Archive 2011

‘Twas the post before Christmas: 2011 in review Waiology Dec 19

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By Daniel Collins

‘Twas the post before Christmas, when all through the ‘sphere
Bloggers reflected on happ’nings this year.
Here at Waiology we’ll do so too.
Two thousand eleven: The year in review.

It started in June with a mission to share
The science of water flows from here and there.
It’s part of our programme, with MSI dough,
To chart and to model the Waterscape’s flow

3000 visits and thirty posts hence
Much have we offered to help you make sense
Of the wonderful watery world that we boast
So gather round all as I recap our posts!

How much freshwater do we get each year?
More than enough to submerge our two ears.
But if you look closely you’ll certainly see
That this amount varies ‘tween windward and lee.

The variability doesn’t stop here
You also will see it between year and year
And if you wait long enough data will show
That even ‘cross decades our streams change in flow.

Looking ahead as temperatures rise
And more or less rainfall descends from the skies
Kaitaia’s river flow’s likely to fall
But how could we know the future at all?

To understand this is to understand science
Building models of nature with healthy reliance
On data you gather, like snow in the alps
Or snow in your yard; really, everything helps.

And how much freshwater may we take and use?
2% overall, eight do some choose.
This we take mainly from land surface sources
From streams and from lakes and from fluvial courses.

Some of this water we save up for later
Storing in dams when rains they are fainter.
But reservoirs don’t give you gains without loss
For somewhere downstream you’ll have shifted a cost.

And under the ground, where aquifers lie,
The much-valued groundwater flows by and by.
The part of the cycle that moves e’er so slow
Sneaking through fractures and pores down below.

But back to the surface, our focus moves higher,
To roots and to leaves and to water transpired.
This water is often embodied in crops
Exported to markets and sold in your shops.

Thus water has value, a means to an end,
But not so financial, as many contend.
Rivers do much more than normally thought,
By offering services that can’t be bought.

With that, my dear readers, I end this review.
So look forward to next year as we write for you
On New Zealand’s freshwaters, and shed much more light.
Happy Christmas to all, and to all a good-night!

Water footprints – What do they mean for us in New Zealand? Waiology Dec 12


Guest post by Dr Sarah McLaren, Associate Professor at Massey University and Director of the NZLCM Centre. This article originally appeared in the Summer 2011 (December) issue of IrrigationNZ News.

  • Have you heard that the water footprint of 1 kg beef is 15,500 litres, and of 1 kg cheese is 5,000 litres?

  • Did you know that Unilever has set itself a target of halving consumer use of water associated with its products by 2020?
  • Or that Walmart is in the process of asking all its 10,000 suppliers to provide information on total water use in their facilities, and their water use reduction targets?

These activities all reflect an increasing concern about the limited availability of freshwater for use in economic activities. Although there is plenty of water in the world, only 2.5% of it is freshwater — and most of this freshwater is stored as glaciers or deep groundwater. Therefore only a small proportion is available for use in human economic activities and by ecosystems. This freshwater becomes available to us via precipitation, and its collection in rivers and lakesa. The increasing demand for this water is a result of population growth, economic development, changes in lifestyles (mainly related to increasing demand for certain agricultural products), and climate changeb.

Much of the media coverage of this issue has focused on calculations of the virtual water content of different products. According to this approach, pioneered by the Water Footprint Network (WFN), volumetric water use at the different life cycle stages of a product is added together to give a total volumetric result for water used by a product. For example, the volumetric water use associated with a merino jumper would be the total of the water used for irrigation on a merino farm, washing and dyeing the wool, and washing by the consumer throughout the jumper’s lifetime (plus water use in associated activities such as electricity generation and fertiliser production).

However, there is a problem with this approach. Assessment of water use, and its environmental significance, is complicated by the fact that the significance of water use depends upon where water is extracted and used. Most people assume that the significance of using one litre water in central Africa is quite different from using one litre water in New Zealand — at least from an environmental perspective. But how can this difference be represented when comparing water use by alternative products and processes?

