Key terms

CHECKLISTS Let’s see what we have managed to cover this half term.

Learning objectives To understand landforms of fluvial erosion and deposition.  Potholes  Rapids  Waterfalls  Gorges  Meanders  Oxbow lakes  Braiding  Floodplains  Levees  Deltas Upper course landforms Lower course landforms

Overview

Landforms Overview Rivers are constantly shaping the landscape as they carry water and sediment along their courses Where a river has excess energy it will erode its channel creating waterfalls and gorges. When energy levels fall deposition will occur forming extensive floodplains Erosion and deposition can combine to form meanders

Can you match up the landforms and the pictures?

1. Potholes Potholes are circular depressions in the river bed Process – Rock fragments are drilled into holes/cavities by the turbulent whisking action of a river – Erosional process = corrasion – Rock will overtime become smooth = Abrasion

Kukdi River, Nighoj, India Pothole and the rock fragment that formed it Kukdi River, Nighoj, India Pothole and the rock fragment that formed it

Over time, they may widen and join with other potholes to form larger potholes, and the whole river bed is deepened. ACTIVITY - Draw two diagrams to show the processes that cause a pothole to form

A river flows over a variety of different rock Tougher rock = eroded less easily Weaker rock = eroded quicker This results in irregular steps in the long profile of a river Cause turbulent flow in a stretch of river This is known as a rapid. 2. Rapids

Rapids form stretches of white water as the river plunges over jagged rocks and mini waterfalls to form dangerous whirlpools and fast-flowing tubes of water

How do you think waterfalls are formed?

Who can name and describe the formation of these landforms?

Learning objectives To understand landforms of fluvial erosion and deposition.  Potholes  Rapids  Waterfalls  Gorges  Meanders  Oxbow lakes  Braiding  Floodplains  Levees  Deltas Upper course landforms Lower course landforms

3. Waterfalls High Force – River Tee

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EXAMPLE High Force waterfall on the River Tees Water plunges 20 metres over the edge of a tough outcrop of dark igneous rock called dolerite Beneath the dolerite are mainly sedimentary rocks like limestone and shale Sedimentary rocks erode quicker causing the formation of a plunge pool This undercuts the waterfall at its base causing the overhanging dolerite to collapse This cycle repeats Formation of a 1.5km gorge. h=648&wrapid=tlif &ie=UTF-8&sa=N&tab=il

Waterfall Formation

ACTIVITY 2 Create a story board to the formation of HIGH FORCE waterfall in the upper course of the River Tees. 1.Use the 6 statements to help you do this. 2.Label your diagrams with these key words DOLERITE LIMESTONE AND SHALE UNDERCUTTING CORRASION HYDRAULIC ACTION 1.5 km GORGE OVERHANGING RETREAT PLUNGE POOL COLLASPE 20 metres

The formation of a waterfall – Example___________________________

The water starts to undercut soft rock underneath the hard rock, creating the beginnings of a plunge pool Water flows over a gap in hard rock Falling rock and the force of water also help to create a plunge pool through erosional processes like hydraulic action and corrasion As the waterfall retreats it leaves a steep-sided gorge. Over thousands of years the waterfall can move several miles The waterfall retreats over time, with the process starting again The overhanging hard rock eventually falls into the water as the base of the waterfall has been undercut

1.Water flows over a gap in hard rock 2.The water starts to undercut soft rock underneath the hard rock, creating the beginnings of a plunge pool 3.The overhanging hard rock eventually falls into the water as the base of the waterfall has been undercut 4.Falling rock and the force of water also help to create a plunge pool through erosional processes like hydraulic action and corrasion 5.The waterfall retreats over time, with the process starting again 6.As the waterfall retreats it leaves a steep-sided gorge. Over thousands of years the waterfall can move several miles

Learning objectives To understand landforms of fluvial erosion and deposition.  Potholes  Rapids  Waterfalls  Gorges  Meanders  Oxbow lakes  Braiding  Floodplains  Levees  Deltas Upper course landforms Lower course landforms

The Middle Course of the River

Learning objectives To understand landforms of fluvial erosion and deposition.  Potholes  Rapids  Waterfalls  Gorges  Meanders  Oxbow lakes  Braiding  Floodplains  Levees  Deltas Upper course landforms Lower course landforms

The Middle Course More tributaries join the River Severn. These increase the volume of water in the River. Increasing the River’s Discharge. Upper Course Middle course

LANDFORM of the Middle/Lower Courses Flood Plains During wet weather rivers increase in size. Sometimes rivers cannot hold all of the water flowing into them. The banks burst and the river floods on a flood plain. Therefore a flood plain is the area of broad flat land either side of the river.

The floodplain creates U shaped valleys in the middle course. FLOODPLAIN

5. Meanders What is a meander? Meanders are sweeping bends in the river’s course MEANDERS ARE FORMED DUE TO EROSION AND DEPOSITION!!

