permaculture

["Australia Felix" <pcorgbgo@bendigo.net.au>]

Hi Frank,

> Oops ...I hit the send now button before I finished the last post
...sorry!
Yeah I've done that a few times now.  I'm really pressed for time - I have
heaps of reports to complete and I'm in South Australia next week attending
a Neal Kinsey (Hand's on Agronomy) lecture on Advanced Albrecht Systems. It
just goes on and on. This stuff is fun though so I'll play at a few
responses before getting back to the stuff that pays the mortgage......

> <<This can only be
> overcome if the dam is large enough for exit and entry batters from the
> island to shore to bottom out to a level close to the maximum.>> Oh,
oh..I'm
> afraid I'm out of my depth :) on this. Please enlighten me further.
The batters are the excavated slopes of the dam: Batters are expressed as a
width to height ratio. A retaining wall has no batter as it is straight up
and down or has a 1:1 batter.  A slope that falls 1 metre vertically over 3m
horizontally is a 3:1 batter. Generally we prefer to restrict batters to at
least 3:1 with walls having 3:1 on the inside and 4:1 - 5:1 on the outside
to the toe. The problems associated with too steep a batters are many.
Erosion, particularly from wave action is the most significant. In addition
where you have dispersive soils the edges will tend to break away and
increase sedimentation. With your island you will find that an excavator
will be able to do the neatest job, although you'll have to make sure that
the batter from shore to bottom doesn't exceed 3:1 with the same slope
applied from bottom to top of island. Its easier to express as a diagram....

> <<What we prefer to do on dams less than 5 Ml is to make penisulas
instead.>>
> What size is <<5 Ml>> ?  The total pond area is about 1 acre with a depth
of
> 8'3" in middle. also like gentle slopes along edges.  What do you think?

There are a couple fo formulae to work this out (I just get my surveyor to
work it out on his computer as a DEM) but for working it out you need to use
the prismoidal formula. Again this needs a diagram and I need more
time....1.25 Megalitres (1 250 000 litres) = 1 acre feet. 25 Ml = 20 acre
feet

> Its OK to try and do this however you are limited by 2 things: the
> landscape/shape and money. I would love to do all of those idealised edge
> features but at $150/hr its often difficult to do to a budget.>>  This has
> got to be a relatively low budget affair...or it's not going to happen.
So
> how do we control the costs?

By using some of the resources I listed yesterday you can make some well
reasoned judgements as to how much dirt you will need to move. Your
earthmover should know how much his particular machine can push per
hour....To satisfy your own curiosity I would catch up with Caterpillar as
they have cubic feet/metres per hour figures for their different machines
(where operated optimally). This planning stuff is where you can save the
dough and quantify the job performance.

> <<We would use a dozer to make
> most dams and they are capable of creating flowing linear edges.>>  Would
a
> loader be better than a dozer? The xcavator would do the work...he 's done
a
> lot of farm ponds. Charge is $70 an hr...claims he could dig it in a day?
Is
> that possible? Seems like a lot of dirt, shaping, top soil moving etc. for
an
> acre. I don't have a clue:)

Sounds ok as long as he can finish the dam off as well. By that I mean can
he smooth off the batters and replace the topsoil. I'm a bit weary of
excavators though and their ability to do this. Again sometimes you need
another machine to work on finishing the same job. Very hard to say without
seeing the dam and what you want to do....

> <<If the dam is of a fairly decent size (ie. 5Ml +) then their is
> usually enough edge area for a dozer to cut out well battered curves.>>
?????

See above.

> <<we need to speculate all options though to return back to the
> what's possible - a point often missed....>>  Agreed!

> <<Very possible however needs consideration of the flood flow rates to
develop
> sustainable engineered widths/depths>> How does one determine these flow
> rates which are probably contingent on rainfall off the steeply forested
> ridges at the back of the pond site? And what are sustainably engineered
> widths?

The resources listed will help as will your local soil conservation
authority. They should have flood flow rates listed regionally, and the
Meteorology people will have rainfall figures. These together with a
catchment area calculation (from the contour map) will allow you work out
the correct sized overflow and any other engineering features needing
consideration. The catchment runoff calculation is roughly as follows: (NB.
Metric is so much easier to work out all this stuff)

100 x A x R x Y litres

A= catchment area (hectares - 1ha = 2.47acres)
R= average annual rainfall (millimeters)
Y= runoff as a % of average annual rainfall

eg.  A=100ha; R=750mm; Y= 7.5%

100x100x750x7.5
=56 250 000 litres
=56.25Ml

> <<I find it better to develop drainage
> depression into forestry/wetland systems so that we don't have water
running
> over bare ground and for nutrient/sediment trapping,>>  This is actually
what
> is happening now as water flows through various drainage ways and channels
to
> creek, wet land areas. Some areas have lots of crawfish...good sized. What
> happens when water dries up..do crawfish die out or can they survive in
their
> holes?

If they're native ones like the yabbies we have here then they are likely to
be well equipped to cope with local seasonal climate fluctuations.

> <<Sometimes where we have to take out large trees to construct a dam we
will
> push them out prior to topsoil stripping then push them back into the dam
> where they will provide multiple functions.>>  We won't need to take out
any
> trees in the pond area...but if it's desireable I have plenty of downed
> trees, and limbs piled up nearby. Please describe how to use them
effectively

You need large trees preferably with durable timber so that they don't rot
too quick in the water. If you have a gentle enough entry slope then drag
them half in so that they are partially submerged. Again pictures would
help.

By having topsoil stripped as a starting point and then pushing it back over
> the excavated areas you will get vegetation coming back after the first
few
> rains. Also try and make the water level so that it comes onto unexcavated
> grass, so that you get shallows/wetlands that resemble a ephemeral
> floodplain.>>  Yup:)
>
> Great post, and insights Darren. Thanks. Look forward to executing this.
> When I get back to NY and learn how to use a scanner I'll scan some
pictures
> for the group.

> Look forward to continuing thread. Should be a great FAQ for anyone
building
> a PC farm pond.  Best to all.   Cheers.  Frank
>

Thanks Frank, yes I look forward to you making the time soon to get that
process happening. Words can only go so far - so I think further discussion
on this point from me can only proceed after we get some pictures scanned
when you get back...

Cheers,

Yours and Growing,

Darren.




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