Controlling Erosion

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ILLUSTRATION: MICHAEL HARNEY
As you can see, a gully is really the result of erosion — not the cause. Yet once the gully gets established, it brings about many severe problems.

A visitor from outer space might have a good laugh at how
we handle — or don’t handle — erosion. Our
homes have locks on the door, latches on the window, and
insurance policies in the dresser drawer, and we support a
huge police and prison system — largely to protect a
few cameras, watches, and other gewgaws. Meanwhile, outside
our windows, every rainstorm carries away thousands of tons
of valuable topsoil upon which we depend for our very
survival. Our scale of values is pathetically confused,
when you stop to think about it. With modern assembly-line
methods, we could replace a stolen stereo in a few hours.
Yet it takes nature almost a thousand years to rebuild one
inch of topsoil.

Controlling Erosion

Some people, especially farmers, have a fatalistic attitude
toward erosion. Land erodes, they feel, just as people grow
old, automobiles sputter and stall, and apple trees
eventually give out. But land is not like that. It does not
have to erode. In fact, a healthy land adds humus and
builds up its fertility every year. Individual plants and
animals die, giving up their lives to help build a healthy,
vital, growing soil for future generations of plants and
animals. This nourishing of the soil is what makes death
meaningful and even beautiful. Think about that for a
moment, and don’t accept erosion as a “fact of life.”

Another conceptual trap you can fall into is the “Grand
Canyon argument.” Erosion built the Grand Canyon, so the
argument goes, implying that erosion is a natural process
that should not be interfered with. But erosion is
“natural” only in desert-like areas where there is too
little rainfall to maintain a thick growth of vegetation.
When the rain does come, it is often in raging torrents
that wash away the sparsely vegetated soil and create the
dramatic canyons and badlands of the American West.
Elsewhere, however, erosion is unnatural, the result of
man’s misuse of the land.

I have an almost missionary zeal whenever I think of
erosion control. But there is one thing I should not gloss
over. Fighting erosion is a hard, heavy battle; and, as
with any other worthwhile battle, there’s a good chance
that you will lose. Water erosion is a strong,
persistent enemy. It’s a fascinating enemy too: crafty,
treacherous, sneaky, unforgiving, unforgetting, mindless,
and merciless. Supposedly you can make a pact with the
devil, but not with erosion.

In this article there are instructions for building check
dams, contour trenches, and wattles. Follow these
instructions and you’ll have good reason to expect success.
Most of the time. But there is also a good chance that an
exceptionally heavy rain, exceptionally unstable soil, or a
minor fault in construction will allow the water to wash
your structure right away. When that happens, what are you
left with? If you and whoever works with you did not enjoy
the experience of working together, you are left with
nothing. Less than nothing! But if the experience of
building and planting was warm, cooperative, compassionate,
and friendly, the project was a success whether the check
dams hold or not.

As an engineering venture, you should build your structures
as if they were going to last forever. Perhaps they will.
But as a spiritual venture you should treat the whole thing
as if success or failure of the structures is totally
irrelevant. Make sure the process is human and loving, have
fun, and open your eyes to the here and now. Saving soil is
important, but not at the expense of losing a group of kids
or a group of friends.

How Erosion Happens

In the following sections I tell you what deeds you must do
to fight erosion. But before you put on your coat of armor
and rush out of the house, let’s stop for a minute to
examine the nature of the beast. Here is a model of
atypically eroding watershed.

To begin at the beginning, drops of rain fall down. Plip,
plip, plip. They hit the ground at a speed of about 30 feet
a second. If your land is healthy and the raindrops fall
onto a thickly carpeted meadow, a wonderful thing happens.
It is something you have to see to appreciate fully. The
next time it begins to rain, try to forget everything your
mother taught you about “catching your death of cold,” lie
down on your belly, nestle your chin into the grass, and
get a frog’s-eye view of how raindrops fall. You’ll see how
the raindrops hit the individual blades of grass, causing
them to bend down. This bending absorbs the energy of the
raindrop, and the raindrop slides gently off the blade of
grass, which immediately springs up again, waiting to catch
another raindrop. Perhaps it’s just my own sense of humor,
but the sight of hundreds of blades of grass bowing down
and popping back up like piano keys strikes me as one of
the merriest sights in the world; I’ve spent embarrassing
amounts of time rolling around on wet meadows in the rain,
laughing at the wonderful antics of the blades of grass.

After the energy of the raindrop is taken up by the grass,
the raindrop slides gently to the ground. On a healthy
meadow with lots of humus, the ground is spongy and
absorbent and the raindrop quickly sinks out of sight.

