16 | REGIONAL DEVELOPMENT Northland Regional Council: Otiria-Moerewa Flood Mitigation T T Richard Loader Flood mitigation project on track Flooding in 2020 caused families to evacuate their homes. Proudly supporting Northland Regional Council. Located three kilometres upstream from Moerewa township, the Otiria-Moerewa Flood Mitigation Spillway and Bridge Development project, will ensure the natural flow of floodwaters is returned to the Waiharakeke River, and no longer threatens the Far North townships of Otiria and Moerawa, or their small communities. A poignant image appearing in the Northern Advocate following the 2020 floods pictured a young mother carrying her infant baby in fast flowing knee-high deep floodwater. The new bridge and spillway, will reduce that flooding to ankle depth or less. For decades, the natural flow of flood waters has been blocked with the construction of Ngapipito and Pokapu Roads and Otiria’s railroad embankment. “There are two rivers; the Waiharakeke and the Otiria and both are perched on lava flows, so, they are very shallow,” explains Northland Regional Council Rivers and Natural Hazards Manager Joe Camuso. “In most Northland streams you would have eighty percent of the flood water in the river and only twenty percent flooding near a town or township. Here, it’s just the reverse. The stream can’t go any deeper because it’s on rock.” 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 “The real Achilles heel is that the existing Waiharekeke bridge was built in the World War Two era and spans the river by eighteen metres wide, when it needs to be sixty metres wide. Also, the roads and railroads have been elevated and block the natural flow of the water getting to the Waiharakeke and when it does get to the Waiharakeke you have this tiny bridge that acts as a bottle neck, and floods. Northland Regional Council is restoring the natural flood flow of this catchment back to the Waiharakeke River, with an upper and lower spillway, and a new bridge, upstream of Otiria and Moerewa townships, so that they will be relatively flood free.” While the existing bridge can handle a 1/10year flood, with capacity for 150 cubic metres of water per second, the new 60-metre wide bridge is designed to handle a 1/200-year flood event, and triple capacity to 450 cubic metres of water per second. The project is being managed by NRC, but will be handed over to the Far North District Council upon completion. Global engineering professional services consulting firm WSP was engaged to develop NRC’s conceptual hydraulic drawings of the bridge into detailed designs, while local Kerikeri firm Haigh Workman completed the civil design of the spillways. “There are three phases in the physical work,” says Joe. “Phase-one was the lower spillway, which was built by Kaitaia Contractors Ltd (KC) in 2022. Phase-two is the bridge project and was awarded to Ventia, and is currently in progress. Phase three is the upper spillway, also awarded to KCL, and that’s being built concurrently with the bridge. The existing bridge will be demolished and we expect the new bridge and spillways to be operational before Christmas this year.” About 60% of the seven million dollar project is being funded by Kānoa, the Ministry of Business Innovation and Employment’s Regional Economic Development and Investment fund. “One of the Council’s procurement requirements was the employment of young local people. We currently have two young Bay of Islands College leavers working on the bridge and two on the spillway.” The bridge is being constructed on multiple-owned Māori land, on which there have been a number of bridges constructed since the 1800s. “There was no compensation paid to the owners of the land that those bridges were built on,” says Joe. “When we went to build this one, we had almost two years of mending emotional bridges before we could build the physical bridge. We have also received very good support from Far North hapu.”
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