The agency has asked the Waitaki District Council for approval to designate under the Resource Management Act (RMA) land for the bridges, which the council agreed to at its meeting on Wednesday.
The agency believes the new bridges will be needed by 2014 if the SH82 link is not to be under threat of closures, negatively affecting Kurow and Hakataramea.
The two-lane bridges will replace the historic single-lane wooden bridges built in 1881 for road and rail traffic.
New Zealand Historic Places Trust approval is needed before they can be removed.
They are in poor condition, with high maintenance costs.
Flooding in December 1995 and January 1996 closed the bridges because of damage.
When the river is high, they have to be monitored.
Having the land next to the existing bridges and state highway designated is the first step in the legal process under the RMA leading to construction.
The agency will also need resource consents from the Waitaki council and Environment Canterbury for the project, which could involve public submissions and a hearing.
The project, which could cost up to $14 million, still needs final approval from the agency before it proceeds.
Obtaining the designation over the land will enable funding to be obtained and detailed design carried out.
However, the decision to build two-lane bridges, with provision for cycles and pedestrians, is welcome news for the Kurow and Hakataramea communities, motorists and the two councils.
The original proposal was for single-lane bridges, which the community and councils opposed.
The land required for the project has already gone through a purchase process.
Most of it is now owned by the agency, except for crown land administered by Land Information New Zealand which is going through a change in ownership.
