It has been suggested that before irrigation runoff into the Macquarie Marshes was 460,000 megalitres and that this has been reduced to 395,000ml by irrigation.
But Ian Mott has argued that pre-settlement runoff into the marshes would have been much less than 460,000ml and most likely less than 395,000ml because much of the upper catchment was once forested. Because it has since been cleared for pasture, runoff would have substantially increased.
Yet the opposite appears to be the case.
In an earlier thread Chris Hogendyk expained that: “Inflows to Burrendong (on the catchment of the Macquarie) for the 68 months from December 2000 to July 2006 was approximately 1700 GL which is the same as the driest similar period on record that occurred from December 1934 to July 1940. The next driest period was December 1903 to July 1909 that received approximately 1950 GL.
“The first data set are actual observations whilst the latter two are modelled. Out of interest, for every 10 megalitres that is captured by the dam, 4 megalitres come into the system as down stream tributaries.”
Interestingly rainfall history as plotted by Warwick Hughes suggests that it was drier during the late 1930s.
This is Warwicks comment on the charts: “These show you some rainfall history for the region from the Bureau of Metereology high quality rain dataset and you can see the obvious cycles in all charts.
“Trangie data is the closest HQ station to the Macquarie Marshes and it shows that in the recent past conditions were similar to dry times times in the 1990’s and 1980’s, if you go back to the 1960’s rainfall was obviously less and even lower in the late 1930’s thru 40’s and earlier again WWI years into the 1920’s look the driest of all.
“The other graphic, also of HQ data, from Mudgee and Bathurst, could be a fair proxy for long term trends higher in the catchment.”
So it has been dry, but not that dry, and with fewer trees, why have inflows been so low lately?
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
What is the catchment area for the Macquarie Marshes? Is the rainfall data from two stations from Warwick sufficient to get a clear picture?
Jen – the preferred answer is to get to river flow if you can.
Riverflow being a water balance integrating rainfall, evaporation, soil water stores, runoff, deep drainage, dam water storage, maintenance flows and farm water use.
There are two bits missing – (1) can Chris Hogendyk get a modelled inflow for the current period to compare with the actual inflow series. (2) What’s the impact of tree clearing – do we have any past land use maps to formalise this aspect ?
If the simulated flow for the current period matches the observations you’d have some basis to accept the historic simulations. In that case it would simply be the patterns of rainfall – what intensity and in what pattern.
The other thing to look at might be evaporation trends.
My guess is that the modellers have conformed to standard NLWA & MDBC practice and failed to adjust runoff for clearing or regrowth. If they have not done it for the entire MDB then they certainly have not done it for the Macquarie.
Over to the modellers, please.
The other point to note is that while the total change in yield is lower in the 600mm to 700mm range, the percentage change in yield from clearing is much higher. At 1000mm the percentage change is only in the order of 50% but at 600mm it is circa 200%. So it is trite but necessary to state that clearing over a large area of low rainfall country can have the same effect as a smaller area of higher rainfall country.
Luke, I will see if it is possible to get a model run on the current period and see how it compares – will be interesting. As you mentioned, river flows tell the best story as rainfall data can be misleading unless coupled with antecedent conditions, intensity and duration. Another factor that can have an impact on runoff is the proliferation of small farm dams in the catchment. I’m not sure how this is accounted for in the models when comparing early 1900’s with today.
At this and other recent posts on ‘drought’ I am amazed how quickly rainfall history/rainfall data is dismissed as only part of the story.
What story? Who’s story?
The public discourse, and earlier discussions at this blog, have been very much about climate change and how the current drought is a result of climate change and how we have ‘exceptional circumstances’ because we have less rain because of climate change?
But now Luke tells me I should be more interested in stream flow? Why?
Spot on Jen.
How the nation has been brainwashed by rainfall history data being locked away and so little referred to. Amazing to contemplate the sheer weight of media lies since 2002.
“But now Luke tells me I should be more interested in stream flow? Why?”
Because this post is about water in the Macquarie Marshes?
