River Landforms

Explain the formation of an oxbow lake (4 mark)

Explain the formation of an oxbow lake (4 mark)

• 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.

Explain how river meanders may change over time. (4 marks)

• A meander is a winding curve or bend in a river.

• Water flows fastest on the outer bend of the river where the channel is deeper and there is less friction.

The development of meanders is due to both deposition and erosion

• Lateral erosion results in undercutting of the river bank and the formation of a steep sided river cliff.

• . On the inside of the bend, where the river flow is slower, material is deposited on a slip off slope, as there is more friction.

• Over time, because of erosion and deposition, meanders gradually change shape and move across the floodplain and migrate downstream.

How does a waterfall and george form? (6 mark)

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-The river flows over an area of hard rock with softer, more easily eroded rock underneath. -Over time the softer rock is worn way more rapidly by processes of hydraulic action and abrasion, creating a waterfall.

• The water hits the bottom of the falls with great force. This erodes a deep hole creating a plunge pool.

• The softer underlying rock is eroded and weakened. The softer layer collapses into the plunge pool, undercutting the hard rock.

• The hard rock cracks and then collapses.

• Gradually, the waterfall retreats upstream, leaving behind a steep-sided gorge. Every time the overhanging cap rock breaks off the gorge retreats further and grows longer. (-There is turbulent fast flowing water in the gorge)

What are levees and where and why do they form?

Levées are long, narrow ridges or raised embankments alongside the river. composed of gravel, stones, and alluvium. Steeper on the channel side than landside

Levées occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.

How are river levees formed (4 Marks)

Levées are long, narrow ridges or raised embankments alongside the river. composed of gravel, stones, and alluvium. Steeper on the channel side than landside

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• Levées occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.

• Sediment that has been eroded further upstream is transported downstream.

• When the river floods, the sediment spreads out across the floodplain. Friction with the land reduces velocity and causes deposition.

• When a flood occurs, the river loses energy. The largest material (sand and gravel) is deposited first on the sides of the river banks and smaller materials (finer silt and mud) further away.

• After many floods, the sediment builds up to increase the height of the river banks, so the levees become higher than the surrounding floodplain.

• If a severe flood event occurs, levées may burst and cause serious damage to the surrounding land.

Explain the formation of estuaries

An estuary is when a river meets the sea. The river here is tidal and when the sea retreats, The volume of the estuary is reduced. When there is less water, the river deposits silt to form mudflats which are an important hobitat for wild life.

Exlain the formation of interlocking spurs

Interlocking spurs are mainly formed by vertical erosion in the upper course of a river.

In such areas, Water is mainly pulled down by gravity due to the steep slopes which erodes the river beds.

The river is near its source so it doesnt have enough energy to erode the hard rocks so the river bends around it/ flows around them forming interlocking spurs

What is a floodplain?

the flat land on either side of a stream that becomes covered with water during a flood

How do floodplains form?

(formed by sediments deposited during flooding)

-Floodplains form due to both erosion and deposition. Erosion removes any interlocking spurs, creating a wide, flat area on either side of the river.

• During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material)

• Over time, the height of the floodplain increases as material is deposited on either side of the river.

Why are floodplains often used as agricultural areas?

Floodplains are often agricultural land, as the area is very fertile because it's made up of alluvium (deposited silt from a river flood). The floodplain is often a wide, flat area caused by meanders shifting along the valley.