One the major prerequisites we need to build the houses we need to combat our housing crisis is infrastructure, without it, the development can’t happen. This post is about a highly but often forgotten element of infrastructure Three Waters – Water Supply, Wastewater & Stormwater. In part 1 I focused on Wastewater, part 2 focused on Water Supply, part 3 will focus on Traditional Stormwater Systems or Grey Infrastructure compared to Green Infrastructure.

The stormwater system is public pipes, manholes, catchpits and other assets which assist in collecting water from rain & safely managing it. The stormwater system in Auckland is managed directly by Auckland Council as opposed to Wastewater & Water Supply which is managed by Watercare.

Stormwater Management
Stormwater Graphic

The recent LTP has the following Stormwater infrastructure as needed

  1. Freeman’s Bay stormwater upgrades ($21m) Due to frequent flooding in Daldy Street, Fanshawe Street, parts of Victoria Street and Victoria Park upgrades are needed to address – 2017 – 2020
  2. Artillery Tunnel ($22m) Due to be completed this year this one-kilometre long tunnel from McLennan Park to Pahurehure Inlet will serve Takanini growth areas – 2015 – 2017.
  3. Takanini Conveyance Cascades ($22) New open channel incorporating cascading weirs and associated green space to convey the 100-year flood in Takanini growth areas – 2015 – 2019.
  4. Ports of Auckland Outfall ($22m) A new stormwater pipe to replace the existing pipe in poor condition on Quay Street – 2015 – 2019
  5. Oakley Creek Conveyance ($30m) Upgrading culverts and widening of Oakley Creek through Walmsley Park to convey flood flow to allow growth in South Auckland –  2015 – 2019

These projects are also integral if we are to provide for the growth to tackle this housing crisis, however, it is key that an integrated approach is taken to infrastructure where AC/AT/NZTA/Watercare/Panuku/Crown work together on each area as a complete package of Three Waters, Transport, Planning & Community/Social Services to make work & not in isolation of each other.

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    1. I take it you mean Watercare? Metrowater ceased to exist in 2010. No, as it says above, stormwater is funded directly by Council, whereas Watercare covers water supply and wastewater.

  1. Permeable ground in Auckland is getting scarcer, and so the stormwater is finding it harder to infiltrate and recharge the groundwater. This is what’s overloading the stormwater system.

    The “other assets” in our Council’s stormwater system need to include raingardens and bioswales which are devices of higher permeability, arranged to collect and absorb the runoff from new impervious surfaces. I’ve seen council put in a few raingardens to take road runoff, such as out in Panmure and in Roskill, but I believe these should be incorporated as much into every development as possible.

    When I was working as a civil engineer in the late 90’s, we weren’t allowed to include a grassy area in the calculations for a property’s permeable area if that area was possibly going to be used to park a car. The compaction caused by the car was – quite rightly – considered to reduce the permeability of the area. In the last few years I’ve seen infill developments go ahead that could in no way achieve the required permeability ratios.

    My gut feeling is that the need for more housing means the stormwater design requirements are being overlooked, so our stormwater (and where they haven’t been separated, our wastewater pipes) are overloaded. But this could be quite unfair. Can anyone in the industry confirm or deny?

    1. As a civil engineer currently working in Land Development, raingardens and other bioretention is definitely a design requirement by Council and AT as part of a sites overall stormwater management plan. Depending on treatment devices that exist in the downstream environment, they may be doing all or partial Total Suspended Solids & Heavy Metals removal. Greenfields sites such as Hobsonville point, Millwater etc all have extensive on road bioretention and larger treatment ponds. Brownfields are more challenging to fit these in within the existing road corridor but it can definitely be done. Incorporating raingardens in existing or new speed management/traffic calming devices is a good solution.