A similar thing happens in a forest. As every kid knows,
the best place to run when a sudden rain comes is under a
tree — unless, of course, there is thunder and
lightning. The leaves of the tree break the raindrops into
a fine mist. What moisture does fall through the canopy is
easily absorbed by the understory, the leaf litter, and the
humus, and it too sinks gently into the ground.

But let’s say that the ground has been logged, grazed,
burned, cultivated, or otherwise disturbed. There are now
bare patches of earth. When the raindrops hit a bare spot,
they strike full force, like tiny hammers, and splatter the
soil. This splattering breaks up clods of earth into fine
particles. The raindrops hold the fine particles in
suspension. As the water sinks into the soil, these fine
particles get filtered out and soon clog up and seal the
passageways through which the water would ordinarily flow.
The clogging and sealing effect is very important: Clear
water percolates through the soil ten times faster than
muddy water. After a brief time the soil becomes crusty and
impenetrable, and the water can no longer sink in. Instead,
it forms puddles on the surface.

On flat land, the puddles loiter around, grow bigger, and
form temporary ponds. The soil structure is damaged
somewhat, but there is no real erosion.

On slopes, however, the water flows downhill over the
surface of the ground, evenly, like a sheet. It carries
dirt particles dislodged from the tops of hills and
deposits them below, creating what is known as sheet
erosion
.

Probably the worst thing that can happen at this point is
that the flow of water becomes channelized, either because
of the topography of the land or because of an accidental
occurrence like a furrow, a tire rut, or a cow path running
downhill. The water gathers speed and the particles of dirt
act like sandpaper. The water soon cuts a small trench, or
rill, which it may eventually widen and deepen into a
gully.

As you can see, a gully is really the result of erosion
— not the cause. Yet once the gully gets established,
it brings about many severe problems. With each rainstorm,
it gets deeper and deeper until it may even cut below the
level of the groundwater, draining it and lowering the
water table.

We now have the beginning of a vicious cycle. As you
probably know, much deep-rooted vegetation depends more on
groundwater than on surface water from the rain. As the
water table is lowered — both from lack of rainwater
penetration and from the draining action of gullies —
vegetation over the watershed becomes more meager and
scruffier. In some places fields of thick grasses are
replaced entirely by sagebrush and chaparral, with scraggly
growth and much exposed soil. Less groundwater leads to
scruffy vegetation, which leads to more bare soil, which
leads to more splatter, more soil clogging, less water
penetration, more runoff, and a further deepening of the
gully. As the gully deepens, it drains the water table
still more, producing a further loss of vegetation, more
exposed soil, more splatter, and so on for another downward
cycle.

Meanwhile, as the gully gets deeper, the earth along its
banks begins to cave in. Soon the gully sends out fingers
that spread over the meadow, eating steadily away at the
soil.

Within a few years, thousands of tons of topsoil are washed
away, along with thousands of tons of subsoil. Where does
it all go? Eventually, the gully probably drains into a
stream. On a healthy watershed, a good cover of vegetation
absorbs water, holds it like a sponge, and releases it
gradually into the stream. The stream runs steadily and
cleanly. But on an eroding watershed, the water runs off
the surface with a heavy load of suspended silt, swoops
through the gullies, and flushes out into the stream after
every rainstorm. Instead of a clear, even-flowing stream,
there is now an intermittent dry creek given over to flash
floods. The silt kills whatever life there is in the stream
and acts like sandpaper to cut into the stream bed and
banks, causing further damage.

Sound dismal? It is! Yet this is exactly what is happening
to thousands of small watersheds around the country. You
should be aware of this process, but if your land has a few
gullies, please don’t freak out. Gullies can be stopped,
and even if the “vicious cycle” has begun, you can do a lot
to reverse it. That’s what this article is about: how to
stop erosion without a lot of money, bulldozers, or a
detachment from the Corps of Engineers.

So far I’ve given you a model of a typically eroding
watershed, which should help you to conceptualize what’s
happening on your land. If all you’re going to do is think
about erosion, you can stop here. But if you’re going to
do something about it, you’ll need a gut-level
feeling for how erosion is happening on your land. This
feeling, more than anything you read, will tell you where
to plant, where to mulch, where to build check dams, and
where to stay out of the way. It’ll prevent you from
building a matchstick structure to stop a raging torrent,
and it’ll save you the trouble of building a Hoover Dam to
control a trickle.

In short, you’ve got to get wet! You’ve got to go out in
the rain, lie belly down on your meadows, squish soil and
mud through your fingers, look at the color of your water,
and poke at the sides of your gullies to see how solid they
are. Water is amazing stuff, and to see what it does,
you’ve got to get intimately acquainted with it.

