River Landscapes

Questão	Responda
Drainage basin	Land that is drained by a river system boundary called watershed.
Source	Where the river begins
Mouth	Where there river meets its end into a larger body of water sea or lake
River channel	Area in which a river flows
Tributaries	Smaller rivers that join the main river
Confluence	where two river meet
Why rivers erode	Banks and bed of river under continual attack from water within river channel and other process like weathering and mass movement.
Hydraulic action	Pressure of the water being pushed against the banks and bed of the river, includes compression of air in cracks as water gets into cracks in rock, compresses air in cracks puts more pressure on cracks and pieces of rock may break off
Corrasion	Particles, load, carried along river thrown against the river banks with considerable force.
Corrosion (solution)	Chemical reaction between certain rock types and river water, particularly evident on limestone where the river often eats through the rock and flows undergound
Attrition	Slightly different process that involves wearing away of the rocks in the river. Upper course of a river rocks continually roll around and knock into each other. Chip away at each other until small pebbles or sand form.
Physical weathering	Freeze thaw weathering when water gets into cracks in rocks, temperature fall below freezing, water will expand as it turns into ice. Expansion puts pressure on the rock around it and fragments of rock may break off. Type of weathering is common in highland areas where temperature is above freezing during the day and below freezing during the night.
Chemical weathering	Rainwater contains weak acids that react with certain rock types. Carbonates in limestone dissolved by weak acids, causes the rock to break up or disintegrate, can be seen on limestone statues or limestone pavements
Biological weathering	Action of plants, animals on the land, sees fall into rock cracks, grow when moist present, roots of plant put force on creack in time break up rocks. Burrowing animals like rabbits also responsible.
Mass movement	When material moves down a slope due to pull of gravity, there are many types of mass movement.
Soil creep	Slowest downhill movement of soil, gravity will pull the water that is contained in the soil down a slope. Soil moves with water. So slow can't see happening but moves more quickly with heavy rainfall. Slope may appear rippled ripples known as terracettes.
Slumping	common on banks of a river, known as rotational slipping, involves large area of land moving down a slope, due to nature of slip leaves a curved surface. Common on clay riverbanks, during dry weather clay contracts and cracks, when it rains, water runs into the cracks and is absorbed until rock becomes saturated. Weakens the rock and due to pull of gravity it slips down the slope on it slip plane.
V shaped valleys	In the upper course river is small so a lot of water is in contact with bed and banks hence lots of frictions. Such that river moves more slowly than in the lowland. Rivers energy used to erode downward so characteristic of V shaped valley formed
Interlocking spurs	As moves down between barriers of resistant rock cannot erode and erode vertically not laterally spurs which interlock are formed
Waterfalls	Formed when river goes over area of hard resistant rock hen less resistant rock. Drop leads to a waterfall, softer rock cut back more qquicly leaving an overhang of harder rock. Overtime due to gravity harder rock collapses. Hydraulic action eroded back of waterfall. Overtime retreats forming gorge. Deep pool below waterfall known as gorge.
Middle Course	River is deeper as a result of being joined by a number of tributaries. less water in contact with the channel means there is less friction and river has more power to erode. River erodes laterally rather than vertically less gradient. Meander bend is one feature of the middle course which is caused by this increase in lateral eroision.
Meanders	Outside of a meander bend has deepest water as greatest erosion takes place and forms a river cliff. Water is moving fastest at this point hence erodes the bank using corrosion. Water moves more quickly on the outside due to the lack of friction because of depth and contact with bed and banks. A slip-off slope forms on the inside of the meander bend due to deposition. occurs because water is slower moving and shallower result in more friction and river less powerful. Therefore river is unable to carry its load and deposition takes place. Underwater current takes some of the eroded material from river cliff across the river and deposits it on the slip off slope
Lower course	Channel is wide and deep and surrounded by a wide alley floor, velocity of the river is greater as there is less friction with the channel. Slopes of valley and gradient of the river channel are very gentle as mostly deposition occur leading to build up of material and rock is less resistant which means that flatter and at a lower level will edit. Main process is deposition as large load of eroded material it is carrying (sand, silt). But lateral erosion takes place
Ox bow lakes	Meander bends become very large continual erosion on outside and deposition on the other meander bends become closer. When flooding occurs river cut through forming a new straight channel. Continued deposition of alluvium at times of low flow, result in the old bend of the river being cut off.
