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Canterbury water use, 2010/11 Waiology Apr 10

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Guest post by James Tricker, Principle Extension Services Officer, Environment Canterbury

There are increasing expectations, both within the Canterbury community and also within a national context, that the relation between water allocation and water use is more strongly understood. The Environment Canterbury Water Use Report presents the information gathered on consented water use in Canterbury between 1 July 2010 and 30 June 2011.

The Canterbury Water Management Strategy sets targets for improved water efficiency and irrigation, as well as targets for better environmental and cultural outcomes resulting from more water in rivers and better water quality. Agriculture and horticulture are the primary uses for water in Canterbury, accounting for around 90% of consented water use.

Within the Canterbury region there were 5,179 consents to take groundwater in the study period. The groundwater allocation for all of these consents amounted to 39,222,849 cubic metres per day, and was taken from 7,022 wells, of which 33.7% were equipped with water measuring devices. The surface water allocation within the region was taken at 1,337 surface water abstraction points, of which 19.7% were equipped with water measuring systems.

Water takes with an abstraction rate of 20 litres per second or more are required to be equipped to measure and report on water use by 10 November 2012. By the end of the 2010/11 water year, of all takes in Canterbury 20 litres per second or more, 43.1% of the groundwater wells were metered and 23.7% of surface water abstraction points were metered. If all water takes, with an abstraction rate 20 litres per second or more, are equipped to measure and report on water use by 10 November 2012, this will account for 97.4% of all daily allocated groundwater, and 99.3% of all daily allocated surface water.

These data showed that 52.4% of the allocated groundwater was used during the 2010/11 water year, although this figure is based on 11.4% of the groundwater takes in the region.

The allocated groundwater volume in the Canterbury region and the proportion of water allocation that was unmetered, metered, and provided information on water use for 2010/11

The allocated groundwater volume in the Canterbury region and the proportion of water allocation that was unmetered, metered, and provided information on water use for 2010/11

The data also show that 49.8% of the allocated surface water was used during the 2010/11 water year, although this figure is based on 7.1% of the surface water takes in the region. Of the 264 metered surface water takes, 95 provided use data that could be used in this report.

The allocated surface water volume in the Canterbury region and the proportion of metered surface water abstraction points (SWAP) that provided information on water use

The allocated surface water volume in the Canterbury region and the proportion of metered surface water abstraction points (SWAP) that provided information on water use

These data highlight the need for consent holders to install water measuring systems and to ensure they are working properly. Having reliable and widespread information about actual use will allow Environment Canterbury to better manage and allocate the huge freshwater resource.

Within the Water Use Report there is an update for each of the Canterbury Water Management Strategy zones on the progress towards installing water measuring devices and actual water use. It is anticipated that this information will be used by the zone committees as they formulate programmes and ultimately will be reflected in river and catchment plans, and Environment Canterbury’s regional land and water management plan.

For more information see:
http://ecan.govt.nz/advice/your-water/water-metering/Pages/water-use-report.aspx

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Clutha River/Mata-Au re-imagined as a public transport system Waiology Apr 03

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By Daniel Collins

Some time ago I came across these maps of US rivers systems depicted as subway routes. They’re nice illustrations of rivers as a connected system of transport corridors, with populated areas as stops along the way. Instead of viewing a map with blue lines in the background and cities brought to the fore, the roles are reversed. They combine hydrology with graphic artistry.

CluthaRiverSystemNow I’ve concocted my own version of these maps using the Clutha River/Mata-Au. This is New Zealand’s 2nd longest river, after the Waikato, but the largest by flow at the coast. The topology of the ‘transport’ network pictured is largely the same as the real river network, with only the larger rivers depicted. I used some artistic license in choosing which rivers to include and how faithfully to follow the rivers’ courses. Population centers and geographical features along the way are represented as stops. Each longitudinal river system is coloured the same, representing specific subway or train lines; the darker they are, typically the greater the flow.

But rivers don’t just move water. They also move eroded rock or sediment, nutrients, pollution, and fish. In the case of fish, this movement is two-way. About 50% of New Zealand’s native fish are diadromous, meaning they migrate between river and sea.

