David

I appreciate all the good initiatives towards improvements with water usage, but there are three things that bother me:

1. As we can progressively grow crops and reap higher yields from the same or less water, the backup mechanisms will have to be that much greater as well, to get us through drought. By increasing efficiency, we are reducing room to move in tough times, unless we plan very carefully. Ironically, there is some merit in operating inefficiently for as long as we can go to higher efficiency quickly when we need to, ie during drought or price downturns.

2. These improvements in efficiency will facilitate a larger population. If improved efficiencies meant improved quality of life for Australians, and not just the producers themselves but for all of us, then great. But that is not likely to happen. Rather, we are simply playing catch-up in providing food for an ever-larger domestic population.

3. Better efficiency will probably mean more exports and hence more support for needy millions overseas, but this will be partly compromised or perhaps cancelled out completely by the need to supply the growing domestic population. The increased export income probably won’t increase domestic per-capita economic growth, it will simply add a bit to the economic growth that will be necessary to try and maintain the same per-capita economic turnover for ever-more people.

I implore everyone who thinks about and works towards improved efficiencies, in water usage and all sorts of other ways, to be very conscious of the total sustainability picture, and to put a good portion of their energies into the other half of the sustainability equation – population stabilisation

Ludwig, all this population stuff is completely irrelevant to the issue. We export enough beef to support 90 million people, we export enough wheat to feed 200 million people, we export enough wool to clothe 2 Billion people and we export enough cotton for 400 million people. So any increase in domestic population will mean only a minor change in export earnings. And if the cities get their act together they could add fertiliser (sewerage) to their roof runoff and value add before sending it to the farmers for higher yields and improved cycling of brown/green water.

Geoff, the flood surge portion of environmental flows is obviously not suited for recycling but all the other flows are. And the real beauty of environmental flow recycling is that a long river can be broken into segments, a sequence of cycles, so the water is only pumped as far as the price of water will allow the project to remain in profit.

And as for the recycling from a river mouth or tidal point, the needs of a brackish zone is usually performed by tidal movement, and to my knowledge there are no species that depend soley on brackish water. Please correct me if you know better, but most estuarine species pass through the brakish zone from salt to fresh and back again, not hang around in it. But logic would suggest that a partial release (leakage) would still be needed to ensure that salt water would not advance past the lower intake point.

The other aspect of the economics of environmental flow recycling is that the river is usually 2.5 to 3 times longer than the straight line that a returning pump would take. So the return journey can be at much higher speed over a shorter distance.

David, the benefits of grain legumes and canola on wheat crops is more through a disease break than through water conservation. Growing wheat in the same field year after year leads to a buildup of soil diseases that limit root growth and hence ability to access water and nutrients. The break crops allow time for the root diseases to dissipate to small numbers before the next wheat crop. This clearly facilitates water efficiency as rainfall is used by the crop rather than being evaporated or leached. OK, water comes into it, but not in the way you seemed to be suggesting.

In adittion to breeding, herbicides have been another major advance in water use efficiency as they have allowed better weed control, hence less water used by weeds, and earlier crop sowing, allowing more water to be used before the terminal drought at the end of the season.

Some argue that cultivation is important in water conservation by sealing off capillary evaporation from uncovered soil. There is some evidence to support this notion in some soil types, but I think that in most soils cultivation leads to greater water loss through exposure of moist soil and water run-off because of poor soil structure. My no-till friends swear that no-till results in better water harvesting and infiltration for crop use. They also say no-till can improve crop root growth and hence lead to better WUE.

Thanks Agronomist, I definitely didn't express that perfectly did I? Yes, of course, the 25% or so boost from rotations with is a major contributer better water efficiency.

Also in my earlier comment the brown? water colour "tag" should read ochre.

:o(

Perseus, your reply makes sense to me.

It has me wondering how much environmental flow water is released from Warragamba Dam for the relatively short Nepean below the dam and the cost of pumping it back compared to other water saving measures proposed for Sydney.

Can you tell me if the harvesting of water at river mouth is practiced anywhere.

I gather The original purpose of the Barrages at Lake Alexandrina was to supply Adelaide with water. It was originally an estuary and the Murray was tidal right up to the bend at Morgan. But the residual salt from sea tides in the bottom of the lake meant that the water was always brackish and barely fit to drink. So it is not a good example of the theory.

In fact, the conversion of Lake A. from a primarily salt water estuary to a fresh water lake is probably the most ill-concieved and wasteful piece of water works in the country. Where we once had a large expanse of salt water that was recycling sea water into blue water, we now have a large volume of blue water that does nothing but evaporate. It also prevents the Coorong from getting the more thorough tidal flushes that it used to get. As it is only 2 to 3 metres deep, my rough estimate is that Lake A. evaporates almost its entire volume each year (ie, 1,000,000 ML). And all for very marginal supply of green water to the surrounding area. There is no way such a project would ever pass a modern EIS process and, given it performs no real function but to make a the lake a bit more navigable, it should be dismantled immediately.

It is almost as bad as the Menindee Lakes, of similar depth, which evaporate about 400,000 ML each year but supply Broken Hill with only 20,000 ML. Terribly inefficient.

I don't know of any river mouth capture projects but will try a google and let you know.