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IB Geography Option E: Leisure, tourism and sport Case Studies Notes
IB Geography Freshwater and Geophysical Hazards case studies
IB GEOGRAPHY HL/SL CORE CONTENT COMPLETE STUDY GUIDE
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Environmental Management and Geography
IB GEOGRAPHY
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The drainage basin
Drainage basin: an area that is drained by a river and its tributaries. They have inputs, outputs, processes and
outputs. It is an open system. Its main input is precipitation which is regulated and its outputs include
evaporation and transpiration. Flows include infiltration, throughflow, overland flow and base flow. Stores
include vegetation, soil, aquifers and the cryosphere.
Precipitation: the transfer of moisture to the earth’s surface from the atmosphere. Can include dew, hail rain,
sleet and snow.
Interception: The capture of raindrops by plant cover that prevents direct contact with the soil.
Throughfall: If there is prolonged rainfall then retaining the capacity of leaves will be exceeded and water will
drop to the ground.
Stemflow: When water trickles along branches and down the stems or trunk. Some is retained on the leaves
while some is evaporated.
Evaporation: The physical process by which liquid becomes gas. Wind, temperature, vapour pressure and rock
surface can cause for evaporation.
Transpiration: The loss of water from vegetation.
Evapotranspiration: The combined loss of water from vegetation and water surfaces to the atmosphere.
Potential evapotranspiration: The rate of water loss from an area if there were no shortage of water.
Infiltration: The process by which water sinks into the ground.
Infiltration capacity: The amount of moisture that a soil can hold.
Infiltration rate: The speed with which water can enter the soil.
Throughflow: Water moving in soil, laterally following natural pipes or between horizons. Water moving
laterally beneath the surface through unsaturated ground towards a river.
Overland runoff: Occurs when precipitation intensity exceeds infiltration rate or when the infiltration capacity
is reached and the soil is saturated.
Percolation: Water moving deep into groundwater zone.
Baseflow: The movement of groundwater.
Aquifer: Rocks that hold water. They provide the most important store of water and regulate the hydrological
cycle and maintain river flow.
Cryosphere: The largest store of freshwater and water may be stored for millenia.
Vegetation: Trees store more water than crops.
,River discharge
Discharge: refers to the volume of water passing a certain point per unit time. It is expressed in cubic meters
per second (cumecs). It usually increases downstream.
What are the different types of erosion?
Abrasion:The wearing away of the bed and bank by the load carried by a river.
Attrition:The wearing away of the load carried by the river it creates smaller rounder particles.
Hydraulic action: The force of air and water on the sides of river and in cracks.
Cross section: The width and mean depth of the channel.
Wetted perimeter: The total length of bed and bank sides.
Solution:The removal of chemical ions, especially calcium, causing rocks to dissolve. Chalk and limestone are
vulnerable to solution.
What are the factors affecting erosion?
Load:The heavier and sharper the load the greater the potential for erosion.
Velocity and discharge:The greater the velocity and discharge the greater the potential for erosion.
Gradient: The increased gradient increases the rate of erosion.
Geology: Soft, unconsolidated rocks e.g. sand and gravel are easily eroded.
pH: Rates of solution are increases, making the water more acidic.
Human impact: Deforestation, dams and bridges interfere with the natural flow of a river and frequently end
up increasing the rate of erosion.
What are the main types of transport?
Suspension:Small particles are held up by turbulent flow.
Saltation:The heavier particles are bounced or bumped along the river bed.
Solution:The chemical load is dissolved in the water.
,Traction:The heaviest material is dragged or rolled along the bed of the river.
Floatation:Leaves and twigs are carried on the surface of the river.
Thalweg: The fastest flowing part of the river.
What happens in the upper reaches of a river?
Narrow channel, steep gradient
Slow velocity → energy lost to friction from transporting larger load
Large load → traction and saltation
What happens in the middle reaches of a river?
