Lesson 9 Channel characteristics

Drawing a river cross section

What are these students doing?What are measurements are they recording?

What errors might they make?

What problems might they encounter?How could you use their data?

How can primary data be used to create a river cross sectional profile?

Learning Objectives:

To draw, label and interpret a river cross sectional profile.

5 November 2013

Learning Outcomes:

Essential – you will draw an accurate river cross sectional profile.

Stretch – you will identify and label all the key river channel characteristics.

Challenge – you will apply your understanding of how river processes influence the cross sectional profile.

A*

B

C

Measuring River Cross SectionsProducing a cross-section of a river channel is a basic river fieldwork skill. The first stage is to measure the width and depth of the river. The data gathered can then be plotted to create a scale diagram of the cross-section, or used to find the cross-sectional area and wetted perimeter of the river.

Year 12 Hanham students measuring the cross sectional profile of the River Harbourne in South Devon.

How to draw a river cross section

Depths Depth Measurements(cm)

Depth 1 6cm

Depth 2 8.5cm

Depth 3 9cm

Depth 4 10cm

Depth 5 10cm

Depth 6 16cm

Depth 7 12cm

Depth 8 8cm

Depth 9 7.5cm

Depth 10 7.5cm

Depth 11 7cm

Depth 12 12cm

Depth 13 14cm

Depth 14 16.5cm

Depth 15 17cm

Depth 16 19cm

Depth 17 16cm

Depth 18 15cm

Depth 19 14cm

Depth 20 12cm

Depth 21 6cm

Use the readings below to plot a cross section of the stream.Key information• Width of stream: 6.40 metres • Distance from the water surface to the top of bank was 1.25 metres • Readings taken at 30 cm intervals

Before you start - pause for thought• What scale will you use for the width and depth?• Where is the bank full line?• In which direction must the depths be measured?

TASK 2: Label the cross section with the following key words; Shallow water, Fast flow, Slow flow, Deep water, Deposition, Steep bank

TASK 3: Hydraulic Radius  In full write the equation for hydraulic radius in your book.

For your channel cross-section, calculate the hydraulic radius.

TASK 4: Check your understandingAnswer the following questions in full sentences in your book; 1. What three main things is velocity influenced by, and how does this affect

the processes working within a river channel?

2. How does an Asymmetrical channel vary to a symmetrical channel?

3. Why does the hydraulic radius vary throughout the year?

4. What can affect the channels efficiency?

5. How does channel shape effect velocity and efficiency of the channel?