Limehills/Centre Bush Hazard Summary
Flood Risk
The existing stop banks along the Ōreti River were upgraded between Wallacetown and Lumsden in the early 1990s and are designed to protect the Limehills – Centre Bush area against all recorded past floods, which include the events in 1978, 1980, 1984 and 1987.
However, in the Limehills-Centre Bush area, those floods only had return periods of 15 to 20 years, so the standard of protection is low in statistical terms. The stop banks are not designed to protect against more significant flows. At Centre Bush, the stop banks are constructed to contain a flow of 1200 cumecs. The February 2020 flood was a 15-year return period event on the Ōreti River with a recorded flow of 1060 cumecs. A 100-year return period flow at Centre Bush is 1699 cumecs. There will always be a residual risk of flooding due to a stop bank failure or the design capacity of the scheme being exceeded.
Future flood risk predictions for Southland
The Ministry for the Environment’s climate change predictions for Southland includes an increased frequency of heavy rainfall events and an increased likelihood of extreme rainfall. It also predicts up to a halving of flood return periods by 2040 and a fourfold reduction by 2090.
Recommendations
The Southland Regional Policy Statement 2017 directs Southland Councils to reduce risk to its communities from natural hazards. Given the low standard of protection in the Limehills area, Environment Southland recommends that any dwelling erected in the area have a minimum floor level of no less than 600 millimetres above the existing ground level and the floor level of non-living areas such as attached garages and laundries is to be no more than 300 mm below the floor level of the dwelling.
For detached garages and sheds, Environment Southland recommends that the garage or shed is constructed with the floor level as high as is practicable to minimise the potential for flood damage to the building and its contents. The interpretation of as high as practicable should be left to the owner’s discretion.
Please note that this recommendation is not based on flood modelling and is a practical approach to mitigating the residual flood risk. You could adopt a more conservative approach to further reduce the residual flood risk.
Understanding return periods
A return period describes the probability of a flow of a specific size occurring in any river or stream, meaning a 100-year return period will occur on average once every 100 years.
Another way of measuring flood risk is using the annual exceedance probability or AEP. AEP is the probability of a specific size of flood flow occurring in a single year. A 1% AEP flood flow has a 1% or 1 in 100 chance of occurring in any one year. If a 1 % AEP flood flow were recorded this year, the probability of another flow of that size being recorded in the following year (or any subsequent year) would still be 1%.
Return period | Annual exceedance probability AEP |
100 year | 1% |
50 year | 2% |
20 year | 5% |
10 year | 10% |
5 year | 20% |
2 year | 50% |
Further information
If you require specific information about an address in Limehills-Centre Bush, please get in touch by email service@es.govt.nz or phone 0800 76 88 45
Useful links
Environment Southland recommends developing a flood contingency plan and familiarising yourself with the Ōreti Catchment flood warning system. This may include removing vehicles to high ground if the flood warning system is activated and storing flood-sensitive items as high as practicable.
https://www.es.govt.nz/environment/flood-warning
https://envdata.es.govt.nz/index.aspx?c=water-level
https://www.es.govt.nz/environment/flood-warning/catchment-sites-and-flood-level-travel-times
Photo taken during, but not at the peak of, the October 1978 flood - with annotated notes.
Photo taken during, but not at the peak of, the October 1978 flood.