Water stress index for different regions of the world

Water stress index for different regions of the world c

This type of question has led to recent interest in water footprinting using a Life Cycle Assessment (LCA) framework. LCA is a technique for assessing the environmental impacts of products, processes and activities along their life cycles from extraction of raw materials, through processing, manufacture, distribution, use and on to final waste management. According to this approach, the environmental significance of water use may depend upon factors such as: water scarcity at the location where water is withdrawn from a water body; whether water is rainwater, surface water in a river or lake, or fossil water located in an underground aquifer; and whether water use ‘counts’ when the water is returned to the location of withdrawal within a short time period. Degradation of water due to pollution is also relevant. These types of issues are currently being addressed by the International Organisation for Standardisation (ISO) which has set up a Working Group to produce a standard (ISO 14046) on ‘Water Footprint: Requirements and Guidelines.’ Interested organisations in New Zealand are invited to become members of the International Review Group (IRG) that discusses and submits comments to this ISO Working Group; contact Sarah McLaren for more details.

Does any of this matter for New Zealand? The answer is yes for two main reasons: (1) we live in a globalised economy with a ‘virtual water trade’ of about 1000 km3/yeara, and so water shortages elsewhere in the world can potentially be compensated by water used in production processes in New Zealand where products are then exported, and (2) we can position our exported products for competitive advantage by measuring their water footprints, driving improvements, and demonstrating their water footprint credentials. The five partners in the New Zealand Life Cycle Management Centre (Massey University, AgResearch, Landcare Research, Plant and Food Research, and Scion Research) have all worked in this area and are able to assist with measuring and reducing the water footprints of our exported products.

a Oki, T., & Kanae, S. (2006). Global hydrological cycles and world water resources. Science, 313, 1068-1071.
b UNESCO-WWAP (2009). The United Nations world water development report 3: Water in a changing world. Paris, France: The United Nations Educational, Scientific and Cultural Organization.
c Pfister, S., A. Koehler, & Hellweg, S. (2009). Assessing the environmental impacts of freshwater consumption in LCA. Environmental Science & Technology, 43(11), 4098-4104.

Where to get information on NZ hydrology Waiology Dec 08

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By Daniel Collins

While we’re building up Waiology to be a useful reference for those of you who are interested in New Zealand’s hydrology and freshwaters, I thought it would also be good to mention some other useful resources available.


Freshwaters of New Zealand. Edited by Jon Harding, Paul Mosley, Charles Pearson and Brian Sorrell. Jointly published in 2004 by the NZ Hydrological Society and the NZ Limnological Society. Forty-six chapters by New Zealand experts on topics ranging from precipitation to lacustrine food webs — an excellent reference.

Groundwaters of New Zealand. Edited by Michael Rosen and Paul While. Published in 2001 by the NZ Hydrological Society.

Floods and Droughts. Edited by Paul Mosley and Charles Pearson. Published in 1997 by the NZ Hydrological Society.


Journal of Hydrology (New Zealand). Published biannually by the NZ Hydrological Society. Includes research articles predominantly by NZ scientists. Articles become open-access when 4 or so years old.

NZ Journal of Marine and Freshwater Research. Published four times a year by the Royal Society of NZ. Includes research articles predominantly by NZ scientists. Open-access content from 1994-2006.


Water Physical Stock Account: 1995—2010. Prepared by NIWA for Statistics NZ, 2011. Provides information on NZ’s national and regional water balance.

Update of Water Allocation Data and Estimate of Actual Water Use of Consented Takes 2009—10. Prepared by Aqualinc Research Ltd for the Ministry for the Environment in 2010.


Regional council hydrometric data collections. Each regional council and unitary authority has its own set of monitoring sites and archives of data: climatic, river flow, groundwater, and lake level.

