Pumped storage to deal with Auckland's water problems?

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#2518352 7-Jul-2020 10:12

ANglEAUT:

driller2000: ... The Waikato will get Auckland through for another 20 years or so - ...

Now is the time to do it. Not in 20 years or so. Reasons for this, in no particular order ...

The "... or so ..." part can be a lot shorter than 20 yrs.
people are thinking that after the lvl 4 lockdown period when we had a chance to experience lower traffic, cleaner air, louder birds, now is the time to start green projects
the govt will get a boost for being forward thinking & working hard to achieve those Paris climate goals
it'll take years to build
it'll take years to finetune
great way to stimulate the economy in a "climate friendly" manner

Yep - planning for infrastructure of this type is planned years / decades ahead as part of their Water Strategy - as per the link below:

https://www.watercare.co.nz/CMSPages/GetAzureFile.aspx?path=~%5Cwatercarepublicweb%5Cmedia%5Cwatercare-media-library%5Creports-and-publications%5Cwater_asset_plan_2018.pdf&hash=96e19756f2361b296467f0c1acdaa66c6491b7501b84dda3cdba2bf93b26403c

One of the issues is that the current drought is looking like it will exceed the 1:200 ARI they had planned for:

https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12333927

PolicyGuy

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#2518433 7-Jul-2020 11:24

Fortunately, there's an easy and straightforward solution:

Auckland Watercare may take unlimited quantities of Waikato water, but
Watercare must return not less than 95% of the volume of extracted water to the Waikato as treated wastewater, and
The discharge point for the treated water must be upstream, but not more than 400m upstream, of the extraction point.

😈

Geektastic

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#2518463 7-Jul-2020 12:49

PolicyGuy:

Fortunately, there's an easy and straightforward solution:

Auckland Watercare may take unlimited quantities of Waikato water, but
Watercare must return not less than 95% of the volume of extracted water to the Waikato as treated wastewater, and
The discharge point for the treated water must be upstream, but not more than 400m upstream, of the extraction point.
😈

I remember having a conversation with one of the water engineers at a treatment plant. He said that the discharge from sewerage treatment plants could actually be fed directly into water treatment plants but the optics meant that they could not do it, so they did exactly what you said - they put it in the river upstream and took it out downstream!

wellygary

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#2518488 7-Jul-2020 13:56

To Be Honest, this is not a weather issue... Its a Watercare management issue, sure it hasn't rained a lot, but as noted above Auckland has lots of storage capacity.

This news article below is from July 2019, which noted that the dam levels were around the same as they are now, but Watercare did not have mandatory restrictions and consumption was well over 400 MLD

A year later we are in the same situation and apparently Armageddon is now coming if we don't get more water from the Waikato....

Sounds like last year someone took a really big punt on spring rains and it ended badly,...

4 Jul, 2019 5:36pm

"Water use climbs in Auckland despite Watercare plea to conserve

A plea for Aucklanders to save water appears to have fallen on deaf ears.On Tuesday Watercare asked people to take shorter showers and turn taps off while brushing their teeth to stave off a looming water shortage, after a record dry six months to June.

But the first figures from Watercare's consumption measurements show water use actually increased the next day - jumping from 413 million litres on Tuesday to 417 million litres on Wednesday. However it was lower than the 425 million litres used on Monday.

.... Watercare head of water value Roseline Klein said the organisation was not disappointed about the lack of movement following media coverage."Traditionally, we do see high water demand mid-week. We don't have any mandatory restrictions in place, so we don't expect to see any sudden drops.

"We would however like to raise awareness about the long-term forecast, which is suggesting a dry end to 2019."

Watercare's dams are sitting at just below 60 per cent capacity when normally they would be 84 per cent full at this time of year.

https://www.nzherald.co.nz/aucklander/news/article.cfm?c_id=1503378&objectid=12246745

Scott3

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#2518534 7-Jul-2020 14:16

Yoban:

why not make all new builds/renovations require rain water harvesting solution as part of the project. Sydney did similar a few years ago now.

use that water to feed washing machines/toilets/etc.

edit: added further dets.