      1. Is on-site retention and detention in rainwater tanks used much on the isthmus? The Stormwater Management Area requirements are usually mostly achieved that way on Waiheke. Even though the sites are big, the soils are not permeable and wastewater also has to be discharged on-site — somewhere separate from the stormwater. The fact that there are already large rainwater tanks for water supply, that can have a bit devoted to capturing and then slow-releasing stormwater, makes it the most economical and sometimes only feasible option. It gets tricky on the steeper sites, dealing with the impermeable areas that are not connected to the tanks (i.e. driveways).

        See SMAF maps:
        The point of these rules is to reduce downstream impacts from run-off from new developments in these areas. The areas were chosen based on the quality of the streams affected, I think (probably a gross simplification).

      2. Thanks Thriller, I hope someone’s getting to have fun with the raingarden and bioswale designs (and their planting plans). Could be a really fun creative area to be in. Brownfields sites are more tricky, but would be more satisfying to design if you’re given enough scope.

        In civil engineering, the stormwater design would generally be brought in at the end of the roading design. In permaculture they would be co-designed. That’s a shift I’d like to see in Auckland.

  2. And the other issue is that road runoff is polluted with heavy metals, which we shouldn’t be putting in our waterways. The faster the water is swept into pipes and into our waterways, the poorer the quality of the receiving water (ie the beaches where we swim.) In permaculture we say, “stop it, spread it, sink it”. This is achievable and desirable in cities; it just needs good green infrastructure design. It’s not ideal to be mixing the heavy metals into soil, either, but it’s better than putting them straight into the sea.

  3. Why does not Auckland encourage the use of rainwater storage tanks in urban areas?
    Deals with roof water (part of the stormwater) which is drinkable and helps reduce the costs of supply of drinking water. We have two 25000 litre tanks, collect rainwater from our roof and never ever (20 years living on the site) run out of freshwater on our rural Franklin property. It is not difficult to build houses with water storage. just put a single 15000+litre concrete tank under the garage floor, and plumb in a pump and you are dealing with significant stormwater flow and water supply. Rural folk have been dealing with this situation for yonks!

    1. I don’t think what you are suggesting would actually significantly reduce the costs of water supply. Basically it would mean during the winter every residence would be happily using tank water and the dams in the Waitakeres and Hunuas would be spilling a lot of water.

      However, during a dry spell in summer many tanks would run dry meaning the water supply infrastructure would still need to be maintained to the level it is today.

      Also I don’t think Ministry of Health support tank water for drinking when it is not necessary. While it is generally safe there are significantly higher rates of water borne gastro illnesses in rural areas compared with urban water supplies.

      I think rainwater tanks plumbed to outside water used for watering gardens, flushing boat motors etc is probably a good idea.

      1. No apparently it doesn’t work like that and installing rainwater tanks could indeed reduce the need for new centralised supplies. This probably isn’t the best paper, but it’s one I could easily find:

        Note that the overall topic is dealing with stormwater, rather than water supply. Water tanks are good at that too – they can be dual use.

        1. Thanks Don, Jezza, Fraggle… for bringing up points I’d been cogitating on for ages. That is a great paper, Fraggle. It explains the mechanisms well, and has changed my mind on a few things. Absolutely we should be putting in rainwater tanks and using it for hot water, laundry and toilets. Both to take the peak off the stormwater load, and to reduce our mains water consumption.

        2. Interesting link, it seems to suggest that it can be beneficial to the amount of storage needed which makes sense, probably doesn’t change the need for pipe capacity, but dams don’t come cheap.

          I think the situation in Auckland is a bit different because the additional capacity is coming from the Waikato and doesn’t involve storage.

    2. That’ll probably add $10k to the price of a house supplied and installed. Is it worth it? If I was building a new house, I’d rather put that money into upgrading insulation and glazing…but each to his own I guess

      1. Indeed, but it becomes more worthwhile if you have been forced to spend money on mitigating stormwater flows from the property and you choose to do it with a water tank. Then you can also get the additional benefit of being able to use the retained water to replace most of your mains water use (which is metered).

