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Physical Geography > Hydrology And Fluvial Geomorphology > Flashcards

Hydrology And Fluvial Geomorphology Flashcards

1
Q

What is a drainage basin?

A

An area drained by a single river and all its tributaries
Vary in size:
Amazon basin (40% of South America with 1,100 tributaries)
To the micro scale of a single river or stream

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2
Q

Lithosphere

A

Geological world

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3
Q

Biosphere

A

Living world

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4
Q

Describe watershed?

A

The boundary of drainage basin, the contour of land surrounding a river or stream

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5
Q

List transfers in the hydrological cycle?

A 
Stem flow
Surface runoff
Infiltration
Through flow
Channel flow
Percolation
Groundwater flow
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6
Q

List outputs in the hydrological cycle?

A

Transpiration
Evaporation
River discharge

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7
Q

List stores in the hydrological cycle?

A 
Interception
Surface storage
Soil moisture storage
Vegetation storage 
Channel storage
Groundwater storage
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8
Q

List inputs in the hydrological cycle?

A

Precipitation

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9
Q

What does precipitation include?

A

Rainfall
Snowfall
Hail
Dew

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10
Q

Describe precipitation?

A

The conversion and transfer of moisture from the atmosphere to the land

Varies due to: amount, extent, intensity, type, duration

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11
Q

Why is the hydrological cycle a ‘cycle’?

A

Continuous ( no start or end)

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12
Q

Why is the global hydrological cycle a closed system?

A

Water is not entering or leaving

Amount of water stays the same

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13
Q

Descrive storage in the hydrological cycle?

A

Parts of the system that hold or retain water for periods of time
They can be open stores on the surface of land within vegetation or hidden deep within the rock structure

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14
Q

What is interception?

A

Refers to water that is caught and stored by vegetation

It is largely affected by the size and coverage of plants with broad leaves trees catching the most water (in summer)

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15
Q

What three main mechanisms is intercepted water transferred?

A

Interception loss
Theoughfqll
Stem flow

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16
Q

Describe interception loss?

A

Water that is retained by plant surfaces and that is later evaporated away or absorbed by the plant

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17
Q

Describe stem flow?

A

Water that trickles along twigs and branches and finally down the main trunk

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18
Q

Describe throughfall?

A

Water that either falls through gaps in vegetation or drops from leaves or twigs

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19
Q

What type of trees has lots of interception?

A

With lots of leaves

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20
Q

What type of trees intercept less?

A

Trees with no leaves

Trees with needles intercept less due to surface tension

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21
Q

Where in the world does interception occur a lot?

A

Tropical areas as broad leaves

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22
Q

Describe levels of interception in woodland?

A

30% of rain falls on woodland is intercepted
Light - increased to 60%
Heavy - drop to 15%

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23
Q

How does interception vary with farm crops?

A

Corn - high

Soy beans - low

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24
Q

What is secondary interception?

A

Undergrowth intercepts water that has already been intercepted by leaves

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25
Q

What function does interception have?

A

Delays time taken from water being rain to being water in river

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26
Q

What is soil water?

A

The subsurface water in soil and subsurface layers above the water table

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27
Q

What is surface storage?

A

The name given to any parts of the system where water lies above the ground on the earths surface
Within a drainage basin water may naturally accumulate in lakes ponds or puddles through human intervention (e.g. Reservoirs or swimming pools)

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28
Q

What is channel storage?

A

Refers to water that is contained within a river channel or stream at any given time

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29
Q

Describe variations in channel storage?

A

Rivers can be seasonal
May disappear underground either naturally (limestone areas)
Or covers in urban areas

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30
Q

Where is surface storage permenant?

A

Swamp marsh or peat bog

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31
Q

What is vegetation storage?

A

When vegetation absorbs moisture directly through its root system it comes stores within the organism or plant

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32
Q

How does the amount of water stored in vegetation storage vary?

A

The size and variety of plants and the local conditions at any given time
A large leafy and thirsty plant will require more than a well watered shrub

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33
Q

Fact about groundwater storage?

A

97% liquid freshwater is groundwater

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34
Q

When does a marsh or bog occur?

A

When water table is at the surface level

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35
Q

What does groundwater refer to?

A

Subsurface water that is stored under the surface in rocks

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36
Q

Difference between soil moisture and ground water?

A

Groundwater may not be recycled for 20,000 years

Whilst soil moisture may be recycled by evaporation into atmospheric moisture within a matter of days or weeks

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37
Q

What does recharge refer to?

A

The refilling of water of water in pores where the water has been dried up or extracted due to human activity

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38
Q

When can groundwater be considered non renewable?

A

When recharge does not take pace

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39
Q

What type of rocks does groundwater occur in?

A

Porous - chalk or sandstone

Pervious - limestone

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40
Q

What is an aquifer?

A

An underground layer of water bearing permeable rock that can be found at any depth

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41
Q

What processes cause groundwater recharge?

A 
Percolation
Infiltration
Precipitation
Leakage
Seepage
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42
Q

What is throughfall?

A

Water that falls through gaps in vegetation or drops from leaves or twigs

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43
Q

What is stem flow?

A

Water that trickles along twigs and branches and finally down the main trunk

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44
Q

What two main ways does surface run off occur?

A

When precipitation exceeds infiltration rate

When soil is saturated (all the pore spaces filled with water)

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45
Q

What is channel flow?

A

The movement or water in channels such as streams of rivers

The speed and flow depends on factors such as gradient and efficiency

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46
Q

Describe why infiltration occurs she to precipitation?

A

When precipitation exceeds infiltration capacity accumulated water will flow downslopensue to the effect of gravity

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47
Q

Define porosity?

A

The capacity of the rock to hold water eg sandstone has a porosity (pore space) of 5-15% whereas clay may be up to 50%

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48
Q

What is permeability?

A

The ability to transmit water through a rock via joints and fissures

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49
Q

What is the infiltration capacity?

A

The maximum rate at which rain can be absorbed by a soil in a given condition

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50
Q

What is infiltration rate measured in?

A

Mm per hour

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51
Q

What influences infiltration rate?

A 
Water in soil already
How loose soil is (sandy)
Size of raindrops (large = less)
Slope angle (steep = less due to runoff)
Amount of vegetation (roots break up soil)
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52
Q

Describe the phreatic zone?

A

Permenantly saturated

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53
Q

Describe how infiltration rates vary with rock types?

A

Clays: 0-4 mm / hour
Sands: 3-12 mm / hour

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54
Q

Describe percolation?

A

Water moves slowly downwards from the soil into the bedrock

Speed depends on the permeability of rock

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55
Q

Describe throughflow?

A

Refers to water flowing through the soil in natural pipes and percolines (lines of concentrated water flow between horizons)

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56
Q

Define surface storage?2

A

Water that has not infiltrated the surface and is stored on the surface in the form of puddles or lakes etc

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57
Q

Define groundwater storage?2

A

Percolated water that is held within the aquifers below the water table

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58
Q

Describe how saturated overland flow occurs?

A

Water is not infiltrated on a slope due to the saturated nature of the soil, and flows across the surface
Most frequently occurs on the lower parts of slopes that have been saturated by water from above

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59
Q

Define percolation?2

A

The downward movement of water through the soil underlying bedrock after infiltration has taken place

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60
Q

Define throughfall?2

A

The movement of precipitation through the branches and leaves of trees and vegetation to the earths surfqce

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61
Q

What governs infiltration?

A

Amount
Intensity

Of precipitation

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62
Q

How can infiltration and precipitation lead to overland flow?

A

Low infiltration than precipitation leads overland flow to occur
Once the soil is saturated, saturated overland flow occurs

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63
Q

What is porosity?

A

The proportion of pore space to solid material

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64
Q

How does the porosity and permeability of clay affect water?

