Explain where and why depositional landforms occur along the course of a river.

Rivers and its landforms are formed and moulded over time chiefly by the processes of , and by the transport and deposition of . These are hydraulic variables, which occur in rivers. Rivers are able to work on the landscape through erosion, transport, and deposition. The amount of potential energy available to a river is proportional to its initial height above sea level. A river follows the path of least resistance downhill, and deepens, widens and lengthens its channel by erosion. Up to 95percent; of a river’s potential energy is used to overcome friction. This energy is defined by the way the landforms are produced. E.g. the more energy the greater build up of sediment so the more landforms. This will be where the river is at its fastest rate. (The middle course) One way of classifying rivers is by their stage of development. An upper course is typified by a narrow V-shaped valley with numerous , , and rapids. Because of the steep gradient of the topography and the river’s height above sea level, the rate of erosion is greater than the rate of deposition, and down cutting occurs by vertical corrasion (erosion or abrasion of the bed or bank caused by the load carried by the river) so there will be less build up of depositional landforms. In the middle course of a river, the topography has been eroded over time and the river’s course has a shallow gradient. Such a river is said to be graded. Erosion and deposition are delicately balanced so there is a greater build up of river meanders (gently curves back and forth), which in turn extends the flood plain. Horizontal corrasion is the main process of erosion. The flood plain is an area of periodic flooding along the course of a river valley where fine silty material called alluvium is deposited by the floodwater. (This silt creates this landform) Features of a mature river (or the lower course of a river) include extensive , , and braiding streams, which are examples of depositional landforms because the deposition far outweighs the erosion so more sediment is deposited off, thus creating greater expanses of landforms..

Straight channels seldomly persist for long in a river. In the middle section of a river, typically between the turbulent headwater streams and its estuary where it reaches base level, its channels begin to form meanders. River channels quickly form into sinuous patterns.

In the middle section of a river, the valley is characterized by broad flood plains, at least as wide as the amplitude of meanders. The valley sides are visited only infrequently by the slowly shifting channels of the streams. As the flood plain develops, oxbow lakes become numerous. Oxbow lakes are crescent shaped lakes formed in an abandoned meander river bend by a meander cutoff. Oxbow lakes are lakes or ponds found in association with river channels. When a river channel becomes obstructed by silt and debris, the river will often cut a new channel around the obstruction. With time the obstructed area may become completely cut off from the river and begin developing as a lake. Over time an oxbow lake may become filled with organic material and be transformed into a marsh.

In conclusion hydraulic variables and physical variables (relief/climate) aid the development of depositional landforms along a river. The more turbulent a river is, the more it will occur. The turbulence differentiates through the three courses; upper, middle and lower. This results in different landforms occurring at different stages.