Rivers Topic Refresh 💧🌳 Flashcards
erosion - hydraulic action
processes affecting a river landscape
the sheer force of the water hitting the river bed and banks.
most effective when the water is moving fast and there is a lot of it.
processes affecting a river landscape
transportation - traction
processes affecting a river landscape
heaviest material is rolled along the river bed - it is too heavy to lose contact with the bed.
this requires the most energy.
processes affecting a river landscape
erosion - abrasion
processes affecting a river landscape
occurs when the load the river is carrying repeatedly hits the river bed and banks, causing some of the material to break off.
processes affecting a river landscape
erosion - attrition
processes affecting a river landscape
when the stones and boulders carried by the river knock against each other.
over time they are weakened, causing bits to fall off and reduce in size.
processes affecting a river landscape
erosion - solution
processes affecting a river landscape
occurs only when the river flows on certain types of rock that are soluble in rainwater. they dissolve in the water and become part of it as a result.
eg chalk and limestone.
processes affecting a river landscape
transportation - saltation
processes affecting a river landscape
sand sized particles are bounced along the river bed in a ‘leap frog’ motion.
processes affecting a river landscape
transportation - suspension
processes affecting a river landscape
small particles (clay and silt sized) are carried within the water by a turbulent flow.
processes affecting a river landscape
transportation - solution
processes affecting a river landscape
the dissolved load (it is not visible).
occurs only with certain rock types that are soluble in rainwater.
eg chalk and limestone.
processes affecting a river landscape
what is river deposition?
processes affecting a river landscape
material transported by a river is dropped.
deposits the largest material first as this is the heaviest to carry.
smaller load is deposited further downstream as it can be transported further.
processes affecting a river landscape
why does river deposition occur?
processes affecting a river landscape
drops some of its load when there is a fall in the speed of the water or the amount of water.
often occurs when the gradient changes at the foot of a mountain or when a river enters a lake/sea.
processes affecting a river landscape
mass movement
processes affecting a river landscape
broken rock fragments (as a result of weathering) move down the slope through mass movements.
these can be rapid eg landslides or slow eg soil creep.
processes affecting a river landscape
weathering
processes affecting a river landscape
as the river flows, it erodes the land, creating a valley.
the river valley and channel sides are broken down by weathering.
processes affecting a river landscape
what is mechanical weathering?
processes affecting a river landscape
physical changes causing rock to break down
eg changes in temperature causing water to freeze and expand, melt and contract, leading to freeze-thaw weathering.
processes affecting a river landscape
what is chemical weathering?
processes affecting a river landscape
rainwater is slightly acidic and over time wears away the rock.
processes affecting a river landscape
what is biological weathering?
processes affecting a river landscape
occurs when plants and animals wear away rocks
eg roots growing in cracks in the rock or rabbits burrowing into rock.
processes affecting a river landscape
what is the river like in the upper course?
how rivers contrast
- steep gradient
- narrow and shallow channel - no flat valley floor.
- erodes vertically
- creating v shaped valleys, interlocking spurs, rapids, waterfalls, and gorges.
how rivers contrast
what is the river like in the middle course?
how rivers contrast
- wider and deeper river channel
- gentler gradient
- erodes laterally
- creating wider and shallower valleys, meanders, and oxbow lakes.
how rivers contrast
what is the river like in the lower course?
how rivers contrast
- low gradient
- wide floodplains
- river channel deep and wide
- bounded by levees
-deposits sediments
how rivers contrast
what is hard engineering?
flood prevention strategies
- building artificial (man-made) structures to stop flooding.
- usually more expensive than soft engineering.
flood prevention strategies
GIVE and DEFINE some examples of hard engineering strategies
flood prevention strategies
- Embankments - raising the banks of a river means it can hold more water.
- Dams and reservoirs - dam traps the water, which builds up behind it, forming a reservoir. water can be released in a controlled way.
flood prevention strategies
EXPLAIN advantages of embankments
flood prevention strategies
Embankments ADVANTAGES:
- one-off cost.
- durable
- increased carrying capacity of the river, making nearby settlements safer from flooding.
flood prevention strategies
EXPLAIN advantages of dams and reservoirs
flood prevention strategies
- can be used to produce electricity by passing the water through a turbine within the dam.
- reservoirs can attract tourism.
flood prevention strategies
EXPLAIN disadvantages of dams and reservoirs
flood prevention strategies
- very expensive
- dam traps sediment so reservoir can hold less water
- habitats are flooded often leading to rotten vegetation.
flood prevention strategies
EXPLAIN disadvantages of embankments
flood prevention strategies
Embankments DISADVANTAGES:
- looks unnatural
- water speeds up and can increase flood risk downstream.
- expensive to install.
flood prevention strategies
what is a flood?
causes and effects of flooding
when a river overflows its bed and banks because the river discharge is greater than the capacity in the river channel.
causes and effects of flooding
what is soft engineering?
flood prevention strategies
techniques which work with the natural environment and don’t harm/change the river environment
sustainable
flood prevention strategies
greater surface area … the chance of flooding
causes and effects of flooding
increases
causes and effects of flooding
greater infiltration … the chance of flooding
causes and effects of flooding
reduces
causes and effects of flooding
when is flooding more likely to happen?
causes and effects of flooding
when water reaches the river channel quickly.
causes and effects of flooding
NAME 3 causes of flooding and EXPLAIN them
causes and effects of flooding
- human: urbanisation - impermeable surfaces
- physical: more tributaries - increases river discharge
- human: deforestation - reduces interception which would slow down rainfall so it doesn’t accumulate.
causes and effects of flooding
name 3 social effects of flooding
causes and effects of flooding
- agriculture affected, shortage of food, affects wellbeing.
- damages buildings.
- road links flooded so no access to flooded settlements.
causes and effects of flooding
name 3 economic effects of flooding
causes and effects of flooding
- agriculture affected, cannot trade, affects wealth.
- businesses may not be insured and go bust.
- infrastructure issues eg power
causes and effects of flooding
name 2 environmental effects of flooding
causes and effects of flooding
- land contaminated - mixed with sewage plants and water treatment plants.
- destruction of wildlife habitats
causes and effects of flooding
when is a meander scar formed?
river landforms
when the oxbow lake dries up.
river landforms
what are floodplains?
river landforms
large, flat area of land next to the river usually in the lower course.
river landforms
what are levees?
river landforms
- small raised embankments along the side of the channel.
- can be cm to m high
- often artificially heightened and straightened to act as flood embankments.
river landforms
how are floodplains formed?
river landforms
when alluvium is deposited on the land.
river landforms
what is alluvium?
river landforms
fine sediment suspended in the river.
river landforms
