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© Boardworks Ltd 2005 1 of 27 These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the.

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Presentation on theme: "© Boardworks Ltd 2005 1 of 27 These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the."— Presentation transcript:

1 © Boardworks Ltd 2005 1 of 27 These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 27 © Boardworks Ltd 2005 Flooding and River Management

2 © Boardworks Ltd 2005 2 of 27 Did you know? Why should we study flooding?

3 © Boardworks Ltd 2005 3 of 27 What is a river flood? Why do rivers flood? What caused the Boscastle flood? What were the effects of the Boscastle flood? How can the flood risk be managed? Learning objectives

4 © Boardworks Ltd 2005 4 of 27 A flood occurs whenever a river overflows its banks (exceeds its ‘bankfull discharge’). What is a flood? However, a flood becomes a problem when the water rises to a level where it threatens property and/or life.

5 © Boardworks Ltd 2005 5 of 27 What is a river flood? Why do rivers flood? What caused the Boscastle flood? What were the effects of the Boscastle flood? How can the flood risk be managed? Learning objectives

6 © Boardworks Ltd 2005 6 of 27 Rivers usually flood due to a range of physical factors. These physical factors can be divided into climatic factors and drainage basin characteristics. Human intervention can also make flooding worse. Why do rivers flood? A major flood devastated the village of Lynmouth in Devon in August 1952. 229mm of rain fell in 24 hours. The impact of this was increased because narrow bridges across the River Lyn acted as dams and stopped the water flowing away quickly.

7 © Boardworks Ltd 2005 7 of 27 Physical causes of river flooding

8 © Boardworks Ltd 2005 8 of 27 What is a river flood? Why do rivers flood? What caused the Boscastle flood? What were the effects of the Boscastle flood? How can the flood risk be managed? Learning objectives

9 © Boardworks Ltd 2005 9 of 27 The Boscastle flood, 16 th August 2004 Boscastle is situated on the North Cornwall coast. For a hundred years the village was a thriving port but the coming of the railways soon saw its decline as a trading port. About 90% of Boscastle’s economy is now reliant on tourism. On Monday 16 th August 2004 major flooding occurred in North Cornwall. The small village of Boscastle was devastated.

10 © Boardworks Ltd 2005 10 of 27 What were the causes of the Boscastle Flood? Climatic conditions were the main reason for the floods in Boscastle. 200mm fell over Ottersham Moor, to the east of Boscastle, within a 4 hour period. This was combined with coastal winds and a rising tide. The ground was also already saturated from previous rainfall events. Explain why these conditions would cause major flooding.

11 © Boardworks Ltd 2005 11 of 27 What factors increased the risk of flood?

12 © Boardworks Ltd 2005 12 of 27 What factors increased the flood risk?

13 © Boardworks Ltd 2005 13 of 27 Examination Question Explain the causes of a flood event that you have studied.

14 © Boardworks Ltd 2005 14 of 27 What is a river flood? Why do rivers flood? What caused the Boscastle flood? What were the effects of the Boscastle flood? How can the flood risk be managed? Learning objectives

15 © Boardworks Ltd 2005 15 of 27 Effects of the Boscastle flood

16 © Boardworks Ltd 2005 16 of 27 Effects of the Boscastle flood

17 © Boardworks Ltd 2005 17 of 27 Effects of the Boscastle flood

18 © Boardworks Ltd 2005 18 of 27 Short- and long-term effects

19 © Boardworks Ltd 2005 19 of 27 What is a river flood? Why do rivers flood? What caused the Boscastle flood? What were the effects of the Boscastle flood? How can the flood risk be managed? Learning objectives

20 © Boardworks Ltd 2005 20 of 27 How can flood risk be managed?

21 © Boardworks Ltd 2005 21 of 27 Dams on the Rhône This is a dam generating HEP near Beauchastel. Dams can be multi-purpose: They hold back the spring meltwater and so stop the floods. They release this water in the dry summer to irrigate the intensive fruit and vegetable growing areas. The water is also used for cooling in the two nuclear power plants near Genissiat – Beugy and Creys- Malville. In addition, the dams produce hydroelectric power (HEP). What are the disadvantages of building dams?

22 © Boardworks Ltd 2005 22 of 27 Floodplain zoning

23 © Boardworks Ltd 2005 23 of 27 After the Lynmouth floods in 1952 revetments wider channel concrete banks Study the photograph. Explain how the changes will help to prevent flooding. What action was taken after the Lynmouth floods in 1952?

24 © Boardworks Ltd 2005 24 of 27 How should the flood risk be managed? Which scheme received the best score? Explain why.

25 © Boardworks Ltd 2005 25 of 27 Examination question Study the diagram of a flood management scheme. Explain why the meander loop has been dredged. List two other ways of managing river flooding.

26 © Boardworks Ltd 2005 26 of 27 Test your knowledge of river flooding?

27 © Boardworks Ltd 2005 27 of 27 Key ideas A river floods when it exceeds its bankfull discharge. Flooding can be a result of both physical and human factors. Physical factors include climatic conditions and drainage basin characteristics. The effects of flooding are short-term and long-term. Flood management schemes can aim to prevent flooding or reduce its impact. Flood management schemes can have both positive and negative effects.


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