Environmental Data Explorer NZ (EDENZ). An online collection of data including measured river flow and climatic conditions are particular sites. Provided by NIWA.

Water Resources Explorer NZ (WRENZ). An online interactive map of rivers, hydrological stations, and estimates of river flow, sediment yield and water quality around the country. Provided by NIWA. [Ed (23/4/2015): This service has been discontinued. A partial replacement (flood frequencies in small basins) may be found here: NIWA Stream Explorer

MetService. Weather forecasts around New Zealand.

Seasonal Climate Outlook. NIWA’s seasonal forecasts of temperature, precipitation, soil moisture and river flow around the country.

Of course, there are many more reports from the various CRIs (NIWA, GNS, Landcare Research), regional councils or unitary authorities, and central government agencies (MFE, MAF), but I’ll leave it there for now. If there are some resources you’d like to recommend, please leave a comment.

More on climatic shifts and river flows Waiology Dec 02

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By Daniel Collins

For those with an interest in how decadal shifts in climate affect our rivers, as Ross wrote about previously about the IPO, NIWA has a press release on the same work:

In 2000, the IPO changed back to the negative phase (as for 1945-77). ‘The whole of South Island is drier now. If you had to make a guess about the coming 10 years, expect a slightly drier South Island. It certainly affects Canterbury and has implications for the design of irrigation and hydro power schemes,’ says Dr Woods.

Ross will be presenting his work on Wednesday afternoon at the HydroSoc conference at Te Papa.

Hydrologists to flood into Wellington for annual conference Waiology Dec 01

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By Daniel Collins

hydrosocIf you notice groups of people in Wellington next week using such vernacular as ‘discharge’, ‘piezometric’ or ‘A block’, then they’re probably attending the NZ Hydrological Society’s conference at Te Papa. It’s the society’s 50th conference, and many of the talks will be on the history of hydrology in New Zealand.

If you’re there, tell us how awesome Waiology is, and give us some feedback!

For my part, I’m giving two talks and presenting one poster. (Yes, I’m a masochist, but I do like to get the science out as you might have noticed.) Fellow Waiologist, Ross Woods, is giving a keynote address on his journey as a hydrologist, having won the Society’s Outstanding Achievement Award last year. He’s also giving a regular talk on our Waterscape programme and the decadal variations of river flow. Over a dozen other NIWA scientists will also be giving talks and posters.

My first talk is on the history of terrestrial ecohydrological research in New Zealand — where hydrology meets plant physiology and ecology. This has been a fascination of mine for years. I will be giving a few vignettes of the research from across the scientific fields, but because I am taking an historical approach, I will also describe the social context of this research. There’ll even be a couple of controversies.

The second talk will be on the hydrological effects of climate change in New Zealand. While it’s easy to find information on how climate change may affect how weather, what is arguably more important to most of us is how climate change may affect our freshwater resources and ecosystems. So I will be presenting a review of research to date. A peer-reviewed review article is also in the works, but it will likely be many months away.

The third presentation — the poster — looks at the relationships between groundwater levels (specifically, piezometric heads) and stream flows around Te Waihora/Lake Ellesmere, Canterbury. The novel development in this piece of work is a physically plausible model that links regional groundwater conditions to local surface water conditions. I also offer advice on how to set up observation networks in order to get the necessary data to create such a model.

I’ll cover each of these presentations more fully on Waiology at some later stage, so if you’re not in the conference audience then stay tuned.

Where does NZ take its water from? Waiology Nov 28


By Daniel Collins

I mentioned previously how much water we are allowed to use in NZ. The amount varies markedly from region to region, and is growing over time, with Canterbury and Otago accounting for well over half of the consumptive takes (excluding the Manapouri hydro scheme). But seeing as Kiwis seem to know less about our aquifers than our rivers, I’d like to turn now to the issue of where we can take our water from — rivers, lakes, aquifers or reservoirs (or storage lakes).


