River Landforms
Defining river landforms
The movement of water is quite significant in understanding the environment. As water moves on land, soil erosion and deposition occurs causing different river landforms. River landscapes change as one moves from river source to the mouth. In the upper course of a river, rapid flowing water is formed by steep gradient. In the middle course, meanders are formed and in the lower course, river braids are formed on flat land.
It is however important to note that a river is not a landform. It is a part of many other landforms including prairies, mountains and valleys including V shaped valleys . Rivers can also be part of many other landforms at the same time.
Different types of river landforms
Potholes
Potholes are cylindrical holes drilled into a river bed and vary in diameter and depth. It can cover a few centimeters or several meters. Potholes are mainly found in a river’s upper course because it has enough potential energy to vertically erode and flow turbulently. In a river’s upper course, the load is usually large and often transported by traction along the bed of a river. Water encounters a bedload when flowing and it is forced over it. Down cuts occur behind the bedload in various swirling Eddie currents. These kinds of currents erode river beds and further form small depressions in it.
Meanders and ox-bow lakes
Meanders and, oxbow lakes are some of the most popular river landforms. They are bends in a river course characterized with water that flows fast on the outside of a bend. This speed leads to erosion and formation of a very steep river cliff. On the outside of a bend, water slows down leading to deposition of sediment. This further forms a gentle sloping slip off slope in the shallow water.
Meanders also cause lateral erosion leading to widening of valley floor or floodplain. This means that meanders migrate downstream in many cases, become wider and larger over a long period of time. In places with well-developed meanders, a river can easily take a short cut across the neck of a meander in times of flood. This will lead to creation of abandoned sections of the river, popularly known as ox bow lakes. As time goes by, ox bow lakes will dry up and leave a meander scar.
Braided channels
Braided channel is a channel that is divided into smaller sub channels by temporary and small islands popularly known as eyots. These channels develop in rivers with a sedimentary load, steep gradient and where river discharge changes regularly. When the volume of the river surpasses the capacity of the river or drops of the river, the river will be forced to deposit its content or load in the islands or channel of created eyots.
Floodplains
A flood plain is another river landform and is a wide, flat area of land on any side of the river. This can form in the middle or lower course of the river. A floodplain often forms as a result of soil erosion and deposition. When material or content is deposited on a meander’s slip slope, it will gradually build up over time. Therefore, if a river overflows, water will flow to the flood plain draining away alluvium or deposited fine particles.
Levees
Levees are natural silt embankments along river banks. They are often located several meters higher than floodplains.
Deltas
A flat area of silt and sand built into the sea is known as a delta or a river delta. When a river enters the seas with large amounts of fine material, its velocity is usually slow and it makes the load to be deposited in layers. The deposited content will over time form small islands that are separated by river channels, also known as distributaries.
Waterfall
A waterfall is a river landform characterized with a steep drop in the course of a river. Waterfalls form a cap rock lies over less resistant and soft rock. The softer rock is easily eroded by abrasion or hydraulic action. This makes the harder rock to remain undercut, overhang until it can no longer support its weight.
The overhang rock collapses and breaks up the water below. The power of water that breaks up in the water below is intense forming a plunge pool. In the end, erosion occurs by splash back just behind the water fall.
Gorges
Gorges are formed following frequent occurrence of a waterfall. A waterfall eventually causes a steep sided gorge because of retreats up the river or stream.
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Sources
https://geographyas.info/rivers/river-landforms/
http://thebritishgeographer.weebly.com/river-landforms.html