The knowledge behind the big decisions
Stop banks in Gore were pushed to their limit as floodwaters raged.
Team leader hydrological response Chris Jenkins has spent his whole working life watching the weather, measuring rainfall and river levels and predicting just what the impacts will be on our river systems.
For him, this year’s event wasn’t really any different to other significant rainfall events. His sense of calm never wavers, he gets on with running a number of models which provide the information on where, when and how high rivers are expected to peak. It’s not an exact science, but one based on formulas, geography and a wealth of knowledge. And it’s pretty accurate, certainly enough to give confidence to those who need to make calls about possible evacuations.
It means long nights for Chris and his team during an event and a reliance on a network of sophisticated equipment doing its thing.
“We were lucky that, given the huge flows, particularly in the Mataura catchment, all our flood warning sites stayed intact and performed as they were supposed to. We did have a couple of river level monitoring sites wiped out by debris, but overall we got through with enough information to know what was happening.”
While Chris was monitoring the rainfall and river levels, Environment Southland catchment operations manager Paddy Haynes and his team were watching over the flood protection systems, many put in place after the 1978 and 1984 floods. These systems, including 458kms of stop banks and many hectares of designated flood spill zones, were facing their biggest test since their construction.
There were some hairy moments, but the catchment team, many of whom have clocked up 30+ years in their roles, were confident the banks would hold – even when predicted peaks were expected to be higher than design capacity.
“The stop banks at Mataura have a design capacity of 2400 cumecs. At one stage it was looking like the peak could hit 2700 cumecs, but fortunately that didn’t eventuate,” Paddy says.
The Oreti River also faced some challenges, with extremely high flows. Sections of stop banks were breached in the upper catchment near Lumsden and Five Rivers. In the Taramoa area, a number of banks overtopped as they were designed to do when certain levels were reached. Surface flooding occurred in a number of areas around the Oreti catchment, blocking roads and flooding farmland but no towns on the Oreti were threatened.
While many in Southland were busy trying to stay dry and away from flooded areas, the catchment team were out inspecting banks, looking for potential trouble spots and flying over to get a view of hard to see areas.
The stop banks did their job, holding the water and protecting the townships.
“We know that we can’t protect everything during a flooding event, but the flood protection systems are firstly designed to protect townships, to protect people and create safe areas for the water to pond. They did exactly that.
“There was a lot of investment in these systems, both at a regional and central government level, and that has certainly paid off.”
Paddy says although there are repairs to be done and investigations to ensure the ongoing integrity of the banks, overall the results have been excellent. He says ongoing investment so the stop banks can cope with future challenges is important.
Flooding 2020 - the numbers...
Emergency management
- 200 Staff worked in the Emergency Coordination Centre
- 1,000 People were assisted at Gore & Mataura Community Centres
- 26 Community Hubs opened
People evacuated
- 2,400 Gore
- 1,500 Mataura
- 500 Wyndham
- 500 Milford Sound
Farming assistance
- 900 Farmers contacted by Southland Rural Support Trust
- 100 Farmers helped by the Farmy Army
River flows
- Mataura River at Gore peaked at 2,400 cumecs (usually 65 cumecs)
- Oreti River at Wallacetown peaked at 1,279 cumecs (usually 40 cumecs)
