Posts Tagged Water allocation

New Zealand captures over 10% of its freshwater resource Waiology Feb 12


By Daniel Collins

RakaiaRiverFollowing a recent Timaru Herald article (3 February, 2015), I learned of a claim that 98% of NZ’s rainfall is left to flow out to sea, and that we only capture the other 2%.

‘‘This country doesn’t have a water shortage issue. What it has is a water storage issue. We capture a mere 2 per cent of our country’s total rainfall, the rest pours out to sea!’’ – Waitaki MP Jacqui Dean’s office.

‘‘It is wasteful that we only capture around 2 per cent of rainfall in New Zealand, with the rest roaring out to sea.’’ – Minister for Primary Industries Nathan Guy, in a speech to Crown Irrigation Investment Ltd.

These statements aren’t quite right, but because the topic is of vital importance, it is worth commenting on what is actually happening. Some of the rain evaporates before it can reach the sea or get used by us, and the “2%” isn’t actually how much we capture anyway.

Evaporation is an important component of the water cycle

The amount of water that falls on New Zealand during an average year is 610,000 million m3. That’s 10 times the volume of Lake Taupo. Roughly 20%[1] of this evaporates before reaching the coast, leaving us with a freshwater resource flowing down our rivers and through our aquifers of 490,000 million m3 per year.

Of this freshwater flow, 27,000 million m3 was consented for abstraction for consumptive uses over 2009-2010. This equates to 5.4% of the total freshwater resource. Most of this is for the Manapouri hydropower scheme, which diverts water from Lake Manapouri through a mountain to Doubtful Sound. Because we typically think of hydropower schemes as “non-consumptive”, removing this allocation from the total leaves 11,000 million m3, or 2.2% of the total freshwater resource. If we were to express this value in terms of national rainfall, it would be 1.8%, the difference relating to water lost to evaporation.

It would make sense to round both the 2.2% and 1.8% to 2%. After all, they are estimates and the actual values vary from year to year, but that is a slippery slope to confusion. Because councils grant consents to take terrestrial freshwater not rain water, 2.2% is more meaningful. In either case, this quantity is apparently the source of the “2%” used in the above quotes.

So by saying that all the rain water that we don’t capture flows to the sea, we neglect the rainfall that evaporates before it can be considered a ‘water resource’.

We capture much more than 2% of the water resource

As explained above, 2.2% of New Zealand’s freshwater supply was allocated for consumptive[2] uses in 2009-2010, excluding the Manapouri scheme. This is not the amount of actual water used or actual water captured, it’s a legal entitlement subject to consent conditions. A very rough estimate of actual use for non-hydropower users is about 50% of the total allocation, but as data are coming in now we should get a more accurate estimate this year or the next.

But we shouldn’t actually exclude Manapouri from this calculation. There is little difference between the hydrological effect of the Manapouri scheme and the hydrological effects of municipal and industrial water use, even if it’s conceptually convenient to separate them. Most if not all of the water used in these different applications is returned as liquid water to a river, lake, or the coast. Even a small portion of irrigation and stock water will likewise return to a water body before flowing to the sea.

It is thus more accurate to say that, as of 2009-2010, we were allowed to abstract 5.4% of the nation’s freshwater supply.

Lastly, there is a difference between “abstract” and “capture”. To abstract water, it must be captured, but water that is impounded in run-of-river dams is also captured while not abstracted, and so is a portion of the rainfall that falls directly on crops.

The water captured by run-of-river dams is substantial – the Clyde Dam, the various dams along the Waitaki and the Waikato, etc – even if you avoid double-counting water that is impounded multiple times. While the exact numbers aren’t immediately available, a quick estimate puts the amount of freshwater that we were consented to capture in 2009-2010, and did actually capture one way or another, well above 10% of the country’s average annual freshwater supply.

Direct rainfall can also not be overlooked. All crops get a free supply of water this way – “green water” in water footprinting parlance. Any irrigation, which is part of our “blue water” footprint, is added on top of this. How much this captured green water amounts to has not been calculated, and therefore we cannot say with much certainty at all how much rain water we capture.

