طبقه‌بندي دشت سرهاي مناطق بياباني براساس پارامترهاي ژيومورفومتري مطالعه موردي (عقدا، يزد)

Desert plains classification based on Geomorphometrical parameters (Case study: Aghda, Yazd)

دشت ها، از مهم‌ترين واحدهاي ژيومورفولوژي بوده و طبقه بندي آن‌ها از اهميت ويژه اي برخوردار است. تاكنون روش ها و شاخص‌هاي مختلفي جهت تفكيك تيپ هاي مختلف دشتي ارايه‌شده كه اغلب برپايه ويژگي هاي توصيفي استوار است. طبقات دشتي مورد استفاده در اين تحقيق شامل دشت سر فرسايشي، دشت سر اپانداژ و دشت سر پوشيده مي باشد. در اين تحقيق اقدام به معرفي و استفاده از شاخص‌هاي جديد ژيومورفومتري تعيين دامنه كمي براي آن‌ها در جهت تفكيك تيپ هاي مختلف دشت سر شده است. شاخص‌هاي ژيومورفومتري مورد استفاده شامل درصد شيب، انحناي سطح، انحناي مقطع، انحناي حداقل، انحناي حداكثر، انحناي متقاطع، انحناي طولي و انحناي گوسيمي باشند. نتايج اين تحقيق نشان مي دهد، در بين پارامترهاي ژيومورفومتري مذكور، پارامترهاي شيب، انحناي حداقل، انحناي مقطع، انحناي طول و انحناي-متقاطع داراي كارايي بيشتري از ساير پارامترهاي ژيومورفومتري در طبقه بندي تيپ هاي مختلف دشت سر مي باشد. تغييرات شيب و همچنين مقدار آن در تيپ دشت سر لخت، بيشتر از ساير تيپ هاي دشتي بوده و دامنه آن به طور تقريبي از 3 تا 8 در صد متغير بوده و در بخش-هايي، شيب تا 20 درصد نيز ديده مي شود. در تيپ دشت سر اپانداژ، تغييرات و مقدار شيب پايين تر بوده و حدود 1 تا 3 درصد متغير مي باشد. در دشت سر پوشيده نيز شيب اغلب نقاط، كمتر از 1 درصد مي باشد. پارامتر درصد شيب، قابليت بسيار خوبي در تفكيك تيپ هاي مختلف دشت سر از خود نشان مي دهد. تغييرات انحناي حداقل نيز در تيپ دشت سر لخت، حداكثر بوده و به سمت تيپ دشت سر اپانداژ، و پوشيده، كاهش مي يابد. تغييرات انحناي مقطع و انحناي-سطح نشان مي دهد كه انحناي مقطع در تفكيك تيپ هاي مختلف دشت سر، قابليت بيشتري از انحناي سطح از خود نشان مي دهد. تغييرات انحناي طول و انحناي متقاطع در تيپ دشت سر لخت، حداكثر بوده و در تيپ دشت سر اپانداژ، مقدار نسبي و همچنين تغييرات آن، كاهش مي-يابد. مقادير اين پارامتر در تيپ دشت سر پوشيده به حداقل مي رسد. اين پارامترها نيز به طور نسبي تفكيك پذيري تيپ هاي مختلف دشت سر را از يكديگر نشان مي دهد.

Introduction In order to classify the variousland form scan be used mathematical analysis of land surface. The analysis ofland surface isone of the important part of natural resources. Geomorphology approach is basic on many case studies of natural resources, such as ecology, soil science, geomorphology, functions of geographic information systems in hydrology, vegetation, sediment and erosion, land degradation, natural resource management, and evaluation of desertification models ,as land unit is used in this study. Analysis of land surface is subject of geomorphometry science. Plain are as have gentle slope sand little topography and mainly form erosion up stream of mountainous are as .geomorphometry is a subset of geomorphology.That has quantitative and qualitativemeasured approachestopographyofland.geomorphometry basicisin the relationship between topography and then umerical parameters. Materials and Methods The study area, located on the west to North-West direction ardakan-nain at a distance of 20 to 30 kilometers from the city ardakan.This region with area of 92,474 hectares, soselectedthat has appropriate diversity geomorphologicallyand there is variety of typical of desert plain. In fact, geomorphometry, is science of quantifying topographic roughness with a focus on mining the parameters of earthʹs surface based on Digital Elevation Model. Input data in geomorphometry studies (DEM) is as raster with square cells.Parameter of the topography and spatial analysis of data, is to find connections between real forms and numerical values numerical algorithms for quantitative description of topography presented by using a small number of samples for morphometry classes and its forms, Defined rules for each class morphometrybased on the slope and curvature founded that both extracted by elevation digital model. For this purpose can be assume surface a constant level that may be based to a polynomial equation: f=?ax?^2+?by?^2+cxy+dx+ey+f In this equation, x and y are location and or geographical coordinates and letters A to F are polynomial coefficients that extracted of topography features. The use of morphometric parameters, Show progress in describing features each of the components of elevation digital models andthese parameters completelyexpression composition and communication pixels expressed in different landforms. to calculate the parameters of morphometryare in the table below: Table3.1Morphometryparameters(Evans, 1972; Wood, 1996; Shary et al, 2002). Morphometryparameters dimension Formula Slope Percent sqrt(d^2+e^2) plan curvature 1?m n×g×?(b×d^2+a×e^2-c×d×e)/(d^2+e^2 )?^1.5 Profile curvature 1?m n×g×(a×d^2+b×e^2+c×d)/(d^2+e^2)(1+(d^2+e^2))^1.5 Minimum curvature 1?m n×g×[-a-b-sqrt((a-b)^2+c^(2)) ] Maximumcurvature 1?m n×g×[-a-b+sqrt((a-b)^2+c^(2)) ] Cross sectionalcurvature 1?m n×g×(b+d^2+a×e^2-c×d×e)/(d^2+e^2) Longitudinalcurvature 1?m n×g×(a×d^2+b×e^2+c×d×e)/(d^2+e^2) Gaussiancurvature 1?m^2 Maximum curvature* Minimum curvature Results The results show that the slope parameter, is one of the mostimportantparameters in separation of different types of plain. The slope changes and its value are on the bare plains, approximately 3 to 8 percent and in the epandage plains, about 1 to 3 percent and covered plains less than 1% registered. The amount and changes of curvature in epandage plain, is less than the bare plains. Since the covered plains form most areas with smooth surfaces. This parameter; are not appropriate parameter to distinguish plain covered from other types plain. The degree of curvature changes, increasesin plain bare and respectively decreases toepandage plain, and covered plain. Profile curvature parameter changesincreasesinbare plain and the changesdropped in epandage plain, and was Minimal In covered plain.Minimum curvature changes was maximum also on the bare plains, anddecreases to theepandage plain, and covered plain. Maximum curvature changes In bare plain, was maximum and in type of epandage plain decreases and was minimal in covered plain longitudinal curvature changes in bare plain, was maximum andreduced in epandage plain andwas minimal in the covered plains crossover curvature changes in bare plain,was maximum and reduced In plain epandageand the was minimal in covered plain Number of Zero, represents flat area and is absence of topography at that point. The numerical value geomorphometry parameters distance from zero. Represents increase topographyat that point. Discussion We can summarize the above, Conclude that if you use the geomorphometricparameters alone be considered in the separation types of plain, Parameters of slope, minimum curvature, profile curvature, longitudinal Curvature and cross sectional curvature have more efficient of other geomorphometry parameters.Absolute of these parameters are increased in areas of high slopeand the around the mountains. The values in downstream areas closed to zero.