I don’t see why you should be amazed. The more we all talk, the more we all learn, the deeper the conversation goes.
I don’t think it is unreasonable – in fact it sounds pretty sensible – to move on from just rainfall, to stream flow and soil moisture and land clearing/runoff and evaporation when talking about drought or water levels.
Also, from what I have read, it is not at all amazing or uncommon to broaden the definition of drought into other things besides rainfall – its mainly meteorologists who define drought in terms of just rainfall deciles.
Ian had a great quote from a previous post about asking a farmer if you want to know about current conditions. Perhaps its the farmers story that is best to listen to.
If you google drought in australia, i’m sure you will find plenty of links to people and farmers reporting on the severity and duration of current conditions in their area.
Here’s a recent landline story about the town of Bourke and their drought: http://www.abc.net.au/landline/content/2006/s1674777.htm
Bourke is not that far from Macquarie Marshes, and again, eyeballing the NSW drought declaration maps shows that the Macquarie Marshes area has been drought declared much of the time since 2002.
http://www.agric.nsw.gov.au/reader/drt-area?picQuant=100
So despite Warwicks rainfall graphs not showing the lowest rainfall on record, it seems like the area is pretty dry, and has been for a while.
Interesting those ‘obvious’ cycles in the annual rainfall series upstream from the Marshes. Other ways to enjoy obvious cycles are to view moving averages of random data. True, decadal patterns such as the IPO have been identified in hindsight. But ‘obvious’ cycles is perhaps meant to imply that what goes down will remember to bounce back. An annual rainfall series probably does not remember the ‘law’ of averages.
Jen – the quick answer is because you’re interested in what’s in Wivenhoe dam (inflow water from runoff) and is this water shortage from the dam the worst on record. You want water in your pipes not rainfall doing whatever it might do.
The loooonger answer is because if you ever do a soil water model or a plant growth model or a catchment model – you will find that there are factors other than simply rainfall that affect how biology and catchment systems work (rainfall mind you all its shortcomings does a pretty good job in a broad sense).
Evaporation factors involve rainfall, radiation, vapour pressure deficit (~humidity), wind run, and temperature. Temperature surprisingly is last – compare Alice Springs and Darwin evaporation rates. Darwin is warmer but Alice evaporates much more.
Low humidities from dry air and high radiation from clear skies can make droughts (especially El Ninos) more intense. Water evaporates more quickly.
Then there are the infiltration characteristics of the soil, how much water the soil can store, drainage and runoff. These factors integrate how the distribution of rainfall (how much rain over how many days) is captured or runs off.
Plants then utilise the soil water depending on the depth of their roots, their leaf area index, their internal water potential, and the evaporative demand across the stomates. The atmsopheric concentration of carbon dioxide affects how much plants need to open their stomates and therefore lose water to photosynthesise.
The above processes need to be calculate daily if you want to model soil water.
Well that’s how I remember it.
People have spent a lot of time investigating measures of drought that “get close” to what a farmer/water manager is experiencing. i.e. lack of yield, lack of pasture, lack of surface water to drink or irrigate with.
The opinion seems to be that getting closer to the variable that is lacking from your management viewpoint often gives more realistic interpretation. So you have crop yield drought, pasture growth drought, surface water drought, and at the very wet end – “protein drought” in very wet years in northern Australia.
A model allows you to integrate these factors and simulate a distribution of crop yields or stream flows over the historical record. You rank them highest lowest and you can make observation as to what year is in what percentile and how bad current is compared to history.
You might get median rainfall – but if all the rain comes in nice little showers you will get good grass growth but little runoff for dams.
Interestingly in SEQ my memory suggests few periods with really really big dumps of rain. Warwick can advise maybe.
Sometimes in semi-arid plant communities you would think you might have had enough rainfall but the plants have not had enough in the right amounts to start growth.
So reassessing the years in terms of other variables than rainfall can make your low end percentiles move around in rank order.
