River discharge & hydrographs

River discharge & hydrographs

1. Definition: The volume of water passing a given point at a given time, measured in cumecs

   • Velocity x cross-sectional area

2. Temperature

   • in low temperatures the ground freezes resulting in less infiltration and more surface run off
   • in high temperatures there is more evapo-transpiration reducing river discharge

3. Size, shape and relief of a river basin

   • Big river basin takes longer to get to the main river channel so there is less river discharge
     • Smaller means less time and more discharge
   • Circular - gets to the river quicker
     • Elongated - longer to get to the river
   • Steep slope means water travels quicker
     • Gentle slope means more infiltration

4. Rock Type

   • Permeable (sandstone, chalk) allows pore to be filled = less discharge
   • Impermeable means increased surface run off

5. Soil Type

   • Space between soil particles
   • Soil moisture storage

6. Precipitation

   • More = saturation = high surface run off
   • High intensity - rain drops splash
   • Snow stored on ground then melts

7. Land Use

   • More trees = more interception
   • Urbanisation = nothing to intercept. concrete is impermeable

8. Hydrographs

   • Flashy
     • Short lag time
     • High peak discharge
   • Subdued
     • Long lag time
     • Low peak discharge
   • Discharge against time