List and describe the most important erosional and depositional features of a river and how these features form.

Meanders

As the river makes its way to the middle course, it gains more water and therefore more energy, so material can be carried in suspension and is used to erode the river banks. Lateral erosion starts to widen the river. When a river flows over flatter land it develops large bends called meanders.

As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed due to less friction and therefore increased erosion (through hydraulic action and abrasion).

The lateral erosion on the outside bend causes undercutting of the river bank to form a river cliff.

There is less water on the inside bend of a meander so friction causes the water to slow down, lose energy and deposit the material the river is carrying, creating a gentle slope.

The build-up of deposited sediment is known as a slip-off slope (or sometimes river beach).

The fast current on the outside bank causes lateral erosion, creating a river cliff. The slow current on the inside bank causes deposition, creaitng a slip-off slope.

Oxbow lakes

Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time. Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together. When there is a very high discharge (usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.

Erosion makes the neck narrow. During floods, the river takes the shortest course through the neck. The river has a new straighter course and the abandoned meander is called an oxbow lake.