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Physical Georgaphy AS > Hydrology + Fluvio-geomomorphology > Flashcards

Hydrology + Fluvio-geomomorphology Flashcards

1
Q

What does the Hjulström curve show?

A
  • it shows the relationship between material size and the energy (velocity) needed to transport and erode it
  • the larger the material, the higher the velocity needed to keep the particles transporting
  • the settling velocity curve is the point at which the material no longer has the energy required to be transported, meaning it is deposited
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2
Q

Erosion

A
  • The process of the wearing away of soil and rock
  • the force of water and fragments of rock cause the river bank to wear away in certain areas over time
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3
Q

Abrasion/Corrasion

A
  • the wearing away of the bed + bank by the load carried by a river - usually causing the river bed to deepen and widen
  • a high river velocity increases abrasion due to the river having enough energy to carry larger rocks
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4
Q

Attrition

A
  • wearing away of load carried by river, creating smaller and rounder particles
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5
Q

Hydraulic action

A

The force of air + water on the sides of rivers + in cracks

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6
Q

Cavitation

A
  • water forces its way into small cracks
  • air in these spaces get compressed and put under pressure - fragmenting and damaging the rock
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7
Q

Corrosion/ solution

A
  • process of water dissolving parts of rock/soil that makes up the river channel
  • factors affecting rate: bed rock, solute concentration of stream, discharge, velocity
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8
Q

Traction

A
  • the movement of large rocks and pebbles through water by rolling them along the river bed
  • rocks are heavier and therefore can not be carried by water
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9
Q

Saltation

A

Pebbles are bounced along river bed

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10
Q

Suspension

A

Small pebbles and material are carried (suspended) within the water

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11
Q

Solution

A
  • soluble materials are carried within the water
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12
Q

Factors affecting the rate of erosion

A
  • load —> heavier + sharper = greater potential for erosion
  • velocity —> increase in velocity = increase in erosion
  • gradient
  • geology —> soft, unconsolidated rocks such as sand are easily eroded
  • pH —> acidic water increases erosion
  • human impact —> deforestation, dams + bridges infers with natural flow
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13
Q

Why does velocity needed to pick up particles vary with size?

A
  • larger particles require higher velocities to be picked up because they are heavier
  • sand (0.1-1.0mm) requires the lowest velocity to be picked up because of its small size
  • clays are more cohesive so require higher velocities to be picked up
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14
Q

Evapotranspiration

A
  • water loss from the ground surface to the atmosphere (evaporation) combined with water given off by plants (transpiration)
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15
Q

Interception

A
  • vegetation, particularly trees, intercepts some precipitation on its way to the ground
  • water is then lost back into the atmosphere by Evapotranspiration
  • the intercepting plants also use some water for growth
  • ## vegetation reduces and slows down water transfer
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16
Q

Depression storage

A

When water is stored temporarily on the ground surface in the form of puddles

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17
Q

Soil moisture

A
  • the existing moisture in the soil determines whether precipitation will be absorbed or be forced to flow as overland flow
  • clay soils can be very wet and boggy - leading to overland flow
  • where as sandy soils tend to absorb more precipitation
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18
Q

Baseflow/ground water flow

A
  • very slow transfer of water through rocks
  • only in limestone areas where there are extensive underground channels, can the flow be faster
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19
Q

River channel

A
  • the river is an important store of water
  • forms the ‘exit’ for water transferred through the drainage basin
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20
Q

Percolation

A
  • the deeper transfer of water into permeable rocks - those with joints (pervious)or those that are porous
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21
Q

Throughflow

A
  • downhill transfer of water through the soil layer to the river
  • this shallow transfer can be quite rapid in very porous sandy soils
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22
Q

Infiltration

A
  • involves water moving from the ground surface into the soil
  • the rate of infiltration (infiltration capacity) depends upon the moisture content of the soil and it porosity (the number of airspace’s contained within)
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23
Q

Overland flow

A
  • this is the rapid form of water transfer over the surface of the ground
  • most likely to occur during heavy periods of rainfall, or when the soil has completely saturated
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24
Q

What is a drainage basin?

A

An area of land divided by a river and its tributaries

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25
Q

The slowest water transfer?

A

Ground water flow

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26
Q

A fast water transfer?

A

Infiltration

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27
Q

The fastest water transfer?

