AQA Geography - Rivers Content

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

Human

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

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

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

• 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 

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

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 

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 

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 

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