شبیه ‏سازی بیلان آب زیرزمینی با استفاده از مدل تلفیقی و جامع آب سطحی و زیرزمینی SWAT-MODFLOW-NWT (مطالعه موردی: دشت مهاباد)

نوع مقاله : مقالات پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه مهندسی آبیاری و آبادانی، پردیس کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران

2 دانشیار گروه مهندسی آبیاری و آبادانی، پردیس کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران

3 استاد، دانشکده مهندسی عمران، دانشگاه صنعتی شریف، تهران، ایران

چکیده

آب‏های سطحی و زیرزمینی در مقیاس‏های مختلف مکانی یا زمانی باهم در ارتباط می‏باشند. از طرفی منابع آب سطحی و زیرزمینی به‌صورت تلفیقی در کشاورزی استفاده می‏شود؛ بنابراین مؤلفه‏های بیلان آب زیرزمینی و سطحی باید با دقت مناسبی تعیین گردند. در این مطالعه، تأثیر مقادیر تغذیه حاصل از مدل SWAT به‏عنوان یکی از مهم‏ترین مؤلفه‏های ورودی مدل‏‏های آب‏ زیرزمینی در شبیه‏سازی تراز سطح ایستابی و مؤلفه‌های بیلان آب زیرزمینی با استفاده از مدل MODFLOW-NWT به‏عنوان یک مدل جامع و یکپارچه منابع آب سطحی و زیرزمینی در دشت مهاباد بررسی شد. با استفاده از مقادیر یکنواخت تغذیه و به‏صورت درصدی از بارندگی و کل آب آبیاری در سطح آبخوان بدون توجه به تأثیر تفاوت برداشت و نفوذ عمقی در سطح کاربری اراضی در موقعیت‏های مختلف نمی‏توان به‏درستی نوسانات سطح آب ‏زیرزمینی در سطح آبخوان را شبیه‏سازی کرد؛ لذا یکی از مراحل مهم، تعیین مقادیر آبیاری با توجه به تفاوت کاربری اراضی و تغذیه ناشی از نفوذ عمقی بارندگی و آب آبیاری از منابع آب سطحی و زیرزمینی بود. این مهم توسط مدل SWAT انجام و به‏عنوان شرایط مرزی به مدل MODFLOW-NWT تعریف شد. واسنجی و اعتبارسنجی مدل آب زیرزمینی نیز به‏ روش‏های سعی و خطا و روش خودکار PEST انجام شد. دوره شبیه‏سازی به مدت 10 سال از سال آبی 89-1388 تا 98-1397 انجام شد که به ترتیب 6 و 4 سال آبی از 89-1388 تا 94-1393 و 95-1394 تا 98-1397 به‏عنوان دوره واسنجی و اعتبارسنجی در نظر گرفته شدند. با توجه به این‌که الگوی تشکیل مؤلفه‌های بیلان آب زیرزمینی برای سال‏های آبی مختلف متفاوت است؛ لذا مؤلفه‌های بیلان آب زیرزمینی برای سه سال معرف خشک‌سالی، ترسالی و نرمال نیز بررسی شد. هدایت هیدرولیکی و ضریب ذخیره آبخوان پارامترهای ورودی و واسنجی در مدل MODFLOW-NWT بودند. نتایج واسنجی نشان داد بیش‏ترین میزان هدایت هیدرولیکی و آبدهی ویژه در نواحی جنوبی، مرکزی و شمال شرقی دشت است و در حاشیه شمالی و در نزدیکی خروجی دشت به کمترین میزان خود می‏رسد. پس از فرآیند واسنجی، نتایج نشان داد به‌طور متوسط حدود 9 درصد از آب بارندگی و 36 درصد از مصارف آب در بخش کشاورزی به آبخوان نفوذ می‏کند. نتایج حاکی از برآورد رضایت‏بخش و قابل‌قبول تراز سطح ایستابی مدل برای هر دو دوره‏ واسنجی و اعتبارسنجی بود. به‌طوری‌که نتایج معیار RMSE برای تراز سطح ایستابی در دوره‏های واسنجی و اعتبارسنجی به ترتیب مقدار خطای 35/0 و 34/0 متر به دست آمد. همچنین، نتایج معیار‏های R2 و NSE نیز برای دوره واسنجی 94/0 و 91/0 و برای دوره اعتبارسنجی 93/0 و 89/0 برآورد شد که مؤید آن است که مدل به‌خوبی واسنجی شده و قادر بوده‏ نوسانات سطح آب زیرزمینی را با دقت مناسبی شبیه‏سازی کند. بررسی نتایج اجزای اصلی بیلان آب زیرزمینی برای سه سال آبی 96-1395 (سال خشک)، 97-1396 (سال نرمال) و 98-1397 (سال‌تر) نشان داد میزان تغذیه ناشی از نفوذ آب بارندگی و جریانات برگشتی آب کشاورزی در هر سه سال متفاوت است. همچنین، فعل‌وانفعالات بین منابع آب سطحی و زیرزمینی بین سال‏های آبی از حدود 30 تا 50 میلیون متر مکعب متغیر است که نشان‏دهنده اندرکنش قابل‌توجه بین این منابع است. به‌طور کلی نتایج این مطالعه نشان می‏دهد اعمال تغذیه تخمینی مدل SWAT همراه با واسنجی هدایت هیدرولیکی و آبدهی ویژه می‏تواند در بهبود برآورد نوسانات سطح آب زیرزمینی توسط MODFLOW-NWT کمک شایانی نماید. نهایتا از مدل تلفیقی می‏توان به‏عنوان یک ابزار کاربردی در تبیین الگوی بهره‌برداری مناسب از منابع آب تلفیقی سطحی و زیرزمینی تحت تأثیر سناریوهای مختلف مدیریتی استفاده کرد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Simulation of Groundwater Balance Using Integrated Surface and Groundwater SWAT-MODFLOW-NWT Model (Case Study: Mahabad Plain)

