Writers : Kaveh Tabatabai,Aliyeh Sadat
Refference : M.Sc.Thesis _ Ferdowsi University,Mashhad
Publishing Year : 1384

Abstract :

The Bar Watershed is a part of Binalood drainage basin located northern west of Neyshabour in Khorasan Razavi Province. This watershed has an elongate to fan shape and its surface area is more than 280 square kilometer. It is a part of Binalood zone and geologicaly is composed of Dalichai, Lar formations, Paleogen, as well as Neogen sediments and Quaternary alluviums.
Various geomorphological features such as folding, faulting, bars, channels, rills, and different types of mass movements have been identified in this watershed. Based on this study, the Bar River has a braided pattern with gravelly bed. Sedimentologic studies along the rivers show that three main factors (sudden changes in slope, lateral supply of sediments and distributary entrance) cased the changes in texture of bed load sediments within the channel as well as the break in sedimentary links. Textural variations in grain size parameters have a regular trend within every one of two sedimentary breaks. Average (mean) and median of grain size decrease along anyone of the sedimentary links. More than 70 to 80 percentage of sediments weight in any sample is gravel and streamflow may have transported most finer grains (mud, sand and even granule) sediments toward downstream. Therefore, selective transport or hydraulic sorting is the main factor that controls the fining trends toward downstream. In addition, positive skewness can be related to this mechanism too. The study of textural changes in grain size parameters along the main Taghan river shows a longitudinal linkage in these parameters. Variations in slope gradient are the most important factor that caused the dispersion in grain size distribution. Lithofacies that have been identified in this watershed are gravelly (Gmm, Gmg, Gcm, Gci, Gh) sandy (Sm, Sh, Sp, SI, Ss, Se) and muddy (Fr, Fm, Fl). Based on lithofacies, the architectural ellement can be classified as: GB, SG, LA and FF. In regard with these elements, four sedimentary models have been porposed over the bar river from upstream toward downstream. These models are: at the first of main branch is gravel braided with sediment gravity flows, around the bar village is shallow gravel braided river, at the center of basin is gravel wandering river and at the end, it is gravel bed meandering river.

Subject List : Geomorphology