1
Q
Drainage divide
A
Also known as WATERSHED, it is the line defining the boundary of a river drainage basin separating it from adjacent basins
2
Q
Interception
A
- The capture of raindrops by plant cover, which prevents direct contact with the soil.
- If rain is prolonged, the retaining capacity of leaves will be exceeded +water will drop to ground (THROUGHFALL)
- Some will trickle along branches + down stems / trunks (STEMFLOW)
- Water retained on leaves later evaporates
3
Q
Evapotranspiration
A
The loss of water from vegetation and water surfaces to the atmosphere
4
Q
Potential evapotranspiration
A
The rate of water loss from an area if there were no shortage of water
5
Q
How does potential evapotranspiration vary?
A
- In Atbara (Sudan) potential evapotranspiration is 6,250mm p/a (High rates recorded in deserts)
- Rates much lower in rainforests due to high humidity (500-750mm)
- Lower in cold climates also e.g London (330mm p/a)
6
Q
Why are evapotranspiration rates in Egypt less than 250mm p/a?
A
- Egypt’s annual rainfall is less than 250mm
- If Egypt received more rainfall (e.g.2000mm), the evapotranspiration rate would increase due to very high temps.
- Thus if there were no water shortage in Egypt, potential evapotranspiration could be as high as 2000mm p/a
7
Q
What is eustatic change?
A
Eustatic change refers to a global change in sea level.
8
Q
What is isostatic adjustment (or isostacy)?
A
The level of the land varies in relation to the sea. Land may rise as a result of tectonic uplift or the removal of an ice sheet. The change in the level of the land relative to the level of the sea is know as isostatic adjustment.
9
Q
Examples of countries experiencing isostatic adjustment
A
Parts of Scandinavia and Canada are continuing to rise at rates of up to 20mm a year
10
Q
What is the Steric effect?
A
seawater expands with higher temperatures. Thus, even if ice sheets and ice caps did not melt, sea levels would rise in a warmer world.
11
Q
Infiltration capacity
A
The amount of moisture that a soil can hold
12
Q
Infiltration rate
A
The speed at which water can enter the soil
13
Q
Percolation
A
Percolation refers to water moving deep into groundwater zone
14
Q
Overland runoff
A
Overland runoff occurs when precipitation intensity exceeds the infiltration rate, or when the infiltration capacity is reached and the soil is saturated
15
Q
What is the zone of aeration?
A
The zone of aeration is a transitional zone in which water is passed upwards or downwards through the soil
16
Q
What factors determine the moisture of soil?
A
- porosity (the amount of pore spaces in soil)
- permeability (the ability to transmit water)
17
Q
What is through flow?
A
Throughflow refers to water flowing through soil in natural pipes and percolates (lines of concentrated water flow between soil horizons)
18
Q
What is base flow?
A
Baseflow refers to the movement of water within the zone of aeration
19
Q
What is interflow?
A
Interflow refers to the movement of water within the zone of saturation
20
Q
Why is the soil moisture deficit low during late winter and early spring in London and Madrid?
A
- high levels of precipitation
- limited EVT
21
Q
What is soil moisture recharge?
A
Soil moisture recharge occurs when precipitation exceeds potential EVT
22
Q
What is soil moisture surplus?
A
Soil moisture surplus is the period when soil is saturated and water cannot enter, and so flows over surface
23
Q
What is soil moisture utilisation
A
Soil moisture utilisation is the process by which water is drawn to the surface through capillary action and may be used by plants or evaporated
24
Q
Discharge
A
The volume of water passing a given point over a set time
25
Why do steeper slopes lead to higher velocities?
Influence of gravity
26
Which river variables increase downstream ?
Discharge, width, depth, velocity
27
Does channel roughness increase or decrease downstream?
Channel roughness decreases
28
How does friction create an uneven distribution of velocity in a stream?
- water closest to the bed + bank travels slowest
| - water nearest centre travels fastest
29
How is the shape of the river channel determined by the type of rock?
- solid rock allows only slow changes
- alluvium allows rapid changes
- silt + clay produce steep, deep, narrow valleys
- sand + gravel promote wide, shallow channels
30
What is the river regime?
The river regime is the seasonal variation in the flow of a river
31
What does a storm / flood hydrograph show?
It measures the speed at which rain falling on a drainage basin reaches the river channel
32
Rising limb
indicates amount of discharge + speed at which it is increasing
33
Lag time
time interval between peak rainfall + peak discharge
34
Advantages of flooding to Bangladesh
- replenish groundwater reserves
- provide nutrient rich sediment for agriculture in dry season
- provide fish (fish supply 75% dietary protein + 10% annual export earnings)
- reduce need for artificial fertilisers
- flush pollutants + pathogens away from domestic areas
35
Flooding in Bangladesh // background info.
