Manaia Causeway and Graham's Creek Flood Works

In December 2015 we completed the Manaia Causeway Bridge extension on time and under budget. Over summer 2016-17 the Regional Council completed stopbank measures so this project is now complete.

The problem

Property owners in the area around Graham’s Creek on Ocean Beach Rd, Tairua, have for many years experienced flooding.

A number of factors are involved including the construction of the causeway bridge on Manaia Rd which was built approximately 50 years ago to link Tairua township with Paku and the Ocean Beach. The narrow bridge opening, causeway and upstream floodway in combination create a significant backwater affect that contributes to the floor levels of buildings upstream being flooded.


The solution

The bridge at the Manaia Rd Causeway has been extended by 16m, which will help keep the road open during flooding and allow floodwater to drain more easily. This work was finished in December on time and within budget.

Grahams Creek ribbon cutting

In late 2015 the Regional Council began  floodway improvement works including stopbanks, re-contouring the floodplain to form a floodway and creek channel works. Both pieces of work need to be done in tandem for a successful outcome


The project benefits

There will be protection against annual to 50-year flood events. Some properties will be protected from even bigger floods.

Less flood damage and disruption to infrastructure.

Continued two-lane traffic access to Paku Bay during flood events.

Improved access to the coastal area from Manaia Road.

Riparian planting and fencing, which will help improve water quality and provide an ecological corridor for fish and birds.

The ability to extend the new stopbank in the future, if needed. It's a 1 in 50 chance that a flood of this size or bigger will happen in any year. Statistically, it's a 2% chance of flooding each year.

It doesn't mean that if a location floods one year, it will definitely not flood for the next 50 years to that extent. Floods happen irregularly.


The Project in Phases

PHASE 1 MANAIA ROAD CAUSEWAY BRIDGE UPGRADE OCTOBER-DECEMBER 2015.

  • Stage 1 Site establishment and pile driving. 
  • Stages 2 and 3. Construction of new bridge abutment and foundations. 
  • Stage 4. Excavation of causeway for new bridge extension.
  •  Stage 5. Jack up northern end of existing bridge. 
  • Stage 6. Placement of new bridge deck. 
  • Stage 7. Construct causeway road, to link with new bridge. 
  • Stage 8 Install guardrail and site disestablishment

PHASE 2 FLOODWAY IMPROVEMENT WORKS OCTOBER-DECEMBER 2015.

  • Stage 1. Land re-contouring and drainage diversion as well as sediment control construction.
  • Stage 2. Stream channel enlargement (outside fish spawning season) and floodway excavation.
  • Stage 3. Stopbank; overflow floodway weir, culvert and floodgate construction. 
  • Stage 4. Grassing, stabilisation and finishing Phase 2 works

PHASE 3 FLOODWAY IMPROVEMENT. WORKS FEBRUARY-MARCH 2016.

  • Stage 1. Excavation and channel enlargement in the Coastal Marine Area (outside bird breeding season).
  •  Stage 2. Raise existing stopbank and in-filling. 
  • Stage 3. Complete stream realignment and infill old stream and drainage channels. 
  • Stage 4. Grassing, stabilisation and finishing Phase 3 works

PHASE 4 RESTORATION AND MITIGATION

  • Stage 1, Plant and animal pest control underway.
  • Stage 2. Restoration planting May-June 2016 

The costs

In 2014-2015 we set aside $620,000 in our Annual Plan towards upgrading the Manaia Rd causeway bridge, while the Waikato Regional Council set aside $600,000 towards flood management improvements around Graham's Creek.

In November 2014 our Council approved and extra $300,000 to extend the bridge at the Manaia Rd Causeway. This will come from Tairua's stormwater depreciation reserves and a loan. The extension by 16m will help keep the road open during flooding and allow floodwater to drain more easily when combined with floodway improvement works done by WRC, which includes stopbanks, re-contouring the floodplain to form a floodway and creek channel works. Both pieces of work need to be done in tandem for a successful outcome.

While our Council will undertake the causeway bridge upgrade, the Regional Council WRC's will be responsible for floodway and stopbank construction. After that there will be restoration planting in the area which will be completely finished in 2017. Some 12,000 plants may be put into the ground and community volunteers will be asked to help


The Working Group

In June 2014 we established a joint working group in conjunction with the Waikato Regional Council to refine and finalise the current work plan. The group held four separate workshops and came up with a preferred solution which included a two-way causeway bridge (rather than a one-lane) as previously indicated.

Community members on the Graham’s Creek Working Party who had input on the agreed design were:

  • Phil Smith (Ocean Beach Road)
  • Jim Jackson (Manaia Road)
  • Joyce Birdsall (Paku Hill)
  • Ian Jowett (Summer Lane)
  • Tony Jacobs (Tairua-Pauanui Ratepayer’s Association)
  • Graham Turner (floodway landowner).

Stream maintenance

For further information on this work please contact Waikato Regional Council, Ph 0800 800 401.

  • Julie Beaufill or Emily O’Donnell – general enquiries and funding
  • Kerry Smith – stream maintenance