Bellwork• Wordsearch on River Features

River FeaturesLearning Objectives:• To improve research and

summary skills• To work on presentation

skills• To understand how river

processes have formed a range of different river features

Homeworks and Reading Feedback

• Reading Feedback in the form of a quiz• Best table get a small prize each (except for Jake and

Chris who can’t cope with small prizes)1. Where is the source of the River Tees?2. What is the name of the waterfall along the river?3. What is the name of the hard rock that helps to form

this waterfall?4. Where can potholes be found along the river?5. What does SSSI stand for?6. Which town is found inside one of the river’s

meanders?7. What can be found at the mouth of the river?

Today and Tomorrow…• You will be working in groups to

complete a presentation on a river feature

• You will need to produce a powerpoint, a handout and an activity that the class can do

• You should aim for your presentations to take between 5 and 7 minutes

• I’ve done one to start us on Waterfalls to set the bar…

Waterfalls….

•https://www.youtube.com/watch?v=fOI7aKvrFn4

Formation of Waterfalls and Gorges

Using the above sequence to help you, write a short paragraph to explain how waterfalls form.

Use the following words somewhere in your answer:Hard RockSoft RockUndercuttingPlunge poolErosion

Groups!1. Potholes2. Rapids3. Meanders4. Oxbow Lakes5. Braided Channels6. Deltas7. Floodplains and Levees

Choose your group…

Tom GJake

Chloe HLucas

HannahEmmaChris

5,4,3,2,1, upper course• Name 5 river upper course features• Give the names of 4 types of river

erosion• Name the 3 courses of a river long

profile• Give 2 names of river features you can

identify on a map• Name 1 upper-course feature that you

are confident in explaining to someone else.

Braided Channels

A river is described as being braided when it becomes sub-divided into many separate channels

The main reason why this occurs is because the river becomes overloaded

This results in sediment being dumped in the channel to form islands

Around the islands, smaller channels are cut into the river sediment – steepening the gradient and increasing their efficiency

Braiding is common in rivers that experience large variations in discharge and where the load of the river is large e.g. rivers that flow from glaciers

Rivers in tropical and dry environments can have wildly fluctuating discharges which leads to braiding

Geologically speaking, an increase in sediment load will over time increase the slope of the river

The White River in Washington USA

Rakaia River, New Zealand

Brahmaputra , Bangladesh

Activity

Sketch the braided channel:

Potholes

What are potholes?

Potholes are small circular depressions found in the river bed carved out of solid rock.

“Potholes are cylindrical holes drilled into the bed of a river that vary in depth & diameter from a few centimetres to several metres. They're found in the upper course of a river where it has enough potential energy to erode vertically and its flow is turbulent.”

How are they formed?

Potholes are formed by corrasion: this is where particles of rock carried by the river bed scrape away at the riverbed and banks.

Rock fragments are drilled into holes and cavities by the turbulent whisk-like action of the river causing circular cavities to form.

Copy this down…

Floodplains and Levees

By Chris, Oliver and Matty.

What is a Floodplain?

A floodplain is an extensive flat area of land on either side of a river which periodically becomes flooded. They are at there largest on low lying areas and they can be kilometres wide.

More information

The silt that is deposited is fertile and so floodplains are often used for farming.

When meanders slowly migrate across the floodplain they cut into the valley edge to form a bluff.

Fertile land used for farming.

What is a levee?

A levee is a ridge of sediment deposited naturally alongside a river by overflowing water. They also can be man made in order to prevent water spilling over the river banks.

Natural levee created by larger/heavier sediment being deposited by the river flooding, therefore over flowing.

More information

During a flood the velocity of the water decreases as the water spills over the bank. This means coarse sediment is deposited.

http://m.youtube.com/watch?v=mftdpNoNnP4

Rapids

River RapidsRiver rapids consist of fast flowing waters which can be small, short rifles or long and violent waters. River rapids can be turbulent and dangerous or they can stretch and tumble over rocky water bottoms or shallow riverbeds. Rapids form whitewater when the current appears white, violent and frothy. Whitewater rivers have significant sections of rapids and are often tackled by adventurist boaters for whitewater rafting.

FormationRapids are caused by water flowing over and around varying resistance of rocks. As the river flows from its upper course, it meanders and bends to avoid areas of hard rock. This creates an interlocking path and alternating layers of hard and soft rock for the water to flow through. This alternating layers cause the water to tumble over because the hard rocks break up the smooth flow, causing the up and down movement of rifles.

Rapid RatingsRapids are divided into different classes based on the severity of the rapids and difficulty in paddling or rafting through them. Class I rapids have fast-flowing water with small waves and riffles. Class I rapids have just a few obvious obstructions. Class II rapids have waves up to 3 feet high with wide channels. Some maneuvering is required; these rapids are often tackled by novice paddlers. Class III rapids are for intermediate rafters; fast current and moderate, irregular waves are found in Class III rivers. Class IV waters have long, violent rapids and high, irregular waves. Paddlers must wind through constricted passages and drops. Class V waters have long, violent rapids, difficult routes and steep drops.

Task: Answer the Key questionsHow are river rapids formed?What are the classes of rapids?Where are some famous rapids – give 3Where along the river are rapids foundWhat are the most dangerous type of rapids

Oxbow Lakes

• An oxbow lake is a horseshoe shaped lake separated from an adjacent river

• The water is stagnant, and in time the lake gradually builds up becoming a crescent-shaped stretch of marsh called a meander scar.

Definition

• An ox bow lake is formed by the increasing sinuosity of a river meander.

• Erosion is greatest on the outer bank and deposition is greatest on the inner bank.

• The neck of the meander becomes progressively narrower.

Formation

• During times of higher discharge, such as a flood, the river cuts through this neck and the new cut eventually becomes the main channel.

• The former channel is sealed off by deposition.

Formation

Sediments deposited on the inside of bend Current strongest on outside of bend

Gap between two arms of

river narrowed by erosion

Rapid erosion of banks on outside of

bends

• https://www.youtube.com/watch?v=8Xer45n-E7w

River breaks through narrow

gap when in flood

River still flows around

meander

Old path of river now dry

Current along straighter path

becomes dominant

Abandoned meander or oxbow lake

By Reub, Bron and Ema

Deltas

What is a Delta?

• A Delta is a build up of deposited material that breaks through the water surface and forms new land.

• A river loses energy when it enters the sea. As a result, vast amounts of silt and clay are deposited in fan shape where the two meet.

• Over time the build up of deposited material breaks through the water surface and forms new land- a delta.

The Nile Delta

The Niles Delta

• The Nile Delta is about 100 miles in length and covers over 149 miles of coastline. According to the World Resources Institute, the Delta only covers about 2.5 percent of Egypt's total land area, yet over one third of Egypt's total population lives there.

Flooding

• Annual flooding of the Nile River brought fertile soil to the region. Extended periods of high water and periods of drought, however, would destroy crops. In 1970, the Aswan Dam was built to regulate the flooding.

Fun Fact

• In 1799, the famous Rosetta Stone was discovered in the Nile Delta's small village of Rosetta. This engraved stone was the key to unlocking ancient Egyptian hieroglyphics.

Types of Delta

• An arcuate delta is a gently curved delta just like the Nile

• A birds foot delta is rather more complex in its shape, and represents deposition along the edges of several distributaries.

• https://www.youtube.com/watch?v=qyVbJukc-Vs

Thank you