The issue is that such tanks contribute relatively little in times of drought, so are a very expensive way to solving the problem of security of supply in dry years.

They are still good from an environmental point of view (less chemicals, & energy from long distance pumping of treated water).

Note that there is currently a boom in demand for rain-water detention tanks. These are required if somebody wants to developed above a certain portion of a site to non-permeable or semi-permeable surfaces. They mitigate the impact of the additional hard surfaces on the storm water system.

Watercare analysis:

Watercare:

Rainwater tanks as a source of water for Auckland

In 2016, Watercare carried out a detailed study to understand the potential benefits of a wide-scale uptake of rainwater tanks for Auckland’s water supply. The aim of this study was to investigate whether or not rainwater tanks could provide the additional water required to meet demand in 2050 (called ‘deficit’), based on Watercare’s two levels of service. These levels of service require us to provide water in a drought with a likelihood of occurring once in a century and to restrict water use no more than once every 20 years.

The work modelled a range of scenarios including the implementation of a programme installing large rainwater tanks on a widespread basis throughout Auckland. This work found that rainwater tanks can provide a significant contribution to household water supplies during a normal rainfall year, but during a drought this benefit reduces so other sources would still be required to meet demand.

Outputs demonstrated that the most favourable scenario would result in tanks supplying up to 16 per cent of the 2050 deficit at the drought level of service and 35 per cent at the peak level of service. The capital cost of implementing such a programme would be four times that of a source able to supply 100 per cent of the forecast demand at both levels of service. The aim of the study was to start quantifying the impact of rainwater tanks – water supply benefits being only one of the benefits they provide.

One of the reason the Waikato is such a desirable source is because it's catchment is diverse, and much of it far from Auckland. It also includes stuff like snow melt. The result is that flow in the Waikato is relatively stable compared to other waterways.

Also the physical distance of much of the catchment from the Hunua's, Waitakeres reduces the chance of a drought in Auckland, concurring with a drought in the Waikato rivers catchments.

wellygary

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#2518541 7-Jul-2020 14:31

Scott3:

One of the reason the Waikato is such a desirable source is because it's catchment is diverse, and much of it far from Auckland. It also includes stuff like snow melt. The result is that flow in the Waikato is relatively stable compared to other waterways.

Also the physical distance of much of the catchment from the Hunua's, Waitakeres reduces the chance of a drought in Auckland, concurring with a drought in the Waikato rivers catchments.

The issues about taking more from the Waikato are political, not hydrological, there is no shortage of water in the Waikato at Mercer,

Waikato Regional Council - River Flow at Mercer

Continuous records began: 1963 to 1987 and 2002 onwards

Catchment area: 13701 square km

Highest recorded river level: 1534 cumecs on July 16th 1998

Lowest recorded river level: 134 cumecs on April 7th 2015

http://rainfallmap.waikatoregion.govt.nz/cgi-bin/hydwebserver.cgi/points/details?point=720&catchment=16

At its lowest flow or 134 Cumecs, that is 11.5 million Cum per day.... Auckland could take its entire 500 MLD (500,000 CuM) and its would still be only 5% of the river flow.... and that is based on its lowest recorded flow... ( if my math is right

Scott3

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#2518542 7-Jul-2020 14:36

PolicyGuy:

Fortunately, there's an easy and straightforward solution:

Auckland Watercare may take unlimited quantities of Waikato water, but
Watercare must return not less than 95% of the volume of extracted water to the Waikato as treated wastewater, and
The discharge point for the treated water must be upstream, but not more than 400m upstream, of the extraction point.
😈

The intake to the watercare waikato treatment plant is currently downstream of treatment plants like Pukete WWTP. As such, being downstream of another WWTP discharge is likely to be of little concern.

The big concern would be the construction costs & operational costs for the pipeline to allow the flow of treated waste water to meet that brief. (Would need to run from Mangere as I doubt the pukekohe has enough flow to meet the breif)

The energy cost alone of pumping the treated waste water (which could otherwise be directly discharged into the harbor from the Mangere WWTP) would be fairly massive.

