1600
The impact of soil compaction on hillslope hy-
Plot used by vehicles
drology and erosion processes is substantial.
Plot not used by vehicles
Rainfall of a given intensity, which usually infil-
1400
trates into undisturbed soils, often does not infil-
trate into the same soils if compacted. Vehicular
1200
ruts formed during maneuvers often have com-
pacted soils beneath and adjacent to them. This
additional surface water adds to runoff volumes
1000
(Eckert et al. 1979, Mathier and Roy 1993) and
makes runoff periods longer (Hinckley et al.
800
1983). I believe that the ruts tend to channel the
additional runoff into rill-type flows, with veloc-
ities that may be measurably higher than veloc-
600
ities in natural rills on the same hillslope. Natural
rills don't carry any additional runoff coming
from compacted soils. I suggest that such higher
400
runoff erosivity in ruts may explain why gullies
on training lands can form and enlarge faster
nusedd
uunuse
200
than they do on adjacent undisturbed soils.
Iverson (1980) showed that, for a given runoff
power, more sediment was eroded from hillslope
0
plots that were used by off-road vehicles than
0
0.01
0.02
0.03
0.04
0.05
0.06
Average Runoff Power (W m2)
from those that were not used (Fig. 1). He report-
ed that the flow capacity on used plots increased
Figure 1. Runoff power vs. sediment yield from
1-m2 erosion plots used and not used by off-road
more than linearly with runoff power because of
increased runoff volume and flow channeliza-
vehicles. (After Iverson 1980.)
tion. Reduced infiltration and frictional resistance
tal requirements. Army land managers, who need
to flow on used plots cause overland runoff to
to preserve natural resources on training lands, are
happen more rapidly and attain an eroding dis-
required to minimize vegetation damage and soil
charge over a larger portion of a used hillslope
disruption, which inevitably occur during train-
than on an unused slope.
ing. Vegetation and soils are important resources
in themselves, but damage to them often leads to
accelerated soil erosion (Dregne 1983).
EFFECTS OF GROUND FREEZING
An armored unit on the move or an infantry
ON MANEUVER IMPACTS
march damages vegetation, breaks up soil crusts,
loosens surface soil, alters soil structure, weakens
Soil compaction
Soil compaction is the compression of unsatur-
soil aggregates, changes soil surface roughness,
ated soil because of reduction of its air-filled pore
changes the shape and number of surface depres-
space without a change in mass wetness. Com-
sions, and often compacts soils. Compaction in-
paction results from simultaneous application of
creases soil bulk density, reduces infiltration and
vertical pressures and shearing stresses from traf-
hydraulic conductivity (Voorhees et al. 1979; Webb
ficking on soils (Hillel 1980). The amount of
1983; Thornes 1980; Braunack 1986a,b; Ayers 1994;
vehicular soil compaction is determined by vehi-
Campbell 1994; Horton et al. 1994), and restricts
cle type, pattern of loading (static, dynamic, sta-
soil aeration, which impairs root growth, plant
ble, vibratory), vehicle-traffic motion (straight or
nutrient uptake, and seedling emergence (Chan-
turning), number of vehicle passes, vehicle pres-
cellor 1977, van Ouwerkerk 1991, Stepniewski et
sures applied, soil texture, density and moisture,
al. 1994). Thurow et al. (1993) report that recovery
and state and stability of soil structure (Voorhees
of damaged plants and new growth is often limit-
et al. 1978, 1986; Akram and Kemper 1979; Hillel
ed on compacted soils. This results in a vegetative
1980; Webb 1983; Gupta et al. 1989; Braunack
cover that is too sparse or composed of species less
1986a,b; Foltz 1992; Thurow et al. 1993).
effective in protecting and binding soil particles
Depending on the interplay of these factors, a
sufficiently to contribute to their stability and flow
compacting vehicular force (applied load)
2
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