عنوان مقاله [English]
Geomorphological changes on meandering courses is quicker than other flow pattern. All changes that is occurred on length and cross of floodplain by migrated of course ,is reflected at size of sediment grains and manner of bedding.With attention at manner of the changes reflection on bedding and grains size of sediment on terrace ,can be distinguished old changes and forecast next events on courses of rivers . With attention of many changing on course of Aji-Chay ,in this article is investigated on manner of changes on its course in during time . Aji-Chay river (situated at 37Â° 58â² to 38 Â° 07â² N and from 46 Â°15â² to 47Â° 50â² E)have many curvature on its length of course and migration this curvature to right and left of main axis is changed floodplain face in during time.Migration events is very rapid on meandering rivers ,as Aji-Chay river.Due to this quick changes,can be damages man made structures on courses these rivers ,as dams. Therefore ,for understanding behavior of rivers and order to suitable policy and based on local property ,must be study changes in during time on meandering rivers ,as Aji-Chay.
In this article is used experimental and field methods for study of manner and rate of active channel changes in during time on length and cross of floodplain of Aji-Chay.For study of rate of curvature radus in during time ,is used areal and sattalit images and for estimation of sinuosity is used S.In order to estimation of bank erosion is used E equation and for estimation of time mirgration is used âT equation.Then in this study ,is take care of sediment beding of terraces and is concluded.For investigation on channel changes ,movement of active channel is measurement courses of channel on areal and sataliet images .In order to distinguishes effect of changes on floodplain,and manner of reflection changes on terraces ,is study bedding of sediment and also percent of grain size .
Changing on floodplain is taking by curvature and movement at position of curvature in active channel .Therefore ,for distinguished of manner changing on floodplain and study on reflected these changes on bedding of sediment in on terraces ,in first time ,is studied rate of sinuosity ,radius of curvature and rate of movement in during time .The results of this study show range of sinuosity rate in length of channel is very high.These results also suggested that R/W is increased in near of Tabriz and is decreased toward Sarab.Field investigation on bedding of sediment in terraces show that width of bed in same sediment is changed in short of distance.On courses of Aji-Chay ,decrease of grain,s sediment suggested that curvature of active channel is changes its direction of flow toward opposite wall and then when power of flow is decreased ,is deposited fine grain on course and in next term,direction of flow again is changed .In this term flow river can be deposited coarse grain on course.These coarse grain suggested that power flow is increased.
Aji-Chay river as typic river is bearing main changes.This river have high energy for changes and for this reason its direction extrados is changed constantly and is changed size of radius in same time on course of active channel.Due to movement of active channel extrados on side of main axis,is very vary size of sediment grains in terraces and manner of sediment bedding on all part of couses. Investigation on bedding and changing of grain size of lateral sediment show that direction extrados is changed in during time and course of active channel is cutting gradually and some time active channel is changed to straight pattern .