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Flooding 1: Causes of river floods

water in field, sheep grazing, hills in distance

Suitable for GCSE

This resource examines the causes of river flooding. It uses evidence from Cumbria which suffered flooding during December 2015 as a result of Storm Desmond. This was the fourth storm of the season and the ground in Cumbria was already saturated by rainfall that had fallen during November. Storm Desmond was a deep area of low pressure. It stalled over Cumbria and delivered record-breaking amounts of rainfall. Flooding may have been exacerbated by human factors such as urban developments that have reduced infiltration and increased run-off, and by previous river management that has reduced the capacity of floodplains to store water.

Specification requirements

The movement of water through a drainage basin is the focus of several GCSE specifications. Some also require understanding of the causes of a weather hazard within the UK. Download the Specification audit.

Learning objectives

This resource can be used to meet one or more of the following objectives:

  • consolidate prior learning about flows and stores within the drainage basin
  • classify causes of floods by asking students to research the evidence and sort between physical and human factors
  • create a case study of Storm Desmond and its impacts.

Download the Assessment Objectives.

Activities

The following are stand-alone activities. It is recommended that students have prior knowledge of water movement through drainage basins and be familiar with key terms such as catchment area, infiltration, throughflow, permeable and impermeable rocks.

 

1.1 Identifying reasons for flooding in December 2015

You might show this short video, made by the Department of Science and Technology in the Philippines, to introduce the idea that there are different reasons for floods.

This Environment Agency document provides an overview of reasons for flooding in December 2015 on pages 6 and 7. Some effects are shown on pages 10 and 11.

At a simple level, the floods were caused by an intense period of rain caused by a low pressure system. The Met Office provides a simple description of Storm Desmond here while this page provides much greater detail and includes a synoptic chart for 5 December 2015. Students could focus on the data provided by this chart.

  • What does low pressure of 946mB actually mean?
  • How does this compare to ‘normal’ atmospheric pressure?

Rainfall was particularly intense over the mountains of Cumbria. Rainwater quickly ran over the already saturated soils and into rivers which have a radial drainage pattern. For those following a specification that includes glaciation, students could consider how this pattern was formed. The map of rainfall totals for 4-5 December on the Met Office website clearly shows that Carlisle only had 21 mm of rainfall in this period.

  • In this case, why did Carlisle flood?

Students need to understand that, in this type of event, flooding occurs as water moves through the drainage basin (see activity 1.2).

Students who want to put the flood event into context should view the hydrographs available on the riverlevels.uk website. The long term hydrograph for the River Eden in Carlisle shows that the river is usually between 0.26 m and 2.5 m deep at this point. The Environment Agency also posts a live hydrograph for the River Eden at Sands Centre, Carlisle.

  • How many times has the water level risen above 2.5 m?
  • How high was the water level in December 2015?

 

1.2 Movement of water in the drainage basin

The risk of flooding within a drainage basin can be increased by a number of human factors.

Watch the video A New Type of River Management is Coming. This animation highlights the ways in which the risk of river flooding can be reduced by working with nature. Students may need to watch the short video twice. The first time they can focus on the key message of the video and identify three ways that rivers could be managed to reduce the flood risk. The second time they watch the video they can focus on the enquiry questions:

  • How have rivers been altered?
  • Why has this had the unintended consequence of increasing the flood risk?

The animation is packed with information. These teacher notes provide some explanation and links with the Cumbria floods.

 

Other lessons in this series:

Flood risk and flood management: Introduction
Flooding 2: Investigating the effects of river floods
Flooding 3: Response to floods: Oxford Case Study
Flooding 4: Managing the upper drainage basin
Flooding 5: Sustainable Drainage Systems (SuDS)
Flooding 6: Managing river floods – exploring the role of the Environment Agency
Flooding 7: Coastal flooding at Chiswell
Flooding 8: Managed realignment
Flooding 9: The role of the Environment Agency in coastal management and the development of shoreline management plans

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