The question is if adding that water to the Waikato would have have sufficient benefits to outweigh the significant financial & environment cost of doing so.

[edit], As the poster above mentions, the volume watercare wants to take from the waikato is tiny portion of it's overall flow. It's not like they want to drain the river dry or anything.

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wratterus

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#2518543 7-Jul-2020 14:37

I can't fathom why they don't make tanks mandatory on all new builds. Is there actually a legitimate reason for this? Apartments etc sure, that doesn't really work, but for all the developments further out, why on earth not?

Scott3

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#2518544 7-Jul-2020 14:41

wratterus:

I can't fathom why they don't make tanks mandatory on all new builds. Is there actually a legitimate reason for this? Apartments etc sure, that doesn't really work, but for all the developments further out, why on earth not?

Did you read my post timestamped 7-Jul-2020 14:16?

In short it is four times cheaper for watercare to develop additional capacity to deal with droughts, that it would cost for widespread installation of rain water harvesting tank to achieve the same goal..

wratterus

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#2518547 7-Jul-2020 14:48

Sorry I did not - I thought I'd read through this thread but must not have read the second page.

Still think it's a sensible thing, in the big scheme of building a house, adding a tank or two is a very small cost and it certainly adds a big 'buffer' when it's dry. But I guess there has not been enough supply in Auckland for years, so fair point that putting in tanks now is not going to help the current issue.

1101

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#2518551 7-Jul-2020 15:00

Scott3:

Did you read my post timestamped 7-Jul-2020 14:16?

In short it is four times cheaper for watercare to develop additional capacity to deal with droughts, that it would cost for widespread installation of rain water harvesting tank to achieve the same goal..

In some areas , new builds etc have to have stormwater collection tanks .
Many of the new houses in my area have them , huge external tanks. Yet they werent allowed to be used for that homes water supply

Scott3

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#2518553 7-Jul-2020 15:04

wellygary:

To Be Honest, this is not a weather issue... Its a Watercare management issue, sure it hasn't rained a lot, but as noted above Auckland has lots of storage capacity.

This news article below is from July 2019, which noted that the dam levels were around the same as they are now, but Watercare did not have mandatory restrictions and consumption was well over 400 MLD

A year later we are in the same situation and apparently Armageddon is now coming if we don't get more water from the Waikato....

Sounds like last year someone took a really big punt on spring rains and it ended badly,...

...

The "Punt on spring rain" last year didn't go too badly. Storage level got back up to around 90% in November 2019, which is pretty close to the historical average.

Should note that the situation this year is markedly worse than last year. Storage got down into the low 40's this year, compared to roughly 60% last year. In 2019 Auckland had the benefit of unusually high storage levels at the start of the year.

Nothing to prevent two consecutive 1:100 year drought events...

That said I think there is some opportunistic strategy from watercare regarding expediting their 7 year old consent application. There target is to only call for water restrictions 1 year in 20. Now they have decided to go for it, they are taking advantage of the public desire for more capacity.

I think Watercare (like many area's) will need re-analyse it's droughts projections in light of climate change. There is a change that the last two years are not extreme events after all, but are infact the new normal. If that is the case, bringing more supply capacity online is a pressing issue.

Geektastic

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#2518657 7-Jul-2020 17:44

wratterus:

I can't fathom why they don't make tanks mandatory on all new builds. Is there actually a legitimate reason for this? Apartments etc sure, that doesn't really work, but for all the developments further out, why on earth not?

When we subdivided our property, one of the conditions was that the owners of the subdivided parts would never get connected to the town main and so would have to provide their own water supply. They have 40,000 litres of storage on site, fed from the roof.

We have 20,000 litres and when we run out, we just call the local transport company who come in a tanker and fill our tank. Costs about $300 for 15,000 litres. We usually have to do it once annually.

Scott3

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#2518740 7-Jul-2020 20:05

wratterus:

Sorry I did not - I thought I'd read through this thread but must not have read the second page.

