PHYSICAL GEO BIG STACK

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What is a recurrence interval?

The average time between events of a certain magnitude, such as floods, based on historical records.

What is intense or prolonged rainfall as a cause of flooding?

When rainfall exceeds the soil’s infiltration capacity, causing surface runoff to increase and rivers to overflow. - saturation

How does impermeable rock or soil increase flood risk?

prevent water from infiltrating the ground, increasing surface runoff and river discharge.

How can snowmelt cause flooding?

Rapid warming melts large amounts of snow quickly, sending large volumes of water into rivers and increasing discharge.

How does urbanisation increase flooding?

Buildings, roads and pavements are impermeable so water cannot infiltrate, causing rapid surface runoff and flash flooding.

How does deforestation increase flooding risk?

Removing trees reduces interception and infiltration, leading to more surface runoff entering rivers quickly.

What are the main social impacts of flooding?

• Loss of life injuries

• displacement from homes

• disease from contaminated water

• psychological stress.

What are the main economic impacts of flooding?

• Damage to homes

• infrastructure and businesses

• loss of crops and livestock

• high rebuilding costs.

What are the negative environmental impacts of flooding?

• Soil erosion

• habitat destruction

• water pollution.

What is a positive environmental impact of flooding?

• Floods can deposit nutrient-rich sediment on floodplain - improving soil fertility.

Give five causes of flooding

• Intense or prolonged rainfall
• Impermeable rock or soil
• Snowmelt
• Urbanisation
• Deforestation

strengths of hard engerniering

• low maintence

• long term

• effective

• multipul uses

weaknesses of hard engineering

• will be replaced

• expensive

• vissualy intrusive

• contruction time

• damage

strengths of soft engineering

• less visually intrusive

• sometimes cheaper

weaknesses of soft engineering

• high maintinence

• short term

What are the main ways humans modify the hydrological cycle?

• Land-use change (deforestation, afforestation, urbanisation)

• water abstraction

• reservoirs and dams

• industrial use, agriculture

• climate change.

How does deforestation affect the hydrological cycle?

• Reduces interception by vegetation
• Reduces evapotranspiration
• Decreases infiltration into soil
• Increases surface runoff
• Increases flood risk

how does deforestation affect river discharge?

• Faster movement of water to rivers
  • Shorter lag time on hydrographs
  • Higher peak discharge

How does afforestation affect water flows?

• Increases interception from tree canopy
• Increases evapotranspiration
• Increases infiltration into soil
• Reduces surface runoff

How does afforestation affect flooding?

• Lower peak discharge
• Longer lag time
• Reduced flood risk

How does urbanisation affect drainage basins?

• Impermeable surfaces reduce infiltration
• Surface runoff increases
• Water enters rivers faster through drainage systems

How does urbanisation affect river hydrographs?

• Shorter lag time
• Higher peak discharge
• Steeper rising limb (flashier hydrograph)

Why might rainfall increase in urban areas?

• Pollution particles act as condensation nuclei
• This can increase precipitation by about 10%

What is water abstraction?

• Removal of water from rivers, lakes or groundwater
  • Used for domestic, agricultural or industrial purposes

How does irrigation affect the hydrological cycle?

• Large amounts of water removed from rivers
• Groundwater extracted for agriculture
• Reduces river discharge downstream

What percentage of global water withdrawal is used for agriculture?

About 70% of global water withdrawal

What are environmental impacts of over-abstraction?

• Rivers and lakes shrink
• Wetlands dry out
• Land subsidence can occur
• Saltwater intrusion into aquifers

What is land subsidence?

• Ground surface sinks
• Occurs when groundwater removal compresses sediments

What is saltwater intrusion?

• Saltwater moves into freshwater aquifers
• Happens when groundwater levels fall

How can water abstraction be managed?

• Government permits limit water extraction
• Environmental agencies monitor water levels

What is water storage?

• Water stored in reservoirs or dams
• Used for supply, irrigation or hydroelectric power

How do dams affect river flow?

• Regulate river discharge
• Reduce peak flood flows downstream

How do reservoirs affect evaporation?

Large surface area increases evaporation losses

Example of evaporation loss from reservoirs?

• Lake Nasser loses around 1/3 of its water each year through evaporation

What is a floating cover used for?

Reduces evaporation from reservoirs

What are the main purposes of dams?

• Water supply
• Irrigation
• Hydroelectric power
• Flood control

How does hydroelectric power affect water quality?

• Generally little effect on water quality
• May affect fish and aquatic ecosystems

How does industrial use affect water resources?

• Water used for cooling and manufacturing
• Can lead to pollution if waste enters rivers

How can mining affect water systems?

• Mining waste can contaminate water
• Heavy metals and chemicals may pollute rivers

How does climate change affect water quantity?

• Changes precipitation patterns
• Increases evaporation rates

How does climate change affect water quality?

