تأثیر تغییرات شیب طولی بستر بر پیشروی شوری در آبخوان تحت فشار ساحلی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانش‌آموخته کارشناس/ ارشد مهندسی آب و سازه‌های هیدرولیکی، گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه آزاد اسلامی واحد تهران مرکز، تهران، ایران.

2 استادیار/ گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه آزاد اسلامی واحد تهران مرکز، تهران، ایران

چکیده

بهره‌برداری بیش از حد از منابع آب زیرزمینی سبب پیشروی آب شور دریاها به سمت آبخوان‌های ساحلی می‌شود. پژوهش حاضر به بررسی اثر تغییر شیب بستر آبخوان بر مشخصات گوه شوری شامل (1) ضخامت ناحیه انتقالی، (2) موقعیت پنجه شوری و (3) حجم آب شور آبخوان می‌پردازد. بدین منظور از کد عددی SEAWAT استفاده شده و با تعریف سناریوهای مختلفی با تغییر در اندازه و جهت شیب طولی بستر، رفتار گوه شوری در یک آبخوان تحت فشار و بزرگ مقیاس ساحلی مشخص شده‌است. در این سناریوها به منظور آنالیز حساسیت، نوع ورود جریان از مرز خشکی و ضخامت آبخوان نیز متفاوت لحاظ شده است. بررسی‌ها نشان می‌دهد که با شرایط دبی ثابت در مرز خشکی، پیشروی شوری به سمت آبخوان و ضخامت ناحیه انتقالی در بستر با تغییر شیب از مثبت (شیب طولی به سمت دریا) به منفی (شیب طولی به سمت خشکی) افزایش یافته که افزایش حجم آب شور را در پی داشته‌است. از اینرو مسطح در نظر گرفتن بستر مقدار پنجه شوری، ضخامت ناحیه انتقالی در بستر و حجم آب شور را کمتر از سناریوهای مشابه با شیب منفی و بیشتر از سناریوهای مشابه با شیب مثبت پیش‌بینی می‌کند. نوع شرط مرزی ورودی جریان آب شیرین نیز بر نتایج تأثیرگذار است، به طوریکه با تغییر مرز خشکی از دبی ثابت به هد ثابت، مشخصات گوه شوری تغییرات کمتری داشته است. تغییر در شیب بستر سبب اثرگذاری در عامل ثقل (بار پتانسیل) در روابط حاکم خواهد شد و به همراه بار فشار نقش اساسی در این رخداد ایفا میکنند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Effect of Bed Slope on Seawater Intrusion into Confined Coastal Aquifer

نویسندگان [English]

  • Maryam Sasani 1
  • Seyed. Sadjad Mehdizadeh 2
1 M.Sc.Graduate of Water and Hydraulic Structures Engineering, Department of Civil Engineering, Central Tehran Branch, Islamic Azad University, Tehran, Iran.
2 Assistant Professor, Department of Civil Engineering, Central Tehran Branch, Islamic Azad University, Tehran, Iran.
چکیده [English]

Excessive exploration of groundwater causes seawater intrusion (SWI) in coastal aquifers. The purpose of this study is to investigate the effect of aquifer bed slope on SWI characteristics including salt wedge toe position, thickness of mixing zone and seawater volume in the aquifer. Different scenarios under various bed slope values and directions are defined and numerical dispersive SEAWAT code is used for modeling. Two different boundary conditions (i.e. constant head and constant flux) are also applied to freshwater inflow at landside. The simulation results demonstrate that in the confined aquifers with landside constant flux, the SWI extent and thickness of mixing zone have increased when the slope changes from a positive value (i.e. longitudinal slope toward the sea) to negative amount (i.e. longitudinal slope toward the land). The results of this study show that when the aquifer bed is considered flat, the SWI specifications including salt wedge toe position, mixing zone thickness at bed and saline water volume are less estimated than those in cases with negative slope and are more predicted than positive slope cases. Type of freshwater inflow at landside boundary also influences the results. In confined aquifers, when landward boundary condition is changed from constant flux to constant head, salt wedge characteristics were not significantly changed. Variation in the aquifer bed slope will affect the gravity factor (potential head) in the related equations that is accompanied with pressure head, which plays a key role on SWI specifications in confined coastal aquifers.

کلیدواژه‌ها [English]

  • Seawater intrusion
  • Confined coastal aquifer
  • SEAWAT Model
  • Toe Position
  • Mixing Zone Thickness
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