Flooding and erosion are potential hazards along all the margin of the Clutha River from Queensberry to Lake Dunstan, a new report says.
None of the area could be considered completely free of flood or erosion hazards, an Otago Regional Council document has concluded. T
he 53-page report, released last night in Cromwell, contains a summary of earlier studies and recent work on flood hazard modelling.
Any decision on land use in the area should give careful consideration to the risk posed by those hazards.
''Additional intensification or development in hazard-prone areas would increase the risk associated with these hazards'', the report said.
The council's engineering, hazards and science director, Gavin Palmer, said the report would be useful for potential landowners and developers, as well as for people who already owned land in the area.
It would also be of benefit to the Central Otago District Council, which was revising its district plan.
''The report shows where properties and other assets are vulnerable to the potential hazards in the area,'' he said.
The margins of this reach of the Clutha were sparsely populated, with about 20 houses on the lower terraces, the report said.
However, there was an increasing demand for residential development in the upper Clutha valley in recent years.
Between 2009 and mid-2014, there were 66 applications to the district council for new rural homes in the Queensberry-Crippletown area, it said.
''The growing population of this area and related demand for development increases the level of exposure to natural hazards and as a result increases the associated risk.''
The largest flood recorded was in November 1999 and the largest flows in that river reach usually happened from November to January.
Every flood was different and despite its size, the 1999 flood did not have a significant effect on people or assets in the study area, the report said.
Sediment in the head of Lake Dunstan also had an impact on flood levels and the modelling had taken that into consideration when calculating the risk of flooding.
There were four categories of erosion hazard at four different locations. Continued erosion would affect farmland on the true left and true right banks in certain places.
If erosion followed the same rate as in the past 20 years, houses near the left bank downstream of the confluence with the Lindis River might be affected in about 70 years.
