Storm hydrograph

• Hydrographs

  • shows how river discharges change over time at particular point at river
  • increased runoff-> reduced lag time and greater discharge= steep hydrograph bc more water gets into river channel quicker
• river discharge

  • volume of water flowing in a river each second and measured in cumecs (m^3/s)
• hydrograph features

  • peak discharge= max discharge in period of time
  • peak rainfall= max rainfall
  • lag time= interval between peak rainfall and discharge
  • rising limb= discharge is rising
  • falling limb= discharge is falling
• Physical factors affecting storm hydrographs(PFASH)

  rock type and soil

  • Permeable= precipitation infiltrate and percolate-> lengthens lag time and reduces peak discharge
  • impermeable= stops precipitation infiltrating= surface runoff increases and lag time reduced and peak discharge increased
  • soil fully saturated or frozen by antecedent conditions= no infiltration-> increased runoff->increasing peak discharge
• PFASH

  relief and vegetation

  • steeper catchment= quicker water reaches river increases peak discharge and reduces lag time
  • river catchment with high levels of vegetation= high interception and evaportranspiration
  • tree roots help promote infiltration= results in catchments with more vegetation having a lower surface runoff and reduced peak discharge
• PFASH

  size,shape and drainage density

  • larger catchment= higher peak discharge but longer lag time
  • circular catchment= shorter lag time
  • denser drainage networks transport water more efficiently= increases flow and peak discharge
• Human factors affecting storm hydrographs( HFASH)

  urbanisation

  • leads to an increase in no of impermeable surfaces
  • lead to a decrease in infiltration, increase in surface runoff-> reduction in lag time
  • shorter lag time= greater peak discharge
• HFASH

  land use

  • ares remain forested or as natural habitat= reduced peak discharge bc of an increase in infiltration of precipitation by vegetation
  • less interception in deforested areas = increases peak discharge
  • ploughing of agricultural land increases surface runoff-> lag time to reduce and peak discharge to increase
• HFASH

  water management

  • dams and reservoirs= regulate flow of river by storing water and choosing when to release it downstream
  • abstractin of aquifers lowers groundwater levels and increases percolation and infiltration when rainfall happens