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Effective Factors on Runoff Generation and Hydrologic Sensitivity in a Mountainous Watersheds (A Case Study: Farsan Watershed, Upstream of Karoun River)
A. Raeisi , A. Talebi , Kh. Abdollahi , A. Torabi Haghighi,
Volume 8, Issue 1 (3-2020)
Abstract
Aims: Affecting factors on runoff generation in mountainous areas, where the hydrological processes are complex, play an important role in the recognition of hydrological phenomena. The aim of the present study was to simulate the water balance of Farsan Basin using the SWAT model.
Materials & Methods: In this semi-distributed research, SWAT model was used to simulate the monthly runoff the basin of interest. The study area was Farsan watershed, it is the part of Beheshtabad Basin. Basin's curve number was estimated using a remotely sensed NDVI. The calibration and validation of the model were carried out by using the SUFI2 Algorithm (sequential uncertainty fitting) for two periods, one from 2001 to 2011 and another from 2012 to 2015.
Findings: The threshold depth of water in the shallow aquifer to start evaporation (REVAPMN) had the least sensitivity, while the soil evapotranspiration (ESCO), the time delay of the transferring water from the last soil profile to the groundwater level (GW_DELAY), and curve numbers in normal condition (CN2) were the most sensitive factors, respectively. To evaluate the simulation, R2 (coefficient of determination), bR2 (weight correlation coefficient), and NS (Nash Sutcliffe model efficiency) at the calibration stage were 0.63, 0.33, and 0.57, respectively. Whereas at the validation phase, these coefficients were found to be 0.69, 0.68, and 0.52, respectively.
Conclusion: A proper specification of these sensitive parameters may be the key factor for runoff simulations. The impact of change in surface parameters may have a great influence in both generating runoff and mountain hydrology.

Optimal Prioritization of Best Management Practices Through a Simulation-Optimization Model to Sediment Load Reduction
Mehdi Vafakhah, Hamzeh Noor,
Volume 9, Issue 4 (9-2021)
Abstract
Aims Watershed management practices are as appropriate solutions to control nonpoint sources of pollution at watershed scale. Nevertheless, the best way to allocate limited resources is a challenge for watershed management efforts. Therefore, to achieve the most suitable strategies, manager requires the use of mathematical techniques to assign management practices priority. In this regards, in the present study, an optimization-based Decision Support Tool (DST) was used to assign the optimal combinations of management practices at the Taleghan Dam Watershed, Alborz Province, Iran.
Materials & Methods To achieve the present research goals, Soil and Water Assessment Tool (SWAT) was applied to determine the sediment yield at outlet of the watershed under different combinations of management measures and was coupled with a genetic algorithm in MATLAB computer software, which provides as the optimization engine.
Findings The results of optimization in the Taleghan Dam Watershed showed that implementation costs for 10% and 20% sediment reduction in optimal solution were obtained 110300$ and 235500$, respectively. The cost-effectiveness ratio of scenarios 10% and 20% sediment reduction obtained about 11030 and 11770.5 (dollars for 1% sediment reduction), respectively. The results also showed that filter strip and seeding are the most cost effective option for sediment load control. Conversely, the grade stabilization structure and detention pond are the least cost-effective option.
Conclusion This tool is transferable to other watersheds and therefore, is one of the effective approaches of watershed management.
Flood Peak Discharge Trend over Iran
Mehdi Vafakhah, Hamed Beigi, Kazem Sadeghian, Hamid Khodamoradi, Samira Karimi Breshneh, Fatemeh Daeichini, Samira Hossinpour, Saeid Derakhti,
Volume 12, Issue 3 (9-2024)
Abstract
Aims:  Studying flood peak discharge trends is crucial to disaster risk reduction in developing countries like Iran. This study aims to analyze the instantaneous peak discharge trend in 301 hydrometric gauge stations using Mann Kendal (MK (and Sen’s Slope estimator tests over Iran.
Material & Methods: Data on all existing hydrometric gauge stations in Iran were downloaded from Iran Water Resources Management Company. The hydrometric gauge stations with at least 20 years of data were selected, and the stations that were then affected by the dams were removed. Trend analyses of instantaneous peak discharge were conducted using MK and Sen’s slope estimator tests.
Findings: The results showed that out of 301 hydrometric stations, 259 stations have no trend, only three stations have a decreasing trend, and 39 stations have an increasing trend. This trend is more evident in southwestern Iran, where the increase in agriculture, human activity, and climate change is more evident. In the watershed of the eastern border, only one station has a decreasing trend; in the central plateau, four stations have a decreasing trend, and the rest have no trend. 
Conclusion: Due to the importance of peak discharge in flood damage, this research can help managers and decision-makers in integrated watershed management. For example, in flood control projects, as well as designing the dimensions of structures such as retard dams, levees, the height of flood control walls, and bridges.

Assessing the Impact of Spatial Accuracy of Digital Elevation Models on Simulating Discharge in Arid Regions Using SWAT Model: A Case Study of the Lar Watershed
Mahnaz Kiyani Majd, Mohammad Nohtani, Mohammad Reza Dahmardeh Ghaleno, Zahra Sheikh,
Volume 12, Issue 4 (12-2024)
Abstract
Aims: The Digital Elevation Model (DEM) plays a crucial role in the SWAT model and significantly impacts its output results. This study evaluated the effect of different spatial accuracy of DEM in runoff simulation using the SWAT and SWAT-CUP models for the Lar Watershed in Sistan and Baluchestan Province.
Materials & Methods: This study examines the impact of different accuracies of Digital Elevation Models (DEMs) with resolutions of 12.5, 30, 50, 90, 450, and 1000-meters on discharge simulation using the SWAT model for the Lar Watershed, located in an arid region. The model was selected for 30 years (1988-2017), with 18 years for the calibration period and 12 years for validation. The SWAT-CUP software and the SUFI-2 method were used. The model’s accuracy was also evaluated using the Nash-Sutcliffe efficiency (NS), coefficient of determination (R²), r, and p coefficients.
Findings: The discharge simulation results reveal that variables such as area, sub-basin, Hydrologic Response Unit (HRU), watershed slope, and mean channel slope are particularly affected by DEM accuracy. With increasing DEM accuracy, the length of the main channels decreases, and lower-order channels are eliminated, reducing the calculated discharge depth. Our sensitivity analysis identified seven key parameters influencing discharge simulation in the Lar Watershed. The most critical parameters were r__CN2.mgt, v__ALpha_BF.gw, and r__SOL_AWC.sol, consistently recognized as highly sensitive in similar studies.
Conclusion: During validation and calibration, DEM resolutions of 12.5 and 1000 meters exhibited lower accuracy than those of 30, 50, 90, and 450 meters, suggesting that extremely high or low spatial data accuracy does not enhance simulation accuracy. Additionally, minimal differences were observed among the results for DEM resolutions of 30, 50, 90, and 450 meters. This can be attributed to adjustments in calibrated variable values and the application of the SUFI-2 method across different DEM accuracies. Finally, based on the results of this research, the DEMs with spatial resolutions of 30, 12.5, 50, 90, 450, and 1000 meters demonstrated the best performance for simulating monthly discharge in the Lar Watershed. Additionally, based on the value of the objective function (NS) during the calibration and validation stages, it can be concluded that the SWAT model can simulate the monthly discharge of the Lar Watershed with acceptable accuracy. Therefore, it can be said that the SWAT hydrological model can be used in arid regions to implement management scenarios quickly and at a low cost for decision-making.

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