Flatter floodplain, flatter gradient
Channel becomes wider → lateral erosion
Load becomes finer → attrition and abrasion
Suspension is the main form of transportation
Cross-sectional area and hydraulic radius increases allowing for greater discharge
What happens in the lower reaches of a river?
Wider and deeper channel
Fastest velocity
Moves into the mouth of the sea to deposit sediment
Dissolved load, load is smallest and roundest
What affects the velocity of the river?
Slope: the steeper the slope the faster the water moves while the gentler the slope the slower the river
moves.
Discharge: the higher the discharge the faster the velocity while low discharge leads to a lower velocity.
Shape of channel: a flat and wide channel snt deep and water comes in contacts with the sides or banks of the
river, this creates more friction and decreases the velocity. A semicircular stream channel is deeper and has
less contact with the banks therefore there is less friction and the river moves faster.
A higher hydraulic radius means that less water is in contact with the cross-section therefore there is less
friction and the velocity is higher.
What are the two kinds of river flow?
Laminar flow is the less common flow that occurs when water travels over sediment without disturbing it.
Turbulent flow is the dominant method of circular motions that occur in a vertical and horizontal eddies in a
downstream direction.
What is the theory of river channel load?
Stream capacity: The largest amount of load it can carry.
Competency:The diameter of the largest particle that can be carried. (The maximum load a river can carry.)
Critical erosion velocity: The lowest velocity at which grains of a given size can be moved.
What 3 things does the Hjulstrom curve suggest?
- The smallest and largest particles need high velocities to lift them.
- Higher velocities are required for entrainement rather than transport.
- When velocity falls below a certain level particles are deposited.
What is the river regime an what influences it?
River regime: The annual variation in the flow of a river.
- The amount and nature of precipitation.
- The local rocks, their porosity and permeability.
, - The amount and type of vegetation cover.
How is a waterfall formed?
- They often occur on horizontally bedded rocks.
- The soft rock is undercut by hydraulic action and abrasion because there is a lack of support.
- The weight of the water and the lack of support cause the waterfall to collapse and retreat.
- Over thousands of years the waterfall may retreat enough to form a gorge.
Where does river deposition occur?
- It occurs as the river flows down and loses energy.
- This happens at the mouth of a river before it enters the sea or behind a dam.
- It is more likely during low flow flow (drought) than in high flow (flood).
Which particles are deposited first? What can depositions form?
- First the larger heavier particle are deposited followed by the smaller lighter ones.
- Levees, deltas and floodplains.
- Flood plain: flat areas found in the lower parts of a river, it composes of clay, silt or alluvium
deposited during a flood.
How do levees form?
- A levee is al flood barrier.
- During flooding discharge of the river increases and the velocity is slowed down by the friction from
contact with the floodplain.
- Large pieces of sediment are deposited on the outside of the river bank.
- It drops the courser, heaver material first, this forms higher banks called levees at the edge of the
river.
- The smaller and finer sediment is deposited on the inner part of the river.
- This builds up over time as flooding continues, material like sand and gravel build up and a border is
eventually formed.
How does a meander, oxbow lake and point bar form?
- A meander is a bend in the course of the river it occurs in the middle reaches where the floodplain is
flat.
- It occurs in conditions where channel slope, discharge and load combine therefore the fastest way for
the stream to continue is by creating a meander.
- The fast paced nature of the river causes for the valley to widen due to lateral erosion.
- Deposition continues on the inside of the river forming a point bar.
- As the deposition accumulates from erosion of the banks, the sediment can cut off the flow of water
creating a ‘U shaped curve’ called an oxbow lake, this allows the rest of the river to continue its
course.
Where does the most erosion/deposition take place?
- Both erosion and deposition occur throughout the course of the river.
- Erosion is most prevalent during floods.
- Deposition mostly occurs when the velocity is reduced.
How do deltas form?
- Formed in the lower courses of the river
- When the river meets the mouth of the river to deposit the sediment its speed rapidly decreases, the
load is finer do to abrasion and attrition
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