ارزیابی کارآیی مدل های فرکتالی در برآورد پارامترهای هیدرولیکی خاک و رابطه بین بُعد فرکتالی منحنی رطوبتی با این پارامترها
محورهای موضوعی : مدیریت آب در مزرعه با هدف بهبود شاخص های مدیریتی آبیاری
شیوا محمدیان خراسانی
1
(دانشجوی دکترا/ گروه خاکشناسی/ دانشکده کشاورزی و منابع طبیعی/ دانشگاه آزاد اسلامی/ واحد علوم و تحقیقات/ تهران)
مهدی همایی
2
(استاد دانشگاه تربیت مدرس)
ابراهیم پذیرا
3
(استاد دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران)
کلید واژه: بُعد فرکتالی, ویژگیهای هیدرولیکی خاک, بافت خاک, منحنی نگهداشت, هندسه فرکتالی,
چکیده مقاله :
روابط آب و خاک به قدری پیچیده هستند که پیشرفتهترین مدلهای ریاضی نیز به سختی قادر به شبیهسازی دقیق آنها میباشند. منحنی رطوبتی و هدایتهیدرولیکی غیراشباع، از جمله عوامل مهم در بررسی حرکت آب در خاک هستند. بهعلت تغییرپذیری بالا و پیچیدگی خاک، بدست آوردن ویژگیهای هیدرولیکی خاکبهطور مستقیم دشوار، وقتگیر و هزینهبر بوده و بنابراین لازم است با استفاده از روشهای غیرمستقیم تخمین زده شوند. هدف از این پژوهش، تعیین بُعد فرکتالیمنحنی رطوبتی خاک با استفاده از مدلهای فرکتالی و بررسی رابطه بین بُعد فرکتالی منحنی رطوبتی با پارامترهای هیدرولیکی، درصد رس، سیلت و شن خاک در یکپهنه گسترده بود. بدین منظور، 40 نمونه خاک با بافتهای مختلف از چهار منطقه کرج، قزوین، ایوانکی و کرمانشاه گردآوری و توزیع اندازه ذرات، جرم ویژه ظاهری،کربن آلی، شوری، pH و رطوبت آن ها در مکشهای مختلف اندازهگیری گردید. سپس پارامترهای مدل نگهداشت van Genuchten و مدلهای فرکتالی Tyler-Wheatcraft و Rieu-Sposito برای توزیع اندازه ذرات خاک محاسبه شد. نتایج نشان داد که مدل نگهداشت van Genuchten رفتاری فرکتالی داشته و با استفاده ازمدلهای فرکتالی میتوان پارامترهای آن را بهصورتی کمّی بیان کرد. همچنین نتایج نشان داد که هر چه مقدار شن در خاک افزایش یابد، بُعد فرکتالی کاهش مییابد،لیکن درصد رس با بُعد فرکتالی مدل Tyler-Wheatcraft رابطهای مستقیم و خطی دارد. نتایج همچنین نشان داد که با افزایش مقدار رس در خاکهای مورد مطالعه،مقدار بُعد فرکتالی مدل Tyler-Wheatcraft ( Dm ( افزایش و با افزایش مقدار شن، بُعد فرکتالی مدل Tyler-Wheatcraft ( Dm ( کاهش مییابد.
Soil and water relations are so complex that the most advanced mathematical models can hardly be able to simulate them accurately. Retention curve and unsaturated hydraulic conductivity are among the most important factors in the study of water flow in the soil. Because the high variability and soil complexity, obtaining soil hydraulic properties directly is difficult, time consuming and costly and therefore it is necessary to estimate indirect methods. The purpose of this study was to determine the fractal dimension of soil moisture curve using fractal models and to investigate the relationship between the moisture curvature fractal dimension with hydraulic parameters, clay, silt and sandy percent in a wide area. For this purpose, some soil samples collected from different tissues from the regions of the country were collected and the variables of particle size, bulk density, organic carbon, salinity, pH and moisture content were measured in different suction. Finally, the parameters of the van Genuchten model as well as models Tyler-Wheatcraft and Rieu-Sposito fractals were calculated for soil particle size distribution. The results showed that van Genuchten model parameters have fractal behavior and can be quantified by using fractal models. The results also showed that the higher the amount of sand in the soil, the fractal decreases, but the clay content has a direct linear relationship with the Tyler-Wheatcraft fractal dimension. This means that by increasing the amount of clay in the studied soils, the fractional dimension of the Tyler-Wheatcraft (Dm) model also increases and with the increase in the amount of sand, the fractal dimension of the Tyler-Wheatcraft (Dm) model decreases.
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