34 | Challenging job on the go The project includes the refurbishment of 67 culverts and floodgates that drain stormwater from the protected side into the Waipaoa River. Gisborne: Gisborne District Council & Earthwork Solutions T T Karen Phelps REGIONAL DEVELOPMENT SUPPLIERS OF EARTHMOVING AND CONSTRUCTION EQUIPMENT HIRE IT. LEASE IT. COUNT ON IT. 0800 225 001 PROUD TO BE ASSOCIATED WITH GISBORNE DISTRICT COUNCIL & EARTHWORK SOLUTIONS In the wake of the cyclones Gabrielle and Hale, the critical importance of the Waipaoa Flood Control project, spearheaded by the Gisborne District Council, has been emphasised, says council senior project engineer Joss Ruifrok. “This has highlighted the importance, urgency and relevance of the project to protect the community and mitigate against flood risk,” he says. Parts of the project have been delayed due to the effects of the cyclones, which have left soils too wet for work to proceed, he says, including completing the remaining stopbank upgrade on the eastern side between Whitmore and Caesar Road and construction upstream from Opou Road working towards Matawhero SH2 Bridge. Work is expected to recommence later this year from October onwards. Highlighting the efficacy of completed sections of the stopbanks, Joss Ruifrok says these sections, covering a span of 32 kilometres, prevented the river from overtopping and directed floodwaters away from the city, thereby averting potential disaster. Additionally a one-kilometre stopbank that had already been completed protected a high-value farm area, saving the farmer an estimated $1 million in capital costs. The timely recovery and reduced losses experienced by the farm further underscore the tangible benefits of the project, says Joss. The original Waipaoa Flood Control Scheme, designed in 1949 and constructed between 1953 and 1969, is considered one of the Council’s most valuable assets, protecting approximately 10,000 hectares of fertile floodplain land. Recognising the need for modernisation and increased resilience, construction work to improve the scheme commenced in February 2019, with the goal of upgrading approximately 64 kilometres of stopbanks along the Waipaoa River by 2030/31. Key to the project is the raising and widening of the stopbanks to provide a 100 year level of protection accounting for climate change out to the year 2090. The current 1.5-metre top crest is being widened to a four metre wide top crest, while stopbank heights are being raised by one to two metres in certain areas. Joss says experts have emphasised the necessity of higher and wider stopbanks to improve the level of flood protection required to safeguard the community. To expedite the project’s delivery, the Gisborne District Council secured external funding support of $7.5 million from the Provincial Development Unit in August 2020. Joss says this financial boost has accelerated the project’s timeline and alleviated the financial burden on the local community. While the Waipaoa Flood Control project primarily focuses on flood protection for the floodplain, the recent flooding in the Te Karaka area, outside the project’s scope, prompted council to seek additional funding from central government for the upgrade and protection of that township. The outcome of the funding application is currently pending a decision. Apart from financial considerations, various factors such as identifying beneficiaries, addressing potential negative impacts, obtaining resource consent, and designing appropriate solutions pose additional hurdles. Furthermore, geotechnical factors related to stability, rock armouring, sourcing soil material for construction and construction methodologies add to a project’s complexity. To overcome these challenges, the Gisborne District Council has taken innovative measures. Soil material for the project has been sourced from large areas of council-owned public land adjacent to the river grass berms, ensuring a high level of compaction necessary for the project’s success. In addition, the council has acquired several parcels of land solely for the purpose of providing material for stopbank construction. The project also includes the refurbishment of 67 culverts and significant floodgates that drain stormwater from the protected side into the Waipaoa River. Local companies, notably Earthwork Solutions Ltd, have played a vital role in the project’s execution. Joss says the introduction of Topcon technology by Earthwork Solutions has significantly expedited the construction process by allowing real-time monitoring and adjustments, reducing rework and overbuilding, and ultimately saving time and money.
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