Stormwater attenuation minimises the effects of increased runoff from small sites in Christchurch.
On undeveloped land, a large proportion of rain soaks into the ground and either flows slowly through the upper soil layers into streams or seeps down into groundwater, as illustrated in the diagram below. Development results in increased impervious (hard) surfaces that have a number of negative effects on stormwater:
Even small sites can have a negative effect on stormwater, and when this is combined with hundreds of other small sites the effect can be significant. It is therefore important to mitigate these effects to help clean up Christchurch’s streams and to reduce flooding. The measures described can also be used by anyone wishing to develop their property in a more sustainable way. Reducing runoff helps to recreate the way that rain behaves on undeveloped land. This can be achieved, in order of preference, by:
Acceptable solutions follow for minimising the effects of increased runoff from small sites in Christchurch.
These solutions are applicable for development on small (less than 1000 m²) residential or commercial sites. However, not all development on small sites requires runoff to be reduced. The criteria below are used by Council to determine whether or not a site requires mitigation.
|Hill sites (>5° slope)||All hill sites are required to install tanks or other suitable mitigation devices when new development (or intensification) takes place.|
|Flat, urban areas||
Mitigation is required only if:
Developers of existing sites where the coverage is already greater than 70% of the total site area will need to discuss attenuation requirements with the Council.