Hydrology and fluvial geomorphology 1.3

Question 1

What are the types of erosion in the river channel?

Answer 1

Corrasion - processes of rocks scraping and grinding causing wearing away.
Solution - processes of water dissolving parts of rock/soil - soluble rocks eg chalk and limestone.
Hydraulic action - sheer force of water can cause rocks to fragment.
Cavitation - where water forces its way into cracks

Question 2

What are the types of transportation in the river channel?

Answer 2

Traction - rolling
Suspension - carried in flow
Solution - dissolved material in flow
Saltation - bouncing

Question 3

What are the different types of river channel?

Answer 3

Straight - single channel mainly in the upper course
Meander - series of bends and curves mainly in middle and lower course
Braided - large deposits of sediment in the channel mainly in lower course

Question 4

What are the different types of flows in the river channel?

Answer 4

Laminar - parallel streams with an orderly flow.
Turbulent - disorderly flow with changes in velocity.
Helicoidal - corkscrew movement responsible for erosion and deposition within meanders.

Question 5

What does the Hjulström Curve show?

Answer 5

A graph that shows how the velocity of a river affects the rivers material

Question 6

What is the order of material size within the Hjulström Curve?

Answer 6

Can Sally Send Pizza Boxes

• Clay
• Silt
• Sand
• Pebbles
• Boulders

Question 7

Mannings Equation measures the roughness of the riverbed. How is it calculated?

Answer 7

Mannings N= (〖Hydraulic radius R〗^0.67 x 〖Channel Gradient S〗^0.5) / (Mean velocity of flow V)

Question 8

Landforms of the upper course: potholes

Answer 8

Potholes are formed by turbulence which swirls pebbles around in a depression on the river bed.
This enlarges the pothole by abrasion. Evidence that vertical erosion predominates in upland rivers.

Question 9

Landforms in the upper course: rapids

Answer 9

Rapids are common in the upper course of the river. Form at places where the gradient is steep and the river bed is rocky, resistent to erosion and irregular.

Question 10

Landforms in the upper course: waterfalls and gorges

Answer 10

Waterfalls form where a horizontal layer of hard rock lies on top of layer of softer rock in a river valley. Soft rock is eroded at a faster rate, gradually forming a plunge pool. Splashing water and eddy currents undercut the hard rock eventually forming an unsupported overhang. The overhang then collapses into the plunge pool. Over time, the waterfall will retreat upstream, leaving a gorge.

Question 11

Landforms of the lower course: floodplains

Answer 11

A floodplain is the flat land next to the river which is liable to flood when the river rises after heavy rainfall. It is formed of alluvium because it is formed by deposition of material from the river. It facilitates lateral erosion which causes the meander belt to migrate across the floodplain.

Question 12

Landforms of the lower course: levees

Answer 12

Natural embankments formed on each side of the river after a rainfall event when the rivers bank is burst. The largest particles are deposited first due to requiring the most energy to be moved.

Question 13

Landforms produced by sediment: deltas

Answer 13

Depositional features which form when the river meets to sea or runs into a lake. The loss of velocity leads to a loss of energy and the rivers load is deposited. Flocculation of clay occurs due to charged ions in the sea water and then settles to the bottom. Deposition blocks the river into smaller channels called distributaries. Over time, the deltas grows outwards into the sea forming a large flat marshy extension.

Question 14

Name an example of a densely populated delta.

Answer 14

Ganges delta in India and Bangladesh

Question 15

What are the three different types of delta?

Answer 15

Arcuate
Cuspate
Bird’s Foot

Question 16

Description and example of an arcuate delta.

Answer 16

Fan-shaped and form when the tidal range is quite low with a strong movement of sediment in one direction along the coast (e.g. longshore drift). This keeps the seaward edge of the delta smooth in shape. Example: The Niger Delta in West Africa.

Question 17

Description and example of a cuspate delta.

Answer 17

Shaped like an arrowhead due to a low tidal range with two offshore currents in opposite directions at different times of the year. Example: Ebro delta in Spain

Question 18

Description and example of a Birds foot delta.

Answer 18

Formed where the tidal range is low and where the river currents are strong. No clear offshore current to shape the delta so each distributary builds the land out into the sea. Example: Mississippi delta in the Gulf of Mexico.

Question 19

Formation of Meanders and Oxbow Lakes.

Answer 19

Found at any point along the course of a river consisting of erosional and depositional processes. Erosion occurs on the outside of the bend due to the soft alluvial floodplain and the helicoidal thalweg; this river cliffs as the bank is undercut. Deposition occurs on the inside bends where water velocity is at its slowest; forming slip-off slopes and point bars. The meander becomes more sinuous and eventually, the thin neck breaks and water begins to flow through its shortest course. The meander eventually becomes cut off due to deposition, forming an oxbow lake.