Three options for Ohau plan

By Mike Mather in Rotorua
The three organisations charged with saving Lake Rotoiti from becoming over-polluted support a radical scheme to "wall-off" nutrients flowing into the lake from the Ohau Channel.
The Rotorua Lakes Strategy Joint Committee - the combined initiative by the Rotorua District Council, Te Arawa and Environment Bay of Plenty - have approved lodging a resource consent application to build a multi-million dollar barrier wall that should vastly improve Lake Rotoiti's water quality.
Rotorua lakes project co-ordinator Paul Dell said staff, scientists and engineering experts were working together to come up with the best option for the diversion structure to stop the nutrient flow.
The project is estimated to cost at least $10 million.
More than 70 percent of the nutrients in Lake Rotoiti came from Lake Rotorua through the Ohau Channel.
A diversion structure would stop the water flowing into the main body of Lake Rotoiti, redirecting it so it runs through the Okere Arm of Lake Rotoiti and into the Kaituna River.
One possibility for the structure would be a long wall of concrete panels between steel piles.
An advantage of this would be its relatively long life and low impact during construction.
However, more of the structure would be visible when lake levels fell.
A second option was a flexible synthetic curtain attached at the water's surface to a float or pontoon and to the lakebed by a dead weight and anchors.
There were three possible routes for a diversion structure, although all started at the Ohau Channel and extended across the entrance to the Okere Arm.
All three options would stop about 60 metres offshore to let boats into Lake Rotoiti and allow "outflow" from the lake.
While the diversion plan would cause a small increase in the level of nutrients entering the Kaituna River, the river's turbulence and flow naturally limited algal growth, reducing algal blooms in Lake Rotoiti within three to five years.
Last June, the Government pledged up to $4 million towards urgent works in Lake Rotoiti. Environment Bay of Plenty will fund the remainder of the project's cost.
It was anticipated that once the preferred diversion option was known, resource consent would be lodged by the end of April.
A public information session on the options will be held at the Rotorua District Council tomorrow between 6pm and 9pm.
A meeting will be held earlier in the day for stakeholders and interest groups, with another for iwi and hapu of Lakes Rotorua and Rotoiti the following week.
Mr Dell said the joint committee wanted as much public feedback on the plans as it could get.
"We want to select the option that is both effective and publicly acceptable."
Rotorua mayor Kevin Winters has been elected unopposed as chairman of the joint committee.
Te Arawa Maori Trust Board chairman Anaru Rangiheuea is deputy chairman of the committee.