geography rivers

• 1. WATERFALLS

  river meets alternating bands of resistant and less resistant rock.

  The less resistant rock is eroded by hydraulic action and abrasion.

  A plunge pool is formed and there is an undercutting of the overhang of resistant rock which collapses into the plunge pool below.

  Waterfall retreats, leaving behind a gorge.
• MEANDERS {erosional and depositional}

  1. Meanders form when a river moves from a straighter course, due to an obstacle.
  2. More erosion occurs where water flows faster and this becomes the outside of a meander.
  3. Deposition occurs where water flow is slowest, forming inside of the meander.
  4. Over time, meander is cut off from the river because erosion occurs on outside.
• OXBOW LAKES { erosional and depositionL}


  Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time. Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together. When there is a very high discharge (usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.
• FLOODPLAINS { depositional}

  Floodplains form due to both erosion and deposition. Erosion removes any interlocking spurs, creating a wide, flat area on either side of the river. During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material). Over time, the height of the floodplain increases as material is deposited on either side of the river.
• LEVEES { depositional}

  • Levees occur when there is an increase in the volume of water flowing downstream and flooding occurs.
  • Sediment that has been eroded upstream is transported downstream.
  • When the river floods, the sediment spreads out across the floodplain.
  • When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
  • After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water and flooding is less likely to occur in the future.
• Transportation types

  • Traction - large, heavy pebbles are rolled along the river bed. This is most common near the source of a river, as here the load is larger.
  • Saltation - pebbles are bounced along the river bed, most commonly near the source.
  • Suspension - lighter sediment is suspended (carried) within the water, most commonly near the mouth of the river.
  • Solution - the transport of dissolved chemicals. This varies along the river depending on the presence of soluble rocks.
• Types of erosion

  • Hydraulic action - This is the power of the water as it smashes against the river banks. Air becomes trapped in the cracks of the river bank and bed, and causes the rock to break apart.
  • Abrasion - When pebbles grind along the river bank and bed in a sand-papering effect.
  • Attrition - When rocks that the river is carrying knock against each other. They break apart to become smaller and more rounded.
  • Solution - When the water dissolves certain types of rocks, eg limestone.
• Deposition

  When the river loses energy, it drops any of the material it has been carrying. This is known as deposition.