Floodplains	Low, flat area of land on either side of a river, can be found in middle course of a river, more usually found in lower course.
Levees	When river contains too much water to stay within its channel it floods surrounding land. As it moves away from its channel becomes shallower and friction increases. River has less energy hence mus drop some of the load it is carry. Drops large amount of material close to the river channel. after number of floods builds up to form levees. River water drops the heavies material first.
Human causes of flooding: Ploughing	Can increase chance of flood if plough up and down slopes rather than around them, channels the rainwater to the river faster.
Human causes of flooding: Vegetation removed	When vegetation removed then there is less interception and water will move to the river more quickly.
Human causes of flooding: Dams	Dams may burst causing excess water in river channels and flooding large areas
Human causes of flooding: Drainage	Storm drains will allow water to move into the river at a greater speed as drains water into the river so flooding more likely.
Physical causes of river flooding: Impermeable rock	When water cannot soak into the rocks and it therefore flows more quickly to the river through the soil or over the surface (surface run off).
Physical causes of river flooding: Sudden rise in temperature	If from a period of cold weather to sudden rise in temperature to hot temperature a rapid thaw can occur, where rivers are unable to cope with the amount of water and flood.
Physical causes of river flooding: Hot dry weather	Through period of hot dry weather the soil is very hard so that its impermeable hence surface run-off occurs.
Physical causes of river flooding: Steep valley slopes	This makes rainwater run off rapidly into the river channel making river more likely t of flood as it bursts its bank
Physical causes of river flooding: Long periods of heavy rainfall	If there are large amounts of rain day after day water will saturate the ground and flow more quickly into the river due to surface run-off.
Physical causes of river flooding: Cloudburst	During such period in a thunderstorm, rain droplets are too large so fall so quickly that there is no time for the water to sink into the ground. So water runs very quickly into the river and causes flooding.
Effects of Flooding: USA 2006	200,000 people were evacuated from their homes in north-eastern Pennsylvania due to rising waters on the Susquehanna River. Largest evacuation took place in Wilkes-Barre in Pennyslvania. Group of children ferried out of a tennis camp by raft in Philly as flooding closed many roads in and around the city. Nine deaths across eastern USA, two truckers killed on Interstate 88 in Sidney, New York, after part of the motorway was washed away by flood water. A motorist died as he swerved to avoid a washed out road in Holmesville, New York.
Effects of flooding: Mexico 2007	1.1 million residents were affected by the flooding of the Grijava River, 70% of the state was under water and all of the crops were destroyed . 300,000 people were trapped in their homes, sandbags were placed around several giant heads carved by the Olmecs, an ancient pre-Columbian people, at Tabasco's La Venta archaeological site.
Effects of flooding: India 2008	Caused by flood during monsoon season more than 2.7 million people in 1600 villages were affected, thousands stranded on rooftops and trees or marooned on thin strips of dry land 55 people were killed. Submerged roads and railway tracks and cut off electricity, road linking Saharsa village to the rest of the region was cut off. Flood water changed the course of the river now flows 120 km east of its original course.
Forecasting and Education	In England 2.1million properties are at risk from flooding. Over 50% at risk of flood by rivers. For the effects of flooding to be reduced householders can be warned about a flood so that they can take precautions. In the UK there are a number of steps first Met Office predicts likelihood and then gives info to public through weather forecasts and new broadcasts. If there is a likelihood Met Office advises householders to be proactive and either ring a flood hotline number or go onto the Environment Agency where there is info on on likelihood of flood. This is will be identified by a system of warning codes (flood watch, flood warning, severe flood warning and all clear). These give people info on what to expect and how to react. Also general advice on how to protect homes from flooding.
