rivers Flashcards
what is a drainage basin
the area from which the river and its tributaries collect rainwater passing through rock and soil
tributaries are
smaller branches of the river, that join the main channel
what is a watershed
high ground separating 2 neighbouring drainage basins
water enters the drainage basin in what form
precipitation
source is
start of the river
mouth is
end of the river (where it meets the sea)
is the drainage basin an open or closed system
open
within the drainage system, water can be :
stored ( into the soil) or transferred
4 stores of water within the drainage basin system
- groundwater store
- soil store
- interception
- surface store
2 processes by which water is transferred vertically downwards into the ground
infiltration: water entering the soil
Percolation: Water flows vertically through the soil and rocks under the influence of gravity.
.Apart from discharge at the river’s mouth, how else might water leave the drainage basin system (outputs)?
Evapotranspiration from water bodies and soils and also transpiration from plants
State the THREE ways in which rainwater can be transferred laterally down a slope into a river channel, in order of speed.
surface runoff
Soil flow
Groundwater flow
What is the other way that rainwater can enter the river channels?
Through surface runoff (water flowing over the land finding its way into the rivers)
What physical characteristics of a drainage basin are likely to promote surface runoff
- Impermeable rocks
- Vegetation cover (thickness of - vegetation)
- Saturation of soil
- Steep slopes
How might human activity in a drainage basin promote surface runoff
It promotes surface runoff when humans create surfaces like pavement and buildings that don’t allow the infiltration of water in the soil.(urbanization)
Removing the interception store (deforestation)
when does flooding of rivers occur
when there is a heavy rainfall and discharge rises over carrying capacity - so the river overflows into the floodplain.
what is a confluence
where two rivers join
what is an estuary
where the mouth is low enough to let the sea enter at high tide
interception
: precipitation lands on vegetation.
infiltration
Water that reaches ground surface will soak into soil.
surface flow
water moving on surface of ground
percolation
Some water sinks deep into the earth (percolates)
through openings in the soil.
through flow
water moving through the soil.
label a hydrological cycle
stores of water in hydrological cycle (4)
groundwater store
interception
surface storage
soil moisture
water transfers (5)
- surface flow
- percolation
- infiltration
- throughflow
- groundwater flow
output of water
evapotranspiration
Attrition
when rocks grind each other down by colliding
Abrasion
riverbed eroded as rocks are dragged on the riverbed
Solution
the water having chemicals that dissolve rocks
Hydraulic action
water flows into cracks, creating pressure and causing banks to break
types of transportation (4)
Traction-
Suspension-
Solution
Saltation
traction
rocks moving on the riverbed
suspension
alluvium being suspended and carried in the water
solution (transportation)
dissolved chemicals being carried in the water, suspended
saltation
rocks being lifted and dropped again creating a ‘skipping’ effect along the riverbed
upper course characteristics
- narrow floored, steep v shaped valleys
- higher than sea level
what type of erosion happen in the upper course
vertical erosion,
why do v shaped valleys form in upper course
because of weathering, the sides of the bank then collapse (mass movement) becoming sediment and v shaped valleys are formed.
is it hard or soft rock in upper course
hard
characteristics of middle course
wider floor, more gentle sides but is a U shape
characteristics of lower course
wide floor and gentle sides
what are levees
a deposit of sand or mud built up along either side of the river
what is the long profile of a river
It is a way of showing the channel slope of a river along its entire length.
Why are V-shaped valleys so steep?
- Because it is above sea level, meaning it erodes downwards deepening the valley
Vertical erosion - The reason the sides are steep is because there has been inadequate time for the processes of weathering and mass movement to reduce the slope angle.
Why are upper course river channels shallow and irregular in shape?
Because the hard rock is too hard to be eroded whilst in the lower course there is silt and clay which is easy to erode
What are interlocking spurs
alternating ridges of high land that jut out into a river valley, typically found in the upper course of a river, where the river’s flow is not strong enough to erode through the hard rock of the ridges. Instead, the river winds around these obstacles, creating a zig-zag pattern.
Where do waterfalls form?
At the upper stage of a river
You find waterfalls when the river flows from hard rock to soft rock
processes operating in a waterfall that lead to its distinctive features.
The processes leading to a waterfall having distinctive features like a plunge pool are; hydraulic action and abrasion on the soft rock which creates the overhang (of hard rock) as well as corrosion further creating the overhang, the overhang then collapses and overtime the waterfall retreats upstream leaving behind a gorge
What happens to waterfalls over time?
They migrate upstream, and leave behind a gorge
why are floodplains the result of both lateral erosion and deposition.
meanders move and when they get to the bluff lines they erode them
what are bluff lines
formed from lateral erosion
the outer limits of a river’s floodplain. It is a steep section of the valley side slopes.
material that makes up the floodplain of a river
silt and clay
why do meanders migrate over time
erosion and deposition, the material is loose and gets eroded by hydraulic action
What processes occur on the outside of a meander bend and why?
