Floods are become frequent occurrence in every part of the world. The field of flood hydraulics has been keenly studied to enhance the understanding on its processes and impacts to the environment. The main impacts of frequent floods incidents are soil erosion phenomenon which leads to sedimentation problems in the drainage and river systems. It is extremely important to understand the sedimentation process and the flow behaviour patterns in the water course for post-flood events. Experimental investigations on the overbank flow in mobile bed straight channels have been undertaken. Significant changes on the bed morphology due to the changes in flow behaviour are studied. The findings on roughness coefficient, lateral distribution of stream-wise velocity, secondary currents, bed shear stress and bed formation are presented in this paper. Results show that the resistance coefficient increased with flow depth in the channel and the increments are about 32% and 42% for floodplain and main channel sections respectively.