explaining hydrographs

• drainage basin size + shape -

  • small basin = less time taken for water to reach river = short lag time
  • circle basins = rapid discharge as all precipitation enters river at the same time
  • narrow + long basins = water takes longer to discharge
• drainage basin density -

  • more tributaries + streams = water enters system quicker = short lag time + higher peak discharge
• basins gradient -

  • steep = water flows into river more rapid = steep rising limb + short lag time
  • steep rising limb + short lag time occur after short periods of heavy rain as soil cant absorb it all
• geology -

  • impermeable = surface run off = short lag time
  • permeable = percolation = long lag time
• land use -

  • urban = tarmac + concrete = surface run off = drains + sewers = quickly diverted to river = short lag
  • rural areas = lower peak discharge + long lag time
• vegetation -

  • plants + trees = less water entering river due to transpiration = low peak discharge + long lag times
• steep rising limb flood risks -

  • deforested areas , urban areas
  • steep slopes
  • heavy rain
  • clay soil , impermeable rock
  • no dams or rivers
• gentle rising limb low flood risk -

  • gentle slopes
  • forests
  • sandy soil , permeable rock
  • light ain , dam or river