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).
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.
- The more that is held in dams the more that is lost to evaporation which
is not useful to anybody including the downstream ecology.
- 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.
- 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.
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
The term does not mean unplanned or left to run free by the owner it means
uncontrolled by the State. All countries limit private enterprise to a
degree, the extent varies quite a bit. It was a whimsical nonce remark, I
don't propose to get into economic or political theory as that is OT for the
I fill above ground house tanks holding 50 kl from roof water for domestic
use but that volume would be useless for the garden and in any case must be
reserved. I have a small dam for stock watering holding 2.4 Ml that will
keep the garden alive in emergencies but that is uncovered and does lose
some due to evaporation.
As I understand it a cistern is used in very dry climates (eg north Africa)
and it is covered like the former but as large as the latter. This would be
extremely expensive, certainly out of my range.
I saw them in France. Why they feel they need them is anybody's guess,
as they get at least 2 - 3 days of rain every month.
In any event, in a cistern there is little evaporative loss of water to
heat, and wind as you find in ponds. A 25' x 45' cistern would be
expensive, no doubt. It was just an idea.
Sorry, error, 25' is the radius.
By 2.4Ml, am I to understand 2.4 million liters (= 84,755 cu.ft.)
which would be contained in a tank 50' in diameter and approximately 45'
tall. V = (pi * r^2) * height = 1962.5 sq. ft. * 45' = 1962.5.
In any event, there is no reason for the perfect to become the enemy of
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?
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.
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).
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
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? :)
you have no reliable rainy season at all? 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...
Yes. The limit is on the size of your dam. Also see below.
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.
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.
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
that seems to really cry out for swales and
:) right, and that second bit is kinda my point,
that you do manage your property well so that it
does capture the water that lands on it. i would be
surprised if you are losing 90% of it to run off.
i.e. those pastures are recharging the ground water
at some level and are contributing to a longer term
flow for the water shed. probably also suffer very
little erosion too.
No the fainfall is too high, in a wet spell with clay soil it would remain
waterlogged for too long. As it is I have to plant all my fruit trees on
mounds and build up the vege garden so water doesn't sit in it. The heart
of the problem is that you must have a compromise between the design that
suits very wet and very dry conditions because you will get both at
The same applies to house design. You have to deal with a temperature range
from -7C to 44C and very low to very high humidity which is not the same as
a cool temperate area where you get (say) -20C to 25C where you want to get
the sun into the house all year round or tropical where you want to keep it
out all year round. As I said its a hard land.
Perhaps I didn't explain clearly in an earlier post. You are allowed to
impound ~10% in practice this limits your dam size according to a formula
based on your land area and rainfall. It doesn't mean the other 90%
necessarily runs off.
smaller and wider swales/catches then. you can
always adjust them as needed. :)
well true, but when someone says they have intermittent
rains with months in between then that tells me that they
want to capture every bit of it. how to do that is the
fun part. :)
here it rarely hits -29C or 41C, but those
are possible extremes. so we need a dual
design which works to both let in light in
the winter and to not let it in during the
we also have low to high humidity conditions
in almost every season.
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