عنوان مقاله [English]
Gully erosion as one of the common forms of erosion causes deformation of the land surface and its spread is one of the main reasons for the destruction of agricultural lands, communication roads and irrigation system of the basin, especially the plains on the slopes east of the basin to Chaho village. The area is eroded and made inaccessible through the creation and development of ditches and the agricultural productivity of the area is reduced. Therefore, by studing the physical and chemical properties of the soil and also determining the topographic threshold, an attempt has been made to identify the factors affecting gully erosion and to prevent the damages caused by it as much as possible with a more accurate prediction.
The study area is the Shoor River watershed in the East and Northeast of Mohr city, which is located in the south of Fars province with an area of 101350 hectares. This watershed is located between 27 degrees, 27 minutes and 22 seconds to 27 degrees, 49 minutes and 41 seconds North latitude and 52 degrees, 24 minutes and 58 seconds to 52 degrees, 59 minutes and 14 seconds East longitude. According to the divisions of the country's catchments, the study area is part of the catchments of the Shoor and Mehran rivers, which eventually enters the Persian Gulf.
In order to initially identify the natural features of the basin and collect theoretical topics, basic topographic maps (scale 1: 25000) of the National Mapping Organization and geological map (scale 1: 100000), Geological Survey and Mineral Exploration Organization were used. ArcMap version 10.3 software was used to draw the maps. Then 15 ditches were randomly selected. To select the topographic threshold, all selected ditches in the relation were used. While to study the physical and chemical properties of soil (sand, clay, silt, PH, EC, TNV, Mg, Ca, K, Ca, SAR, Na) and geometric measurements, gullys based on cluster analysis It was classified in which geometric measurements were considered as dependent variables and soil physical and chemical properties were considered as independent variables. Tests were performed on the data in SPSS software.
Results and Discussion
The results of clustering analysis showed that the gullys were classified into three groups. Since more than 53% of gullys are in group one, they have been used for statistical analysis. Correlation and multiple regression models were performed to analyze the relationship between dependent and independent variables. The results of Pearson correlation showed that the length and width of gullys had a very strong relationship with the variable of sodium (/ 866) and SAR (/ 826) while it had a negative relationship with the variable of soil PH (-258). Then, using multivariate regression, the relationship between the independent variables and the gully length and gully cross section was determined. The results showed that the amount of sand, SAR, TNV and sodium had the greatest role in the longitudinal and cross-sectional area of the gullys , respectively. However, the presence of OC and K prevents the spread of moat erosion in the region. According to the results of the topographic threshold formula of the region (S=6759.756A^(-.556) ), the surface runoff process was recognized as the dominant hydrological process affecting the spread of gully erosion.
gully erosion plays a major role in soil degradation. Rapid progression of moat erosion at the eastern end of the basin In addition to the destruction of a large area of agricultural land and rangeland of the basin, are a serious threat to several villages, especially the villages of Qala-e-Seyed and Chahoo and even part of the city of Mohr. The results of the longitudinal expansion and cross-sectional area of the gullys show the high impact of SAR, TNV and sodium in the soil in creating and spreading the gully erosion. However, OC and K prevent the formation and spread of gully erosion. the soil texture is mainly sandy and loamy and sand has the highest percentage in all samples. Sand particles weaken the soil structure and in spite of water, they lose their cohesion and the underlying layers dissolve and then the upper surface of the gully collapses and causes the development of the gully. The results of topographic threshold showed that surface runoff causes gully erosion so that the lower the slope of the area, the more upstream area and more runoff is produced and easily washed with aggregates with low stability and creating valleys along the route. It causes gully erosion. Based on the results of the research, it is suggested that due to the high amount of sodium, chemical modification should be done first and then the vegetation in the area should be modified and created. Due to the high production of surface runoff, mechanical runoff can be collected through temporary methods including creating temporary dams, rock dams, and soil dams at the end of gullys. It is suggested that combined methods such as CF statistical methods and ME algorithm for modeling be used to more fully investigate the gully erosion of the area.