songbird wrote:
David Hare-Scott wrote:
songbird wrote:

I had to start a new thread for this as my news server kept
rejecting my reply (perhaps it is a laissez faire capitalist
machine).

maybe the long references line...


...
for the longer term i think the ground water
situation would benefit from a higher percentage
of capture of rainfall. has anyone tried to
increase that percentage?

Your idea doesn't work because:

- Irrigation water is held in dams that don't leak (or shouldn't) so
that doesn't lead to groundwater recharge.

i'm not necessarily talking just irrigation water,
but ground water recharging, which can involve
methods as described by Yeomans and others.

would you be fined if you ripped your land deeply
to capture more rainfall and soak it in instead
of letting it run off?


Yes. The limit is on the size of your dam. Also see below.


- The more that is held in dams the more that is lost to evaporation
which is not useful to anybody including the downstream ecology.

that i agree with.

not all dams are water tight and so they do
contribute to ground water levels and thus
indirectly to stream and river flows.


- It is used for irrigation where most is lost to evapotranspiration
not to groundwater, if your irrigation is soaking down below the
root level you are doing it wrong and may be raising the water table
and so contributing to salination. This has happened in too many
irrigation systems around the world including the Murray-Darling.

arid climates are different, but they are
manageable. some folks use trees to lower the
water table (and increase shade, wind protection
and to provide food and habitat for critters).


- The figure was arrived at to allow sufficient flow in the rivers
for environmental, agricultural and domestic purposes downstream,
many rivers cease flowing none the less in dry times. If the figure
was more it would be favouring those where the rain falls at the
expense of those users downstream. And yes higher figures have been
suggested by those who would benefit at the expense of others.

yes, and true if the water is going to dams and
irrigation, but if alternative approaches are
used it can recharge aquifers even in an arid
climate.

likely nobody actually get audited until someone
complains or has a grudge or the entire watershed
has issues and they do a survey... or is your
area and administration somehow highly enlightened?


Some of both. Where catchments are regulated with meters the water
authority checks and where it is also highly competitive and water licenses
are bought and sold everybody knows what the others are doing. In my case
it isn't so closely monitored.


You must also take into account that the system must respond to el
nino - la nina cycles as well as any seasonal pattern. This is not
a reliable annual rainfall nor a reliable seasonal pattern such as
annual snow-melt. It's a hard land.

you have no reliable rainy season at all?

No. My area is failrly high rainfall about 1100 mm PA but can come at any
time of year. Nothing for three months and then 200mm in a week is not
uncommon. This is from normal variability. If we have el nino we can get
as little as 300m or in la nina 1800mm in a year.

i
thought you managed to grow a decent pasture on
a part of your property? you don't get that in
unreliable arid climates without sequestering a
significant amount of rainfall...



It is done in two ways, by having clay subsoil that acts as a big sponge and
ensuring the topsoil has high infiltration so that it collects all but heavy
falls. The first is from choosing the right block the second from good
management. I can have grass growing for up to two months after the last
rain.

David