          1. That’s what I’d thought too. But read the article Fraggle gave a link for. If you are drawing down the tank for your hot water, laundry and toilet uses, then the tank has capacity for the next rain event.

        1. There would have to be some sort of incentive to use it for the benefit of the overall storm water system. I imagine metering storm water would be controversial given we cant control the amount of rain so it is not a known cost.

          1. The whole metering thing actually becomes a nightmare. Using rainwater reduces mains water use and also potentially reduces the load on the stormwater system. Currently, though, the wastewater charges are calculated from mains water use. In fact you’d be using the wastewater system more than your mains water meter would show. (Opposite of the other situation where using mains water in the garden means you’d be using the wastewater system less than your meter would show.) Now add in some responsible greywater reuse, which might mean your mains water use gets closer to your wastewater load. Or it might not because you might not do it all the time. And the solution isn’t metering wastewater as that’s not cheap.

            Is the solution to go “off grid” 🙂

          2. Agree, it’s not a simple solution. One thing for sure though if people are going to be managing infrastructure (such as tanks) within their properties there needs to be an incentive to use their infrastructure for the benefit of the city.

            For example if someones tank were to get scummy and was no longer drinking water quality they would have three options – pay someone to clean it out, clean it out themselves or close it off and use mains water. Many would just choose to close it off given how little mains water costs.

            Off grid would be ideal, but storing sufficient water to get a family through a a dry summer would be a challenge.

          3. Yes, I can see that. An obvious incentive is a higher cost of mains water, but that would be politically difficult. What were you thinking of?

  4. We fail to learn from the experiences of others. Wellington has realised they have a very vulnerable water supply subject to earthquake risk, so every household has to store 200 litres of roof water for emergencies.
    Auckland’s water supply is vulnerable to failure and old age. Panuku Development has recently found major losses in the mains network round Westhaven for example. The leaks were more than what the boaties used!
    The costs are very low $10k on a $550k+ Auckland house (that is a cheap new one) is nothing……if it is going to make us all have a resilient reliable water supply.
    We have underground well water in Franklin that has excessive nitrogen levels – unsafe for babies.
    Tank water is very safe . Why spend excess on getting rid of it when it is delivered to your roof?

    1. Yes, it seems Auckland came reasonably close to running out of potable water after the recent storms because of the high level of suspended solids in the reservoirs that the treatment system couldn’t cope with. Not a bad idea to have some emergency water storage at people’s homes, in a country that has lots of emergencies.

  5. the stormwater system has two parts. the man made bits and the overland flow paths (which take the excess that the primary system cannot cope with (which depends on when it was built and what people thought at the time)). the secondary network is much larger than the 1st. the secondary bit is required too.

  6. There are a lot more upgrades needed than those specified in the LTP I believe. What is in the LTP is all Council can get budget for.

  7. Further to Heidi’s early comment re permeable ground and groundwater recharge:
    We should note that much of the older development on the Auckland isthmus is located on ground consisting of basalt and highly permeable volcanic deposits. In these areas stormwater disposal is typically through soakage pits (these can typically provide soakage flow in the order of 10 – 50 L/s, which is pretty decent). Soakage in areas where it is available is use for both public infrastructure as well as private development. So there is very little burden on the traditional ‘piped’ infrastructure in those areas, and the groundwater recharge into the basalt is well maintained. Much of these flows end up in places like Western Springs lake.

    In much of the rest of Auckland the groundwater within the true basement rock is controlled by sea level, and some major streams / rivers. Some of the shallow groundwater in north/central/west Auckland is actually confined, perched groundwater that may only persist laterally over some 10s to 100s of square metres, particularly on the ridges (i.e. not necessarily regionally significant).

    Notwithstanding the above, I’m not a groundwater expert, and I’d be fascinated to hear from some hydrogeologists about long-terms trends in regional groundwater levels across Auckland. I know that any developments that dig into, or modify the groundwater regime (e.g. basement for a building) must have a resource consent for taking water. And Auckland Council have been very strict about assessing these affects in the last few years…

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