AQA Geography - Rivers Content

HideShow resource information
  • Created by: Catherine
  • Created on: 29-03-13 13:01

Factors Affecting Discharge.

Physical

Weather

  • Snow - melt, frozen ground no infiltration
  • Precipitation - heavy rainfall
  • Temperature - evaportranspiration (reduce discharge)

Drainage Basin

  • size - rounder quicker
  • Shape - smaller responds more rapidly
  • Slope - steep, water reaches more quickly
  • Vegetation
  • Porus soil type/ permeable rock - slow
  • Impermeable rock - faster
1 of 10

Factors Affecting Discharge.

Human

  • Urbanisation - permeable structures, artificial drainage, machinery
  • Land use - dams, argiculture
  • Deforestation 
2 of 10

Long Profile & River Processes.

Erosion

  • Hydraulic Action - water compresses air making small explosion
  • Abrasion - wearing away of rock by the river
  • Attrition - wearing away of rock from other rocks
  • Corrosion - rocks are dissolved

Transportation

  • Traction - large boulders rolles along river bed
  • Saltation - small stones bounce and leapfrog
  • Suspension - sand/silt picked up and carried
  • Solution - minerals transported within the water

Deposition 

  • Discharge reduced
  • Shallow water
  • Increased size of load (tributary)
  • River floods
3 of 10

Long Profile & River Processes.

Vertical 

  • Cuts down to base level leaving steep sided valleyes by the processes of abrasion and hydraulic action

Lateral 

  • Energy used in widening the valley by hydraulic action erosion

Capacity

  • Amount of material it can carry

Competence 

  • Diameter of the largest particle that it can carry for a given velocity
4 of 10

Factors Affecting Load (Material Transported)

  • Climate/seasonal variations
  • Land use - deforestation
  • Precipitation - more water more velocity
  • Vegetation cover
  • Reservoirs
  • Geology - some may be dissolved
  • Runoff
  • Soil properties
  • Topography - relief - height and shape of land
  • Size of basin 
5 of 10

Valley Profiles.

Channel cross profiles

  • View from side
  • Changes throughout - UP: narror and uneven. MID: meanders. LOW: widen and deepens
  • Upper - large wetted perimeter more friction
  • Higher the hydraulic radius more efficient channel

Potential and kinetic energy

  • Determined by volume (discharge) and gradient - increase = increase kinetic
  • Processes depend on this
  • Excess = erosion, insuffient = deposition 

Graded profile

  • Inputs should balance outputs - changes in system = change in profile 
  • Graded river - all energy used so no further erosion 
  • Profile of dynamic equilibrium - blance between erosion and deposition
  • Overtime river decrease in gradient - smooth concave shape, adjusted discharge and load
6 of 10

Valley Profiles.

Cross profile

  • View of a valley from one side 
  • Lower course - very wide, lack erosion, reduced competence 
  • Middle course - wider, lateral erosion
  • Upper course - narrow steep sided, vertical erosion

Long profile

  • Knick points - rejuventation
  • Change in altitude
  • Steeper upper course - gentle at mouth
  • Irregularities - rapids, waterfalls 
7 of 10

Rejuvenation & Knick Points.

Rejuventation - increase in energy 

Cause

  • Isostatic - rise and fall of land
  • Eustastatic - change in sea level

Knick points

  • River gains cutting power - vertical erosion
  • Adjustment to new base level
  • Knick points - where old long profile meets new 
  • Recedes upstream 
8 of 10

Causes Of Flooding.

Human

Urbanisation

  • Impermeable
  • Natural rivers
  • Smooth surface drainage
  • River strengthened - delivered quickly

Deforestation

  • Loss of root soil erosion
  • Reduce interception and evapotranspiration
  • Decrease in channel capacity - increase in sediment

Farming

  • Ploughing - soil erosion
  • Planning strategies
  • Over grazing
  • Reduce lage time 
9 of 10

Causes Of Flooding.

Physical

  • Climatelogical
  • Increased temperature - snow melt - reduced infiltration
  • Coastal 
  • Storms
  • Planning control
  • High season tides
  • Nature of Basin 
  • Rock types
  • Shape basin - vegetation, relief, runoff 
10 of 10

Comments

No comments have yet been made

Similar Geography resources:

See all Geography resources »See all Rivers and fluvial processes resources »