Planning and building designs	Flood risk assessment must be carried out before local authorities allow houses to be built. By the 2010 government indicated that planning laws will change so that all new housing in flood risk areas must be flood resistant. Improvements in houses can cost from 3000 to 10000 pounds to protect houses from flooding. Less if flood already damaged from flood. Type of measure used depend on the flood risk of the property. Examples: moving electricity sockets higher up the walls replacing doors with one lightweight that can be moved upstairs if necessary concrete floors instead of wooden ones so they don't rot if wet yacht varnish on wooden skirting boards to protect them from water building on stilts Overall don't stop flooding but mean houses become habitable much quicker if they are affected by flooding in the future.
Hard engineering	It's a method of river flood management which involves major construction work
Soft Engineering	A method of river flood management which work or attempts to work with natural river processes such that it doesn't tend to involve major construction work.
Hard engineering techniques: Embankments	Raised banks along the river. Can be used as pedestrian paths along ther river, concrete so stop bank erosion, earth embankments provide habitat for wildlife. However banks not often high enough, concrete embankments are aesthetically displeasing.
Hard engineering techniques: Channelissation	River channel widened or deepened allowing it to carry more water, may also be straightened so that water can travel faster along the course. It effectively protects immediate areas as water is moved quickly away, long term solution. Alteration may lead to greater risk of flooding downstream, as water is carried there faster and unnatural and visually intrusive.
Hard engineering techniques: Flood relief channels	When channel course can be altered diverting flood water away from settlements. Immediate area protected and can be used for water sports. However requires a large amount of land which may be difficult to purchase, particularly if farmland and extremely expensive.
Hard engineering techniques: Dams	Often built along the course of a river to control the amount of discharge, water is held back by the dam and released in a controlled way. Advantages are water is usually stored in a reservoir behind the dam which can be used to generate hydroelectric power and for recreational purposes. However expensive, sediment often trapped leading to erosion further downstream, settlements and agricultural land lost when valley flooded to form a reservoir.
Hard engineering techniques: Flood walls	Vertical barrier usually made from prefabricated concrete. Can be used in areas with little space, easily and quickly erected in pre-constructed sections. They have to be assembled very well so the water doesn't get through joints.
Hard engineering techniques: Storage areas	Large depression close to the river that will fill with water if the river overflows and therefore protecting the surrounding the land. Advantages are natural looking and does not damage the environment however large area of land that isn't used is needed and only come into use when the river has flooded.
Soft engineering techniques: Floodplain zoning	Local authorities and national government introduce policies to control urban development close to or on the floodplain. Very cheap of reducing effects, sustainable as reduces impact of flooding and building damaged is limited also surface run-off less likely to cause flooding. However can be resistance to resisting development in areas where there is a shortage of housing and enforcing planning regulation and controls may be harder in LIC's
Soft Engineering techniques: Washlands	River allowed to naturally flood in wasteland areas, to prevent flood in other areas like settlements. Its cost effective, provides potential wetland sites for birds and plants, deposited silt can enrich the soil, turning area into agricultural land. However large areas of land taken over and are built on and productive land turned into marshland.
Soft Engineering Techniques: Warning systems	network of sirens which give people early warning of possible flood. Environment agency use TV, radio, email, fax, text and phone messages to inform people. Advantages are very cheap, electronic communication effective for informing people, as people have warning most valuable possessions taken to safer place. Although sirens could be vandalised so tested annually, might not be enough time for residents to prepare.
Soft engineering techniques: Afforestation	Treees planted in the catchement area of a river to intercept the rainfall and slo downthe flow of water to ther river. Relatively low cost, improves environment quality, soil erosion avoided as trees prevent rapid run off after heavy rain fall and sustainable. However often conifers are planted which can make soil acidic, dense tree plantations spoil the natural view of landscape and increases fire risks because of leisure activities in the forest.
Bolivia 2007	Unusual heavy seasonal rains caused rivers to burst banks, at least 19 died result of flooding of the Rio Grande, tributary of the Amazon. Estimated 340,000 affected and 100,000 homeless. Roads in Santa Cruz and Beni were blocked by mudslide.
