Revision sessionRevision session

Rivers

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The next 5 weeksThe next 5 weeks•Will all have a similar format.

•Each week will be a different section:

•Week 22: Rivers

•Week 23: Hazards

•Week 24: Eco activity & energy

•Week 25: Urban

•Week 26: Fragile environments

•After that – a mixed bag of any questions I can locate!

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Weeks 22 - 26Weeks 22 - 26• Each again will be similar:• First there will be a few of sheets of keywords (my

aim is put them all into zondle quizzes for you to do at your leisure) and diagrams, processes and general theory.

• Then there are case studies - what you could asked and some key points to get under your belt.

• The final section will be going over an exam question or 2 and you will get one for homework.

• Now this will be easy, except for coasts, as coasts were new to the syllabus and so there is only the mock material and 2011, so we do not have a great deal of choice there. The others were all present in the old syllabus so I can cut and paste a bit and we will have enough to practice.

• See over for details of this unit …..

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• The world’s water supply is contained within a closed system — the hydrological cycle. Water is transferred between its various stores.

• The hydrological cycle: characteristics, stores and transfers.·

• Features of a drainage basin: watershed, source, mouth, channel network.·

• The hydrograph (discharge, base flow, stormflow) and river regimes: factors affecting them (precipitation, temperature, water abstraction, dams).·

• Running water has a significant influence on the development of landforms.

• Processes: weathering and mass movement; erosion and deposition.

• Factors affecting these processes (stream velocity, slope, geology).·

• Formation of valleys, interlocking spurs, waterfalls, meanders, ox- bow lakes, flood plains and levees.·

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• Water is vital to people, varies in availability and therefore needs careful management.

• The uses of water: agriculture, industry, human hygiene and leisure including the reasons for a rising demand resulting in areas of water surplus and water shortage.·

• Reasons for differences in water quality. Sources of pollution (sewage, industrial waste, agriculture).

• Managing the supply of clean water (dams and reservoirs; pipelines; treatment works).·

• Flooding: causes (intensity of rainfall, snowmelt, steep slopes, impermeable surfaces, human activities) and control (construction of spillways, embankments). Case study of the rising demand for water in one country

o E.g UK A case study of a dam or reservoir project.

o E.g. Three Gorges A case study of a flood defence scheme

o Bangladesh: Ganges- Brahmaputra

• fieldwork not included as you should already have that elsewhere

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Hydrological cycleHydrological cycle

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A drainage basin system (not cycle) as it is open. This means that it has water coming in (inputs) and water leaving (outputs).What are the inputs to this system? (colour?) What are the outputs to this system? (colour?)All the greens are what?All the oranges are what?The key is covered up - but the next slide might help!

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List the inputs, outputs, stores and flowsThen return to slide 6 and add any more stores and flows not on this diagram

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HydrographHydrograph

• Can have 2 meanings: Either a graph showing the annual discharge of

a river at a particular point Or a storm hydrograph shows the changing

discharge following a storm

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Need to know and understand all Need to know and understand all these termsthese terms

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How does one storm hydrograph vary How does one storm hydrograph vary from another?from another?

• Area:

Large basins receive more precipitation than small therefore have larger runoff

Larger size means longer lag time as water has a longer distance to travel to reach the trunk riverSlope

Channel flow can be faster down a steep slope therefore steeper rising limb and shorter lag time

• Rock Type:

Permeable rocks mean rapid infiltration and little overland flow therefore shallow rising limb

Go through these and sketch out different hydrographs compared

with a ‘normal’ one

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How does one storm hydrograph vary How does one storm hydrograph vary from another?from another?

• Soil:Infiltration is generally greater on thick soil, although less porous soils eg. clay act as impermeable layersThe more infiltration occurs the longer the lag time and shallower the rising limb

• Land use:Urbanisation - concrete and tarmac form impermeable surfaces, creating a steep rising limb and shortening the time lagAfforestation - intercepts the precipitation, creating a shallow rising limb and lengthening the time lag

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How does one storm hydrograph vary How does one storm hydrograph vary from another?from another?

•Precipitation & Temperature:Short intense rainstorms can produce rapid overland flow and steep rising limb

If there have been extreme temperatures, the ground can be hard (either baked or frozen) causing rapid surface run off

Snow on the ground can act as a store producing a long lag time and shallow rising limb. Once a thaw sets in the rising limb will become steep

If it is warm summer weather, more of the precipitation will evaporate, so less will reach the river, so the peak flow will be reduced

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A drainage basinA drainage basin

•Now the meanings of all these words and be able to define them

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Processes that change sceneryProcesses that change scenery• What do rivers do?• Rivers have energy. That means they can do

work. The work they do is erosion and transportation. When they run out of energy they have to stop doing work, so they drop what they’re carrying. That’s called deposition

Solution often called corrosion

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Weathering and mass wastingWeathering and mass wasting

Mass wasting is the downward movement of materials propelled and controlled by gravity down a slope.

scree

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What you need to be able to draw and What you need to be able to draw and explain:explain:

* Some really good diagrams pages 10 and 12 in textbook

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What you need to be able to draw and What you need to be able to draw and explain:explain:

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Water usage: Water usage: • Water surplus = more precipitation than is used• Water shortage = need more water than

rivers/precipitation can supply -• Know the world figures (70,20,10 will do fine) and

be aware of differences between HIC use and LIC use (but not the numbers).

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Reasons for differences in water Reasons for differences in water quality - Causes of water pollution?quality - Causes of water pollution?