A

High porosity
Low permeability

Clay soils will inhibit the flow of water
Preventing groundwater flow

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65
Q

What happens if water flows over sandy soils?

A

It will pass through
Reducing overland flow
Increasing through flow

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66
Q

Descrive pressure release?

A

The creation of joints and other weakness in rocks by the removal of overburden and the release of pressure

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67
Q

What is chelation?

A

The chemical weathering of rocks by organic acids

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68
Q

Why might the death rate fall less in some areas of a country than others?

A

More rapidly URBAN areas - provision of and access to better healthcare
- improvement schemes provide clean water and efficient sewage system

PROSPEROUS POPULATION
- higher standard of living with clean water, better food, high quality medical care

DEMOGRAPHIC STRUCTURE - falls less rapidly with ageing population

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69
Q

What is base flow?

A

The normal level of water in the channel determined by the groundwater flow prior to a rainfall event

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70
Q

What is lag time?

A

This is the period between the peak precipitation and the peak discharge

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71
Q

What is peak flow?

A

This is the maximum river discharge for any given event measured in cubic metres per second

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72
Q

What is the rising limb?

A

The part of the graph that initially rises
Indicates the increasing level of water as determined by the combined rate of surface runoff
Throughflow and groundwater flow following a precipitation event

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73
Q

What is storm flow?

A

This is the additional discharge created as a result of precipitation event

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74
Q

What is the falling limb?

A

This is the part of the graph that shows the discharge decreasing and river levels falling back towards base levels

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75
Q

what is the watershed?

A

the boundary of a drainage basin

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76
Q

what can hydrography be useful for?

A

identifying the potential flood risk for an area

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77
Q

How does urbanisation affect a storm hydro gray?

A

Water can’t infiltrate through tarmac and concrete as they are impermeable

Gutters and drained that channel and direct runoff, water can be carried very quickly to water ways

78
Q

how can the presence of clay ina. soil change the way water interacts with it?

A

the greater the clay content the more water retentive the soil is as clay particles bond together tightly restricting the flow of water

79
Q

how can the presence of sand ina. soil change the way water interacts with it?

A

free draining as the larger sand particles provide gaps and spaces for water to pass through

80
Q

how can relief influence infiliteation rates?

A

less than 5 degrees has a greater chance of infiltration

the greater the gradient the rate of surface runoff as there is less opportunity for infiltrating

81
Q

example of how vegetation can influence infiltration rate?

A

80% in tropical areas

10% in arable land

82
Q

what forms of transportation are common in the upper course of the river?

A

traction - largest stones boulders and cobbles are rolled along the riverbed by strong turbulent follow

satiation - smaller bedload such as pebbles bounce along the riverbed

83
Q

Describe the material carried by the river in the upper course?

A

High level of bedload

Large angular material eg screw

84
Q

Describe the environment of the upper course?

A

High energy
High levels of erosion
Turbulent flow

85
Q

how is the middle course of the river characterised?

A

decreasing gradient
greater lateral erosion

river becomes more sinuous (winding)
greater number of tributaries mean additional water

high proportion of suspended load
bedload is smaller and less angular than upstream

86
Q

Characteristics of the lower course?

A 
low lying where the river joins the sea
wide flat sweeping flood plains
large meander bends
depositional
small rounded stones

high proportion of suspended material

87
Q

what are the three types of flow?

A

turbulent
helicoidal
laminar

88
Q

describe laminar flow?

A

horizontal smooth motion
too simplistic and complex for natural river environments (due to steps and gradients)

may be found in carrefuoly managed chanelised sections on a relatively small scale where there are few additional influences

89
Q

describe turbulent flow?

A

dominant method of flow in a river
series of erratic horizontal and vertical spiral flows (eddies)
that disturb the smooth appearance of the river

amount depends on the velocity of the flow as well as friction and energy available

the greater the velocity he greater the amount of spare energy after friction so the greater turbulence

90
Q

describe helicoidal flow?

A

cork screw like flow mainly found as water travels around river bends

associated with meanders and the formation of point bars and slip off slopes

91
Q

define the thalweg?

