The plan will be presented to Otago Regional councillors today, recommending a more detailed hazard assessment be undertaken on 13 of the 22 river catchments to understand future flooding scenarios.
Following the 2017 flooding event, only five of the river catchments have been investigated.
The tricky mountainous terrain above the small town means it is likely to flood again during a heavy rainfall event. The Old Man Range has several creeks which can flow steeply and directly down to State Highway 8, Roxburgh town and the Clutha River/Mata-Au.
In its Roxburgh Natural Hazards Management report, the council outlines what will be presented to elected members later today, including procurement for the new study.
The report, written by council’s natural hazards analyst Julion Wright and acting hazards manager Tim van Woerden, estimates the study will be completed before the end of the 2024/25 financial year.
"Debris flows can pose a significant threat to individuals, property, and infrastructure because of their high impact force, and the fact they may occur with little warning," the council report says.
The report outlines how the 2017 event was one of many recorded floods since 1938 that have caused "significant impact to property and infrastructure", and it suggests that with climate change, these events could increase in frequency and impact.
A 2019 report completed by Golder Ltd on behalf of the regional council found that several of the culverts above SH8, named Pumpstation, Goldcourse and Blackjacks Creek, might not be sufficient to stop large debris flows into the town, after NZTA upgraded the river culverts in response to the recent flood.
Roxburgh orchard grower Norman Dalley said the 2017 event saw "truckloads of rock, trees and silt" flow into the town and the Clutha River.
Radio New Zealand reported at the time the town received 40mm of rain in three hours, and Mr Dalley remembers his orchard flooding very rapidly, and said the culvert blocked quickly too.
"You don’t live your life in fear, but you’re hoping it doesn’t happen again and lessons are learned ... the valley was shut off for nearly three weeks."
After the flood, the council installed a rain gauge by Reservoir Creek to detect rainfall patterns.
The regional council plans to engage further with the Roxburgh community and stakeholders.