- one of world's poorest + most densely populated countries (over 1000 people per square km)
- during Monsoon season 30-50% of country flooded
- 70-80% Bangladesh less than 1m above sea level
- 31.5% population below poverty line
- many people landless so forced to live + cultivate flood plains
36
Flooding in Bangladesh // human activity
1- reducing flooding by building embankments have prevented backflow of water into rivers
- leading to drainage congestion + backflooding
2 climate change = more tropical storms + rising sea levels = more floods
37
1998 flood in Bangladesh // possible causes
- increased urban infrastructure increases surface runoff
- dams in India cause sedimentation of river, reducing cross section
- high groundwater tables
- deforestation (annual rate: 3.3% p/a)
38
1998 flood in Bangladesh // impacts
- 2/3 country underwater for 50 days
- 4750 people killed
- 28 million homeless
- 130,000 cattle died
39
Aswan High Dam, River Nile, Egypt // advantages
- provides hydroelectric power
- improved navigation
- recreation + tourism
- worth $500million to Egypt economy every year
40
Aswan High Dam, River Nile, Egypt // disadvantages
- dams provides half expected amount of water
- 100,000 Nubian people removed from ancestral home
- erosion of Nile delta: 25mm a year
- sardine yields down by 95%
- 3000 jobs in Egyptian fisheries lost
41
Aswan High Dam, River Nile, Egypt // why was it built
- essential to increase water supply
- building a dam reduces risks on water control politics
- needed to increase agriculture to keep up with growing population
42
Abrasion
Sand and pebbles are dragged along the riverbed, wearing it away
43
Attrition
Rocks wear each other away as they knock together
44
Hydraulic action
Fast flowing water is forced into cracks, breaking up the bank over time
45
Solution (erosion)
Alkali rocks e.g. limestone are dissolved in acid rainwater
46
Suspension
Tiny particles of sediment are carried in the river's current
47
Saltation
Small stones are picked up and then dropped again along the riverbed
48
Solution (transportation)
The chemical load carried dissolved in the river
49
Traction
The heaviest material dragged or rolled along the riverbed
50
Flotation
Leaves and twigs carried on surface of the river
51
How are oxbow lakes created?
- Oxbow lakes are the result of erosion + deposition
- Lateral erosion, caused by helicoidal flow, is concentrated on outer, deeper bank of meander
- in flooding, erosion increases
- river breaks through + creates new, steeper channel
- in time, old meander closed off by deposition to form oxbow lake
52
Where do rapids frequently occur?
Rapids frequently occur on horizontally bedded rocks. Layers of hard rock resist erosion + form shallow areas of turbulent flow within rivers e.g. Nile cataracts
53
How are levées formed?
- when river floods, speed reduced (slowed down by friction caused by contact w. floodplain)
- reduced velocity means river deposits its load
- drops coarser, heavier material first to form raised banks (levées) at edge of river
54
What is a river terrace?
A river terrace is an eroded floodplain that is separated from the new floodplain by a steep slope
55
When natural land is altered, storm sewers must collect the rainfall that otherwise would have been absorbed into the ground. What is the problem with these storm sewers?
- sewers speed up flow of water into rivers
- sewers are smoother than natural channels, so water drains away quickly, reducing storage
- storm water washed off roads can contain contaminants, polluting rivers
56
How does encroachment on the river channel lead to increased flooding?
- encroachment on river channel occurs as a result of embankments, reclamation...
- resulting reduction in channel width = higher floods
- bridges also restrict free discharge of floods + increase levels upstream
57
How do dams lead to reduced flooding ?
- help reduce flood peaks, by storing water in a reservoir
- make flood peaks lower + more predictable
- e.g.Aswan High Dam reduces high flood water + supplements river when flows are low
58
Groundwater pollution in Bangladesh // background
- since 1970s, following lead of UNICEF, Bangladesh has extracted groundwater
- alternative to contaminated water that was killing 1/4million kids p/a
- as a result, infant mortality fell by half
- now found 1/5 groundwater wells contaminated with arsenic
- 1/10 people who drink arsenic water will die of cancer
59
Groundwater pollution in Bangladesh // solutions
- concrete butt, collecting surface water by pipe from gutters
- filter system
- better watershed management may make surface water safe
60
Groundwater recharge occurs as a result of:
- infiltration
- seepage through banks + beds of surface water bodies (oceans, rivers)
- groundwater leakage + inflow from adjacent aquifers
- artificial recharge from irrigation, reservoirs...
61
Losses of groundwater result from:
- evapotranspiration (esp. in low-lying areas)
- natural discharge (spring flow + seepage into surface water bodies)
- leakage + outflow from adjacent aquifers
- artificial abstraction
62
Groundwater depletion in India
- groundwater irrigation transformed lives of millions
- rectified problems of waterlogging + salinisation
- 1/3 India's groundwater blocks defined in 2004 as 'critical, semi-critical or over-exploited'
- 15% India's food produced by unrenewable extraction of groundwater (World Bank)
- In 18/20 Punjab districts, groundwater levels have dropped 10m+ since 1979
63
What is a wetland?
