These activities focus on what erosion and deposition are, erosion and deposition on a meander and how materials are transported by a river. ACTIVITY ONE : Soil, Pebbles and Sand. This activity can either be done as a whole class (divided into three groups) or as a group work exercise (no more than 6 in each group). Explain to the children that water is capable of moving materials like sand, pebbles and soil. Ask the children if anyone has seen any evidence of this in their garden or elsewhere. Explain that the children are going to be doing an experiment on erosion, deposition and transportation. Ask the children if they know what these words mean (let them refer back to Worksheet 10 if they want). Explain that erosion is the removal of material; transportation is the movement of the eroded material; and deposition is the dropping off the eroded material. Take the children out into the playground and divide them into 3 separate groups. Ask a member of each group to pour 2 litres of water (using the rose fixture) slowly from the can onto the top of each pile of material. Make sure that the children pour the water from the same height and roughly the same speed over each type of material. The teacher could then ask why this needs to be done (in the interests of a fair test). Ask the other group members to carefully note what happens to the sand, soil and pebbles. Use a metre stick/tape measure to find out how far the water has spread for each pile. Then ask the following questions and discuss the answers: 1) How far does the water spread for the sand, soil and pebbles? 2) What colour is the water at the end of the activity for the sand, soil and pebbles? 3) Is more sand removed than soil or pebbles? 4) Why do you think more sand is removed than soil or pebbles? (link this to the weight of the materials). 5) Ask a member of each group to show some evidence of erosion on the pile of sand, pebbles and soil. 6) Ask a member of each group to show some evidence of deposition from the pile of sand, soil and pebbles. 7) Ask a member of each group to find some evidence of where the sand, soil or pebbles have been transported. 8) What is erosion? 9) What is deposition? 10) What is transportation? This activity can be varied by either using 4 litres of water (with the rose attachment); or by using 2 litres of water without the rose attachment. The teacher can then ask the children how the results are different and why they might be different. RESOURCES REQUIRED 3 watering cans with a rose fixture. Playground. 1 pile of sand, 1 pile of gravel, 1 pile of soil, each half a metre high. Water. Metre Sticks/Measuring Tapes. ACTIVITY TWO : Rivers Shaping the Land. This activity also focuses on erosion and deposition and the transportation of material. This is a good small group exercise. An area 4 metres by one metre is required ending by a drain. Cover the surface with a layer of sand approximately one inch thick. Using two fingers get one child to trace a twisting course/path of a river into the sand (using coloured sand on the river bed provides a greater effect with erosion and deposition). Cover the drain with the muslin to prevent any sand being washed down the drain. Pierce a hole in the bucket (close to the bottom) and fill it with water. Position the bucket over the top of the stream (source). Alternatively use a hose pipe with a trickle of water running through it. It is a good idea for the teacher to take the children outside and go through the activity first so that all the children know what to do. The children can then work in small groups afterwards once they know what to do. Get the children to observe where most erosion is taking place and where there is deposition. Also get them to show evidence of how the river has changed it's course/path once the water has stopped flowing. 1) Point out an area of erosion. 2) What evidence is there that erosion has occurred here? 3) Why do you think erosion is occurring here? 4) Are there any other areas of erosion? If so, get the children to point them out. The children could then put a cocktail stick with a blue coloured flag attached to it by the areas of erosion. 5) Point out an area of deposition. 6) What evidence is there that deposition has occurred here? 7) Why do you think deposition is occurring here? 8) Are there any other areas of deposition? If so, get the children to point them out. The children could then put a cocktail stick with a red coloured flag attached to it by the areas of deposition. 9) What can you say about where erosion is occurring? 10) What can you say about where deposition is occurring? 11) How has the river changed it's course? Repeat the experiment again making the river more twisted i.e. having more meanders and note what happens with regard to erosion and deposition. Repeat the experiment again making the river straighter and note what happens with regard to erosion and deposition. RESOURCES REQUIRED Sand. Old Plastic Bucket or Hose Pipe. Playground (with a slope) close to a drain. Muslin. Coloured Sand. Cocktail sticks with blue and red flag attachments. ACTIVITY THREE : River Patterns. This activity provides an alternative to Activity Two as it is recognised that not every school will have a suitable area of land for Activity Two. See picture on next page:
