An explanation of natural hazard common terminology

Brewery Creek and Reavers Lane Areas

The Brewery Creek and Reavers Lane areas are Alluvial Fans. Click here to view an example.

Stage Three of the District Plan review will look to assess what land use rules are appropriate to control the effects of natural hazard risk across these two areas. This review process has enabled further geotechnical investigations of already known natural hazards and provides a much deeper understanding of the nature of risk in this area.

Alluvial Fans 

Alluvial fans are cone shaped landforms made of alluvial sediments. These tend to form where streams emerge from hill country onto valley floors. They can be associated with natural hazards such as debris flows, rockfall, soil liquefaction and flooding.

Debris flow

Debris flows are hazards that can be associated with alluvial fans.

They occur where a moving mass of loose mud, sand, soil, rock, water and air that travels down a slope under the influence of gravity. 

Click here to view an example of debris flow at Brewery Creek.

Rockfall 

When individual rocks or boulders roll, fall or bounce down a slope.

Click here to view an example of rockfall in Christchurch.

Liquefaction

Liquefaction is a process that can be triggered by an earthquake.

The strength and stiffness of the soil is reduced by earthquake shaking and this causes the ground to act like water.

Click here to view an example of liquefaction from the Christchurch earthquake of 2011.

Flooding

Flooding is when river levels or lake levels are higher than the surrounding land, or when stormwater cannot drain away and builds up in an area.

Click here to view an example of flooding that occurred during the 1999 Queenstown CBD flood.