برآورد ضریب شکل تابع هدایت هیدرولیکی مدل ون‌گنوختن ـ معلم با استفاده از ویژگی‌های زودیافت خاک

نوع مقاله : مقاله پژوهشی

نویسندگان

1 کاندید دکتری آبیاری و زهکشی گروه مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد

2 استاد گروه مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد

3 استاد گروه علوم خاک، دانشکده کشاورزی، دانشگاه فردوسی مشهد

چکیده

برای پژوهش در زمینه‌ی جریان غیر اشباع در خاک، داشتن توابعی هیدرولیکی که در پیش‌بینی منحنی مشخصه و هدایت هیدرولیکی خاک دارای عملکرد مطلوبی باشند، برای پژوهش در زمینه‌ی جریان غیر اشباع در خاک ضروری است. در این پژوهش، ابتدا با انتخاب 8 خاک از بافت‌های مختلف بانک UNSODA، به بررسی صحت ضریب شکل بهینه خروجی از رابطه‌ی رطوبت ـ مکش (n) مدل ون‌گنوختن ـ معلم (VGM) در پیش‌بینی مقدار هدایت هیدرولیکی غیراشباع در رطوبت‌های مختلف بررسی شد. با توجه به نتایج ضعیف حاصل از پیش‌بینی این مدل و نیاز به بررسی ضریب شکل جداگانه‌ای همچون ( ) برای رابطه‌ی هدایت هیدرولیکی ـ رطوبت (K-θ) مدل VGM، 24 خاک از کلاس‌های بافتی مختلف UNSODA انتخاب و پارامترهای اندازه‌گیری شده‌ی آنها، به منظور یافتن تابع انتقالی مناسب در برآورد  به روش تحلیل رگرسیون مورد تحلیل قرار گرفت. رابطه‌ی ایجاد شده، ارتباط ( ) را با دو پارامتر رطوبت اشباع s) و مقدار ماده آلی خاک با دارا بودن ضریب همبستگی (r=0.745) و معنی­داری آماری (P-value=0.0005) تایید نمود. همچنین، برای صحت‌سنجی تابع انتقالی ایجاد شده، مقدارهای (K-θ) اندازه‌گیری شده برای 8 خاک منتخب بخش صحت‌سنجی با مقادیر محاسباتی K حاصل از ضریب شکل تابع انتقالی ( ) و نرم‌افزار RETC (n) مقایسه شد. مقدار شاخص‌های آماری جذر میانگین مربعات خطای مدل (RMSEM)و ضریب کارآیی نش‌ساتکلیف (NSE) نشان داد که استفاده از ضریب شکل تابع انتقالی ایجاد شده در این پژوهش در مقایسه با نرم‌افزار RETC، عملکرد مطلوب‌تری در پیش‌بینی مقادیر هدایت هیدرولیکی غیراشباع داشت.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Estimation of Shape Factor of Soil Hydraulic Conductivity Function of van Genuchten – Mualem Model Using Easily-Available Soil Properties

نویسندگان [English]

  • Mojtaba Shiasi Arani 1
  • Bijan Ghahraman 2
  • Hojat Emami 3
  • Kamran Davary 2
1 PhD Candidate of Irrigation and Drainage., Dept. of Water Eng., Faculty of Agriculture, Ferdowsi University of Mashhad
2 Professor, Dept. of Water Eng., Faculty of Agriculture, Ferdowsi University of Mashhad
3 Professor, Dept. of Soil Sciences., Faculty of Agriculture, Ferdowsi University of Mashhad
چکیده [English]

Proper soil hydraulic functions that accurately predict soil water characteristic curve and hydraulic conductivity are essential for studies of unsaturated flow in soils. In this study, 8 soils from different texture classes of UNSODA soil bank were selected and the optimal validity of shape factor (n) of the RETC software (using retention curve function of van Genuchten-Mualem (VGM) model) was investigated for predicting the value of unsaturated hydraulic conductivity at different moisture contents. Since the predicted results of this model were poor, we attempted to investigate a separate shape factor such as  for the hydraulic conductivity-moisture (K-θ) function of VGM Model. To this end, 24 soil samples from different texture classes of UNSODA were selected and their measured parameters were analyzed by regression analysis to find a suitable pedotransfer function for estimating . The developed function confirmed the relationship of  with both saturated moisture (θs) and organic matter contents with a correlation coefficient of r = 0.745 at significant level of P = 0.0005. Also, to validate the developed pedotransfer function, the hydraulic conductivity values ​​corresponding to the measured moistures for the 8 selected soils in the validation section were calculated based on the two shape factors obtained from the pedotransfer function ( ) and the RETC (n) and the results were compared with the measured values. The statistical indices of root mean square error of model (RMSEM) and Nash-Sutcliff model efficiency coefficient  (NSE) showed that the shape factor of the developed pedotransfer function compared to the RETC, had a better performance in predicting unsaturated hydraulic conductivity values.
 

کلیدواژه‌ها [English]

  • Pedotransfer functions
  • Unsaturated flow
  • Shape factor
  • Soil Water Characteristic Curve
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