We use even more

The last point to make is that we use water in more ways than are encapsulated above, so it would be inaccurate to say that any uncaptured water is necessarily wasted. In addition to water used for hydropower, irrigation, stock watering, municipal supply, and industrial operations (all consentable volumes), we also use water for recreation (swimming, kayaking), for provision of habitat for fish and mahinga kai, as a conveyor belt for sediment that we extract, and also as a spiritual, cultural, or aesthetic resource. All of these are what we term “ecosystem services” – goods or services provided to us by the water, whether yielding economic, societal, or cultural benefit.

By the numbers

  • 610,000 million m3 of water falls on New Zealand in an average year.
  • At least 20% of this evaporates.
  • This leaves 490,000 million m3 of freshwater to flow via rivers or aquifers to the coast.
  • In 2009-2010, 26,000 million m3 of freshwater was allocated for abstraction, equating to 5.4% of the freshwater supply, most of this would have been used.
  • In 2009-2010, over 10% of New Zealand’s freshwater supply was captured for one use or another.

[1] This may be on the low side, but it is very difficult to be sure.
[2] “Consumptive” water uses are those that move water from one point in a water body and deliver it somewhere else. Some or all of this water may return to the original water body. “Non-consumptive” water uses simply interrupt the flow of water along its normal course.

Dr Daniel Collins is a hydrologist at NIWA.

The legitimate use of science in managing water Waiology Mar 18

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By Ian MacKenzie

WaterGovernanceWaiology2013The Government has just released the discussion paper “Freshwater Reform 2013 and beyond“. It has three main recommendations: establish a national objectives framework, allow for collaborative community planning, and manage within quality and quantity limits using best industry practices.

All three of these need sound information, preferably undisputed, and based on sound interpretation of the underlying science.

Interestingly, we are not in a position yet to implement a national objectives framework as we need more information on the values and water body types (p29 of the report).

Similarly, for communities to develop their own water plans, they will need a huge amount of information. In Canterbury, where collaborative governance is being pioneered through “zone committees“, support staff are struggling to provide the information required to enable sound decision-making. This is especially evident in the areas of economic and social consequence, which highlights how little information our regional councils have had to go on. A little frightening really.

In terms of managing for quantity and quality, farmers have known for a while that all is not well with the information being used to make decisions. This is all too obvious when members of the same consultancy argue both sides of a dispute over water availability for allocation. Or when the regional authority sets allocation limits assuming that layered aquifer systems are linked, but then requires a consent applicant to conduct aquifer tests for the degree of linkage.

So where to?

The Government has gathered many of our top water scientists into the National Objectives Framework with undisputed parameters. Some subjective judgements will be required to set values for thresholds between bands of water quality, but given the clear intent of the National Policy Statement for Freshwater Management, that does not have to be too contentious.

But providing information around managing to water quality and quantity limits has further to go.

The Government’s “Freshwater reform 2013 and beyond” discussion paper identifies a need to strengthen our science, research and information around water quality, and that industry, scientific institutions, councils and Government need to work together to develop good management practice (GMP) toolkits.

That is good stuff because too many people believe GMP is unable to meet community water quality aspirations. I find this counter intuitive for two reasons. Firstly, in most cases communities have not decided on their water quality aspirations in any detail. Some regional authorities have done this on their behalf but with limited consultation and even less supporting information. Secondly, no one has a clear idea of what GMP is, let alone what it could deliver.

This is where the agricultural industry bodies, our best farmers, and our smart scientists need to be working together: to develop a template for GMP. It would provide advice on what the farmer should or shouldn’t be doing.This could also be linked to financial benefits derived from more efficient resource use, which should alone provide motivation for farmers to use this technology. Industry requirements to comply with GMP as part of that industry’s quality assurance system could be used to provide further motivation.

Furthermore, Industry Audited Self Management could then be used to measure and report the modelled improvements (say 37% reduction in N loss, 80% reduction in sediment loss, 95% reduction in faecal contamination in 10 years). The regional authorities could measure how that translates into improved water quality, and then and only then determine whether GMP was making sufficient progress.

What we do know is that we all want better water quality. It is clear to me, and apparently also the Government, that GMP is the best way forward. Let’s stop arguing over that. Let’s work together and get on and articulate what it is we expect from GMP, what technologies we can use and what science we need, and start delivering better quality water.

