علل گسترش فرسایش خندقی و خسارت های ناشی ازآن در ایران

Introduction and Goal
One of the types of water erosion that causes erosion and sedimentation in watersheds and causes a lot of damage to agricultural lands, range lands and infrastructure is gully erosion. Identifying the causes of gully erosion is one of the activities that will enable land managers to prevent the spread of gullies by considering and Compliance with effective management factors. In this research, the investigation of gully erosion in the provinces of the country has been carried out with the aim of identifying factors affecting the spread of gully erosion, obtaining the area of the areas affected by gully erosion, and estimating the damages caused by it. In addition, the extent of the expansion of gullies in the classes of different factors and the damage caused by gullies in Iran were investigated
Materials and Methods
The materials used in this research are research projects that directly and indirectly focus on the expansion of gully erosion. The research method has been such that at first, were investigated a number of the most important factors affecting gully erosion in the watersheds of the country, and then all the factors, Classified and their relationship with the areas affected by gully erosion were investigated. In this research, the climate classification of gully areas was done using the extended Demartonne method, and the relationship between different climates and the frequency of gullies was investigated and calculated. Comparison of old and new uses in gully areas, soil texture and range of soil particle changes, EC changes, organic matter changes, SAR changes in gully areas, slope, road construction, and plowing in the slope direction as some of the most important The effective factors were investigated in the expansion of gully erosion. Finally, the area of gully erosion occurred along with the type of damage and the estimated amount of damage has been estimated based on daily prices for the provinces.
Results and Discussion
Examining the relationship between different climates and the frequency of gullies showed that 32% of gullies are in semi-arid climates, 17% in dry climates, 14% in dry and hot desert climates, 14% in dry and temperate desert climates, and 9% in Mediterranean climates. 5% occurred in semi-humid climates, 4% in humid and dry cold desert climates respectively, and 1% in very humid climates. The comparison of old and new land uses in gully areas showed that 55 percent of the gullies were created as a result of changing the land use of rangeland to dry farming agriculture. Silt Loam, Loam, and Sandy Loam are the dominant soil textures in gullies with 26, 23, and 20%, respectively. 14% of the studied areas have very severe restrictions in terms of salinity. The amount of organic matter in the researched areas varies between 0.02% and 2.9%, and about 94% of the gully areas have less than 2% organic matter. About 6 percent of the areas have organic matter between 2 and 2.9 percent. Analysis of the SAR showed that 24% of the investigated areas have a sodium absorption ratio greater than 15. 70% of gully areas are located in a slope of less than 12%, 16% in the slope class of 12 to 25% and 14% of gully areas are located in a slope of more than 25%, Which is consistent with the results of Shadfar et al.'s research (2007) in the Qeshlaq Alborz watershed, where 98% of the gullies occurred in the slope layer up to 5%. In 38 areas, road construction and In 27 regions, plowing in the direction of the slope is known as one of the effective factors on gully erosion.
Conclusion and Suggestions
The highest number of gullies occurred in the semi-arid climate with a frequency of 32% and the lowest in the very humid climate with a frequency of 1%. 55% of the gullies were created due to the change of land use of rangeland to dry farming agriculture. Silt-loam texture with 26% frequency is the dominant soil texture in gullies. 14% of the areas have very severe restrictions in terms of salinity and about 94% of the gully areas have less than 2% organic matter. 24% of the studied areas have a SAR of more than 15% and 70% are located in a slope of less than 12%. In several investigated areas, road construction and plowing in the direction of the slope are also known as effective factors in gully erosion. The damage caused by the expansion of Iran's gullies is estimated to be around 700 billion Tomans. Protection plans of biological type and in some circumstances biological and mechanical integration are suggested to reduce the expansion of Iran's gullies. Especially since we have entered a long drought period. In areas where improper agricultural operations have caused the expansion of gullies, Farmers should be trained.about correct plowing. In addition, land use change is the most important human factor affecting gully erosion in the studied areas, so it is suggested to avoid land use changes.