Introduction
The Iranian Institute of Soil Conservation and Sanitation has estimated the annual soil erosion rate in Rata, Iran, at 33 tons per hectare, which is 5 to 6 times the permissible limit.Due to the large extent of most watersheds in Iran, it is not possible to implement conservation and sanitation plans throughout the basin.For this reason, in order to increase the performance of watershed plans, critical areas should be identified and prioritized in terms of soil erosion potential. And then, by implementing proper management programs, priority should be given to reducing and preventing soil erosion, respectively. The Ghezel Ozen-Sefid Rood Watershed is the largest sub-basin of the Caspian Sea which is the largest irrigable basin after the salt lake basin and it is important because of the different climates and rich soil and water resources. Due to extensive agricultural lands, Manjil dam located downstream of Ghezel Ozen River and beneficiary of 8 provinces of this basin, soil erosion studies and identification of susceptible areas to waterlogging are one of the most important programs and priorities for watershed management activities. This basin is intended to prevent erosion and consequently the economic and social consequences thereof.
Materials and Methods
In this research, in order to estimate morphometric parameters of linear and linear morphometric parameters, the digital layer SRTM height of 30 m was used in Arc GIS environment.Also, a MODIS image frame was used to map the basin vegetation at the time of basin maximum vegetation cover using NDVI index.TRMM satellite precipitation data along with the Fournier index were used to estimate the erosion rate of the basin digitally-spatially. CP ranking was also used to prioritize.
Discussion and Results
Results of mean CP rankings from morphometric point of view show that Taleghan basin with the highest value of 0.9 and Astaneh basin located downstream of Sefidrood with the lowest value of 0.9 have the least sensitivity to erosion.According to CP, basins often have roughly the same stress-strain conditions, all of which fall into two classes of medium and high.54/54% of watersheds in middle class and 45/46% in high sensitivity class
Soil erosion is the highest priority in Taleghan, Divandareh and Mahan basins, respectively.
The results of basin erosion based on erosion rate and vegetation cover showed more varied classes than morphometric based erosion rate, indicating that the basins have more differences in vegetation cover and erosion rate than their morphometry.Based on erosion rate and vegetation cover, 3.4% of Sefidrood basin, which includes Gol Tapeh basin, has very high priority, 2.9% which includes Taleghan, Mahan, Qorveh, Divandarjeh, Manjastan, Zanjan, respectively. At high priority, 1.2%, which includes the Sajas Basin and the Lunar Basin, are at medium priority and 1.2% of the basin, which includes the Tarom basin, is of low priority.Based on the combination of mean morphometric parameters, erosion and vegetation cover, the lowest CP values of basins were3.87 and the highest values were 8.2 for lunar and Manjil basins.Similar to the classification of morphometric parameters, the results of integrated prioritization fall into two classes of medium and high. High-priority basins with 45.45 percent of medium-sized basins also include 55/54sub-basins of the Great White River.
Conclusions
In this study, in order to prioritize Sefidroud-Ghezel Ozen subsoil against soil erosion, morphometric parameters were used as physiographic factors involved in erosion of watersheds along with annual erosion rate as external dynamic factor and vegetation cover as a conservation factor.In order to prioritize sub-basins based on morphometric parameters, all sub-basins of Sefidroud-Ghezlozen in two classes of intermediate with frequency of 54/54 and high with frequency of45/46They take their place.Basin prioritization based on erosion rate and vegetation cover shows more diversity of sub-basins from the perspective of these two parameters.Therefore, sub-basins were classified in four very high, very low and medium classes, indicating that the erosion and vegetation cover of the sub-basins were more than their morphometric differences. Since the morphometric parameters of the watersheds are mainly influenced by tectonic movements and due to the most part of Ghezel Ozen-Sefidrood basin in northern geomorphologic units (Alborz and Talesh) and northwestern of Karestan and Azarbayjan in Azarbaijan The unevenness follows and there is not much difference between them.From the perspective of the data used, the TRMM data are the most recent data used to increase the speed of operation in prioritizing and estimating the rainfall parameter and subsequently the erosion. Accuracy evaluation results showed that R2 and RMSE coefficients have good performance in Sefidrood basin and can be used in estimating erosion rate.The present study demonstrates the optimum performance of spatial digital data for morphometric, vegetation, erosion, and ... studies of watersheds that are useful for comparative studies of watersheds and can be used in the shortest time.