A firsthand understanding of how your land is (or isn’t)
eroding will have its side benefits. It’ll get you out in
the rain, which is sort of magical in its own right. It
will also give you an appreciation for the strength,
determination, and beauty of the erosion process. If you
are going to fight erosion, it’s much better to fight a
beautiful enemy that you admire rather than an ugly enemy
you hardly know.

One more thing. The Soil Conservation Service is an
excellent ally in fighting erosion. You can find it by
looking in the phone book under U.S. Government, Department
of Agriculture. I’ve called upon these people for various
meadow, forest, stream, and gully problems. They have sent
me (free!) grassland experts, stream experts, and soil
engineers — persons who knew their subject well and
who gave me not only advice but usable advice at that. My
own good experiences with the Soil Conservation Service may
have been accidental, but by all means give it a try.

Fighting Erosion With Plants

Of structures and plants. Later on, I’ll
explain how to build structures that will stop erosion and
hold soil together. Building these structures can be fun,
like playing with an oversized erector set, but please
don’t get hung up on them. The Army Corps of Engineers
seems to view erosion-control structures as monuments, and
in many places its cement bulwarks are even more prominent
and obtrusive than the original erosion. Don’t make that
mistake. The structures I recommend are merely temporary,
even rinky-dink, devices to hold the soil together until a
permanent vegetative cover can get established.

The only successful and lasting way to fight erosion is
with plants. One of the nicest things about using plants is
that plants want to fight erosion. In fact, they want to
fight erosion even more than you do, and what’s more, they
know how to do it. Take a blade of grass. Grass depends for
its survival upon topsoil, and over the last several
million years it has developed ways of holding on to and
increasing the earth’s supply of topsoil. Grass intercepts
raindrops; it forms a tough, tangled mat that prevents
raindrops from flowing downhill; its fibrous roots embrace
the soil and hold it together. Decaying roots create
passageways through which water can penetrate, while
transpiration allows the grass to pump water out of the
soil before the soil gets waterlogged. At the end of its
life, grass falls to the ground, decays, and becomes humus,
which is the best of all possible elements in the topsoil.
Plants depend upon a healthy soil, and they have learned
how to serve and preserve that soil. Every time you drop a
seed into the ground, you are introducing an ally with
millions of years of genetic experience in fighting erosion
and tremendous willingness to put that experience to use.

Temporary cover. The first thing you
should think about when you are faced with an erosion
problem is a temporary (or emergency) cover. You will
eventually want to plant a permanent cover of native plants
that will perpetuate themselves and restore the soil. But
if you have a lot of bare land and an immediate danger of
erosion, you have to act fast. You need some sort of
temporary vegetation just to hold things together until the
permanent vegetation can get established.

Certain plants have a special capacity for stopping
erosion. I wish I could tell you exactly what you should
plant on your land — I know it would make your life
easier — but I can’t. There are too many variables. I
know that in the hills above Oakland I can get good results
with a mixture of rye, barley, trefoil, mustard, and a few
other flowers. But I doubt if this information will help
you if you’re in Indiana, Georgia, Vermont, or Alaska.

All I can do is give you general advice about what you
should look for in an emergency cover plant. For the
specifics you’ll need local guidance from your Soil
Conservation Service, your county agricultural extension
agent, your local hermit and organic gardener, or your
local seed dealer (who often has a special “erosion-control
mix”). Or you can look into some of the books I recommend
at the end of this article which give a species-by-species
rundown of many valuable erosion-control plants and tell
where they can be used.

The ideal erosion stopper is a plant that:

[1] Germinates quickly and easily.

[2] Grows fast before the first heavy rains.

[3] Has a dense, fibrous root system.

[4] Is frost resistant.

[5] Is temporary — make sure
the recommended “wonder plant” won’t take over everything
in sight.

[6] Is a mixture. Don’t depend on one plant,
no matter how good its reputation. And make certain that at
least one element of the mixture is a legume (member of the
pea family). Legumes do for the soil what yogurt does for
the intestines — they foster lots of beneficial
microorganisms that do much of the real heroics in creating
healthy soil.

How to plant a temporary cover. The best
way to establish a temporary cover is first to dress the
ground with a light sprinkling of very well rotted manure
or compost. You might want to work it into the soil a
little bit with a hoe and then rake it some — but not
too deeply, please. If you have erosion, you want to
disturb the soil as little as possible. Once you’ve
prepared the soil, simply broadcast the seeds a day or two
before you expect rain.

