Geography River Landscapes

	River Lanscapes
	Drainage Basin

	Drainage Basin System

	From Source to Mouth
	River Near the Source. •Narrow •Shallow •Slow-flowing •Large bedload River in the Middle •Wider •Deeper •Faster flowing •Smaller material in it River near the mouth. •Wide •Deep •Fast-flowing •Mainly suspended load

	Processes of river erosion
	Erosion is the wearing away of the land. The material around the river has already been broken down and loosened by weathering. Some soil and stones have already been carried to the river by rain and gravity.
	Transportation of the material a river carries, it’s called its load. The more energy it has, the larger the load a river can carry.
	Deposition is the leaving of sediment by the river. As the river slows down, it deposits the largest stones and pebbles first, then smaller ones and finally the smallest particles. But dissolved material stays in the water and is carried out into the lake or sea.

	UPPER COURSE
	Definitions
	Hydraulic Action This process involves the force of water against the bed and banks. Abrasion/Corrasion This is the process by which the bed and banks are worn down by the river’s load. The river throws these particles against the bed and banks, sometimes at high velocity. Attrition Material (the load) carried by the river bump into each other and so are smoothed and broken down into smaller particles. Corrosion This is the chemical action of river water. The acids in the water slowly dissolve the bed and the banks.

	Landforms in the upper course
	V-shaped valleys and interlocking spurs Rapids Waterfalls

	Interlocking spurs
	In the upper course the river does not have a huge amount of energy to erode as it does not have a high discharge and it has to transport large pieces of sediment. When the river meets areas of harder rock that are difficult to erode it winds around them. A series of hills form on either side of the river called spurs. As the river flows around these hills they become interlocked. So, a series of interlocking spurs are often found in the upper course of a river valley.

	What are rapids and how do they form?
	Rapids are part of a river where the water is relatively shallow but the flow of the water is quite fast and turbulent as the water descends over a series of small steps. Rapids are formed due to a sudden steepening of the stream gradient, but without a sufficient break in slope to form a waterfall, or from the river flowing over a series of thin layers of hard and soft rock.

	MIDDLE COURSE
	Main processes that operate in the middle and lower course of a river.
	Erosion is still an important process. The river is now flowing over flatter land and so the dominant direction of erosion is lateral (from side to side). The river has a greater discharge and so has more energy to transport material. Material that is transported by a river is called its load. Deposition is also an important process and occurs when the velocity of the river decreases or if the discharge falls due to a dry spell of weather.

	How is material transported downstream?
	Traction Boulders and pebbles are rolled along the river bed at times of high discharge. Saltation Sand sized particles are bounced along the river bed by the flow of water. Suspension Fine clay and sand particles are carried along within the water even at low discharges Solution Some minerals dissolve in water such as calcium carbonate. This requires very little energy.

	Landforms are found in the middle and lower course.
	1)Meanders 2) 2)Oxbow Lakes 3) 3)Flood plains and Leveés 4) 4)Deltas

	Meanders
	As the course of a river approaches its middle stages it flows over flatter land. Lateral erosion dominates as the river swings in large bends known as meanders. Meanders constantly change their shape and position. Water is pushed to the outer bend . This reduces friction with the bed and banks. So the river has more energy for transporting material which can erode the outside bank via abrasion.

	Formation of an oxbow lake
	When the river floods it breaks through the thin meander neck and the river takes the easier, straight course. This leaves the meander loop ‘cut off’ as an oxbow lake. Over time, the oxbow lake will become colonised by vegetation.

	Floodplain formation.
	Floodplains and leveés are formed by deposition in times of river flood. The river’s load is composed of different sized particles. When a river floods it deposits the heaviest of these particles first. The larger particles, often pebble-sized, form the leveés. The sands, silts and clays are similarly sorted with the sands being deposited next, then the silts and finally the lightest clays. Every time the river floods deposition builds up the floodplain.

	Estuary
	An estuary is a wide, deep mouth, they are really useful for shipping, so they usually have ports and factories along them.

	Deltas
	Deltas are found at the mouth of a river, where the river meets the sea. At this point the river is carrying too much load for its velocity and so deposition occurs. The top of the delta is a fairly flat surface. This is where the coarsest river load is dropped. The finer particles are carried into deeper water. The silt is dropped to form a steep slope on the edge of the delta while the clay stays in suspension until it reaches the deeper water.

	What is a drainage basin ?
	Mouth Where the river flows into the sea, or sometimes a lake. Watershed The boundary dividing one drainage basin from another- a ridge of high land. Confluence The point at which two rivers join. Tributary A river which joins a larger river. Catchment The area from which water drains into a particular drainage basin. Source The upland area where the river begins.