001 - Flood Risk

Geographic Knowledge and Understanding

How urbanization, deforestation and channel modifications affect flood risk within a drainage basin, including its distribution, frequency and magnitude.



Concepts

Physical and human factors exacerbate and mitigate flood risk. Understanding the processes involved and relative power of the human and physical factors facilitates how the risks can be managed.




Aims

To have knowledge and understanding of how urbanization, deforestation and channel modifications affect flood risk within a drainage basin, including its distribution, frequency and magnitude.



Key Terminology

  • Channel Modification

  • Weirs

  • Dredging

  • Revetments or rip raps

  • Mitigate

Define the terms above using the useful links below and your 'Freshwater' textbook by Codrington.

Useful Links




Activity One - Why?

The causes of flooding have been debated for some time but why is it an important type of disaster to focus on? North Western Europe is relatively lucky and does not tend to suffer from hurricanes or volcanic eruptions. What we do have to worry about is the increasing frequency of our flood events. Watch the youtube clip below and make notes on the causes and consequences of flooding in the UK from 2014.

Canoeing across the UK floods




Activity Two - Magnitude and Frequency

As you are now aware hydrographs are critical in aiding Flood Agencies to predict when and where the next major flood event may occur. Generally the stronger the magnitude the lesser the frequency which is why severe floods are often referred to as a 25 or 50 year flood event. This can be illustrated in the graph below.

        1. Spend 2 minutes on the internet gathering headlines of strong magnitude and low frequency flood events.
        2. Describe the graph below.
        3. Read the article in the 'Useful Resource' box and make notes on why the term '100 year floods' is disliked by hydrologists.


Image One - A graph to show the magnitude and frequency of flooding on the Red River, USA.
Taken from - www.tulane.edu
Taken From:
https://serc.carleton.edu/quantskills/methods/quantlit/floods.html

 Useful Resource


Image Two - 100 Year Flood Article
USGS - 100 Year Flood
Taken from:







Activity Three - Urbanisation

When we looked at flood hydrographs we began to explore the impact that urban areas had on the increased risk of flooding. Now is the time to formalise that discussion by looking at the flow chart below.

      1.  Explain why an increase in urban environments can cause an increase in flooding.
      2. Why is there a need to keep greywater and sewage separate?
      3. There are nine boxes below the image where do they fit into the diagram?
      4. Produce a detailed example of a flood event that was exacerbated by the increase in urbanisation.
      5. How does urbanisation impact the distribution of floods?
      6. How does urbanisation impact the frequency of floods?
      7. How can urbanisation impact the magnitude of floods?

Image Three - Impact of Urbanisation on Flooding - Taken from www.geographyalltheway.com



Activity Four - Deforestation

Whenever something is built it is inevitable that trees will be chopped down to make way for the new building or road. Unfortunately as soon as you deforest an area the interception rates will be reduced, the infiltration rates may decline and this can cause an increased amount of overland flow. To assess the impact that deforestation has on flooding answer the following questions.

    1. How can deforestation make flooding worse?
    2. Read the article in the 'Useful Resources' box and create a detailed examples of how deforestation can impact flood risk.
    3. Find an example of where afforestation has been used as a form of management to reduce the risk of flooding.
    4. How does deforestation impact the distribution of floods?
    5. How does deforestation impact the frequency of floods?
    6. How can deforestation impact the magnitude of floods?





Activity Five - Flood Management

Many believe that flood management is a way to try and stop the issue of flooding but in some instances it can actually make things worse. If schemes are not maintained then there is a chance that dams can be breached and levees can burst. So what can actually be done to try and prevent flooding and how successful are those schemes? 

    1. Describe four different ways that a river can be managed.
    2. Create a detailed example of how channel modification has actually made a flood worse.
    3. Create a detailed example of how channel modification has actually made a risk area less problematic.
    4. How does flood management impact the distribution of floods?
    5. How does flood management impact the frequency of floods?
    6. How can flood management impact the magnitude of floods?



Exam Style Question
Explain how deforestation impacts the magnitude of flood risk within a drainage basin [3 marks].