Dannevirke's reduced water supply and its murkiness may be due to slip

Dave Watson, Tararua District Council's group manager of plant and property, at the impound water supply before it was filled. Photo / Christine McKay

Battling continuing turbidity in our town water supply, the district council has decided to send a diver under the cover and into the depths of our impound supply dam.

The aim is to put a foot valve at the bottom of the pipe, to prevent the pump pulling in turbid water.

And while there are quality problems, there are also supply problems as the intake gallery isn't giving council the quality supply it needs, so water is being taken from the impound supply dam.

Normally council would harvest up to 110 litres of water a second from the river, but the ongoing turbidity and possible obstructions in the intake gallery in the Tamaki River have resulted in only a maximum of 80 litres a second being taken.

With Dannevirke's usage of treated water sometimes exceeding 120 litres a second from the number two reservoir, the impounded supply has been used significantly more to supplement the water supplied to the treatment plant.

Currently the level of water in the dam is 8.5 metres. It normally runs at 13 metres.

"This problem is having a significant affect on the Alliance Meat Works," Dave Watson, council's group manager of plant and property, said.

"They have their own filtration system, but when they are double shifting, it takes time for the water to pass through their filtration."

A drone has been sent up to check the lines coming from the intake of the river, with one branch showing clear water flowing through, while the second branch, where council is currently drawing our water from, is cloudy.

"Using council's drone is better than (people) bush bashing their way up," Watson said.

Slips in the Ruahine Ranges are the suspected cause of the problem.

"We're hoping and praying it clears up soon," Watson said.

"We're taking water well below our consent limits because it's so turbid."

Councillor Ernie Christison said he had been working on farms upstream and believed there was a big slip "somewhere".

"The water up there is brown," he said.

Watson said council was considering engaging an engineer familiar with intake galleries to advise on remedial or extension work to the existing intake gallery.

There is also the option of hiring a containerised plant and dropping it in at the intake gallery, at a cost of $20,000 a week for three or four weeks.

This would allow council to harvest a clean water supply up to the resource consent limit and feed the surplus back into the impounded supply.

"We need to bring the impound supply up to full, as we haven't got a buffer (if something goes wrong)," council chief executive Blair King said.