The Long Profile & Cross Profile

The Long Profile of a River

The long profile of a river is a graph or diagram showing the change in the rivers gradient (slope) from its source to its mouth. It typically has a concave shape, steep at the start and gently sloping near the end.

Upper Course: This is where the river begins, usually in upland areas like hills or mountains. The gradient is steep, meaning the river flows quickly downhill. The channel is narrow and shallow. The rivers discharge (volume of water flowing) is low because fewer tributaries have joined yet. Velocity is relatively slow due to obstacles and rough bed.

Middle Course: The gradient becomes less steep, so the river flows more gently. The channel widens and deepens as more water joins from tributaries, increasing discharge. Velocity increases because the river has more water and fewer obstacles. The river starts to meander (bend).

Lower Course: The gradient is very gentle, almost flat. The river channel is wide and deep, carrying a large volume of water (high discharge). Velocity generally increases because of the large volume and smoother channel bed, allowing the river to flow powerfully towards the sea or lake.

Overall, the gradient decreases downstream, discharge and velocity increase downstream due to tributary inputs and smoother channel conditions.

For instance, the River Severn starts in the Welsh hills with a steep gradient and narrow channel but flows into the wide estuary near the Bristol Channel with a gentle slope and large discharge.

The Cross Profile of a River

The cross profile shows the shape of the river valley and channel when viewed from the side, across the river.

Upper Course: The valley is typically narrow and V-shaped due to vertical erosion cutting downwards. The channel is narrow and shallow, with large, angular rocks and boulders. The valley sides are steep because of limited lateral erosion.

Middle Course: The valley becomes wider and less steep. Lateral erosion (sideways erosion) increases, widening the valley floor. The channel is wider and deeper, with smaller, smoother sediment. The valley sides slope more gently.

Lower Course: The valley is very wide and flat, often forming a floodplain. The channel is at its widest and deepest, carrying a large volume of water. The valley sides are very gentle or almost flat. Sediment is fine and rounded.

For example, the upper course of the River Thames near its source in the Cotswolds has a narrow V-shaped valley, while near London in the lower course, the valley is wide and flat with a broad channel.

Processes Affecting River Profiles

The shape of both the long and cross profiles is influenced by erosion, transportation, and deposition processes, as well as the sediment load the river carries.

Erosion Types Influencing Profile: Vertical erosion dominates in the upper course, deepening the valley and channel, creating steep V-shaped valleys. Lateral erosion becomes more important in the middle and lower courses, widening the valley and channel.

Transportation Methods: Sediment is moved downstream by traction (large stones rolled along the bed), saltation (small stones bounced), suspension (fine particles carried in water), and solution (dissolved minerals). The amount and type of sediment affect the rivers energy and shape.

Deposition Impact on Profile: Although deposition mainly affects landforms, it can influence the rivers profile by causing the channel to become shallower or wider where sediment is dropped. This usually happens in the lower course where velocity decreases.

Role of Sediment Load: A high sediment load can cause the river to deposit material, changing the cross profile by building up the riverbed and banks. Sediment size decreases downstream due to attrition and sorting.

For example, in the upper course of the River Wye, large boulders are transported by traction, while in the lower course near Chepstow, fine silt is carried in suspension.