A

Surface run off

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28
Q

What does a storm hydrograph show?

A
  • how a river responds to a rainfall event
  • annual hydrographs are called a river regime
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29
Q

What is lag time?

A

Time in hours from peak precipitation to peak discharge

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30
Q

What is base flow?

A

Discharge of the river before and after rainfall

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31
Q

What is storm flow?

A

Discharge above base flow - mostly from overland flow

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32
Q

What conditions can lead to overland flow?

A

Freezing - reduces infiltration capacity + rate

Precipitation - affects rate

Saturation- infiltration capacity full

33
Q

What is infiltration capacity

A

How much water the soil can store

34
Q

What is infiltration rate?

A

The velocity at which water enter the soil

35
Q

How does precipitation affect storm hydrographs?

A
  • prolonged rainfall -> flooding most frequently occurs following a long period of heavy rainfall -> the ground has become saturated-> infiltration replaced by overland flow
  • intense rainfall -> intensity may be greater than the soil infiltration capacity -> resulting in high levels of over land flow
  • snowfall -> heavy snowfall means water is held in storage -> temperature rises, snow melts -> infiltration capacity is exceeded or ground may still be frozen -> overland flow
36
Q

How does sandy soils affect storm hydrographs?

A
  • large pore spaces = high infiltration capacity + allows rapid infiltration (greater throughflow)
  • reduces peak discharge and increases lag times
37
Q

How does clay soils affect storm hydrographs?

A
  • much smaller pore spaces = low infiltration capacity + allows little infiltration (less throughflow)
  • increases peak discharge + reduces lag time
38
Q

How does thin soils affect storm hydrographs?

A
  • thin soils can only store small amounts of water (soil moisture storage)
  • soil becomes saturated quickly -> increasing the amount of throughflow and/or overland flow
  • high peak discharge + short lag time
39
Q

How do deep soils affect storm hydrographs?

A
  • can store a large amount of water (soil moisture storage)
  • field capacity/full saturation is rarely reached -> increasing the amount of infiltration
  • low peak discharge + long lag time
40
Q

How does forest vegetation affect storm hydrographs?

A
  • forest vegetation have high levels of interception -> increasing the amount of water stored in the drainage basin + slows down flow of water to river
  • as more water is intercepted, interception loss increases + less water enters the river
  • soils underneath forested areas have high infiltration capacities -> allows increased amounts of water to enter the river by throughflow
  • low peak discharge + long lag time
41
Q

How do grasslands and moorlands affect storm hydrographs?

A
  • lower vegetation density = less interception loss + more water will travel through the drainage basin to the river
  • soil infiltration capacity is lower -> intense rainfall will exceed infiltration capacity -> overland flow
  • soil moisture capacity low -> less water need for soil to reach 100% saturation -> overland flow
42
Q

How do lakes and reservoirs affect storm hydrographs?

A
  • reservoirs and lakes may control the flow of a river
  • water entering the drainage basin after a rainfall event will be stored in the reservoir
  • this will have an affect of ‘flatting’ the profile of a storm hydrograph
43
Q

How does urbanisation affect storm hydrographs?

A
  • less permeable surfaces -> less surface storage and interception, as well as less infiltration by soil and rocks
  • reduced surface storage and interception = less evaporation outputs
  • water cannot infiltrate through tarmac and concrete -> increased overland flow
  • increasing peak discharge, reducing lag time and lowering base flow
44
Q

How does agriculture affect hydrographs?

A
  • farming activities may speed up or slow down delivery of water to rivers
  • soil conservation measures are designed to reduce run off and soil erosion = reduced overland flow
  • hill slope terracing or planting of permanent grassland on vulnerable slopes = reduces overland flow
  • BUT land drainage systems is to accelerate the transfer of water to the stream
  • intensive farming modify natural processes -> changes in vegetation coverage will affect interception, surface run off, infiltration and percolation
  • ploughing of fields, application of fertilisers, and impact of machinery alter soil texture -> damaging storage and infiltration capacities
45
Q

How does shape of a drainage basin affect a storm hydrograph?

A
  • a more circular basin = higher peak discharge and shorter lag time than an elongated basin
  • all points on the watershed of a circular basin are approximately an equal distance from the gauging point
  • in a elongated basin it takes longer for the rainfall from the extremities of the basin to reach the gauging point
46
Q

How does size affect the hydrograph?

