rivers

• what is a drainage basin


  an area of land drained by a river and its tributaries
• what is a source


  the start of a river
• what is a tributary


  a small stream that joins a larger river
• what is watershed


  the edge of the river basin
• what is the mouth of the river


  the end of the river, usually where the river joins the sea
• what is a confluence


  the point where two rivers join
• what are the characteristics of the upper course of a river?


  • steep
  • narrow
  • rocky bottom
  • boulders
  • carry sediment - large rocks (jagged)
• what are the characteristics of the middle course of the river?


  • flat valley floor
  • smaller and more rounded stones
  • wider and deeper
  • pasture
• what are the characteristics of the lower course of the river?


  • very wide flood paths
  • low energy
  • mostly fine sediment
  • wider and deeper - at its fastest
• what is abrasion


  rocks carried along the river wear down the river bed and banks
• what is hydraulic action


  the force of the river against the banks can cause air to be trapped in the cracks and crevices. The pressure weakens the banks and gradually wears away
• what is attrition?


  rocks being carried by the river smash together and break into smaller, smoother and rounder particles
• what is corrosion/solution


  some rocks such as limestone are subject to chemical attack and slowly dissolve into the water
• what is lateral erosion


  • the river erodes sideways into the banks which can create meanders and a wider valley floor
• what is vertical erosion


  • the river erodes downwards into its bed which can create a steeper valley sides, which encourages mass movement
• what is traction


  materials are rolled along the bed of the river
• what is saltation


  materials bounce along the river bed
• what is suspension


  materials float on the surface of the water
• when will a river be most able to transport material

  downstream as the sediment is smaller and velocity is more
• what is deposition


  the process which material being transported by a river can no longer be carried and is dropped.
• how is an ox bow lake formed


  • meander migrate across the valley floor and can erode towards each other
  • the neck of the meander narrows until it is completely broken through
  • this then forms a new, straighter channel
  • old meanders loop and are cut off by deposition to form an ox bow lake
• what is a meander


  wide bends in the river found in the lowland areas that are constantly changing shape and position due to lateral erosion and deposition
• what is the thalweg


  line of fastest flow (velocity) within the river which swings from side to side causing erosion on the outside bend and deposition on the inside bend
• what is a levee


  a raised river bed found alongside a river in the lower course due to flooding over many years
• what is a floodplain


  a wide flat area of marshy land on either side of the river in the middle and lower course
• how are v shaped valleys formed


  erosion by the flow of the river carves out in a V shape leaving the sides exposed to weathering
• what are estuaries


  transitional zones between river and coastal environments affected by wave action and river processes
• what is the main process in an estuary 


  • deposition
• what is groundwater flow


  water flowing underground
• what is surface runoff


  water flowing over land to reach the main river
• what is evapotranspiration


  the collective term for water evaporating from plants and grounds/river/lakes etc.
• why are interlocking spurs made?


  • the river near the source is not powerful enough to cut through 'spurs' of land, so has to flow around them
• how are waterfalls formed?


  • when a river flows over a relatively resistant band of rock and the rock beneath is softer the softer rock is undercut by abrasion or hydraulic action.
• what is a gorge


  a narrow steep sided valley found downstream of a waterfall
• how are gorges formed?


  the overhanging rock in a waterfall collapses and the waterfall retreats upstream and over many years it will leave behind a steep - sided gorge
• what physical factors cause flooding?

  • precipitation
  • geology or rock type
  • relief
• what human factors cause flooding

  • deforestation
  • urbanisation
  • agriculture
• how does heavy precipitation cause flooding?


  • it increases the discharge which exceeds bank full capacity
• what is discharge


  the amount of water passing a specific point at a given time. It is calculated as cross sectional area x velocity and is measured in cumecs (cubic meters per second)
• how can deforestation lead to flooding


  the decrease in vegetation leads to a decrease in interception and therefore the water is quicker in reaching the river and discharge increases

  increased speed + more total water = increased risk of flooding