1.3 River Channel processes and Landforms Flashcards
(30 cards)
What is abrasion?
Waters throw sand, shingle and cobbles at the landscape to erode banks. aka Corrasion
What is Solution (erosion) ?
Chemicals is the water dissolve rocks such as chalk and limestone. aka Corrosion
What is Hydraulic action?
Erosion produced by the energy and power of the water as it hits banks and landscape. Pressure create by water forced into cracks.
What is attrition?
Erosion where particles bang together so they become smaller and more rounded.
What is traction?
Movement of large boulders and stones as they roll along the river bed
What is saltation?
Small rocks bounce along the river bed
What is suspension?
Very small particles of sand and silt carried in the flow
What is solution (transport) ?
Dissolved minerals from rocks within water move with water
What is the Hjulstrom Curve?
A graph used by hydrologists and geologists to determine whether a river will erode, transport, or deposit sediment.
What is velocity?
The speed in a direction.
What is discharge?
The amount of water flowing down a river at any one time. Discharge is measured in cubic meters of water per second (cumecs)
What is laminar flow?
The horizontal movement of water downwards, over a smooth surface, in a simple sheet, with no eddies or meanders. Very rare but most common in lower course of river and straight channels.
What is turbulent flow?
Occur in complex, winding channels where water flowing in a river is subject to friction, both with the bed and the banks. This leads to chaotic flow and a series of erratic ‘eddies’ which are both horizontal and vertical.
What is helicoidal flow?
The line of fastest flow in a river channel follows a corkscrew or spiralling path as the river moves downstream. Occurs in meanders and is responsible for alternating erosion and deposition in meanders.
Why are straight river channels rare?
Helicoidal flow dominates in most rivers and makes them meander.
Where are the most pronounced meanders found?
Floodplains where lateral erosion occurs due to soft nature of river banks. Rivers mainly meander due to helicoidal flow.
What are braided river channels?
Channels that contain a large number of islands and bars made of sediment. Braiding results from deposition of sediment in river bed during a time of falling discharge. River splits as it flows around these deposits
What is a river cliff?
The steep outer bank of a river meander.
What is a point bar?
The material deposited on the gentle inner bank of a river meander.
What is an oxbow lake?
An old meander which has become cut off from the river. Often filled with marshy vegetation.
What are riffles?
Areas of shallow water along the course of a river, often spaced regularly between deeper areas known as pools.
What is a gorge?
A deep, steep-sided valley.
What is a bluff?
A low hill at the side of a flood plain.
What is a floodplain?
Flat land next to a river which is liable to flood when river rises after heavy rainfall. Often badly drained with marshes and oxbow lakes.
