Start made on new $3.5m bridge
A start has been made on a new 60-metre-long, $3.5 million road bridge at the heart of new works to better protect Otiria and Moerewa from the impacts of flooding.
Construction of Otiria’s Pokapu Rd bridge – under way on multiply owned whanau land with the blessing of its shareholders – began in January after a dawn blessing ceremony late last year.
Newly elected Northland Regional Council member Geoff Crawford (chairperson of the Taumarere Flood Mitigation Working Group) says the project is unusual in that unlike most flood mitigation projects it is not trying to ‘‘tame’’ nature.
‘‘This one is actually restoring the Otiria Stream to its natural flow in accordance with new national freshwater ‘Te Mana o te Wai’ principles.’’
The natural flow had been blocked decades ago with the construction of Ngapipito and Pokapu Roads and Otiria’s railroad embankment.
Crawford says the area is also unusual in that in a 1-in-100-year flood, 70 % of the flow from the Otiria Stream and 80% from the Waiharakeke River would travel across the associated flood plain.
‘‘In most rivers, this would be reversed, with roughly 80% of floodwaters contained within a riverbank and only 20% on a flood plain.’’
The anomaly is largely because Otiria and Waiharakeke are perched atop lava flows thousands of years old, which have been too hard for the streams to carve deep channels into.
‘‘However, the Waiharakeke River falls off the lava flow at Pokapu Rd into a series of waterfalls and over the years has carved out a massive canyon increasing the cross-sectional area from just 36 square metres at Pokapu Rd to more than 600 square metres at Otiria Marae.’’
Crawford says it was the community that had several years ago come up with the idea of returning the water to its natural flow (as it was before any built infrastructure) and into an area historically much better able to cope with the large volumes of water which floods involved.
When the project is finished, water will once again flow into the places it had for thousands of years before human influences.
To achieve this, the Northland Regional Council has been working on a staged plan with the local community, the Taumarere Flood Mitigation Working Group, local marae, Ngati Kopaki and Ngati Te Ara kaumatua, kuia and kaitiaki, the Far North District Council and Kānoa – Regional Economic Development and Investment Unit.
Stage I of the project – construction of the downstream section of new $1.4 million 80m-long spillway at Otiria – was completed last year. (Flood infrastructure is completed from downstream to upstream.)
The recently started Stage II – due for completion before Christmas this year – will see the replacement of an existing 18m-long road bridge with the new 60m structure, and effectively triple the flow of floodwaters that can pass beneath it.
‘‘In previous floods, this water would typically be diverted – in part by the existing bridge structure and railroad – downstream to land at Otiria and Moerewa.’’
A final and third stage will be completed at the same time as work on the bridge and will see excavation of the remaining 800m of spillway and the removal of the existing Pokapu Rd bridge.