Welcome back to Beyond’s AQA Geography Blog! This exciting entry focuses on the river component of the ‘Physical Landscapes of the UK’ topic. This week, we’re exploring a wide range of different river landscapes within the UK. We’ll be looking at Fluvial Processes, Deposition and Transportation, to Erosional Landforms such as Interlocking Spurs.
Revision is made easy with the key points of the exam topic broken down into easy bite-sized chunks. So get ready to recap (or learn) all the important elements you need for your ‘Physical Landscapes of the UK’ exam! Prepare for some note-taking!
Changing Long Profile and Cross Profile of a River
The long profile of a river shows how the gradient of the land changes as the river travels downstream. The cross profile of the river shows the cross-section of the river and the river valley.
- Hydraulic action – as the water is forced into the sides of the river channel, air is compressed in the small cracks in the rock. Tiny fragments of rock get broken away as the process is repeated many times.
- Abrasion – the river picks up eroded rocks, pebbles and sand. The material then rubs against the channel, wearing it away.
- Attrition – eroded materials in the river bump into each other and eventually wear each other down. Over time, the materials become smaller and more rounded.
- Solution – water reacts with minerals in rocks and the structure of the rock is changed.
- Vertical Erosion – deepens the river, forming a v-shaped valley/channel. High turbulence carries material which wears away the river bed, especially in the upper course.
- Lateral Erosion – widens the river valley/channel, especially in the middle/lower course.
- Traction – material carried by the river is rolled along the river bed.
- Saltation – material carried by the river is bounced along the river bed.
- Suspension – material is carried by the river water.
- Solution – soluble material is dissolved and carried by the river water.
Rivers deposit eroded material as they lose speed (velocity) when:
- the river becomes shallower
- the discharge (volume of water) is reduced
- the amount of transported material increases
- the river reaches the mouth
Distinctive Fluvial Landforms Result from Different Physical Processes
Form in the upper course of a river where vertical erosion creates steep- sided v-shaped valleys. The river winds and bends avoiding areas of hard rock creating interlocking spurs (which look similar to the interlocking parts of a zip).
Form in the upper course where a layer of hard rock overlays a layer of softer rock. The softer rock erodes much more quickly and the hard rock overhangs, until eventually it becomes too heavy and collapses causing the river to retreat upstream.
Form where a waterfall has retreated upstream creating a valley with steep-sided walls.
Erosional and Depositional Landforms
Form in the middle and lower course where lateral erosion causes the river to widen. The outside of a river bend will erode more quickly as the water is forced to the outside bend as it turns.
The water on the outside bend is deeper and faster causing even more erosion, enlarging the bend.
The water on the inside bend of the river is much shallower and slower. As a result, material is deposited (forming a slip-off slope).
Form where meanders have become so enlarged that the river breaks through the narrow ‘neck’. The river will flow along this new route as it is the shortest course. Deposition will eventually completely cut the old meander loop off from the river channel creating an ox-bow lake.
Form in the lower course along the river banks due to repeated flooding. As water overflows the main channel, it loses energy, depositing material creating natural embankments.
The floodplain is the wide valley floor on either side of the river in the lower course. When this area of land floods material will be deposited because the water loses velocity.
An estuary is the tidal part of the river. It will be near the mouth of the river, where the river meets the sea. The water level in the estuary rises and falls with the tide. During high tide, large areas of valley floor will be flooded. As the tide falls, material will be deposited, creating mudflats which will be exposed during low tide.
Different Management Strategies Can Be Used to Protect River Landscapes in the UK from the Effects of Flooding
The Use of Hydrographs to Show the Relationship Between Precipitation and Discharge
- Discharge – the volume of water that flows in a river per second. It is measured in cubic measures per second (cumecs).
- Hydrograph – show the rainfall (bar graph) and river discharge (line graph) of a river over a period of time.
- Lag time – the delay between the peak rainfall and the peak discharge.
