Fact inf hydro graophs ap
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Fact inf hydro graophs ap

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Fact inf hydro graophs ap Fact inf hydro graophs ap Presentation Transcript

  • •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
  • 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
  • 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. • 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.
  • 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 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.
  • 3. Previous weather conditions
  • 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.
  • 4. Relief
  • • Overland flow can be faster down a steep slope therefore steeper rising limb and shorter lag time 4. Relief (shape of the land)
  • 5. Rock Type
  • 5. Rock Type • Permeable rocks mean rapid infiltration and little overland flow therefore shallow rising limb and longer lag time.
  • Land Use
  • Land Use
  • 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
  • Hydrographs What could cause 2 peaks in a hydrograph?