Geography revision notes-rivers

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  • Created by: Veniece
  • Created on: 04-06-16 09:44

what a river is like at the upper, middle and low

Long profile

  • River flows downhill from the source to the mouth-long profile curves down-river then divided into 3 parts- upper,middle,lower-this is where the river reaches sea level

Upper -steep

  • v-shapped valley
  • steep sides narrow
  • shallow channel

Middle-meduim

  • gentally sloping valley sides wider
  • deeper channel

Lower-gental

  • very wide
  • almost flat due to widness
  • deep channel
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Erosion&transportation

(fast water  = more erosion and higher carrying capacity. Slower water  = weaker, less erosion, more deposition)
4 types of erosion

  • Hydraulic action- Force of water breaks rock particals away from river channel
  • Abrasion- eroded rocks picked up by river scrape&rub against channel, wearing away. most erosion happens by abrasion
  • Attriction-Eroded rocks picked up by river-smash into each other-break into smaller fragments.Edges get roundded of as they rub together
  • solution-river dissolves some types of rocks

Transportation

  • Traction-large particals (eg boulders) pushed along river bed by force of water
  • Saltation- pebble sized particals bounce along river bed by force of water
  • Suspension- small particals carried along by water
  • Solution- soluble materials dissolve in the water and are carried along
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Deposition

Deposition- when river drops eroded materials

-River drops eroded materials its transporting

-Happens when river slows down(loses velocity)

REASONS WHY:

  • Volume of water in river falls
  • Amount of eroded material in water increased
  • Water shallower (eg inside of a bend)
  • River reaches its mouth
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River landforms (Meanders/Ox-bow lakes)

Meanders- formed by erosion and deposition ---in the middle and lower courses rivers develop bends- meanders

1)the current(flow of water) faster on the outside of bend as channel is deeper.(less friction to slow water down)

2)more erosion takes place on outside of the bend forming river cliffs

3)current is slower on inside of bend as river channel is shallower(more friction to slow water down)

4) erdoed material deposited on inside of bend forming slip off slopes

OX-bow lakes formed by meanders

1-erosion causes the outside bends to get closer

2-until their is only a small bit of land left between the bends (the neck)

3-the river breaks through this land,usually during floods

4-the river flows along the shortest course

5-deposition eventually cuts of meander

6-forming an ox-bow lake

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River landforms (Gorges and waterfalls)(v-shapped

  • Waterfalls form where river flows over an area of hard rock followed by an area of soft rock
  • soft rock eroded more than hard rock xreacting a new step in river
  • As water goes over step it eroded more and more of the soft rock
  • Steep drop eventaully created=waterfall
  • Hardrock eventually undercut by ersoion, becomes unsurported and collapses
  • Collapsed rofcks swirled around as foot of waterfall where they erode the softer rock by abrasion, this creates a plunge pool
  • over time more undercutting causes more collapses. waterfall will retreat(move back up to the channel) leaving behind a steep sided Gorge                                                   V-shapped valleys
  • River begins high up in mountains so it can flow quickly downhill eroding landscape vertically.
  • River cuts a deep notch down into landscape using hydraulic action, corrasion and corrosion
  • As river erodes downwards the sides of valley exposed to freeze thaw weathering losening rocks (some fall into river) and steepens valley sides
  • Rocks which have fallen into river help process of corrasion and leads to furture erosion
  • .River transports rocks downstream and channel becomes wider and deeper creating v-shapped valley between interlocking spurs
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River landforms (flood plains and levees)

Both formed by deposition

Flood plain:

  • Wide valley floor on either side of river occasionally get flooded
  • when river floods onto flood plain water slows down and deposits the eroded material that its transporting. this builds up the flood plain and makes it higher
  • meanders migrate /move across the flood plain making it wider
  • deposition that happens on the slip off slopes of meanders also builds up the flood plain.

Levees:

natual embankments along edges of river channel. during flood weroded material is deposited over the whole flood plain . Heaviest material deposited closest to river channel as it gets dropped first when river slows down. over time deposited material builds up creating levees along edges of channel.

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Flooding

causes of flooding:

  • Prolonged rainfall- long period of rain soil becomes saturated. More rain can't be infilrate which increases runoff into rivers. Increases discahrge quickly,can cause flooding
  • Heavy rainfall- more runoff. Increases discharge quickly, can cause flood
  • Snowmelt-When snow or ice melts lot of water can go into river in short amount of time. Increases discharge can cause flood
  • Relief(how heigh of land changes)-If river is in steep sided valley water will reach river channel much faster as water flows quicker on steeper slopes. Increases discharge could cause flood.

