Reprinted from:
p. 155-161. In Present and plospective technology for predicting
sediment yields and sources. U.S. Dep. Agric., Agric. Res. Serv.
ARS-S-40, 285 p. (Proc. Sediment-Yield Workshop, Oxford, Miss.,
Nov. 1t,12.) June 1975.
STAGES OF DEVELOPMENT OF GULLIES
IN THE WEST
1 v Burcharci H. Heed
STAGES OF DEVELOPMENT OF GULLIES
IN THE WEST
By Burchard H. Heedel
THE PROBLEM
Mountain lands in the West, in general, receive
less intensive use and management than agricultural croplands. Ephemeral gullies on these lands
carry flows only at times of severe storm or
spring snow melt. They may develop in such
major vegetation zones as desert, grass and
brush lands, and open forests such as pinon-juniper and ponderosa pine types.
This discussion is based on research from the
eastern and western flenlcs of the Colorado
Rocky Mountains, as well as observations in New
Mexico, Arizona, Nevada, and California. An attempt will be made to relate the development and
morphology of ephemeral gully systems to stages
of development. Present gully-classification systems do not yield sufficient information for the
land manager who is confronted with problems
of priorities in gully control, erosion rates, and
sediment yields. Gullies not only develop from
discontinuous channels, but probably change
with time as part of general landscape evolution
from youthful to old-age stages. As in landform
development, these changes may cause substantial differences in erosion rates and sediment
yields. Unfortunately, scarcity of data does not
provide for the thorough understanding of gully
processes that are basic to a definition of gullydevelopment stages. Once we can describe gullies
quantitatively in terms of stages of development,
decisionmaking in land and water management
will be substantially improved.
MSTORY
Gullies occur throughout the West in many
different vegetation-soil complexes. But gullies
are not often found on sites that support a
healthy, dense vegetation cover, excepz where
they invade from adjacent land. Gullies are rarely found in the well-forested subalpine region of
eastern Colorado or in the oak brushIseids of
western Colorado. The ground surface of the latter is covered by humus, litter, and herbaceous
vegetation such as Thurber fescue, and infiltration rates are nearly 5 times as high as for nearby sagebrush sites where gullies are abundant,
according to data collected by the Reeky Mountain Forest and Range Experiment Station.
It appears te be fairly well established that
many, if not most, of our present gully systems
began their development or were reactivated in
the last quarter of the last century, when population increases in the West led to an abrupt increase in grazing. Resulting depletion of the cover, coupled with droughts followed by abnormalHydraulic engineer, Rocky Mountain Forest and
Range Experiment Station, Forest Service, U.S. Department of Agriculture. Central headquarters located at
Fort Collins in cooperation with Colorado State University. Author is heated at Tempe, in cooperation with Arizona State University.
1
ly frequent, large, high-intensity storms, trenched many valley floors. We also know that soil erosion, including gully formation, accelerated during the great drought of the 1930's, when an economic depression forced the population to rely
heavily on the products of the land, with resulting overuse.
More recently, Loyd Barnett, of Forest Service Region 3 at Albuquerque, studied the development of a gully system on the Cibola National
Forest near Magdalena, western New Mexico.
Using aerial photographs and ground checks, he
determined that the gully system on the Silver-'
hill-Montosa watershed, 26.6 m.2 in area, had 16
ml of gullies in 1936. In 1963,27 yr later, the system had increased by 68 ml (425 pct). During the
observation period, no new gullies formed. In
contrast, aerial photographs indicated that during the same 27 yr, all gullies on the Monica watershed of the Cibola National Forest2 (total
length 7.6 ml) developed after 1936. These figures illustrate what we all know—gullying is
still active on our watersheds.
2
Barnett, Loyd. 1965. Monica watershed condition
survey, San Mateo Ranger District, Cibola National Forest. Open-file report, Region 3, Forest Service, U.S. Department of Agriculture, Albuquerque, N. Mex.
155
PROCESSES
Yet at present, from our knowledge of processes,
Gullies have been classified as continuous or
it is not clear when a rill becomes a gully.
discontinuous (7) .8 They are strikingly differThe formation of discontinuous gullies is
ent in appearance. Continuous gullies begin their
easier
to comprehend than that of continuous
downstream course with many small rills, while
gullies. Locally lowered resistance to erosion by
discontinuous gullies start with an abrupt heat
grazing, trampling, tire, or other agents can lead
cut. The headcut of the discontinuous gully may
to the formation of an initial furrow, scarplet, or
be located at any position on the slope of a hillsmall basin. Subsequent storms cause the head of
side, while a continuous gully always starts high
the initial erosion feature to progress up-valley,
up on the mountainside and continues its course
while at its toe a small fan develops. As soon as a
down to the main valley floor. The discontinuous
channel exists, a vertical headcut is formed. Congully may intersect the surface of the slope at
centration of water in the teench reduces chanany point, and thus be terminated.
