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UNIT 2 The Natural Environment SECTION A- The Physical World

RIVER LANDSCAPESRiver processes produce distinctive landforms

What is a drainage basin?

Rivers begin in upland area and flow downhill to the sea.SOURCE - where the river starts.MOUTH- where it meets the sea.As makes its way to the sea,RIVER CHANNEL (area which a river flows) and VALLEY change- River becomes WIDER and DEEPER as joined by smaller rivers(TRIBUTARIES).CONFLUENCE – point at which rivers meet.-River valley - sides become less steep, gradient decreasesshape of valley changes from V-shaped broader UDRAINAGE BASIN - land drained by river systemWATERSHED – boundary of drainage basin (usually highland)Activitiesa) Define : WATERSHED, CONFLUENCE, TRIBUTARY, SOURCE. MOUTH (5 marks) (10 marks)b) Draw a diagram of a drainage basin and label key features.

How do rivers erode?

Banks and bed of a river are continuously attacked by water within the channel(EROSION) and processes out of the channel such as WEATHERING and MASS MOVEMENT.

PROCESSES OF RIVER EROSION (in river channel)HYDRAULIC ACTION- pressure of water pushing against bank and bed of river. Includes air compressing into cracks more pressure rock breaks.

CORRASION- particles (load) carried by river thrown against banks with force.

CORROSION (solution)- chemical reaction between certain rock types and river water. Seen in limestone as river eats through rock and flows underground.

ATTRITION- Rocks in the upper course roll around and knock each other until smooth pebbles or sand are formed.

What are the main types of weathering? (the breakdown of rock in situ- not moving)

Physical weathering Chemical weathering Biological weatheringFreeze thaw or frost action- water gets into cracks temperature falls below freezing water will expand as turns to ice.Expansion puts pressure on rocks around it fragments of rock break off.Common in highland areas. (above freezing daytime, below freezing at night)

Rainwater contains weak acids which react with certain rocks.Carbonates in limestone dissolved by these weak acids break up or disintegrate the rock.Seen in limestone statues or pavement eg. Malham

Action of plants and animals on land.Seeds fall into cracks grow with moisture. Roots of young plant force through cracks and break up rock over time.Burrowing animals (rabbits) also break up the rocks further.(see figure 2 p64 textbook)

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What is mass movement?

It is when material moves down a slope due to the pull of GRAVITY. Two types are soil creep & slumping.

SOIL CREEP SLUMPING (rotational slipping)-The slowest downhill movement of soil.-Water in the soil is pulled down the slope by GRAVITY so the soil will move downhill with the water.-This happens very SLOWLY so we can’t see it happen but moves quicker after heavy rain.The slope may appear rippled (TERRACETTES)-see photo below and fig 3 p65

-Common on river banks.-Involves large area of land moving down a slope.-Due to the nature of the slip, leaves curved surface-Common on CLAY riverbanks:i) during dry weather clay contracts and cracks.ii) when rains, water gets into cracks where absorbed until rock is saturated.iii) weakens rock, due to gravity slips down on slip plane. (figure 4 p65)

Activitiesa) Define: weathering and erosion. (4 marks)b) Outline the process of slumping. (2 marks)c) State one impact of slumping. (1 mark)d) Mass movement can occur in river valleys. Explain the process of mass movement. (3 marks)

How do the characteristics of a river and its valley change?