A

the path of least resistance where the river flows fastest

92
Q

in a straight channel describe the location of the thalweg?

A

middle of the channel under the surface of the water furthest from the influence of friction from the riverbanks river bed and the air

93
Q

in a bent channel describe the location of the thalweg?

A

will continue in a straight line before hitting the outside bend and being reflected downstream

94
Q

describe hydraulic action?

A

the force of the water pushing into cracks and hitting against the rivers banks
this repeated action weakens the riverbank as air in the cracks is compressed and pressure builds up

in rivers it is slow and ineffective

95
Q

what is cavitation?

A

when air bubbles collapse and create small shock waves - a form of hydraulic action

96
Q

describe corrosion?

A

when sediment in the river is thrown into or scraped along the banks and bed or the riv e

during times of high flow or flood the river has a greater capacity to transport larger material which results in the greatest amount of damage

potholes may form as stones become trapped in depresssions and hollows and are continually swirled around by eddies in turbulent flow

97
Q

describe attrition?

A

the process by which stones and sediment within the river become increasingly rounded
as material is transported it collides with other objects in the river
the collisions cause the stones to break off into smaller pieces and the edges and points of the stones break off

98
Q

describe solution?

A

a continuous chemical process that occurs independently from river flow
water that has elightly acidic properties (e.g. as a result of decomposing organic material - humid acid - or acid rain - carbonic acid) will chemically dissolve and weaken certain types of rock

limestone id particularly vulnerable

99
Q

what is a rivers capacity?

A

the name given to the total load of material actually transported

100
Q

what is a rivers competence?

A

the name given for the maximum size of material that a river is capable of transporting

101
Q

describe the process of traction?

A

when the largest stones boulders and cobbles are rolled along the riverbed by strong turbulent flow
often these sediments will lie undisturbed on the riverbed until sufficient discharged is reached to displace them

102
Q

describe the process of saltation?

A

smaller bedload such as pebbles stones and gravel are lifted and carried temporarily in the flow in a hopping or bouncing motion
as turbulent flow is it constant the river will have varying amoints of energy to carry and lift the load

103
Q

describe the process of suspension?

A

very fine particles of sand and silt are carried in the water itself when it is fast flowing
the faster and more turbulent the water the greater the amount and size of material transported

104
Q

describe the process of solution?

A

the pr fees by which small dissolved sediments and minerals are transported within the river
they form just a small proportion of the total load but are significant as constantly occurs

105
Q

when does deposition occur?

A

when the river no longer has energy to transport material it deposits it

106
Q

list the conditions when deposition is most likely to occur?

A

low periods of precipitation where river levels drop
where the river flow meets the sea
in areas of slow flow within a channel such as on meander bends
when the load suddenly increases above the capacity e.g. landslide
i water has carried material outside of the channel such as in flood

107
Q

what will never be deposited?

A

material in solution

108
Q

what does the hjustrom curve show?

A

the relationship between particle size and velocity

109
Q

why does clay need a greater velocity to be transported?

A

the particles stick together

110
Q

why does gravel need a higher velocity to be transported?

A

size

weight

111
Q

how does an interlocking spur form?

A

when the river flows downstream and is forced to wind through he landscape
this creates protrusions of the riverbank in the valley known as spurs
as the river continues to wind downstream in a zig zag pattern the view along the course of the river may be redirected as the spurs appear to knit together like clasped fingers

112
Q

how does a v shaped valley form?

A

the upper reaches of a catchment often experience large seasonal variations and as a result the rate of erosion can vary greatly

large angular boulders often choke the upper channel creating more friction and distrusting flow

during times of peak discharge such as periods of snow melt, vertical erosion will be high as there is tester capacity

113
Q

what are rapids?

A

areas of high velocity and turbulent flow

114
Q

what are waterfalls?

A

large steps in the river as a result of differential erosion usually attributed to bands of hard and soft rock

115
Q

explain how a waterfall is created?

