Bad planning is the root cause of the flooding we have seen, argues recently-retired water engineer Jan Heijs. Climate change just makes the consequences a lot worse
Opinion: In the 2000s I was the three waters planning manager for the then North Shore City Council. During this time, our team carried out flood modelling for the already developed light industrial/commercial suburb of Wairau Valley.
Wairau Valley was built on a swamp a long time ago. The flood calculations showed that large parts of the area were at risk of flooding and that the consequences of flooding would be significant.
It was concerning, but the outcomes of this work were met with scepticism by some locals: they told us they never experienced flooding, and suggested we were overstating the flood predictions. Meanwhile options we developed to reduce the risk of flooding in the suburb turned out to be very expensive.
READ MORE: * Why the Onehunga sluice-gates didn't open: 'We're petrified it will happen again' * Auckland's historic flooding explained in five charts * The gathering stormwaters: Pressure to reduce reforms to just Two Waters.
By the time I left the by-then-Auckland Council in 2013, nothing significant had been done to deal with the flooding risk. Local board meeting minutes from 2020 suggest the conversations were still ongoing even then.
[Auckland Council sent a response to Newsroom's enquiry about what stormwater mitigation had gone on in Wairau Valley in recent years. We have included it below.]
The flooding in Wairau Valley on Friday night was some of the worst around Auckland. Two people died, roads were closed, properties flooded, and the clean-up continues. Pak’n’Save and Bunnings are still closed after extensive damage.
Wairau Valley is just one example. My experience with flood planning in other places confirms the idea that inconvenient truths are always hard to get accepted. Replacing streams with a pipe is potentially risky when there’s a lot of rain, yet that is still very common in New Zealand. Sometimes streams are eliminated altogether.
Of course, the smaller the pipe, the less capacity for water to flow through. But smaller pipes tend to be cheaper pipes. Engineers size these stream replacement pipes based on predicted flows - during a one-in-100-year storm, for example - and at the same time assumptions are made about future development to calculate increases in future flows.
The trouble is, these assumptions are often based on what development intensities are allowed for at the time, while in practice it is very likely that these will be exceeded in the future. And in many cases, increasing the intensity of a development means the capacity of the stormwater network will be exceeded. It’s asking for trouble.
An attempt was made to stop the piping of streams in the Auckland Unitary Plan, but it was watered down to apply only if the pipe in question is longer than 40 metres. Which is crazy, since most streams on properties in Auckland use pipes shorter than this.
Basically, this is a permit to continue to pipe.
Earthworks (land modification) are often used to increase the yield of a development. Streams are eliminated or piped for the same reason. Development takes place on floodplains.
Often when local councils try to stop development proposals which are inappropriate for any of the reasons mentioned above, or when they try to change their rules to better protect against flooding, they face fierce opposition from the development community. Councils often are forced to back off because they simply cannot afford to go through costly legal processes.
Squeezing just a few more properties out of a development is enough justification for developers to challenge a council. Even within councils, those advocating for a more future-proof process often meet internal resistance. It is often see as inconvenient that these matters are raised, and this probably has gotten worse because of the pressure to build more houses.
In water management, unlike some other industries, many professionals design with very little margin of safety built in. If someone can reduce the size of a pipe and thereby reduce the cost of a project, that's a win. Future proofing and the use of safety factors is only slowly being accepted.
Take another project, where new infrastructure was being scoped. An argument was made that the new pipe should be ‘oversized’ to allow for development that was not yet in the plans, but was very likely in the future. But this didn't happen, because other parties argued that decision could not be justified based on what development was allowed for at the time. Short term thinking.
Land-use planning is critical
I totally support the arguments for ‘sponge cities’ or ‘water-sensitive design’ we have seen in many newspapers in response to the recent flooding. In fact, some in the industry have been trying to advocate for water-sensitive design in New Zealand for many decades, with a very disappointing uptake.
However, in practice, even if these principles had been applied successfully, they would have had limited effect during the storms we experienced recently. Water-sensitive design must be complemented by good land-use planning. Eliminating streams and building in floodplains should be avoided or prohibited, and land compaction should be minimised. In many places, existing planning rules aimed at requiring water-sensitive design or just good future-proof stormwater management - including avoiding building on flood plains - are extremely weak.
The Three Waters reform is likely to make all of this worse. Stormwater is predominantly a land-use challenge and in that way dealing with stormwater is tied up with planning and development of our towns and cities. In addition, given the huge funding and other problems around drinking water and wastewater, stormwater is likely to be a low priority for the new Water Entities. And looking after other things than pipes will not be in the DNA of these entities, whereas the challenge of stormwater management is about avoiding pipes!
It is interesting to see how many in the water industry appear to fall in line with the suggested Three Waters reform. I know of many people in the industry who bite their tongue. The consequences of not falling into line can be career limiting.
I agree that stormwater management needs to improve across all councils. The regional councils, our regulators, also fail to enforce meaningful improvements. But it would be wrong to push stormwater management into the Water Entities and separate it from land-use management. Instead, the way to improve our stormwater system and avoid the catastrophic flooding we have seen recently in Auckland and elsewhere, would be by providing clear direction, changes in legislation and guidance - and not leave this to each and every local and regional council to figure out. We also need specialised environmental and economic regulators, with land-use planning an important part of this.
In response to Newsroom's questions about flooding mitigation in Wairau Valley, Nick Vigar, Auckland Council's head of planning Healthy Waters sent us this update:
“Wairau Valley is a low-lying area and a known flood risk zone. Over the last 10 years several stormwater improvement projects have taken place in the catchment to increase network capacity and detain rainfall in safer areas including ponds and reserves.
“Auckland has experienced the largest rain event on record and the impacts have been regionwide... Auckland’s stormwater system wasn’t designed to take so much intense rainfall in such a short time. Improvements to localised areas would not have prevented the widespread flooding experienced, considering the amount of water the region received.”
