Journal of Watershed Management Research

  

Extended Abstract
Introduction and Objective: Soil erosion is one of the most serious environmental and serious threats to agricultural lands and natural areas. Among the various forms of soil erosion, gully erosion is the most dominant process of land degradation and an advanced form of soil erosion. therfore identifying effective factors and predicting areas susceptible to gully erosion are key factors for land management and planning.
Materials and Methods: In this study, first, the location of the gullys created in the Maroon Dam watershed was recorded using a global positioning system, and Google Earth images. Based on gully polygons were converted to the points. then recorded points were divided into two groups of training data (70%) and experimental data (30%) for the purpose of calibration and validation of the models, respectively. Based on scientific sources and watershed conditions, 23 factors affecting the occurrence of gully erosion were identified and a map of  all factors were prepared. The weight of these factors were determined based on the frequency ratio (FR). Correlation relationship among factors were examined using the collinearity test. In the next step, three models of maximum entropy, Dempster-Schaffer and weight of evidence were calibrated and validated using the weighted data of the effective factors and the training and experimental spatial data of ditch distribution. A ditch erosion zoning map was prepared for each model and then the optimal model was selected based on the validation data. The jackknife test and Operating Characteristic (ROC) curve were used to determine the thresholds of the factors affecting the occurrence of gully erosion and to evaluate the efficiency, respectively.
Findings: The results showed that the ratio of gully frequency in very high class has the highest amount based on the cell area index. The validation results in maximum entropy, Dempster-Shaffer and weight of evidence models based on the ROC index WERE 0.85, 0.81 and 0.78, respectively, which indicates a higher accuracy of the maximum entropy model than the Dempster-Shaffer and weight of evidence methods. Also, the weight of evidence method had the lowest accuracy among the studied methods. In general, all three models had an acceptable percentage of ROC, which indicates the high performance of all three models. The results showed that land use and geological parameters had the highest contribution in occurrence of gully erosion with a contribution of 24 and 18 percent.
Conclusion:
Gully erosion is one of the most important natural hazards in the Maroon Dam watershed, which requires attention to soil conservation and gully erosion control issues. In this regard, one of the initial and required measures to determine sensitive areas and control and implement appropriate management measures is to prepare a gully erosion map. For this purpose, different methods and models of weight of evidence, Dempster-Shaffer model and entropy method have been used to prepare a gully erosion sensitivity map. 23 parameters effective in gully erosion at the watershed level were identified and used as independent variables to predict gully erosion. The results of the factors affecting gully erosion showed that the lithological factor had the greatest impact on the ROC. different parameters have different levels of participation in the occurrence of gully erosion, so that land use and geology parameters with a contribution of 24 and 18 percent had the highest contribution to the occurrence of gully erosion. In general, high accuracy of the gully erosion sensitivity map obtained from the maximum entropy model, that can be used to take appropriate management measures to prevent of gully erosion in very sensitive areas.
Keywords: Takht Daraz Watershed, Kohgiluyeh & BoyerAhmad Province, Erosion, Model, Entropy, Zoning