rivers

• drainage basin


  an area around of land the river that is drained by the river and its tributaries
• tributary


  a small river or stream that joins a larger river
• channel


  where the river flows
• source


  start of the river
• mouth 


  where the river meets the sea
• watershed


  high land at the edge of the basin
• confluence


  where two rivers meet
• fluvial


  water in the river
• Bradshaw Model


  a theoretical model that shows how the river is expected to change as it moves downstream

  width of triangle shows how much change has happened in that area

  A) mouth

  B) source

  C) width of triangele shows how much change has happened

  
• discharge


  amount of water in river
• velocity


  speed of water
• upper course of a river


  narrowest

  highest altitude

  slowest

  mostly erodes and transports

  hills, mountains
• middle course


  erosion on outside of meander, deposition on inside

  closer to sea level

  wider then UC
• lower course


  widest

  fastest

  floodplains

  slowing down

  reaches sea- sea level

  deposits remaining sediment
• long river profile


  when the river channel slope is shown across its entire length (side)

  
• cross river profile


  river split into cross profile which shows each section of the river from a different angle (head on)

  Upper course- V shaped valley, steep valley sides, thin channel

  Middle course- U shaped valley, gentler slopes the UC, wider channel develops

  Lower course- wider channel, floodplains, very gentle slopes, flat shaped

  
• Interlocking Spurs

  1. River moves downstream
  2. hits a band of more resistant rock
  3. because it doesn't have a lot of energy, the river winds around the areas of hard rock (spurs), to avoid them
  4. this creates interlocking spurs

  found in the upper course
• waterfalls and gorges


  erosion type- abrasion mainly (but also other 3)

  middle course

  how?

  1. the soft rock at the bottom erodes quickly, undercutting the hard rock on top
  2. the hard rock is left overhanging and because it isn't supported, it eventually collapses
  3. the fallen rock crashes into the plunge pool. they swirl around creating more erosion
  4. over time, the process is repeated and the waterfall moves upstream (waterfall retreat)
  5. a steep-sided gorge is formed as the waterfall retreats
• types of erosion


  erosion involves the wearing away of rock and soil found along the riverbed and banks

  the process causes rocks to become smoother as they go downstream

  strongest upstream

  types

  • hydraulic action- the force of the river against the bank causes air to be trapped in cracks. the pressure weakens the banks and gradually wears it away
  • abrasion- rocks hitting the river bed and banks as they move downstream
  • attritions- rocks hitting each other as they go downstream breaking into smaller, smoother and rounder particles
  • solution- soluble particles are dissolved in the river
• vertical erosion


  when the river cuts down the river into the ground

  creates a V-shaped valley

  upper course
• lateral erosion


  river erodes laterally, left to right, across the valley

  creating a flat bottomed valley

  lower course
• transportation


  types:

  1. traction - large boulders and pebbles are rolled along the river bed -UC
  2. saltation - small stones, pebbles and silt bounce along the river
  3. solution - dissolved minerals are carried by the river
  4. suspension - fine material is carried by the river
• deposition


  when the river loses energy, it will deposit (drop) some of the material its carrying

  may take place when the river enters an area of shallow water or when the volume of water decrease

  common towards end of rivers

  deposition at the mouth can form deltas
• meander


  formed by erosion and deposition

  bend in river

  faster current on outside causes lateral erosion

  slow current on inside (can't keep up ->river bends)

  slower current as river bend, causes sediment to be deposited due to lack of energy - slip off slope

  erosion causes neck to narrow over time

  
• ox-bow lakes

  1. the neck of a meander is gradually eroded
  2. water now takes the shortest route
  3. meander is cut off forming an oxbow lake by deposition
  4. over time, the oxbow lake dries up leaving a meander scar
• flood plains


  large flat areas of land found either side of the river

  extremely prone to flooding

  when a river floods, material being deposited on the floodplain, overtime this raises the height of the floodplain

  soil is very fertile

  formed from lateral erosion (widens the valley, taking away interlocking spurs near the source, creating flat land) an deposition (river overflows, deposits sediment)
• levees


  formed when river banks fare built up during floods

  in between floods, silt (fine, lighter sediment) is deposited on the river bed

  over time, the levees are built up as the river continues to flood

  lower course
• estuaries


  river approaches the sea, slowing down and getting wider

  the velocity of the water slows down and drops sediment

  the sediment forms sand banks and mudflats across the estuary

  the mudflats are covered during high tide

  good for wildlife

  river mouth meets the sea
• River Tees - case study


  where - NE of England, source = Cross Fell, mouth = North sea. Travels through Darlington, Yarn and Middlesbrough (lower course), Barnard castle (middle course) and Cow Green Reservoir (upper course). Travels westward. 137Km long
• river tees - case study