-As a river moves downstream its ENERGY changes.-In an upland area the river is way above sea level so has the power to erode downwards (vertical erosion)so forms a V-shaped valley.-As gradient (slope) of valley decreases, river uses energy to transport material it has eroded.-Due to lack of gradient, river erodes sideways (laterally).- As river moves closer to the sea, gradient decreases further.- Deposition becomes most important process so valley becomes wider and flatter.-Change from erosion to deposition explains change in landforms and shape of river valley as move to sea.-LONG PROFILE shows steep gradient at source, becomes more gentle towards the sea- These changes show river split into UPPER, MIDDLE and LOWER course. (figure 5 p65, fig 6 p66)Activitiesa) Draw a long profile of a river on an A3 sheetb) Add arrows to show how variables change downstreamc) Add photos of landforms found at the different stages d) Annotate the A3 sheet to explain the changes

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-As river moves downstream DISCHARGE also changes:DISCHARGE: amount of water passing a specific point at a given time and is measured in cubic metres (m³) per second [cumecs]. Depends on the river’s velocity and volume. Volume: is the amount of water in the river Velocity: is the speed of the river. DISCHARGE = VELOCITY x VOLUMEAs rivers moves towards the sea, DISCHARGE increases as increased volume as more tributaries join.VELOCITY determined by amount of water in contact with bed and banks. If deeper, less contact between river and its banks and bed therefore less FRICTION river velocity greater.

Describe and explain the changes in width, depth, discharge and gradient of a river valley as it moves from its source to its mouth.

Channel becomes wider and deeper River valley: sides less steep, gradient decreases, shape changes from a V to a broader shape, almost like a flat-

bottomed U. Reasons for these changes:

Discharge increases as the river flows downhill to the sea because tributaries join the main river increased river energy.Friction decreases from upper course to lower course increased power of erosion.Upper: only vertical erosion as the river is small, most of the water is in contact with bed 95% of energy used to overcome friction small velocity and small volume of water= lowest discharge. V-shaped valleyMiddle: lower gradient lateral erosion[ higher discharge + transported material increase erosion; lower friction as discharge is higher]Lower: still lateral erosion. But low gradient, deposition most important process valley wider and flatter.

What landforms can be found in river valleys? River’s course split into 3 sections: UPPER, MIDDLE, LOWER.UPPER COURSE

• Vertical erosion is the dominant process • River channel narrow and shallow, often lined with large angular boulders • Quite steep gradient • Velocity quite low because so much energy used in overcoming friction with the rocky bed and banks

of the river FEATURES: V-shaped valleys, interlocking spurs and waterfalls

V-shaped valleys and interlocking spurs

Activities a) Outline how river characteristics change. (4 marks) b) Compare the characteristic features of a river in its upper and lower stages. (4 marks) c) Activities 1 & 2 p67 (map work)

-Upper course river is small, most water contact bed and banks lots of friction-95% energy used to overcome friction.-River flows slowly. Rest of energy used to erode downwards(vertical erosion) V-shaped valley- As river winds its way down between barriers of more resistant rock, spurs which interlock down the valley are

formed interlocking spurs.

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WATERFALLS-Form when river crosses a band of less resistant rock, after flowing over relatively hard, resistant rock.-A waterfall is a steep, sudden drop in the course of a river.

(also fig 11 p68)

MIDDLE COURSE• River is deeper as result of being joined by a number of tributaries. • Gradient less steep • Less water in contact less friction and river more power to erode.

• River continues to erode vertically but lateral erosion becomes more important as less gradient as valley flatter and more gentle slopes.

• Begins to meander due to increase in lateral erosion. • Erosion on the outside of meanders removes interlocking spurs and the valley becomes wider.

MEANDERS: Cross-section of a meander (label using fig 14)

LOWER COURSE• Channel is wide and deep, surrounded by wide valley floor• River flows through a wide flat valley called the FLOOD PLAIN.• Velocity greatest as less friction.• Slopes of valley and gradient of channel very gentle.• Deposition of sand and silt (alluvium) most important process as has large load of eroded material.• However, still some lateral erosion. FEATURES: Ox-bow lakes, floodplains, levees and deltas.