Fertilizers and exotics. What if you are
dealing with a huge area, or if you don’t have enough
manure or compost for even a small area? Here’s what you
do. Scratch the surface of the ground slightly with a rake.
Then spread the seed before you expect a rain. Wait until
the seed has germinated and growth is under way, then
carefully add an appropriate chemical fertilizer. (The Soil
Conservation Service or a local seed dealer will tell you
how much seed to scatter and what kind of fertilizer is
“appropriate.”)

Aside from chemical fertilizer, there is another bitter
pill you may have to swallow. Some of the most effective
plants for erosion control are exotic grasses and clovers.
Call me a native-plant chauvinist, but I normally abhor
foreign exotics. I have very high standards about not using
them. For that matter, I have very high standards about not
forcing growth with chemical fertilizers. Yet when the soil
is bare and the rains are due, I am faced with a clear
choice: I can either hang on to my standards, or I can hang
on to my topsoil. Standards can be replaced, rationalized,
or even forgotten within a week. Topsoil takes thousands of
years to form. Whenever I’ve had to make a choice, I’ve
opted in favor of topsoil.

If you do decide to use an exotic, there are special
guidelines you should follow. Make sure the exotic has been
around for a long time and is well tested in your area.
Make especially certain that it won’t escape and spread all
over the place.

After seeding. If your land is relatively
flat, you can seed and forget. But what if you’re working
on a steep slope where the soil is so unstable that you’re
afraid it will wash away, or where the land is so hard that
you think the seeds might simply float down the hill? In
such cases you’ll have to devise some way of holding the
seeds and earth in place — at least until the seeds
germinate, the roots work their way into the soil, and the
green stuff rises up like flags of victory to tell you
everything is going well.

Willow stakes. In the following sections I
describe several structures that will hold the soil
together for a while. You can use any materials to build
these structures, but if you use willow cuttings, you will
reap an extraordinary advantage. Not only will they serve a
mundane mechanical function as posts or stakes, but they
will very likely sprout, send down roots, help bind the
soil, and carry on an exuberant and useful existence of
their own. Willows are especially valuable wherever you’re
dealing with moist land and bad drainage.

In addition to willows, there are other cuttings you can
use for living stakes or posts. In our part of California,
for example, elderberries and “mule fat” sprout easily from
cuttings. Under hard conditions they may last for only one
or two seasons — but while they last they’ll do a lot
of good.

Black locusts. The black locust is not an
insect; it’s a tree with a supergood reputation for erosion
control. It establishes itself on poor, dry sites, has a
spectacular rate of growth and a good root structure, and
adds a lot of nitrogen to depleted soil. It is not unusual
for a three-year-old locust to be 15 feet tall with a root
system spreading 25 feet.

You can plant locusts as seedlings or from root cuttings.
For erosion control, plant them close together — say,
five feet by five feet, or even three feet by three feet in
really bad places.

Permanent vegetation. Temporary vegetation
is meant to give out, and even willows and locusts are not
usually climax species. You should plan for what you hope
the permanent vegetation will be. Talk it over with your
land. Find out what was there before the land was misused.
Decide whether the land can support its climax vegetation,
or whether you should begin further down the line of
succession. I can’t advise you what to plant — it
varies from one area to another, and in fact from one acre
to the next — but by studying uneroded, undisturbed
land in your neighborhood, you should be able to figure it
out.

The best time to plant a permanent vegetation is just as
soon as the temporary vegetation has stabilized things
— usually toward the end of the first rainy season.

Conquering the Splatter

It may sound silly and quixotic to you, but if you are
going to control erosion, you must begin by fighting
raindrops. Raindrops hammer insistently at your land, and
to prevent damage there are two things you must do. First,
you’ve got to make sure there is something waiting to
intercept the raindrops before they hit bare soil:
vegetation, if possible, or some sort of mulch. Secondly,
once the raindrops fall, you’ve got to stop them; corral
them, and let them sink into the ground. If, perhaps with
trenches, brush mats, or wattles, you can get the raindrops
to sink into the ground wherever they fall, there will be
no runoff, and thus no erosion.

How to recognize sheet erosion. Sheet erosion, according to
the people who measure such things, causes 80% of all
topsoil losses. Gullies cause only about 20%. Yet a gully
stands out like a wound, screaming for attention, while
sheet erosion happens so gradually, almost invisibly, that
it’s hard to detect. You think everything is all right
until one day you wake up and realize that your topsoil is
gone. Sheet erosion is very insidious.

