JWSS - Journal of Water and Soil Science

This research was aimed to simulate and prioritize the effective factors on water erosion using USLE-M in the system dynamic model. In this integrated model, by using the system dynamic simulation software (Vensim), all variables and factors involved in erosion and soil loss were considered according to the USLE-M model. After model implementation, the estimated values and observations were compared and then sensitivity analysis was done to determine the sensitive parameters. Then, calibration was performed on the sensitive parameters. This study found that that the results of the model were acceptable for soil erosion simulation due to considering all the effective factors in soil erosion. The results of the sensitivity analysis also indicated high model sensitivity to the slope and vegetation cover in high and low slopes, respectively. By investigating the changes in various parameters such as vegetation cover and slope on erosion, the optimal vegetation cover with 67 and 40% slope, was estimated to be 20 and 60%, respectively.

Due to the growing population, crop production is one of the essential needs of the society. Since soil and water salinity can have a great impact on the crop yield loss; so, the appropriate irrigation method can be applied to reduce these effects. In this study, the system dynamics model was developed using VENSIM. The model simulated the effect of salinity and water stress on the crop yield, moisture and salinity of the root zone. In order to calibrate and validate the model results, 9 treatments data were collected from the Right Abshar Irrigation Network, on the Zayandehrud basin. After statistical analysis and calculation of RMSE index and the standard error, the fit between the measured and simulated crop yield, the moisture and salinity of root zone was calculated. The average of these indexes for all treatments was 2776.98 kg/ha and 0.07 for crop yield, 0.026 and 0.09 for soil moisture and final, 0.54 dS/m and 0.08 for the salinity of root zone, respectively. The results showed that the model could be calibrated accurately and completely in estimating the crop yield with the reasonable accuracy.

In the present study, a model was developed using a system dynamics approach to simulate and optimize the profitability of crops of the Jofeyr (Isargaran) Irrigation and Drainage Network located in Khuzestan Province. To validate the results, the statistical indicators of root mean square error (RMSE), standard error (SE), mean biased error (MBE), and determination coefficient (R²) were used. To validate the simulation results of the benefit-cost ratio, the values of these indicators were obtained 0.25, 0.19, 0.005, and 0.96, respectively. Then, to determine the optimal cultivated area of the network and increase the profitability, the cropping pattern was determined both non-stepwise and stepwise in 2013 to 2017 cropping years. In the non-stepwise, the cultivated area of each crop changed from zero to 2 times of current situation. In stepwise, due to social and cultural conditions of inhabitants, this change was slow and 10% of the current situation every year. The analysis of the results showed the success of the model in optimizing and achieving the desired goals and the total benefit-cost ratio increased in all years both non-stepwise and stepwise. For example, in 2017 compared to 2016, production costs decreased by 7.1 percent and sales prices increased by 5.8 percent, and increased the benefit-cost in 2017 compared to the previous year. The results showed that the present model has good accuracy in simulating and optimizing the irrigation network, its cropping pattern, and defining other scenarios.