Rivers And Flood Management Key Terms book 2

Question 1

Define potholes

Answer 1

Cylindrical depressions in the solid rock of a river

Question 2

Define drilling and describe the process

Answer 2

A special type of abrasion where pebbles collect in a depression as the water flows past it causes the rocks to rotate in the hollow and ‘drill down’ into the bed rock

Question 3

Define attrition

Answer 3

When eroded rocks collide and cause them to become smaller and more rounded

Question 4

Define hydraulic action and say when it is at its strongest

Answer 4

The pressure of the water breaks rock particles away from the bed and banks. Its strongest in Rapids and during floods

Question 5

Define corrosion

Answer 5

The dissolving of rocks by chemical processes C02 dissolves in water to form a weak acid which reacts with rock like limestone and chalk, breaking them down

Question 6

Define cavitation

Answer 6

Air bubbles in turbulent stretches of water implode causing shockwaves that break pieces of rock off the banks and bed

Question 7

Define solution

Answer 7

Dissolved substances that are carried in the water

Question 8

Define suspension

Answer 8

Very fine material such as silk and clay, whipped up by turbulence and carried along

Question 9

Define saltation

Answer 9

Larger particles, such as pebbles or gravel that bounce along the river bed

Question 10

Define traction

Answer 10

Very large particles e.g. Boulders that are pushed along the river bed

Question 11

Define base level

Answer 11

The level at which a river would erode to

Question 12

Define rapids

Answer 12

Found in steeper sections of the long profile characterised by a solid rock bed with a very turbulent flow

Question 13

Define a meander

Answer 13

A sweeping or looping bend that forms in the middle and lower stages where a river can become very sinuous

Question 14

Define sinuous

Answer 14

Very bendy

Question 15

Define base flow

Answer 15

Low flow

Question 16

Define the thaweg of a river channel

Answer 16

The area in a channel with the fastest flow

Question 17

What are pools and riffles in a river channel?

Answer 17

A pool is a deepened area in a river channel

Riffles are shallower areas in a river channel

Question 18

Define helicoidal flow

Answer 18

A corkscrew like flow which swings from side to side of the channel as well as moving vertically

Question 19

Define a point bar/slip off slope

Answer 19

An area on the inside of a meander on which deposition occurs

Question 20

define meander migration

Answer 20

When the entire meander moves downstream, the movement is both lateral and downstream

Question 21

Define a bluff

Answer 21

A type of broad rounded cliff which occurs at the edge of a river valley after meander migration

Question 22

Define an oxbow lake

Answer 22

A curved horse-shoe shaped body of water that forms when a wide meander fro, the main stem is cut off creating a free-standing body of water

Question 23

Define a flood plain

Answer 23

Areas of low-lying ground next to rivers that is naturally subjected to flooding

Question 24

Define a levee

Answer 24

A natural embankment, long ridges of sediment deposited alongside a river by overflowing water

Question 25

Define the competence of a river channel

Answer 25

The maximum particle size a river channel is able to transport

Question 26

Define a braided channel

Answer 26

Rivers that have multiple channels within them

Question 27

Define an eyot

Answer 27

The islands that are created in braided rivers due to deposition

Question 28

Define the hydraulic radius of a river channel

Answer 28

How much water is in contact with the river sides and riverbed, it is usually measured in metres squared

Question 29

Define a river delta

Answer 29

A landform, formed when a river deposits its load at its mouth

Question 30

Define the capacity of a river

Answer 30

The maximum load a river can transport

Question 31

Define flocculation

Answer 31

Where an electrical charge causes clay particles to stick together and as a consequence increase their weight and cause deposition

Question 32

Define rejuvenation

Answer 32

This is the renewed vertical erosive power of a river and is caused by a change in sea level

Question 33

Define a knickpoint

Answer 33

A sudden change in a river’s gradient, it marks the point where cutting down due to rejuvenation is taking place

Question 34

Define river terraces

Answer 34

Formed when a rejuvenated river cuts down through a flood plain, leaving the old flood plain above the level of the present river

Question 35

Define incised meanders

Answer 35

A meander which has experienced down cutting through rejuvenation