Water on the land- March 2015

River Processes
1. Erosion
  1. Erosion is the wearing away of the land.
    1. Rivers erode in two directions vertically and laterally
      1. As a river moves down its course vertical erosion becomes less and lateral erosion increases
  2. Dominant near source
  3. Vertical downwards erosion
  4. Hydraulic Action
    1. The sheer force of the water hitting the beds and banks.
      1. Most effective when the water is moving fast and there is alot of it
  5. Abrasion
    1. When the load the river is carrying repeatedly hits the river bed and banks causing some of the material to break off
  6. Attrition
    1. when some of the stones and boulders carried by the river knock against each other and over time are weakened, causing bits to break off and so the stones become smoother and smalller
  7. Solution
    1. only occurs when the river flows on certain types of rock, such as chalk and limestone
      1. these are soluble in rainwater and become part of the water as they are dissolved by it
  8. Waterfall, Gorge, Interlocking spurs, Floodplains, Ox-bow lakes, meanders & V-shaped valleys
2. Transportation
  1. Traction
    1. moves the largest material, that is too heavy to lose contact with the bed so boulders are rolled along the river bed
  2. Saltation
    1. moves the small stones and grains of sand by bouncing them along the bed
      1. the lighter load leaves the river bed in a hopping motion
  3. Suspension
    1. it is a means of carrying very fine material within the water, so it floats in the river and its moved as it flows
  4. Solution
    1. is the dissolved load and occurs only within certain rock types that are soluble in water (chalk&limestone)
      1. The load is not visable
  5. once material has been eroded from the bed or banks, the river then moves the load it has via transportation
  6. the missisipi river is 3800km long. it carries on average 4200 tones of sediment each day and 130 million tonnes a year
3. Deposition
  1. this is where the river dumps or leaves behind material that it has been transporting
    1. it deposits the largest material first as this is the heaviest to carry
      1. The smaller the load, the further it can be transported, so it is then deposited much further downstream than the larger load
        large boulders are usually found in the upper course and fine salt and clays are found in the lower course
        The river deposits its load when there is a fall in the speed of the water or the amount of water is less. For example: after a flood or during times of drought
        often happens when there is a change in gradient at the foot of a mountain or when a river enters a lake/sea - deposition is common at the mouth
  2. deposition at the mouth of a river can form deltas for example: the mississipi delta
  3. Leeves, Floodplains, meander, Ox-bow lakes Deltas & Estuarys
4. Long Profile
  1. the long profile shows how the river changes in height along its course (source-mouth)
  2. a rivers source is the highest and the mouth is at its lowest being at sea level.
  3. there is a steep gradient at the rivers source, which then gives way to a more gradual reduction further downstream, giving a typically concave profile
    1. the river has much more potential energy near its source because of its steep drop and height above sea level.
      1. later on this is replaced by kinetic energy as the amount of water increases and it gains momentum
        However such a perfect concave profile is rare. this is due to land being uplifted by tectonic movement, sea level changing and differences in geology (soft and hard rock types) along the whole profile
Definitions
1. Hydrological cycle
  1. the sequence of conditions through which water passes from vapour in the atmosphere through precipitation upon land
  2. River Channel
    1. Waterfall
      1. gorge
        Meanders
        Oxbow lake
        Levees
        Flood Plain
        Interlocking Spurs
        Hydrograph
        Rising/falling limb
        Peak Discharge
        Groundwater
        Surface Run-off
        Hard Engineering
        Soft Engineering
        Resivoir
        Deforestation
        the cutting and removal of trees in a forested area
        a natural/artificial place where water is collected and stored for use
        less expensive and are more long term and sustainable
        Expensive with high impact on the environment
        Flow of water that occurs from rain which flows over the Earth's surface
        water that is held in the soil and in rocks
        when the river reaches its highest level
        shows the increasing discharge
        Graph shows water level/flow water
        As river descends it begins to meander between narrow necking rivers
        Area of land prone to flooding
