rivers

• Drainage basin


  An area of land drained by a river and its tributaries with a boundary (known as the watershed), which are usually hills and mountains
• River stages

  • Upper course
  • Middle course
  • Lower course
• Upper course


  • Tributaries are narrow and v-shaped
  • Low volume of water
• Middle course


  • Channel is rounder in shape and deeper than upper course
  • More energy due to higher volume of water
  • Floodplain around river channel
• Lower course


  • Largest volume of water in a very wide and very deep channel
  • Ridges either side of river banks called Levees
  • Valley is wider and flatter than middle course
• Friction between water and riverbed


  Slows down the water
• More contact between water and riverbed

  Slower rate of flow
• Larger river channel


  Faster velocity of water
• Erosional processes

  • Abrasion
  • Attrition
  • Hydraulic action
  • Corrosion (solution)
• Transportation processes

  • Solution
  • Suspension
  • Saltation
  • Traction
• Deposition occurs when water in a river decreases in speed
• Heaviest materials get deposited first in the upper course, finer sediment travels to lower course
• Landforms in each river course

  • Upper course: Waterfalls, Interlocking Spurs, V-Shaped Valley
  • Middle course: Gorges, Meanders
  • Lower course: Floodplains, Ox-Bow Lake, River Estuary
• Interlocking Spurs


  • Found in upper course where water doesn't have a lot of energy
  • River re-routes and curls around resistant rocks
• Formation of Waterfalls

  1. River flows over rocks with different resistances to erosion

  2. Soft rock erodes more quickly

  3. Soft rock erodes away around hard rock over time, creating a step

  4. Soft rock continues to erode, undercutting the hard rock

  5. Hard rock is left suspended in the air as an overhang

  6. Rotational movement of water quickens erosion, creating a deep plunge pool

  7. Unsupported overhang collapses, broken rocks fall into plunge pool

  8. Erosion continues to undercut underneath the hard rock, creating an overhang again further upstream

  9. Continual process of overhang collapsing causes the waterfall to retreat upstream over time
• Gorges

  • Form from waterfalls as the waterfall retreats upstream, leaving behind a steep valley carved into the rock with the river running along the base
• Waterfall formation

  1. Unsupported overhang collapses

  2. Broken up rocks fall into plunge pool

  3. Plunge pool acts as tools for erosion

  4. Plunge pool deepens

  5. Erosion undercuts hard rock

  6. Overhang forms further upstream

  7. Overhang collapses

  8. Waterfall retreats upstream

  9. Plunge pool continues to deepen

  10. Hard rock continues to be undercut
• Gorge

  Steep valley carved into rock with river at base, formed by retreating waterfall
• Victoria Falls

  • Located on border of Zambia and Zimbabwe
• Meander formation

  1. Water travels faster on outside of bend, causing lateral erosion and river cliff

  2. Water travels slowly on inside of bend, causing deposition and slip-off slope
• Thalweg

  Path of fastest water
• Ox-bow lake formation

  1. Meanders form due to water speed

  2. Erosion bends river, neck of meander breaks

  3. Deposition separates old meander, creating ox-bow lake
• Ox-bow lakes

  • Kinabatangan River, Malaysia
• Floodplain

  Flat land along lower course of river, formed by deposition of fine sediment during floods
• Levee

  Higher banks along river in lower course, formed by deposition of sediment during floods
• Estuary

  Where river meets sea, affected by tides and deposition
• Cardiff Bay

  • Mudflats formed during low tide, later redeveloped with barrage
• Human factors increasing flood risk

  • Urbanisation
  • Deforestation
  • Reduced river capacity
• Physical factors increasing flood risk

  • High precipitation rate
  • Impermeable geology
  • Steep topography
• Storm hydrograph

  • Shows variation in river discharge over time
  • Features: peak precipitation, rising limb, peak flow, lag time, falling limb, base flow
• Flash flood

  Flood with little warning, large volume of water suddenly overwhelming river
• Subdued flood

  Flood taking up to a week, consistent rain causing saturated ground and runoff
• Peak flow

  The maximum discharge, delayed after maximum precipitation has occurred
• Lag time

  The time delay between peak rainfall and peak river discharge
• Falling limb

  As the storm precipitation levels decrease, river discharge will in turn decrease over time
• Base flow

  Eventually, the discharge returns to its normal level
• Flashy flood

  A flood with little warning, where a very large volume of water suddenly overwhelms the river
• Subdued flood

  A flood that could take up to a week of consistent rain, where there isn't a large quantity of water falling per day but the ground is saturated so any rain runs straight into the river
• Storm hydrograph

  1. Rising limb

  2. Falling limb

  3. Peak flow

  4. Lag time
• Flashy storm hydrograph

  • Short lag time
  • High peak
  • Steep rising limb