Ian MacKenzie is Federated Farmers Grain & Seed chairperson and is an arable and dairy farmer in Canterbury.

Water governance – we’re getting into overdraft Waiology Mar 06


By Andrew Fenemor

WaterGovernanceWaiology2013Like the challenge of balancing the household budget, we NZers are finding that despite being a ‘pluvial country’ we’re reaching allocation limits in many of our catchments.

Looking back, 100+ years ago exploitation of water resources focused firstly on rivers. Then water use especially for irrigation and urban supplies moved to groundwater takes. Now as pumping from our aquifers starts to deplete river flows and aquifer storage too much, we are seeing greater interest in water storage. Case in point, the Government’s Irrigation Acceleration Fund is supporting feasibility assessments for large schemes in Canterbury, Otago, Hawkes Bay, Wairarapa and Tasman, most involving new dams.

The trouble is, it’s a tough job for regional councils to set catchment limits in their regional plans (PDF) before the symptoms of excess appear. That’s not surprising, given the sizable investments in catchment science needed, the long time frames required to understand the inherent variability in water fluxes, water quality and aquatic ecosystems and the long time period required to establish new regional planning regimes. Setting catchment limits certainly focuses the mind. Most councils are now getting on with the job.

In a recent project for the Ministry for Primary Industries (MPI), we identified five high level outcomes being sought through water management:

  • LIMITS: Values identified for protection are protected
  • EQUITY: Fair, equitable sharing of access to water, and land uses that affect water
  • EFFICIENCY: Maximise the benefits from use of the available water and land resources
  • PARTICIPATION: Everyone with an interest has an opportunity to participate, and Treaty of Waitangi partnership obligations are honoured by the Crown and Māori
  • DECISION-MAKING: Decisions about use and protection of water, and land uses which affect water, are made in a timely, cost-effective, integrative and adaptive manner

Limits need to address both cumulative water extraction and water quality impacts from the mix of upstream land uses and discharges. Objectives of limit-setting usually maintain sufficient flow and water quality to support aquatic life, recreation, iwi values and other uses authorised through consents and the regional plan.

Either your catchment has room for more allocation (lucky you!) or it is over-allocated. The latter requires claw-back, restoration or water augmentation. These measures restrict peoples’ perceived property rights, wallets or both. Over-allocation is always harder to remedy than setting limits early.

Water allocation states corresponding to four levels of allocation.

The figure to the right is a schematic of water and land resource development when limits are set in a regional plan. Perversely, the announcement that limits may be set can often cause a ‘gold rush’ as potential users seek an allocation before the limit is reached.

Limit-setting is a socio-political process informed by biophysical sciences and economics, even though we hydrologists would love to be in the driving seat. As discussed by Hugh Canard, in their three reports to government, the Land and Water Forum recognises the benefits of collaborative processes and of an integrated catchment management approach to limit setting. Judgements must be made to balance development opportunity and conservation interests, so ideally all stakeholder and iwi groups should be engaged in understanding the trade-offs involved.

Financial benefits for water and land uses are weighed against less tangible values such as the ability to swim, the habitat left for fish, landscape values and the mauri of the waters. As a trout fisher commented in a workshop for our ‘Freshwater Values Monitoring & Outcomes’ research programme, “I wake up in the morning and wonder what I’m going to lose today”.

The figure shows that we should expect limits to change over time. After all, knowledge about catchment dynamics is improving all the time (grey shaded). But more importantly, the balance of values considered important will change over time.

Once a catchment becomes fully allocated, we’re confronted with the ‘Re-Allocation Problem’: how to accommodate deserving new uses of water – or land, with consequential discharge implications – from within the legislated fully allocated block. This is where economic drivers can play a part. Allowing transfers of water or discharge allocations, provided the environmental and third party effects of the transfer are not made any worse, seems the best available mechanism. Maori, environmental and farming interests have various objections to ‘water trading’. The devil is in the detailed design of the policy. In the absence of an ability to transfer consents, we have to ask ourselves what other policy mechanism would address the Re-Allocation Problem. I don’t think the answer is to extend the overdraft.

Andrew Fenemor is a hydrologist and water management researcher with Landcare Research in Nelson

Water allocation and limit-setting in a changing climate Waiology Nov 20

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By Daniel Collins

Last week, the Land and Water Forum released its third and final report on water management in New Zealand. It is a substantial piece of collaborative work with 67 recommendations. Number 29 is that allocation limits be set by taking into account “any flow and water level fluctuations caused by seasonal or other climate variations”. While this primarily refers to natural variability, such as the Interdecadal Pacific Oscillation, it’s also important to consider climate change. And along the same lines, last year’s National Policy Statement for Freshwater Management stated the need to account for the “foreseeable impacts” of climate change.

This is an important issue, as climate change is expected to bring about a raft of changes to New Zealand’s freshwaters (more details on that soon). Among these changes are reductions or increases in the amount of water available for use. Also importantly, climate change makes assessments of future water resources less certain.

So how should resource managers set allocation limits for long-term consents in the context of climate change, accounting for both a change in supply and an increase in uncertainty?

To explore this issue, I propose the following method. It is still in its formative stages, so feedback is welcome.

Let’s start by considering a hypothetical New Zealand river. Its allocation limit is currently set at 40 m3/s. And let’s put aside any complications like priority rights.

Now suppose that results from a climate change impact assessment indicate that allocable flow will reduce by 7% by 2050. This is a middle-of-the road projection, associated with a moderate greenhouse gas emissions scenario and using the median result from 12 global climate models (GCMs). But if you account for the uncertainty of the scenarios, the GCMs and the hydrological models that convert climate changes into runoff changes, then the impact could be anywhere between a 4% and a 12% reduction. That is, it is almost certain that the allocable flow will drop by 4%, it will likely drop by a further 3%, and it might drop by another 5% again.

To set a conservative new allocation limit, first reduce the existing limit by 12% to 35.2 m3/s You can be pretty sure that this water will still be available in 2050 and so you should have no qualms about allocating it for the longest possible duration under the RMA of 35 years (2012 + 35 = 2047). This gives water users the confidence to invest in long-term infrastructure, and it will mean that over-allocation is unlikely to occur.

Second, take an additional 5% of the water (2 m3/s) and allocate this for a shorter period of time, say 10-15 years. It is likely that this water will also be available in the future, but we can’t be as sure. For those water users who are willing to accept the higher risk, they should be allowed to, thus making better use of the available resource.

(If the climate change projections were for an increase in water availability, the same method applies, but the numbers are shifted in the opposite direction.)

Every few decades or so, the long-term allocation limit is re-assessed and changed as needed. Every 10-15 years or so, the short-term allocation limit is also re-assessed and changed as needed.

This allocation scheme meets users’ needs for long-term consents for most of the water (the “certain” water), giving them the confidence to invest in long-term infrastructure, while also allowing them to seek additional water if they are not too risk averse. The scheme also allows the limits to be managed adaptively as new information comes to light – new data on water availability or better climate change projections. And finally, it means that the social, cultural and environmental limits are met whatever happens with climate change, and that the detrimental effects of over-allocation are avoided.

In terms of climate change adaptation, the scheme ticks the boxes of adaptive management and balanced risk-based assessment, and is robust to uncertainties in climate change. As far as I can tell, it also meets the different stakeholders’ needs while accounting for the realities of climate change (that is, change plus uncertainty).

But what do you think? Your feedback would be appreciated in refining this time-dependent allocation scheme.

Canterbury does not have 70% of New Zealand’s freshwater, it has 12% Waiology Oct 29


By Daniel Collins

In the Christchurch Press today there is an article about the race to irrigate Canterbury. In it is the following statement:

“Canterbury had 70 per cent of New Zealand’s fresh water resource, and 34 per cent of its hydro-generation capacity.”

Unfortunately the 70% is an error that has appeared in the past and it is timely to make a correction and provide some other statistics that describe water resources in Canterbury more generally.

Canterbury has about 12% of New Zealand’s freshwater. This number is obtained from a Statistics NZ report, written by NIWA, on the water stock accounts of New Zealand.

To check for yourself, download the two Excel files from the Statistics NZ website, calculate the annual average of “Outflow to sea and net abstraction” for both Canterbury and the country as a whole, and divide one by the other.

This error has already been noted by the Christchurch Press in an article from March 2010.

For a fuller picture, here are some more useful statistics, from the Ministry of the Environment’s 2010 water allocation snapshot compiled by Aqualinc Research:

    Canterbury’s percent of national water consents (number): 30%
    Canterbury’s percent of national irrigation consents (number): 35%
    Canterbury’s percent of national annual consumptive allocation (m3/yr): 19%
    Canterbury’s percent of national annual consumptive allocation, discounting Southland’s Manapouri hydro scheme (m3/yr): 46%
    Canterbury’s percent of national irrigation allocation (m3/yr): 62%
    Canterbury’s percent of national consented irrigated area (ha): 63%

And from the Canterbury Water Management Strategy:

    Canterbury’s percent of national water allocation (m3/yr): 58%
    Canterbury’s percent of national irrigated area (ha): 70%

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:

Rainfall recharge to groundwater Waiology Jan 17


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

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.


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?

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.

How much water do we use? Waiology Oct 21


By Daniel Collins

One of the arguments being used at the moment to promote water storage and irrigation schemes is that much of the water that falls on New Zealand flows to the sea, not to the farm. Conor English, CEO of Federated Farmers, wrote in an opinion piece earlier this year:

“It’s not that New Zealand is running out of water, it’s that water is running out of New Zealand.”

As it turns out, about 80% of the water that falls on New Zealand flows out to sea, the rest evaporates back into the atmosphere.

As for what we use, Lachlan McKenzie, previously from Federated Farmers, is cited as saying that 97% of New Zealand’s water flows wastefully to the sea (audio). Similarly, in a Q&A file released in May, the Government states that 2% of our freshwater resource is used.

McKenzie’s 3% used and the Government’s 2% are basically the same. They ultimately come from two sources: the 2006 Statistics NZ report mentioned previously, and a report on water allocation by Aqualinc Research Ltd. The numbers refer to the fraction of total annual water supply that can be abstracted legally, as an average for New Zealand as a whole. (It’s important to remember that water doesn’t need to be abstracted to be useful or beneficial, even for commercial purposes, but that’s a discussion for another time.)

According to the Aqualinc report, nearly 27,000 x 106 m3 of water may be abstracted from rivers and aquifers each year. That’s almost half the volume of Lake Taupo*. Of this, 16,000 x 106 m3 is for the Manapouri hydropower scheme that takes water from the Waiau River and discharges it directly to the sea. If we’re just thinking about water that can be consumed for irrigation, drinking and so on, then we’re left with 11,000 x 106 m3. Using the Statistics NZ data (either 2006 or 2011 reports), this is 2% of New Zealand’s annual freshwater supply.

But this is a national and annual average, which is adequate for a big-picture view but irrelevant for practical purposes. It implicitly assumes that the water is equally available everywhere, all the time. It is not. The water in Southland is of no use to Canterbury or Hawke’s Bay, and unless we build pipes or tunnels across the Southern Alps, nor is the West Coast’s. The water in winter is of no use in summer unless we build reservoirs, hence the drive for more water storage. (Expect more on the hydrology of water storage in the future.)

For a more useful description of the annual water used in each region, check out the figures below. Omitting Southland’s hydropower, most of the water allocated for consumptive purposes is in Canterbury, followed by Otago. Canterbury’s allocation is 5,000 x 106 m3/yr — nearly half of New Zealand’s total. As a fraction of each region’s annual water supply, Canterbury and Otago are also on top, at 8.3% and 7.7% respectively. Cool and wet Southland and West Coast come in at the bottom with 0.2% each, as does less developed Gisborne.

It’s easy to see how the regional picture is a lot different from the national picture, but in terms of how we use our water, this is really only part of the jigsaw puzzle. Stay tuned for more pieces.

Water Allocation

* The volume of Lake Taupo is about 59 km3 or 59,000 x 106 m3. 27,000 x 106 m3/yr is about 21 Olympic swimming pools worth of water per minute.

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