[permaculture] Suitablility of clay for building ponds
Dieter Brand
diebrand at yahoo.com
Tue May 5 07:02:47 EDT 2009
My soil is about 2 to 3 feet of yellow clay mixed with stones on top of a thin layer of grey clay which is formed on top of the rock bed. Sorry, don't know the technical names for these types of clay.
Anyway, the yellow clay will dry out slowly during the dry season through capillary action, surface evaporation and plant transpiration. However, some of the humidity in the yellow clay layer will slowly percolate down the hillsides through water lines on top of the grey clay which is 100 % water-impermeable and which therefore doesn’t let through any water.
I made a number of water catchments by excavating the soil down to the grey clay and by using some of the grey clay to form a barrier downstream. This forms a catchment hole fed by waterlines from upstream that doesn’t let through a single drop of water downstream. I lined the catchment holes with large stones to prevent the grey clay from washing out and to prevent the water from getting cloudy. The position of the intake tube assures that the water in the catchment hole is always at a certain level so that there is no risk of cracking in the clay when it gets dry. Except for the tubing, I only use materials found on-site.
Upstream of the water catchment, I made a large hole which I filled with coarse sand, pebbles, small and large stones to filter the water before it goes into the catchment. We have a lot of white quartz stones on our land which are ideal for that purpose. I planted different types of plants into this natural filter so that the roots spreading between the sand, pebbles and stones may take up impurities in the water. I cover the catchment holes to prevent evaporation during the summer.
The algae, frogs etc. in the water catchments provide a biological environment that is beneficial for the garden soil which I irrigate with that water. With a daily flow-through of a few thousand liters in winter and a few hundred liters in summer, I'm not unduly worried about nasty things that may develop in stagnant water.
What do you mean by a “two acre foot pond”? Is that a pond of two acres surface area with a depth of one foot? That wouldn’t be of much use in my opinion. It would be like a paddy field which you can do when you have more than enough water anyways.
Dieter Brand
Portugal
PS: In France and some of the other Celtic regions they used a technique for making a pond impermeable by a microbial layer made from organic materials. I can’t remember the name (that’s what old age does to you ;-)) nor how exactly this organic layer is formed (perhaps by compressing manure and straw???). I never used it because it can only work if the pond is permanently filled with water. In severe arid conditions, as here in the Saouth of Portugal, the water level in ponds or artificial laces can fall by several inches per day for 6 or more months of dry season with high temps. If I can remember what the technique is called I will let you know. But perhaps someone else can chip in here.
--- On Mon, 5/4/09, Gene Monaco <efmonaco at comcast.net> wrote:
From: Gene Monaco <efmonaco at comcast.net>
Subject: [permaculture] Suitablility of clay for building ponds
To: permaculture at lists.ibiblio.org
Date: Monday, May 4, 2009, 12:06 AM
I have a little background in this, and I am also trying to fix a leaking
pond made by a predecessor.
The type of clay and how it is compacted is what it is all about.
Ideally, you can find clay that is a deposit from eroded volcanic ash. This
is very very fine and highly expansive. Around here it is known as
montmorillonite. Bentonite is a type of montmorillonite, and is commonly
used in construction.
Modern methods sandwich about 5 or 6 mm (1/4") of bentonite between two
sheets of something. Earlier products used paper (like drywall) as the
binder, but now they use geofabrics as well for the pond liners, especially
for landfills. They also sell bentonite pellets in 50 lb bags that you can
till into the insitu soil if it is already clayey and dry enough to till.
The liners are very effective but are expensive. They are however efficient
as far as the clay is concerned because the manufacturing process puts
precisely that 1/4" between the sandwich sheets. If you try to till it in
by hand or spread it out, you could never get 1/4" uniformly spread out
over
the surface; rather, you have to put about a 2" layer down and then till
it
in as best you can, or cover it with 18" of packed cover.
The key is that the expansive clay has to be contained by pressure over it.
This means in practicality, that you have to over excavate the pond 18" or
so, lay down the sheet (or till in the 2" layer) and then cover it with
18"
of overburden, preferably clay. That way when it gets wet and expands, it
will have nowhere to go and will form the seal you're trying to achieve.
If you till it in to the top 6" without the overburden, you are taking
your
chances that when it expands it will lock into the surrounding particles
instead of fluffing and allowing the water to run around it, rendering it
useless.
The principles described here are applicable to any clay site. You need
something impervious enough and packed down enough under enough pressure so
that when it expands, it won't fluff so much as to allow the water to run
around (through) it. So the type of clay and how it is installed is
everything.
One detail is at the top. I've seen a number of ponds that held water to
the design level at the beginning, but then dropped a foot or two or more
after a few years. This is because the clay at the edge is not under the
weight of the water and tends to fluff. Also, animals climb in and out
right at the top edge and tear it up as well (especially true for EPDM
liners). To deal with this, you need to run the clay seam back far enough
outside the edge of the pond and pile up an 18" or 2' berm around the
edge,
plus add rocks for weight and protection from animals.
Gene
Date: Sat, 2 May 2009 12:47:26 -0700 (PDT)
From: Rain Tenaqiya <raincascadia at yahoo.com>
Subject: [permaculture] suitablility of clay for building ponds
To: permaculture at lists.ibiblio.org
Message-ID: <655408.34901.qm at web38107.mail.mud.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
I'm building a two acre foot pond to irrigate our permaculture
demonstration
site and I'm having difficulty identifying appropriate soil for building
the
dam and lining the pond.? We have quite a mix of soils varying from
sandstone-derived loam to serpentine-derived clay.? Is the clay content the
most important variable?? We have some very high clay content soil that has
a crystal like structure when exposed.? It is very expansive, and when dry,
it gets blocky and is easily broken up.? I think it would be fine where it
will be under other layers or always wet.? Does anyone have any answers or
comments on this?
?
Thanks,
?
Rain
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