How much of this stuff moves along the rivers depends a lot on the flow. Where there is abundant sediment, its movement downstream is roughly proportional to the river’s flow rate to the power of an exponent greater than one (i.e., Qsediment ~ Qwaterb, where b > 1), which means that the conveyance of sediment down rivers mainly occurs during high flows and floods. The same applies to phosphorus, which typically binds to soil particles to get anywhere. Nitrogen, on the other hand, is more readily dissolved and doesn’t need high flows so much. If all flow stops, so does the transport system; no sediment downstream and no migrating fish. (In fact, not many fish at all, unless they burrow into the ground or climb over to more hospitable locations.) In a way, this all means that the train timetables differ from passenger to passenger, but at least for the Clutha basin you can expect trains to be running non-stop.

If people ask nicely, I’ll make a similar map for the Waikato, but with New Zealand’s size, shape and population distribution there aren’t many options for good system maps.

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The hydro-illogical cycle Waiology Mar 06

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By Daniel Collins

Seen during a presentation by water resources expert Professor Robert Glennon last month.

HydroIllogicalCycle

This says a lot about the costs of complacent water resources planning in a variable climate. The principle here is much like the Latin adage:

Si vis pacem, para bellum – if you wish for peace, prepare for war.

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Canterbury Lysimeter Network: Measuring the hydrologic inputs to aquifers Waiology Jan 30

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By MS Srinivasan

Irrigated agriculture is growing in Canterbury. This growth has resulted in a greater rush for accessing water resources – surface and ground waters – across the region. Since these water resources are finite, limits on their takes are imposed to conserve them and make them available for other uses. However, setting limits on groundwater has remained a challenge. There are more unknowns than knowns. Does groundwater recharge occur uniformly over a year? Does irrigation add to recharge? How much groundwater could be allocated for irrigation sustainably?

To answer these questions, we need to take a closer look at how much water is draining through the ground and recharging the aquifers, as Paul White discussed two weeks ago. In Canterbury, where there is substantial abstraction from groundwater and where groundwater-fed streams and rivers are vitally important, a new initiative has begun to provide some much-needed data.

The Canterbury Lysimeter Network (CLN) is a scientific endeavour to identify how much land-based recharge, from rainfall and irrigation, happens across the Canterbury Plains at daily, monthly, seasonal, and annual time scales.

The CLN was originally an Environment Canterbury initiative, with NIWA, Aqualinc Research and HydroServices brought in to make it happen. Currently, the CLN has four sites spread across the Canterbury Plains, representing a variety of conditions – foothill vs coastal, high vs low rainfall, well-draining vs poorly-draining soils. All sites are under irrigation.

Each site has a set of three drainage lysimeters, and each lysimeter is 700 mm deep and 500 mm in diameter. A drainage lysimeter is a large cylinder, buried vertically in the soil. These lysimeters measure how much water drains through a soil column. The volume of water draining through a lysimeter is a direct expression of recharge of groundwater. The lysimeters are buried with their top at the soil surface. Water that infiltrates through the lysimeters is collected and measured at the bottom.

CLNSites

CLNlysimeters

Using these continuously recording lysimeters, we can find out how much water drains towards aquifers and when. Monthly data from one of the lysimeter sites, below, shows that groundwater recharge is largely occurring in autumn and winter, outside the irrigation season, even if more water falls during the summer.

CLNmonthlydepths

If we look more closely, we can see that it’s the longer or more intense storms that tend to generate large groundwater recharge.

CLNrechargeevents

What’s next? Our data collection has just started. What we have shown here are preliminary results. We are looking to continue this network over the next few years to quantify precipitation and irrigation recharge over time. Data from this network will also be useful in verifying models of recharge and soil moisture developed by NIWA and others, and allowing better management and allocation of groundwater in Canterbury.

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Kinky relationships among Canterbury’s springs Waiology Jan 23

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By Daniel Collins

As Ross mentioned some time ago, one of the frontiers of hydrological research at present is the interface between surface water and groundwater. On the one hand, we need to understand how aquifers are recharged from the surface; on the other, how aquifers in turn discharge water back to the surface. This is important to water resource managers so that they can determine how water use at one location may affect water availability and aquatic ecosystems elsewhere.

One question, particularly relevant to both Canterbury and Hawke’s Bay, is how fluctuations in groundwater levels affect spring flow near the coast. This is actually part of a larger research programme we have looking at the environmental effects of water use.

