It has now begun building the temporary supports that will allow the bridge to reopen.
KiwiRail chief infrastructure officer André Lovatt said, with lower river levels, contractors would be able to undertake a detailed inspection of the damage to the bridge.
Work began immediately to divert the river flow away from where the pier was.
"Our civil contractors have been working up and downstream to temporarily divert the main river flow from the north to the south bank and drain water from around the pier site," he said
"There is a staged process to go through from here. Our work now is focused on first making the bridge safe by ensuring the sagging spans do not collapse, which could fall into the river and damage the adjacent road bridge. We will then install a temporary structure to replace the pier and allow trains to resume running over the bridge."
Work began yesterday on building the structure, known as a pigsty, to get the sagging spans back into alignment.
A 250-tonne crane is on site and will be used to drive steel caissons into the river bed from tomorrow. These will form part of the temporary support for the bridge.
Mr Lovatt said at this stage KiwiRail expected to have the bridge reopened to trains towards the end of next week, provided the river flows remain at current levels and conditions remained safe.
If would then begin work on the permanent replacement of the pier.
KiwiRail was also undertaking work to find the missing pier, which could be buried in the river downstream.
KiwiRail continues to work with its customers to keep their freight moving while the bridge is being repaired.
Freight is being carted by road between Ashburton and Timaru.
