Hydrograph

• hydrograph: discharge time series that provides information about behaviour of catchment
• discharge dynamics are gradual due to water being stored in catchment and released slowly afterwards
• amount of delay and attenuation depend on catchment characteristics, channel network, precipitation event and catchment wetness
• rain-fed rivers: discharge responds on rainfall events and discharge decreases in periods without rain

  • fed by rain
• mixed rivers: discharge does not respond to rainfall events

  • fed by snow and rain
• baseflow: minimum discharge

  • originates from groundwater in catchment
  • includes slow processes
  • amount depends on underlying soil
• recession: slow decrease in baseflow during drier periods
• perennial streams: carry water yearround
• ephemeral streams: run dry part of year
• quickflow: causes peaks on top of baseflow

  • quick rise in discharge and water level
  • often causes floods and inundations
• factors increasing probability of quickflow and high discharge peaks

  • steep topography
  • low infiltration capacity
  • high drainage density
  • hydrophobic soil
  • high precipitation intensity
  • uneven precipitation distribution
  • wet initial conditions
  • rain on snow
• network of channels in catchment determine total distances river water has to travel before reaching catchment outlet

  • elongated channel = smooth discharge peaks due to contribution of quickflow is more spread out
• concentration time (Tc): time it takes surface water at most upstream point to reach catchment outlet
• response time (Tr): time difference between rainfall event and resulting discharge peak

  • depend on shape of channel network and runoff processes which take place in catchment
• width function: plotting number of network links as function of distance to catchment outlet
• retention basins constructed to store water during flood peaks and release it when river water levels drop