@article { author = {zaman zade, mohammad and gafar bighlo, mansour and pirani, parisa and shabani eraghi, arefe and geravand, fateme}, title = {A Comparison between changes of sediment size and texture t in three patterns of bars in braided, meandering and straight channel at two locations of Abdanan river (poshte-ghalle in upstream and Hezzarani in downstream)}, journal = {Quantitative Geomorphological Research}, volume = {8}, number = {2}, pages = {138-154}, year = {2019}, publisher = {Iranian Association of Geomorphology}, issn = {22519424}, eissn = {}, doi = {}, abstract = { IntroductionRiver morphology is one of the main factors to control the geometric shape of river sediments which is determined by two parameters of braiding and sinuosity (Rust, 1977: 187). Sinuosity or sinuosity ratio represents how much curved a channel is (Charlton, 2007: 138) and braiding parameter represents the number of braids or bars in any wave length of meander. According to these two parameters, rivers are divided into four groups: straight, braided, meandering and anastomosing (Mousavi Herami, 1991: 261-263). There are differences in texture and size of sediments deposited in the channel, braided bars and point bars (Mousavi Herami, 1991: 264). The purpose of this research is to compare sediments from different forms of straight, braided and meandering channel in order to determine the changes of sediment size and texture in: different parts of an individual bar, among bars of three channel forms and between selected locations in upstream and downstream of river.MethodologyThe study area is in Abdanan county which is located in Ilam province in the west of Iran on its most important stream which is Abdanan river. At the beginning, two appropriate locations of Abdanan river at the upstream (Posht-qaleh) and downstream (Hezarani) parts of this river were chosen after considering items such as topography, geology map and google earth images and also GIS software. Afterwards on each bar (braided or point) 4 points were chosen for sampling. Then, half a kilogram sediment sample was obtained from each point and after encoding, these samples transferred to the laboratory and granulometry analysis was carried out on the samples. Grains categories and their weight percent obtained using the granulometric analysis and necessary graphs were plotted by Excel and Gradistate. In the next step Statistical parameters such as mean (MZ), sorting (Iσ), skewness (SKI), Kurtosis (K) were calculated and the results were represented in phi unit. Result and discussionThe upstream sediments of river are mostly classified in gravel, sandy gravel and muddy sandy gravel on triangular diagram of Folk (1954), but the downstream samples include sand and muddy sand sediments. Histogram of samples represents some modes on medium and very coarse sand size but the mode on gravel is predominant in all of samples. The latter point shows that samples are poorly sorted and have polygenetic origin. Breaks on cumulative plots represent the different groups of grain sizes which were moving in different mechanisms from suspension to traction. The percentage of coarse grains is high in most samples; and plots are parabolic. This represents the changes of energy in environment. Calculating the statistical parameters such as mean, sorting, kurtosis, skewness using graphical method of Folk and Ward (1957) showed that upstream and riverside parts of the braided channels underwent one-sided washing, so that their sorting is higher and percentage of coarser grains is more than downstream part of these channels which experienced washing from both sides. In the meander bars, sedimentological characteristics of sediments are close to a normal pattern of a meander. The difference, however, is that a newly formed river crossed the flood plain and reduced the sorting of sediments, so that the sedimentological characteristics of these sediments in downstream meander is similar to braided pattern. contrary to what expected, sorting decreases in the straight channels, due to gravels shed from sub-branches and slopesConclusionthe differences seen sedimentological characteristics of the samples are due to the role of branches of main stream, periodic floods of Abdanan river and sediment-shedding from channel slopes that has changed the texture and size of sediments. These changes in the samples which were obtained from Hezarani location in the meandering channel are due to development of river sub-branches and in the straight channel are because of sediments resulting from channel slopes. generally speaking, sediment texture and size at upstream (Posht-qale) vary from well to moderate sorted gravel in the north to poorly sorted sand in the south but this pattern is not seen in sediment texture and size at downstream (Hezarani) location where effects of river branches and floods are illustrated by increasing gravel and irregularity of sediment pattern.}, keywords = {Keywords: river sediments,Granulometry,Braided,meander,striaght}, title_fa = {مقایسه تغییرات اندازه و بافت رسوب در پشته های سه الگوی کانال بریده‌بریده، مئآندری و مستقیم در دو بازه از رودخانه آبدانان (پشت‌قلعه در بالادست و هزارانی در پایین دست)}, abstract_fa = { رودخانه‌ها بر اساس پارامترهای سدی و پیچش، به انواع مستقیم، بریده‌بریده و مئآندری تقسیم می‌شوند. مورفولوژی رودخانه‌ها یکی از عوامل اصلی کنترل کننده شکل هندسی رسوبات است. رودخانه دربرگیرنده رسوبات مختلفی است که از نظر بافت و اندازه دانه و مورفولوژی پشته‌ها متفاوتند. هدف تحقیق حاضر مقایسه رسوبات پشته های کانال‌های مختلف از نظر تغییرات در اندازه و بافت رسوب در پشته‌های انواع کانال‌های مستقیم، مئآندری و بریده‌بریده انتخابی، و همچنین تغییرات در قسمت های مختلف یک پشته منفرد  و تفاوت‌ این تغییرات  در بالادست (پشت قلعه) و پایین دست (هزارانی) رودخانه است.در این مطالعه مجموعا 30 نمونه برداشت و کدبندی شدند و در آزمایشگاه به روش غربال مورد آنالیز قرار گرفتند. پس از عملیات گرانولومتری با استفاده از نرم‌افزارهایEXCEL و GRADISTATE منحنی‌های موردنیاز ترسیم شد و پارامترهای آماری از جمله متوسط ذرات (MZ)، جورشدگی (Iσ)، کج‌شدگی (SKI) و کشیدگی (K) به روش ترسیمی و با مقیاس فی به دست آمد و مورد مقایسه قرار گرفت. نتایج نشان می‌دهد که کانال‌های بریده‌ بریده بیشترین و مئآندری و مستقیم کم‌ترین شباهت رسوبی را ب اقرینه خود در سمت دیگر رودخانه دارا هستند. تفاوت‌های رسوبی مشاهده شده نقش انشعاب‌های جریان اصلی، سیلاب‌های دوره‌ای رودخانه آبدانان و تغذیه رسوبات از دامنه کناری را در تغییر بافت و اندازه رسوب نشان می‌دهد که گاها ًسبب شده کانا لمئاندری الگوی رسوبی یک کانال بریده ‌بریده را منعکس کند. بطور کلی در بازه بالادست (پشتقلعه) اندازه و بافت رسوب از شمال به جنوب از گراول با جورشدگی خوب تا متوسط به ماسه با جورشدگی ضعیف تغییر می‌کند دربازه پایین دست (هزارانی) اندازه و بافت رسوب از شمال به جنوب الگوی بالا دست را نشان نمی‌دهد که تأثیر جریان‌های انشعابی و سیلاب را در به همریختن الگوی رسوب و افزایش گراول می‌توان مشاهده نمود.}, keywords_fa = {کلید واژگان: رسوب,رودخانه,بریده‌بریده,مئآندر,مستقیم}, url = {https://www.geomorphologyjournal.ir/article_98652.html}, eprint = {https://www.geomorphologyjournal.ir/article_98652_d7a5c4190d7acccdb1e72c1ccb2bc84b.pdf} }