چكيده لاتين :
1. Introduction
Water erosion has been a problem worldwide, which causes the phenomenon of land degradation in semihumid
areas of dry land. The risk of soil erosion in arid and semiarid areas, especially in mountain ranges is of
significant cases in land use planning. Soil erosion in these areas is one of the important consequences of
climate change, or in general, the obvious impacts of environmental and ecological changes. The erosion
implications include soil loss, sediment deposition in reservoirs, and vegetation loss, and vegetation cover.
Among the different cases of water erosion, gully erosion is one of the most important factors affecting soil
destruction, land aspect change, and degradation of water resources and land setbacks. Due to the importance
and role of gully erosion inland waste and land depletion, especially in the study area due to the existence of
fertile agricultural land with high potential production and proximity of these lands to urban areas in
Darrehshahr county, the aim of this study is identifying effective soil factors in the development of gully
geometry characteristics and their prediction. Identifying effective factors in the development of this process
can be an approach for helping managers and authorities to control and prevent the development of gully
erosion.
2. Methodology
There are many gully areas in the province of Ilam, where the study of Darrehshahr has been investigated. It
is located in the Darrehshahr county and the eastern city of Ilam in the geographic range between 47 30 8 to
47 46 03 longitude and 33 12 14 to 33 23 03 latitude. Geological formation is composed of the
sediments of the lake, which is caused by the landslide. It is a cold semi-arid climate that is based on synoptic
stations at an average temperature of 21 C and the average precipitation in the region is 497 mm. The basic
data and statistics required are topographic maps of scale 1: 25,000 military organizations and the country's
mapping organization, on a scale 1: 100,000 geological maps of the country, map of soil and land resources on
a scale of 1: 25,000 of the institute for water conservation and soil. The measurement of gully geometric
properties, including depth, length, high and low level, cross-sectional area, lateral slope, was done by
surveying in the field using the Total survey camera at three cross-sections (head cut, median and outlet) of the
gully. Then the region was divided into 12 work units, and in each case, three replicates were selected, and
finally, 36 gullies were selected in the study area. The geometrical features of the gully using aerial
photographs, digital maps and field operations, and physical-chemical properties of soil were determined using
laboratory methods. To determine the impact of these factors on each of the geometric characteristics of the
gully and the relationship between the dependent and independent variables was obtained using multivariate
regression.
3- Results
After grouping the gullies, the relationship of soil properties with geometry properties, including depth,
length, Up and down width, was investigated based on the methods of correlation analysis and multiple
regression models. The results showed that EC (3.43), SAR (7.55) and Na+ (3.95) have the highest impact
factor and the most important role in the development of the gully. Whereas the amount of organic matter and
total of Ca++Mg++, will be the role of adherence to the soil and prevent gully development. Also, based on the
cross-section development model, the amount SAR (3.41), Na+ (2.87), and the Gypsum (2074) has the highest
impact factor in the increasing cross-section of the gully. But the amount of total of Ca++ and Mg++ (-0.36) and
OM (-0.097), playing the most important role in the control and prevention of the gully development. The
validation of the geometric characteristics of the gullies using statistical indexes (MRE and RMSE) was
calculated. Due to very low RMSE values for both models, we can say that the proposed models are highly
valid and can be used for regions with similar conditions of the study area.
4- Discussion & Conclusions
Due to the importance and role of gully erosion in soil loss, especially in the case study area, this study
aimed to identify effective soil factors in the development of protective gully characteristics. Therefore,
according to the findings of this study, it was found that:
- Based on the conceptual model of extension of gully length, the amount of EC, SAR, and Na+ have
the highest impact and the most important role in the development of the gully. Conversely amount
of organic matter and total of Ca++Mg++, will be the role of adherence to the soil and prevent gully
development.
- Based on the cross-section development model, the amount SAR and the Na+ have the highest impact
in the increasing cross-section of the gully. But the amount of gypsum and total of Ca++ and Mg++
playing the most important role in the control and prevention of the gully development.
- Soil texture, especially silty texture, plays a more effective role in gulling and sedimentation of gullies.
