Writers : Khanehbad, Mohammad; supervisor:R. Moussavi Hrami, A. Mahboobi; advisor:M. Ghafoori
Refference : M.Sc.Thesis _ Ferdowsi university, Mashhad
Publishing Year : 1381

Abstract :

The Band-e-Golestan drainage basin is located southwest of Mashhad with a surface area of about 320Km2 sin consists of three subbasins:Three (Mayan, Dehbar له This drainage b and Jaghargh Rivers) flowing from southwest toward northeast and connecting to kashafrud River. Grain size variations and causes for fining downward were studied at 57 sites Rivers are mianly gravelly in the study area with a bedload and single .channel and consequent stream types In many gravel-bed rivers, the grain size changes exponential toward downstream and is mainly related to selective deposition of material on the ,streambed ( according to size, shape and density), downstream distance lateral and vertical sorting, crushing, abrasion superficial cracking, grinding), splitting, chipping sandblasting) during transport and weathering effect .when particles are at rest However, most studies on the cause of downstream fining in the river emphasize hydraulic sorting ( or selective transport( as the dominant fining mechanism. This sediments are poorly sorted, positively skewed and mainly platykurtic.
Gravels in the study reach consists of three different lithologies: phyllite,slate, and Quartzite.
Grain-size changes toward downstream canbe correlated with compositional changes in gravel. In the upstream , most of the boolders are phyllites while in the downstream, slate makes up the framwork of gravel The percentage of abrasion in slate is about 25.5 while the phyllite .( 28(estimated by Los Angles machine is about??Grain-size distributions show a weakly bimodality in the upstreams and becomes strongly biomodal toward downstream. finally,at the end reach,three modes appeared,two are gravelly and one is sandy. In the study area, the rapid reduction of slope is one of the main geomorphological factor that causes finig toward downstream. Another main factor in downstream fining of grain size is selective transport due to changing hydraulic conditior which is controlled by hydrology of drainage basin as well as catchment slope.

Subject List : Geomorphology