WJEC GCSE Geography A Unit 1 The Core

WJEC GCSE Geography A Unit 1 – The Core A- The Physical World Theme 1 Water

Theme 1 Water 1 What are river processes and what landforms do they create? Ø 1. 1 What processes are associated with rivers? Ø 1. 2 What landforms result from these processes? Ø 1. 3 How do these landforms and processes affect the lives of people living along rivers? 2 How should rivers be managed? Ø 2. 1 How successful are different management approaches to the problems of flooding? Ø 2. 2 Should we change our approach to river and floodplain management in the future?

Theme 1 Water 1 What are river processes and what landforms do they create?

1. 1 What processes are associated with rivers? Before looking at the processes associated with rivers, we must understand that rivers operate within a drainage basin system. n A drainage basin (or river basin) is an area of land drained by a main river and its tributaries. n Tributaries are streams or rivers which flow into another, usually larger, stream or river.

Drainage basins The boundary of the drainage basin is called a watershed. It is usually marked by a ridge of higher land. n Where a stream begins is called the source. n Where a river enters the sea (or lake) is called the mouth. Wide river mouths are called estuaries. n

Drainage basins n When one stream or river joins another or meet is called a confluence.

Drainage basin system n n n A drainage basin forms part of the hydrological cycle. It is an open system with inputs and outputs. Within the system are stores and transfers (or flows).

1. 1 What processes are associated with rivers? A river needs energy and most of a river’s energy (95% under normal conditions) goes to overcome friction. The channel of a mountain stream which is full of boulders creates a lot of friction and the water flows slowly. The channel in lower ground is wider and deeper and has less friction so the water moves faster.

Transportation When the volume of water in a river increases, friction is reduced and the river’s surplus energy can be used to pick up and transport material. Material transported by a river is called its load. n A river can transport its load by one of four processes: n

Transportation TRACTION = when stones roll along the river bed (this needs the most energy). n SALTATION = when sand-sized particles bounce along the river bed in a ‘leap-frog’ movement. n SUSPENSION = silt and clay-sized particles are carried within the water flow. n SOLUTION = when some minerals dissolve in the water (this needs the least energy). n

Erosion A river uses the transported material to erode its banks and bed. As the velocity of a river increases, so too does the load it can carry and the rate at which it can erode. There are four processes of erosion:

Erosion n n ATTRITION = when material carried by the river collide and break up into smaller pieces (more likely in highland areas) HYDRAULIC ACTION = the sheer force of the water dislodging particles from the river’s banks and bed. CORRASION (ABRASION) = when small material rubs against the banks of the river (more likely in lowland areas). CORROSION = when acids in the water dissolve rocks such as limestone.

Deposition occurs when a river lacks enough energy to carry its load. The heaviest material is deposited first. Deposition can occur when the river level drops (following a dry spell, for example) or where the current slows down (on the inside of a meander, for example).

1. 2 What landforms result from these processes? A landform is a physical feature on the earth’s surface. n They are created due to erosion, transportation and deposition of material. n Other factors that affect the creation of river landforms are rock type and rock structure. n They are different in highland areas and lowland areas. n

River landforms in a highland area n Waterfalls and gorges

River landforms in a lowland area Meanders and ox-bow lakes. n Floodplains and levees. n

1. 3 How do these landforms and processes affect the lives of people living along rivers? n Many people all around the world live near rivers. Living near a river can give many benefits but can also have drawbacks. Task Sort the following statements into the correct column in the table:

Benefits of living near a river floods tourism high water levels water supply changing river channels Drawbacks of living near a river leisure activities flat land better weather good farmland building materials easy travel nature silting effluent and sewage disposal

Flooding n A flood is when land not usually covered in water becomes covered in water. There is too much water for the river channel to hold.

River discharge Discharge is the amount of water in the river passing a certain point (gauging station) at a given time. n Discharge is measured in cubic metres per second (m 3/s) – also called cumecs. n It is calculated by using the formula: DISCHARGE = VELOCITY X CROSSSECTIONAL AREA OF CHANNEL Velocity = the speed of the river in metres per second (m/s) The cross-sectional area = width x depth of the river channel [in square metres (m 2)]. n

A flood hydrograph The first water to reach the river will be surface runoff. n Later in the storm there will be more throughflow. n The gap between peak rainfall and peak discharge is called lag time. n

The flood hydrograph n n A hydrograph is a graph showing the discharge of a river at a given point over a period of time. A flood (or storm) hydrograph shows how a river responds to one storm.

Factors affecting the shape of the flood hydrograph n n n n Relief Rock type; Soil; Vegetation; Land use; How much use is made of the river; Drainage density. Task Explain how each of the factors listed above affect the shape of a hydrograph. You may find drawing a diagram (or diagrams) will help you.

What causes flooding? Flooding happens when water moves quickly into a river. This could be due to: n A prolonged period of heavy rain (and saturated land); n A storm; n Melting snow; n Steep valley sides; n Impermeable bedrock (does not let water through); n Thin soils; n Lack of vegetation; n Urbanisation; n Silting of the river channel.

Flooding Do remember that flooding is a natural process. n Flooding is made more serious by the actions of people n

Example: Boscastle Floods Flooding happened in the area of Boscastle, Devon in August 2004. Do some research into this flood event and prepare a written report on it. Include maps, diagrams and photographs if you wish. You should include: n Where is Boscastle and what happened there (briefly); n What factors were responsible for the flooding? n What were the impacts of the flooding? You should mention Ø Ø n physical impacts (e. g. on land) demographic impacts (e. g. deaths) economic impacts (e. g. how much money it cost) social impacts (the effects on daily life). What has been done to stop this type of flood from happening again?

Boscastle Floods – Useful Websites www. bbc. co. uk (good for articles and photographs) n www. wikipedia. org n www. google. co. uk (good for images and to find other useful websites). n www. metoffice. gov. uk/education/teens/casestu dy_boscastle. html n www. ordnancesurvey. co. uk/getamap n