A
  • as size increase, peak discharge becomes higher and lag time increases
  • bigger drainage basin collects water from a greater area - therefore more water enters the river
  • the distance the water has to travel to reach the river is however larger - increasing the lag time
47
Q

How does drainage basin density affect the hydrograph?

A
  • density refers to the number of surface streams in a given area
  • the higher the density the shorter the lag time and greater the peak discharge
  • short lag time due to the shorter distances that the rainfall has to travel to reach the river
48
Q

How does relief affect storm hydrographs?

A
  • in a steep sided upland valley, water is more likely to reach the river quickly than in a gently sloping valley
  • shorter lag time
49
Q

How does rock type affect a storm hydrograph?

A
  • permeable rocks are either porous or pervious
  • porous (e.g. sandstone and chalk) - lots of pores able to store water
  • pervious (e.g. limestone) - allows water to flow down joints within the rock
  • peak discharge lower + greater lag time
  • impermeable rocks (e.g. granite) - don’t allow percolation -> more throughflow and overland flow
  • peak discharge higher + shorter lag time
50
Q

What is discharge?

A

The volume of water flowing through a river channel in a given time

51
Q

What is a water budget?

A

Inputs (precipitation/flows into basin) - outputs (flows out, evapotranspiration, loss to deep flows)

52
Q

What is laminar flow?

A
  • flowing in layers -> happens on efficient rivers flowing in smooth channels
  • top + bottom layers slower due to friction, middle flowing fastest
53
Q

What is turbulent flow?

A
  • vertical + horizontal eddies caused by obstruction in the river + pressure imbalance
  • leads to the creation of fast + slow areas of the river
  • erosion + deposition happens in the river, creating deeper pools and shallow riffles
54
Q

What is helicoidal flow?

A
  • corkscrew motion generated by pressure differences on a meander
  • higher pressure on the outside of the bend - undercutting banks to form a river cliff
  • lower pressure on the inside - deposits material to form a point bar
55
Q

What is sinuosity?

A
  • the measurement of how meandering a river is
  • if channel length is less than 1.5 x it’s valley length it is ‘straight’
  • over 1.5 x = sinuous or meandering
56
Q

What is Thalweg?

A

Line of fastest flow

57
Q

How does a meander + oxbow lake form?

A
  • turbulent flow leads to the formation of pools and riffles, with pools occurring at points of greater erosion and riffles forming due to deposition
  • the thalweg flows from side to side and a cork screw like motion called helicoidal flow moves material from the outside of one meander bend and deposits it on the inside of the next bend
  • the outside of the bend has a higher pressure - undercutting the bank to form a river cliff
  • the inside of the bend has a lower pressure - river deposits load to form a point bar
  • continuous erosion on the outer bank + deposition on the inner bank forms a meander
  • over time the shape of the meander will change + the neck will be cut off to form an oxbow lake
58
Q

How do gorges form?

A
  • retreat of the river
  • antecedent drainage
  • glacial overflow
  • collapse of underground caverns
59
Q

How do levees + floodplains form?

A
  • caused by rivers bursting banks (flooding)
  • hydraulic radius increases
  • efficiency decreases
  • velocity decreases
  • deposition increases
  • so, material deposited by river due to the drop in energy, with repeating floods this will continue to build up the levee over time
60
Q

How is flood risk measured?

A
  • measure using recurrence interval
  • e.g. 10 year flood is the largest flood you can reasonably expect in the next 10 years
61
Q

Causes of flooding

A
  • high precipitation - e.g. in uk caused by Atlantic depression, season rainfall (the monsoon) or extreme weather such as hurricanes
  • river management - e.g. dams/defences push flooding down stream
  • impermeable surfaces - urbanisation
  • deforestation
  • climate change
62
Q

Forecasting/ warnings for floods

A
  • use of weather satellites - geostationary
  • river gauging + monitoring
  • uk - 50% of dwellings have 6+ hrs notice of flooding
63
Q

Loss sharing of floods

A
  • insurance -> spreads cost of flood damage
  • disaster relief
64
Q

Hard engineering for flood prevention

A
  • embankment + sluice gates -> controls flow into + out of urban areas
  • enlarged channels -> can silt up in low areas
  • flood bypass channel
  • dams/flood storage -> can be temporary
  • intercepting channel to take water away
  • removal of urban area
65
Q

Land use zoning for flood prevention

A
  • using flood maps to create where houses can’t be built etc.
66
Q

Soft engineering : flood reduction

A
  • reforestation
  • reseeding sparsely vegetated areas
  • contour ploughing/ terracing -> slows overland flow + therefore infiltration increases
  • protection of vegetation e.g. national park
67
Q

Soft engineering: flood diversion

A
  • allow certain areas to flood + increase infiltration in these areas
68
Q

How do delta’s form?

