VITA             TECHNICAL BULLETIN
 
                         GULLY CONTROL AND RECLAMATION
 
                             by ROBERT D. FLANNERY
 
This manual by VITA Volunteer Robert D. Flannery was first published
by the Lesotho Agricultural College in Maseru, Lesotho. It describes
how soil erosion causes gullies, what can be done to stop gullies
from deepening, and how to reclaim eroded soil.
 
The manual deals specifically with conditions in southern Africa.
However, the many photographs and clearly written text make it
useful for readers in other countries as well. Deforestation, poor
soil management, and other factors have made erosion a growing
problem for developing countries worldwide.
 
Mr. Flannery was a lecturer in resource conservation at Lesotho
Agricultural College when he wrote this manual. He is an expert on
soil management with wide experience in many countries, and now
lives in Berkeley, California.
 
The manual was originally edited, illustrated, and printed by the
Lesotho Distance Teaching Centre. Some changes in the text and
photographs have been incorporated in this VITA edition. Reprinted
by permission.
 
Please send test results, comments, suggestions, and requests for
further information to:
 
               Technical Bulletins
               VITA Publications Service
               1600 Wilson Boulevard, Suite 500
               Arlington, Virginia 22209, USA
 
                              First printing October 1980
                                   Revised September 1981
                                        ISBN 0-86619-143-7
 
 
                      VOLUNTEERS IN TECHNICAL ASSISTANCE
                       1600 WILSON BOULEVARD, SUITE 500
                        ARLINGTON, VIRGINIA 22209, USA
 
 
                                 GULLY CONTROL
                                      AND
                                  RECLAMATION
 
 
                         Lesotho Agricultural College
                                Maseru, Lesotho
 
 
                                   CONTENTS
 
Introduction
 
Extent of Gully Erosion in Lesotho
 
Active Gully
 
How a Gully is Formed
 
Control of Gully Erosion by Structures
 
How to Stop a Donga from Lengthening
 
How to Stop a Donga from Deepening
 
Control of Gully Erosion by Vegetative Growth
 
How to Stop a Donga from Becoming Wider
 
Gully Control by Diversion or Retention
 
Maintenance of Structural and Vegetative Measures
 
Causes of Gully Erosion
 
Plants that Help to Stabilize Structures
 
Protection
 
                         GULLY CONTROL AND RECLAMATION
 
INTRODUCTION
 
Most of the land in Lesotho has been greatly damaged by gully
erosion. This book is written to help you and all communities
interested in fighting soil erosion and in restoring the land
to productive use.
 
The book suggests simple but effective ways to combat this
disease that is gradually eating into the land. It tells you
how you can prevent dongas (gullies) from forming; or, if they
are already formed, how you can stop them from becoming deeper,
longer, or wider.
 
This book will teach you how to stop a donga that is running
through your field. You can also use it in your community to
control dongas that are threatening your pasture land or that
are ruining your village and destroying your roads.
 
Some people will use this book with school children while
others will use it with their local groups. You can also use
the book individually or with your family. The important thing
is that all of us do something to control gully erosion and
reclaim the land already marred by dongas.
 
This book was written by Robert D. Flannery, Lesotho
Agricultural College lecturer in resource conservation, with
the financial assistance of the Catholic Relief Services. It
was first published by the Lesotho Distance Teaching Centre.
 
EXTENT OF GULLY EROSION IN LESOTHO
 
Soil erosion is one of the biggest problems of this country.
Lesotho dongas are formed mainly by rain falling on bare soil.
Gradually little streams of water are formed. These streams
wash away particles of soil and form small furrows, which ultimately
deepen and become dongas. Gully erosion has damaged most
of the land in Lesotho. It has taken away most of the soil and
left us with a bare, ugly country.
 
Dongas interfere with farming. They encroach on our fields,
carry away fertile soil, and leave us with poor subsoil that
cannot supply our plants with nutrients.
 
Dongas are dangerous. They ruin our grazing land, leaving our
animals thin and malnourished.
 