Is your land suffering from sheet erosion? Looking for
sheet erosion is a little bit like searching for a snake.
If you merely walk around, sniffing flowers and
lackadaisically enjoying whatever strikes your eye, you are
unlikely to see a snake. But if you make a special effort
to find one, turning over logs and stones, looking hard
between the blades of grass and around bushes, you will
probably find several snakes in a few hours.

The same is true of sheet erosion. You have to go out into
your fields with nothing else on your mind except looking
for sheet erosion. Don’t get waylaid by flowers,
butterflies, or ripe strawberries. Keep your mind on your
task. Climb to the top of a hill, forget about the view,
and look down at the soil. Here is what you should be
looking for.

BALD SPOTS: On the hilltops and slopes,
often with a buildup of fertile soil down below.

EXPOSED ROOTS: Roots of trees, shrubs, and
other plants do not grow out of the ground. If the
roots are exposed, it is because the soil has been washed
away.

STAINS ON OLD FENCE POSTS: These sometimes
show that the soil was once deeper than it now is.

EXPOSED ROCK: If you feel that your meadows
have been getting rockier and rockier each year, unless
your land is a gathering spot for meteorites, this is a
sign that the soil is being washed away.

Mulch. Once you discover sheet erosion,
don’t waste too much time either admiring it or bemoaning
it. Get the right mixture of seeds, put them in a wide,
shallow basket, and go skipping across your meadows like
Ceres strewing the seed. Be joyful — and the seed,
the land, and perhaps the universe will respond to your
joy.

In most places you can seed and forget. But if the soil is
loose and unstable, or if it is so hard that you’re afraid
the seed will wash off, or if the slope is exceptionally
steep, you should apply a mulch after you’ve seeded. A
light covering of mulch does wonders. It cushions the
impact of the raindrops, like those blades of grass, and
allows the water to settle in gradually. It creates a
network of little dams on the ground that impound the water
and prevent it from getting a running start down the hill.
It absorbs water. And as it decays, it adds organic matter
that eroding land usually needs so desperately.

But remember: Underneath the mulch are seeds, and you want
to encourage, not smother, their growth. So keep the mulch
covering thin — no more than an inch or two —
and avoid any mulch that tends to mat down.

Straw is far and away the best mulch you can get for
erosion control. But don’t be too fussy; other mulches also
work very well.

Brush mats. Brush mats are for really
nasty places — places where you want to use a mulch
but where the slope is so steep that you’re afraid a loose
mulch will wash down the hill. Believe me, an eroding
hillside with a huge pile of soggy mulch at its base is a
nightmarish sight. The way to avoid it is to use brush as
your mulch and tie the brush together into mats.

To make a brush mat, first lay two wires parallel to each
other on the ground, about two feet apart. Lay the brush
over the wire. If you use fir boughs or pine boughs, pile
them very thin; otherwise, they’ll smother the seed. If you
use sparser chaparral brush, you can make the mats as much
as six inches thick.

After you arrange the brush over the wires, bring the wires
back over the top of the brush. Use baling wire to connect
the upper and lower strands of wire. Pull them tightly
together and tie them off, making a connection every six
inches or so. The loose ends can be twisted tight with
pliers.

You now have a brush mat that will hold together very
effectively, even on quite steep slopes. If you want to be
extra safe, you can stake your brush mats down to the
ground — preferably with sproutable, rootable stakes.

Contour trenches. Here is still another
technique you can use in addition to mulching. If by some
chance you don’t have any mulch, you can sometimes use this
technique instead of mulching.

Contour trenches are simply ditches that you dig along a
hillside in such a way that they follow a contour and run
perpendicular to the flow of water. They catch water and
allow it to sink into the ground before it can get a
running start down the hill. Contour trenches are
particularly valuable on hardened soil — like old
logging roads — where water penetration is painfully
slow.

To make contour trenches, first gather all your friends and
issue them picks, mattocks, and shovels. When the moaning
and groaning stop, begin digging several short trenches
five or six inches deep and no more than about two or three
feet apart. Keep this project short! Digging ditches on a
hard-packed, heavily eroded slope is nobody’s idea of great
fun.

Brush wattles. Simple seeding, mulching,
brush mats, and contour trenches will take care of 98% of
your sheet erosion problems. For those rare times when you
have an exquisitely nasty and persistent problem with sheet
erosion, you can resort to brush wattles.

Begin by making a series of contour trenches at least eight
inches deep, preferably deeper. As you remove the dirt,
somehow, somewhere, get it out of the area. Next, lay some
brush in the trenches. Stagger the brush along the trench
so that it all interlocks, like strands within a rope. As
you build up the brush, stomp it hard so that it packs into
the trenches. If it keeps springing up, you can try cursing
it or packing it down with some dirt. The last several
pieces of brush that you lay in the trench should stick up
above the level of the land. To help keep the brush in
place, knock in stakes (preferably stakes capable of
growing) just behind the trench on the downhill side. Space
the stakes one foot, or at most two feet, apart. If you
have lots of long, limber branches, you should weave them
between the stakes to form a wattle fence.

