Achieving flood risk management - Greater Wellington's approach
Greater Wellington's Flood Protection group works with communities to manage flood risk from the region’s rivers and streams.
Our approach is to understand the processes affecting a river/stream and its floodplain within a wider catchment, and to provide a co-ordinated response through our floodplain management plans (in partnership with the community) to reduce the impact of flooding.
Greater Wellington’s policy
Our policy is that new development is avoided in areas of flood risk. Where development does take place in these areas (including infill development), we recommend that residual risk is recognised.
Residual risk is the risk that a flood larger than the flood risk management measures are designed for, occurs. This is also known as a greater than design period event.
What is a design period event?
A design period event comes from a design standard - this is the size or return period to which flood risk management measures are built to contain.
House raised to above the 1-in-100 year flood level
For example, a 100-year return period flood is an event that is predicted to happen (or be exceeded) on average once in 100 years. This does not mean that if such a flood occurs it will not re-occur for another 100 years. It means that it has a 1% chance (1 in 100) of happening in any one year. The greater the number of years identified, the more intense the flood will be.
During development of a floodplain management plan, the 100-year return period flood event may be used as the design period event for developing measures used to manage the flood risk. In some areas like in the Hutt catchment a larger design period event has been used (1 in 440-year return period).
What is floodplain management planning?
Floodplain management planning is a process that results in a long-term strategy for managing flood risk, helping improve the security and quality of life for present and future generations living on a floodplain. It better prepares them for coping with a flood when it occurs, and aims to ensure that any future development considers flood risk. A floodplain management plan (FMP) emphasises the need to ‘keep people away from the river’ rather than ‘the river away from people’.
The outcome of the floodplain management plan process is a document that guides how a catchment should be managed to achieve the following:
- Minimising risks to life, health and safety
- Reducing severity of flood damage, and coming up with options to manage the flood risk
- Promoting sustainable use of flood and erosion prone land
- Promoting sustainable development of the wider catchment.
The outcomes above are achieved by:
- Using planning and community preparedness to ensure sustainable land use
- Looking at options to reduce the flood risk
In general, an FMP provides long-term management strategy (e.g. 40 years), and provides guidance to those involved in making decisions about the management of the river, the floodplain and the wider catchment.