Hydrology - the real measurement???

[Slunnie]

Reading the rain gauge everyday and wondering about how much of it is effective rain, I was recalling a conversation from a few years ago with the bird in the lower art gallery at Silverton (north of Broken Hill) where she was telling me of water conservation, wastage and the shandying process which they use to produce enough water for the region. Another thing she said that I thought was interesting is that Broken Hill has a higher evaporation rate than the precipitation which they receive.

So I thought I'd try this in humble O-town.

I filled the rain gauge to 50mm on a Sunday and then checked it each following Sunday. The rain gauge was setup per normal raingauge setup.

Wk1: -12mm
Wk2: -12mm
Wk3: -20mm

In the last 3 weeks we have lost 42mm of water through evaporation.

Looks to me that our personal water management strategies shouldn't be focussed only on minimising water use and wastage, but also managing to minimise water loss through evaporation.

I guess there isn't a great deal that we can do about dam losses, but it highlights the need to cover water tanks and perhaps even the soil around irrigated/all plants with something that lets the rain through, but not the sun etc etc etc.

Here is one of my solutions with the Ghost Gum I'm trying to grow.

https://www.aulro.com/afvb/images/imported/2009/03/1175.jpg

[rick130]

This is why zero till farming is making a huge impact.
I don't pretend to know all the inns and outs, I'm not farming but I talk to a lot of cockies in these parts, and while not without its own issues, conserving water is one huge plus.

Intelligent grazing, eg. rotation or cell grazing can help immensely too (I can talk from experience on that one :D ) by maintaining a healthy density of pasture, encouraging dung beetles by carefully considered stock worming practices and improving soil humous.

Even on a smaller scale, we use lots of mulch around all the trees and shrubs we've planted to reduce evaporative losses.

[Utemad]

I guess there isn't a great deal that we can do about dam losses,

Evaporation is a big problem in most of Australia.

You can get covers for dams to reduce evaporation but I imagine they are hugely expensive. Also why deep dams with minimal surface area are better than shallow dams with a high surface area.

It is possible to have more evaporation than rainfall as the evaporation is calculated not actual.

https://www.aulro.com/afvb/images/imported/2009/03/1174.jpg

[Utemad]

I should also add that had you filled a dish with water instead of a rain gauge, the evap rate would have been higher. The rain gauge in your experiment would have protected the water from the wind.

Your rain gauge would be more like the deep/low surface area dam.
I think they use a dish in the official calculations.

We have a meteorologist on AULRO don't we?
I can't remember who it is. EDIT: Just searched and it is Frenchie. Probably still in Antarctica by the looks of it.

[Slunnie]

Ahhh, thats some interesting stuff there! Looking at the map it looks like almost all (perhaps with the exception of coastal areas) of Aus has higher evaporation rates in comparison to rainfall.

Likewise with Agricultural practices. I''ve got some acres but am nothing like a farmer.

[spudboy]

Not 100% related to what you are saying, but we "discount" the first 10mm of rain that falls as not being worth anything to our vines.

An 8mm rainfall is nice for the grass, but does practically nothing for the vines.

If we get 30mm, that's about 20mm of useful watering we can count on, and then reduce the irrigation.

So, we'd rather have rain in big lumps, than spread out over a number of days, even if the total that fell is the same.

[rick130]

If I can expand slightly (there are books and books and reams of papers on these topics) getting the water into the ground in the first place is a major issue.
Most of our soils are very old, nutrient deficient, very fragile and heavily compacted from 200 years of hard hoofed grazing animals and vehicles. A lot of rainfall isn't readily absorbed, it has a tendency just to run off.
It's amazing how something small like the humble dung beetle can be a player in helping to restore compacted soils, unfortunately things like ivermectin based wormers kill the larvae, undoing the point of having beetles in the first place.

[Bushie]

Not 100% related to what you are saying, but we "discount" the first 10mm of rain that falls as not being worth anything to our vines.

An 8mm rainfall is nice for the grass, but does practically nothing for the vines.

If we get 30mm, that's about 20mm of useful watering we can count on, and then reduce the irrigation.

So, we'd rather have rain in big lumps, than spread out over a number of days, even if the total that fell is the same.

Similar story when looking at fire events - we discount the first 5mm as it is seem as being intercepted by tree canopy and not making it to the ground.

Looking at the map, even around Sydney the evap rate is 1400mm - 1600mm but rainfall where I am is <1200mm and I'm within 10km of the coast.

Martyn

[Slunnie]

I was thinking the same, but didn't say much as I'm not into viticulture or any other form of agriculture (ie. I'm not the pro), but from the little bit that I do I also thought that consistent and enduring irrigation (or rain) better saturated the soils than quick heavy falls because the soils will only absorb at a certain rate which seems to depend on the soil type, but it takes time to get the water down deep where it can be held. This is one of the reasons why I'm now a big fan of drip irrigation for what I'm doing

[Xtreme]

The general farming practice for some time has been to channel runoff into a storage area (the farm dam) for future use.
However there is a guy in the Widden Valley who has channelled runoff away from the creek/river to spread out across his paddocks.
Apparantly it has proven quite successful and his property suffered very little during the drought.

Roger

[Sly]

Google Pan evaporation, some interesting results of changing evaporation rates around the globe.

[StephenF10]

Evaporation is a big problem in most of Australia.

You can get covers for dams to reduce evaporation but I imagine they are hugely expensive. Also why deep dams with minimal surface area are better than shallow dams with a high surface area.

It is possible to have more evaporation than rainfall as the evaporation is calculated not actual.