1) The softer rock is cut back more quickly leaving an OVERHANG of harder rock.2) In time collapses due to GRAVITY3) PLUNGE POOL develops with HYDRAULIC ACTION eroding the soft rock of the back wall.4) Over time the waterfall RETREATS up valley forming a GORGE.PLUNGE POOL: deeper, contains boulders from overhang and back wall. River erodes rocks by CORRASION.ACTIVITY: Explain how a waterfall is formed. (4 marks)

-Outside of bend-deepest water because greatest erosion forms RIVER CLIFF. -Moving fast and erodes bank by CORRASION. Moves fast due to depth and lack of contact less FRICTION.-SLIP-OFF SLOPE forms inside due to DEPOSITION.-Here water shallower, slower, more friction,so river less powerful unable to carry LOAD DEPOSITION.ACTIVITY: a) Explain the formation of a meander(4 marks)b) Complete activities 1-3 p69 (4,3,4 marks)

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OX-BOW LAKES (Also fig 20 p70)

ACTIVITIESa) Explain the formation of an ox-bow lake. (4 marks)b) Activity 1 (1 mark), 2 (4 marks), 3 (3marks) p70

FLOOD PLAINS AND LEVEES

(also fig 21 p71)

Lower course= very large meanders. Continual erosion of outside banks, deposition on inside bank meander neck narrower if flooding [high discharge] river cuts through the gap and forms a straight channel.Old bend cut off and called OX BOW lake.

Formation of a flood plain-The river carries large quantities of load.-As the water floods onto the flood plain there is greater friction, the water is shallow and the velocity falls so its load is deposited onto the flood plain as alluvium. The migration of meander bends across a valley also contributes to formation of a floodplain.Levees-As a river floods, its channel width increases increased friction as more water in contact with land. -River has less energy and drops the load it is carrying.-Largest material [heaviest] deposited first close to the river channel after a number of floods builds up to form levees.

FLOOD PLAIN- low, flat area either side of river.Found middle course but more usually lower.

ACTIVITIESa) Explain the formation of levees (4 marks)b) Question 2 p71 (4 marks)c) Question 3 p71 (3marks)

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Flooding and flood preventionWhat are the human and physical causes of river flooding? Flooding occurs when a river gets more water than its channel can hold. HUMAN CAUSES OF FLOODING PHYSICAL CAUSES OF FLOODINGDams may burst leading to excess water in channel. Steep valley slopes rainwater into channel quickerIf town on floodplain ,storm drains will move water quicker into channel. Higher risk of flooding.

If large amount of rainfall ground become saturated and flow quicker into river channel

If vegetation removed, less interception and water move into river channel quicker.

During cloudburst in thunderstorm, rain droplets so

big and fall so quickly no time to sink into ground water runs very quickly into river flooding

Ploughing up and down slopes channels water into river quicker.

River beds become silted make channel smaller and more likely to flood.Impermeable rocks not allow water to soak so flows quickly to river channelSnow and ice thaw quickly, large amount of water in river and unable to cope and risk of flood.Dry period, ground becomes hard, unable to soak in, runs off quickly into channel, risk of flooding

What are the effects of flooding on people and the environment? (MAP p74-75)-Effects of flooding depend upon: area of flood + where flood happens. Effects greater in DENSELY pop.area.MEXICO 2007The River Grijaiva flooded in the state of Tabasco.-Approx. 1 million people were affected by the flood.-70% of the state was under water.-All the crops were destroyed.-Tabasco’s capital, Villahermosa, was turned into a brown lake with only tree tops and roofs visible.-300,000 people trapped in their homes.-Sandbags used to protect carvings at Tabasco’s ancient archaeological site.KENYA 2007The River Tana burst its banks.-Much of the town of Garissa was under water, with houses near river submerged.-Flood destroyed bridges and made roads impassable, so aid drops by plane only way deliver food to people.INDIA 2008The Kosi river burst its banks. 1600 villages affected.-Thousands of people were stranded on rooftops and trees or marooned on thin strips of dry land.-55 people were killed.-Road linking Saharia village to the rest of the hard-hit Saharsa district was completely washed away.USA 2006Floods caused problems in a number of states.-200,000 people evacuated from homes in Pennsylvania because of rising waters on Susquehanna River.-State of emergency declared across large parts of New Jersey, New York and Pennsylvania states.-Largest evacuation in Wilkes-Barre, Pennsylvania.-A group of children ferried out of a tennis camp by raft in Philadelphia.-Numerous roads and bridges closed.-Nine people killed in eastern USA.BOLIVIA 2007Many rivers burst their banks.-340,000 people were estimated to have been affected.-About 100,000 people left homeless. Roads in Santa Cruz and Beni were blocked by mudslides.

