section of river along Toa Street. Planning is underway to create protection for winter. Due to the size and scale of work, options include hard rock placement or Kyowa rock bags or dolos, like what we’ve done in Whareponga. As an estimate this section would need around 800 rock bags.

Trees have been removed to prevent risk to the Mangahauini Bridge. Our concern was the trees could have been taken out by the river and destroy the bridge.

Work will be done to remove the slash under the bridge. We’re working in with Waka Kotahi and will update you when we know the timeframe for this.