3. Rivers Flashcards
abraison
a type of erosion where rocks are thrown against the side of the river and they get grounded into smaller pieces
attrition
a type of erosion involving rock fragments being grounded together to become smaller, smoother and rounder
braiding
a river feature consisting of islands of sediment deposited in the river channel in its middle course
confluence
the point where two rivers (including tributaries) meet
corrosion
a chemical process involving the dissolving away of rock, particularly limestone and chalk
drainage/river basin
an area of land which is drained by a single river and its tributaries
fault
a line of weakness in rock
floodplain
the flat area either side of a river which is regularly flooded
gorge
a deep, steep-sided valley
hydraulic action
when the water bashes against the side of a river and rock break off
impermeable
not allowing water to pass through
infiltration
the movement of water from surface into the soil
interception
precipitation landing on plants, trees or buildings
mouth
the point where a river enters a sea, ocean or lake
oxbow lake
the cut-off remnant of a meander found in the lower course of a river
porous
able to hold water like a sponge, allowing it to flow through
permeable
allowing water to flow through
plunge pool
found at the bottom of a waterfall and is formed by erosion
reservoir
a lake behind a dam
river cliff
a steep, undercut area on the outside of a river meander
run off
the movement of water across a surface
saltation
the transport of sediment in a hopping fashion in water
scree
piles of broken rock found beneath steep rock faces
slip-off slope
a gently-sloping area formed on the inside of a river meander
spur
a rocky projection found in the upper stage of a river’s course
source
the beginning of a river
suspension
the transport of silt in water
throughflow
the movement of water through the soil as part of the water cycle
traction
the transport of heavy sediment in a rolling motion on the sea bed
tributary
a river joining a larger river
waterfall
a point on a river where water falls vertically
describe a drainage basin
- It starts at the source
- All of the tributaries eventually connect to the main river channel
- Eventually, it meets the mouth
- It drops all of the remaining sediment and that causes a delta
describe transportation
the movement of materials
describe deposition
the laying down of sediment carried by the river
describe weathering
the breaking down of the surface of a material
describe erosion
the wearing away of material
upper valley characteristics
*Hydraulic action, abrasion & attrition dominant processes
*Traction and saltation at high flow
*Load size is large and jagged
*V-shaped valleys
middle course characteristics
*Channel is deeper and wider
*Vertical erosion decreasing in importance, more lateral (side) erosion and deposition
*Suspension is the main transportation type
*Load becomes smaller and less jagged
lower course characteristics
*Channel is at its widest and deepest
*Deposition more important than erosion
*Fine material (suspended load - what makes the river look dirty) deposited
*Large amount of load but the size is very small and very rounded
how are V-shaped valleys created
- River erodes downwards
- The sides are cut down and attacked by weathering
- The loosened material slowly creeps down the slope by gravity or is washed by rainwater
- It results in a steep sided valley with the shape of a V.
how are waterfalls created
- The top part of the rock is hard and the bottom part is soft. The water erodes the soft rock more than the hard rock as the soft rock is less resistant, which makes it steep.
- The erosion of the soft rock creates the plunge-pool and the overhang. Here hydraulic action and attrition start to make it deeper and dig in more.
- The ledge above the plunge pool collapses over its own weight and also since it has northing to support it. The rock is then transported by different types of weathering. The material is carried downstream.
- The waterfall retreats upstream and a gorge is created. Now, the cycle is restarted.
how are ox-bow lakes created
- It starts as a river with bends.
- Erosion makes the river wider
- Then, due to erosion, it becomes circular. The water still goes round the curve
- The water starts to go in a straight line.
- Deposition makes the curve separate and then the top looks like a horse magnet.
examples of flood causes
*Climatic conditions (rain, steep-sided valley, urbanisation)
examples of flood effects
*Buildings damaged, people die, crops ruined, insurance claims, drinking water becomes dirty
examples of flood management
hard = more expensive and uses more raw materials e.g. dam
soft = cheaper and works with nature e.g. planting plants to soak up water
describe a floodplain
1 before flood: wide, flat valley plain caused by erosion and deposition by moving meanders & river contained within banks during normal flow
2 during flood: Smaller material carried further & during flooding, river flows over its banks & larger material deposited next to channel as speed and energy is lost
3: Layers of material from successive floods & leevees (bank) increase in height & fertile flat floodplain
delta
the dropped sediment once the river reaches its mouth
rapids
areas of shallow, fast-flowing water in a stream
meander
a bend in the river
cross section of a meander
*sediment deposited on the inside bend and that creates the slip-off slope
*on the inside (shore) there is a slower current
*on the outside there is a faster current
*fine material is in suspension
*bank on the outside being undercut by lateral erosion
