تخمین هدایت هیدرولیکی اشباع و غیر‌اشباع زمین‌های شیبدار در حالت‌های ماندگار و غیر‌ماندگار

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده کشاورزی دانشگاه تبریز

2 دانشکده کشاورزی دانشگاه بوعلی سینا همدان

چکیده

یکی از روش­های ساده، دقیق و مناسب برای اندازه­گیری هدایت هیدرولیکی خاک در زمین­های شیبدار، استفاده از استوانه­های مضاعف و دستگاه نفوذسنج مکشی می­باشد. تحقیقات متعدد نشان می­دهد که شیب زمین روی خصوصیات هیدرولیکی از جمله هدایت هیدرولیکی اشباع و غیراشباع خاک تاثیر می­گذارد. هدف از این مطالعه تخمین و مقایسه مقادیر هدایت هیدرولیکی خاک با استفاده از داده­های نفوذ، در دو حالت ماندگار و غیر ماندگار در زمین­های با شیب مختلف می­باشد. آزمایش­های نفوذ با استفاده از دستگاه­های استوانه­های مضاعف و نفوذسنج مکشی در پنج شیب 0، 10، 20، 30 و 40 درجه و در چهار مکش صفر (با استفاده از استوانه­های مضاعف)، 6، 9 و 15 سانتیمتر (با استفاده از نفوذسنج مکشی) به انجام رسید. در حالت ماندگار، مقادیر هدایت هیدرولیکی اشباع با روش رینولدز و همکاران و هدایت هیدرولیکی غیر اشباع به روش آنکنی و همکاران محاسبه شد. در حالت غیر ماندگار، ابتدا پارامتر وابسته به هدایت هیدرولیکی معادله دو جزئی فیلیپ، از انطباق داده­ها با معادله استخراج گردید و سپس مقدار هدایت هیدرولیکی محاسبه شد. نتایج نشان داد در هر دو حالت ماندگار و غیر ماندگار با افزایش شیب زمین و مکش خاک هدایت هیدرولیکی کاهش می­یابد. در مکش­های کم میزان کاهش هدایت هیدرولیکی بیشتر است. در حالت ماندگار، با افزایش زاویه شیب از صفر به 40 درجه، کاهش هدایت هیدرولیکی در مکش صفر حدود 1/4 برابر کاهش آن در مکش 15 سانتیمتر بود. این مقدار در حالت غیر ماندگار 7/3 برابر بر آورد شد. مقادیر هدایت هیدرولیکی حاصل از معادله گاردنر تطابق بیشتری با حالت ماندگار جریان نسبت به حالت غیر ماندگار نشان داد. مقادیر اختلاف هدایت هیدرولیکی نسبی بین روش ماندگار و غیر ماندگار در تمام شیب­­ها و مکش­ها، کمتر از 7 درصد به دست آمد که بیانگر نزدیک بودن نتایج به دست آمده از دو روش مذکور می­باشد. 

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Estimating Saturated and Unsaturated Hydraulic Conductivities of Sloping Lands under Steady and Transient States

نویسندگان [English]

  • M Raoof 1
  • AH Nazemi 1
  • SAA Sadraddini 1
  • S Maroofi 2
چکیده [English]

Double ring and tension infiltrometer are simple, fast and suitable instruments for determining soil hydraulic conductivity. The effect of land slope on soil properties such as saturated and unsaturated hydraulic conductivities has been reported by various researchers. The aim of this study was to estimate and compare soil hydraulic conductivities at different slope gradients under steady state and transient flow regiones. Field experiments were conducted in a loamy soil with different slope gradients in Gonbad research station, Hamadan, Iran. Soil surface slope gradients, of 0 (level), 10, 20, 30 and 40 degree were selected in this station. For each slope gradient, water infiltration experiments were carried out using a double ring and a tension infiltrometer at tensions of 0, 6, 9 and 15 cm in three replications. Totally 60 infiltration experiments were carried out. In steady state, values of saturated and unsaturated hydraulic conductivities were estimated using Reynolds et al. and Ankeny et al. procedures, respectively. In transient statevalues of  the hydraulic conductivity, for different land slopes and water pressure heads, were calculated from the parameter of the second term of Philip’s two-term equation, Results indicated that the hydraulic conductivity values for both steady state and transient flow regines were decreased with increasing in tension and slope gradient values. The higher rate of hydraulic conductivity decreases was obtained for lower tensions. In steady and transient state, by increasing  in slope gradient from 0 to 40 degrees, decreasing of hydraulic conductivity in 0 tension was 4.1 and 3.7 times more than these in 15 cm tension, respectively. The fitness between the Gardner exponential model and steady state flow procedure was higher than that of transient flow procedure. In all experiments, values of relative difference of hydraulic conductivities were less than 7% that indicated good fitness between the steady state and transient flow procedures.
 

کلیدواژه‌ها [English]

  • saturated hydraulic conductivity
  • Unsaturated hydraulic conductivity
  • double ring and tension infiltrometer
  • steady and transient flow

مراجع

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