A long profile is a line representing the river from its source (where it starts) to its mouth (where it meets the sea). A river changes with increasing distance downstream from its source towards its mouth. It moves through its upper course, to its mid-course and finally into its lower course.
Steep valley sides are typical of a river's upper course in upland areas. The valley here has steep sides and the valley bottom is narrow. This is why valleys like this are called V-shaped valleys.
Upper course - this is where the river starts and is usually an upland area. Slopes are steep - this can increase the velocity of the river after heavy rainfall, when discharge is high. The river channel is narrow and shallow here. The river's load is large in the upper course, as it hasn't been broken down by erosion yet. When discharge is high vertical erosion erodes the river bed and larger sediments are transported by traction.
Mid-course - here the gradient becomes less steep. The river channel gets deeper and wider as the bed and banks are eroded. The sediment load of the river gets smaller in size. Small meanders and a small floodplain can be found in this part of the river.
Lower course - the final course of the river is where the land is a lot flatter. The river's load is fine sediment, as erosion has broken down the rocks. The river channel is at its widest and deepest as it flows towards its mouth. Deposition is the main process in this part of the river, which creates large floodplains and deltas.
The Bradshaw Model shows the changes that occur as a river flows from its source to its mouth.