عنوان مقاله [English]
One of the key issues of erosion and stability of the river is the beginning the movement of sediment particles. River sediment yield caused water turbidity, nutrients and pollution problems of water, buried in the water diversion facilities as well as filling the water storage lakes. Flow that will start moving particle, called the critical flow. The initial move threshold sediment particles has been investigated in several different methods, most important of which are the average critical velocity, critical shear stress and critical unit discharge. To investigate the stability of the Lavij river bed sediments in the city of Noor, according to river conditions used the critical shear stress and critical unit discharge methods. To determine initial move threshold sediment particles in the bed of the river were two cross-section of the river, two cross-section conditions were assessed. After that, the critical shear stress and critical unit discharge for four particle size D16, D50, D84 and D95 in each cross-section was calculated, and showed that in cross-section (1) in the bankfull discharge conditions all particles with sizes D16, D50, D84 and D95 begin to moving, and so in the bankfull discharge, sediment conditions will generally change. In cross-section (2) particles with a diameter D95 and the more it will be remain stable in the river bed, and other smaller particles of this size are starting to move. Due to further slope of the bed and width less active channel in the cross-section (1) has caused that all particles are unstable. Finally, the results from both methods were highly concordant, and this confirms that the use of these methods for stabilizes studies and sediment yield of river are appropriate.