Flooding and River Management 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. 1 of 27 © Boardworks Ltd 2014

Learning objectives 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

What is a flood? A flood happens whenever a river overflows its banks. However, a flood becomes a problem when the water rises to a height where it threatens property or lives.

Learning objectives 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

Why do rivers flood? Rivers usually flood due to physical factors (to do with nature) [but humans can also make the floods happen too.] These physical factors can be divided into the weather (called climatic factors) and the area around the river (called the drainage basin)

Physical causes of river flooding

Learning objectives 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

The Boscastle flood, 16th August 2004 Boscastle is situated on the North Cornwall coast. About 90% of Boscastle’s economy is now reliant on tourism. On Monday 16th August 2004 major flooding occurred in North Cornwall. The small village of Boscastle was hit hardest – it was devastated.

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 - 1. Onshore coastal winds; 2. A rising tide; and 3. The ground was also already saturated from previous rainfall events. Explain why these conditions would cause major flooding.

What human and physical factors increased the risk of Boscastle flooding?

Physical or human factors (sorting task)

Examination Question Explain the causes of a flood event that you have studied.

Learning objectives 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

Effects of the Boscastle flood

Effects of the Boscastle flood

Effects of the Boscastle flood

What were the short - and long-term effects? Short- and long-term effects should be discussed with students prior to this task. Short-term effects are those that occur immediately as a result of the flood event. The long-term effects, or secondary effects, are those that are on-going after the flood has occurred. It may be useful to discuss an example – e.g. buildings being destroyed are a short-term effect but the loss of business as a result of building destruction is a long- term effect.

Learning objectives 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

How can river flood risk be managed?

Dams on the Rhône 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). This is a dam generating HEP near Beauchastel. What are the disadvantages of building dams?

Floodplain zoning

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

How should the flood risk be managed? Which scheme received the best score? Explain why.

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.

Test your knowledge of river flooding?

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.