Detailed groundwater monitoring to start in lower Waitaki valley

Meridian Energy is implementing a groundwater monitoring programme throughout the Waitaki valley, as part of its investigations for its proposed Project Aqua hydro-electric scheme.

“The monitoring programme will be implemented over the coming month or so,” says Project Aqua Engineering Manager Tony McCormick, “and is part of the ongoing and extensive investigations of groundwater conditions in the lower Waitaki valley.”

The monitoring programme will be based on test bores drilled as part of the Project Aqua geotechnical programme, test bores from previous hydro-electric investigations in the area, as well as many existing privately owned bores, wells and galleries.

The monitoring will cover areas where groundwater will potentially be affected by the construction and operation of Project Aqua. These areas, which are within a few kilometres of either the lower Waitaki River or the canal zone, are shown in detail in the Project Aqua AEE Appendix AF (Hydrogeological Assessment of Effects).

“Any landowners who are not already in contact with Meridian Energy and who are concerned about the effects of Project Aqua on groundwater, should contact the Project Aqua Kurow office,” says Tony McCormick. “It may be appropriate that they join the monitoring programme, if they are not already part of it.”

Areas near power-stations will experience the greatest groundwater effect, particularly during the construction phase, as a result of the pumping of water from the deep excavation pits required to build the power-stations. Groundwater near these pits may be drawn down by as much as 15 metres. This effect will reduce to a drawdown of around half a metre at a distance of 4km from some of the most affected power-station construction sites. The drawdown effects during the routine operation of the Project Aqua scheme would, however, be much less. The deep excavation pits will allow Meridian Energy to keep the height of the canals immediately upstream of power stations to a maximum of 20 metres. Although water would start only 20m above the ground, it would in effect fall about 10m below the ground, which would provide a net 30m of head at each power-station.

“Where drawdown effects as a result of Project Aqua cause a problem with water supplies for landowners or residents, Meridian Energy will provide appropriate mitigation,” says Tony McCormick. This could include deepening existing wells, providing water-pumps, or even delivering water.

“The monitoring programme will provide a base-line for groundwater conditions, and will provide an objective measurement of the effects the construction and operation of Project Aqua would have on groundwater in the lower Waitaki valley.”

The information from the ongoing monitoring programme will be fed into the computer model of lower Waitaki valley groundwater, which has been prepared by expert consultants acting for Meridian Energy. This model has been built up using information from the Waitaki River low-flow trials that Meridian Energy conducted in mid-2001, as well as information that has been available from most water bore and water users in the lower Waitaki valley.

The new information will further improve the quality of the model, and should enhance the accuracy of its predictions, says Tony McCormick.

For more information about the groundwater monitoring programme, please contact the Project Aqua Kurow office on 03 436-0920 (Pip Nicolson or Anna Greenslade) or call 0800 AQUA INFO (0800 278-246).

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