About two thirds of the water NZers are allowed to take is from surface water — rivers and lakes. This is for all non-hydro schemes and other non-consumptive uses; the data come from a 2010 report from Aqualinc Research for MfE. About a third comes from groundwater. Five percent comes from reservoirs, which are largely fed by rivers.

Looking across New Zealand, we see that the relative importance of surface water, groundwater and reservoirs differs among regions. In Otago, surface waters are relied upon for 84% of the allocated water supplies; in Auckland, it’s 4%. In Hawke’s Bay, groundwater accounts for 74%; in Otago and Taranaki it’s 7%. And in Auckland, reservoirs account for 74%; in Waikato and Manawatu-Wanganui it’s zero.

So why do these proportions vary so much?

There are three key factors behind this: whether there’s enough water in the rivers; whether there are accessible and productive aquifers; and how important reliability of supply is to the water user.

Otago, for example, only has a smattering of significant aquifers, so they get most of their water from rivers. Hawke’s Bay, Southland and Tasman each have productive aquifer systems available. In the Auckland region, where over a third of NZ’s population needs to be provided with a reliable supply of drinking water, they turn to reservoirs and more recently to a reliable supply from the Waikato River via a tunnel. On the Canterbury plains, water from rivers and aquifers are both readily accessible and both highly used, though it is typically easier and cheaper to take water from rivers, even if the reliability of supply isn’t as high. You can see maps of NZ’s key aquifer systems here.

So we can see, yet again, that the physical environment has a huge effect on the availability and reliability of water supply in New Zealand. In posts to come, we’ll see what exactly this water is used for.

Recent NZ research from climate change to tussock | Journal of Hydrology (NZ): 50(2) Waiology Nov 24

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By Daniel Collins

For those of you who don’t receive New Zealand’s own hydrology journal, or for those who want to save some time, here’s an overview of this month’s edition — the journal’s 100th.

1. Barry Fahey (Landcare Research) et al. use their water balance model, WATYIELD, to assess whether tussock in Otago’s uplands can really intercept appreciable amounts of fog, turning it into runoff. Their conclusion: no. This is actually one in a long line of studies that have considered the same question, a question that has turned out to be a veritable controversy, with different papers firmly coming down on opposing sides.

2. Suzanne Poyck (formerly NIWA) et al. use their catchment hydrology model, TopNet, to forecast the impacts of climate change on the Clutha River basin, with a particular focus on changes to snow. Annual precipitation is forecast to increase, as is streamflow (mainly in winter and spring), while the role of snow diminishes.

3. Michael Stewart (Aquifer Dynamics and GNS Science) et al. use isotopic analysis to identify the sources and ages of nitrate in the Waimea Plains, near Nelson. Two kinds of contamination were identified: diffuse contamination from inorganic fertilizers and manure, and point source contamination from a large piggery (now closed). This has been a problem because Ministry of Health guidelines for drinking water have been exceeded for some years. And while input of nitrogen has been decreasing, best practices and nutrient budgeting are still encouraged.

4. Luke Sutherland-Stacey (University of Auckland) et al. test a mobile rain radar device in Tokoroa, central North Island, during 2008 and 2009. Their X-band radar system was able to make observations with high spatial (~100 m) and temporal (~15 s) resolutions, which helps resolve rainfall patterns during convective weather systems at least compared with existing rainfall monitoring systems. But as accuracy declined with distance, particularly over 15 km, the device is best suited for small study areas.

5. Tim Kerr (NIWA) et al. develop a new map of mean annual precipitation for the Lake Pukaki catchment, which includes Aoraki/Mt Cook, using data from 1971-2000. The catchment average is 3.4 m/yr, with over 15 m/yr falling in the north west of the catchment.

6. Clare Sims (BECA) et al. study the dynamics of snowmelt in the Pisa Range, Central Otago. Their focus was how the meteorological conditions that develop over fault-block mountain ranges in the region affect snowmelt. They showed that net radiation (basically sunlight) was slightly more important than sensible heat flux (basically wind), resulting in a sustained pulse of meltwater. They went on to suggest that changes in winter snow could have a significant effect on summer river flows.

