4.6 Flashcards
River Discharge
The amount of water discharged from a river at a certain point.
Increases downstream, due to a larger drainage basin, more tributaries and a larger river channel
Channel width
How wide a river is at a point.
Increases downstream due to larger amounts of discharge and therefore more lateral erosion, as well as softer and flatter land in the lower course
Channel depth
How deep the channel is at a point in the river
Increases downstream due to larger discharge and therefore more vertical erosion, as well as a softer river bed in the lower course
Velocity
How fast water flows in a river.
Increases downstream due to less roughness of the river bed and larger river channel meaning a higher hydraulic radius as less proportion of the water comes into contact with the river bed, increasing river efficiency.
This counteracts the flatter gradient than the upper course
Sediment load volume
The amount of sediment held by the river
Increases downstream due to higher river volume, which can hold more sediment and higher energy/velocity to hold it. The sediment is also smaller and easier to carry in large volume by saltation and suspension
Sediment particle size
The size of the sediment particles in a river
Decreases downstream due to higher velocity and therefore more attrition, meaning large pieces become smaller
Channel bed roughness
How rough the river bed is
Decreases downstream because large rocks are eroded or removed faster by abrasion and attrition or traction due to larger river volume and higher velocity
Slope angle
The gradient of the river
Decreases downstream. Vertical erosion becomes less prevalent than lateral and saltation becomes more prominent than traction lower down
Hydraulic action
The sheer force of water eroding river banks and beds
Abrasion
The load in a river eroding its banks and bed
Attrition
The load of a river clashing together and eroding
Vertical erosion
The river erodes mainly downwards into the bed due to gravity
Lateral erosion
The river erodes mainly outwards into the banks due to soft rock and river volume
Formation of waterfalls
Waterfalls occur when a layer of hard, resistant rock lies over one of soft rock in the upper course of a river.
The river bed load swirls around at the foot of a cliff it runs off, gradually eroding the river bed at the foot of the waterfall creating a plunge pool.
The soft rock is eroded more quickly, undercutting the harder rock to make an overhang until it collapses under its own weight, causing the waterfall to retreat and the process to repeat
Formation of gorges
When a water retreats over many years, it creates a steepsided valley with a river running through it and a waterfall at one end, called a gorge
Formation of V-shaped valleys
V- shaped valleys occur when, in the upper course of a river, the water vertically erodes through hydraulic action and abrasion.
Then on either side of the river, the rock is eroded by biological, chemical and mechanical weathering. Eventually, once lubricated by precipitation, the rock slides along the bedding planes , by mass movement, into the river, where it is removed as load, leaving a v shaped valley
Formation of interlocking spurs
These are formed when in the upper course, a river flows around the hard rock of hills, where the rock is softest, following the easiest route downstream and eroding to creating interlocking spurs
Traction
Large sediment like boulders are pushed along the river bed by the force of the water
Saltation
Pebble sized particles are bounced along the river bed by the force of the water
Suspension
Small particles like silt and clay are carried along by the water
