•Rainfall Intensity
•Rising Limb
•Recession Limb
•Lag time
•Peak flow compared to Base flow
•Recovery rate, back to Base f...
Recap on Hydrographs
• Have a go at the Living Hydrograph exercise
…where do you think each statement would be
best placed...
Two different Hydrographs A & B – can
you describe them?
Factors effecting
flood hydrographs
1. Amount and type of precipitation
1. Amount and type of precipitation
• Short intense rainstorms can produce
rapid overland flow and steep rising limb.
• Sn...
2. Temperature
2. Temperature
2. Temperature
2. Temperature
• Snow on the ground can act as a store
producing a long lag time and shallow rising
limb. Once a thaw sets...
3. Previous weather conditions
3. Previous weather conditions
• If it has rained a lot before the storm, the
ground will be saturated. This would
encoura...
4. Relief
• Overland flow can be faster down a steep
slope therefore steeper rising limb and
shorter lag time
4. Relief (shape of th...
5. Rock Type
5. Rock Type
• Permeable rocks mean rapid infiltration
and little overland flow therefore shallow
rising limb and longer l...
Land Use
Land Use
6. Land Use
• Urbanisation - concrete and tarmac form
impermeable surfaces, creating a steep
rising limb and shortening th...
Hydrographs
What could cause 2 peaks in a
hydrograph?
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Fact inf hydro graophs ap

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Fact inf hydro graophs ap

  1. 1. •Rainfall Intensity •Rising Limb •Recession Limb •Lag time •Peak flow compared to Base flow •Recovery rate, back to Base flow You need to refer to: Basin lag time 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge(m3/s) Base flow Through flow Overland flow mm 4 3 2 Peak flow Interpretation of Storm Hydrographs
  2. 2. Recap on Hydrographs • Have a go at the Living Hydrograph exercise …where do you think each statement would be best placed on the graph? • Now watch this video
  3. 3. Two different Hydrographs A & B – can you describe them?
  4. 4. Factors effecting flood hydrographs
  5. 5. 1. Amount and type of precipitation
  6. 6. 1. Amount and type of precipitation • Short intense rainstorms can produce rapid overland flow and steep rising limb. • Snow will be stored on the ground and not effect the hydrograph until it melts. This means in spring there may be steep rising limbs.
  7. 7. 2. Temperature
  8. 8. 2. Temperature
  9. 9. 2. Temperature
  10. 10. 2. Temperature • Snow on the ground can act as a store producing a long lag time and shallow rising limb. Once a thaw sets in the rising limb will become steep. • If there have been extreme temperatures, the ground can be hard (either baked or frozen) causing rapid surface run off.
  11. 11. 3. Previous weather conditions
  12. 12. 3. Previous weather conditions • If it has rained a lot before the storm, the ground will be saturated. This would encourage more surface runoff, causing a steeper rising limb on the hydrograph.
  13. 13. 4. Relief
  14. 14. • Overland flow can be faster down a steep slope therefore steeper rising limb and shorter lag time 4. Relief (shape of the land)
  15. 15. 5. Rock Type
  16. 16. 5. Rock Type • Permeable rocks mean rapid infiltration and little overland flow therefore shallow rising limb and longer lag time.
  17. 17. Land Use
  18. 18. Land Use
  19. 19. 6. Land Use • Urbanisation - concrete and tarmac form impermeable surfaces, creating a steep rising limb and shortening the time lag • Afforestation (planting trees) - intercepts the precipitation, creating a shallow rising limb and lengthening the lag time
  20. 20. Hydrographs What could cause 2 peaks in a hydrograph?

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