Activities: Explain how flooding can be caused by physical factors. (6 marks)

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-At least 19 people died as a result of flooding of the Rio Grande, tributary of the Amazon.

How are the effects of river flooding reduced by prediction and prevention?EDUCATION FORECASTING

-Governments give advice to the general public via the internet. The advice includes information on how to protect your home.-On the Environmental Agency website there is information on the likelihood of a flood. This will be identified by a system of warning codes: flood watch, flood warning, severe flood warning and all clear. These warning codes give people information on what to expect and how to react. In this way the government is helping the effects of floods by providing an effective warning system.

-The Met Office predicts (forecasts) the likelihood of a flood. The information gets to householders through weather forecasts and news broadcasts on TV and radio.-Also on their website.-If there is the likelihood of flooding the Met Office advises householders to be proactive and either ring a flood hotline number or go to the Environment Agency’s website to check the likelihood of a flood in their area.

BUILDING DESIGN PLANNINGIt can cost between GB£3000 and £10000 to protect a house from flooding. Some techniques are:-Moving electricity sockets higher up the wall.-Replacing doors with ones that are lightweight and can be moved upstairs if necessary.-Concrete floors instead of wooden ones so they do not rot if they are wet.-Using yacht varnish on skirting boards to protect from water.-Waterproof MDF can be used instead of wood as a door frame.-Building on stilts

-Before houses can be built the local authority has to give planning permission. Not granted in flood risk areas unless flood-risk assessment is carried out.-In 2010 the law requires all new housing in flood-risk areas to be flood resistant or resilient.- Defra (department for the Environment, Food and Rural Affairs) has the responsibility for deciding which areas are going to be defended against the risk of flooding. The Environment Agency then organises for the defences to be built and maintained. Defra provides the money for most of the work that is completed.

Severe flooding UK –August 2008: Doncaster Council and St Leger homes implemented series of flood resilient repairs to 138 council homes.● Waterproof plaster and wall covering.● Chemical waterproofing of concrete floors.● Waterproof medium density fibreboard used instead of wood for skirting boards.These measures will not stop flooding but mean homes can be habitable quicker after a flood in the future.

Hard and Soft Engineering TechniquesHARD ENGINEERING- method of river flood management which involves major construction work.SOFT ENGINEERING – method of river flood management which works or attempts to work with natural river processes. Does not involve major construction work.

Activity: Explain the effects of flooding on people and the environment. Use examples (6 marks)

Activity: Explain how planning and building design can reduce the effects of flooding. (6 marks)

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Advantages and Disadvantages of Hard and Soft Engineering (p77-79)

HARD ENGINEERING TECHNIQUE

DESCRIPTION ADVANTAGES DISADVANTAGES

EMBANKMENTS These are raised banks along the river

-Can be used as a path for pedestrians beside the river.-Concrete embankments are effective at stopping bank erosion.-Earth embankments provide habitat for plants and animals.

-The banks are often not built high enough.-Concrete embankments are ugly and spoil the view.

CHANNELISATION River channel may be widened or deepened to carry more water.May be straightened to carry water faster.

-Effectively protects immediate area because water is moved away quicker.-Long lasting.

-Altering the river channel may lead to a greater risk of flooding, as water is carried there faster.-Unnatural and visually intrusive.

FLOOD RELIEF CHANNELS

Channel course of river can also be altered, diverting floodwaters away.

-People close to channel safer as flood water diverted to relief channel.-Used for water sports.

