﻿Good day geographers, and welcome to this river's lesson, about the landforms of erosion of deposition. We're going to look at the formation, of meanders and oxbow lakes, as well as graphing some rivers data. My boys love kayaking, and we go out on our local river quite a lot. And it's got some great meanders. If you catch on the wrong side though, should try to kayak around it, very tricky to paddle, as a current is so strong. There's a great slip off slope though, that makes a brilliant spot for a picnic. For today's lesson, you're going to need a pen, a pencil, a ruler and paper. In a second, I'm going to ask you to pause, and take a moment to get those, clear away all the distractions around you. Alternatively, you might need to move to a quieter place, so you're not going to be disturbed. So pause now, and I'll see you back in a second. Amazing. So your title today is Landforms of erosion and deposition. Meanders and oxbow lakes need to be a subtitle. If you could unplug both of those really neatly for me. We know we're looking today at landforms, that are created by erosion and deposition. Let's place where these fit, when the river's long profile. A river split into three courses, upper, middle and lower. In the upper course, you find erosional landforms such as waterfalls, and V-shaped valleys. We're looking today at those middle course landforms. These are landforms of erosion and deposition. In the lower course, we get landforms of deposition. If we're looking at erosional and depositional landforms, let's really clarify we know what these terms are. Erosion is the wearing away and removal of material, by a moving force. And in our example, is a river. If you need to drop that down, pause now to do so. There are four types of erosion. The first type of erosion is hydraulic action. Here, the sheer force of the water, on the riverbanks, and going into cracks will cause, parts of the river bed to break off. We then have a abrasion. Particles that are being carried, and transported by the water, scrape away at the river bed. Within the river channel, when rocks bash against each other, this is called attrition. The final type of erosion is solution. This is where sediment is dissolved in the water. Finally, rivers can erode vertically, which is downwards, but the one that we're interested today, is lateral erosion. Where rivers erode sideways. Deposition is the opposite. This is where material being transported by the river, is dropped due to a loss in energy. So let's work out what meanders are, first of all. This photo shows a beautiful meander. A meander is a bend in a river. They form in the middle, and the lower course of the river. They are formed by lateral erosion, so sideways erosion and deposition. We can see deposition happening here. Where there is material that has been dropped. We can undertake fieldwork to investigate rivers. Here we have two students measuring the width. We can also measure the depth of a river. We going to have a look today, at river gets across a meander. We would measure from A to B. We would take that distance, and divide it into equal intervals. We're going to be measuring, the depth of the river at 50 locations between, the slip of slope A, and the river cliff up B. So we need to get prepped for this, really important you've got your ruler, and your pencil for this. I'm going to talk you through it, then you can pause and complete your prep yourself. Number one, you're going to draw a line down your margin. It should be 12 lines. You're going to number these lines zero to 12, and I want to you to label the access, river depth in centimetres. Your next job is to draw a line across the top, say from zero. It's going to be 15 centimetres wide, and I want you to just put a small line, every single centimetre. We can label these sites one to 15, and we're naming the access, site across the meander. Final thing you can do, is your going to add a title. Remember this graph is going to show us, river depth across meander. So pause the video now, take as long as you need to make sure it's neat. Don't forget about ruler. Well, I'm hoping that is super neat. I don't want to see any scruffy graphs today. So you should have a title, river cross profile, across a meander, or river depth across a meander. We're going to plot this data. We've collected look 15 sites worth of data. Depths in centimetres. Site one had a depth of one centimetre. So on your graph, you would plot that here, with a small cross in pencil. Site two had a depth of one centimetre as well. Site three had a depth of two centimetres. And finally, the last one I'm going to help you is, with that site four, the depth was three centimetres. Once you've plotted, the rest of the 15 points, you're then going to in pencil, draw a smooth line, joining those points. Please start at the access. So your turn. Take your time, make sure it's accurate. Did you graph it like this? So you've plotted these 15 points. You've made sure you've joined the river up to the line each side as well. And it's done in a smooth line. You could colour this in blue, to show that it represents the water. We can see that at the slip off slope, the water is much shallower. By the river cliff, a meander is much deeper. So the cross profile of a river now, I've cut across that meander. The thalweg is the fastest flow of water, and the water flows fastest always, at the outside of the bend. So that word is thalweg. Erosion occurs on the outside of the bend. That's where water is fastest, so it's got more energy. This creates a river cliff. On the inside of the bend, the water is much slower. And so therefore deposition occurs. This creates a slip off slope. So can you remember, A is the, is it river cliff, or slip off slope? Point to the right word now? It is slip off slope. So the river cliff is a steep a bit up B. So where does erosion occur? A or B? Pointing, it is B. So we have erosion at B, deposition would be occurring at A. We know what they look like, we've plotted some data. Now let's consider how they form. Meanders are bends in a river. The thalweg is the line of fastest flow. And this swings from side to side. The water is always fastest on the outside of the bend. This causes