نویسندگان [English]

  • O. Raja 1
  • M. Parsinejad 2
  • M. Tajrishi 3
1 Ph.D. candidate, Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
2 Associate Professor, Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
3 Professor, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
چکیده [English]

Introduction
 Surface and groundwater conjunctively interact at different spatial or temporal scales within a plain. In many plain, surface and groundwater resources are used in combination in agriculture. Therefore, it is important to accurately predict the components of groundwater and surface water balance. Despite the rapid expansion of numerical models over the past two decades, there is still a need for comprehensive and integrated assessment of surface and groundwater components. In particular, the interconnection of both surface and groundwater models is important to connect both surface and groundwater, especially the water balance in the unsaturated root zone. In this study the effect of water recharge due to deep percolation from simultaneous supply of irrigation water from surface and groundwater sources, and rainfall from the SWAT model were used to simulate groundwater balance using the combined MDOFLOW-NWT model.
Materials and Methods
 In this study, the effect of recharge values obtained from the SWAT model was analyzed to simulate the fluctuation of water table, and groundwater balance components using the integrated model of MODFLOW-NWT model in the Mahabad plain. One of the important steps in quantifying the impact of irrigation management, and the change in land-use on the surface and groundwater balance was the simulated recharge due to the deep percolation of rainfall and irrigation water. This was done by the SWAT model, and was used as the boundary condition to the MODFLOW-NWT model. Calibration and validation of groundwater model were also done by trial-and-error and automatic PEST methods. The simulation period was performed for 10 years from the hydrological year of 2009-2010 to 2018-2019, from which 6 and 4 years were used as the period for calibration and validation were from 2009-2010 to 2014-2015 and 2015-2016 to 2018-2019, respectively. Groundwater balance components are naturally different for different years. Therefore, the study was conducted for dry, wet, and normal years. Hydraulic conductivity and specific yield were the used as initial calibration parameters in the MODFLOW-NWT model.
Results and Discussion
 The results showed a higher hydraulic conductivity and specific yield values for the aquifer was in the southern, central, and northeastern areas of the plain, and the lowest values were in the northern and near the outlet of the plain. After the calibration process, the results showed that an average, 9% of rainfall, and 36% of irrigated water percolate to the aquifer. These observations were confirmed based on a satisfactory and acceptable estimate of the water table level of the model for both calibration and validation periods. The statistical RMSE criteria for calibration and validation periods were 0.35 and 0.34 m, respectively. Also, the results of R2 and NSE criteria were estimated as 0.94 and 0.91 for the calibration period, and 0.93 and 0.89 for the validation period, which indicates that the model was properly calibrated and was well able to simulate groundwater level. The groundwater hydrographs developed from piezometers’ readings, show that the recharge values estimated by the SWAT model, considering the change in land use and irrigation management across the plain, were able to properly simulate groundwater level across the aquifer. Specifically, the studies showed a continuous drop in groundwater level created in the southern and southwestern regions of the aquifer (piezometers of Fakhrighah, Gorg tapeh, and Serah Haji Khosh) due to the presence of high-consumption crops such as apple and alfalfa, and the higher number of operation wells.
Conclusion
The results of this study showed that the recharge values obtained from the calibrated SWAT model was crucial parameters for proper simulation of groundwater, and can significantly improve the model results. The results of the main components of the groundwater balance for different years showed that the amount of recharge due to the infiltration of rainfall, and irrigation were different for each year. Also, interactions between surface and groundwater resources vary from about 30 to 50 million cubic meters between years, indicating a significant interaction between the water resources. In general, the SWAT-MODFLOW-NWT model can be used as a practical tool for proper management of surface and groundwater resources under different management scenarios.

کلیدواژه‌ها [English]

  • Mahabad plain
  • MODFLOW-NWT
  • Recharge Component
  • SWAT
  • Water table
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