Geography physical

• Evidence that weather is becoming more extreme in the UK
• Evidence of extreme weather in the UK

  • Drought and extreme heat - European heatwave 2003
  • Prolonged rainfall - UK floods 2014 (Somerset)
  • 'Beast from the East' - heavy snow and extreme cold March 2018
  • Thunderstorms - July 2014, 3000 lightning strikes across southern Britain
• The main types of weathering are mechanical, chemical, and biological.
• Mechanical weathering is caused by the expansion and contraction of rocks due to temperature changes or water freezing inside cracks.
• Chemical weathering occurs when acidic rainwater reacts with minerals in rocks, causing them to break down into smaller particles.
• 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
  • Sides are like a valley with a large gradient
• Middle course


  • Channel is rounder in shape and deeper than upper course
  • More energy due to higher volume of water
  • Area around channel is flat and low-lying (floodplain)
• Lower course


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

  Slows down the water
• Upper course


  Shallow channel, most water passes riverbed, slower rate of flow
• Middle/lower course


  Bigger channel, less water in contact with riverbed, faster velocity
• 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 upper course, finer sediment travels to lower course
• Upper course


  • Erosion is predominant process, typical landforms are waterfalls, interlocking spurs, v-shaped valley
• Middle course


  • Mixture of erosional and depositional landforms, typical landforms are gorges, meanders
• Lower course


  • Deposition is predominant process, typical landforms are floodplains, ox-bow lakes, river estuary
• Interlocking spurs


  Found in upper course where water isn't powerful enough to erode resistant rocks, so river re-routes around them
• 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, creating a step

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

  5. Unsupported overhang of hard rock collapses

  6. Erosion continues to undercut hard rock, causing waterfall to retreat upstream
• Gorges


  Formed from waterfalls as they retreat upstream, leaving behind a steep valley carved into the rock
• 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


  Erosion bends river, neck of meander breaks, creating separate ox-bow lake
• 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


  Area where river meets sea, affected by tides, leading to deposition of mudflats and saltmarshes
• Human factors increasing flood risk

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

  • High rainfall rate and volume
  • Impermeable geology
  • Steep topography
• Storm hydrograph


  • Shows variation in river discharge over time
  • Includes 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