Appendix 11 Natural Hazards

​​11-1 Low, Medium and High Flood Hazard Area Categories Descriptions

The table below describes the flood water depth, velocity and combined depth and velocity factors in a 1% annual exceedance probability event that are used to define the High, Medium and Low Flood Hazard Areas.

Flood Hazard Area
Waikato River flooding
Surface ponding and overland flowpaths (beyond flooding from the Waikato River)
High​​
i. The depth of the flood waters exceeds 1m; but
ii. Excludes flood water depths less than 0.1m.
 
i. The depth of the flood waters exceeds 1m, or
ii. The speed of the flood waters exceeds 2m per second, or
iii. The flood depth multiplied by the speed exceeds one, but
iv. Excludes flood water depths less than 0.1m.
Medium
i. The depth of the flood waters is equal to or less than 1m, but
ii. Excludes flood water depths less than 0.1m.
 
i. The depth of the flood waters is equal to or less than 1m but greater than 0.5m, or
ii. The speed of the flood waters is equal to or less than 2m per second but greater than 1m per second, and
iii. The flood depth multiplied by the speed is less than or equal to one, but
iv. Excludes flood water depths less than 0.1m.
Low
N/A
i. The depth of the flood waters is equal to or less than 0.5m, and
ii. The speed of the flood waters is equal to or less than 1m per second, but
iii. Excludes flood water depths less than 0.1m

Note
1. Details about the flood hazard modelling methodology, assumptions, limitations and validation, and a more detailed breakdown of flood water depth and speed components of the flood hazard mapping is held by Council.
2. Catchment boundaries for surface ponding and overland flowpaths are shown in the planning maps as ‘Flood Hazard Catchment Boundary’. The balance of the High and Medium Flood Hazard Areas shown in the planning maps relates to Waikato River Flooding.

Page reviewed: 15 Apr 2016 3:29pm