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Rivers Ysgol Rhyngrwyd IGCSE Geography

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Rivers Ysgol Rhyngrwyd IGCSE Geography Powered By Docstoc
					                                  Rivers


The water cycle
Places water can be stored:
On the surface as snow or
ice
In the plants and trees
In the lake
In the marsh
In the grass, on the surface
In the soil
In the water table
In the sea in the clouds




Gradient

Steep                  Moderate            Gentle

Features

Rapids, waterfalls     Meanders            Flood plain, levees
‘V’ shaped valley
Drainage Basin:
Watershed – Edge of drainage basin, joins high points in basin
Source – point at which a river begins
Mouth – point at which a river meets the sea, or inland lake
Tributary – Stream or small river that leads to a bigger one
Confluence – the point at which 2 streams meet
River basin – area drained by a single river system (drainage basin)
Interfluves – ridge of higher ground that lies between 2 rivers




Erosion Processes
Hydrolic power:
The force of water on the bed and banks. Water force removes material from
bed and banks. Particulay strong during floods.

Corrasion:
The sediment rubs against the bed and banks at times of high flow

Corrosion:
Rock minerals eg. Calcium carbonate slowley disolve in river water, which is
sometime acidic.

Attrition:
Sediment rub against each other, breaking themselves up and reducing each
other to sediment.
Transportation
Traction:
Large boulders roll along the river bed

Saltation:
Small pebbles are bounced along the river bed as the flow changes

Suspension:
Finer sand and silt particles are carried along in the flow giving the water a
brown appearance

Solution:
Minerals eg. limestone and chalk are dissolved into the water and carried by
the flow, they can’t be seen

Upper course features
Waterfalls:

Falling water and rock
particles wear away soft rock




The hard rock is undercut as
erosion continues




Hard rock collapses and if moved
by the flow. The waterfall moves
backwards




Erosion continues and the waterfall
continues to move upstream
leaving a gorge of recession
Interlocking spurs:




The river flows a twisting course in between the spurs


V-shaped channels and narrow channels, steep gradient and rapids.

Middle course features
Moderate gradient, almost flood plains widening channels. Meanders.
Slip off slope: gentle slope on the inside of a meander
River cliff: steep river bank on the outside of a meander
Meanders:
Ox - bow lake: Semi circular lake
formed by a meander being
sealed off from the main course
of a river.

Meander Scar: Dried up ox – bow
lake.
Lower valley features




Flood plain:
Wide, flat area either side of the river, in its lower course. It is used for
flooding.

Bluff: Slope that rises steeply from a rivers valley.

Levees:
Natural embankments of silt along the banks of the river.

The river in flood
As the flow looses energy it drops
the coarser material by the banks
and the finer material further away.



The River in Low flow
The rivers velocity slows meaning
material is deposited on the river
bed.




After repeated floods
The river banks form levees and the
river may be raised so that the water is
above the level of the flood plain, which
can lead to flooding.
River Mouth
Estuaries: Downed river mouth in a lowland area, because of a rise in the sea
level or fall in the land level.



Deltas: Often triangular – shaped flat land jutting out into the sea at the
mouth of a river. Formed by river deposition, when the velocity of the river
drops it deposits its load. If there are no strong sea currents the sediment will
stay there.




                       Arcuate Delta: Nile. Egypt




                        Birds Foot or Digiate Delta: Mississippi. USA




                         Estuarine Delta: Elbe. Germany




River Management
River Management is ways in which the river is controlled. It stops flooding
and helps monitor and develop the rivers course.
River Wey and Lower Tees Valley:
Reservoir – control how much water in is the channel at one time. It also
ensures that there is a steady supply of water.
Flooding has been decreased due to new advanced flood warnings,
embankments, gabions, concrete walls and flood gates. Also building on flood
prone land has been discouraged. In the Tees, The Tees Barrage, dredging
has been used, and meanders have been cut off.
Yarms flood defense: - Reinforced flood walls with gates for access
       - Earth embankments
       - Gambions (baskets filled with stones) protects decrease erosion
       - Fishing platforms, street lighting and replanting to improve the
       environment.

Hard engineering involved large scale engineering works and are usually
expensive. Soft engineering schemes cost less, do not have a major impact
on the environment, and are thought to be more sustainable.

Flood Management
Reduces Flooding: Embankments, Flood diversion channels, Flood storage
zones, Catchment management, Dams

Reduces Damage: Early warning system, Flood proofing, Regulations of
building on a flood pain

Other: Insurance, Polders


River Regimes
Discharge is measured in m3 / seconds, called CUMECS. To calculate the
discharge you multiply the velocity by the cross section area.

The Regime of a river is the variation in the discharge of water carried at
different times in the year.
Hydrograph
Graph showing the discharge of a river at a give point over a period of time. A
flood or a storm hydrograph shows how a river responds to one particular
storm.




Floods

Boscastle:
Lies on the west coast of Cornwall. 2004 flash floods from the river Valency
and Jordan. Biggest rescue operation since WW2. Nobody was killed.
Summer means heavy rainfall, which there was in the source of both rivers.
There is little woodland near, so no trees could absorb the water. Steep hills
near Boscastle. Narrow valleys increased the rivers velocity. 2 streams joined
meaning an even bigger volume of water

Bangladesh:
Reasons: Two very large rivers; Ganges and Brahmaputra meet
         Very low lying land
         Monsoon
         Costal storm surges
         Deforestation upstream
         Silting up of riverbeds, decreased capacity
         Population increased
         Urban growth increased surface run off

River Tees:
Uses:
Bridging points and larger towns such as Yarn. There are huge mud flats such
as Seal Sands, which are important wildlife areas for migratory birds and
seals.

				
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