- Rising limb – shows the increase in discharge as rain enters the river channel. A steep rising limb indicates an increased flood risk as water quickly enters the channel. The lag time occurs because most rain water does not land in the river and has to travel to the river overland (surface runoff) or slowly underground (after infiltration). The lag time can be sped up by steep slopes, saturated ground and impermeable surfaces.
- Falling limb – shows the decrease in discharge as the river returns to its usual level.
How Physical and Human Factors Affect the Flood Risk
The amount and duration of precipitation can affect flood risk:
- Heavy precipitation will cause flooding as there is too much water to infiltrate into the ground causing water to run over the land (increased surface runoff).
- Prolonged precipitation will cause the soil to become saturated preventing further infiltration. Therefore, rainwater will run over the land (increased surface runoff).
- If surface runoff is increased the discharge of the river will increase, increasing the likelihood of a flood.
Impermeable rocks (e.g. shale and granite) and clay soils do not allow precipitation to infiltrate; increasing surface runoff. If surface runoff is increased the discharge of the river will increase, increasing the likelihood of a flood.
Steep slopes will cause surface runoff to enter the river more quickly, less water will infiltrate and as a result more water will end up in the river. If the discharge of the river is increased, it will increase the likelihood of a flood.
Buildings and roads are often impermeable (e.g. concrete and tarmac) and can increase the likelihood of a flood in two ways:
- less water will infiltrate and more water will end up in the river
- drains are designed to remove rainwater quickly from urban areas (reducing the lag time). This rainwater is normally directed towards rivers, increasing river discharge
Trees help to reduce the discharge of a river in two ways:
- trees intercept rainwater which can then evaporate
- trees can soak up groundwater
If trees are cut down, more water will end up in the river.
Different Management Strategies can be used to Protect River Landscapes in the UK from the Effects of Flooding
The Costs and Benefits of Management Strategies:
Dams and Reservoirs
Reservoirs (artificial lakes) are formed behind a dam (a wall across a river) usually in the upper course.
- Pros – reservoirs store water and provide a reliable water source. HEP can be generated. Flood risk is reduced.
- Cons – very expensive to build. Flood settlements/habitats. Alters the river course downstream as land no longer floods, resulting in less fertile land as silt is no longer deposited. Eroded material is trapped behind the dam, which alters river processes and landforms downstream.
Rivers are artificially straightened.
- Pros – flood risk is reduced as water is transported away from the area quickly.
- Cons – water is carried downstream quicker. As a result, flooding and erosion is more likely downstream.
Raised walls along the river banks.
- Pros – flooding will be less frequent as the river channel can hold more water.
- Cons – if the river floods severely, flood waters will be trapped on the floodplain. Can be expensive.
Flood Relief Channels
Water is diverted from areas that are being protected.
- Pros – water can be controlled by opening and closing flood gates.
- Cons – expensive. Water is carried downstream quicker. As a result, flooding and erosion is more likely downstream.
Flood Warnings and Preparations
The Environment Agency alerts the public with apps, radio and TV.
- Pros – reduce the impact of flooding by giving people time to prepare (e.g. evacuate, protect their homes/belongings).
- Cons – the flood will still occur. Some people might not be alerted.
Flood Plain Zoning
Building is restricted in parts of the flood plain to reduce the impact of a flood. Hard surfaces would increase the likelihood of a flood.
- Pros – impact of flooding is reduced. Floodplain retains its natural function.
- Cons – restricts development/economic growth of an area. Offers limited help to areas already built on.
Trees will intercept rainwater, increasing the lag-time and reducing discharge.
- Pros – cheap. Soil erosion is reduced. Increased wildlife due to habitat creation.
- Cons – less farmland is available.
Making the river more natural and allowing natural river processes to happen.
- Pros – reduces flood risk downstream. Increases wildlife through habitat creation.
- Cons – increases local flood risk.
River Landscapes in the UK Lesson Pack from Beyond
If you’re in need of further River Landscapes in the UK revision, click here.
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