Answer C is the gradient greatly reduced when water flow down from the upper course it flows with a high velocity downwards. An example is a waterfall.as the water enter the lower course the gradient( the rate of regular ascent or descent) is reduced because the slope of the bed is gentle and also, materials washed down from the upper course are deposited there. the vegetation cover does not determine water movement as rivers are not vegetative. tress can only cover the surrounding areas and not the river itself Human activities and water volume also does not determine the flow of river at the lower course. water either small or mass will always find its way