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Integrated Optimization of Surface and Groundwater Use for Soil Salinity Control (Case Study: Mahabad Plain, Urmia)

Hossaini Baheri, Mohammad Hassan | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58373 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Tajrishy, Massoud
  7. Abstract:
  8. Sustainable management of soil moisture and salinity is a fundamental challenge in semi-arid regions such as the Mahabad Plain, located in northwestern Iran. In this study, the HYDRUS-1D model, calibrated using field data from in-situ sensors, was employed to simulate water and salt dynamics in a 4-hectare sugar beet field. The Mahabad Plain, covering approximately 249 km², receives an average annual precipitation of 402 mm and experiences annual evaporation of about 1560 mm. Despite its relatively fertile soils, the region faces sustainability issues such as waterlogging, salinization, and inefficient irrigation practices—problems that have been exacerbated by agricultural expansion and climatic fluctuations. Soil moisture and electrical conductivity data were collected at four soil depths (0–25, 25–50, 50–75, and 75–100 cm) on alternate days from late June to late July 2024. These measurements were used to calibrate the HYDRUS-1D model and optimize parameters such as residual and saturated moisture content, hydraulic conductivity, and dispersion coefficient. Statistical indices, including RMSE and Nash–Sutcliffe Efficiency, confirmed the model’s accuracy in replicating observed conditions. Model results revealed critical inefficiencies in the current irrigation system. Deeper soil layers retained moisture well above the optimal range (20–25%) for sugar beet growth, while surface layers (0–25 cm) frequently experienced saturation after irrigation. However, electrical conductivity values remained within a safe range (0.6–1.3 dS/m), indicating effective salt leaching and no immediate threat to crop health. Scenario simulations based on the calibrated model showed that reducing irrigation volumes by 35–40% could lower the leaching fraction from 0.39 to approximately 0.2, without increasing soil salinity or dropping moisture levels below critical thresholds. These findings highlight the potential for substantial water savings while still meeting crop requirements. The model also evaluated the role of groundwater depth and quality (TDS ranging from 1216 to 3040 ppm) in maintaining soil moisture and controlling salinity. Results indicated that in areas with shallow water tables and moderate water quality, deeper soil layers can retain sufficient moisture and prevent salt accumulation. This analysis underscores the broader applicability of the model across the plain and its value in sustainable irrigation planning and the restoration of Lake Urmia. Furthermore, to assess groundwater dynamics and predict water table fluctuations at the regional scale, the GMS/MODFLOW software was used. This modeling aimed to provide a predictive tool capable of estimating groundwater levels at any time (past, present, or future), even in the absence of direct piezometric data. This study is the first in the Mahabad Plain to integrate field measurements with advanced HYDRUS-1D and MODFLOW modeling to propose practical and scientific strategies for sustainable water and soil resource management. The findings are particularly relevant in the context of increasing agricultural demand and environmental stress, especially for the revival of Lake Urmia. Enhancing agricultural water use efficiency could play a key role in redirecting water resources to the lake and restoring ecological balance in the region
  9. Keywords:
  10. Soil Moisture ; Simulation ; Environmental Flow Sustainability ; Soil Salinity ; Mahabad Plain (Urmia) ; Integrated Optimization ; Soil Moisture Monitoring

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