Investigation of morphometric characteristics of gullies and its relationship with soil characteristics in Shoor Chai Basin

Gully erosion is considered to be one of the most destructive and complex types of water erosion. The gully is a stream with steep slopes and active erosional forehead which has been routinely created by erosion due to the alternating surface flow during intensive rain or after it. Gullies are deep canals that are not destroyed by normal plowing, but temporary gullies in agricultural fields, such as ravines, are so small that their repairing is possible by usual plowing. Formation and expansion of gully erosion are influenced by various factors such as physical properties and distribution of its forming particles and amount of salts in the soil and geological formations. Incorrect using of land and changing land use, excessive grazing, lack of correct management of agricultural lands, plowing in the direction of slope, road construction and mining in basins also lead to dredging. The purpose of this study is to investigate the physical and chemical properties of soil and morphometry of gullies in order to identify and control this type of erosion to proper regional planning and actions of water management to control and reduce the damages caused by soil erosion in line with sustainable development goals in the study area.

 It was used from the library documents, topographic maps with the scales of 1: 25000, 1:50000 and the geological maps of 1:100000 of the area for primary identifying of the natural features of the basin. Then 10 samples were selected from identified gullies with surveys and measured the morphometric characteristics of the gullies including the length, width and depth of them. 10 soil samples were collected, transferred to the soil laboratory for analyzing and measured for the specimens. The Pearson coefficient of correlation and regression analysis were used to investigate the correlation between dependent and independent variables. Regression analysis is a statistical process to estimate the relationship between variables, how the amount of the dependent variable changes with the turn of each independent variables and fixing other independent variables.

The morphometric features include the average depth, width, length and volume of the gully. According to the table data (2), the average length is 67/3 meters, width is 3/43 meters and depth is 2 meters which is from small and little depth of the gullies. The volume of the gully is correlated with other variables, which has the highest correlation with EC with the amount of (./796). The correlation between sodium and electrical conductivity with the growth of the gullies is positive. The reason of this, is the release of sodium in the replacement of calcium or potassium, and the increase of soil propagation and the spread of its particles, and provides the field of the development of gully erosion. Accoding to the obtaied results of creating of regression relations between the volume of gullies with soil features, it is seemed that there is a significant correlation in the surface of 95% with high correlation coefficient, which indicates the high soil propagation property in the location of gullies and the formation of gully erosion .Different factors influence in creating and expanding the gullies that physical and chemical characteristics of the soil are very important among them.

 The obtained results of gullies’ morphometry by regression methods show that the volume of the gully is correlated highly and directly with its depth as among the morphometric parameters, (the width, depth, length and volume of the gully) the depth and length of the gully have more relation with its volume and the amount of wasted soil. The obtained results of the correlation between gully volume and soil properties (PH, electrical conductivity, organic matters, sodium, calcium, magnesium and lime) showed that the volume of gullies is increased by decreasing PH, organic matters, lime and potassium.  This means, these parameters have a significant correlation with the volume of the gullies in the opposite direction. The correlation between the volume of the gully with the sodium parameters and the electrical conductivity is positive, and being high of these parameters causes the soil spreading and expanding of the volume of the gullies. The correlation between the expansion of the gullies is also positive relation with electrical conductivity, as by increasing solutes in the soil, the volume of the gullies is also increased.