This follows an Environment Court final decision publicly released yesterday which confirmed four resource consents to take, use and discharge water.
The scheme, a 34km-long, 10m- to 12m-diameter tunnel with one power station taking up to 260cumecs of water from Lake Waitaki and discharging back to the river at Stonewall, would add between 1100GWh and 1400GWh a year - equivalent to powering all the houses in Christchurch - to New Zealand's electricity supply.
Meridian applied to Environment Canterbury (ECan) in 2006 for water-only resource consents for the scheme, which were granted in December 2008.
That was appealed to the Environment Court, which issued an interim decision in September last year which said it was likely to grant the consents if issues over some of the conditions could be settled.
A two-day hearing to resolve those issues was held in Oamaru last month before Judge Jon Jackson, commissioners Dr Alex Sutherland and Helen Beaumont and deputy commissioner Ken Fletcher.
The issues covered the effects on existing and future irrigation, trout, salmon and native fish, braided river birds, wetlands, measuring the river flow, didymo and correction of drafting errors or ambiguities.
The final decision makes changes to some conditions.
One issue was the effect of the scheme on didymo, including evidence it would be more prolific than was predicted.
In its decision, the court said didymo research was continuing and, while information provided to the court was new, it did not alter its findings and the need to adopt an adaptive management approach to control.
The court said Meridian's proposal to rehabilitate or create wetlands to replace those lost if the scheme was built was "good as far as it goes".
But the court was uncomfortable with a limitation on wetland restoration and enhancement.
It amended a condition to ensure 75ha was made up only of created and enhanced wetlands.
The court also made changes to ensure existing irrigation schemes on the lower river were not disadvantaged by the scheme, losing reliability of supply.
Meridian spokesman Alan Seay said yesterday the state-owned company was "delighted" to get final approval but that was only the first step towards building the scheme.
A detailed engineering study commissioned by Meridian is nearing completion.
It looks at the preferred layout (including whether the single power station should be at the start or end of the 34km-long tunnel), more detailed design and costings.
The results of the study, along with a recommendation, will go to Meridian's board of directors before the end of the year for it to decide whether to proceed to the next step - applying for land use consents from the Waimate District Council to build and operate the scheme.
That is likely to be less contentious than the consent process to obtain water for the scheme, but it was expected to take about a year, with another year if there were any appeals to the Environment Court.
The earliest construction could start if it was decided to proceed would be 2014, generating electricity in 2021.
If it is built, it could add $350 million to the local economy during the seven years of construction and $4.5 million a year once operating.
