Floodplain management
A floodplain is the area of land next to a river or stream that is susceptible to flooding when rivers or streams overtop. Much of Waitaha/Canterbury is located on a floodplain and is prone to flood hazards.
We use several methods to reduce the impact of flooding on people and property: river and drain management, land use planning and warning systems.
River and drain management
We do river and drain management work around Waitaha to reduce the likelihood of floodwater leaving river channels and flowing onto floodplains where it can interact with people and property and create a flood hazard.
This work includes:
These flood protection works are effective at reducing the frequency of ‘out-of-river’ flooding in small to medium-sized floods.
Larger flood flows may breach physical flood protection structures.
This will vary from one river to the next.
Flood protection works are expensive. The level of protection is usually driven by the number of people and the value of assets that benefit from them. In areas with higher population and infrastructure density, like the south side of the Waimakariri River, flood and erosion protection works are designed to contain significant flood flows – those with an average recurrence interval (ARI) of more than 200 years. This is different from flood protection work in areas such as the Selwyn River, which can be overwhelmed by smaller flood flows with an ARI of less than 20 years.
The cost, time and practical limitations involved in river and drain management means we can’t only rely on this method to reduce the effects of flooding. We use land use planning alongside river and drain management to further reduce the impact of flooding in Waitaha.
Find out more about our river and drain management work and the work we do to reduce flood impacts.
Land use planning for flooding
The Canterbury Regional Policy Statement (CRPS) provides policies on flood avoidance and mitigation.
The CRPS requires avoiding new development in areas that may have severe flooding in a 500-year ARI event. Outside of these areas, floor levels of new buildings must be above the 200-year ARI flood level.
District councils must give effect to the CRPS policies through their district plans.
We can provide flood hazard information to ensure your new building or development meets district plan requirements.
Flood warning system
We try to lessen the effects of flood events through flood protection work and land use planning, but floods will happen. We monitor weather forecasts, rainfall and river flows, and keep people informed of observed and likely flood impacts