What you’re left with is admittedly a weird structure, and
one that is hard to build — especially on a steep,
unstable slope where you are most likely to need it. It
has, in fact, only one redeeming feature: It works! The
water running downhill sinks into the trenches. Silt
suspended in the water also gets caught in the trenches and
builds up within the protruding branches of the brush and
behind the wattle fence. A wattled slope soon forms little
terraces of relatively stable silty soil — excellent
places for plants to get a start.

Gullies

Patrick Henry (of “liberty or death” fame) once said,
“Since the achievement of our independence, he is the
greatest patriot who stops the most gullies.” I used to
think this statement a bit outlandish, but the more I’ve
gotten to know about land, gullies, and patriotism; the
more I’ve come to agree.

Rills. The easiest way of stopping a gully
is to catch it early. Whenever you see small rills (or
channels), get right to work. Use a mattock or a hoe to
break them up. Work in some compost or rotted manure, if
you can, and rake the area smooth. Then treat the area as
you would for sheet erosion — seed it, mulch it, or
possibly use brush mats or contour trenches.

Gully monsters. A neglected rill may grow
up to be a monster gully. In the next two pages I’ll tell
you how to go about fighting and conquering gullies. It’s a
long, complicated fight, but very much worth the trouble.
We no longer have fire-eating dragons, but we do have
land-eating gullies to fight. Just to make sure you can
find your way through the following instructions, here is
an outline of the battle plans.

[1] Stabilize the gully bottom. The bottom is more
important than the sides. If the gully continues to dig
deeper, no matter what else you do, the sides will cave and
slump. You’ve got to prevent the gully from getting any
deeper, and you should even attempt to build up the bottom.

[2] Grade the walls of the gully to their angle of
repose
— the angle at which they will no longer
slump or slide.

[3] Stop or reduce the flow of water entering the gully.

[4] Plant an immediate cover of grasses and legumes that
will hold everything together for a season or two.

[5] Plant a permanent cover of native shrubs, trees, vines,
and grasses that will eventually stabilize the area,
perpetuate themselves, build up soil fertility, encourage
wildlife, and completely restore the land.

Check dams. The way to stabilize the gully
bottom and build it up again is with check dams. Please
don’t be intimidated by the thought of building a dam.
You’re not going to be competing with Grand Coulee or
Aswan. In fact, your check dams won’t even hold any water.
They are merely obstructions that will slow the water down.
And the best of all possible obstructions (as we all know
from our various misadventures in life) is a big mess.
Basically that is what a check dam is: a big mess of brush
or perhaps straw packed into the bottom of the gully, with
a simple structure to hold it all in place.

Why a check dam works. I think we all have
an intuitive sense of why a check dam works: A slow-moving
stream carries far less silt and does far less damage than
a raging torrent. But to understand how dramatically true
this is, you might want to consider a few hard-core
engineering facts. If you reduce the speed of the flow of
water by one-half, here (according to certain laws of
hydraulics) is what happens:

The erosive or cutting capacity of the water is reduced
about four times. The quantity of silt that can be carried is
reduced about thirty-two times. The size of particle that can
be transported by pushing or rolling is reduced about
sixty-four times.

As you can see, by slowing down the flow of water, you
reduce the amount of damage it can do, and you very
spectacularly reduce the amount of silt it can carry. If
there is lots of silt suspended in the water, once you slow
the water down, most of the silt will be dropped —
thus building up the bottom of the gully again.

The principles of check dam architecture.
There are many possible designs and materials for building
check dams, but whichever one you choose must adhere to
certain architectural principles of check dam construction.

HEAD-TO-TOE ALIGNMENT The most effective way of building
check dams is to build them in a series where the base of
the upper dam is on a level with the top of the lower dam.
This will eventually stabilize the whole gully bottom and
will create a series of steps or terraces.

SMALLNESS “The bigger they are, the harder
they fall” applies particularly to check dams. For most
gullies, the check dams should be no more than about two
feet high. Anything much higher than two feet will
necessitate anchors, deadmen, and other retaining-wall
features. Several small dams are far more effective and
easier to build than one or two big dams.

DIGGING IT IN The dam must be dug into the
walls of the gully, not just laid genteelly up against
them. Unless the dams are dug far enough in, water will
sweep around them.