Serbia, Romania and Bulgaria 2006	Water of Danube flooded, hundreds of houses submerged, in Bulgaria 2 million affected and at least 20 killed and 10,000 homeless. Tent city space for 1200 put up near Vidin, damage to economy estimated one billion leva (625 million dollars) large amounts of infrastructure and farmland destroyed. Railway system damaged company lost hundreds of thousands leva daily. In Serbian capitaal Belgrade streets underwater for several days forced evacuations. Hundreds taken to safety Smederevo, 40km east of Belgrade.
Nepal 2008	Dam burst on Saptakoshi River caused flooding near 1000 homes destroyed, power supplies and transport severly affected. Hundreds had illnesses diarrhoera and pneumonia. 50,000 homeless, 40,000 of which forced to live in government run camps. cost to economy 14.25 million dollars
Sudan 2007	3.5 million people at risk from water borne diseases like Cholera, river nile flooded in Sudan: 89 killed and 73,000 homes destroyed.
somalia and Kenya 2007	Shabelle, Tana and Juba Rivers flooded banks, affecting towns and villages, town of Garissa submerged with houses near Tasa submerged. Floods destroyed bridges, made roads impassable so aid drops by plane only way to deliver food to population. Said lived in trees and attacked by wild animals.
River Nene, Northampton	Heavy rain on 9 April 1998 caused the River Nene and Grand Union Canal to overflow flooding parts of the town and leading to two deaths. The cause of the flood was constant torrential rainfall and on the 10th of April 1998 the flood peaked and many rivers burst its banks. The overall catchment area is 2270km^2 with a population of 75,000.
River Nene, Northampton: Effects	Nene badly affected flooding low parts of Northampton, Wellingborough, Earls Barton, plus Cotton End, Far Cotton and St James areas of town occupying the floodplain were badly affected.
River Nene, Northampton: Embankments	In 2002 a 450m clay flood embankment was built in Weedon across the river valley upstream of Northampton, raising the level of the land by 6.8 metres. Creating a food storage area behind the embankment costing 2 million pounds. During times of flood, water can be stored here preventing flooding downstream in Northampton. Moreover the river flow is regulated by a culvert through the embankment. Plus the embankment has been constructed to minimise visual impact and the storage areas have been developed as a habitat for aquatic flora and fauna. An embankment are raised banks along the river. Major roads in the area Upton near Sixfields up to 6m high. These embankment join up with specially built floodgates to create an area of open land where up to 1.2 million cubic metres of flood water can be stored during times of heavy rain can store flood water.
River Nene, Northampton: Floodwalls	In addition at Foot Meadow close to the railway station 4m high flood walls have been installed to protect housing, industry and the Castle Inn. Led to creation of open area of land which the river can flood into giving protection to the railway station situated on one side of the river. Debry was also cleared so the rivers velocity would increase and rainwater would be taken away more quickly so that the river is less likely to flood as it bursts its banks. A flood wall is a vertical barrier usually made from prefabricated concrete.
River Nene, Northampton: Afforestation	This is where trees are planted in the catchment area of the river to intercept the rainfall and slow down the flow of water into the river. On River Nene this was built along earth embankments set back 10 metres from the river which have footpaths along the top the trees to planted to visually improve the area.
River Nene, Northampton: Warning Systems	In 2003 warning system was upgraded areas at risk of flooding are covered by the environment agency Flood WArning service where the aim to give two hours notice of the possible onset of flooding. Test in Far Cotton and St. James areas and a Flood Season Awareness Campaign was put into operation.
River Nene, Northampton: Washlands	In 2007 aim of work was to create a washland where water can be diverted manner in order to reduce the risk of flooding downstream. Water can be harmlessly in open grassland when rain has passed, gates will be opened to allow the water to flow steadily back into the River Nene. A washland is when a river is allowed to naturally flood in wasteland areas, in order to prevent flooding in other areas usually settlements. In 2007 the British Governemt announced it would spend 6 million pounds on flood defences at Upton MIll in the west of Northampton as wetland and embankments were to be constructed along the river.

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	Criado por Chima Power mais de 10 anos atrás