Watch this!!!

Processes that cause a meander to form…. When a river emerges from the upper course, it begins to ‘swing’ or meander in order to use up surplus energy This is because water moves in a helicoidal flow! SWIRLS! Pool and Riffles are created due to the ‘corkscrew’ (helicoidal) like flow. Pools and riffles often occur in meandering channels during low flow conditions Riffles – shallow, fast flowing water Pools – deep, slow flowing water Pool and Riffles are created due to the ‘corkscrew’ (helicoidal) like flow. Pools and riffles often occur in meandering channels during low flow conditions Riffles – shallow, fast flowing water Pools – deep, slow flowing water

Water flows faster on the outside bend, due to centrifugal force. This fast flowing water is called the THALWEG. This causes LATERAL EROSION through ABRASION. This creates a RIVER CLIFF. Water flows much slower on the inside bend as the river lacks energy to carry its load. This causes DEPOSITION. This creates a slip off slope. A A B B Processes AND features of a meander Draw a plan view of a meander

Can you label the correct processes and landforms of a meander? What is a cross section?

Cross Section From A to B Outside- The volume and velocity of the river are higher Information on the outside of the meander… The water has more energy to transport its load Material is carried in SUSPENSION The force of the water ERODES and UNDERCUTS the river bank by ABRASION UNDERCUT This feature is called a River Cliff Fastest flowing water is called the THALWEG A - outside B - inside

On the inside of a meander…. The river is shallow and slow flowing The river lacks the energy to carry its load Material is therefore deposited This feature is called a POINT BAR A - outside B - inside Cross Section From A to B

Processes creating meanders… LATERAL EROSION On the outside of a bend DEPOSITION On the inside of a bend

6. Oxbow Lakes

Lateral erosion on outer bend Continued erosion results in the narrowing of the neck of the meander The two outer bends meet.The river takes the shortest route. Deposition occurs in slack water. The river cuts the most efficient course. It cuts off the former bend, leaving an oxbow lake

PREP Create a A3 summary sheet of landforms of rivers as they move downstream UPPER, MIDDLE AND LOWER COURSE Use as many key words around the diagrams as possible!

6. Formation of a Oxbow Lake

Cross Section of a meander From A to B

The Lower Course landforms

Learning objectives To understand landforms of fluvial erosion and deposition.  Potholes  Rapids  Waterfalls  Gorges  Meanders  Oxbow lakes  Braiding  Floodplains  Levees  Deltas Upper course landforms Lower course landforms

= an extensive flat area of land on either side of the river which periodically becomes flooded. Mostly in lowland areas, where they can be several kilometres wide Often used for farming as the silt that is deposited there is very fertile 7. Floodplains

Formation of floodplains – Every time the river floods it deposits a fresh layer of silt on top of the existing floodplain – The width of the floodplain depends upon the amount of meandering of the river – If lateral erosion is high at the apex of each bend the river will meander across the floodplain and cut into the bluff (valley edge) – This widens the valley and extends the floodplain. ACTIVITY Copy diagram 1.52 page 38 in your books underneath your notes.

8. Levees

= when the river’s banks become raised. Formation of Levees During high flow conditions – due to high rain fall or snow melt rivers are unable to contain the increased volume of water flowing into it. Water flows over banks Coarse, larger and heavier sediment is deposited on top of the banks. WHY? – as the velocity of the river is slower here. Coarse sediment traps smaller sediment Banks become raised. 8. Levees ACTIVITY Draw three labelled diagrams is illustrate the formation of natural levees.

9. Braiding What is it?

= when a river becomes sub-divided into many separate channels. Why? River is overloaded with sediment that it is unable to carry Sediment is dumped Forms islands in the middle of the river Smaller channels are made around the island – steepening the gradient and increasing efficiency. 9. Braiding

Braiding is common in rivers where the load is large e.g. at the snouts of a glacier OR fluctuating discharge e.g. semi arid areas

They occur at the mouth of a river A river rapidly loses energy when entering the sea or a lake Sand, silt and clay are deposited in a fan shape Overtime there is a build up of material – creates new land called a delta. Deposition rate exceeds the rate of removal by the sea. This can happen when; 1.When the sediment load is large 2.Weak currents or a small tidal range 10. Deltas

Often delta is split into separate channels = distributaries Two main types of delta; 1. Arcuate delta =gently curved E.g. River Nile

2. Birds foot = deposition along the edges of several distributaries E.g. Mississippi

Learning objectives To understand landforms of fluvial erosion and deposition.  Potholes  Rapids  Waterfalls  Gorges  Meanders  Oxbow lakes  Braiding  Floodplains  Levees  Deltas Upper course landforms Lower course landforms