  UC- Pennine hills (source), largest water fall in the UK(20m high), interlocking spurs, gorges, 700m long, V shaped valley, steep, 300-750m above sea level

  MC- meanders, Banard Castle, slip off slope, river cliffs, lateral erosion 60-300m above sea level

  LC - bigger meanders, oxbow lakes, large floodplains, levees, estuary + mudflats, mouth = big, >60m above sea level, deposition, flat and wide
• Hydrograph


  base flow - the normal river level

  falling limb - the fall of the river after discharge

  peak discharge - the time of the highest river channel flow

  rising limb - the increase in river discharge

  lag time - the difference between peak rainfall and peak discharge

  peak rainfall - the time of the highest rainfall

  
• types of hydrographs


  flashy - steep rising and falling limb, short lag time and high peak discharge

  slat- long lag time, low peak discharge
• factors that effect hydrographs - FLASHY


  basin size - small basin often leads to a rapid water transfer

  drainage density - high density speeds up water

  rock type - impermeable rocks encourage rapid water transfer

  land use - urbanisation encourages rapid water transfer

  relief - steep slopes lead to rapid water transfer

  soil moisture - saturated soil results in rapid overland flow

  rainfall intensity - heavy rain may exceed the infiltration capacity of vegetation and can lead to rapid overland flow
• factors that effect hydrography - FLAT


  basin size - large basin = slow water transfer

  drainage basin - a low density of water leads to a slow water transfer

  rock type - permeable rocks encourage slow transfer by ground water

  land use - forest slow down water transfer- -interception

  relief - gentle slopes slow down water transfer

  soil moisture - dry soil will soak up water and slows down transfer

  rainfall intensity - light rain will transfer slowly and most will soak up into the soil
• flood management - hard engineering


  DAMS

  • huge man-made structure (concrete) built across rivers
  • traps water behind it, water builds up and forms a reservoir, to stop overflowing water is released slowly (controls how much water gets releases)
  • no dam = risk of flooding

  advantages - tourists, multipurpose - can create energy - hydro-electric power

  disadvantages - expensive, habitats + settlements are often destroyed in construction
• flood management- hard engineering 


  CHANNEL STRAIGHTENING

  • channel is altered so its straighter - allows water to flow quicker
  • larger volumes of water can pass through, reduce flood risk
  • Dredging - makes channel deeper so it holds more water-not straighter

  advantages- limits flood risk, allows river to move quicker, holds more water
• flood management- hard engineering


  EMBANKMENTS

  • banks of river are built up so the are bigger
  • the river bank is high, the river can hold more water without flooding, without it, the river levels rise due to heavy rainfall - burst banks, whereas with, water will be held by river

  advantages- decreases flood risk, cheap (one off cost), flood water kept in river

  disadvantages- looks unnatural, increases water speed=increase chance of flooding downstream
• flood management- hard engineering


  FLOOD RELIEF CHANNEL

  • man-made river channel-> takes away flood water from main river - to an area where it can be absorbed in land or re-joins the river further downstream
  • takes away excess water so river doesn't burst its banks+flood, without it, river will burst its banks

  advantages- removes excess water to reduce rick of flooding

  disadvantages- expensive, if water levels continue to rise, the flood channel could flood if it tries to hold too much water
• flood management- soft engineering


  RIVER RESTORATION

  rivers have their course adapted back to its original shape

  reduces flood risk because natural features such as meanders slow river down
• flood management- soft engineering


  FLOOD PLAIN ZONING

  land use is restricted on floodplains close to the river

  this means high value land will be at less rick from flooding as they are further away from the river