The Rangitaiki Floodway project is a multi-stage project to take pressure off the flood-prone Rangitaiki River by diverting some of its flow.
Increasing the capacity of the Floodway reduces flood levels in the Rangitaiki River from upstream of Edgecumbe to the river mouth. This will in turn reduce pressure on Rangitaiki River stopbanks during large flood events.
Figure 1: Rangitaiki River and Reid's Central Canal during 2004 floods
The Project works are in several stages
Figure 2: Stages in the Rangitaiki Floodway Project started in 2011
- Stage 1: Channel widening. Physical works were completed in the 2011/12 construction season ($3.2 million)
- Stage 2a: Channel widening. Physical works were completed in the 2013/14 construction season ($2.7 million)
- Stage 2b: Channel widening. Physical works completed in the 2014/15 construction season ($2.5 million).
- Stage 3: Stopbank raising. Physical works completed in the 2015/16 construction season ($2.05 million).
- Stage 3a: Channel widening and wick drains. Physical works completed in the 2016/17 construction season ($2.4 million).
- Stage 4: Channel widening. Works currently underway.
- Stopbank raising in 2018/19 ($3.4 million budgeted)
- Stopbank raising and spillway in 2019/2020 ($2.6 million budgeted). Read more on the spillway below.
Figure 3: Stage 2a of the Rangitaiki Floodway Project - Channel widening
Stage 4 works are on the true left bank of the Floodway, downstream of Thornton Road. This stage includes earthworks to relocate stopbanks, channel widening to increase capacity, and works on internal drainage systems.
There is currently a variation to the resource consent being sought for the creation of a fork in the Floodway resulting in two outlets into the lower Rangitaiki River, this is known as a bifurcation. The bifurcation will reduce the amount of upstream floodway works needed to achieve the required capacity of the floodway.
Figure 4: Stage 4 of the Rangitaiki Floodway Project - Channel widening
A crucial part of the Floodway project is an upgrade of the existing fixed crest weir spillway - the mechanism used to divert floodwater from the Rangitaiki River into the Floodway.
The existing spillway is planned for an upgrade in 2019/2020 and Council has looked extensively at several options: a lower crest weir, a collapsible tipping block, and a rubber inflatable dam. There are significant differences in the costs, advantages and disadvantages of these options.
Council is currently consulting on two options; lower crest weir and rubber inflatable dam. The lower crest weir would require a change to the resource consent granted in 2008. Consultation is at an early stage and there will be a number of opportunities for you to receive information, ask questions, and to express your views and any concerns you may have about the project.
For more information about the Rangitaiki Floodway Project, please contact:
0800 884 881 x7497
021 687 300
0800 884 881 x9437
027 222 0298