Ranczelands 2(5). October 1980
193
Reducing Man-Caused Gully
Erosion
Jerome V. DeGraff
Gullies are not uncommon features on westernrangeland.
Their presence should concern everyone responsible for
range management,or dependent on continuing range productivity. Gully erosion directlycauses loss of productive
soil, reduces ground water availability, and may even be a
barrier to stock movement.The indirect effects of accelerated sediment supplied to natural and man-made waterworks is equally undesirable.
Erosion is at its peak in semiaridareaslike our Southwestern region. Thisreflects acombination of storm runoffcapable of causing erosion and availablemoisture ableto support
only limited vegetation. It does not take a major decreasein
plant cover to greatly increase storm-related erosion. The
acceleration of gully erosion in the West afterthe 1880's is
often linked to circumstances which reduced vegetation.
Land abuses clearly can reduce plant cover and disturb soil
to the extent that gully networks forms. There is little doubt
that man-relatedactivities, in the not-to-distant past, created
This gully retreatedabout 40 feet from 1972 to 1979. Water color enhanced local gully development on the Fishlake lected
andchannelled by anoldroadinitiated it. Notethe gate where
National Forest in central Utah. Watershedcondition inven- the fence crosses the gully. Expansion of the gully was largely
tories identifygullies caused by roads, overgrazing, water unaffectedby changing the roadto the,present alignmentandrestransmission ditches, and other man-relatedactivities. (See toring the old roadbed. Rapid expansionis enhancedby the finegrained alluvium present at this site.
photos.)
Many people mistakenly think we understand the gully
erosion process.It is certainly truethat we can describeand surface mining, increase soil, detachability and/or
measurethe erosion and expansion of a gully. Likewise,we transportability.
We can apply this viewofman-caiased gullies to help in two
know how gully formation is linked to some specific factors
First, we can recognize whith activities have gullyways.
such as slope steepness and soil particle sizes. But this is
we can identifywhat information
only part of the process. We do not yet understand the causing potential. Second,
if
is
needed
to
establish
that
potential will be realized.
interaction of factors that leadsto gully erosion in one area,
but not in a similar neighboring area. Nor can we predict
threshold values, points at which gullies first begin to form.
Asa geologist, Ifinditfrustratingtobeunabletoshowwhich
areasare prone to gully erosion and which ones are not.
If we cannot yetshow whichareasare prone, or not prone
to gully erosion, how can we effectively reduce man-caused
gullies? One way is to view man-relatedactivities in light of
their gully-causing potential. A similar effort has been applied to reduce man-causedlandslides. Man-caused landslides result from (1) changing slopeshape, or (2) increasing
moisture in surface layers. We can view man-causedgullies
as forming where activities: (1) increasethe amount and/or
velocity of runoff, or (2) increase, soil detachability and/or
transportability. By increasing or eliminating plant cover,
changing natural drainage patterns, steepening slopes, or
compacting the ground, we increase the amount and/or
velocity of runoff. Overgrazing and fire, improper road
design, and paving areasare activities that influence runoff.
Surface disturbance, such as logging, and chaining of
Stockwaterislimited on ThousandLakeMountainplateau. Cattle
pinyon-juniper, and excavation, such as construction and follow
the same paths between grazing areas and the only water
source. Compacted trails collect runoff in sufficient quantities to
The author is environmental geologist, USDA Forest Service, Fishlake
National Forest.170 North Main, Richfield, Utah 84701.
cause gully development.
Ranqelands 2(5), October 1980
194
and/or transportability, we consider only those with gullycausing potential. The otheractivities need no further consideration for this problem. For example, a range
improvement project may include constructing stock driveways and buildingseveral miles of fence. Thefencing work
affects neither runoffor soils. It requiresno further consideration in terms of gullyerosion. Thestock drivewaysmight be
bulldozer cuts improving movement across rough terrain
separating grazing areas. This activity has gully-causing
potential because it can increase soil detachability and
transportability.
Once we recognize which activities have gully-causing
potential, we must decide if that potential will be realized. In
our example, evaluating potential for the stock driveways
requires soils information. This information might include
soil particle-size distribution, rockiness or stoniness, and
slope steepness.A gently sloping driveway across a stony,
sandy-texturedsoil is lesslikely to cause gullies than amoderately sloping driveway across a stone-free,silty-textured
Milesof watertransmissionditches dug byhandandhorse-drawn
soil. By knowing whatinformation isneededto assess potenequipment collected water on the upper slopes of ThousandLake
tial, two additional benefits result. First, the required inforMountain. Most were constructed tosupply watertohomesteadsin
the 1800's andearly 1900's. Lack ofcontinuedmaintenanceinrecent mation indicates which specialist is needed when an
yearshasledtobreaches. Diversionofcollected waterOnto adjacent interdisciplinary team effort is involved. Second, it helps
slopesinitiated numerousgullies. One breach and resultinggullyis identifywhich mitigating measures maybe most effective in
visible in the middle ofthe photo.
assuring that gullies do not develop.
Research and resulting managementpractices in recent
Much of what we do on rangelands is a combination of years have focused on rehabilitating existing gullies.
activities rather than a single action. This is especiallytrueof Researchersare continuing to add to our understandingof
land managementprograms. It would be inefficient to rou- the entire gully erosion process.Their work will eventually
tinely evaluateevery activity in a program for gully erosion enable us to map areas in terms of relative gully erosion
potential. In manycasesthe potential would be nonexistent. potential. Until that is possible, our preventative efforts
By recognizing which activities either increasethe amount should concentrate on assessing man-related activites for
and/or velocity of runoff, or increase soil detachability their gully-causing potential.
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