Land with soils that are permanently flooded
64
Factors causing load + degradation of wetlands
- increased demand for agricultural land
- population growth
- infrastructure development
- river flow regulation
- invasion of non-native species + pollution
65
Changing river management - the Kissimee River // background
- 165km Kissimee river once meandered through Florida
- floodplain reached up to 5km wide
- inundated by heavy seasonal rains
- home to wetland birds, plants + fish
- frequent flooding = severe impacts for people
- between 1962-71 river channelised into 90km, 10m deep drainage canal for draining floodwaters
66
The Kissimee River Restoration Project // aim
- aim was to restore over 100 square km of river + associated wetlands by 2015
- project started in 1999 + has benefited over 320 species, including bald eagle + wood stork
- restoration of river requires Dechannelisation
- entails backfilling 1/2 flood-control channel + reestablishing water flow through natural channel
- in residential areas, flow-control channel remained
67
The Kissimee River Restoration Project // costs
- project cost $414million, a bill shared by Florida + federal government
- restoration of river's floodplain may result in higher water losses due to evapotranspiration in wet periods
68
The Kissimee River Restoration Project // benefits
- higher water levels support natural river ecosystem
- populations of key avian species e.g wading birds have returned to restored area + numbers increased
- dissolved oxygen levels doubled (critical for survival of aquatic species)
- increased recreational usage on restored river enhance local + regional economies
69
Types of irrigation
- total flooding (paddy fields)
| - drip irrigation (precise amounts measure out to each individual plant)
70
How has irrigation affected water table levels?
- In Texas, irrigation has reduced the water table by 50m
| - In the fertile Indus Plain in Pakistan, irrigation has raised the water table by almost 6m since 1922
71
Irrigation can reduce the earth's albedo (reflectivity) by as much as 10%. How?
A reflective sandy surface may be replaced by one with dark green crops
72
Why are storms and tornadoes more frequent over irrigated areas?
When irrigated areas have moist soils in summer + a complete vegetation cover. Evapotranspiration rates increase, resulting in greater amounts of summer rainfall. e.g. in Texas
73
Managing the Murray-Darling basin // background
- Murry-Darling = Australia's longest river system
- no longer carries enough water to reach the sea
- 10 years of drought + many years overexploitation + pollution
- region affected by periodic El Niño weather pattern
- the flow of the Darling varies wildly, from 0.04% to 911%
- so a region that accounts for 40% of Australia's agriculture was on verge of ruin
74
Managing the Murray-Darling basin // what happened
- by 1994 human activity was consuming 77% of river's average annual flow
- reduced flow + increase runoff from saline soils made river unhealthily salty
- tap water in Adeliade, which draws 40% municipal supplies from river, was tasting salty
- number of indigenous fish was falling, since floods that induced the to spawn were becoming rarer
- toxic algae flourished in warmer waters
75
Managing the Murray-Darling basin // reforms
- New South Wales, Victoria + South Australia capped amount of water they took from river
- no more subsidies for irrigation
- farmers responsible for maintenance of channels+dams
- scientists calculated maximum sustainable yield for each river + tributary and made certain extractions didn't exceed it
76
Managing the Murray-Darling basin // progress made?
- the states have made much progress
- by 1999 avg salinity had fallen by 20%
- construction of fish ladders around dams + weirds has spawned a recovery in native species
77
Managing the Murray-Darling basin // problems that still remain
- farmers in certain states can still drill wells for groundwater
- tree plantations absorb much of rainwater that would otherwise find its way into the river
- small dams on farms, which block small streams // trap runoff, also prevent water reaching river
78
Possible measures to reduce nitrate loss: (northern hemisphere)
- avoid using nitrogen fertilisers in Autumn + Winter when soils are wet
- don't apply nitrogen to fields next to stream // lake
- don't plough up grass as releases nitrogen
- incorporate barley straw to prevent algal growth (uses nitrogen as it decays)
79
Demand for water (local / national scale): The Middle East
- for decades Israel has obtained 80% of water provided by mountain aquifer under the West Bank
- West Bank has 120,000 Jewish settlers who use 60 million cubic metres p/a
- 1.5million West Bank Arabs use 137million cubic metres
- West Bank settlers irrigate 70% cultivated land
- only 6% Palestinian land irrigated
- most domestic water in Palestinian Gaza Strip is saline as comes from badly depleted aquifer
Geography IB
flashcards
Decks in class (8)
# Cards
-
Core Theme 1 - Patterns And Change85
-
Core Theme 2 - Disparities In Wealth And Development86
-
Option Theme - Hazards and Disasters86
-
Optional Theme - Freshwater79
-
Global Interactions280
-
Core Theme 3 - Patterns in Environmental Quality + Sustainability47
-
Core Theme 4 - Patterns in Resource Consumption56
-
Option Theme - Oceans and their Coastal Margins126
