Theme A- Part 2- River Processes And Features Flashcards
What is discharge
The amount of water flowing in a river at any point in a certain time
What is load
The amount of material a river is carrying ranging from small sediment to large boulders
What changes occur to the river as we go downstream
Why
Gets wider and deeper because of more lateral and vertical erosion taking place
Increasing discharge because of adding tributaries
Increasing velocity= less friction to overcome as upper couse has angular rocks and shallow channel
Why is the upper course angular and the lower course rounded
Weathering of bare rock happens in upper course because it is more exposed, the rock falls down the steep valley sides into the river. It will still be very angular
As the rocks go down the river the rocks hit the side of the river bed and other rocks which are apart of the load.
This knocks off any sharp edges making the rock smooth and rounded by the time it reaches the lower course
What is vertical (downwards) erosion
When the load of a river consists of coarse products that scrap and rub against the channel of the river, creating steep sides
The happens in lateral erosion?
Points of a river channel where the river is flowing especially fast, the water itself has so much energy it can wash away the banks which cause the bank to be undercut and collapse
Side wards erosion
What is abrasion
The grinding of rock fragments ,carried by the river, along the river bed and banks which deepen and widen the channel
What is the process of solution
When the river water reacts with the soluble minerals in the rocks which dissolves them
What is attrition
The collision of rock fragments, which break down rocks and makes them smoother
What is hydraulic action
The mechanical weathering based on the shear force of water, eg. Undermining river banks on the outside of the meander and forcing air into exposed rocks in waterfalls
What is traction
The rolling of large rocks along the river bed
Requires a lot of energy
The bed’s biggest load is only moved in times of floods
What is saltation
The bouncing along of a medium sized load along the river bed
What is suspension
The smallest load of the river eg. Clay and sand
Held up by the water making it look opaque
What is the transportation process of solution
When soluble minerals are dissolved in water and carried by river
This can change the colour of the river
What is deposition
How does it occur
When is it likely to occur
When the velocity (speed and direction) of the river decreases therefore the energy also decreases, this mean the river cannot hold the load anymore dropping of the load starting with the biggest first
When a river meets the sea as the flow decreases
Where the river gets shallow
When there has been a sudden increase of load eg. a landslide
When a rivers floods on to a flood plain, where it flows slowly
How does a water fall form
Usually in the upper course, where it is mountainous
When there is a layer of hard rock with softer rock underneath it
The river erodes the softer rock so a step is formed
Due to hydraulic action and erosion the step is deepened and a waterfall is formed
Eventually erosion undercuts the hard rock making it unstable and it falls
The waterfall retreats backwards leaving a gorge
What is a meander
Formed when the gradients (slope) of a river levels out
Has continuously changing features of the result of a changing velocity (speed and direction) across the river channel
What changes occur on the outside of the river
The water flows very fast (high velocity) so vertical erosion takes place, this undercuts the side bed creating a river cliff and deepening the channel
What happens in the inside bend of a meander
Velocity (speed and direction) is lowest here so little energy so little erosion
Cannot hold load any more, so the river deposits creating a slip-off slope
What part of a course of a river is a meander being formed and réforme d
The middle and lower course
How is an ox-bow lake formed
When a two meanders get bigger and bigger and their necks become closer and closer, until they join and the meander has been cut of
How are flood plains formed
When a meander goes back and fourth it creates flat land on each side of its channel
Due to floods dropping its load sediment is built up
It is called alluvium which is very fertile meaning crops can grow on it
How are levees formed
When rivers flood it loses the velocity and therefore the energy, so it deposits, the big load first
What happens during a low flow
The river doesn’t have any energy to carry its load so it deposited on to the river bed
If the velocity comes really slow the amount of water 💦 falls and the river may dry up altogether
If load is deposited on the bed and not washed away at the end of the season the river bed can rise and therefore floods are more common
How are floodplain protected from floods
Levees, they can be artificially strengthened and raised
What are rivers used for in MEDCs
Cattle for grazing
Factories, water for cooling
Housing
What are some river uses in LEDCs
The floodplain provides good patty for rice 🍚
The alluvium provides good fertile land for crops
What is a river
An important resource to everyone so that any changes to them have to be sustainable for future generations
What are other uses of rivers
Water- irrigation and water supply
Power- hydroelectricity and water mills
Food- 🐟 is main source of protein in LEDCs
Transport- 🚂 and roads
Waste outlet- effluent is drained out to 🌊
What are five physical reasons for floods
Heavy rainfall= surface runoff= flash flood
Prolonged rain eg. monsoon= saturates the ground= long, slow flood
Melting of snow ❄️ or glaciers= increased discharge in spring= rivers overflow
Impermeable rock or clay soil= infiltration cannot happen, increased surface runoff= area of high risk of regular floods
Frozen ground= when precipitation cannot be infiltrated into ground, more surface runoff= area high risk of regular floods
Give four more human factors that contribute to floods
Deforestation= less roots support for soil, less water being used up by 🌱, 🍁 to break big rain droplets=more surface runoff = more chance of flooding
Urbanisation= more tarmac, concrete and impermeable surfaces= more surface runoff= more chance of floods
Narrowing a channel eg. building a bridge= river has less water capacity= more chance of flooding
Building of levees (embankments)= provides short term protection, but…= if flooding exceeds it= severe flash flood
Give some detail about the River Derwent flood
Happened in 1999
The River Derwent, Yorkshire, experienced worst flood in 70 years
Some areas effected where 1.5 meters deep in water and two main roads had to be closed
What are the physical reasons the River Derwent flooded
Heavy rainfall, from 28th February to 11th of March 125mm of rain fell over North Yorkshire moors
Already saturated ground, from recent events
Time of year, ❄️ was melting which added on to discharge
What are the human reason the River Derwent flooded
Peat removal, less soil to soak up water as peat acts like a sponge
New building, on the floodplain eg. new estate in Malton, so increased surface runoff
What are three positive impacts and three negative 👎 four impacts of floods
Replenishes water 💦, leaves sediment eg. alluvium and silt on floodplain which fertilises the floodplain soil, countries such as Bangladesh and Egypt are dependent of floods
Spreads water born diseases, can destroy buildings and infrastructure eg. roads and railways 🚃, can leave animals and people homeless or they can even drown, destroy crops on the floodplain
What are two positive and negative effects of flooding
Fish can breed in standing floodwater, in dry areas floods can bring relief from drought providing drinking 💦 for animals
Floods can bring chemicals and sewage into the local rivers polluting them, wild 😜 animals may lose their homes 🏡 or drown