A

water flowing over hard rock had a relatively negligible impact erosively
once it meets a band of soft rock is eroded more
over time the erosion will be so great that a noticeable overhang forms (step in profile)
continu d erosion may cause undercutting or the rock layers leading to the overhang collapsing into the plunge pool
the plunge pool is created as the material that falls is often large and angular and is forced to swirl around scouring out a depression

116
Q

example of a gorge?

A

niagra falls

retreats 1m a year

117
Q

erosionsl features list?

A

v shaped valley
interlocking spurs
waterfalls
rapids

118
Q

depositinal features list?

A

flood plains
levees
braiding
deltas

119
Q

when does helicoidal flow occur in a meander?

A

wh m surface water flows towards the outer banks while the bottom flow is toward the inner bank

120
Q

how do river cliffs form?

A

on the outside bend
erosion is greatest
combination of hydraulic action and abrasion weakens the riverbank causing it to collapse
over time a steep bank will be formed with some of the collapsed material remaining on the river bed

121
Q

how does a point bar form?

A

on the insider bend of a meander
discharge is at a minimum and friction is greatest
deposition is greatest
sediment accumulated to grate a gentle sloping bar

the particles are graded in size with the largest material being found on the upstream side of the bar

122
Q

describe riffles and pools?

A

riffle is a shallow area of fast flowing oxygenated water

pools are deep but slow moving water

123
Q

what is a yahoo tributary?

A

a tributary that runs parallel to the river within the same valley for some distance

124
Q

what is a floodplain?

A

a large area of flat land surrounding a river channel
it’s an area most susceptible to flooding
fertile and used for agriculture
as initially cut by the river it is made up of a large amount of alluvial deposits dropped during times of floods

125
Q

how do flood plains formed?

A

when’s. river floods alluvial deposits are dropped
as the river spills over the food plain in time or floor th is an increase in friction
a loss of energy and a resulting deposition of material
repeated flooding causes he deposits to build up in height forming a s for iand s or layers above the bedrock

126
Q

what is the edge of the flood plain?

A

a slightly raised line known as a bluff

127
Q

describe how a leveeforms?

A

when a river floods its banks the largest and coarsest material is deposited first
creating a ridge along the edge of the riv r channel
over time more sediment is added to the ridge through the same process
creating a natural preventative barrier to flooding

128
Q

explain how braiding forms?

A

when there is a high proportion of load in relation to discharge eg result of seasonal snow melt in the alphs

at times or low flow the river may be forced to cut a series or paths that converge and diverse as they weave through large expanses or deposited material

braiding begins with a mid channel bar that grows downstr an as the discharge decreases (after a flood)
the coarse bedload is deposited first
this forms the basis of bars and as the flood is reduced finer sediment is deposited

129
Q

how does flood hazard mapping work?

A

using historical data on river stages and the discharge of previous floods
along with topographic data
maps can be constructed to show areas rdpect e to be covered in floodwater for various discharges or stages

they highlight risk but are very inaccurate

130
Q

describe the differences between laminar and turbulent flow?

A

laminar is very smooth where channel is deep

turbulent flow is a series of rapid eddies caused by channel roughness

131
Q

in the formation of a waterfall, how is the back wall and plunge pool eroded?

A

CAVITATION
implosion if air bubbles
hydraulic action in joints and cracks

132
Q

how can river erosion produce rapids?

A

over outcrops of resistant rock that often bring about a steeping ofnchannel slope
increasing turubulencr and hence erosive capacity

133
Q

describe how river floods occur?

