تحلیل رتبه‌بندی آبراهه‌های حوضه‌های آبریز ایران

افزایش رتبۀ آبراهه‌های حوضه‌ای آبریز بر کانتکست‌های مختلف ژئومورفولوژیکی، ژئولوژیکی، کلیماتولوژی، اکولوژیکی و ... اثر می‌گذارد. به‌طور معمول، محققان در بررسی سیستم‌های باز، فرض را بر اثرگذاری بردارهای مشخص و در دسترس قرار می‌دهند و رفتار سیستم را در ارتباط با آ‌نها ارزیابی می‌کنند. در این پژوهش، افزایش رتبۀ آبراهه‌های حوضه‌های آبریز ایران در غالب 984 زیر حوضه در ارتباط با نسبت انشعاب، طول و میانگین کل آبراهه‌ها و مساحت حوضه بررسی شده است. به این منظور، ابتدا لایۀ رودخانه‏های اصلی و آبراهه‏ها از 30*30 dem مستخرج از ماهوارۀ srtm تهیه شد. پس از استخراج آبراهه در نرم‌افزار arcgis 10.3، براساس نظریۀ هورتناسترالر رتبه‌بندی شد. رابطۀ بین رتبۀ برابر آبراهه با مساحت حوضۀ آبریز و همچنین ارتباط بین ثابت نگهداشت ویژه با شیب و تراکم زهکشی، به‌عنوان خصوصیات فیزیوگرافی حوضۀ آبریز ارزیابی شد. بین دو پارامتر، مجموع رتبۀ آبراهه‌ها و مساحت حوضۀ آبریز، رابطۀ مستقیمی وجود دارد؛ به‌گونه‌ای که در بیشتر حوضه‌های آبریز، ضریب تبیین این دو پارامتر 99 درصد برآورد شده است. در حوضه‌های آبریز ایران مقدار ضریب، تبیین نسبت انشعاب و افزایش رتبۀ رودخانه‌ها از 35 درصد در حوضۀ کویر سیاه کوه تا 82 درصد در حوضۀ آبریز سفیدرود متغیر است. مساحت حوضۀ آبریز امکان دارد بر نسبت انشعاب با ضریب تبیین 99 درصد اثر بگذارد. در برخی از حوضه‌های آبریز ایران، که تکتونیک فعال دارند یا رودخانه‌ها منحرف شده‌اند، گاه طول جریان در رتبه‌های پایین کمتر از رتبه‌های بالاتر است؛ به‌شرط آنکه توپوگرافی حوضه طی زمان، متعادل شده باشد. با افزایش رتبۀ آبراهه‌ها، میانگین طول جریان در همان رتبه افزایش می‌یابد. این فرض که هرچه ثابت نگهداشت حوضه بیشتر شود تراکم زهکشی حوضه کاهش می‌یابد، در بیشتر حوضه‌های آبریز ایران با ضریب تبیین بیشتر از 90 درصد قابل تعمیم است.

