Report spells out risks of building in Moeraki

Buildings can continue to be built in Moeraki but any development needs careful consideration, an engineering report says.

A large chunk of land in the town has been classed as high risk by a geotechnical firm investigating an extensive landslip in the township. Other small sections have been classed as very high risk.

The 9000-year-old landslip worsened in the May floods in 2010, and caused 28 claims to be lodged with the Earthquake Commission (EQC).

In the Tonkin and Taylor report to the Waitaki District Council, released this month, the township has been divided into five categories – very high risk, high risk, moderate risk, low risk and very low risk.

The landslip was highly sensitive to any increase in groundwater, report authors Graeme Halliday and Graham Salt said.

"Any action which risks increased groundwater flows or groundwater pressure will be harmful to slip stability."

Any action that removed groundwater, or removed or diverted surface from the slip, would reduce the risk of further movement.

The report recommended urgent action in issuing engineering reports for building consents in the moderate and high-risk areas.

It also recommended urgent action addressing groundwater flows in the affected areas. "The injection of stormwater into the ground within the landslip catchment area... has the potential to reduce the stability of the landslip.

"Council needs to seriously consider establishing a whole of community approach to the disposal of stormwater and require existing properties to pipe all runoff from any hard surface to a council maintained drain."

Full reticulation of stormwater would help reduce current movement rates of the landslips.

The report advised the EQC could seek to change the council's stormwater policy.

"The report... does not mean that no more buildings can be built in the Moeraki township, nor does it in any way suggest the great majority of the existing structures are likely to be significantly reduced.

"The report identifies...[the] risk can be reduced to acceptable levels in many parts of the settled area by avoiding certain parts of the slip by building or developing the land in a way that accommodates the particular issues with the land, and by avoiding actions that may make the slip less stable."

For new developments, proper consideration was needed for it to occur in a safe manner.

The Timaru Herald