What is also interesting if that if you go to derived variable like yield, crop growth or streamflow you will get amplification in forecast signals like El Nino/Southern Oscillation Index. The correlations and forecast skill can often be higher. Of course one of the biggest factors in prediction is the persistence from the antecedent conditions (do I have a wall of grass outside now or a wet catchment).
The yanks use a thing called the Palmer Index not rainfall.
Anyway that’s what I reckon.
P.S. Get a copy of DPI’s RAINMAN and you can play to your hearts content with rainfall and streamflow stats. You have to see these things for yourself. No I don’t get a commission.
Errr Burrendong Dam sorry ..
Steve, I am always amazed – the “science” of water usage has been known for decades, first in the US, perfected in Israel, further tweaked in Australia – irrigation technology incorporates factors such as
rainfall duration
rainfall quantity
evapotranspiration
soil depth
soil type
soil compaction
soil water holding capacity
wilt point
irrigation scheduling for root development
fertigation
deficit irrigation
\etc
What amazes me is that non farmers/irrigators also hold expert opinions on the matter.
Browsing on this topic, I came across the following abstract.I would seem to be right on what you are discussing. Anyone familar with it?
Environmental change and flooding in the Bogan River catchment NSW
Nakken, M
1999
“This thesis examines the nature and effect of vegetation, land-use, geomorphic, and hydroclimatic changes on flood magnitude and frequency in the Bogan catchment.”
For those who want another view:
http://en.wikipedia.org/wiki/Palmer_Drought_Index
A variety of drought indices described at http://www.drought.unl.edu/whatis/indices.htm
Meanwhile, back at the model. Any word from the modellers as to the incorporation of vegetation flux? Yield changes from veg flux was, after all, what the whole clearing/salinity thing was all about. Or was it just part of the “truth as drop down menu” system where one just selects a factoid to suit the occasion?
And although no longer being published, a great range of international management and science issues on drought at the Drought Network News archive. 1994-2001
http://www.drought.unl.edu/pubs/dnn/dnnarchive.htm
Jeez you know how to be rude Ian – “Truth as Drop Down Menu” my arse. It was a radio buttons. No -even better there was only one outcome, one button and it was pre-pressed in the factory. No user intervention required.
Yes the modellers have had a go at tree water use and are having another go. Not as simple as rooting depth to 1.5m with grasses. And trees also seem to live on water vapour during drought in the deep root zone – amazing. Gotta stop that xylem cavitating. Yes trees are the next step.
OK shouldn’t encourage Ian, but if you want to see some of the evolution in trees and salt modelling get this into ya : “Biophysical Approach To Predict Salt And Water Loads
To Upland REALM Nodes Of Victorian Catchments”
You’ll have to bet on Bet Bet !
http://www.mssanz.org.au/modsim05/papers/weeks.pdf#search=%22bet%20bet%20catchment%22
That ModSIM had all manner of interesting stuff on related issues. Should keep your envelope smoking.
Keep posting Luke!!
Thanks for this url, Luke. It is consistent with the work of Zhang et al. Curiously, it has not broken the data down into a yield per hectare basis but left it at a cumulative yield/ha basis over 26 years.
For the ‘upland alluvial’ scenario the catchment wide average yield is 0.57ml/ha and the addition of trees reduces total yield by the equivalent of 0.79ml/ha of added trees. A reduction in original tree cover would produce a corresponding improvement in yield of 139% on a per hectare cleared basis.
The change in percentage yield/ha is directly related to annual rainfall. The following relationship has been developed from work on 21 Victorian catchments by Holmes & Sinclair in 1986. It indicates that;
Of 1000mm RF, 830mm is used by forest and 170mm is runoff. Pasture uses 650mm with 350mm of runoff so the change involves a 106% yield increase for each cleared hectare.
For 800mm RF, 710mm is used by forest and 90mm is runoff. Pasture uses 580mm with 220mm of runoff so the change involves a 145% yield increase for each cleared hectare.
For 700mm RF, 650mm is used by forest and 50mm is runoff. Pasture uses 545mm with 155mm of runoff so the change involves a 210% yield increase for each cleared hectare.
