Layer: All Flooding Hazard 200 Year (ID: 0)

Name: All Flooding Hazard 200 Year

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Description: While the Waimakariri District Council has taken all reasonable care in providing correct information, all information should be considered as being illustrative and indicative only. Your use of this information is entirely at your own risk. You should independently verify the accuracy of any information before taking any action in reliance upon it.Read full disclaimer here.Abstract:200 Year Flood Hazard data which incorporates the combined output of the three modelling methods used: Localised flooding, Ashley Breakout flooding, and Coastal flooding (see links below to explore the model types individually).The maps show modelled water depths for 200 year average recurrence interval floods.The terms Average Recurrence Interval (ARI) and Annual Exceedance Probability (AEP) describe the probability of a flow of a certain size occurring in any river or stream. ARI is the average time period between floods of a certain size. For example a 200-year ARI flow will occur on average once every 200 years. Alternatively, AEP is the probability of a certain size of flood flow occurring in a single year. A 0.5 per cent AEP flood flow has a 0.5 per cent, or 1-in-200 chance of occurring in any one year, and a 5 per cent chance of occurring in any 10 year period.1. Localised Flooding. This is flooding due to the direct result of rainfall falling on the ground. This type of flooding is sometimes referred to as Pluvial Flooding.2. Ashley Breakout Flooding. This is flooding due to a stopbank breach on the Ashley River. These flood events include flow directly from a stopbank breach plus localised rainfall that would occur at the same time. This type of flooding is sometimes referred to as Fluvial Flooding. The Pluvial Flooding component of these scenarios was 10% of the Fluvial component (ie a 200 year breakout was modelled in conjunction with a 20 year localised rain event).3. Coastal Flooding. This type of flooding can occur in the coastal regions of the district and is due to the interaction between storm surge, river flows from the Ashley and Waimakariri Rivers plus groundwater effects. Storm surge was the overriding component of these models. A 100 year storm surge was modelled in conjunction with a 20 year river flow. The groundwater component was modelled assuming median groundwater levels (adjusted for climate change impacts).The flooding has been classified as follows:High Hazard – Extremely high depth and/or water velocity. Potential for significant damage to buildings due to scour, flotation and debris impact. Possible danger to personal safety. Evacuation by trucks and/or wading difficult. High potential for water ingress into buildings.Medium Hazard – Depth greater than 0.3m. Evacuation by light vehicles difficult due to flotation. Wading generally possible. Small likelihood of damage to structures. Potential for water ingress into buildings.Low – Depth less than 0.3m. Evacuation by all vehicles generally possible. Wading possible. Some potential for water ingress into sheds and other structures with floor levels at or near ground level.Information about the natural hazards district plan process can be found here.Update Frequency:As RequiredPoint of Contact:Waimakariri District CouncilLineage:Flood modelling has been completed for all areas of the Waimakariri District with the exception of Lees Valley and flood exclusion zones (the flood exclusion zones are areas where the modelling has not been undertaken as these areas have recently had their land levels altered). Efforts have been made to update the Flood Modelling for new and proposed development areas, however the modelling may not be accurate in all areas where development has occurred since 2014.Information on flooding probabilities can be found here:Environment Canterbury Flood Probabilities

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