Natural disturbances such as thunderstorms and volcanic activities as well as man-made activities such as urbanization, agriculture, removal of dams and specially flushing of reservoir sediments may cause an increase in sediment supply to rivers. The objective of this paper is to show the most remarkable features of the morphological responses of alluvial sand-bed channels reacting to changes in sand supply. To achieve this, a set of flume experiments was conducted in order to study the changes in hydraulic geometry of straight sand-bed channel under various water and sediment discharge values. The observed results of this research indicate that the dominant response of alluvial channel to increase in incoming sediment concentration may be followed by bed aggradation and channel widening. Also, channel widening trend with flow and sediment supply is steeper than no supply condition while increasing in sediment concentration increases the rate of change of widening. It was concluded that the stable channel width is greater with sediment supply than that of no supply conditions.