For 600mm Rf, 580mm is used by forest and 20mm is runoff. Pasture uses 510mm with 90mm of runoff so the change involves a 350% yield increase for each cleared hectare.
So the results for the Bet Bet catchment (139% yield increase) would indicate an average rainfall in the order of 800mm. I don’t have a close estimate for the Macquarie but it is likely to be between 700mm and 800mm so this would put the average yield increase from clearing in the order of 175%.
I ran 3 scenarios for all MDB catchments based on an average yield increases of 100%, 150% and 200% per cleared hectare based on NLWA cleared catchment data, (not the back of envelope that Luke/Phil likes to mention) and it came up with some interesting results for the Macquarie/Castlereagh/Bogan catchment.
The MDBC estimates total runoff to be 1656GL per annum while the NLWA estimates that 33% of this catchment is cleared. And this means that, at an assumed yield increase/ha of 150%, the current runoff is made up of 67% supplying natural yield plus 33% supplying natural yield + 150%.
That is, the total of natural runoff was 1108GL with another 548GL of clearing related surplus runoff. And as the total surface water use was only 468GL this left 80GL of the clearing related surplus yield that was flowing down stream on top of the unused natural flow.
When a more modest 100% yield increase is used we found that the natural runoff would have been 1245GL with 411GL of clearing surplus and a very modest 57GL being extracted from natural flows for irrigation purposes. At the upper end of the likely outcomes, at 200% yield increase, natural runoff would have been 998GL with 658GL of clearing surplus of which 190GL was not being used by irrigators. This produced a 19% increase on the natural flows.
More detailed examination of the catchment clearing and regrowth history is needed but it is safe to assume that the Macquarie irrigators are not fully utilising the surplus runoff that has been produced by clearing in the upper catchment. It should also be noted that clearing is likely to have taken place in the lower catchment and this surplus would not be available to up stream irrigators. However, it could certainly offset any (unlikely) reductions in natural flows to restore downstream flows to their original volumes.
What we do know for certain is that clearing took place long before the dam was built. And this means that much of the remembered anecdotal material on past flood peaks etc, would incorporate the significant clearing related yield increases. And any attempt to try and replicate these surplus flows would not constitute a restoration of natural values. Any duty of care to maintain or restore ecological values must be based on pre-settlement flows not on modified ones.
It is also obvious that the clearing related surplus water yields are of the nature of “improvements” that have been undertaken by the landowners up stream and which rightly belong to them. The fact that the government has allocated those waters to downstream users does not diminish their rightful claim to ownership. The states have allocated waters on the basis that they were apportioning part of the natural flow so it is only appropriate that they should actually do so.
The significance of the percentage yield increases at lower rainfall levels highlights the critical relevance of woodland thickening in the western zone. For there is little room for doubt that this thickening is seriously reducing the health of riparian ecosystems through major volume reductions. And to reduce irrigation allocations in the eastern highlands and slopes for no other purpose than to feed a voracious regrowth appetite for water in the west is criminal negligence of the first order.
Struth – property rights morphing into evapotranspiration rights. Motty’s envelope has Intel inside.
Of course if the increase in runoff is due to enhanced water use efficiency from increases in atmospheric CO2 (reduced stomate opening losing less water) it is actually some cab driver in New York that owns the extra water.
Not so, Luke. When that cab driver owns land he can enjoy his own rain. But your attitude is fairly consistent with a common departmental perception that everyone else gets to enjoy the benefits of change except farmers, the new ecoserfs. They just get blame for any adverse effects while the state captures any benefits.
But not a bad attempt at changing topic. Do you accept that, given the clearing history of the Macquarie catchment, and the rainfall range, that there must be a substantial anthropogenic water surplus of the order I have indicated?
Jeez – touchy – can’t even have a techo joke. I’ll remember your hard cold logic when the next gazillion in drought aid gets handed out.
I accept the detail of your argument – as long as you can demonstrate the land use and thickening issues with some “real world” data. There is still also an issue of how effect there would be on shallow mountainous soils, but get out on the plains and it would be different.