• Lower water levels increase pollutant concentration

give an example of irrigation extreeme

large-scale commercial farming e.g. asparagus on the Peruvian coast caused severe groundwater overextraction

what is saltwater intrusion

• falling groundwater allows seawater to enter freshwater aquifers, making them unusable

• Water tables have dropped globally since 2002

what soil conditions lead to a shorter lag time (flash)

high antecedent soil moisture conditions 
impermiable soil

what soil charecteristics lead to a subdued hydrograph 

dry soil 
permiable soil 

what is the water table

the upper surface of the zone of saturation where soil are permenantly saturated with water

what drainage basin lead to a subdued hydrograph 

low drainage density 
shallow slopes 
permiable rocks 
high vegitation cover 
deep soil 
lakes 
rural land 
good agricultral practices 

what precipitation types lead to a subdued hydrograph

low intesity rainfall 
small amounts of rainfall 
slow snow melt 
high rates of evapotransperation 

what climatic conditions lead to a shorter lag time (flash)

high intensity rainfall 
large amounts of rainfall 
fast snow melt 
low rates of evapotransperation 

what are the two types of storm hydrographs 

flash and subdued

what are the two types of rock

sedmentry and ignious 

what are the drainage charecteristics that lead to flash hydrographs 

high drainage density 
steep slopes 
impermiable rocks
little vegiation cover
thin soil 
urban development 
poor agricultral prectices 

waterfall

a place where a river decends vertically usually where hard rock overlies soft rock

v-shaped valley 

a river valley with evenly sloped sides in the shape of a v cuased by erosion and weathering

urbanisation

the proportion of people living in towns and cities increases and so therefore does the size of towns and cities

transportation

the removal of weathered matitial and eroded matirial in rivers 

river regime

expected seasonal pattern of discharge over the year at one particular point

ox bow lake

Cut off crecent shaped lake left after a meander neck has been cut through

Meander

A loop or bend in a river with a slip off slope on the inside bend and a river cliff on the outside

input/output

when something is either added or taken away from a system

Hydrograph

Graph showing variations in river discharge over a piriod of time

hydrocolic cycle 

the circulatory system by which water is transfered between oceans atmosphere and land

human use 

the way in which people make use of rivers to futher economic development and water supply

how does urbanised areas effect overland flow

increaced overland flow due to unpermiable surface preventing infiltraition

how does steep slopes effect overland flow

increase speed of overland flow reducing rate and time taken for interception to be able to take place

how does overgrazing effect overland flow

reduces vegitation and thus interception increacing overland flow

how does frozen of saturated soils effect overland flow

increaces over land flow as there is no unsaturated soil preventing infiltraition

how does deforestaiontion effect overland flow

reduces rate of interception increacing overland flow 

how does bare rocky surfaces effect overland flow

increaces overland flow due to unpermiable surface preventing infiltaition

flood plain 

flat low lying are of the valey floor which floods from time to time

flood 

when a river channel recives more water than it can hold 

Field capacity

The amount of water a drainage basin can hold 

erosion

the wearing away of the beds and banks

drainage density

total length of all streams in the drainage baisen divided by total area of drainage basin

drainage basin

an area of land drained by a river and all of its tributrys 

discharge

the volume of water in a river passing a mesuring point in a given time cubic meters per second

Delta

Landform produced by the deposition of sedement at the mouth of a river as it enters lake or sea

what is the hydrological cycle flows and stores

what is recharge

When precipitation exceeds evaporation causing soil moisture to increace 

what are the 6 factors that increace overland flow

• deforestation

• steep gradient 

• Frozen + saturated soil 

• overgrazing 

• bare surfaces 

• urbanisation

What are the three types of river flow

Helicoidial

laminar

Turbulent

what are the three types of river channels

Straight

meandering

braided

what charicteristics can be atributed to braided channels

Braided channels

• Trubulent flow

• steep and complex system

• eyots form

what are the charecteristics of a straight channel

straight channel

• Laminar flow

• middle and lower cource

• symetrical

• Rare in real life

what are the charecteristics of a meandering river

Meandering river

• corkscrew motion

• asemetrical

• helicoidial flow

what are the four transportation process

• Traction - large stones roll

• suspension - small particals

• soloution - disolved minerals

• saltation - small stones skip

what factors effect transportation in a river

• Competence - the diameter of the largest partials it can carry at a given velocity

• Capacity - the total volume of load a river can carry

what are the four types of erosion

• Hydraulic action - pressure of water

• abrasion - scraping and rubbing of matirial

• attrition - reduction in size of fragments in river

• soloution - carbonates dissolved

what factors effect rate of erosion

• Speed/velocity

• Discharge

• Climate

• Geology

• PH

• Load

what is sineocity

curvyness of a river over time

what are the all the causes for a subdued hydrograph

• Low intensity

• High evapotransperation

• Dry soil

• permiable soil

• low drainage density

• gentle slopes

• permiable rock

• forest and vegitation

• lakes

• rural land

• good agricultral practive