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Re: Swales & Mudslides (fwd)

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From:     YankeePerm@aol.com
Subject:  Re:  Re: Swales & Mudslides (fwd)
Date:     Tue, 17 Feb 1998 08:39:27 EST
To:       yount@csf.Colorado.EDU


In a message dated 2/17/98 7:59:57 AM, you wrote:

<<As everyone knows, Noorthern California is Mudslideville. Here's my
question: will swales reduce/prevent mudslides? Obviously, they stop
erosion by slowing water and putting it into the dirt - but when the dirt
is saturated, we get mudslides. If I could make a coherent argument to
FEMA/SBA, I think we could get a major loan program (4%, 30 years) to build
swales everywhere. I was in this program after the '82 floods and they are
very loose about flood damage/damage prevention IF the landowner can make a
coherent argument.  So - any evidence to support the hypothesis? Thanks.>>

It depends.  If the swales enable deep rooted plants to establish because they
retain moisture, they should reduce mudslides.  However if they become extra-
concentrated zones of water and water-saturated soil, they could hasten
mudslides.  

Swales are often regarded as a panacea which they are not.  As a major change
in the surface of the Earth, they require careful design integrated with all
other design factors.  Repeat, integrated with all other design factors.
Swales by themselves have potential for harm that is amplified by the extent
of the swale, the steepness of grade, and the amount of catchment above them.

Swales are obviously not an end, but one tool.  We need to look, on a site-
specific basis, at the SOURCE of the water, getting as high on the landscape
as possible, and then evaluate the best means of control.  If we control water
working from the top down, we don't end up with more water than we can handle
at any point on the slope.  Because swales represent a great deal of
disturbance, we restrict their use on sensitive sites where little disturbance
of other kinds is anticipated.  Where major disturbance is anticipated, such
as a housing project or a road, then swales may be one of the compensatory
measures attempted.

At some point we have to say, we can't help you because you have chosen to
live where you will slide away no matter what we do.  Basically, the
definition of a type 1 error is that expenditure of reasonable amounts of
energy can't fix it and the situation constitutes persistent danger or
continuous work.

In general, I would look to stablising subsidance prone slopes with
appropriate vegitation.  In the philippines, for example, they have a pine
tree with a extremely long tap root that pins the soil to the mountain, with
very strong lateral roots radiating out ever half meter or so improving the
hold.  They cut these trees and they get subsidance.  

So I would start studying root structure of native trees, come up with a good
mix of those adapted to the site, and lay in bands on contours.  These can be
watered with very small "swales" or catchment diversions on contour which feed
a basin where the tree is planted.  The "mix" may be in time, with accelerated
succession to more fire resistant species coming up through the original
planting as understory.  

While this would work in most cases, you will find that real estate people
will resist to the deaththe idea of "wasting" all that space with forested
bands.  

However if done, not only would the soil be anchored as well as is possible,
but the bands of trees if covering a large enough area, would soften weather
to some extent by pulling in more moisture during dry periods and reducing the
severity of many (but probably not all) "bad" storms. 

Anyone who has practiced permaculture for any length of time knows, however,
that biological solutions are known.  The problem is always land
ownership/tenure patterns and territorial irrationality.  California mud
slides are evidence for natural selection.

For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since 1982),
Elfin Permaculture workshops, lectures, Permaculture Design Courses,
consulting and permaculture designs (since 1981), and now correspondence
courses via email.  One is now underway.  Next live program:  Paraguay,
8/10-22/98.  Copyright, 1998, Dan & Cynthia Hemenway, P.O. Box 52, Sparr FL
32192 USA. Internships available. YankeePerm@aol.com  

We don't have time to rush.

A list by topic of all Yankee Permaculture titles may be found at
http://csf.colorado.edu/perma/ypc_catalog.html

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