Gully erosion frustrates our efforts to improve this country.
It washes our roads away and breaks communication between
various parts of the country.
Dongas divide our villages and often become dens for murderers
and robbers.
 
Gullies are a threat to the lives of our animals.   Sometimes
animals grazing along the edges of dongas slip and tumble in.
All too often the fall is fatal.
 
Dongas are a threat to our
lives also.  Some people
fall to their deaths in
the dongas.
 
Our children like to play on the slopes of dongas.   At times
they miss a step, fall into a donga, and become crippled
permanently.
 
At present, most of the dongas in Lesotho are becoming wider,
deeper, and longer.
 
There are already 25,000 dongas in Lesotho today.   Unless something
is done to bring this situation under control, we will
soon have land that is unusable.
 
ACTIVE GULLY
 
An active gully is one that is continuing to widen, deepen, and
lengthen.  Most of the gullies in Lesotho are becoming wider,
deeper, and longer.  They still carry away much of our soil
whenever it rains.  The dongas of Lesotho are very active.
 
HOW A GULLY IS FORMED
 
A donga is formed by water.  Where soil has been left loose and
bare, water can move easily along the ground.   As the water
moves on loose unvegetated soil, it carries away the topsoil
and begins to form a small channel.   A donga lengthens because
the water that flows over the head erodes backwards and bores
into the head's profile leaving an overhang.
 
This overhang will fall with time, and the cycle will begin all
over again.  The water that moves in a donga flows at a greater
speed than the water
that moves in a wide
valley.  This increases
its erosive strength.
 
If there is nothing to
control the speed of
water in a donga, it
washes away more soil
from the bed and the
donga then deepens.
 
As the donga deepens,
its walls force the
water into a smaller
channel.  When water
moves down a donga at increased
speed, it requires
more room.  It makes more
room by washing away particles
of soil from the
walls, particularly towards
the bottom of the donga.
Gradually the sides of the
donga weaken and hang over.
Ultimately, the overhanging
walls fall and the donga
widens.  A donga will widen,
lengthen, and deepen unless
some measures are taken to
control the head, bed, and
walls.
 
CONTROL OF GULLY EROSION BY STRUCTURES
 
There are measures that can be carried out to prevent the soil
of this country from being taken away.   You can stop a donga
from enlargening by building loose stone structures at the head
of the donga and at certain points on the donga bed.   The stone
structures help to collect soil that, after some time, can be
used for growing vegetation.
 
HOW TO STOP A DONGA FROM LENGTHENING
 
A donga lengthens because the head keeps collapsing and therefore
receding.  The head of a donga becomes an overfall.  As
water pours over this overfall, it erodes the bottom of the
overfall and creates an overhang.   The overhang eventually collapses,
leaving the profile of the head straight.   Then the
cycle starts over again and the donga lengthens.   Once more,
this situation can be controlled by stopping the head from
receding.  To do this, you need to construct stone structures at
the donga's head to reduce the speed of water.   Here are the
steps you should follow.
 
1.  Dig out the head of the donga to create a gentle slope
    rather than a steep slope.  This will reduce the erosive
    power of the water.
 
2.  Put stones on the area you have dug out.  These stones will
    slow the movement of the water.  If you are dealing with a
    shallow donga, you
    should slant the head
    right to the bed.  Then
    fill the part that you
    have slanted with flat
    stones.
 
3.  At the end of the slanted part, dig a shallow foundation in
    which to put some stones.  Throw in as many stones as necessary
    to form a loose wall of about 30cm from the level of
    the ground.   The loose stone structure prevents water from
    digging into the soil and causing damage.  It also helps to
    check the fast-flowing water from washing away soil.  This
    structure must, however, be loose so that water may easily
    pass through the stones.
 
4.  In the middle of the stone structure you  must leave a small
    passage called the spillway.  This is an outlet that will
    allow running water to pass through.  Unless you allow for
     this outlet, the force of the water will break and wash away
    your structure.
 
