IT WAS fitting that last Sunday’s public tour of the Candowie reservoir was held on one of the hottest days this year, in the middle of a two-week heat wave in one of the driest summers on record.
While some of the visitors were civil engineering fans, most were residents of Phillip Island, Grantville, San Remo and the coastal villages keen to hear about an upgrade of the reservoir that will double their water supply. In the summer of 2006-07, they learned just how vulnerable they were when the reservoir got down to just 7 per cent.
Some, like me, may have been under the impression that enlarging a dam involves digging it deeper. In fact, it means the opposite: the reservoir walls will be raised by three metres, doubling water storage capacity from 2263ML to 4463ML.
Allowing for an expected 166 per cent population increase by 2055, the supply is expected to serve the community for at least the next 50 years.
The reservoir, which was built in 1964, is fed from the Tennent Creek catchment. Storage capacity was first increased in 1978 and again in 1982. After the 2007 drought, Westernport was licensed to take excess store water from the Bass River and Corinella bore fields.
The dam extension required Westernport to buy 32 hectares from farmers surrounding the dam. Some trees had to be cleared but 28 hectares will be replanted with locally indigenous shrubs and trees.
Eight hundred metres of the Grantville-Glen Alvie road north of the dam will also need to be raised a metre to prevent flooding.
If nothing else, the dry weather has been a godsend for the construction team. Most of the precast concrete panels are in place and many of the preliminary perimeter works near completion. The $9 million project is expected to be completed by the end of June, in time for the winter rains.
Asked whether it might not have been cheaper to buy desal water, Westernport Water’s managing director Murray Jackson just rolled his eyes. Capturing the rain that falls from the skies, via the local streams, is a much cheaper option, he said, but a connection to the desal pipeline would provide a back-up in extreme drought conditions.
Mr Jackson said the reservoir currently spills 3000ML a year on average, so the upgrade enables them to store water that’s already available and to reduce flooding downstream.
While the reservoir is low, Westernport Water is also upgrading infrastructure to cope with a “one in 100,000 year” flood event and improve earthquake safety and dam surveillance.