A
  • form where a river flows into the sea(estuary) - where the rate of deposition is greater than the rate of erosion
  • they grow outwards + benefit from flocculations, which is when opposite charges of fresh water + salt water cause clay particles to clump together + be deposited
  • e.g. the river Nile into MED, Mississippi into Gulf of Mexico
69
Q

What are the types of delta’s?

A
  • arcuate —> longshore drift affects shape - stays smooth, fan shape - e.g. river Nile
  • cuspate —> pointed, foot shaped - caused by opposing currents - e.g. Ebro
  • Birds foot delta - huge amounts of deposition, delta twos along pattern of rivers
70
Q

Outputs in the drainage basin

A
  • evaporation (liquid to gas) - occurs when water in the system is heated by solar energy causing it to evaporate into gas + rise into atmosphere
  • evapotranspiration - occurs in plants when they respire through their leaves, releasing water they absorb through their roots, which then evaporates due to heating by sun
  • river discharge - volume of water passing through a cross-sectional point of the river at any point in time (cumecs ) - water leaves through streams which drains the basin, may flow as tributaries into other rivers or directly into lakes + oceans
71
Q

Stores in drainage basin

A
  • interception - water intercepted by plant branches + leaves before reaching the ground - water is stored short term
  • soil water - water stored in upper levels of soil which is utilised by plants
  • surface water - water stored in puddles, ponds, lakes etc. - depending on size can last from hours to years
  • ground water - stored in pore spaces of rock or lower soil
  • channel storage - stored in the rivers channel
72
Q

Flows in drainage basin

A
  • above ground flows: throughfall, stemflow, overland flow, channel flow
  • below ground flows: infiltration, percolation, throughflow, groundwater flow , base flow
73
Q

What is the water table?

A
  • the level at which the pore spaces + fractures in the ground become saturated
  • meaning above the water table is unsaturated soil + below is saturated soil
74
Q

How can the water table change?

A
  • if the surface dips below the water table, groundwater will fill the surface space to become surface water
  • if the surface water dries up, groundwater will continue to replenish the area that is underneath the water table
  • if water table rises/falls = surface water rises/falls
75
Q

What is groundwater recharge?

A
  • when groundwater levels deplete (by human extraction or by groundwater replenishing surface water levels) groundwater can be recharged
  • ground water levels fall when its being used more - e.g. hot temps = less rainfall, more surface water dries up so groundwater will try to replenish these stores
  • causing water table to fall as no water is replenishing the used groundwater
76
Q

How is groundwater recharged?

A
  • precipitation infiltrating the ground until it reaches ground water - when precipitous is high, evaporation is low (e.g. winter) - groundwater levels will be recharged
  • surface water bodies (e.g. lakes + rivers) seeping into groundwater stores
77
Q

How do waterfalls + gorge form?

A
  • river flows over soft rock + hard rock - soft rock erodes away more quickly creating a step
  • overtime soft rock erodes away further - undercutting the hard rock
  • hard rock suspended in the air as an overhand
  • rotational movement of water quickens erosion = deep plunge pool
  • gravity causes overhang to collapse - broken hard rock accelerates erosion + deepens plunge pool
  • erosion continues to undercut hard rock causing it to collapse
  • the waterfall retreats upstream over time - gorge
78
Q

How is a bluff formed?

A
  • formed on the outside bend on a meander where erosion is dominant
  • water erodes the lower section of the river bank
  • upper section is unsupported + collapses
  • creating a steep bluff
79
Q

How does water storage cause flooding?

A
  • reservoirs can raise the water table + can affect soil saturation if not careful
  • usually very large = more water enters atmosphere through evaporation + increases cloud formation - affecting precipitation

Physical Georgaphy AS (5 decks)

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