Erosion because there is greater velocity, depth and more force
abrasion and hydraulic action
What outside bend channel feature results from the migration of a meander
river cliffs
What process occurs on the inside of a meander bend and why?
deposition as the water moves slower
What inside bend channel feature results from the deposition inside a meander bend
A point bar (low, curved ridge of sand and gravel along the inner bank of a meandering stream)
formation of an oxbow lake
Oxbow lakes form when meandering rivers gradually abandon one of its loops. The outer bend of the meander erodes, while sediment deposition occurs on the inner bend. During floods, the river can cut a shorter path (because of greater volume of water, so more velocity), leaving the meander loop isolated
what are deltas
an area of low, flat land shaped like a triangle, where a river splits and spreads out into several branches before entering the sea.
wetlands that form as rivers empty their water and sediment into another body of water
why do deltas form at the mouth of rivers
- A river moves more slowly as it nears its mouth. Which causes sediment, solid material carried downstream by currents, to fall to the river bottom. (deposition)
- Vegetation, salt marshes form and they slow the velocity down and traps more sediment.
Why don’t all rivers have deltas at their mouths
for a delta to form, the flow of a river must be slow and steady (velocity at 0) enough for silt to be deposited and build up, strong tides, high wave action, or human activity could prevent this.
Why does a river split up into distributaries on a delta?
When sediment accumulates, it begins to block the main river channel causing distributaries to form.
hazards of a river flooding (3)
- It can destroy infrastructure which costs millions to rebuild
- Loss of lives can affect the economy as workers are lost
- The water can be filled with bacteria and diseases and so a lot of people need to be treated which costs a lot
opportunities of living near a river (5)
- Flat land -Makes it easy to build: roads, settlements and carry out settlements
- Fertile soils- The mineral rich soils due to the silt and mud deposited by the river during floods makes agriculture is profitable
- Trade and transport-The rivers being navigable allow/Rivers being navigable also allow trade to happen
- Job opportunities- a lot of agriculture is possible
- Fishing- Fish living there, so people being able to eat a lot of fish.
factors affecting flood - physical (3)
-Climate ( rain, ice melt, snow melt)
-Stream flow and tidal conditions
-Earthquakes landslides
factors affecting floods - human
- Urbanization and urban growth because of more impermeable surfaces
- More rapid discharge in urban area due to impermeable surface and increased number of drainage channels
- Human induced climate change
Why is the death toll from flooding usually much higher in LEDCs than in MEDCs?
(4)
- Buildings are not flood proof and can break more easily killing people.
- Lower income countries also generally don’t have the resources or money to prevent floods
- Lower income countries also don’t have the material/resources enough to deal with the aftermaths (healthcare for people)
- In LEDCs there is generally a higher population which also leads to poorer building construction can lead to building collapsing on more people
Apart from flooding, in what ways can rivers be hazardous to people living near to them?
(3)
- Rivers can carry diseases like malaria ( water spread diseases)
- Erosion of the banks can endanger people and properties
- The alluvium (silt and clay) ca sometimes make it harder for people to build on it and it is unstable/unsafe because it could fall easily
advantages of hard engineering methods (3)
- people cope with floods less often
- river will flood less often
- multi purposeful, dams can produce hydroelectric power
disadvantages of hard engineering methods (3)
- structures need to be maintained
- Dams hold back fertile silt that would otherwise travel down the river and replenish alluvial soils
- Very expensive to build
hard engineering methods of managing floods (4)
Building dams and reservoirs
Raising levees
Dredging the channel
Straightening river channels
why is Straightening river channels good management of flooding
the river channel is straight, that means the velocity will be more and high volumes of water can pass through quickly which reduces the probability of a flood as the water reaches the mouth of the river sooner
why is dredging the channel good management of flooding
removing material from the bottom which creates less friction and allows the rivers velocity to be greater And it becomes deeper
why is raising levees good management of flooding
allows the rivers capacity to be more.levees prevent the water from passing through as they act like a physical barrier
why is Building dams and reservoirs-
management of flooding
traps the water in one place and is easily manageable as we can control the amount of water leaving and entering it.
soft engineering methods of flood management (4)
monitoring and predicting
Afforestation
flood insurance
Flood plain zoning-
why is monitoring and predicting a good way of flood management
The data on rainfall (precipitation) and stream discharge can help produce accurate predictions of the timing of flood surges which allows people to prepare and get ready for it to happen or evacuate.
- Reduces damage and death but does not prevent flood
why is flood plain zoning a good way of flood management
Authorities can ban land uses in certain flood prone areas which helps because the distance from river is increased, more floodplain and people don’t build on floodplains
why is afforestation a good way of flood management
The roots of the plants absorb some water, there are more obstacles and more friction for the water to pass through the soils
why is flood insurance a good way of flood management
Does Not help with preventing floods but could help diminish the impacts as it is insurance for people who are affected by the floods, don’t have to worry about their homes, safety, health.
Advantages of non-structural methods of flood management (4)
- Reduces the impacts of flooding
- Less government spending on managing rivers
- Soft engineering is described as sustainable
- Should last longer than hard engineering
disadvantages of soft engineering methods for flood management (2)
-Soft engineering doesn’t stop floods from happening
-Tree planting doesn’t provide immediate protection
at the bottom of a waterfall, what forms
a plunge pool
label and describe formation of a waterfall