NOTCHING A notch is a place where the
water can flow over the dam. This is essential. Without
one, the silt builds up behind the dam, the water flows on
top of the silt, and instead of being led through the
notch, it may start eating away at one of the slopes.
Eventually, it may make a new channel around the dam. I’ve
seen many erosion-control dams standing proudly and nobly
on dry land while gullies flowed merrily around them.

APRON Once the silt builds up behind the
dam, the water flows through the notch like a waterfall.
You’ll need an apron to catch it befores it digs out a pool
and undermines the dam. The easiest apron is a bed of
stones where the water can simply knock itself out and flow
tamely to the next check dam.

Building a check dam. There are several
possibilities for building very good check dams: a rock
dam, a wire dam, a stake dam, a pole dam, and a plank or
slab dam. Which one you choose to build will probably
depend more upon the materials you can scrounge up than
upon anything else. I built mostly pole check dams because
we had plenty of poles. Whichever one you decide on,
remember to follow the general principles already laid out,
and you will make out very well.

Grading the slopes. After you build the
check dams, your next step is to break down the steep gully
walls to their angle of repose . To my ears,
“angle of repose” is one of the most beautiful phrases in
the language. Unfortunately, it’s far easier to say it than
to do it. I know of no easy way of breaking down steep,
cliff-like slopes. Professionals sometimes use dynamite and
bulldozers, so I’ve been told, but all the bulldozer
operators I’ve ever met are scared to death of working
along the rim of a sizable gully. When it comes to grading
gully slopes, the machine age has deserted you, my friend,
and what you are left with, wonder of wonders, is your
hands! So get together a collection of picks, mattocks,
shovels, and digging bars, round up everyone you know who
owes you a favor, and get on with it. Knock off the sharp
edges, and wherever you can, gentle out the steep slopes.

As you are working, you’ll be knocking tons of earth down
into the gully bottom. The first rains will dissolve this
earth, spread it out, and deposit it behind the check dams
to raise the bottom. You can help this process along, and
also prepare the bottom for planting, by breaking up
whatever heavy clods fall into the bottom. If you have any
water, you might also wet the dirt down to compact it and
further ready it for planting.

Once the slopes have been graded to their angle of repose,
you should treat them for sheet erosion, with seed, mulch,
or the other devices recommended in the previous section.

Limiting the water flow. You now have to
make certain that as little water as possible enters the
gully. Where is the water coming from that originally
carved it out? You must find that water, even if it means
going out in the middle of a rainstorm.

You can usually restrict the flow by treating the area
above the gully head for sheet erosion. Contour trenches
usually work quite well, and as a last resort brush wattles
are nearly infallible. Whatever treatment you use, make
sure you extend it far up the slope.

Occasionally an expert will appear in your life and suggest
that you divert the flow of water away from the gully. He
will urge you to build a “diversion ditch,” perhaps with an
“entrapment compound.” He will probably pull out a pencil
and paper and make a few fancy diagrams. When you meet such
an expert, the first thing you should do is grimace, pound
your chest, jump up and down, and point excitedly to the
sky. If this doesn’t scare him off, grab your hat and run.
As you can guess, my own experience with “diversion” has
been disastrous. Diversion does not solve any problem; it
just moves the problem somewhere else.

Planting. Once you’ve stabilized the
bottom of the gully, graded the slopes, and reduced the
flow of water, you have completed the mechanical aspects of
controlling the gully.

Now you should plant. Use the previously mentioned routine
of temporary planting followed by permanent planting. Don’t
plant anything in the bottom until the silt has collected
into terraces. Then you can plant moisture-loving trees
right in the silt, where they’ll usually thrive.

Maintenance. Remember the little Dutch boy
who put his finger in the dike, held back the ocean, and
became a culture hero to all five-year-olds? I don’t
suggest you spend all next spring with your finger in a
check dam, but the Dutch-Boy Principle still holds: Small
leaks can be easily plugged. Sometimes all that is
necessary is for you to shove a few pine boughs in at the
right place. If you do, silt will continue to collect. If
you don’t, the leak will often get bigger and bigger,
bringing the whole dam down. You should also check to see
that the mulch is still in place, the grass has germinated
well, and no heavy flow of water is entering the gully.
Visit your check dams as often as you can during the first
one or two seasons to see how well they are holding up and
to solve minor problems before they grow.

Culverts. Culverts are pipes that bring
water under a road or trail. They are responsible for
thousands of gullies in every state. Road engineers have a
strange idea that if they install these culverts at a steep
pitch, the water will flow through them very fast and keep
the culverts clean of debris. Road engineers really get
turned on by “self-cleaning” or “self-maintaining”
culverts. But as I’ve already mentioned, the fast flow of
water increases its erosive powers many times over. And
often at the dump end of the culvert you will find a huge
gully.

