Rivers And Flood Management Key Terms book 2 Flashcards
Define potholes
Cylindrical depressions in the solid rock of a river
Define drilling and describe the process
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
Define attrition
When eroded rocks collide and cause them to become smaller and more rounded
Define hydraulic action and say when it is at its strongest
The pressure of the water breaks rock particles away from the bed and banks. Its strongest in Rapids and during floods
Define corrosion
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
Define cavitation
Air bubbles in turbulent stretches of water implode causing shockwaves that break pieces of rock off the banks and bed
Define solution
Dissolved substances that are carried in the water
Define suspension
Very fine material such as silk and clay, whipped up by turbulence and carried along
Define saltation
Larger particles, such as pebbles or gravel that bounce along the river bed
Define traction
Very large particles e.g. Boulders that are pushed along the river bed
Define base level
The level at which a river would erode to
Define rapids
Found in steeper sections of the long profile characterised by a solid rock bed with a very turbulent flow
Define a meander
A sweeping or looping bend that forms in the middle and lower stages where a river can become very sinuous
Define sinuous
Very bendy
Define base flow
Low flow
Define the thaweg of a river channel
The area in a channel with the fastest flow
What are pools and riffles in a river channel?
A pool is a deepened area in a river channel
Riffles are shallower areas in a river channel
Define helicoidal flow
A corkscrew like flow which swings from side to side of the channel as well as moving vertically
Define a point bar/slip off slope
An area on the inside of a meander on which deposition occurs
define meander migration
When the entire meander moves downstream, the movement is both lateral and downstream
Define a bluff
A type of broad rounded cliff which occurs at the edge of a river valley after meander migration
Define an oxbow lake
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
Define a flood plain
Areas of low-lying ground next to rivers that is naturally subjected to flooding
Define a levee
A natural embankment, long ridges of sediment deposited alongside a river by overflowing water
Define the competence of a river channel
The maximum particle size a river channel is able to transport
Define a braided channel
Rivers that have multiple channels within them
Define an eyot
The islands that are created in braided rivers due to deposition
Define the hydraulic radius of a river channel
How much water is in contact with the river sides and riverbed, it is usually measured in metres squared
Define a river delta
A landform, formed when a river deposits its load at its mouth
Define the capacity of a river
The maximum load a river can transport
Define flocculation
Where an electrical charge causes clay particles to stick together and as a consequence increase their weight and cause deposition
Define rejuvenation
This is the renewed vertical erosive power of a river and is caused by a change in sea level
Define a knickpoint
A sudden change in a river’s gradient, it marks the point where cutting down due to rejuvenation is taking place
Define river terraces
Formed when a rejuvenated river cuts down through a flood plain, leaving the old flood plain above the level of the present river
Define incised meanders
A meander which has experienced down cutting through rejuvenation