HOW TO STOP A GULLY FROM DEEPENING
 
After building the first stone structure, you still need to
check the flow of water along the bed.   If water is allowed to
move freely along the bed after passing through the first stone
structure, it will continue to erode soil on the floor of the
donga.  You will, therefore, need other structures that will
slow the movement of water and even trap some silt.   Such structures
are called stabilization structures.
 
The best place for building a stabilization structure is at a
spot where the gradient of the donga changes.   First, dig a
small foundation 60cm deep and 60cm wide.   Then, fill in this
foundation with stones.  Continue to pile loose stones until the
wall of stones is about 30cm high.
 
Leave a spillway either at each side or at the center.
On the downstream side of the wall, make a layer of flat stones
called an apron. Towards the end of the apron, make a
perpendicular line of stones to slow down the speed of the
run-off water.
 
CONTROL OF GULLY EROSION BY VEGETATIVE GROWTH
 
The main aim of gully control is to stabilize the gully by
vegetative growth. The structures mentioned will help some
plants to grow in a donga because they will trap some water and
soil on which the plants can grow.
 
Vegetation is effective in controlling the erosive power of
water and in trapping the silt carried by the water. The plants
that grow naturally on the bed of a donga need to be protected
from animals and fires so that they can cover the gully and the
erosion scars.
 
Once the bed cover has been established, the donga will cease
to deepen; but the walls will have no cover and the donga will
continue to widen. Further steps must be taken to prevent this.
 
HOW TO STOP A DONGA FROM BECOMING WIDER
 
To stop the donga from becoming wider, you need to grow some
vegetation on the walls. The vegetation that you grow to cover
the walls should have an extensive root system. You should
plant this vegetation near the bottom of the donga where it
will have moisture. Once it has taken root, it will extend over
the walls and stop the donga from widening.
 
Walls are not the same in all dongas. Some dongas have sloping
walls that can easily accept vegetation; others are too
straight so no vegetation
can grow on
them. To prevent a
donga with straight
walls from widening,
you should dig out
the walls to make
them slope. This
will enable creeping
grasses and legumes
to spread across the
sloping walls.
 
When the grasses and
legumes seem to have
become established near
the bottom and along
the walls of a donga,
you can begin to plant
trees. Trees can only
survive where shrubs
and grasses are already
growing. Trees, shrubs,
and grasses help to
reduce the speed of the
water and trap a lot of
silt and dead plants
that are carried by the
water.
 
During the establishment stage, you should not allow animals
to graze on the gullied areas. Grazing hinders the growth of
the vegetation. If you protect the area where you are controlling
gully erosion, your land should be reclaimed in a few
years.
 
GULLY CONTROL BY DIVERSION OR RETENTION
 
Diversion
 
 
You can also control donga formation by changing the course of
run-off water. You can divert the water from your field,
pasture land, or road by constructing a ridged furrow on the
higher slope. The furrow made above your field or pasture land
should be half-moon shaped, and it should empty the water into
a protected or well-vegetated area.
 
In an area where gullies are beginning to form, you can make
one diversion furrow above the heads of the gullies. This
furrow can have an outlet into a location that has stabilized
structures. This would be an economical way of controlling many
small dongas with one diversion furrow leading into one controlled
area.
 
At the outlet of the furrow, you can Construct a loose stone
structure. This should have an apron that will control the flow
of water into the stabilized area. If there are enough stones,
you can install some stone structures along the diversion
furrow to control the velocity of the water. You should leave a
spillway in the center of every structure for times when there
is too much water running through the furrow.
 
You should make sure that these structures are well maintained,
for if they are destroyed by water, they can do more damage.
 
Retention
 
There are other means of controlling the speed of run-off
water. You can construct terraces on gentle slopes in your
field to check the flow of water. These terraces should be made
on open soil. If the terraces hold any water, the water will
easily soak into your field.
 
The terraces should be left open to allow excess water to
escape. Remember that you should have some structures at the
open ends, to prevent the water from beginning a gully.
 