If there is already a gully, you have no choice but to go
ahead with the gully trip. But if you can catch the problem
early, the best thing you can do is dump a lot of rocks,
broken asphalt, or cement rubble under where the culvert
lets out. This will break the force of the water, acting
much like an apron beneath a check dam. If you do this
wherever you have a culvert, you will save a lot of
aggravation and a lot of soil as well.

Afterwards. I don’t want to minimize the
fact that controlling a gully is hard work. But it is
necessary work, and in the long run extremely satisfying.

Once you have brought a gully under control, watch it
closely and uncritically. You may be in for a surprise.
Some of the most beautiful places I know are old,
stabilized gullies. When you are fighting a gully, you are
primarily fighting erosion damage. But you are also
creating a shady, potentially lovely, miniature canyon
which will collect. moisture, support many plants, and
become a wonderful refuge for wildlife. Turning a barren
gully into a lush pocket of life is the nearest a human
being can come to an oyster, which turns its injuries into
pearls.

Suggestions for Erosion Control Reading

In other areas of conservation there is pitifully little
information. Not so with erosion control. The 1930s were
dust bowl years, gully years, and Civilian Conservation
Corps years. The CCC, the Forest Service, and the Soil
Conservation Service all published loads of erosion-control
pamphlets and books. Every field worker who developed a new
style of check dam — and there were hundreds —
published a description of it. Sometimes the check dams
collapsed within a few years, but the publications live on
to clog our minds. The problem I’ve had with
erosion-control literature is wading through it all for
what seems sound, relevant, trustworthy, and useful. Here
are some of the books I have found especially handy for
small-scale erosion-control projects.

Handbook of Erosion Control in Mountain Meadows ,
by Charles J. Kraebel and Arthur F. Pillsbury. California
Forest and Range Experimental Station: U.S. Forest Service,
1934.

For most people this is probably an impossible book to get
hold of, but by all means try your best. It’s the most
thoroughly practical book I know, with lots of simple
suggestions for controlling gullies. There are excellent
diagrams and a strong emphasis on using native materials.

A Study of Early Gully-Control Structures in the
Colorado Front Range
, by Burchard H. Heede Paper No.
55. Rocky Mountain Forest and Range Experiment Station:
U.S. Forest Service, 1960.

This publication is a review of several Civilian
Conservation Corps structures, examined 25 years after they
were built. It shows which ones stood up, which ones
failed, how they failed, and why they failed. It’s very
instructive. Here is your chance to learn from someone
else’s mistakes.

Grass in Soil Erosion Control , by Layman Carrier.
SCS-TP-4. Washington, D.C.: Conservation Service, 1936.

This pamphlet gives a short list of various grasses and
discusses their erosion-fighting values.

Results of and Recommendations for Seeding Grasses and
Legumes on TVA-CCC Erosion Control Projects
, by J.H.
Nicholson and John E. Snyder. Norris, Tennessee: Tennessee
Valley Authority, 1938.

This list of grasses and legumes rates them according to
where they will grow, what their moisture and soil needs
are, how well they bind the soil, and how well they build
up soil fertility.

Trees and Shrubs for Erosion Control in Southern
California Mountains
, by Jerome S. Horton. California
Forest and Range Experiment Station: U.S. Forest Service,
1949.

Giving a plant-by-plant list of several species of trees
and bushes, this book tells where to plant them, when to
plant them, and even how to plant them. It also has
detailed diagrams of various erosion-control structures.
It’s too bad this valuable book is so limited in
geographical area. You might check to see if your own
Forest and Range Experiment Station has a similar
publication.

The Stream Conservation Handbook, edited by
Nathanial P. Reed. New York: Crown Publishers, 1974.

This book claims that “the primary objective of stream
improvement is the restoration and enhancement of trout
habitat.” It was written for fishermen, many of whom are
beginning to band together into groups like Trout Unlimited
to maintain their streams. The big-stream scale of this
book will probably make it not very handy for small
landholders. But if you do happen to have a fishing creek,
it will tell you what you have to know to keep it fishable.


EDITOR’S NOTE: This article is an excerpt from
Malcolm Margolin’s book,
The Earth Manual: How to Work
with Nature to Preserve, Restore, and Enjoy Wild Land Without
Taming It (copyright © 1975, 1985 by Malcolm
Margolin). The book is available for $8.95 postpaid
(California residents add state sales tax) from Heyday Books,
Berkeley, CA.