Human Factors:

  • Deforestation- Trees intercept water on leaves which evaporates. Trees take up water from ground and store it. Cutting down trees increases volume of water that reaches river channel whcih increases discharge making a flood likely
  • Buliding construction-Buildings often made from impermeable materials, surrounded by roads. Impermeable surfaces increase runoff and drains quickly take runoff into rivers. Increases discharge quickly can cuase flood

River flooding in UK more comman

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Flood management

Dams:Trap and store water which can be realesed later. Can be used to generate electricity.

Embankments: Raised banks which make rivers cross section larger so it can hold more water. Can be expensive but effective.

Flood walls: Built around settlemnets to protect from floods. Look artifical and are expensive.

Straightening and deepeing the channel:makes water move faster through flood prone area but could cause flooding further downstream

Storage areas: where water can be pumped out of river and stored in temporary lakes, then can be pumped back. Effective but much spcae required

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Hard Engineering

What  Benefits   Disadvantages

Dams: Dams(huge walls) built across river usually in upper course. Reservior(artificial lake)is formed behind dam. Reservoirs store water especially during prolonged rainfall or heavy rainfall which reduced risk of flooding. Water in reservior used as drinking water ange generate hydroelectric power. Dams expensive to build. Creating new reservior can flood existing settlements. Eroded material deposited in reservoir and not not along rivers natural course so farmland can be less fertile.

Channel straightening: Rivers course is straightened- Meanders cut out by builiding artifical straight channels. Water moves out area quicker as it doesn't have to travel as far,reducing risk of flooding. Flooding may happen downstream of the straightened channel instead as flood water carried out faster. More erosion downstream as water is flowing faster.

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Soft Engineering

what   benefits  disadvantages

Flood warnings: Enviroment agency warns people abouts possible flooding through media and news papers. Impact is reduced as warnings are given in advance giving people more time to prepare. Warnings don't stop flood from happening. Living in a place where floods are comman could make it hard to get insurance. People may not have access/hear warnings.

Preparation: Buildings are modified to reduce amount of damage a flood could cause. People make plans for what to do in the case of a flood and keep important things in a handy place. Impact of a flood is reduced, less damage to buildings ad people are prepared/know what to do when a flood occurs. People are less likely to worry about the threat of a flood if the are prepared.

Flood plain zoning: Restrictions prevent building on parts of a flood plain that are likley to be affected by flooding. Risk of flooding is reduced,impermeable surfaces aren't created. Impact of flooding is reduced, houses aren't damaged. Expansion of a urban area is limted. No help to areas which ahve already been built on.

Do nothing: No money is psent of new engineering methords/ maintaing existing ones. flooding is natural process and people should accept the risk of living near a flood prone area. River floods eroded material deposited onto flood plain making farmland more fertile. Risk of floodingand impacts aren't reduced. flood will cause more damage.

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Flood case study- MECD UK

causes:

  • Heavy rainfall-200m of rain fell in 36 hours, continuous rainfall saturated ground, increasing runoff
  • Many impermeable materials increased run off=Caused discharge

  Primary effects:

  • small amount of deaths (3)
  • people made homeless-homes lost power
  • schools closed due to flooding/businesses shut down
  • roads and bridges closed+rivers polluted with rubbish and sewage

Secondary effects

  • children lost out on education
  • stress related illnesses increased
  • jobs were at risk as businesses were affected by floods

Immediate responses

  • people evacuated from areas that flooded
  • reception centers opened to provide food and drink for evacuees+temporary accommodation set up for the homeless

Long term response

  • community groups set up to provide emotional support and give practical help for those affected by floods
  • flood defence scheme set up to improve flood defence systems
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Flood case study- LEDC Bangladesh

cause:

  • Heavy rainfall, continous rainfall saturated soil increasing runoff into river
  • Melting snow from glaciers from Hymalayan mountains, increased discharge
  • peak discharge of both rivers happened at same time increasing discharge downstream

Primary effects:

  • large amount of deaths (2000)-large amount of people made homeless(25million)-homes destroyed=(112000)
  • Schools were serverly flooded and destroyed
  • factories closed, livestock killed
  • roads destroyed- river polluted with sewage and rubbish

Secondary effects

  • children lost out on education-4000 schools effected
  • 100000 people caught water brone diseases(diarrhoea)
  • flooded feilds reduced rice yeilds, price rose by 10%. Many farmers and factory workers unemplyed

Long term responses:

  • international charities have funded to rebuild homes and the agriculture and fishing industry
  • some homes have been rebuilt on stilts so they are less likely to be damaged by floods in the future
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