Geography Lesson – River Processes

LESSON AIM

1) To develop students’ understanding on River Processes.

2) To let the students familiar with the differences of the River Erosion, Transportation and Deposition.

Outline

Here, we will learn on these processes:

– River Erosion

– River Transportation

– River Deposition

River Erosion

River Erosion

River Erosion is the river erodes away the bed and banks of its channel vertically and laterally.

Vertical erosion is the downward erosion which deepens the river channel.

Lateral erosion is sideward erosion which widens the river channel.

The work of erosion depends on the energy of the river.

When a river has greater energy, it has more erosive power

Types of River Erosion

There are the 4 ways on how the river erode the bed and the bank.

• —  Corrasion
• —  Attrition
• —  Solution
• —  Hydraulic Action

Corrasion

—  It is the grinding of rock fragments carried by the river against the banks and bed of the channel.

—  This grinding action widens and deepens the channel.

—  This process is also called as Abrasion

Attrition

—The knocking of rock fragments in the water against each other. The fragments are broken into smaller and become smoother pebbles.

Solution

—The process of the water reacts chemically with soluble minerals in the rocks and dissolve them.

Hydraulic Action

—The force of river flow helps to break the rock and dragging them away from the bed and the banks of the river.

River Transportation

—A river uses its energy to carry or transport eroded materials such as mud, sand, boulders and dissolved materials. These materials are called its load.

—River transport their load by 4 processes.

Types of River Transport

• Traction
• Saltation
• Suspension
• Solution

Traction

—Large particles such as pebbles and boulders roll and slide along the river bed.

Saltation

—Large particles such as gravel are lifted and then dropped again so that they bounce along the river bed in a series of hops.

Suspension

—Smaller particles such as clay, silt and fine sand are carried along without touching the river bed.

Solution

—Dissolved materials containing minerals such as calcium and sodium are carried in the water.

—They cannot be seen by our naked eye.

Exercise: Please draw and label all the River Processes

Since we have learned all the River Erosion and River Transportation, click here to get the summary of all the types of River Processes.

River Landforms

—Potholes are holes in the river bed.

—They vary in size from a few centimetres to several metres in diameter.

Potholes are formed by Corrasion.

Potholes

—Pebbles carried by the river are swirled around on the river bed. This action erodes the rock on the river bed forming potholes.

—Over time, they may widen and join with other potholes to form larger potholes, and the whole river bed is deepened.

Rapids

—Rapids are stretches of fast-flowing water tumbling over a rocky-shallow riverbed.

—Different resistance among rocks cause rapids.

—They are formed when the water goes from one hard rock that resists the water’s erosion to a softer rock that is easier eroded.

—As result, the rapids form a series of steps.

Waterfalls

—A waterfall is formed where there is the sudden fall in height. The river plunges and hits the bottom of the river bed with great force.

—Rocks are swirled around to form a deep pool at the river bed known as a plunge pool.

Gorges

—Gorges are formed when rivers erode vertically through resistant rocks.

—Since these rocks are not easily erode , the sides of the valley remain steep.

—Gorges is a deep valley, narrow and steep sided.

River Deposition

There are many types of River Deposition such as:

1. Floodplain
2. Meanders
3. Delta
4. Ox-Bow Lake

Floodplain

—A floodplain is a low-lying plain on both sides of a river that has repeatedly overflowed its banks and flooded the surrounding areas.

—When the floods subside, alluvium is deposited on the floodplain.

—The larger materials, being heavier, are deposited at the river banks while the finer materials are carried and deposited further away from the river.

—The larger materials at the river banks build up into embankment called levees.

Delta

—A delta is a flat piece of land built-up from layers of sediments deposited by a river where it enters a lake or calm sea.

—The river may have to branch into smaller distributaries to carry the water to the sea.

Meanders

—Meanders are loop-like bends in a river. The water flows round the meander in a spiral manner.

—This causes erosion to take place on the outer bank and deposition on the inner bank.

—Gradually, a steep river cliff is formed on the outer bank, making it concave in shape.

—On the inner bank, deposition of alluvial materials produces a gentle slip-off slope and the bank takes on a convex shape.

Ox-Bow Lake

—An oxbow lake is a crescent -shaped lake formed on a river when a meander has been cut through and abandoned.

—When a river meanders in very big loops, the outer bank is so rapidly eroded that the river cuts through the narrow neck of the meander.

—The river then flows straight through the channel. When deposition seals off the cut-off from the river channel, an oxbow lake is formed. It may silt up and eventually dry up.

1) The river is starting to meander. Erosion is greater on the outside of the bend, deposition more on the inside.

2) Large meanders have formed

3) The river cuts through the meander, leaving a straighter section and an ox-bow lake.

—

Conclusion

So, we all have learned on all about River Erosion, River Deposition and River Transportation

Here is a short clip of showing on all the types of River Processes.

Note: Download the notes for a quick simple revision on about the processes. If you have missed it,  here is the link again