بررسی رابطه ی بین عوامل زمین شناسی و توپوگرافی با تراکم زهکشی در حوضه ی بهرستاق (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
تراکم زهکشی یک شاخص مهم هیدروژئومورفولوژی در تعیین چگونگی فرآیندهای رواناب سطحی، ش دت س یلاب و میزان فرسایش خاک م ی باشد. حوضه ی بهرستاق ی کی از زیرحوضه های رودخانه ی هراز است که شرایط زمین شناسی و توپوگرافی متنوع و جریانات سطحی زیاد در آن موجب فرسایش خاک و تخریب مراتع و باغ ها در منطقه می شود. هدف از این پژوهش بررسی اثر عوامل زمین شناسی و توپوگرافی در میزان تراکم زهکشی و تعیین تفاوت آن در متغیرهای مورد مطالعه است. برای این منظور ابتدا نقشه ی آبراهه های حوضه با استفاده از DEM منطقه تهیه شد. سپس ویژگی های زمین شناسی و توپوگرافی منطقه شامل لایه های جنس سنگ، طب قات ارتفاع، شیب و جهت دام نه مدنظر قرار گرفته و در محیط ArcGIS طبقه بندی و با شبکه آبراهه ها به عنوان متغیر وابسته همپوشانی شد. بر این اساس مجموع طول آبراهه ها در واحد سطح هر یک از عوامل محاسبه و تراکم زهکشی به دست آمد. برای تحلیل داده ها از آزمون آماری آنالیز واریانس یک طرفه (ANOVA) استفاده گردید. نتایج آزمون آماری نشان دهنده ی رابطه ی معنی دار جنس سنگ و شیب با میزان تراکم زهکشی به ترتیب در سطح اطمینان 95 و 99 درصد است، اما میزان تراکم زهکشی در طبقات ارتفاعی و جهت دامنه در منطقه تفاوت مشخص و معنی داری نداشته است. سازند ملافیر کرتاسه (km)با میانگین تراکم 79/8 و طبقه شیب 30-20 درصد با میانگین تراکم 7/10 بیشترین حساسیت را نشان داده اند. با دانستن این ارتباط می توان از این متغیرها در برنامه های مدیریت شبکه زهکشی و کنترل شدت فرسایش نیز استفاده نمود.Survey of Relationship between Geology and Topography Factors with Drainage Density in Behrestagh Watershed
Introduction
Drainage density is an important hydrogeomorphologic indicator in determining activity quality of processes of overland run-off, flood intensity, soil erosion and sedimentation load in the basin. Drainage density was defined as the ratio of the total length of streams in a watershed over its contributing area. It describes the degree of drainage network development and was recognized by many authors to be significantly effective on the formation of flood flows. Drainage density is higher in arid areas with sparse vegetation cover. The higher the drainage density, the lower the infiltration and the faster the movement of the surface flow. The structure of watershed topography depends to a large extent on the interaction between slope and channel processes. The applicability of these relatively simple summaries, however, needs to be examined carefully. It is still uncertain how the development of drainage systems with time affects the relation of drainage density with lithology, slope, aspect and elevation. The Behrestagh watershed is a sub-basin of Haraz River basin where in varied geological and topographic conditions and the many overland flow cause soil erosion and destruction of pastures and gardens of the area. This study examines the relationship of drainage density with Geology and topography factors for Behrestagh watershed.
Materials & Methods
The Behrestagh watershed lies between the latitudes of 35° 56΄ N to 35° 59΄ N and longitudes of 52° 16΄ E to 52° 22΄ E. The main stream in the area is Haraz River. Topographic elevations in the study area vary between 1172 to 3548 m. Here, in order to examine drainage density in the studied area, map of the watershed’s streams was prepared first using GIS and Digital Elevation Model (DEM) of that area. Then, effective Geology and topographical properties including lithology, elevation, slope and aspect was considered and classified in ArcGIS environment and finally were overlaid with the streams as a dependent variable. Accordingly, sum of streams length per unit of each factor was calculated and drainage density was obtained. Data were analyzed in SPSS 20. Moreover, collected data were described using descriptive statistics (tables, charts, abundance distribution, mean and standard deviation). Data analysis was performed using one-way ANOVA to obtain differences with other studied variables.
Discussion of Results
In this study, data analysis was performed using one-way ANOVA to obtain differences with studied variables. Results of the statistical test indicated that the relationship of lithology and slope with drainage density in the considered area was significant at .95 and .99 level of confidence, respectively. The relationship of drainage density with elevation and aspect was not significant, as well. The results showed that the most drainage density of the area was observed in elevation lower than 1400 meters (average density of 8.24). Also, the cretaceous melaphyre formation (km) with average density of 8.79 and the slope class of 20 -30 percent showed an average density of 10.7 and the western aspect (domain direction) indicated an average of 5.57.
Conclusions
To determine the geology and topography factors influencing drainage density, data layers of lithology, slope, aspect and elevation were analyzed through overlaying the dispersion map of the watershed’s streams. The results showed that cretaceous melaphyre formation, elevation below 1400 meters, slope of 20-30 percent and the west aspect are sensitive to streams. Also, results indicated a significant relationship between lithology and slope with drainage density in the considered area and slope was found to be the most important topography factor affecting drainage density. Therefore can used from these variables to assess erosion intensity and its control.
تبلیغات
