Wyndham Hazard Summary

Flood risk summary for Urban Zoned land in Wyndham

Virtually all of Wyndham Township has a history of flooding, the earliest records of flooding occur in 1861, 1878 and 1913. Wyndham flooded in the April 1968 flood (see figures 1-4). The photograph (see right) shows the Post Office building on the north-east corner of Redan and Balaclava Streets taken during the November 1957 flood suggests extensive flooding of Wyndham during that event.

The stopbanks at Wyndham were upgraded in 1985 to enable them to contain a 1978 sized flow with at least 500 mm of freeboard. However, that protection relies on sandbagging across the main road into Wyndham during large floods.

See planning maps from the Operative Southland District Plan for the mapped floodplain of the Mataura River and the Mimihau Stream. Links to planning maps 83 and 83A.

1978 Flood

Before the February 2020 flood the 1978 flood was the largest on record at Wyndham with a return period in the order of 50 to 60 years. A 50 year return period flood has a 2.0% chance of occurring in any single year. During the February 2020 flood the Mataura River recorded the highest flows measured at Pyramid, Gore, Mataura, Wyndham and Seaward Downs. At Gore the peak flow was 2400 cumecs. Prior to this event a flow of 2400 cumecs was estimated to have a return period of approximately 90 years (annual exceedance probability 1.1 %). Following the event a flow of 2400 cumecs is estimated to have a return period of approximately 70 years (annual exceedance probability 1.4 %). See figures 5-10.

2020 Flood

The February 2020 flood was near the maximum capacity of the stopbank system through Gore and Mataura. The risk of the stopbanks being overtopped at Wyndham was less than expected due to water spilling onto the floodplain to the west of the town.

Floods in Southland are likely to become more frequent as a result of climate change and the associated predicted increases in rainfall. The Ministry for the Environment’s climate change predictions for Southland include 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 up to a fourfold reduction by 2090.

Recommendations

The Southland Regional Policy Statement 2017 directs Southland Councils to reduce risk to its communities from natural hazards.

Although the standard of flood protection in Wyndham is considered to be high, as with any stop banking system, there is always a residual risk of flooding due to stop bank failure or the design capacity of the scheme being exceeded.

To further reduce the residual risk, Environment Southland recommends that any dwelling erected on Urban Zoned land in Wyndham has a minimum floor level no less than 600 millimetres above natural 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 detached garage or shed is constructed with its 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 is practicable should be left to the owner’s discretion.

Environment Southland recommends that owners/occupants develop a flood contingency plan and make themselves familiar with the Mataura Catchment flood warning system. Please see flood warning page on Environment Southland’s website.

Wyndham flood image gallery

1968 flood

1978 flood

2020 flood

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