Otago Regional Council manager natural hazards Jean-Luc Payan said the study evaluated the debris flood hazard and risks posed by alluvial fans.
It showed what could happen now and in the future during very heavy rainfall, Dr Payan said.
"This new study, commissioned by the Otago Regional Council’s Natural Hazards team and carried out by consultants WSP, looked at 13 catchments that feed water into the area between Coal Creek Flat to Dumbarton. The new mapping identifies areas where debris floods are more likely to occur and assessed the level of risk for people and property."
On Wednesday there would be a drop-in session from 3pm at the Roxburgh Golf Club followed by a public meeting at 6.30pm.
"The Roxburgh community can learn more about the new findings and also discuss them with staff. The full report and an easy-to-understand summary was available online.
"There’s no reason to be alarmed; we’re simply sharing information so the community can understand the risk, stay safe and make informed, early decisions."
There were no planning changes or mitigation measures on the table, Dr Payan said.
"Any future decisions about land-use planning, adaptation or mitigation options would need to be community led and require significant input from our partners at Central Otago District Council, New Zealand Transport Agency and other stakeholders such as Otago Civil Defence Emergency Management."
Roxburgh sits on alluvial fans — cone-shaped landforms built up over many years by loose material (such as rocks, gravels and silt) — washed down from the Old Man Range.
Dr Payan said the fans had helped make the area great for growing produce and were also where some buildings and infrastructure were located. But they also allowed flows of water, mud, rocks and trees to move down the catchments quickly, sometimes spilling out of the usual creek channels, when intense rainfall happened.
Debris floods were fast-moving flows of water and debris triggered mainly by very heavy rainfall with the floodwater picking up loose material in the catchment and channel and moving it downstream, Dr Payan said.
In 2017, debris floods occurred in Pumpstation, Reservoir, Golf Course and Black Jacks Creeks around Roxburgh. Rocks, soil, silt and trees travelled downslope toward the Clutha River/Mata-Au, causing disruption to roads, properties and power.
Debris floods were a natural part of how alluvial fans evolved, Dr Payan said. Climate change meant intense rainfall events may become more frequent. — Allied Media