Fill the tray with sand so that it is approximately 1-2 inches deep. Angle the tray so that there is a slope or alternatively place the tray on an area of sloping land. Make a twisting course/path for the river (about 2cm deep). Sprinkle some coloured sand onto the river bed so that the children will see the erosion and deposition better. Then pour the water into the river system and get the children to observe where the erosion and deposition is taking place. Make sure that the children understand that deposition occurs mainly on the inside bend of a meander because the water is travelling slowest there; and erosion occurs on the outside bend of a meander because the water is travelling the fastest there. 1) Point out an area of erosion. 2) What evidence is there that erosion has occurred here? 3) Why do you think erosion is occurring here? 4) Are there any other areas of erosion? If so, get the children to point them out. The children could then put a cocktail stick with a blue coloured flag attached to it by the areas of erosion. 5) Point out an area of deposition. 6) What evidence is there that deposition has occurred here? 7) Why do you think deposition is occurring here? 8) Are there any other areas of deposition? If so, get the children to point them out. The children could then put a cocktail stick with a red coloured flag attached to it by the areas of deposition. 9) What can you say about where erosion is occurring? 10) What can you say about where deposition is occurring? 11) How has the river changed it's course? RESOURCES REQUIRED A very long tray ( 50cm by 200cm) with no holes in it and approximately 25-20cm deep. Sand. Water (either in a watering can) or access to a tap. Coloured Sand to use of the river bed. Cocktail sticks with blue and red flag attachments. ACTIVITY FOUR : Evidence of Erosion and Deposition. For this activity the children need to study photographs closely to look for any evidence of erosion and deposition. They should already have an idea of what sort of evidence they are looking for. Worksheets 22 and 23 show erosion and deposition on their own respectively. But Worksheet 24 shows a combination of both erosion and deposition. RESOURCES REQUIRED ACTIVITY FIVE : Erosion and deposition on a meander. Arrange the children into pairs and give each pair a skipping rope. First tie a length of the rope at one end. Then shake the rope so that it moves like a snake. The rope looks as if it is moving backwards and forwards but in actuality, it is the bends that are moving. Explain to the children that a river's meanders move in the same way. Explain to the children that meanders occur in any part of a river's course. Keep the children in pairs and give each pair a book. Ask each pair of children to find a picture of a meander. Then ask the children to do the following: 1) Put your finger on the outside bend of the mender. 2) Put your finger on the inside bend of the meander. 3) Where is the water likely to be flowing the fastest on a meander? 4) Where is the water likely to be flowing the slowest on a meander? 5) What process is likely to be happening on the inside bend of a meander? Why? (erosion as the water should be flowing the fastest here and has enough energy to wear away parts of the banks). 6) What process is likely to be happening on the outside bend of a meander? Why? (deposition s the water hasn't enough energy to transport the eroded material). Then give the children a copy of Worksheet 25 RESOURCES REQUIRED ACTIVITY SIX : The Formation of an Oxbow Lake. Explain to the children how an oxbow lake is formed. It is a good idea to print out Worksheet 27 onto an OHP transparency and explain the process of how an oxbow lake forms using the OHP transparency as a visual reference for the children (note that special computer compatible OHP paper is required). Point to the different parts as you explain the diagram. EXPLANATION : As the water flows round a meander, gradually the meander becomes more like an S shape or a giant loop. This is because sediment is being deposited on the inside bend and erosion is occurring on the outside bend. The meander neck is the narrow piece of land between the start and end of the meander bend. When the neck of the meander becomes so narrow, the river eventually breaks through it. When this happens for a short time the river water is flowing both round the meander which is now known as the backwater and across the meander neck. But over time sediment is deposited and the backwater or meander is cut off. A kidney shaped lake is left behind which is called an oxbow lake. The name oxbow came from the U shaped pieces of wood which were once used for harnessing oxen. An oxbow lake is usually formed when a river enters old age. Worksheet 26 provides work for the children to do on oxbow lakes. RESOURCES REQUIRED Worksheet 27 - OHP transparency
Worksheets
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