How the Otago Regional Council's consultants used or did not use historic flood data in their design of the Leith Lindsay Flood Protection Scheme in Dunedin has been questioned in the second day of an Environment Court appeal of the resource consents granted for the project.
Appellants Neil Johnstone and John Gillies yesterday questioned why the 1923 flood had not been taken into account during the council's calculations of the level of flood protection needed in the Leith-Lindsay catchment.
The case is being heard at the Dunedin Court House before Judge Jeff Smith and commissioners Diane Menzies and Russell Howie.
Three witnesses for the regional council were cross-examined yesterday - consultant hydrologist Horace Freestone, Dr Alistair McKerchar, whose evidence was on climate variability, and hydrologist Dr Grant Webby.Mr Freestone said calculations had been made with and without 1929 flood figures, as reasonably reliable estimates of that flood were available. However, no such figures were available for the 1923 flood.
Judge Smith asked Mr Freeman whether he had run calculations on what effect including the 1923 flood would have had on the design flood standard.
Mr Freestone said while he was unsure of the exact figures, an estimate using the 1923 flood data took the 171cumec standard to just under 200, but he questioned the validity of those figures.
‘‘It's not an accurate assessment.''
Mr Howie asked why the three floods were not all put into the calculation.
Mr Freestone said he had great difficulty plugging in numbers that were not accurate when they knew they had 45 years of accurate recording data.
‘‘I consider we have taken a measured approach to a whole range of things. Weighing it up we are reasonably confident in a 100-year flood.''
Judge Smith said having 45 years of data did not necessarily mean they had captured an extreme event and reliance on historical floods had been used in the past.
It was also fair to say the Leith Lindsay catchment had been changed since 1929 by flood protection works which would have improved the performance of the waterway significantly, meaning a flood of the magnitude of 1929 would possibly be contained today, he asked.
Mr Freestone said that was a reasonable assumption.
During cross-examination of Dr Webby by Mr Johnstone, who was representing himself, Judge Smith said he was becoming increasingly concerned about issues of fairness given Mr Johnstone's cross-examinations seemed to be raising material already covered.
He advised him to stay focused on the issue and on material not yet heard by the court as the panel was struggling to see any rationale for the appeal, beyond an intellectual dispute between engineers.