Wouldn’t it be so much more comforting if everyone could just agree on a “hands-off” approach to Nature? Forget the numbers, forget the analysis, just worship Her, and hope that if we produce nothing of consequence, and consume nothing of consequence, that She will bestow Her most mysterious, abundant and unknowable blessings?
We could know the peace that surpasses all understanding, and yield up our tumult to the gentle, impartial Mother of all and exude harmony, and excrete good will, if we could only submit ourselves to the generous advice of Her exponents, who by their writings prove themselves to be completely independent of fact or reason.
Seek ye peace, and yield up your fractious and contentious reasoning!
Not. Gaia will not put shingles on your roof or provide electricity.
just so u al no it is al bull poo. beep the goverment beep Beattie hahaha
Don’t worry, Phil, there was no bile in that post. I just can’t pass up an opportunity for repetition of departmental demonisation. I hope to become the first farmers rights activist to be prosecuted under the new sedition laws.
Ian,
If you truly want to be the first farmers rights activist to be prosecuted under the new sedition law, I’ll back you every inch. But make sure of your elevation and windage, collateral damage can make it hard to keep friends.
CORRECTION to my main post above. If I had checked with Warwicks original graphs I would have noted that the actual historical rainfall record puts the mean rainfall at Bathurst and Mudgee at about 650mm while Dubbo is 586mm and Warren, at the start of the marshes, is only 512mm. And this means the catchment wide average (for cleared land) will be closer to 600mm with a 350% yield increase from clearing.
When a 300% yield increase was fed into the model we found that the natural runoff would have been 832GL with 824GL of clearing related yield increase. That is 50% of current flows are anthropogenic. And when the current extractions of 468GL are deducted we still get a surplus of 356GL in river flow.
The only logical conclusion to be drawn from this data is that the pre-settlement flows to the marshes was;
1 much less in volume, and
2 much less frequent than is currently the case.
The arguments in favour of releasing additional water for ‘environmental’ purposes have minimal basis in fact. Indeed, this surplus of water that is currently being delivered to the marshes may be undermining the resilience of species that have evolved over millenia to cope with much less frequent inundation.
A decline in a previous artificial set of ecological values does not constitute environmental harm. Even if those artificial values are more pleasing to human observers or in apparent beneficial effect for dependent species.
According to the Bet Bet paper by Weeks et al. The 2CSalt model was “developed by state agencies and associated partners of the CRCCH and the Murray-Darling Basin Commission”. But to date, the use of the model, in a policy context, appears to have been limited to determining the impact of planted vegetation. And one must ask, why has it not been applied to the far more urgent need to understand the implications on water yield of past clearing and current vegetation thickening?
Could this be another example of top class science that has been ignored for political convenience?
Thanks, Schiller, your earlier post described a “Prozac Holiday” perfectly. In the brave new green utopia you don’t even have to go outside. You can have all the virtual environmental values you could possibly want. And don’t bother with any opinions, DPI/DNRM/EPA have all the opinions you could ever need. Every one of them personally vetted by Aila Keto so you can be certain they will be acceptable.
All you ever need is three cones, a jar of cookies and an aquarium with back lights.
By the way, Jen, you misquoted me in your opening post. The numbers you used were the irrigation extractions from runoff, not the actual runoff as you suggested. My claim was always that the increase in water yield from clearing was significant and was most likely in excess of the irrigation extractions. And in light of the revised data above, that is clearly the case.
(Posted by Ian Mott)
The only logical conclusion to be drawn from this data is that the pre-settlement flows to the marshes was;
1 much less in volume, and
2 much less frequent than is currently the case.
The arguments in favour of releasing additional water for ‘environmental’ purposes have minimal basis in fact. Indeed, this surplus of water that is currently being delivered to the marshes may be undermining the resilience of species that have evolved over millenia to cope with much less frequent inundation.
