003 - Hydrographs

Syllabus Point

Describe (AO1) the characteristics of a hydrograph.

Examine (AO3) the reasons for spatial and temporal (short-term and long-term) variations in hydrographs.

Examine (AO3) the role of hydrographs in forecasting the magnitude, spatial extent and timing of floods.

Key Terminology

Define the terms below using your 'IB Geography. Course Book' by Cooke and Nagle, the command term posters in the classroom and the links below.

• Describe
• Examine
• Hydrograph
• Spatial
• Temporal
• Magnitude

Activity One - Read

Go through the following slide show and answer the following questions to give you a basic understanding of what a hydrograph is and how it can be interpreted.

1. What is a hydrograph?
2. Why are hydrographs important for forecasting flood events?
3. Draw a fully labelled hydrograph. Remember to define the key terms; rising limb, falling or recessional limb, peak flow, lag time and base flow.
4. How is discharge measured?
5. What factors influence the shape of a hydrograph? Explain them. To help with this question look at the prompt images below and refer to your 'Geography Course Companion' by Cooke and Nagle.

Image Four Image Five

Image Six

Activity Two - Design

It is your task to design a YouTube clip that is no more than 3 minutes in length to explain what a hydrograph is and factors which effect its shape. You will be working in teams of three.

Format

• 3 minutes in length.
• Only images and your voices to be used.
• Discuss the physical and human factors which effect the hydrograph shape.
• Explanation is key!!

Activity Three - Magnitude and Frequency

Hydrographs are critical in aiding Flood Agencies predict when and where the next major disasters 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.

Image Seven - A graph to show the magnitude and frequency of flooding on the Red River, USA.

1. Spend 2 minutes on the internet gathering headlines of strong magnitude and low frequency flood events.

Activity Four - Read

Taken from: https://www.commerce.alaska.gov/web/WelcometoourNewWebsite.aspx

Read the article in the useful link above and make notes on why the term '100 year floods' is disliked by hydrologists.

Useful Resource

• USGS - Flood:Recurrence Intervals

But...

That doesn't mean that hydrographs are only useful in estimating when the next major flood disaster will occur. They also help to illustrate which rivers flood on a regular basis and are causing a menace to local residents and businesses. This will inform companies such as insurance firms which home owners are more likely to make water damage claims, as well aid Flood Agencies where they should spend money developing flood defences or plans.

Exam Style Question

Draw a fully labelled hydrograph. (6 marks)