DATE: 05-09-2014 CLASS: Year 10 SUBJECT: Geography TOPIC: River Processes

DATE: 05-09-2014 CLASS: Year 10 SUBJECT: Geography TOPIC: River Processes TEACHER: Mr. Abiola TEACHER’S E-MAIL: abiola.ibukun@nisng.com

You can check the links below after going through the lesson The textbook is on • http://ih-igcse-geography.wikispaces.com/1.4.+Processes+ • LEARNING OBJECTIVES • By the end of the lesson the student should be able to : • Identify and name river processes. • Differentiate and describe each river process.

Content: Introduction • Main job of river is to transfer water from source to sea. • Most energy is used to keep the water flowing, as it needs to overcome the friction of the bed and the banks. • Any spare energy wears away the banks and carries a load. • What is the load of a river likely to be?

Besides getting to the sea, …. • The 3 processes a river is involved in are • The wearing away of the river banks • The movement of rocks and silt from one place to another • The setting down of the river’s load • River is • an agent of erosion • an agent of transport • an agent of deposition • Agent = something that is capable of causing a certain effect.

Erosion Transportation Deposition

Corrasion or abrasion is the grinding of rock fragments carried by the river against the bed and banks of the river. This action causes the channel to widen and deepen. This grinding is most powerful in flood time when large fragments of rock are carried along in the river bed. Erosion

Attrition is the collision of rock fragments in the water against one another. The rock particles are broken into smaller pieces and become smoother the longer the process continues. Erosion

Erosion – the last 2! • Solution or corrosion is the process by which river water reacts chemically with soluble minerals in the rocks and dissolves them. • An additional process is also at work caused by the force of the water itself known as Hydraulic action. • In this rocks are dragged away from the bed and banks by the force of the running water. • When water from a fast moving stream enters minute cracks in a rock, the pressure exerted weakens and eventually breaks up the rock

Transportation • Tractionis where boulders or stones are rolled along the stream bed by the force of the water. • Saltationis where pebbles or small stones are bounced along the stream bed by the force of the water.

Transportation • Suspension is when fine particles such as clay, silt and fine sand are carried along in the river. • Solution is when dissolved materials containing minerals like calcium and sodium are carried in the water and are invisible to the naked eye.

Deposition • This happens when the river no longer has enough energy to carry the load • When the river is in full flood like the Wye last weekend, the river has enough energy to transport large rocks and tree trunks as well as smaller stuff and mud in suspension, turning the river a murky brown • However, at some point later on, after the rain has eased off, less run-off will be reaching the river and the larger stuff, will be deposited as the river slows and the is less capacity. • In addition, in general, the more level the river channel, the smaller the load that can be transported, with anything to large being deposited.

So if you look on the river bank and see what has been deposited there, you have a good idea of whether you are looking at the upper course, the middle course or the lower course.

For: Transportation Erosion Deposition Which of these dominate depends on the geology, the slope and the speed of the river. For instance, if the rock is hard, there will be very little erosion In the upper course the speed of flow is slower due to friction so vertical erosion, counts more. Transportation only takes place when there is heavy rainfall and the capacity is raised. In the middle course, the speed is greater. However larger load items deposited while the sediment is still carried because there is quite a bit of lateral erosion. In lower course it is even slower and only silt is carried and very little erosion is carried out. However, after rain, there is more water going faster and so there is more erosion and transportation. So in general the gradient becomes more gentle as the river goes down stream, the channel becomes wider and deeper; velocity and discharge increases; more sediment is carried. What the river does and where

In summary • You need to the know the 3 processes and the various ways they are achieved • Erosion: Corrasion or abrasion, Attrition, Solution or corrosion, Hydraulic action. • Transportation: traction, saltation, suspension & solution • Deposition • That there is vertical erosion in the upper course, lateral erosion in the middle course and not much erosion in the lower course. • That was is being transported gets smaller as it moves down stream until only sand grins and silt are carries in the lower course.

Homework • Name and describe four conditions that is required for the river processes to be a (a) Erosional (b) Transportational (c) Depositional

Note to students: • Please note that all class/lesson tasks MUST be done and submitted promptly (Daily). • If and when there is any topic or concept you don’t understand kindly highlight it using a yellow colour band e.g.the force of Gravity is the force that keeps the earth in orbit around the sun, Gravity also holds us to the earth's surface. • Submit all the finished tasks through the email provided.

DATE: 05-09-2014 CLASS: Year 10 SUBJECT: Geography TOPIC: River Processes