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River flooding hazards maps

As part of the Thames Coast Project, a series of river flooding hazard maps have been developed for Tararu, Te Puru, Waiomu/Pohue, Tapu and Coromandel. You can use this page to view or print these maps in PDF format.

On this page:

About river flooding hazard maps

River flooding hazard maps help show the areas within a given locality that are most likely to be flooded, given a certain scenario (in this case the 100-year flood event). Flood hazard maps also show how the level and effects of flooding change across a township.

To determine the flood extent area as accurately as possible, flood hazard maps are usually based on the following sets of information:

  • Historical flood events.
  • Damage reports.
  • On-site observations verified by local residents and Civil Defence personnel.
  • River modelling work (computer programmes that predict how a river behaves under certain conditions - particularly where information is scarce).
  • Survey work that determines peak flood heights and an assessment of the flood extent after each event.

Map zones

River flood hazards have been split into three zones (red, orange and yellow coloured areas) to reflect the severity of a flood:

  • In areas where water depth and speed of flow are greatest, risks to life and property are also the greatest. These areas would be in the high (red) zone.
  • Properties closest to streams and places where rivers or streams overflow (overland flow channels) generally experience the fastest flows and deepest water depths so are most likely to experience the worst damage.
  • Properties located further away generally experience less damage, since water depth and speed of flow are not as high. Some properties only experience ponding where water depths are lower still and water just accumulates without any noticeable flow.

National and international studies have also used this method to map and assess flood hazard areas.

The three hazard areas used are defined as follows:

Graphic image showing predicted flood risk assessment levels

While the main purpose of a hazard map is to show the extent of flooding under a given scenario (for example, a 100 year flood), it can also be used as a basis to identify appropriate river and catchment management works to reduce the impact of flooding. Options may include pest control and retirement fencing to improve the condition of the upper catchment (for example, to reduce erosion rates and amount of debris). Stopbanks, channel improvements and overflow channels on the other hand may be used to contain floodwaters in the lower reaches. Both options complement each other to ensure that the overall hazard and risk to each community is reduced.

Download the maps

Check out our map disclaimer information.1

Taruru River Flood Hazard Map - 100-year event
(86 kb, 12 seconds to download, 56k modem)  

Te Puru River Flood Hazard Map - 100-year event
(92 kb, 13 seconds to download, 56k modem)  

Waiomu River Flood Hazard Map - 100-year event
(93 kb, 13 seconds to download, 56k modem)  

Pohue River Flood Hazard Map - 100-year event
(78 kb, 11 seconds to download, 56k modem)  

Tapu River Flood Hazard Map - 100-year event
(69 kb, 9 seconds to download, 56k modem) 

Coromandel Town River Flood Hazard Map - 100-year event
(189 kb, 27 seconds to download, 56k modem)  

You can also check out our Thames Coast Project Summary Report, Investigation Report and the Flood Risk Assessment Report in PDF format.

See our publications pages to order a printed copy of the Thames Coast Project Summary Report and Investigation Report.

More information

 

Footnotes

  1. Cadastral information derived from Land Information New Zealand's Landonline Cadastral Database Crown Copyright Reserved. The property boundaries (land parcels) may not always correlate with the location of the present stream channel. This is due to the dynamic nature of the stream bed (particularly during flood events). The Flood Hazard areas have been based on anticipated flows from the 100-year return period event (1% AEP). This has been assessed from known flood events, damage reports, site inspections, surveys, modelling, local accounts and historical events. This work has been carried out jointly by Environment Waikato and the Thames-Coromandel District Council.