Subject: Re: Tree revetments - request for info

From: [email-masked]
Date: Thu, 13 Jul 1995 13:25:54 -0700

On 13 Jul 1995, Vince Busto wrote:

> I am presently working with a biologist who is interested in utilizing trees
> for bank protection in rivers,  The trees (fir or pine) are tied into the 
> riverbank with cables.  The biologist explains that the trees slow the water 
> velocity at the bank to the extent that sedimentation occurs.  In time this
> sedimentation allows plants to re-establish themselves along the bank.  The
> tangle of branches also provide a place of refuge for small fish; refuge from
> high water velocity and reguge from large predators.
> 
> Does anyone have any experiences, or references to case studies, with tree
> revetments that they care to share with me?  I am especially interested in 
> finding out if there are clear guidelines as to where tree revetments may,
> or should not, be used.  References for tree revetment design would also be 
> appreciated.   
> 
> My thanks in advance for your responses.
> 
> Vince Busto
> 
> 

I'm surprised that fir and pine are being used...they tend to be dry-site 
species.  In the NW USA, we use willow, alder, or poplar...hydrophytic, 
fast-growing, and they develop a pretty dense root mat.

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From: [email-masked] (Vince Busto)
Date: 13 Jul 1995 16:17:03 GMT

Vince Busto

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From: [email-masked] (Dave Fluri)
Date: Mon, 17 Jul 1995 17:01:51 GMT

In <[email-masked]> [email-masked] (Vince Busto) writes:

>riverbank with cables. 

In Ontario, we prefer _Thuja_occidentalis_, which we call cedar, for such
applications.  We call them "cedar sweeps".  Alternatively, we use almost
anything handy, but our other lowland woods don't have the longevity of
cedar when in the water.  Non-cedar sweeps are usually called "brush
bundles".  Bundles are often installed in a "scale" arrangement; overlap
bundles beginning at the lower end.

Sweeps or bundles are placed at the very head of the inside bend of a
meander, just where the water begins to pull away from the bank.  They
should be installed parallel to the direction of flow.  The trunk of the
tree, or the bound end of the bundle, is wired to a post driven into the
stream bed.  One or more posts can be placed along the bundle to give it the
proper orientation relative to the current.

I don't really consider them as "bank protection" _per_se_, at least not in
the sense of a revetement.  We sometimes use log revetements along the
retaining bank (outside) of a meander, but their installation and philosophy
are somewhat different (EMail me for details).  I view sweeps and bundles,
rather, as aids in directing the stream flow.  By judiciously placing them,
you can encourage the re-establishment of some sort of meander pattern in
stream sections which have been channelised or which have had their meanders
"blown out" by some sort of catastrophic event.  They seem to work best when
installed so as to _slightly_ constrict the base flow.  The increased
velocity enhances sediment transport.  It is also important that they be
installed so as to be completely submerged at the "bank full" stage.  As
flows decline, they provide the sediment-trapping function you describe
hereunder.

>The biologist explains that the trees slow the water 

This really works!  I've seen cedar sweeps that, when installed, appeared
huge, with large, gaping areas behind them.  Five years later, the area
behind was completely filled in and revegetated; you'd have had a tough job
to find the sweep.  Often it was only the stubs of the posts sticking up
that were still visible!  You're right that sweeps provide refugia for small
fish, but this is fairly transitory, since the sweep is designed to
eventually fill in with sediment.

>Vince Busto

I should indicate that I've only used sweeps and bundles in fairly low
gradient applications on streams with moderate to high bed loads composed
largely of fines.  Judging by the way they work, I don't think they'd be
appropriate in high gradient situations.

Hope that helps.

-- 
				|
Dave Fluri			|	"No me agaro ya de nada, para
North Bay, Ontario, Canada	|	 asi no tener nada que defender."
				|		-Carlos Castaneda