A

due to an overvsnkful level of discharge leading to the inundation of surrounding areas
notably flood plains

sudden excess of input in terms of precipitation

sudden event e.g. storm or cyclone
or seasonal event such as snowmelt

effects can be exacerbated by human activities of deforestation or urbanisation

134
Q

why is the drainage basin system an open system

A

it allows movement of energy and matter across its boundaries

135
Q

what are the main characteristics that affect local hydrology

A

intensity mm per hour
type of precipitation e.g. rain or snow
geographical distribution
temporal variability eg seasonality

136
Q

what is throughfall

A

water that either falls through gaps in vegetation or drops from leaves twigs or stems

137
Q

what is interception loss

A

water retained by plant surfaces and which is later evapoursted away or absorbed by the plant

138
Q

what conditions increase transpiration

A

warm and dry

139
Q

what is the most important factor affecting evapotranspiration

A

temperature

140
Q

what is infiltration inversely related to

A

surface runoff

141
Q

factors influencing infiltration capacity

A

antecedent soil moisture
duration of rainfall
soil porosity
vegetation cover

142
Q

what is soil moisture

A

subsurface water in soil

143
Q

what is baseflow

A

the part of a rivers discharge that is provided by groundwater seeping into the bed of s river
relatively constant
but increased slightly in a wet period

144
Q

what is recharge

A

the refilling of water in por s where the water has dried up or been artificially extracted

145
Q

what effects the character or regime of a river

A 
amount and nature of precipitation
local rocks porosity and permeability
shape of drainage basin (area and slope)
amount and type of vegetation dover
amount and type of soil cover
146
Q

what effect does urban development have on hydrographs

A

increase peak flow

decrease lag time

147
Q

what factors vary a storm hydrographic

A

drainage density
rock type
basin shape
gradient

148
Q

what are the three causes of deposition

A

reduction in gradient which decreases velocity and energy
a decrease in the volume of water in the channel
an increase in the friction between water and channel

149
Q

how does a slope influence a flood hydrograph

A

more overland flow
shorter lag time
higher peak flow

150
Q

how can soil influence infiltration

A

sandy soil allows it

clay is much more impermeable and causes water to pass overland

151
Q

how can antecedent moisture influence a flood hydrograph

A

if it has been raining before
and ground is saturated or near saturated

rain produces overland flow quickly
and a high peak flow
and a short time lag

152
Q

how can low intensity rainfall influence a hydrographic

A

infiltrate into soil
slowly percolate

increased lag time
reduced peak flow

153
Q

what does the hydraulic radius measure

A

stream efficiency

154
Q

what factors lead to the formation of braided channels

A

large proportion of coarse material
easily eroded bank material
highly variable discharge

155
Q

when does braiding occur

A

when channel is divided by islands or bars

islands are vegetated and long lived
bats are unvegetayed less stable and often short term

156
Q

what forms pools and riffles

A

riffles form of coarse gravel

pools form of erosion

157
Q

reasons for gorge formation

A

retreat of waterfalls eg niagara
glacial overflow channeling
collapse of underground caverns in carboniferous limestone areas
Gordale Scar

158
Q

where are alluvial fans found

A

semi arid areas

where swirly flowing mountain streams enter a main valley or plain at the foot of the mountains

159
Q

how does an alluvial fan form

A

a fast flowing mountain stream enters a valley or plain at the door of a mountain
sudden decrease in velocity
deposition occurs

fine material spread out as an alluvial fan
with a slope angle or leee then one degree

160
Q

what are deltas

A

river sediments deposited when a river enters a standing body of water with negligible currents

eg Mediterranean
eg lake sea or ocean

161
Q

define water table

A

the line seperating the unsaturated zone and the saturated zone
or the upper level of the saturated zone

162
Q

define recharge

A

the refilling of the zone of saturation by percolated water

lack of water or water abstraction lowers it

163
Q

throughfall

A

precipitation reaching the ground via leaf drop

164
Q

stem flow

A

precipitation which has been intercepted by vegetation and subsequently trickles down the stems of the plants