You can also make dams in gullies to retain the run-off water.
A dam should be made near the head of a donga so that the
steepness of a donga may be reduced. This will lessen the force
of water over the head and stop the head from lengthening.
 
The dam should be big enough to hold the water. It should also
have a spillway for emergencies. The spillway should have stone
structures to prevent the escapinq water from cutting into the
ground to form a deeper donga. The spillway should be built in
such a way that it is not used very often, i.e., only when the
dam is very full.
 
If the spillway is not well maintained, it will be washed away
by water and a donga will result. If there is no natural vegetation
below the dam, you should encourage vegetative growth.
 
MAINTENANCE OF STRUCTURAL AND VEGETATIVE MEASURES
 
When you have constructed the stone structures along the channel
of a donga, you must check that they are not destroyed by
water, humans, or animals.
 
If the stone structures begin to collapse, make immediate
repairs. Inspect the sides of the structures and repair all the
cracks that might have been caused by animal burrows, dry
weather, or flood water. Repair the structures before they fall
apart. If you maintain the structures properly, you will save
yourself costly repair jobs when unusual storms occur.
 
When the vegetation you have planted begins to grow, protect it
from grazing animals. Even when the vegetation is established
you should only allow limited grazing. The young vegetation
should be protected from fires and from being trampled on.
Spread manure around any plants that are not growing well, but
you do not need to manure the whole gully.
 
By maintaining structures and caring for plants grown in
stabilized dongas, you will be able to restore your land.
 
CAUSES OF GULLY EROSION
 
You have learned how the dongas that eat into this land and
leave us with a desolate and ugly country can be controlled.
You should now learn how they are caused so that you can prevent
them from occurring again.
 
There are many causes of gully erosion in this country. Some
causes are man-made, while others are due to animal traits.
 
1. Improper land use. Men sometimes become a cause of gully
   erosion by using their land improperly. They plow the
   slopes; and when rain falls, it carries away the soil that
   has already been loosened by plowing. A small gully begins
   to form. If it is not controlled in time, run-off water will
   enlargen it until a big gully is formed.
 
   Before you plow along the slopes, you should build a diversion
   furrow to protect your land from run-off water from the
   higher slopes. The furrow should reduce the speed of the
   water that runs down the slope. once you have made the
   diversion furrow, you should make sure that it is not
   destroyed by water. You can strengthen it with the stone
   structures that I have mentioned and by planting grasses or
   legumes that have extensive root systems.
 
   This diversion will prevent your field from being cut in two
   by run-off water. It will also protect your crops from the
   run-off water that can take your plants away.
   Land can carry a certain amount of run-off water as long as
   the surface of the land is not disturbed. Sometimes farmers
   plow their land up and down. This enables the water to move
   easily along the furrows made by the plow. The water that
   moves along the furrows will carry soil as it flows down the
   field. If this is allowed to go on year after year without
   any check, a gully will be formed in the field. It is,
   therefore, advisable to stop this type of plowing, as it is
   a definite cause of gully erosion.
 
2. Farm tracks.   These are other sources of gully erosion. If
   you look at farm tracks between fields, you will realize
   that the tracks become deeper and deeper. This is caused by
   sledges and carts that are pulled by animals. The sledges or
   carts cut into the ground, sometimes uprooting grasses that
   have grown along the track.
 
   They break up the track into loose soil, which is easily
   carried away by water. Given time, the farm track will
   eventually turn into a donga. To protect this country from
   gully erosion, we should make terraces or other structures
   along farm tracks and roads to reduce the erosive power of
   run-off water.
 
3. Footpaths.  Through frequent usage, footpaths become torn
   and small channels begin to form. When a footpath begins to
   deepen, men stop using it and begin a new path alongside the
   old one. When it rains, the run-off water is channeled into
   the deepened path. The channeling of water increases its
   erosive power; and with time, the path will deepen more and
   more until a donga is formed. To protect this country from
   gully erosion, we should never leave abandoned footpaths
   unprotected. We should build terraces or other structures to
   reduce the erosive power of the run-off water.
 