BOM does measure actual evaporation at some sites by means of a Class A Pan (see MEA | Products - Class A Evaporation Pan | Measurement Engineering Australia (http://www.mea.com.au/products/evaporation-pan/2/)

At observation time water is added to bring the water level back up to a fixed point and the amount added is converted to an evaporation figure.

Stephen.

[Xtreme]

Although I agree with the foregone comments and accept the fact that we live in a 'dry' continent, the comparison of raifall and evaporation is not as bad as it may appear. If it was then Australia would be a much drier place than it is. eg Refer to Bushie's figures for a location only 10km from the coast.

When comparing evaporation and rainfall one must not overlook the area over which each occurs.
Whereas rainfall generally falls over a reasonably broad geographical area, the majority of evaporation occurs over the relatively (by comparison) small areas of 'stored' water.

In other words, to calculate total gain or loss, volumes (area x depth) must be considered and not merely 'depths'.

Roger

[rick130]

The general farming practice for some time has been to channel runoff into a storage area (the farm dam) for future use.
However there is a guy in the Widden Valley who has channelled runoff away from the creek/river to spread out across his paddocks.
Apparantly it has proven quite successful and his property suffered very little during the drought.

Roger

Peter Andrews. Natural Sequence Farming Home (http://www.naturalsequencefarming.com/)
He started off by slowing the water flows in the creeks and depressions by reeds, weeds, trees, whatever.
Basically slowing the flows everywhere helped retain moisture where you wanted it. Makes sense to me.

His theory is that this is how the country and watercourses worked before whitefella came along and deforested everything including all the watercourses, creeks and rivers. Hell, 15 years ago SoilCon came along and ran a dozer right through the Pages River here (a tributary of the Hunter) to take out all the she oaks and weeds to speed up the flow. It also filled all the natural holes etc. (you can't swim anymore, all the hoples have gone.)
According to those that have lived here all there lives, the flows have never been the same since, but slowly the holes and trees, etc are reappearing.
His position is that drought is a natural and regular occurrence in Australia, maybe even more regular than rainfall. He ended up losing his farm (and his marriage ?) as he became obsessed with it, but Gerry Harvey became a convert (one of his studs is nearby)

Actually, it goes along with a comment supposedly made by a CSIRO scientist once at a grazing conference " there is no such thing as drought, only over stocking "

[abaddonxi]

Peter Andrews. Natural Sequence Farming Home (http://www.naturalsequencefarming.com/)
He started off by slowing the water flows in the creeks and depressions by reeds, weeds, trees, whatever.
Basically slowing the flows everywhere helped retain moisture where you wanted it. Makes sense to me.

His theory is that this is how the country and watercourses worked before whitefella came along and deforested everything including all the watercourses, creeks and rivers. Hell, 15 years ago SoilCon came along and ran a dozer right through the Pages River here (a tributary of the Hunter) to take out all the she oaks and weeds to speed up the flow. It also filled all the natural holes etc. (you can't swim anymore, all the hoples have gone.)
According to those that have lived here all there lives, the flows have never been the same since, but slowly the holes and trees, etc are reappearing.
His position is that drought is a natural and regular occurrence in Australia, maybe even more regular than rainfall. He ended up losing his farm (and his marriage ?) as he became obsessed with it, but Gerry Harvey became a convert (one of his studs is nearby)

Actually, it goes along with a comment supposedly made by a CSIRO scientist once at a grazing conference " there is no such thing as drought, only over stocking "

I exchanged a couple of emails with that bloke a few years ago.

While talking to someone about him, can't recall who, they suggested that there might be a problem with, I think, water sequestration.

Dunno I was pretty impressed.

Simon

[rick130]

I exchanged a couple of emails with that bloke a few years ago.

While talking to someone about him, can't recall who, they suggested that there might be a problem with, I think, water sequestration.

Dunno I was pretty impressed.

Simon

Possibly, as the water that falls on your land isn't owned by you but the state and you aren't allowed to stop, divert, etc, etc, yet all he's advocating is slowing it.
This is why farm dams over one megalitre have to be licensed in NSW. Department of Water and Energy: Harvesting runoff (http://www.dwe.nsw.gov.au/water_trade/rights_farmdams.shtml)

[Bush65]

P.A. Yeomans (http://www.soilandhealth.org/01aglibrary/010125yeomans/010125homage.html) is also attributed with great solutions for conserving water in the land. He developed the keyline design system (http://www.keyline.com.au/)

[Graeme]

Possibly, as the water that falls on your land isn't owned by you but the state and you aren't allowed to stop, divert, etc, etc
It OK to change its route it as it flows through your property but you cannot change the point at which run-off exits your property.

[rick130]

P.A. Yeomans (http://www.soilandhealth.org/01aglibrary/010125yeomans/010125homage.html) is also attributed with great solutions for conserving water in the land. He developed the keyline design system (http://www.keyline.com.au/)

Yes, and apparently his original demonstration farm at Nth Richmond or Kurrajong is under threat of development.
The FIL was a great Yeomans advocate, used his keyline system and vibrating ripper. (and told as often as he could :rolleyes: :lol2: )

[Searover]

Here in WA the water authority already pump excess dam water underground,now the younger generation never get to see the dams over flow.

[slug_burner]

To reduce evaporation from farm dams you can place plastic softdrink bottles on the surface. I saw this done on some yabbie farm in South or Western Australia. If the surface is covered by plastic bottles it reduced the moisture loss to wind as well as reducing the amount of surface area exposed to the sun.