rivers

rivers

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The river Tees

  • groundwater store-Percolation
  • 120 Km from source longest river
  • Source- pennine, 700m above sea level

Upper course

  • ground water logged, moor land, 3 months of snow, rains alot, narrow fast moving shallows, vertical erosion

Mid course 370m above sea level

  • revoirs, farm land, fields sheep, wider, water falls, rocks in the river are smoother, lateral erosion

Lower course

  • temperature warms, farm land for crops, pasture, market villages, meanders, slow water flow wider, sandy
  • mouth- north sea

the river erodes, transports and deposites, the faster the it falls the more power it has

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River Erosion

  • abrasion/ corrasion- The wearing away of material
  • hydraulic action- like a power wash the water brakes the sides and bed
  • solution- the dissolved rock
  • Attrition- the material smashes together the get smaller and smaller

Weathering

  • Physical- Rain, Wind, Sun, Human
  • Chemical- Acid rain
  • Biologyical- Plant roots

Interlocking Spurs

  • In the upper course has low energy to erode. It has low discharge and transports large pieces of sediments
  • When the river meets hard rock, which is differcult to erode, the river wines around the hard rockand cuts into the softer rock
  • A series of hills form on either side of the river called spurs
  • As the river flows around this hills and eats away at the softer rock these hills become interlocking spurs
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creation of waterfalls and flooding

Waterfalls

  • A river meets a band of softer, less resistance rock
  • The underlying softer rock is eroded more quickly
  • Hydraulic action also helps to create a deep pluge pool
  • processes of erosion such as abrasion causes undercutting
  • The more resistant rock is left unsupported and overhangs
  • The rock cuase abrasion on the river bed
  • Eventually the more resistant rock collapses onto the river be
  • The process is repeated and the waterfall retreats up-steam

Flooding

  • The river load is composed of different sized particles
  • When a river floods it deposits the heaviest of particles first
  • Larger pebbles form levees
  • everytime the river floods the depostion build up on the floodplain
  • The levees get bigger and bigger they act to keep the river within the levees
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Meanders and creaion of Oxbow lakes

Meanders

  • water is directed to the outside of the bend. Water is deepen here and therefore there is less friction and velocity increase
  • This means there will be more energy to transport material and to erode the bank by the process of abrasion
  • The bank is undercut and can collapse to form a river cliff, on the inside bend there is less water and so more friction and the velocity is reduced
  • Depostion then occurs and a gentle sloping area is form, know as aslip-off slope.

Oxbow lakes

  • The meander neck gets narrow because the outter bend of 2 meanders wear away and move together
  • When is floods water brakes throught the neck meaning the river fins a new faster route
  • The new route is much straigher, this leaves an arc of the older river bed this is an oxbow lake
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Lower course: deltas

At the mouth, the river is carrying to much velocity and so deposition occurs, the silt is dropped to form a steep slope on the edge of the delta.

Conditions favouring deltaic accumulation

  • High sediment load **** as the Nile
  • Large rivers (marine deltas)
  • shallow water offshore, very deep water inhibits deltas building like The Congo this has no delta
  • low wave energy like the mediterraneon or the gulf of mexico

types of delta

  • Arcuate- found in area where regular longshore drift of other currents keep the seaward edge of the delta smooth (the niger in Nigeria)
  • Cuspate- shaped by regular but opposing, gentla water movement (the Ebro in spain)
  • Bird's foot- river brings down alot of silt, deposition can occuir in a still sea area ( the mississippi in the USA)
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