the outside of the bend to erode, through processes like abrasion and hydraulic action. This creates a river cliff over time. You can see with the dotted line, where the river originally used to be, and you can see how is eroded. This photo shows the river cliff on the right hand side really clearly. Velocity is slower on the inside of the bend. So here deposition occurs, and I've represented that with black dots. This creates over time a slip off slope, or a river beach. In the photo, you can see that, on the left of the photo. This continues over time, so erosion on the outside, deposition on the inside. And the meander becomes more sinuous. The meander becomes more and more bendy. It migrates across the valley floor, through lateral erosion. So let's recap what we've got so far. Water in a river is fastest on? The inside or outside of the bend? Point for me, three, two, one, water's fastest on the outside. Say the word for me, the fastest flow of the river was that what? Thalweg. Deposition creates a slip off slope, or river cliff? Pointing in three, two, one, it is slip off slope. The river cliff is created through erosion. B is a slip off slope, or river cliff? Three, two, one, it is river cliff. A is a slip off slope, that's created by erosion, because on the inside of the bend, the water is slower. You're going to explain the formation of a meander. I've given you the answer, but I've missed off nine words. I would like you to pause the video in a second, and match the nine words to the correct letter. Pause now and write them down on your piece of paper. Meander are bends in a river. Water flows faster on the outside of the bend, so erosion occurs through processes like abrasion. This creates a river cliff. Velocity is slower on the inside of the bend, so deposition occurs creating a slip off slope. This continues over time, making the meander more sinuous. It migrates across the valley through lateral erosion. But meanders can turn into oxbow lakes. So if we remember, the thalweg swings from side to side, it's always on the outside, eroding the outside bend. And this causes lateral erosion. We can see in this diagram, lateral erosion on these outside bends. But actually there are three outside bends now. These bends slowly migrate towards each other, and we call that bit of land between them, the neck of the meander. The neck narrows over time. And when there's a flood, it can sometimes cut through the meander neck, when it's narrow enough, forming a new straighter channel, Deposition will now occur on the edge, because there the water is slower. This deposition will cut off the old meander loop. An oxbow lake is formed. Over time, they may become marshes, and eventually vegetation will grow. Sometimes we can see these on a map as meander scars. Your turn now. You are going to create an annotated, so a labelled, but labelled with sentences explaining. An annotated diagram to explain the formation of oxbow lakes. It's going to be six marks. So I'm looking for six steps in your sequence. I want you to use numbers to show this sequence. And don't forget to join that diagram in pencil. The words I want to see on your diagram are, Thalweg, that's the fastest flow of the river. River cliff, meander, deposition, slip off slope, erosion, lateral erosion, Migrate and neck. To help you out a little bit, I've drawn three diagrams, I think might be useful. To get this in, I think I would put it on three separate diagrams, right? Best of luck. Don't forget those numbered bullet points. Pause the video. You can do it. Right here in my diagram. So, number one, the water is fastest on the outside of the meander bend. So erosion occurs through processes like abrasion. This creates a river cliff. So I need the word river cliff, and I want to see some lines, to show that the outside of the bend erodes. Number two, deposition occurs, on the inside of the bend, as water is slower, creating a slip off slope, tick. I've drawn an arrow now, to show that over time, the meander becomes more bendy, and migrates across the valley, through lateral erosion. I've then moved down to another diagram. Number four, over time, the bends grow closer, narrowing the neck, tick. Number five, during a flood, the river cuts through the neck, creating a straightened channel, tick. And then finally, an oxbow lake is created. Just go through, and highlight these key words. Make sure you've got them all. Well, that brings us to the end of today's lesson. We've meandered around the formation of erosion, like deposition landforms, in the middle course of a river. Meanders form due to erosion on the outside of the bend. A deposition on the inside. Over time they slowly migrate, widening the river valley through lateral erosion. Sometimes, they get cut off to create oxbow lakes. Before you go, I need you to deposit, not a slip off slope, but your learning in the end of lesson quiz. Pick on the next page to get it. And I can't wait to see how you've got on. Thanks so much for your time today. I look forward to you joining me soon, as we move down into the lower course of the river, to see which landforms of deposition form that. Have a great day today.

In this lesson, we will learn how meanders and oxbow lakes are formed through erosional and depositional processes.

Geography

Y10 Geography

Key Stage 4

Year 10

Landforms of erosion and deposition: meanders and oxbow lakes

Rivers

UNIT

What are river long and cross profiles?

How do rivers erode, transport and deposit their load?

Landforms of erosion: V-shaped valleys and interlocking spurs

Landforms of erosion: waterfalls and gorges

Landforms of deposition: levees, floodplains and estuaries

Landforms in a UK river valley: The River Tees

How does the river drainage basin system work?

What are the human and physical factors that increase flood risk?

What are hydrographs and what do they show?

How can rivers be managed using hard engineering strategies?

Soft engineering river management (Part 1)

Soft engineering river management (Part 2)

A UK Flood Management Scheme: Oxford

Lesson overview: Landforms of erosion and deposition: meanders and oxbow lakes

Intro Quiz

Video

Presentation

Exit Quiz

Transcript

14 lessons in Rivers: