5.3C Storm hydrographs

• • Storm hydrographs show changes in a river’s discharge during and after a storm
  • Usually, they are drawn to show how a river reacts to an individual storm
  • They compare two variables - rainfall received during an event in mm and river discharge m3/sec
• Storm hydrograph:

  
• Flashy hydrograph:

  • short lag time with high peak discharge   

  
• Subdued hydrograph:

  • low peak discharge and a long lag time

  
• Factors affecting the shape of a hydrograph:

  • rock type
  • soils
  • weather/climate
  • antecedent conditions
  • vegetation
  • drainage basin size
  • Human activity
• How antecedent conditions affect storm hydrographs:

  • Saturated soil so infiltration is low and surface run off greater (Flashy)
  • Unsaturated soils so infiltration is high and surface run off low (Subdued)
• How the drainage basin size affects storm hydrographs:

  • Smaller basins have steep rising limbs and short lag times as water reaches the rivers more quickly (Flashy)
  • Large basins have longer lag times and gentler rising limbs as the water takes longer to flow through the drainage basin (Subdued)
• How weather/climate affects storm hydrographs:

  (Flashy)

  • Heavy or prolonged rainfall and rapid snowmelt can exceed the capacity of the soil leading to increased surface run off
  • Low evaporation rates increases surface run off 


  (Subdued)

  • Steady rainfall and slow thaw of snow don't exceed the infiltration capacity of the soil
  • High evaporation rates lead to lower surface run off