Sea level fall and floods due to massive evaporation Waiology Nov 21

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By Daniel Collins

On average, about 87% of the Earth’s evaporation takes place over the oceans. 9% of this water then makes it over the land and falls as precipitation, the rest falls back to the sea. But this is just an average. Over much of 2010, there was so much evaporation from the oceans that the global average sea level actually dropped 6 mm.


With more water circulating in the atmosphere, some parts of the planet received much heavier rainfalls, triggering the floods in Australia, Pakistan and Venezuela. This extra water can be detected by its effect on the gravitational pull around the Earth, as measured by GRACE (Gravity Recovery and Climate Experiment). (GRACE figure courtesy of NASA/JPL-Caltech.)


These changes were associated with a dramatic shift from El Nino to La Nina conditions. For New Zealand, La Nina conditions tend to bring more rain to the north-east of the North Island and less to the south and south-west of the South Island, but we’ll talk about this more in the future.

Of course, as the extra water on the land eventually flows to the sea, we can expect a similarly abrupt rise in sea level, on top of the trend associated with global warming.

(H/T: Hot Topic)

Long-term fluctuations in river flow conditions linked to the Interdecadal Pacific Oscillation Waiology Nov 17


By Ross Woods

Within the Waterscape research programme, we’re doing some case studies on the potential effects of climate change on water resources, in water-limited parts of New Zealand, such as Canterbury and Hawkes Bay. In effect, we’re asking how these water resources might look in the future. In another post, I’ll look into the results of a couple of the climate change studies we’ve done that relate to water resources in Canterbury, as part of wider team efforts.

Before thinking about climate change, it’s a good idea to understand the variations in water resources that are happening already. The weather is different from one year to the next, and one decade to the next, so water resources also vary on these various time scales. Understanding those variations will let us put any potential future changes in the context of the changes that water managers already deal with.

Here I’ll look specifically at decadal-scale variability in river flows. This is a peek at some new work that isn’t published yet — I’ll be presenting a fuller story at the Hydrological Society’s Symposium in Wellington in December. Understanding decadal variability in streamflow can be critical for the design of water infrastructure for hydropower, irrigation and water supply. Without this understanding, it is difficult to use river flow data from the past as a guide to the future.

IPO? The Interdecadal Pacific Oscillation (IPO) is one of the causes of decadal-scale variability in New Zealand streamflow statistics, for some parts of New Zealand. The IPO is a cyclical change in the Pacific ocean-atmosphere system. A characteristic circulation pattern predominates for a 20-30 year period, and then the system changes to having a different characteristic circulation pattern. These patterns are known as phases of the IPO; the IPO was in a negative phase from 1945-77 and in a positive phase from 1978-99. During the positive phase, El Nino events and westerly winds are more frequent than usual, and rainfall in the west and south of the South Island is higher than usual. The opposite applies during the negative phase.

Does the IPO affect river flows? McKerchar and Henderson (2003) (PDF) showed that there was a significant difference between streamflow statistics for the periods 1945-77 and 1978-99, especially in the west and south of the South Island. For example, the mean flow in the Clutha River at Balclutha over 1978-99 was 14% larger than during 1945-77.

So why look at it again? In 2000, the IPO changed back to the negative phase (i.e., like 1945-78), though the magnitude of the recent IPO is closer to zero (neutral). So now I’m asking, in the ten years since 2000, have the river flow statistics changed back to the values they had for the negative phase (1945-77)?

Analysis. I looked at long river flow records for 35 sites across New Zealand. I calculated annual values of the mean flow, maximum flow, and 7-day low flow. The figure below shows an example of the results, for floods, mean flows and low flows in the Buller River at Te Kuha, on the West Coast of the South Island. The mean annual flood over the period 2000-09 was 17% lower than the corresponding value for 1978-99. Mean flows and mean annual low flows were also lower in 2000-09 than in 1978-99, by about 10%.

