rivers
rivers
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- Created by: sarah corrigan
- Created on: 20-05-09 16:33
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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