-Needs large area of land,Difficult to buy if farmland.-Very expensive.

DAMS Built along course of river to control amount of discharge.Water held back by dam and released in controlled way.

-Water usually stored in a reservoir behind dam. Then used to generate hydroelectric power or recreation.

-Very expensive.-Sediment trapped behind wall of dam leading to erosion further downstream.-Settlement and agricultural land may be lost when the river valley is flooded to form a reservoir.

FLOOD WALLS Vertical barrier usually made from prefabricated concrete.

-Can be used in areas where space is limited.-Easily and quickly erected in pre-constructed sections.

They have to be constructed very well so no water leaks through.

STORAGE AREAS Large depression close to the river that will fill with water if the river overflows and therefore protecting surrounding land.

-Natural looking.-Does not damage the environment.

-Need a large area of land that is not being used.-Only come into use when the river is flooded.

SOFT ENGINEERING TECHNIQUE

DESCRIPTION ADVANTAGES DISADVANTAGES

FLOODPLAIN ZONING

Local authorities and national government introduce policies to control urban development close or on floodplains.

-Very cheap way to reduce riskof damage to property.-Sustainable as reduces impact of flooding and building damage.-Surface runoff less likely to

-Resistance to restrictions in areas of shortage of housing.-Enforcing planning controls difficult in LIC’s.

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cause flooding as floodplain not built on.

WASHLANDS River allowed to flood naturally in wasteland areas to prevent flooding in other areas.

-Very cost effective as nothing built.-potential wetland sites for birds and plants.-deposited silt may enrich the soil turning it into agricultural land.

- Large areas of land taken over and cannot be built on.-productive land can be turned into marshland.

WARNING SYSTEMS Sirens give warning of possible flooding.Environment Agency use TV, Radio, fax, text, email, phone to inform people.

-Very cheap system.-Electronic communication very effective.-Can move valuable belongings to safer location with early warning.

-Sirens vandalised so tested every year.-Might not be enough time for residents to respond.

AFFORESTATION Trees planted in catchment to increase interception and slow flow of water to river.

-Relatively low cost system.-Improves quality of the environment.-soil erosion avoided as trees prevent rapid runoff after heavy rainfall.-Very sustainable.

-Often conifers planted which makes soil acidic.-Dense tree plantations spoil natural look of landscape.-Increase fire risk due to leisure activities in forests.

River Management Case Study: River Nene, Northampton,UKIntroduction-April 9 1998 heavy rain caused R.Nene and Grand Union canal to overflow. Parts of town flooded. 2 dead.-Decision made to manage River Nene against future flooding.-By 2002, Environment Agency completed £6.8million project to protect areas of Northampton hardest hit by past flooding.-2003 and 2007 further defence works were carried out in town.(refer to map p80-81)Note: You need to DESCRIBE and EXPLAIN the management techniques.Management Techniques:A- In 2002 a flood embankment was built across the river valley at Weedon. £2million. (describe) -This raised the level of the land by 10m.- In times of flood, water can be stored behind the bank. (explain)B-Built earth embankments setback 10m from river.-Increased river channel capacity at UptonC-In 2007, work began to build defences in the Upton area. These cost £8 million.-Aim to create an area called a washland, where up to 1.2 million m³ of water can be stored during flooding. -Major roads in this area such as Upton Way(A45) are on embankments up to 6m high.-Means communications not disrupted if flooding occurs.D-At Foot Meadow 4m high floodwalls have been installed to protect the railway station, housing, industry and the Castle Inn.-Has created an open area of land onto which the river can flood.E-The areas at risk of flooding are covered by the Environment Agency’s flood warning service-aims to give 2 hours warning of possible flooding.

Activities: a)Outline the advantages and disadvantages of soft engineering techniques. (4 marks)b) Question 2, p79 (9 marks)

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-Gives local people time to prepare and evacuate if need be. Flood warning system upgraded in 2003.Testing of system took place in the Far Cotton area of Northampton.