Dam may get new PVC face
A geosynthetic (PVC) membrane may be used instead of a concrete face for the Waimea dam, which is now under construction.
Such a swap is tipped to improve resilience. It is also expected to deliver time and cost savings to the project, for which the forecast build cost has blown out by an estimated $25 million to $129.4m.
Waimea Water Ltd – a joint venture between the Tasman District Council and Waimea Irrigators Ltd – is responsible for managing the construction, operation and maintenance of the dam. Chief executive Mike Scott said moving from a concrete face to a flexible geosynthetic membrane on the upstream side of the dam would help to improve its resilience. ‘‘It also helps us with some budget savings.’’
Asked if it would save millions of dollars and months of time, Scott said this was commercially sensitive while negotiations were concluded, ‘‘but in that realm’’. However, those savings were already factored into the $129.4m revised cost.
If the originally proposed concrete face was used, ‘‘we would need to back out the savings and increase the projected cost’’, he said.
From the site yesterday, Scott said the membrane was in its final stages of design and would be peer reviewed, with a final decision expected in the next three months.
‘‘The geosynthetic membrane and its integration into the dam has been designed by competent, professional, experienced and qualified dam engineers, Damwatch, with support from material engineers in the USA. The design will be reviewed . . . by GHD engineering.’’
However, concerns have been raised about the potential effect of PVC on people and the environment, and whether such a change might require a review of consents for the project.
Tasman District councillor Anne Turley said she had been given research showing that PVC was toxic. ‘‘Add phthalates and metal stabilisers for flexibility, as required in the dam membrane, then you introduce a far greater toxic mix of contaminants to the environment and potential exposure to humans.’’
Forest & Bird top of the south regional manager Debs Martin said the organisation would have to assess whether PVC would be a problem.
‘‘That is not something we have internal expertise on, but we are aware there is some controversy surrounding it,’’ Martin said.
‘‘We would urge investigation into possible in-stream and downstream impacts, and would be concerned about the potential for contamination of our waterways and any resulting impact on the fish, birds and animals that rely on the water if concerns were founded.’’
However, Scott said PVC was inert. ‘‘The membrane will
behave no differently to a PVC dashboard in a car or PVC water pipes,’’ he said. ‘‘The design report will verify this property.’’
Scott said he did not believe that the change to a PVC membrane would warrant a review of the resource consent.
‘‘No significant change on impact to the environment,’’ he said. ‘‘Water sits on inert PVC rather than inert concrete.’’
The expected lifespan of the membrane was more than 70 years, but it would be ‘‘straightforward to replace/repair at modest cost’’.
‘‘It is much easier to repair than a concrete face and, in fact, the membrane has been the go-to repair for failed concrete faces.’’
Meanwhile, Water Information Network Inc (WIN) has released a statement outlining its members’ concern at ‘‘the huge increase in the estimate for the construction of the Waimea dam announced at this very early stage of the project’’.
‘‘We believe that further substantial increases are inevitable,’’ says the statement, which was sent to Regional Economic Development and Infrastructure Minister Shane Jones.
‘‘We have no confidence in Tasman District Council to protect the ratepayers’ interests, and we call on the Crown to intervene.’’
Tasman District resident Lewis Solomon, who is WIN’s secretary, said WIN members wanted the Government to put equity into the project.
■ Waimea Water plans to hold a public meeting at the Richmond Town Hall from 6.30pm on March 31. Anyone interested in attending is asked to register and provide any questions or an outline of what they would like to hear about by emailing info@waimeawater.nz by March 27.