wAbstract
@Globally, a large amount of research has been dedicated to furthering
our understanding of the factors and mechanisms affecting gully
erosion. However, despite the importance of gully erosion in arid
and semi arid regions of Iran there has been no comprehensive
study of the geomorphic threshold conditions and factors influencing
gully initiation. The aim of this article is to investigate the
gullying processes and threshold conditions of permanent gullies
in an arid region of Iran based upon examination of the slope-area
(S = ΏA-ΐ) relationship. The data were collected through
field and laboratory studies as well as Digital Elevation Model
(DEM) analyses. In total, 97 active headcuts were identified across
the three study sites and classified based on dominant initiation
process including piping, landsliding and overland flow. Soil
properties, including EC, SAR and soil texture, as well as landuse
practices were found to be the major factors initiating piping
and bank gullies. All gullies initiated by landsliding and seepage
processes were found to be located in steep areas(28-40 slope)
with their distribution further influenced by the lithology and
presence of a cohesionless sand layer within the soil profile.
An inverse relationship between upslope area (A) and local slope
(S), in which the Ώ and ΐ coefficients varied, was further investigated
based on the dominant gullying process and land use. Gullies occurring
in the rangelands that were dominated by overland flow had the
strongest relationship while landsliding dominated gullies did
not have a statistically significant S-A relationship. In comparison
to theoretical and literature based relationships for gully initiation,
relatively low values for ΐ were obtained (-0.182 to -0.266),
possibly influenced by the presence of seepage and subsurface
processes in many gullies. However, this is consistent with other
studies in arid regions and may reflect greater potential for
gullying in arid zones due to low vegetation cover and high variation
in rainfall. In addition, the soil attributes together with land
use practices influenced gully initiation thresholds. Application
of the solved S-A relation for predicting vulnerable areas to
gullying indicates that it is possible to predict the location
of gullies with an acceptable level of accuracy; however other
environmental factors should be integrated with the S-A relationship
to more accurately identify the location of permanent gullies
in arid regions.
Keywords: Gullying processes; Erosion; Area-slope; Landuse impact;
Threshold: Topography; Soil attributes; Iranx
1. Introduction
2. Study area
3. Materials and methods
@3.1. Field measurements
@3.2. Area-slope analysis
4. Results and discussion
@4.1. Gullying process and characteristics
@4.2. Area-slope relationship
@@4.2.1. Gully and catchment area-slope relationship
@@4.2.2. Field measurement vs. DEM derived slope
@@4.2.3. Coefficient and exponent comparison of the S-A relationship
@@4.2.4. Factors affecting the S-A relationship (landuse, dominant
process and climate)
@@4.2.5. Application of threshold to predict areas vulnerable
to gully initiation
5. Conclusion
Acknowledgments
References