تعیین نوع رابطه بین شروع آستانه همزمان رواناب و فرسایش با خصوصیات شیمیایی خاک

Extended Abstract
1. Introduction
Knowledge of the erosion and runoff simultaneous threshold and knowledge of the factors affecting it is essential to provide a management solution to delay the occurrence and reduce the amount of runoff. By focusing and converting water repelling to annual floods, in addition to life and financial damages to industrial, urban and rural centers, it causes washing and transferring fertile soil. Therefore, estimation of erosion and runoff threshold leads to optimal use and management of atmospheric precipitation. By determining the erosion and runoff threshold by rain simulator, it is possible to estimate the amount of precipitation that causes runoff in different conditions with higher speed and accuracy and lower cost. One of the most eridibility of Iran is the Gahsaran formation. Gahsaran formation has a thickness of about 1600 meters. A viewpoint of lithology is consisting of salt, anhydrite, colorful lime, and some shale. Gahsaran formation age is lower Miocene.

2. Methodology
In this study, in order to determine the relationship between the erosion and runoff simultaneous threshold and soil chemical properties in different land uses of Gachsaran Formation deposits, a part of the 1202-hectare Kuhe Gach watershed of Izeh city was selected. In this study in other to determine the relationship between erosion and runoff simultaneous threshold and soil chemical properties in different land uses of Gachsaran Formation was performed using univariate regression. Then, sampling of erosion and runoff simultaneous threshold at 6 points with 3 replicates and at different rainfall intensities of 0.75, 1 and 1.25 mm/min in three land uses of the range, residential area and agricultural lands with the help of the rain simulator was done. In addition, the same number of runoff and erosion threshold sampling was performed sampling of soil chemical properties such as organic matter, soil salinity, soil acidity and carbonate calcium. SPSS and EXCEL software were used for statistical analysis. In this study, Kamphorst rainfall simulator was used. This rainfall simulator to plot size of 625 cm2 designed, it is portable. This rainfall simulator to determine the characteristics of soil, erosion, water infiltration used and it is suitable for soil research.

3. Results and discussion
The results showed that in total in Gachsaran Formation and in all three rangeland, agricultural and residential land uses and in all three intensities of 0.75, 1 and 1.25 mm/min, soil organic matter in three cases had a negative relationship and in six cases had the relationship Positive with the erosion and runoff threshold. Soil salinity showed a negative relationship in nine cases and soil acidity had a negative relationship in seven cases and a positive relationship in two cases, and soil carbonate calcium had a negative relationship in six cases and a positive relationship in three cases with erosion and runoff threshold.

4. Conclusion
by determining the exact relationships between erosion and runoff threshold and soil chemical properties, it was tried to express the importance of determining erosion and runoff threshold in comprehensive management of watersheds and to lead further researches on of erosion and runoff simultaneous threshold in preventing severe erosion and devastating floods.This research also showed that by examining the exact details of the relationship between water and soil, better planning can be done for water and soil resources of the country.

Extended Abstract
1. Introduction
Knowledge of the erosion and runoff simultaneous threshold and knowledge of the factors affecting it is essential to provide a management solution to delay the occurrence and reduce the amount of runoff. By focusing and converting water repelling to annual floods, in addition to life and financial damages to industrial, urban and rural centers, it causes washing and transferring fertile soil. Therefore, estimation of erosion and runoff threshold leads to optimal use and management of atmospheric precipitation. By determining the erosion and runoff threshold by rain simulator, it is possible to estimate the amount of precipitation that causes runoff in different conditions with higher speed and accuracy and lower cost. One of the most eridibility of Iran is the Gahsaran formation. Gahsaran formation has a thickness of about 1600 meters. A viewpoint of lithology is consisting of salt, anhydrite, colorful lime, and some shale. Gahsaran formation age is lower Miocene.

2. Methodology
In this study, in order to determine the relationship between the erosion and runoff simultaneous threshold and soil chemical properties in different land uses of Gachsaran Formation deposits, a part of the 1202-hectare Kuhe Gach watershed of Izeh city was selected. In this study in other to determine the relationship between erosion and runoff simultaneous threshold and soil chemical properties in different land uses of Gachsaran Formation was performed using univariate regression. Then, sampling of erosion and runoff simultaneous threshold at 6 points with 3 replicates and at different rainfall intensities of 0.75, 1 and 1.25 mm/min in three land uses of the range, residential area and agricultural lands with the help of the rain simulator was done. In addition, the same number of runoff and erosion threshold sampling was performed sampling of soil chemical properties such as organic matter, soil salinity, soil acidity and carbonate calcium. SPSS and EXCEL software were used for statistical analysis. In this study, Kamphorst rainfall simulator was used. This rainfall simulator to plot size of 625 cm2 designed, it is portable. This rainfall simulator to determine the characteristics of soil, erosion, water infiltration used and it is suitable for soil research.