Results for 15 other rivers in the South Island also showed this general result: that all of these three flow statistics were lower in 2000-09 than they had been in 1978-99. Not all the differences were statistically significant, but in almost every case the flows for 2000-09 were lower than for 1978-99. Results for North Island rivers were more mixed, and didn’t display a consistent pattern of change. I’ll need to investigate more to understand the reasons behind both results.

Results. Flow data from 2000 onwards in the South Island support the notion that flows in those rivers are lower during the negative phase of the IPO. The data suggest that the post-2000 reduction in flow has been of the order 10%. We don’t know how long the IPO will remain negative for, but previous IPO phases have lasted 20-30 years, so the current negative phase may last another 10-20 years. Similarly, we don’t know whether the observed correlation between flow and IPO will continue.

Implications. If we look at this from a water resource manager’s point of view, it’s probably a good idea to treat South Island flow data from the period 1978-99 as being slightly higher than the long-term average. So when making forecasts of future water resources for planning purposes, it’s sensible to make allowance for the possibility that flows for the next 10-20 years could be lower than the long-term average. Towards the end of that time horizon (i.e. 2020-2030), we must begin to consider the potential effects of climate change, which is expected to increase precipitation in the South and West of the South Island. But that’s another story …

The importance of groundwater Waiology Nov 14


By Tiejun Wang

Groundwater is one of the most important natural resources in New Zealand, which by one estimate accounts for about 80% of the water present at any one time across and beneath the country. According to a 2010 review of water allocation [2], the number of groundwater consents accounts for 68% of all national consents. In terms of the allocated volume for consumptive use, groundwater allocation is about 12% (3.3×109 m3/year; equivalent to 6% of the water in Lake Taupo) of the total annual allocation (26.9×109 m3/year). Over the last decade, the demands for groundwater have increased dramatically in New Zealand, which is manifested in the volume of groundwater allocated and the percentage of groundwater allocation in the total allocation [2]. Most of the groundwater resources have been allocated to irrigation purposes in NZ. For example, in the Canterbury region alone, 55% of the agricultural lands are irrigated by groundwater.

tsingtao_logoCompared to surface water, groundwater possesses some unique features. For example, groundwater is typically a more reliable resource, particularly in dry regions, and sometime has higher quality (e.g., temperature and minerals). My hometown (Qing Dao) is famous among other things for its beer (Tsingtao beer). The beer is made of groundwater that is brought up to the surface by springs that are rich in minerals. In fact, it’s the number one branded consumer product exported from China, which you can occasionally find here in NZ. However, the growing demand for groundwater resources in China has raised concerns about the sustainability of both agriculture and the economy. The overdraft of groundwater not only has economic consequences, but also may pose serious threats to the environment.

To start off, dropping groundwater tables, for example due to pumping, can significantly increase the cost of irrigation because the energy required to bring groundwater up to the surface increases with the depth to the groundwater. Secondly, there are numerous cases regarding the adverse impacts of overdraft of groundwater on the environment, which we should learn from. To name one example, the excessive pumping of groundwater, particularly in arid and semi-arid regions, can produce massive depression cones (e.g., in the North China Plain, more than 20 depression cones stretch over 50,000 km2), which can cause the Earth’s surface to subside just like earthquakes (most of the time it is an irreversible process!!), and intensify groundwater contamination.

The water problems that New Zealand is facing right now require us as hydrologists to take immediate actions on how to sustainably manage our water resources. As Ross mentioned earlier, groundwater and surface water are tightly coupled. Therefore, in order to more effectively manage water resources, hydrologists from different sub-disciplines (e.g., surface water hydrology, groundwater hydrology, and ecohydrology) should work together to tackle the problems. This is one of the major goals for the Waterscape project.

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