Thread: Hydrology - the real measurement???

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 ) 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.

Originally Posted by Slunnie

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.

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.

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.

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.

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.

Originally Posted by 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.

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

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