Describe the changes that occur in the long profile and cross profile of a river valley as you move downstream.

As you move downstream from the source of a river to the mouth, a number of changes occur to the long profile and cross profile; which can be displayed in a graph plotting distance downstream against elevation. The long profile begins steeply near the source and reduces quickly in height as the slope of the river valley reduces , becoming increasingly a more gradual decrease nearer the mouth. For this reason the shape of the long profile of a river valley could be attributed to a exponential function. The cross profile of the river valley also has a number of observable changes with distance downstream. At the source erosional processes dominate and so the valley is a clear V- shape and often has features such as interlocking spurs present. As you progress downstream the river erodes more laterally than vertically and the valley widens, as the sides become less steep as you reach the mouth. The cross profile of the valley in the lower course of the river is wide and flat, as a large floodplain develops either side of the river, developing from a V-shape valley to more of a U-shape. There can be levees associated with the river in the lower course due to deposition, if the river exceeds it's transport capacity. These will alter the cross profile somewhat as they are higher areas, protruding from the gradual, flat cross profile of the lower course.