Listed below are the answers to questions frequently asked about flooding.
Make sure you are familiar with evacuation routes, listen to emergency announcements and follow the directions to evacuate if required. Visit the civil defence website www.getthru.govt.nz for further information regarding flood preparation measures.
Flooding occurs when the amount of rainfall is more than the drainage system it flows into can cope with. The drainage system can be natural or artificial and includes streams, rivers, estuaries, lakes, dams, open or piped drainage channels.
There are two main types of flooding:
A sudden local or nearby heavy rainfall can cause sudden and unexpected "flash flooding" in either system. Council currently relies on computer modelling based on actual events to determine whether or not land or property is flood prone.
Flood heights are measured in relation to Mean Sea Level (MSL). Because of a river or stream's downhill flow, the level of peak floodwaters for the same flood event will vary throughout the catchment, i.e. the flooding height will reduce as it gets nearer to the sea. The depth of flooding is dependent on the flood height in relation to local ground levels, i.e. the lower the ground level the deeper the flooding will be.
Projected flood levels are determined from rainfall intensity data based on previous floods, and from hydraulic modelling with computers. The actual levels may vary over time. Depending on where you live you may need to contact both Councils (KCDC and GW) to establish the projected flood level for your area.
You can view flood maps and contour plans on our GIS online mapping tool. To accurately determine the level of your particular land, you will need a registered surveyor to prepare a survey plan to identify spot heights on your land.
Council controls development through the District Plan to manage flood risk . Council is currently undertaking a Flood Risk Management Study and Plan for all urban areas in accordance with the provisions of the Resource Management Act.
The main purposes of the study and plan are to define the nature and extent of the flood risk and develop options to minimise the social, ecological and economic impacts of flooding.
The flooding standard applied is based on the 1 in 100 year or 1% flood frequency level. Bigger floods than the 1 in 100 have occurred in the past and may occur in the future.
The 1 in 100 year flood event level is a probability measure which means that there is a 1 in 100 or 1% chance in any one year of a flood occurring at that level. It does not mean that the land will flood only once every 100 years. On the contrary, there could be a number of 1 in 100 year floods in the same year.
You will need Council approval and in most cases you may have to raise the floor level of the extensions if the existing floor level is below the recommended building level.
The District Plan requires developments to be flood free. This means that any new allotment as a result of the subdivision will normally be required to have a flood free building site.
Flooding has the potential to:
Home owners should contact their insurance company to find out what their particular requirements and limitations are.
Council seeks to ensure any new development provides for flood safety in the event of a flood. This is achieved by locating development above the 1 in 100 level where possible and providing safe evacuation routes for flood affected areas.
It is important to remember flooding is a natural process that will occur and there will be storms greater than the 1 in 100 year event.
In an emergency dial 111 for:
Ring this number if lives or property are at risk
04 296 4700 or 0800 486 486
Other emergency contact details: