Undermining Water - Accounting for Flow Reducing Activities |
December 06, 2006 |
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Posted by Joseph Taylor at December 6, 2006 03:03 AM |
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This issue of the Droplet explores options for dealing with two of Australia’s most severe water accounting challenges. The question of how to deal with the impacts of land use changes on water supplies.
Droplet No. 3, December 2006
Water reaches our waterways and aquifers by landing on soil and then either passing through the soil or running over it. And, how much gets there depends upon the nature of the soil, barriers to overland flow and amount of water extracted by plants.
There's a hole in the bucket, dear Liza, dear Liza,
There's a hole in the bucket, dear Liza, a hole.
Plant trees in high rainfall areas, build a dam, establish contour banks, spread clay on a sandy soil or make any other land use change that affects water flow adversely and the amount of water that reaches groundwater systems and rivers is reduced. Reduced dramatically.
Recently, CSIRO scientists estimated that, over the next 20 years, farm dam growth will reduce annual flows in the Murray Darling system by 250 to 3,000 GL. Ranges are provided because there is considerable uncertainty about projections of this nature. Somewhat controversially, CSIRO also estimated that plantation forestry will reduce flows in the Murray Darling system by 550 to 700 GL. Industry and BRS estimates suggest that these estimates may be high. Lower estimates are in the vicinity of 165-215 GL each year. Whatever the correct estimate, these volumes are significant.
To put these numbers in perspective, the first step in restoring River Murray flows aims to find an additional 500 GL. In contrast, the possible outcome, depending upon the rate of growth in dams and plantations may be a loss of as much as 10% of the water used in irrigation in high allocation years.
Significantly, the impact of such water intercepting activities depends on whether or not the land-use change occurs above or below a dam. Interception above a dam has the same impact as less rain and thus is considered when allocation decisions are made. Changes in interception below a dam, however, typically are ignored – even though they can be predicted to reduce the amount of water available.
This is a classic example of a water accounting problem. When some but not all water use is metered, how can one ensure that when one person uses more water, someone else uses less? Other accounting problems, left for a subsequent droplet, will address the effects of climate change, increased salinity, forest fires and salinity interception.
So fix it dear Henry, dear Henry, dear Henry,
So fix it dear Henry, dear Henry, fix it.
With what should I fix it, dear Liza, dear Liza,
With what should I fix it, dear Liza, with what?
Conceptually, there are two ways to fix it.
1) Reduce allocations to other water users as un-metered use increases.
2) Require the effects of any increase in un-metered use to be offset.
Progressive reduction?
If the progressive reduction approach is taken, then all water users need to be made aware that increases in un-metered water use may reduce the quantity of water likely to be made available to them. Provision of an annual land-use change impact statement is one way of providing such information.
In the River Murray system, one could imagine River Murray Water producing an independently-audited annual assessment of the extent of inflow reduction caused by increased forestry, farm dams construction and all other land-use changes. The audited report would then be used to help decision makers decide how much water to allocate to licensed water users.
Off-sets?
The other approach is to make permission to undertake a flow reducing land-use change conditional upon acquiring water entitlements equivalent to the size of the effect. Increases in non-metered water use are permitted only when arrangements are put in place to reduce metered water use elsewhere.
In the Lower South East of South Australia’s groundwater system, above a threshold area, those who wish to establish a new blue gum or pine plantation are now required to hold an irrigation licence equivalent to the impact of the proposed plantation on water supplies.
Administrative detail
Whenever an off-set approach is taken, regulations are used to require a permit to undertake a significant water-intercepting activity. Likely impact per hectare of forest or per ML of dam is then estimated by reference to a set of look-up tables. That amount of water can be set aside so that the impact of the interception on allocations to other water users and the environment is negligible.
If this water is “quarantined” in a special account and actual use estimated annually, administrative costs can get prohibitive. A simpler approach is to require surrender of a water entitlement equivalent to the average amount of water to be used.
In recognition of the value of a water entitlement, the plantation establishment or dam construction permit issued can guarantee entitlement re-issue when the interception stops and the permit cancelled.
How much does un-metered water use cost?
A very conservative estimate of the impacts of un-metered interception in the River Murray system over the next 20 years is 1,000 GL per annum. At average prices of around $1,500/ML for high security water, it would cost in excess of $1,500,000,000 or $1.5 billion to replace this water.
A different way of thinking about the impact is to ask how much it would cost to off-set a hectare of forest plantation or 5 ML dam. Clearly this depends upon where the dam or forest is located.
Located high up in the Eastern Divide where annual rainfall exceeds 1120 mm per annum, plantation establishment reduces water yield by around 2.5 ML per hectare. Assuming that around 80% of this yield reduction affects river flow, the cost of buying back the water used is around $3,000 per hectare.
Every ML of farm dam storage is estimated to reduce flow by 0.84 ML. At a price of $1,500/ML, the cost of offsetting a 10 ML dam would be around $12,600.
Further work
Under the National Water Initiative, governments agreed to include measures to have water interception under control “no later than 2011.” Recently, the Prime Minister and River Murray Premiers agreed to accelerate actions associated with water accounting.
Awkward issues include the question of whether or not offsets should be required for increases in the area under native vegetation and what is to be considered a significant effect.
Mike Young, The University of Adelaide, Email: Mike.Young@adelaide.edu.au
Jim McColl, CSIRO Land and Water, Email: Jim.McColl@csiro.au
Click here to access our previous droplet “Thinking like an accountant about rivers and aquifers.”
Acknowledgements
The contributions of Albert van Dijk, Peter Hairsine and Glen Kile to this Droplet is acknowledged with appreciation. ”There’s a Hole in the Bucket” is a folk song of unknown origin made famous by Harry Belafonte and Odetta.
Further reading
Risks to shared water resources, http://www.mdbc.gov.au/nrm/risks_to_shared_water_resources
Sharing water, http://www.myoung.net.au/water/publications/Sharing_water_060221p.pdf
National Forest Inventory http://affashop.gov.au/product.asp?prodid=12774
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Prof. Mike Young
Water Economics and Management
Earth & Environmental Sciences
The University of Adelaide
AUSTRALIA
Email: Mike.Young@adelaide.edu.au
Website: www.myoung.net.au
Copyright © 2006 The University of Adelaide
This work is copyright. It may be reproduced subject to the inclusion of an acknowledgement of its source. Production of Droplets is supported by Land and Water Australia and CSIRO Water for a Healthy Country. Responsibility for their content remains with the authors.
Comments
An excellant article, access to water in some areas af australia is a major issue, many people don't think about the impact of their action on others
Posted by: commercial water treatment specialist at December 21, 2006 06:50 AM
Nicely Done. Good research on the Murray, surely a critical test case for the viability of water initiatives across all of Australia. Unfortunately, our Ferderal Government is quick to talk and slow to act on big issues, fearing public or corporate backlash against any change.
Thanks for the insight,
Mike Thomas
http://urbanworkbench.com
Posted by: Mike Thomas at January 10, 2007 05:02 PM