After coalescence of many fingerlike rills, the
nel storage and thus increases peak flows. These
peaks are much larger than those of the former
continuous gully soon attains relatively great
ungullied valley floor. Larger peak flows have
depth. It maintains approximately the same
greater velocities and cutting power, and the
depth until the lowest reach above the gully
severity of the gullying processes is thus inmouth is approached, where depth decreases
quickly along a concave profile that terminates
creased.
at the gully mouth. A discontinuous gully rapidly
Several case histories document how &Aeondecreases in depth downstream and thus develtinuous gullies fuse to form one large, continuous
channel. For example, the Nursery gully system,
ops a gully bottom gradient much gentler than
that of the original valley floor. Where the gradion the Manitou Experimental Forest in the Coloents intersect, a sediment fan is built. There, a
rado Front Range, still consists of both types A
new gully may begin with a headcut. Discontinugullies. The headwater part of the system inous gullies (fig. 1) generally occur in series along
cludes several discontinuous channels, located on
the length of the drainageway (2) .
the main drainage but separate4 by ungullied
Discontinuous gullies develop into continuous stretches and alluvial fans. A. continuous channel
system forms the downstream part of the • Nurgullies. Although we did not observe the development of a continuous gully from a continuous sery gully. In its upper reach, coalescence is still
channel, such a possibility cannot be dismissed.
visible, indicated by a rapid succession of proWe all may have seen the formation of a continu- ' nounced channel nick points that, judged by gully
ous rill on a recent road-cut slope during a storm.
depth and gradient development, represent fused
discontinuous gullies. The nick points are 0,5 to
s Italic numbers in parentheses refer to items in "Lit1.5 ft deep. Gully depth decreases from the first
erature Cited" at the end of this paper.
nick point to the lip of the second downstream,
increases abruptly below the second nick point,
and loses this increase rapidly again at the lip of
the third nick point. This development is repeated several times until the channel depth reaches
4 to 5 ft, the average depth of the continuous system (4) .
Two gullies of the discontinuous Nursery system were selected to test whether fusion of discontinuous gullies is part of the mechanics of
gully-system development and to investigate the
o - ConOnwous sysiom
conditions that lead to gully fusion (3). At the
b -131seonthwoo. sys000
beginning
of the investigations, one gully was
c -Wotershaa bo wider,
3 II 4 -Disco oflouou
286 ft long and had an average gradient of 0.07.
A headcut (4 in fig. 2) , 2.4 ft deep, marked the
upper end of the gully; and alluvial fan termiFIGURE 1.—The continuous and discontinuous systems of
nated
the gully on the undissected drainageway.
the Nursery Gully at Manitou Experimental Forest.
156
CONCLUSION
Gully development should be recognized in
terms of landform evolution, proceeding from
youthful to old-age stages. In this study, youthful
and early mature stages of gully development
were defined; development to the early mature
stage coincides with the transformation of discontinuous into continuous gullies. Comparison
of hydraulic geometry of gullies with that of rivers suggests that the mature stage should be
characterized by dynamic equilibrium. Although
this stage was approached by some study gullies,
its existence could not be verified. Gully development is not controlled by waterflow alone, how-
ever. In ephemeral gullies, vegetation grown during dry channel periods can exert major influences. Criteria for the mature gully stage may,
therefore, not be given by stream equilibrium
alone, but may include other aspects of stability
such as channel vegetation.
Because insufficient data are available on
stages of gully development, gullies cannot be
quantified in terms of gully mechanics and morphology. Watershed managers would have a useful tool if gully stages could be expressed in
terms of erosion rates and coediment yields.
LITERATURE CITED
Hack, J. T. 1960. Interpretation of erosional topography in humid-temperate regions. American
Journal of Science 268-A: 80-97.
Heede, Burchard H. 1960. A study of early gullycontrol structures in the Colorado Forest Range.
U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station Paper 55, 42 pp. Fort Collins,
Colo.
Heede, Burchard H. 1967. The fusion of discontinuous gullies. Bulletin, International Association of Scientific Hydrology, XII* Anne., No.
4: 42-50.
Heeds, Burchard H. 1970. Morphology of gullies
In the Colorado Rocky Mountains. Bulletin, International Association of Scientific Hydrology,
XV (2) : 7949.
Heede, Burchard H. 1971. Characteristics and
processes of soil piping in gullies. U.S. Department of Agriculture, Forest Service Research
Paper RM-68, 15 pp. Rocky Mountain Forest
and Range Experiment Station, Fort Collins,
Colo, •
Heede, Burchard H. 1972. Influences of a forest on
the hydraulic geometry ri two mountain
streams. Water Resources Bulletin 8: 528-580.
Leopold, L. B., and Miller, John P. 1956. Ephemeral streams—Hydraulic factors and their relation to the drainage net. U.S. Geological Survey
Professional paper 25.2-A, 87 pp.
Leopold, L. B., Wolman, Gordon M., and Miller,
John P. 1964. Fluvial processes in geomorphology. 522 pp. W. H. Freeman and Co., San Francisco and London.
Mackin, J. H. 1948. Concept of a graded river.
Bulletin of the Geological Society of America
59: 468-511.
Thornburg, William D. 1961. Principles of geomorphology. 618 pp. John Wiley and Sons, Inc.,
Neiw York and London.
161