For explanation see notes

below slide

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Despite the problems …Despite the problems …• We do have systems in place that (a) clean up water

before we use it and (b) clean it again after we use it before let it back in the rivers!

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This is a screen print from a really good site that explains it very clearly – it can be found on

http://www.metrocouncil.org/environment/Kids/01.htm

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Causes of river floodingCauses of river flooding

•Return to slides 11 to 13 and write down those areas most likely to flood.

•Make sure that you could write a because to go with it - if you have time, if no go back and check it out later.

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Ways of managing floods - 2 typesWays of managing floods - 2 types

•Hard engineering - Refers to the more traditional engineering methods of damming, piping and channelling stormwater run-off, rather than working with more natural method.

•Soft engineering - Engineering methods which are more closely aligned with the way natural systems work - sometimes called adjustment or mitigation

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Ways of managing floods - 2 typesWays of managing floods - 2 types• Hard engineering• Dams to control water

levels up stream• Raised artificial banks• Relief channels

(spillways)• Straighten rivers to

speed flood water on its way

• Dredge channels to enlarge channel size

• Overflow basins to take extra water

• Soft engineering• Flood warning systems

to allow evacuation • Sand bagging to

prevent homes being flooded

• Zoning development to avoid areas that flood often for all building

• Only permit landuse that can flood without long term damage e.g. sports fields, nature reserve

• Preserve marshlands which will soak up water

Case studiesCase studies

Rising water demand - UK; pages 18-20

Dam reservoir - 3 Gorges; pages 30-31Flood defence - Bangladesh; pages 25

- 26

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Country with rising demand - UKCountry with rising demand - UK• Consumption 120 litres a day (book), 160 litres a day

(Offwat) -not a lot when compared with the USA at 575 litres a day

• Rising due to population growth (domestic currently 20%) - also rising expectations - more washing machines, dishwashers - gardens in SE England becoming drier

• Main use in electricity generation• Increasing use in crop irrigation - note recent drought

warnings mean that even more will be need this year• Climate change is threatening long term deficit in East

and Southern England. But we have a real problem this coming year in 8 counties already under drought orders.

• Mismatch of supply and use = water stress and this is a serious issue.

• But how are they coping?

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Country with rising demand - UKCountry with rising demand - UK• But how are they coping in SE England where things

are worst?• Boring deeper into the aquifers (ground water

stores) - about 10 years ago a bore in Essex was lengthened from 200m to 600m - and the engineers said that was likely to go dry inside 20 years.

• Construction of reservoirs in the wetter parts of the UK and piping the water in, e.g. Elan Valley has supplied Birmingham with water for over 100 years.

• New idea talked about in the last few weeks - using canals and pipes to build a water grid similar to the electricity grid, so water can flow anywhere it is needed.

• Encouragement for people not to waste water - wash your teeth everyone?

• Grey water usage - water that has been used for baths, dish washers etc or captured rainwater recycled via your toilet.

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Dam reservoir - 3 Dam reservoir - 3 GorgesGorges

•Where? China on the Yangtze River.

•Why? Originally for flood control. During the 20th Century there were 3 catastrophic floods, plus many smaller ones. Over 300,000 people have been drowned. The dam will prevent flooding, thereby saving thousands of lives.•The dam will prevent flooding, thereby saving thousands of lives

•But later it became obvious it could supply up to 10% of the electricity needed by a fast industrialising China, which at the time was dependent on dirty coal fire power stations., which were contributing increasing to global warming.

•Also it meant the Yangtse River would be navigable must further upstream, reducing road transport costs and pollution.

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Dam reservoir - 3 GorgesDam reservoir - 3 Gorges

• Disadvantages:• Need to displace over 1 million people -

including 13 cities• Flooded valley would lead to loss of some of the

most fertile farm land• Dam would trap silt that would have otherwise

replenished farmland down stream, leading to increased use of artificial fertilizer.

• Concerns that the recent earthquake just before the last Olympics occurred on the same fault line that is the 3 Gorges Dam on.

• Also concerns about disease and loss of fish stocks in the water trapped behind the dam.

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Causes of floods in BangladeshCauses of floods in Bangladesh

•80% of Bangladesh and 90% of its people live below 1metre above sea level.

• It is formed from the flood plains of 3 huge rivers, Ganges, Brahmaputra, and Meghna.

•Causes of flood: monsoon rains - summertime Spring melt water from the Himalayas Deforestation in the Nepal

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Flood management in BangladeshFlood management in Bangladesh

•Bangladesh Flood Action Plan (FAP): Build mud embankments around towns and

cities Dredge channels that have become silted up Straighten channels to reduce erosion and

speed flood water on its way Construct dams upstream to trap water

before it floods the cities Construct spillways to redirect flood water Improve forecasting and public flood warnings Build raised shelters of concrete on higher

ground.

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What does a case study answer needWhat does a case study answer need• 1. Make sure you know what they want to hear? Is it:

causes or reason Or Consequences or management?

• Do not tell them anything they have not asked for!• Have they used any technical terms like ‘water

stress’ or similar? If so explain what these mean at the start.

• If there are some general answer to the question for example causes of flooding for example - list all those you worked out slide 24 in summary.

• Then going to the Bangladesh study and say for example in Bangladesh …..

HomeworkHomework

The homework sheet has 3 questions on

Be sure to do at least one nowKeep the others for later, but do

let me mark them when you decide to do them - thinking about

what you could do better is a great revision tool