165
Q

difference between porosity and permeability

A

priority is amount of pore spaces the soil has
so is ability to hold water

permeability is the ability of soil to transmit fluids

166
Q

explain the formation of delta

A

boundary between a river and a reviving body of water e.g. lake or sea

the deposition of sediment due to the loss of energy and competence

clay particles are deposited through flocculation as a result of river water and sea water intervening

deltas are built up as the heaviest material is deposited first and the finest being deposited later

distributaries build up as the channel braids and it becomes less efficient

167
Q

when does braiding occur

A

when rivers are carrying a large amount of eroded sediment

168
Q

why does braiding occur

A

sediment load too heavy for river to carry
velocity drops
varying dischrages

169
Q

when is the only time deltas form

A

when the rate of sediment removal is less than the rate of depositon

170
Q

when does flocculation occur

A

in clay particles when fresh water meets sea water

sink due to increased weight

171
Q

what is a delta composed of in terms of layers

A

bottom set bed a
clay (via flocculation) fine grained sediments
reaches fair distance from river mouth as fine sediment can be transported further

forset bed
coarser medium sized sediments
doesn’t travel very far from mouth

top set bed
composed of larger and heavier particles

shape depends on river currents

172
Q

Describe how saltation occurs

A

the transport of medium sized particles by hopping along the bed of the river
as a result of sufficient energy

173
Q

how are bluffs formed in river valleys

A

created by the undercutting of the valley sides on either side of the flood plain
by the migration of meander
swinging in the channel

174
Q

what does the Hjulstrom curve show

A

the relationship between sediment size and velocity needed to ERODE TRANSPORT AND DEPOSIT

175
Q

where does saturated overland flow most commonly occur?

A

lower parts of slopes

that have been saturated by water from above

176
Q

what factors lead to high overland flow

A

impermeable soil
lack of vegetation and interception
steep slopes
heavy precipitation

177
Q

how does soil type influence flooding?

A

greater the clay content the more water retentive (clay particles bond tightly together), restricting the flow of water

sandy soil is free draining as the larger sand particles provide gaps and spaces for water to pass through

178
Q

how can rock type influence flooding

A

sedimentary rocks are pervious eg limestone with cracks and bedding planes
water can pass through the rock

metamorphic rocks depends on the nature of its transformation

igneous rocks eg basalt and granite do not let water through and are impermeable

179
Q

what does a circular drainage basin mean for a storm hydrograph?

A

flash floods
rapid response
as precipitated water more likely to reach river at same time treaclleing an equal distance

180
Q

what does a steep drainage basin mean for a storm hydrograph?

A

short lag time
due to gravity
increased the rate of flow to the river

181
Q

what does a large drainage basin mean for a storm hydrograph?

A

greater potential discharge

longer lag time as precipitation is caught over a wide area

182
Q

soft engineering river quaggy

A

EA sustainable approach

park lowered and shaped creating flood plain where water naturally collects (capacity of 85,000)

quality of park improved 
wetland environments (redness trees wild flower meadows)

1990

183
Q

hard engineering jubilee river

A

artificial channel diverts water
4,800 properties
700 commercial toperties

£110m to construct (£40m protected)
12km long

38 reedbed constructed
250,000 trees
woodpeckers

National cycle route and footpaths

184
Q

Dam construction in Egypt

A

55km3 released each year

control floods
supports farmland (cotton)
electricity (12 generators)

100,000 people relocated
archaeological sites relocated

185
Q

explain the formation of an alluvial fan? i

A

heavy sediment load
sudden change in gradient

river leaves the confines of s narrow channel and the ability for the flow to spread laterally

outward zina took of sediment size

186
Q

explain how throughflow occurs

A

the movement of infiltrated water under gravity downslope towards a streak fhannel

the water can move through soil by a form of piping

187
Q

describe evapotranspirstion?

A

evaporation from leaves

release of water from plant stomata

188
Q

define salt crystal growth

A

phydcial process

involving the growth of salt crystals in the pores of rock by the evaporation of water rich in salts

189
Q

define hydration

A

the physical process whereby water is absorbed by certain minerals leading to stress and possible fracture
reversible

190
Q

briefly describe what drainage density is

A

area found by measuring the total length of all the streams with a basin
divided by the area of the whole basin

average length of stream in an area

Physical Geography (6 decks)

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