4. Road drainage.  Road drainage may also encourage gully erosion.
   When drainage ditches are dug, they should be properly
   protected so that water does not flow freely on the already
   prepared surface. If the water moves freely, it will carry
   away the soil, and finally a donga will form because of the
   drainage channel.
 
   Since you cannot avoid making farm tracks, footpaths, and
   drainage ditches, it is important that you should make sure
   that these are protected so that they do not encourage donga
   formation. You will need to make terraces and stone structures
   and plant vegetation to ensure that water does not
   flow freely along the tracks, footpaths, and road drainage.
 
5. Livestock. Animals also contribute towards gully formation.
   Excessive grazing on the same pasture every day leaves the
   ground bare. When sheep graze where grass is short, they
   remove all the grass from the soil. This leaves the soil
   bare and unprotected. When it rains, water flows freely over
   this bare ground and at greater speed than it does where
   there is grass cover. If there is no grass growing on this
   bare land, a small gully will begin to form.
 
   To preserve the grass cover on the pasture land, you should
   practice grazing rotation. Do not let the animals graze on
   the same pasture day in and day out. Keep animals away from
   one area to encourage the grass to regrow. This is not easy
   to do; but, if you want this country to be restored to vegetative
   growth, some effort is necessary.
 
   Like men, animals tend to form trails where they walk. Their
   hoofs loosen the soil. When it rains, the water carries the
   loose soil away. Animals will trample on the same trail
   again and loosen the soil more. After some time, you will
   see a small channel beginning to form. If you do not take
   immediate measures, a donga will result from the livestock
   trails. To avoid this, make sure you do not drive your
   animals along the same trail every day.
 
PLANTS THAT HELP TO STABILIZE STRUCTURES
 
When all your structures seem to be working well, you should
supplement them with some vegetation. It is better to encourage
the vegetation that is already growing in the controlled area.
You can Supplement the natural local vegetation with other
plants that you can find within your area or buy from local
nurseries.
 
As mentioned before, grasses and legumes can be planted to grow
up the walls of dongas. These can be planted near the bottom of
the dongas. The best plants to grow are sod-forming grass,
creepers, or leguminous plants. Grasses such as the Kikuyu,
Mohlomo (Kweekgrass), Ookoa, Thitapoho, and many other grasses
you know can be transplanted to the controlled gully area. You
can plant some grasses by using their seeds, e.g., Mohlomo,
Qokoa, and Thitapoho.
 
Two legumes can be used at the base of dongas. These legumes
creep along the walls of dongas. They are called Kudzu and
Crown Vetch. You can probably obtain plants or seeds from local
nurseries or agriculture departments. The grasses and legumes
make a good base for future growth of trees. Trees cannot
easily grow on a bare area.
 
There are several native kinds of trees that can be grown to
stabilize the controlled eroded area. The trees will grow well
providing there is a grass base already prepared for them.
 
If there are trees already growing in the gullied area, it is
better to plant trees of the same species. If the gullied area
has some poplar trees already, continue growing a similar
species in the area. It would be useless to grow wattle trees
for they may not adapt themselves to this area as easily as the
poplar trees.
 
You should not forget that if you grow trees in a gullied area,
the banks of the dongas will need to be sloped. Trees that have
proved to be useful in stabilizing gullied areas are locusts,
poplars, wattles, willows, and wild olives. You can also try
cheche, kolitsane, leloka, and lesika, if these are available.
A local nursery can advise you about other stabilizing species.
 
PROTECTION
 
Once you have established vegetation in the gullied area,
animals should stop grazing on that land. There should be no
disturbance to the plants or structures. Check the vegetation
and structures regularly to see if there is any need for
repairs or to allow limited grazing to control competitive
weeds and shrubs. The area should also be protected from
fires. A fire will burn the seeds and roots of the plants.
 
========================================
========================================