Floodviewer

Hamilton City Council has an ongoing programme to understand what would happen in areas of Hamilton if we had a very large, and rare, amount of rain. The measure we use is an event which would happen, on average, once in 100 years. Statistically, this means there is a 1% chance of this happening in any given year.

We call this a 'one-in-100-year event' and it provides a consistent measure for Councils to use across the district. Mapping of potential flooding in a one-in-100-year event is developed with computer modelling that uses land contours climate change information and known and predicted rainfall and water flow patterns. This information has been identified for around one third of Hamilton so far.

Our information shows whether affected properties would have a low, medium or high flood hazard if we have a one-in-100-year rain event. It means people can be prepared for an event like this and can also inform what residents do on their property.

For example, owners of properties with a flood hazard showing should consider where flood water would go if there were changes to the property such as a raised garden, a shed or playhouse. It helps people avoid inadvertently directing water where it is not wanted, for example, towards the door of a building.

The last widespread 100-year flood event in Hamilton occurred in 1958. The Waikato River was last at a 100-year flood level in 1998. Waikato River flooding is affected by rainfall upstream of Hamilton. Flooding in Hamilton, other than in the river corridor, is affected by rainfall directly on the city.

The flood mapping shows the effect of water on the land, not whether it would enter the building if there was a one-in-100-year event. Whether flood water gets into a building depends on how high off the ground the floors are compared with the depth of the surrounding flood water. 

Council can supply you a detailed map showing maximum flood depth and velocity and design flood level for individual properties in a 100-year flood for flood-modelled areas.

These maps may be requested by phoning 07 838 6699 during normal business hours or emailing city.development@hcc.govt.nz

Council is required to produce the best available flood information and make it available to the public on request. A LIM outlines all information a council holds on a property, including permitted land use, consents, stormwater and sewer drains, rating information and potential natural hazards including erosion and flood hazards.