Data presented by the Otago Regional Council showed while peak river flow was higher in 1980, at more than 2500cumecs compared with just below 2000cumecs, a greater volume of water came down the river in last week’s flooding.
Council engineering, hazards and science director Gavin Palmer shared details about the magnitude of the flood and how its flood protection schemes on the Taieri Plain were working at two briefings on Wednesday.
"From a volumetric point of view, this is one of the largest floods, in terms of volumes of floodwater, that has entered the East Taieri," Dr Palmer said.
However, the river flow receded more quickly than in 1980. It did not drop, then climb back up again as it had in 1980 and at other times.
The faster rate of recession meant flood ponds would drain more quickly, which was helped by the flood protection schemes operating well and extra pumps being brought in.
"Things are going well and we expect that the upper pond will be completely empty by [Wednesday] next week, assuming no major weather comes through."
The flood control infrastructure remained "mostly OK" but some repairs would be required. Costs had yet to be assessed.
The main priority was to remove water from flooded areas, including farm paddocks, as quickly as possible.
A high volume of water from the Taieri River had filled the protection scheme’s upper pond, which had a capacity of about 35 million cu m of water, but that was draining "very quickly" and on Wednesday afternoon only 11 million cu m remained, 31% of the weekend peak volume.
A "critical decision" had been taken to call in the military to help regional council staff and contractors to "block a hole" in the stopbank beside the Mill Creek pump station on the Taieri River on Saturday morning. About 20 NZDF personnel assisted.
Council environmental monitoring and operations director Scott MacLean, who earlier also served as Emergency Management Otago group controller, said the council was "very grateful" to the NZDF for the timely help. The council has said the backflow was threatening to undermine and demolish the stopbank, flooding the Mill Creek subdivision.
Dr Palmer said the swift intervention helped keep "a lot of water" out of the scheme’s lower pond area and greatly limited the extent of potential flooding from the Taieri River.
• The flood in June 1980 caused widespread devastation across the Taieri Plain leaving Dunedin Airport closed for 52 days and causing the death of nearly 2000 farm animals, some found in trees.
