Water Ponding/Management

keller ak.and.ak at on-line.de
Sun Dec 23 10:21:58 EST 2001


> If water converges into a single gulley, you could divert
> the water higher up. Typically a key line is identified as
> the line where the land changes from convex to concave.
> It is here that water tends to collect, therefore can be
> diverted laterally by opening the soil with a key line plow
> or subsoiler.

If you look at a contour map of a valley you will find, that in the upper
part, contour lines diverge if you follow them out to the ridge. Further
down, countour lines converge if you follow them from the valley to the
ridge.

The key line is the boundary between these two areas.

If you draw lines on the map that run parallel to this key line, you will
notice that above the key line, the distance of these lines from the next
higher contour line will increase (because of the divergence). Below the key
line, these lines are going to cross the next lower contour line (because of
the convergence). This means that theses lines are actually going _down_
from the middle of the valley. They conect points higher up on the valley
bottom with points lower down on the ridge. (see Figure 9 on page 46 in
"Water for every farm, Ken Yeomans Keyline Plan" - I think that picture is
also in Mollison's Designer's Manual, but I am not sure. I have just sent my
last copy to Cameroon, and the new one has not yet arrived. Maybe somebody
can check.) If you plow with a chisel plow along such lines, water would
flow allong the furrows from the valley to the ridge. In contrast to this,
normally water will flow down into the valley on paths perpendicular to the
contour lines.

Further down below the keyline, if you continue to plow parallel to the
keyline, the slope of the furrows will become too steep. You must then
select a new contour line as a guide line and plow parallel to it. The key
line is the highest line that can be used like this.

If you plow this way, water will spread evenly over the whole area instead
of being concentrated in the middle of the valey. Because of the furrows, it
will also penetrate much deeper into the ground. More water will be stored
in the soil instead of leaving your farm quickly. Plant roots will reach
deeper, thus bringing organic matter further down. In subsequent years, you
can repeat this and plow a bit deeper each time. According to Yeomans, this
way subsoil can be turned into top soil relatively quickly.

In any case, get a copy of that book (or CD). May be the best investment in
your lifetime. Ken Yeomans is also working as a consultant, not cheap, but
probably well invested money (see his web site).

Sesons greetings
Andreas








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