Rivers cause changes to the environment - "River landforms" - Information for Gr 4-5

We have learned about different landforms and also rivers, but did you know that rivers can also change the environment?  What does that mean and what changes will happen?

If water flows over a certain area - like a river- it will take pieces of the soil and small stones with it and leave it in other places.  We say that the river will cause erosion and it can take the ground away from the banks of the river or from the bottom to make the river deeper and wider.  

It can even create a new pathway so that the river will flow in another direction.

As you go down the river, you will see the landscape will also change.  

The river will start in a mountain where the area is steep and the water will flow quickly.  In the middle of the river which is called the 'meander', the area will become more flat

Lets have a look at two different landform that a river can cause

1. 'V-shaped valley
2. Waterfalls

V-shaped valley

We learned that a river start in the mountains where the area goes down quickly, which means the 'gradient' is steep.  The water flows fast and then erosion takes part at the bottom of the river and makes the river deeper.  This is called 'vertical erosion'.  It also happen that other things which we call 'weathering agents' like rain and wind will break down the river bank and cause erosion and the valley to become larger.

All this 'weathered material' (the ground and small rocks) end up in the river and flows with the river.  These materials will then take away more from the riverbed and cause more erosion.

Waterfalls

Many times you will find a waterfall in a mountain.  The water flows over the rock and some of the rocks are very soft and breaks down (erodes) easier than the hard rocks  and the hard rock will hang over the soft rock.

The rocks that are broken off will fall to the bottom of the waterfall where a pool has formed and will be moved around and around and this will also cause more erosion.

• Have a look at how a waterfall forms and answer the questions

1. In which part of the river will a waterfall form.
2. How will the top layer and the bottom layer of the rocks differ?
3. What is a 'plunge pool'?
4. What does it means that a waterfall 'retreats'?
5. What does this 'retreat' form?

Activity

• Draw a river and label the different part starting from the source
• Do research and name more examples of 'river landforms' and find a picture of each.
• for revision have a look at the different landforms formed by water http://kinooze.com/landforms-that-water-creates/
• You are going to 'build' your own waterfall - it can be one that you and your dad/mom do in the garden or it can just be a model you build.  Get some ideas from 'youtube' if you do not want to use the one that is shown here.