Physical landscapes

• long profile

  how the river changes from the source to the mouth
• source

  the start of a river
• mouth

  the end of a river
• tributary

  a small stream that joins a river
• confluence

  where a tributary joins a river
• main channel

  the main course of a river
• watershed

  the edge of a river basin
• drainage basin

  the area of land drained by the river and its tributaries
• upper course of a river

  - zone of erosion

  - narrow and shallow river channel

  - landforms: v-shaped valley, waterfalls, interlocking spurs
• middle course of a river

  - zone of transportation

  - wider and deeper river channel

  - landforms: ox-bow lakes, meanders, flood plains
• lower course of a river

  - zone of deposition

  - wide and deep river channel

  - landforms: levees, floodplains, estuaries
• when does deposition occur

  - when the river runs out out energy

  - velocity decreases

  - can no longer transport its sediment so its deposited
• vertical vs lateral erosion

  - vertical erosion: increases channel depth

  - lateral erosion: increases channel width
• types of erosion

  - hydraulic action

  - abrasion

  - attrition

  - solution
• hydraulic action

  force of water breaks into cracks and makes them wider
• abrasion

  eroded rocks picked up by the river scrape and rub against larger materials
• attrition

  eroded rocks picked up by the river smash into each other
• solution (erosion)

  rocks dissolve in water
• types of transportation

  - traction

  - saltation

  - suspension

  - solution
• traction

  large particles like boulders are pushed along the river bed
• saltation

  pebble-sized particles are bounced along the river bed
• suspension

  small particles like silt and clay are carried along by the water
• solution (transportation)

  soluble materials that dissolve in water are carried along
• v-shaped valley

  - a valley shaped like the letter V

  - a river flows along the bottom
• scree

  jagged, angular rock that has been broken up by freeze thaw weathering
• interlocking spurs

  ridges of land that stick out into the river valley
• how are interlocking spurs formed

  when the river flows around obstacles of harder rock that cannot easily be eroded
• meanders

  wide bends found in the middle course of a river

  
• river cliff

  undercutting of the river bank on the outside bend of a meander
• point bar / slip off slope


  a small beach of deposited pebbles on he inside bend of a meander
• thalweg

  the line of fasted flow in a river
• water flow in a meander

  helicodial flow

  - corkscrew movement

  - fast flow occurs on the outside bend of the meander, and therefore causes erosion, leaves a river cliff

  - slow flow occurs on the inside bend of a meander, and therefore causes deposition, leaves a point bar
• ox-bow lake


  a horse show shaped lake formed when a meander is cut off at its neck
• levee


  raised banks on the side of a river
• alluvium


  fine silty mud left behind by a river after a flood
• brackish water

  an area of water in he middle of an estuary where fresh water from river mixes with the salt water from the sea
• estuary


  a funnel shaped river mouth surrounded by mud flats and marshes
• why does salinity vary throughout the year

  during winter and spring, there is less salt content:

  - there is more fresh water input from rain, which dilutes the salt content

  - snow melts in winter and spring so there is less evaporation

  during summer and autumn there is more salt content:

  - the is less fresh water input from rain, meaning less salt water is diluted

  - heat evaporates the water leaving the salt behind to make it saltier
• causes of variations is precipitation

  - depression and storms in winter

  - heavy downpours from thunderstorms

  - prolonged light rain

  - sudden snow melt
• physical factors that increase flood risk

  - steep slope ~ encourage rapid run off

  - impermeable rock ~ prevent infiltration, results in more surface run off

  - clay soil ~ more compact, little room for infiltration, more surface run off

  - high drainage density ~ more ways for water to be discharged and enter the river

  - sudden, heavy rainfall ~ infiltration rates are slow, results in surface run off