Flood shows hard calls must be made
This week's big flood shows that Christchurch faces tough decisions about which areas it can afford to protect and where it will be necessary to retreat, Deputy Mayor Vicki Buck says.
Buck said the council was on the verge of releasing the Natural Hazards chapter of its District Plan review. Consultation on the fast-tracked document was to begin on March 15.
With the earthquakes having created new flood-risk areas like St Alban's Flockton cluster, Buck said Christchurch faced difficult questions about what it could afford to protect and where instead it might have to retreat.
Behind the scenes, the new council has pushed flood issues to the top of its list, she said. It commissioned an assessment on climate-induced sea level rise from geo-technical consultant Tonkin and Taylor that was delivered just before Christmas.
And it has just been through the Stronger Christchurch Infrastructure Rebuild Team (Scirt) budget to give greater emphasis to flood-prevention measures.
"We've gone through and re-prioritised the things that weren't below the ground but were associated with the mitigation of rain events and storm surges, so that they're definitely included where they might not have been."
But she said that the full picture needed to be put on the table so the public could decide how best to respond to the complexities of the situation.
Evan Smith, of the Avon-Otakaro Network, who has met council officials to discuss the flood risk for Avon River park projects, said there were some worryingly big choices to be made.
The council has said it sees red-zoning neighbourhoods like the Flockton cluster as a last resort. The streets have become trapped in a bowl after the surrounding land lifted, but there are schemes to widen streams and increase the capacity of stormwater drains.
And there will be other minor controversies like a proposal to save money by removing the Archimedes screw pumps that drain the Horseshoe Lake area.
"Obviously, there is no community to protect there any more and apparently that could save quite a bit," Smith said.
But he said the Tonkin and Taylor report threw up several problems caused by the changes the earthquakes had made to ground levels and the advancing threat of global sea-level rise.
Smith said one that had remarkably little publicity so far was a recommendation that the current Flood Management Area (FMA) minimum floor height needed to be lifted yet again to meet revised climate projections.
The council adopted Variation 48 of the District Plan in 2011 to force new building in shoreline and river suburbs to allow for 50cm of sea-level rise over the coming century. Now, argue Tonkin and Taylor, that ought to be a metre.
Smith said it would be revealing if this made it into the Natural Hazards chapter. Likewise, it should deal with the problems being created as people started to rebuild quake damaged homes according to even the existing FMA floor levels.
"If houses and sections are being raised, then you end up with individual homes all on different levels and that changes the way water drains from one property to the next. So now there ought to be general planning rules which deal with those implications put into the District Plan."
At an emergency press conference on yesterday's flooding, Earthquake Recovery Minister Gerry Brownlee agreed the Christchurch public had to decide where the balance lay. Did it pay to future-proof the city or just to protect one set of residents for perhaps the next 10 years, he asked?
Buck said Christchurch - being built on a swamp - at least knew how to deal with drainage issues. "In the past, we've almost over-invested in our infrastructure compared to others."
Buck said another advantage was Christchurch had the most detailed geo-technical maps of any city. "We've actually got the best information to make these decisions."