        Naturally formed banks by river
        when the river changes path leaves a stream this becomes a lake
        The river follows a winding path
        A deep channel formed by the river
      2. The river flows off a rock-cliff
    2. An area that contains flowing water confined by banks
2. interception
  1. Precipitation
    1. Infiltration
      1. Run off
        Through flow
        Soil Moisture
        Groundwater flow
        Ground Water
        Evapotranspiration
        Percolation
        Water Table
        Porous
        Saturation
        When rock or soil can hold no more water
        Holds water like a sponge
        Upper layer of saturation in porous rock
        Movement of water from soil to rock
        Water passing through plants and leaves to atmosphere
        Water held in porous rock
        Movement of water through rocks
        water held in soil
        Movement of water through soil
        Movement of water over surface
      2. Movement of water from surface into soil
    2. Rain, Snow or hail
  2. water trapped on leaves
  3. tributary
    1. Confluence
      1. Drainage Density
        Drainage Basin
        WaterShed
        Storm Hydrograph
        Discharge
        The volume of water passing a given point in a river at any moment in time. Measured in cubics (cubic metres per second)
        shows how a rivers discharge responds to a period of rainfall
        The boundary between two drainage basins marked by a ridge of high land
        The area which is drained by a river and its tributaries
        The total length of all the streams in the basin divided by the total are of the basin
      2. The point at which two rivers join
    2. A smaller river that joins a larger river
Landforms of erosion
1. Upper course
  1. Deep narrow valley
    1. Vertical erosion predominant
      1. pot holes in river bed
        abrasion and hydraulic action
        traction and saltation
  2. interlocking spurs
2. Interlocking spurs
  1. upper course hasn't got a lot of energy to erode
    1. has to transport large pieces of sediment
      1. when the river hits harder rock that is difficult to erode it winds around them
    2. a series of rocks form on either side of the river as the river flows around these hills they become interlocked
      1. interlocking spurs are often found in the upper course of a river valley
Waterfalls
1. As the gorge retreats due to headward erosion the less resistant rock gets undercut and eroded
  1. Because the less resistant rock erodes there is an over hand of more resistant rock
    1. Due to gravity the overhang collapses and the waterfall retreats upstream
      1. this continues in a headward erosion manner as the waterfall retreats upstream a gorge is formed
Meanders
1. bend in the river
2. water does not flow in a straight line
3. over time meanders become very bendy - this is because of abrasion and hydraulic action eroding laterally
4. erosion occurs on the outside, most downstream side of the meander and this widens the valley
5. Formation of an Ox-Bow lake
  1. in the meander the water is pushed to the outside bend
    1. Greater velocity means that the river has more energy to erode
      1. Processes such as corrasion will cause lateral erosion
        Continual erosion on the outside bend narrows the meander neck
        the river floods and takes the shortest, cutting through the neck
        the fastest current is now in the centre of the channel
        deposition occurs along the banks of the river
        the meander becomes cut off to leave an ox-bow lake
Floodplains and leeves
1. a wide, flat area of land either side of a river in its middle and lower course
2. formed by repeated deposition of sediment when the river floods, the wide flat valley is formed by dominant lateral erosion and meander migration
  1. Formation of Floodplains and Leeves
    1. floodplains are the effect of erosion and deposition of sediment building up to create a floodplain
    2. erosion widens the valley taking away the interlocking spurs present nearer the source and creating a wide, flat area next to the river, the migrating meanders also help too
    3. when the river overflows/floods, material is transported and dropped on the floodplain, over time the layers of sediment - build up helping to create the floodplain
    4. Floodpalains are formed by deposition in times of river flood. The rivers load is composed of different sized particles. When a river floods it deposits the heaviest of these particles first. The larger particles, often pebblesized form the leeves. The sands,silts and clays are similarly sorted witht the sands being deposited next, then the silts and finally the lightest clays. Everytime a river floods deposition builds up the leeves and the floodplains
