Work has started on the true right bank of the Mataura River bank at Mataura to protect the stop bank.
A 2022 geophysical survey of the stop banks found there was no obvious structural damage to them as a result of the 2020 flood.
However, river engineers raised concerns about a 600m section along the true left bank in the Mataura township that was at risk of erosion.
As a result about 24,500 tonnes of rocks were were placed along the river bank.
Work on the right bank was planned for the 2023 construction season.
Environment Southland river engineering officer Stephanie Gray said rock would be laid along a 710m stretch of the river bank.
‘‘It’s putting a solid barrier in place so the river can’t come and undermine the stop bank.
‘‘It’s going to prevent erosion.’’
As well within the 710m, a 500m long trench would be dug near the stop bank, alongside the river.
The trench would be filled with rock and rubble and then topped with soil to give added protection to the stop bank.
In a flood any water that left the riverbed would not be able to reach the stop bank because of the buried rock.
About 32,600 tonnes ofrock would be used.
The height of the rock wall on both sides of the river would be the same so as not to put additional pressure on one stop bank or the other.
The work would mostly be completed by Mataura business K2 Contracting who had completed an ‘‘impeccable job’’ of the left side.
‘‘We’re proud that we can use Mataura contractors for it and supporting the local economy.’’
Environment Southland integrated catchment management general manager Paul Hulse said recent flooding had increased erosion in this area.
‘‘We want to get the work undertaken as quickly as possible.’’
While the protection work is under way, community safety is paramount.
‘‘Heavy vehicles will be moving in the area around the Alliance Group Mataura Plant, so please take extra care.’’
