02 April, 2014

Water Storage and Irrigation

An article written by Craig Simmons, professor of hydrogeology at Flinders University and director, National Centre for Groundwater Research and Training,prompted me to endeavour to collect my thoughts on irrigation and water storage in the contemporary political climate. It follows.
"A very interesting article. There is no doubt that IF we could store water just beneath the surface (need to avoid excessive pumping costs when extracting) and thus avoid evaporation losses, the yield in recoverable water terms would be much better. The articles reference to loosing about half the quantity of stored water is, based on my experience in hot climates with relatively shallow storages, on the money. This assumes the water is stored for 12 months. But, lots of factors come into the equation i.e. length of time stored, depth of storage (ratio of surface area to quantity), time of year, wind, etc.

I have often speculated that if we could use mining technology to create a sealed underground (but not too far underground) cavity in which we could store large quantities of water it would be very valuable.

Let me try and give you my general reasoning:-
  • The key characteristic of inland Australia is variability. We have a "feast or famine" regime and the spread around our river flow averages is so great that averages are almost meaningless.
  • Our big events are massive and our dry periods are horrendous! My best example is the Darling at Bourke. It has an average annual flow of 2,500 GL. With a maximum of 12,000 GL and a minimum of zero (no flow whatever for 12 months). In any discussion on the subject it is variability that is central.
  • It seems to me to make abundant common sense to "take the top" off big events and save them for the inevitable dry periods ahead. A very small percentage (1 or 2%) of a big event can amount to a big volume of water. But, evaporation is the enemy.
  • Some argue that evaporation is a natural phenomenon and we should accept it. I retort that 70% of the earth surface is covered by (salty)oceans and surely that is enough for cloud formation. Look at the size of the big weather systems that sweep across Australia. By comparison, the piddling amount of evaporation of valuable fresh water from our  storages would really have negligible impact on rainfall.
  • In most circumstances an inefficient (in evaporation terms) storage is better than no storage, because of what you can do with what's left. Our two most inefficient storages in the Murray Darling Basin are Lake Alexandrina (Lower Lakes) and the Menindee Lakes. (In the Lower Lakes case there is now no need for these to always be maintained with fresh water.Evaporation is huge and there is no productive use to be made from what is left over. Irrigators around the Lakes now have piped fresh water from upstream and water for Adelaide (and other irrigators and many northern S.A. towns) is also extracted from the Murray well upstream).
  • It seems to me that we struggle to understand ground water. (Why it's not called "underground" water, I know not). There are relatively shallow aquifers which appear to more or less follow the river courses and which are an important source of water for many irrigators. There are also quite large areas like the Liverpool Plains which have relatively shallow water below the surface. Extraction of this water, like that from rivers/dams is tightly controlled.
  • Then there is the deep (minimum of around 700 metres) Great Artesian Basin (G.A.B.). This water is generally not usable for irrigation due to its mineral content, but has been a blessing for livestock and non-drinking human use.This water comes to the surface under pressure and can be very hot. There is considerable evidence that we have been profligate with its use. The Government scheme to encourage "capping and piping" artesian bores is demonstrating that we can rebuild flows and pressures by only taking what is needed rather than having open flowing bores.
  • There is speculation as to the original source of this artesian water. Most seem to believe it originated in the North Queensland tropical Great Dividing Range, others believe it comes from New Guinea. The problem with ground water generally is that we can't see it and there remains much uncertainty as to its source and path.
  • Returning to surface water, it is no coincidence that most of our major dams are in higher rainfall hilly areas where valleys provide the ideal terrain for dams. There are still suitable sites for additional dams. Note that the Clarence River (on average) pours 5,000Gl into the ocean annually and a diversion of 20% of this, providing it is diverted at the right time (big events), could make a huge increase in the Darling catchment without harming the North coast environment.
  • For my fellow "economic rationalists", note the price irrigators were prepared to pay for the recent Gwydir allocations released by the Commonwealth Environmental Water Holder (CEWH). Capital expenditure on water infrastructure generally has a long life and could be written off over a long time period with water users paying the amortisation (and maintenance) costs.
  • The article refers to Australia's recognised expertise in water management. This reputation has suffered considerably as a consequence of the Commonwealth takeover of water management in the Murray Darling Basin. The need to draw on international environmental agreements resulted in an unbalanced plan and the preparedness to throw $10bn at the problem has resulted in a political "dog fight" rather than proper resource management in the national interest. The fact that management of the Snowy Scheme in the important headwaters of the Murray and Murrumbidgee and the management of the Lower Lakes at the bottom of the system were not even addressed in the planning process, bears testament to this assertion.
For further background see this post also. 
David Boyd
02.04.14
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