———————————————-
I’m backing Ian Mott’s theory all the way here. It’s consistent with my observations of the marshes and many other riverine wetlands, as being a “Drownedlands”. A lot of the tree death that is occurring in these systems at the moment is death of young redgum regrowth that has been brought on in the last 50 years by too-frequent flooding.
This is good reasons to push for tree regeneration in the catchment areas. But hey that’s what us greenies are already doing!
Thanks, Michael. Your observations are entirely consistent with those of my Brother in-law Vic Eddy who has been managing the 80,000 odd hectares of Red Gum on the soon to be nationalised Glenn Avon Station.
The beauty about getting closer and closer to the problem is that it leaves less and less room for ideologies of any kind.
So what is Chris Hogendyk’s response? When will the Macquarie irrigators demand that the Catchment Management Authority provide detail of the exact area and location of cleared land, the exact area and location of regrowth, and overlay the rainfall data to get a clearer picture of the origins of the current flow volumes? When will they invite the CRC to run their model on the Macquarie?
Still no word on whether Chris’s modeller adjusted for clearing or simply assumed that all flows are natural flows?
Hello? Is that a deafening silence I hear?
Hi Ian, have been away from computers for a number of days. My modeller has not got back to me which I will chase up.
You certainly put up some really good aguments on changes to catchment flows with clearing occurring. It is something as an irrigator we believed was could be happening but could never quantify. Unfortunately all the modelling done in the valley is using the IQQM model run by DNR and they will not let us get involved with its use.
Other reasons why the marshes get more effective water is that through the dam water is regulated to keep it in the river so it gets to the marshes. Under natural conditions with big peaks in flood conditions, much of the water leaves the Macquarie and goes into the Bogan system. The Macqarie river basically becomes an effluent river downstream of Narromine.
Michael’s comment is spot on regarding the death of rivergums. The greatest causal agent of tree death in the marshes has been clearing and flooding, particularly during the late 50’s, a prolonged wet period.
Chris, it may be appropriate to write to the DG to advise him that the IQQM model is not current best practice in that it fails to consider changes in water yield due to vegetation flux. Then advise him that the continued failure to ascertain the true state of historical catchment flows could lead to your members suffering serious and entirely foreseeable detriment that can be easily quantified.
Then urge him to take all reasonable and practical steps to avoid this harm by implementing the CRCCH models to determine the true historical range of variation in natural flows.
And if he doesn’t shift his ass, just tell all your members to flick the meter on for the class action and wait, patiently, until the accumulated losses are enough to make Slater & Gordon salivate.
Class action. You have to be joking. Ever thought of engaging without a baseball bat.
IQQM will be well calibrated to the system but not include vegetation cover or grass cover. You need land use maps of such data. Grass cover will also vary how much runs off depending on the season. And the CO2 transpiration use efficiency isse. Better make sure you do the job properly or the urbanites might have to take up their own class action for hurried pressured science. Spatially explicit hydrological models with land use feedbacks are just coming into development.
What’s your validation strategy?
The beauty about class actions, Luke, is that in most cases the critical mistakes have already been made. And actions for damages in negligence have this great habit of having the final say on the judgement of history over someone’s career.
And even if you lose, you still benefit by stripping away the facades of just and equitable treatment and record, for all posterity, the fact that certain policies created victims. It exposes the fact that we are governed by people who are capable of calculating how much “public good” they can gain for a given level of unremedied injustice.
Or are you now suggesting that farmers should no longer have recourse to the legal system for injurious affection?
And Luke, these “spatially efficient” models may be new but they are long overdue. And they are far from insurmountable modelling problems. A simple “lookup” reference consistent with landuse proportions will provide 99% of the truth. Failing to implement it because one cannot resolve the last 1% of implementation issues cannot be passed off as good science. It is nothing more than obfuscation to maintain a set of deliberate misrepresentations by omission.
That’s spatially explicit – i.e. many new maps of land use and vegetation from GIS and remote sensing maybe down to 30 metres or better – but only in recent years. If you want to the salinity game too you need maps of historical land use – not as easy.
Thats I have —
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