عنوان مقاله [English]
Soil degradation by water is the most serious form of land degradation in many parts of the world, especially in arid and semi-arid areas, where soil formation rates are usually less than soil degradation due to rapid soil erosion, the impact of human abuses And incorrect use of soils. For this reason, crushing land control strategies such as agricultural agriculture, mulch, environmental improvement or land expansion are necessary to avoid drought in agricultural land. Awareness of the process of soil erosion and sediment transport as an effective factor in reducing soil fertility and soil loss, filling dams, catching and blocking irrigation channels, polluting water from rivers, and reducing water quality have long been considered by geoscience experts. Understanding the factors affecting sediment production plays an important role in determining the amount of sediment yield of a basin and understanding the phenomenon of erosion and its consequences and can be used to prioritize sub basins in a watershed. Areal characteristics encompass morphological characteristics such as drainage density, stream frequency and watershed shape parameters. Ease access to Digital Elevation Models, remote sensing data as sediment yield predictors, simplify the calculation of the watershed geomorphic characteristics. The purpose of this study was to use the geographic information system to extract the watershed geomorphic characteristics and determine their relationship with sedimentation in the Gharanghoo basin.
This study was conducted in 19 subwatersheds in Gharanghoo basin. In order to select appropriate subwatersheds, the hydrometric and rainfall data for hydrometric and meteorological stations were obtained from East Azarbaijan Regional Water authority for the selected watersheds. Annual sediment load was calculated using sediment rating curve method. Physiographic and geomorphic characteristics including 25 geomorphic parameters were calculated for each sub watershed using digital elevation model with spatial resolution of 30 m. In order to determine the relationship between geomorphic characteristics and sediment yield of the subwatersheds, a multivariate regression stepwise analysis was used. In the multivariate regression, the important geomorphic characteristics which affect watershed sedimentation are identified and based on those parameters, the best annual sediment yield and geomorphic characteristics equation were presented.
The annual amount of sediment varies from 63500 tons per year in the Kalghan sub basin (Kalghan dam) to 4636762.6 tons per year in the gharanghoo area at the intersection with Ghezel Ozan. Basin sedimentation weight as dependent variable and other parameters were considered as independent variables. The variables of flow volume, area, environment, equivalent rectangular length, equivalent rectangular width, drainage density, branching index, minimum height, coefficient of elongation and roughness of the basin were compared. Other variables have higher correlation with sediment yield. The result of the study of the relationship between geomorphic characteristics and sediment of sub-basins showed that the amount of sediment produced with flow volume and basin coefficient was positively correlated and was significant at 5% level. The principal components analysis (PCA) method was used to identify the factors affecting sediment yield of the existing variables. The results show that the four factors of area, area, length and coefficient of form of basin are 50, 20.9, 13.6 and 7.7 percent of the variance of all variables, respectively. In total, the four finalized factors have been able to explain 92.2% of the variance of all research variables.The results show that the four factors of area, area, length and coefficient of form of basin are 50, 20.9, 13.6 and 7.7 percent of the variance of all variables, respectively. In total, the four finalized factors have been able to explain 92.2% of the variance of all research variables.
4. Discussion & Conclusions
The results of this study indicate that there is a significant relationship between the geomorphic characteristics of the studied watersheds and annual sediment yield. Watershed Form factor is a dimensionless index for flood flow and movement, erosion severity and sediment transport capacity of watersheds. This factor is a function of watershed area and length. Run off and amount of flood peak in bigger watersheds will increase sediment yield. Many researches have reported high correlation between rainfall and sediment yield. Arid climate and poor vegetation cover in selected watersheds is the main reason for high correlation of rainfall and sediment yield. Soil erosion and sediment yield will increase due to high intensity and low duration of rainfall along with scarcity of vegetation cover and erodible soils in this region. Overall, study results indicated that with the development of new technologies and the possibility of extracting different physiographic and geomorphic parameters of watersheds from a digital elevation model, it is possible to present regional equations for prediction of sediment yield using geomorphic characteristics that can be used in sediment control and Watershed Management Programs.