5.3c

• what are storm hydrographs?

  show river discharge around the time of a storm event - short time period
• what is the peak discharge?

  the highest point on the graph, when the river discharge is at its greatest
• what is the lag time?

  the time between peak rainfall and peak discharge. this delay happens because it takes time for the rainwater to flow into the river . a shorter lag time can increase the peak discharge because more water reaches the river in a shorter period of time
• what is the rising limb?

  the part of the graph leading up to the peak discharge - the river discharge increases as rainwater flows into the river
• what is the falling limb?

  the part of the graph after peak discharge. discharge is decreasing because less water is flowing into the river. a shallow falling limb shows water is flowing in from stores long after its stopped raining
• what is baseflow?

  groundwater flow that feeds into rivers through river banks and river beds. this is the normal discharge flow of the river
• what is bankfull discharge?

  the point when the water level reaches the top of the river channel without flooding --> if it's exceeded the river will flood
• what are the two types of hydrographs?

  flashy or flat
• flashy hydrograph?

  • steep rising and falling limbs
  • rapid runoff and limited storage capacity = short lag time and high peak discharge
• flat hydrograph?

  • gradual rising and falling limbs
  • slow runoff and large storage capacity = long lag time and low peak discharge
• what factors affect the shape of hydrographs?

  • size of drainage basin
  • shape of drainage basin
  • drainage density
  • relief
  • permeability of rocks and soil
  • vegetation
  • land use
• how does size of drainage basin affect?

  • larger drainage basins catch more precipitation so they have higher peak discharge than smaller basins
  • larger drainage basins have longer lag times because precipitation has more distance to travel so it reaches the main channel more quickly
• how does drainage density affect?

  • water enters a river faster in drainage basins with high drainage density = flashy hydrograph
  • this is because there are more rivers and streams for the water to flow into
• how does the shape of drainage basin affect?

  • circular basins = flashy hydrograph because water arrives from all directions at the same time = decreases lag time
• how does relief affect?

  • water flows faster downhill in drainage basins with steep sides as throughflow and overland flow = shorter lag time
  • water has less time to infiltrate the soil so runoff is higher = flashy hydrograph
• how does permeability of rocks and soil affect?

  • impermeable rocks and soils don't store water or let water infiltrate = increases direct runoff
  • peak discharge increases and lag time decreases as more water reaches the river faster = flashy hydrograph
• how does vegetation affect?

  • more water is lost through evapotranspiration so less water reaches the river channel due to reduced runoff so there's a lower peak discharge and a flat hydrograph
  • vegetation intercepts precipitation and slows its movement to the river channel
• how does land use affect?

  • deforestation reduces interception = increases direct runoff = shorter lag time
  • urbanisation = impermeable surfaces + guttering drains water into the river systems faster --> increases direct runoff and reduces lag time
  • agriculture - crops increase infiltration but heavy machinery compacts the soil = increases its permeability