Middle and Lower Course Landforms
This page develops middle and lower course landforms, including floodplains, levees, meanders and ox-bowlakes
Lesson Time: 1-2 hours
Lesson Objectives:
- To describe and explain different river landforms such as floodplains, levees, meanders, ox-bow lakes and deltas
Student Activity - Processes - Recognising Floodplain Features
Use the resource provided and see how many correct features of the floodplain you can identify
1. Technical vocabulary - Introduce the floodplain; it's good to get students to write a definition. Students should then attempt in pairs to complete the labelling activity by adding the names of features to the floodplain diagram. (This is quite difficult)
- Place exemplification - Show the animation of floodplain evolution; this shows the importance of lateral erosion and meander migration for widening the floodplain up to the bluffs. See what discussion the animation prompts. Then show them the River Kissimmee video clip to show how unregulated rivers flood regularly. There is no need to show the management stuff in this video.
Levees and floodplains
- You could recap with the Kissimmee animation above step 5 to show the importance of annual floods and the consequential deposition associated with it.
- Explaining physical processes - Students can then make a copy of a diagram showing the deposition associated with levee formation. Key words in explaining deposition and levees are falling competence, and falling hydraulic radius. Check they fully understand these two terms
- Place exemplification - Then show the students the River Tees video on meander formation. Allow some students Q&A time - it's nearly always important to slowly draw the sequence of meander formation on the board to show the separate processes. These include:
- fast flow (thalweg): erosion and river cliff
- slow flow (low competence): deposition and slip-off slope
- secondary cells linked to further deposition
These features and processes are illustrated on-site and can be projected.
- Student knowledge can then be assessed through the well-supported worksheet called meander-ox-bow lake
- ICT: Explaining physical processes - Get students to make a time-lapse video of the evolution of the river from straight to sinuous to meandering and then oxbow lakes.
They should draw the river sections as illustrated on the worksheet provided and cut out the different features to add to the river profile as it evolves.
The purpose of the cutouts is to speed things up. The students enjoy the activity, and can also be done with Plasticine
Delta investigation
- Students should watch the video on delta formation and attempt to identify as many river landforms as they can and factors that lead to delta formation
- Students should then use the resources to describe the characteristics of deltas and explain the factors that lead to their formation
Assessment - Essay Question - "Landforms in the middle course of the river are generally formed more by deposition than erosion". To what extent do you agree with this statement (10)
Floodplain FeaturesMiddle and Lower Course Landforms
As we move further down the river, discharge increases, largely due to the increase in inputs from tributaries. As a result, and with reduced gravitational energy, the river erodes laterally, widening the channel. Furthermore, channel migration cuts out wide, flat floodplains. Although floodplains are predominantly depositional features, in their early stages the migrating channel with meander loops helps to cut it out from its bluffs. The resulting floodplain has many interesting features, including levees, meanders and ox-bow lakes.
The following diagram shows the floodplain with its many characteristic features.
Source: Pearson
Student Activity - Processes - Floodplain Evolution
Watch the following animation which shows the evolution of the floodplain.
What process appears to be most important?
A second phase of floodplain evolution relates to the cycle of flooding and deposition of alluvium. This continued process helps form the flat profile of floodplains.
Watch the animation showing the historical unregulated flood cycle of the River Kissimmee in Florida.
Student Activity - Processes - Explaining Deposition through Levees
Make a copy of the following diagram and make notes on how to explain deposition. A good example is to refer to natural levee formation.
Student Activity- Processes and Place- Exploring Meanders
Watch the following clip based on a meander section on the River Tees, England and complete the photo story explaining its evolution to an oxbow lake.
Meander Flow and the Secondary Cell
Three types of river flow are important when explaining meander processes. Firstly, the flow of the river separates into the fastest flow on the outside, which is called the thalweg. The thalweg has a helical corkscrew motion, which makes it very abrasive, and so it erodes the outside bend to form a river cliff. The thalweg follows the pattern of deeper pools and is pushed to the outside by centripetal force.
Secondly, water caught on the inside is held up by shallower water and so causes deposition. This feature is known as the slip-off slope.
Thirdly, a secondary cell exists which transfers water and sediment across the channel from the outside bend to the slip-off slope. This is caused by the force of the flowing water hitting the cliff and so rebounds across the channel.
Meander Features
The Secondary Cell
Student Activity - Processes - Meanders and Ox-bow Lakes
Using the resources provided, make a time-lapse video of a changing meander. Develop your river from a straight section to a meander loop and oxbow lake.
Use the jigsaw pieces provided and base your time-lapse on the diagram below.
Use the following diagram to help get you thinking about how to phase the time-lapse into different stages. The first three are illustrated for you
Use the following resource to add the correct features to your time-lapse
Student Investigation - Place and Scale - River Deltas
Watch the following video on river processes and delta formation. Try to identify:
- As many river landforms as possible
- Factors that lead to delta formation
Deltas are deposition features formed at the mouth of some rivers as they enter a sea or lake. They have some distinctive features, including a divided channel into distributaries, extensive alluvial mudflats or bars and creeks and lagoons. A simplified delta can also be profiled into topset beds, foreset beds and bottomset beds.
The following diagram shows the three types of river delta
Watch the following animation and annotate the screenshots on your worksheet
Student Assessment - Essay Question
Assessment - Essay Question - "Landforms in the middle course of the river are generally formed more by deposition than erosion" To what extent do you agree with this statement (10)
- To what extent - requires an evaluative approach but a focused argument.
- The theoretical context should develop the processes at work in the middle course as well as the dominant process. The student should develop at least two middle-course landforms to develop their argument. The features of the landforms and the processes that form them should be fully understood.
- The essay's conclusion should be focused on the main point of the question and be consistent with the argument that runs through the essay