As part of this research I have been examining streamflow and groundwater data around Lake Ellesmere/Te Waihora, Canterbury. Environment Canterbury has an extensive network of groundwater monitoring wells and streamflow monitoring sites in the area. The wells measure what is known as the piezometric head of an aquifer, derived from the Greek piezein meaning “to press or squeeze”, and which refers to the height that water would rise to if subject to atmospheric pressure. For the top-most aquifer, this height basically means the water table (see this earlier post on groundwater anatomy for more).

IrwellSWGWBy comparing piezometric and streamflow data, we can develop a picture of how fluctuations in groundwater translate into fluctuations in streamflow. In the figure below I’ve chosen just one well (L36/0141) and one stream (Irwell River). The first thing you see is a roughly linear increase in flow with piezometric height, at least on the right. Linear relationships like this are typical of water flowing through a saturated porous medium (see Darcy’s law for more). But where the flow drops to around zero, at a piezometric height of about 68 m above mean sea level, there is a hint that this line bends – a kink in the groundwater-streamflow relationship. In fact, it has to bend because you can’t go lower than zero flow.

This kink indicates a threshold groundwater level that divides streamflow behaviour in two. Above the threshold, streamflow increases roughly in step with groundwater level; below the threshold, there is basically no flow at all, no matter how low the groundwater drops. So if the level in well L36/0141 drops below about 68 m AMSL, Irwell River is likely to go dry.

While in some instances this drying is entirely natural, changes in groundwater recharge (say, due to climate change) and abstraction for irrigation could shift the hydrological regime of the stream to become more ephemeral. It could also mean less water flows into Lake Ellesmere. This is all very important when allocating water while avoiding undue water resource or environmental impacts.

Threshold behaviour like this is actually quite common in hydrology, and can be traced back to the underlying physics of water movement. Having a physical explanation of the interaction between aquifers and streams allows us to make more robust predictions of spring flow, and of the ecological and water resource implications that follow.

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Rainfall recharge to groundwater Waiology Jan 17

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Guest post by Paul White, Senior Groundwater Scientist at GNS Science.

Groundwaters are very important water resources in many New Zealand regions – important because they are used for water supplies (urban and rural) and because they supply flow to many springs, streams, rivers and wetlands. The two major inflows to groundwater are from rainfall and from surface water.

We need to know the rates of recharge to groundwater so we can manage groundwater use. For example, groundwater use must be significantly less than groundwater recharge to ensure that groundwater wells and springs do not go dry.

Groundwater recharge from rainfall is the subject of this post which will cover some concepts, how it is estimated, measured, uncertainty and some relevant New Zealand water management polices.

Groundwater recharge from rainfall occurs as rainfall trickles through the soil into aquifers. However, only a portion of all rainfall actually reaches aquifers as recharge. This is because some rainfall evaporates from the ground, and some rainfall is transpired by plants back into the atmosphere – processes termed evapotranspiration. Groundwater recharge first reaches a shallow aquifer (termed the water table or unconfined aquifer). Then the recharge may discharge from the unconfined aquifer to surface waters or to deeper, confined aquifers. Flow paths in aquifers are typically understood using models of groundwater flow systems including geological models and groundwater flow models.

It is common for rainfall recharge to be the largest source of groundwater recharge. In those circumstances sustainable groundwater allocation policies should ensure that allocation is less than recharge and that actual use is less than allocation, i.e.

R > A > U

where
R = rainfall recharge estimate provided by science, e.g. projects to characterise rainfall recharge and uncertainty undertaken in the Waterscape research programme;
A = allocation of groundwater, which is a policy decision by the groundwater management authority;
U = use of groundwater.

Estimates and measurements of rainfall recharge are very useful for the development of groundwater allocation policies. Regional councils are responsible for policy decisions on groundwater allocation. Central government also has an input to decision-making. For example a National Environmental Standard, proposed by Ministry for the Environment (2008), recommends a default (in lieu of regional policies) maximum groundwater allocation as 35% of groundwater recharge.

Estimates of groundwater recharge from rainfall are often made using computer models that typically consider rainfall, evapotranspiration and soil properties. Measurements of groundwater recharge can be made with lysimeters – this is typically a tube sunk into the ground that encases a soil column. Water flow from the base of the lysimeter column is measured over time. Models of rainfall recharge at the local scale are typically tested against measurements of groundwater recharge at the local scale. Quantifying rainfall recharge at the regional scale involves the use of models and up-scaled measurements from lysimeters.