The Ordering Analysis of Waterways Drainage Basins of Iran

IntroductionPhysiography is a part of earth science studies in which the physical characteristics of the drainage basin such as area, perimeter and relief, slope, direction, etc. are studied. The studies that examine the physical characteristics and shape of a basin are called Physiography. Knowledge of the physiographic characteristics of a basin along with information about the climatic conditions of the region can provide us with a relatively accurate image of the quantitative and qualitative function of the hydrological system of that basin (Pitlick, 1994). The increase in the rank of waterways in a drainage basin is under the influence of various geomorphological, geological, and climatological ecosystems and contexts. In dealing with open systems, the researchers’ assumption is usually on the effectiveness of specific and accessible vectors and the evaluation of the system’s behavior in relation to those vectors. The area of study in this research includes Iran. Iran with an area of about 1648195 square kilometers is approximately located between 2540 degrees north latitude and 4464 degrees east longitude. Materials and MethodsIn this study, the accuracy of physiographic relationships in the basins was discussed. The existing relationships and the connection between them represent the relation of physiographic characteristics of the basin. In dealing with open systems, the researchers’ assumption is usually on the effectiveness of specific and accessible vectors and the evaluation of the system’s behavior in relation to those vectors. Accordingly, in this study, the increase in the rank of the waterways drainage basin of Iran in the form of 984 subbasins was investigated in terms of the bifurcation ratio, total length of waterways, the total average of waterways, and basin area. The relation between the equal rank of waterway and drainage basin area and also the relation between specific retention constant and slope and drainage density are among the physiographic characteristics of the drainage basin that were evaluated in this study. For this purpose, first, the layer of main rivers and waterways was prepared from DEM 30*30 extracted from the SRTM satellite. After extraction of the waterway in Arc GIS 10.3 software, Iran’s rivers were ranked based on the HortonStrahler theory. The relation between the equal rank of waterway and drainage basin area and also the relation between specific retention constant and slope and drainage density are among the physiographic characteristics of the drainage basin that were evaluated in this essay. DiscussionIn the drainage basin of Iran, a regression equation was established between the ‘area’ as an independent variable and the sum of flow ranks as a dependent variable, and the obtained equation responded positively to this hypothesis with a favorable level of significance. The amount of the explanation coefficient of most subbasins is more than 0.99, which indicates the great effectiveness of the expanse of the basins on the sum of the ranks of rivers flow. The lowest explanation coefficient is in the AbarkoohSirjan basin (0.89) and then in DarAnjir Desert subbasins (0.92) (probably due to the basins being dry and playa), Aras (due to having just one bank) And HarazQarah Su (0.96), and SefidrudHaraz (0.97) (due to the different climate of the basins), respectively. The bifurcation ratio has an inverse relationship with the ranks so that as the waterway rank increases, the bifurcation ratio coefficient decreases.The highest percentage belongs to the SefidrudHaraz (82%), Gavkhouni 72%), and Namak Lake (62%) basins. The common feature of the three basins is that their final drain is located in a corner of the basin and not in the center. Siahkuh Desert subbasins (35%), Bandar AbbasSadich (36%), Karkheh and AbarkoohSirjan (37%) have the lowest frequency percentage of high ranks. In the drainage basin, a regression equation was established between the area and equal ranks according to their frequency. In this equation, the area was the independent variable and the bifurcation ratio was the dependent variable and according to the level of significance obtained from the equation, the drainage basin responded positively to the hypothesis. Basins with smaller areas also had smaller bifurcation ratios. The highest explanation coefficients belong to QarahSu Gorganrood (99%) and DurAnjir Desert (98%) subbasins, and the lowest explanation coefficients belong to Sefidrud and Hamune JazMurian (50%), Hamune Mashekl (54%), Urmia (59), and Helleh (62%) subbasins.The flow length of each rank is measured and categorized in all basins. The prevailing result is the existence of a negative relationship between total flow length and rank. A regression equation was established between retention constant and slope, and regression equations were estimated with a positive procedure. In this examination, the slope was considered the independent variable and the retention constant was considered the dependent variable. Some basins were excluded from the examination, most likely due to the topographic and lithological effects of the basins that have changed the specific retention constant. Basins may be more expanded in the mound area, reducing drainage density in these areas. Even among the basins where acceptable regression equations have been obtained, the explanations coefficient varied between 50% (HamunHelmand, AbarkoohSirjan, Sefidrud) up to a maximum of 79% (Gavkhouni) and most of them had been between 50% and 60%. ConclusionThere is a direct relationship between the two parameters that is, the sum of the rank of waterways in a drainage basin and the area of the drainage basin of Iran so that in most drainage basins the explanation coefficient of these two parameters is estimated to be 99%. In the drainage basin of Iran, the amount of the explanation coefficient of the bifurcation ratio and increasing the rank of rivers varies from 35% in the Siahkuh Desert basin to 82% in the Sefidrud drainage basin. The area of the basin with a 99% explanation coefficient may affect the bifurcation ratio. In some basins of Iran that have active tectonics or rivers are captured or diverted, sometimes the flow length is fewer in the lower ranks than in the higher ranks. Provided that the topography of the basin is balanced over time, by increasing the rank of waterways, the flow length average increases in the same rank. The assumption that as much as the retention constant of the basin increases then the drainage density of the basin decreases, can be generalized in most of the drainage basins of Iran with an explanation coefficient higher than 90%. Keywords: Physiography, Specific Retention, River Ranking, Drainage Basin.