Construction And Analysis of Hydrographs © Microsoft Word clipart © Microsoft Word clipart
Hydrograph Record of River Discharge (the level of water flowing down a river channel) over a period of time, they show ho...
Why Construct & Analyse Hydrographs ? <ul><li>To find out discharge patterns of </li></ul><ul><ul><li>a particular drainag...
Construction Of  Storm (flood) Hydrographs © Microsoft Word clipart
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Through flow Overland flow Ris...
The discharge of the river is measured in  cumecs  - this stands for cubic metres per second 0  12  24  36  48  30  72 Hou...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) mm 4 3 2 Rainfall shown in mm, as a bar ...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) mm 4 3 2 Discharge in m 3 /s, as a line ...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb mm 4 3 2 Rising limb The nor...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb mm 4 3 2 Peak flow Peak flow...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb mm 4 3 2 Peak...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb Basin lag tim...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Rising limb Recession limb Bas...
0  12  24  36  48  30  72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Through flow Overland flow Ris...
Volume of water reaching the river from surface run off Overland flow Through flow Volume of water reaching the river thro...
Analysis © Microsoft Word clipart
Interpretation of Storm Hydrographs <ul><li>Rainfall Intensity </li></ul><ul><li>Rising Limb </li></ul><ul><li>Recession L...
Some Factors influencing Storm Hydrographs <ul><li>Area </li></ul><ul><li>Slope </li></ul><ul><li>Rock Type </li></ul><ul>...
Area <ul><li>Large basins receive more precipitation than small therefore have larger  runoff </li></ul><ul><li>Larger siz...
Slope <ul><li>Channel flow can be faster down a steep slope therefore steeper  rising limb  and shorter  lag time </li></u...
Rock Type <ul><li>Permeable rocks mean rapid infiltration and little overland flow therefore shallow  rising limb   </li><...
Soil <ul><li>Infiltration is generally greater on thick soil </li></ul><ul><li>The more infiltration occurs the longer the...
Land Use <ul><li>Urbanisation - concrete and tarmac form impermeable surfaces, creating a steep  rising limb  and shorteni...
Precipitation & Temperature <ul><li>Short intense rainstorms can produce rapid  overland flow  and steep  rising limb </li...
Remember! These  influencing factors  will: <ul><li>Influence each other </li></ul><ul><li>Change throughout the rivers co...
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Hydrograph explanation and animation

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Hydrograph explanation and animation

  1. 1. Construction And Analysis of Hydrographs © Microsoft Word clipart © Microsoft Word clipart
  2. 2. Hydrograph Record of River Discharge (the level of water flowing down a river channel) over a period of time, they show how certain rivers respond to a rainstorm. River Discharge (the level of water flowing down a river) (is calculated) Storm Hydrographs Show the change in discharge caused by a period of rainfall = cross sectional area rivers mean (average) velocity X (at a particular point in its course)
  3. 3. Why Construct & Analyse Hydrographs ? <ul><li>To find out discharge patterns of </li></ul><ul><ul><li>a particular drainage basin </li></ul></ul><ul><li>Help predict flooding events, </li></ul><ul><ul><li>therefore influence implementation of flood prevention measures </li></ul></ul>© Microsoft Word clipart
  4. 4. Construction Of Storm (flood) Hydrographs © Microsoft Word clipart
  5. 5. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Flood Hydrograph
  6. 6. The discharge of the river is measured in cumecs - this stands for cubic metres per second 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s)
  7. 7. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) mm 4 3 2 Rainfall shown in mm, as a bar graph
  8. 8. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) mm 4 3 2 Discharge in m 3 /s, as a line graph
  9. 9. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb mm 4 3 2 Rising limb The normal (base) flow of the river starts to rise when run-off, ground and soil water reaches the river.
  10. 10. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb mm 4 3 2 Peak flow Peak flow Maximum discharge in the river, the time when the river reaches its highest flow
  11. 11. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb mm 4 3 2 Peak flow Recession limb shows that water is still reaching the river but in decreasing amounts
  12. 12. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Basin lag time The time it takes for the water to find its way to the river
  13. 13. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Base flow Normal discharge of the river
  14. 14. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Overland flow Through flow + = Storm Flow
  15. 15. Volume of water reaching the river from surface run off Overland flow Through flow Volume of water reaching the river through the soil and underlying rock layers
  16. 16. Analysis © Microsoft Word clipart
  17. 17. Interpretation of Storm Hydrographs <ul><li>Rainfall Intensity </li></ul><ul><li>Rising Limb </li></ul><ul><li>Recession Limb </li></ul><ul><li>Lag time </li></ul><ul><li>Peak flow compared to Base flow </li></ul><ul><li>Recovery rate, back to Base flow </li></ul>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 (m 3 /s) Rising limb Recession limb mm 4 3 2 Peak flow Base flow Through flow Overland flow
  18. 18. Some Factors influencing Storm Hydrographs <ul><li>Area </li></ul><ul><li>Slope </li></ul><ul><li>Rock Type </li></ul><ul><li>Land Use </li></ul><ul><li>Soil </li></ul><ul><li>Precipitation / Temp </li></ul>© Microsoft Word clipart
  19. 19. Area <ul><li>Large basins receive more precipitation than small therefore have larger runoff </li></ul><ul><li>Larger size means longer lag time as water has a longer distance to travel to reach the trunk river </li></ul>Area Rock Type Soil Slope Land Use Precipitation / Temp
  20. 20. Slope <ul><li>Channel flow can be faster down a steep slope therefore steeper rising limb and shorter lag time </li></ul>Area Rock Type Soil Slope Land Use Precipitation / Temp
  21. 21. Rock Type <ul><li>Permeable rocks mean rapid infiltration and little overland flow therefore shallow rising limb </li></ul>Area Rock Type Soil Slope Land Use Precipitation / Temp
  22. 22. Soil <ul><li>Infiltration is generally greater on thick soil </li></ul><ul><li>The more infiltration occurs the longer the lag time and shallower the rising limb </li></ul>Area Rock Type Soil Slope Land Use Precipitation / Temp
  23. 23. Land Use <ul><li>Urbanisation - concrete and tarmac form impermeable surfaces, creating a steep rising limb and shortening the time lag </li></ul><ul><li>In wooded areas, trees intercept/absorb the precipitation, creating a shallow rising limb and lengthening the time lag </li></ul>Area Rock Type Soil Slope Land Use Precipitation / Temp
  24. 24. Precipitation & Temperature <ul><li>Short intense rainstorms can produce rapid overland flow and steep rising limb </li></ul><ul><li>If there have been extreme temperatures, the ground can be hard (either baked or frozen) causing rapid surface run off </li></ul><ul><li>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 </li></ul>Area Rock Type Precipitation / Temp Soil Slope Land Use
  25. 25. Remember! These influencing factors will: <ul><li>Influence each other </li></ul><ul><li>Change throughout the rivers course </li></ul>
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