Deltas
1. a flat area of sand and silt built into the sea
2. formed by river deposition
3. As the river meets the sea, velocity decreases and the load is deposited.
  1. this can cause the main channel to split into disbrutries
4. in sheltered areas 'no strong tides/currents' and builds up to form a fan shaped delta eg. Mississipi Delta
Estuary
1. land which is below river and sea level
2. the river channel is very wide with mud flats and salt marshes
3. is a partly enclosed coastal body of water with one or more rivers or streams flowing into it
  1. there is a free connection to the open sea
    1. they form a transition zone between river enviroments and ocean enviroments
      1. they are subject to both marine influences, such as tides, waves and the influx of slaine water; and riverine influences such as flows of fresh water and sediment
Case Studies
1. Somerset Levels - Winter 2013-2014
  1. EFFECTS
    1. Social
      1. Stress (medical problems)
      2. Anxiety
      3. Loss of personal belongings
      4. Houses destroyed, inhabitable
        Rebuilding life
      5. No insurance
    2. Economic
      1. Roads flooded
      2. Buisinesses destroyed
      3. no electricity etc
      4. 120 homes destroyed
      5. farmers lost 11500 hectacres inundated by 65 million cubic litres of water
      6. A361 closed for three months
    3. Enviromental
      1. polluted water
      2. Animals evacuated
      3. Debri
      4. Human Waste in water
  2. CAUSES
    1. Human
      1. Stopped dredging rivers 10 years ago
    2. Physical
      1. moors were already saturated
      2. the levels were once covered by the sea
      3. Wettest winter for 250 years
      4. Narrow Rivers
      5. Somerset levels are very flat
  3. RESPONSES
    1. Short TERM
      1. More pumps
      2. Evacuating
      3. Volunteers from around the country
      4. Sand Bags
      5. Military
      6. people doing labour for free
    2. Long TERM
      1. 20 year plan
        Dredging
        tidal barrage
        more permanent pumping sites
        £100 million cost
      2. FLAG - flooding on the levels action group
2. Pakistan Floods - July-August 2010
  1. EFFECTS
    1. Social
      1. 1600 deaths directly
      2. 5000 schools destroyed and hospitals damaged
      3. Malaria Outbreak- stagnant water
      4. 2 million made homeless
      5. mines and unexploded bombs washed upstream
      6. 23% of the years harvest washed away
      7. Food Shortage
      8. 6 million need aid, food, shelter and medicine
      9. 800,000 people only reachable via air
    2. Economic
      1. 2000 miles of roads destroyed
        $158 million to replace
      2. high cost to the tax payer
      3. Cane and rice lost
      4. Prices increased of basic food because of short supply
        Effects WORLD TRADE
      5. 5.3 million jobs lost- especially in the textiles industry
    3. Enviromental
      1. polluted water supplies
      2. cane and rice lost
      3. Submerged 17 million acres of Pakistans most fertile crop land
        killed 200,000 livestock
      4. Soil erosion resulted in infertile soil
      5. Dead bodies and cattle in water
      6. disease
  2. CAUSES
    1. Physical
      1. Snowmelt from the Himalayas spring
      2. Heavy monsoon rains
    2. Human
      1. Deforestation
      2. Building schemes ie. roads & buildings
      3. Managing the land more changing the course of the river
    3. CLIMATE CHANGE
  3. RESPONSES
    1. Short TERM
      1. Flood Emergency (saudi arabi, turkey, kuwait are the largest donars)
      2. Food, medicines, clothing and blankets distributed
      3. US embassy in Pakistan provided 7 helicopters
      4. Paistan Navy helped with rescue
    2. Long TERM
      1. pledges $1 million to Pakistan
      2. people begin to rebuild their homes
      3. UN launched appeal for $460 million
      4. World Bank gave a loan to pay for repairs
      5. Flood warnings and flood shelters on stilts have been put in place
What factors increase the risk of flooding?
1. Vertical Ploughing
  1. Usually in spring or summer, adds lots of water quickly to the drainage basin
2. Snow Melt
  1. Overwhelms rivers
3. Too much rain
  1. Rock cannot store water so more surface run-off
4. Deforestation
  1. Ground is hard and so water cannot infiltrate easily, lots of surface run-off quickly to river
5. Previous Drought
  1. Less interception means water gets to the river more quickly
6. Urbanisation
  1. Can make river move more slowly and more likely to flood
7. Altering river course
  1. Means that more surfaces are impermeable so more surface run-off
8. High tides
  1. Surface run-off moves more quickly because of gravity
9. Steep valley sides
  1. Means water 'backs-up' at the mouth and water cannot leave river by entering the sea
10. Impermeable rock
  1. Makes it easier for surface run-off to get to rivers by directing flowing to it

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Water on the land- March 2015

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