Rivers

Question 1

What are the 4 types of erosion in a river and what does each type involve?

Answer 1

Attrition- The load of a river grinds against itself making it smaller, rounder and smoother.

Abrasion- The load of a river hits the sides of the river channel.

Corrosion- Acids and salts in the river dissolve the sides of the river.

Hydraulic Action- The river forces air into cracks in the river channel under high pressure. As the river flows, the air is released suddenly with an explosive force.

Question 2

Name the four different types of transportation in rivers and describe them.

Answer 2

Traction- Large boulders and rocks are rolled along the river bed, most common near the river source, since the load is larger.

Saltation- Small pebbles and stones are bounced along the river bed, most commonly near the source.

Suspension- Sediment is held in suspension in the water because it is fine and light. Near the river mouth.

Solution- Soluble particles are dissolved in the water. This may cause the water to become slightly acidic. Varies along the river depending on the presence of soluble rock.

Question 3

What is the discharge of a river and how is it measured?

Answer 3

River discharge is the volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in cubic metres per second (cumecs)

Question 4

What does the discharge of a river depend upon?

Answer 4

Precipitation- Large amounts of precipitation means more water will enter the river channel via surface runoff.

Permeability of ground around the river bank- If the ground is impermeable, there will be more surface runoff.

Vegetation- Vegetation will intercept any precipitation and it will take longer for it to reach the ground, increasing the chance it will infiltrate the ground.

Question 5

How is a Delta formed?

Answer 5

Depositional landform: formed when a river meets a body of water with lower velocity
Flocculation occurs and causes deposition

Deposited materials are not washed away due to low tidal range and a lack of current

Question 6

Different types of Delta

Answer 6

Arcuate Deltas:
River meets sea, triangle shape

Cuspate deltas:
V-shaped, river meets sea

Bird’s foot delta:
When river current has more energy than waves.

Question 7

What are Levees and how do they form?

Answer 7

Natural embankments when the river floods (not permanent)

When a river floods, it deposits its load on the flood plain due to a dramatic drop in the river’s velocity due to increasing friction

Largest and heaviest load is deposited first and closest to river bank, often on the very edge forming raised mounds

Repeated floods cause the mounds to build up and form levees

Question 8

What is an oxbow lake and how do they form?

Answer 8

An evolution of meanders that undergo extensive deposition and lateral erosion

Strong erosion takes place on the outside bend of a meander while deposition takes place on the inside bend

The river erodes the outside of the bends where the energy is greatest due to helicoidal flow, and deposits on the inside, narrowing the neck of the meander over time

Over time the two sides of the neck erode backward until the neck breaks to form a new river path

New deposition seals off the ends and the cut-off becomes an oxbow lake

Question 9

What are the types of drainage pattern?

Answer 9

Dendritic, radial, trellised

Question 10

Explain why many people live near to rivers.

Answer 10

Fertile land;
Farmers obtain high yields of crops;
Land is flat so easy to build on/transport/trade; Communications on land are easy along flood plain;
Fishing/food supply from river;
Water supply from river;
HEP/generate energy;