Still think it's a sensible thing, in the big scheme of building a house, adding a tank or two is a very small cost and it certainly adds a big 'buffer' when it's dry. But I guess there has not been enough supply in Auckland for years, so fair point that putting in tanks now is not going to help the current issue.

You are most welcome do it, My last office block had rainwater harvesting. It is good environmentally as it avoids the need for chemicals to be used in water treatment, and the energy to pump that water long distance. It is also popular in area's where the town's supply (or bore water) has minerals that stain toilet bowls. I have a family member that has a system for that reason.

Note that it is generally not cost effective. The payback time on the equipment is long, and as with all equipment, maintenance (though rare) is required such as pump replacement. In Auckland, wastewater disposal is more expensive than fresh water. At my place drinking water is $1.555/kL, and waste water disposal is $2.704/kL +$225 a year. Wastewater use is assumed to be 78.5% of freshwater use as to avoid the cost of metering. Rainwater users (that are connected to the wastewater system) either need to pay a mugh higher fixed fee for waste water or have a meter fitted to their rainwater system so water-care can bill them for wastewater based of their fresh water use.

With regards to the cost, yes it is small as a percentage to a new build, but everything adds up.

A 4000L slimline tank is about $2500 (foundation additional), an 4000L underground tank is about $3,200 (earthworks & uplift restraints additional). A nice submersible pump & water switch kit is $2,600 (Change over to mains water in power cut or if out of rain water). A 120L first flush diverter is $600. Non-potable water sticker is $7. More pipe & Plumber labor to run the non-potable system. All up it is likely to cost $8000+ for an above ground system, and even more for a below ground system. Note in much of Auckland, land values are high. 4m^2 of land to put an above ground tank in can be worth in excess of $20,000.

While the above is still small in the scheme of a say a $0.5m build, every extra regulation adds to the total cost, so best to keep them to a minimum. (Especially in a city with housing affordability issues). From a purely economic perspective it is better not to spend that money.

Regarding a big buffer when it is dry. The buffer is not actually that big. When the system is stressed in a summer drought, the majority of rain water harvesting tanks will be empty and the systems fallen over to using feeding potable water into toilets etc.

As such the peak water treatment capacity water-care would need to design for is largely unchanged despite the presence of the tanks, so not much capital cost would be saved at watercare's end.

1101:

In some areas , new builds etc have to have stormwater collection tanks .
Many of the new houses in my area have them , huge external tanks. Yet they werent allowed to be used for that homes water supply

They are storm-water detention tanks.

In short they collect rain water via a fat pipe, and discharge it via a very skinny pipe. This provides a buffer reducing the peak flow into the storm water system.

Essentially spreading the water captured in say minutes of torrential rain over several hours, preventing the storm-water system from being overloaded.

They are often used as an option to get around maximum hard surface percentages on sites when they are being developed (lawn, vegetation etc has the same affect detention effect).

For them to work as designed they can't be kept full, and need to be allowed to drain such that they have the required buffer capacity for the next heavy rain event.

It is possible to have a dual purpose tank. Tank would need to be specified say 50% bigger, and the skinny discharge pipe would be put 1/3 of the way up the tank. A pumped system could use the harvested rainwater, while the top 2/3 of the tank is used for rainwater detention (once the bottom third is filled).

It appears that the developer did not spring for the extra cost of the dual purpose system.

Note that it is generally recommended to only use untreated rain water for non-potable uses in urban area's. (Toilet flushing, labeled outdoor taps, and laundry)

neb

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#2518744 7-Jul-2020 20:09

wratterus:
I can't fathom why they don't make tanks mandatory on all new builds. Is there actually a legitimate reason for this?

Where would you put them? Looked at this for the Casa de Cowboy redo and there's literally nowhere where we could put a tank of any reasonable size. In fact for most people on less-than-quarter-acre sections there's nowhere to put it without giving up a significant chunk of your garden and/or light/view/whatever.

This is another one of those "why doesn't everyone bike to work" solutions that help derail or stall infrastructure improvement projects for years, sigh.

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