Answer: C. Stream elevation
Stream velocity is the speed of water in a stream. It can be measured in meters per second or feet per second. Stream velocity is highest in the mid stream and lowest along the bottom of the stream. Stream discharge depicts the flow of water from it's source of origin. Stream gradient indicates difference in pressure levels between different water layers. Channel size is the width of water surface acquired by the water body. Stream elevation is the rise in the superficial layer of water. Stream discharge, stream gradient and channel size all influence the stream velocity as they are related to the flow of water. Stream elevation does not influence flow of water hence, does not influence stream velocity.