Rainfall recharge measurements demonstrate significant inflows of rainfall to groundwater. For example, the Canterbury lysimeters measured groundwater recharge in the range 26% (Lincoln) to 37% (Winchmore) of rainfall in the period 1999 – 2000 (White et al. 2003). These results were used to estimate regional rainfall recharge to groundwater in the area between the Waimakariri River and Rakaia River in the range 19.2 to 23.9 m3/s providing a useful indication of groundwater sustainability in comparison with annualised groundwater allocation (approximately 42.6 m3/s) and estimated groundwater use (6.8 m3/s) in the period.

Environment Canterbury established groundwater allocation zones in 2004 and adopted allocation limits based on estimates of land surface recharge (rainfall plus irrigation). Zones in which total allocation exceeded those limits were designated as being fully allocated and referred to as ‘red zones’. The Rakaia-Selwyn groundwater allocation zone has been classified as a ‘red zone’ from the initial adoption of this management policy and Environment Canterbury has recommended decline of further groundwater allocation (e.g. in the Rakaia-Selwyn hearings), reviewed groundwater consents, and placed annual volume limits on groundwater pumping.

This post shows some of the applications rainfall recharge measurements to groundwater resource management and groundwater resource characterisation.

References:

Ministry for the Environment 2008. Proposed National Environmental Standard on Ecological Flows and Water Levels. Discussion Document. 61p.

White, P.A., Hong, Y-S., Murray, D., Scott, D.M. Thorpe, H.R. 2003. Evaluation of regional models of rainfall recharge to groundwater by comparison with lysimeter measurements, Canterbury, New Zealand. Journal of Hydrology (NZ) 42(1), 39-64.

Related Waiology posts:

The low down on groundwater
The importance of groundwater
Where does NZ take its water from?

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Edmond Halley, an underappreciated hydrologist Waiology Jan 09

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By Daniel Collins

I remember in 1986 going to the Beverly-Begg Observatory, in Dunedin, to see Halley’s Comet. At the time, I was a young kid fascinated with astronomy. I had discovered a book on the topic the previous year while on holiday in Central Otago, and soon joined an astronomy club. Through the club, I built a basic telescope (with a lot of help) and dreamed of becoming an astronaut. But this dream was short-lived and that career never eventuated. Instead, I became a hydrologist.

HalleyEdmond Halley (1656-1742), after whom the comet is named, is best known for his role in astronomy. But of his 107 or so published papers, only 36% were on the topic. 34% of them were on geophysics, a few of which covered the water cycle and in turn helped usher in a fundamentally new approach to hydrology.

It’s likely that Halley became interested in the water cycle after reading a book by France’s Edme Mariotte, published in 1686. Mariotte argued, with the support of experimental measurements, that rainfall is sufficient to supply the flow of water in rivers. (You think this is obvious? It wasn’t at the time.) But Halley then wondered: Is evaporation sufficient to supply rainfall?

After a basic lab experiment and a back-of-the-envelope calculation, Halley believed it was indeed sufficient. And in doing so he completed the water cycle: rainfall feeds rivers; rivers flow into the oceans; oceans evaporate into water vapour; and water vapour condenses into rainfall.

The fundamentally new approach to hydrology, then, was the quantitative measurement of the water cycle. Halley shares the honour of ushering in this revolution with Mariotte and a second Frenchman, Pierre Perrault. It arguably remains the most important element of hydrology to this day.

Halley’s sortie into hydrology didn’t last long, though. He published only four papers on the topic, the most important in 1687 and 1691, and never put his other interests on hold, hence his fame in astronomy. Yet among historians of hydrology, Halley’s contributions on the water cycle are very much appreciated.

References:

Dooge J.C.I. 1974. The development of hydrological concepts in Britain and Ireland between 1674 and 1874. Hydrol. Sci. Bull., 19(3): 279-302.

Malin S.R.C. 1993. Edmund Halley – geophysicist. Q. J. R. astr. Soc., 34: 151-155.

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‘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!

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

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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.

References:
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.

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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.

BOOKS

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.

JOURNALS

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.

REPORTS

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.

DATA

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.

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.

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