Runoff and Hydrograph

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Runoff and Hydrograph

  1. 1. NUST Institute of Civil Engineering/Engr Sajjad Ahmad<br />1<br />
  2. 2. Engineering Hydrology(CE- 235)<br />CHAPTER - 3<br />2<br />Runoff & Hydrographs<br />(Contd…)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Runoff & hydrograph - Outline<br /><ul><li>Estimation of evaporation
  3. 3. Direct measurement
  4. 4. Indirect or theoretical method
  5. 5. Measurement of infiltration</li></ul>3<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Runoff & hydrograph - Outline<br /><ul><li>Computation of runoff by various methods
  6. 6. Characteristics of hydrograph
  7. 7. Components of a hydrograph
  8. 8. Hydrograph separation
  9. 9. Unit Hydrograph
  10. 10. S-curve</li></ul>4<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>5<br />Engineering Hydrology(CE- 235)<br />Direct measurement of evaporation by Pan<br /> There are three types of pan<br /><ul><li>Sunken pans
  11. 11. Above ground or surface pans
  12. 12. Floating pans
  13. 13. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>6<br />Engineering Hydrology(CE- 235)<br />Sunken pans<br /><ul><li>Buried in ground
  14. 14. Wall effects such as heat exchange and ration effects are neglected
  15. 15. More accurate results
  16. 16. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>7<br />Engineering Hydrology(CE- 235)<br />Sunken pans drawbacks<br /><ul><li>Difficult to clean
  17. 17. Error due to leakage
  18. 18. Height of vegetation around pan is critical
  19. 19. Plant leaves, seeds and debris can enter easily
  20. 20. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>8<br />Engineering Hydrology(CE- 235)<br />Bureau of plant industry (B. P. I) pan<br /><ul><li>Circular in shape
  21. 21. 1.80 m in diameter and 0.55m deep
  22. 22. Edges are 0.05m above ground
  23. 23. Total depth is 0.60m
  24. 24. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>9<br />Engineering Hydrology(CE- 235)<br />Colorado pan<br /><ul><li>Square in shape
  25. 25. Dimensions are 0.90m x 0.90m and 0.45m deep
  26. 26. Rim projection from ground is 5 cm
  27. 27. Water maintained 2 inch below rim
  28. 28. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>10<br />Engineering Hydrology(CE- 235)<br />Young’s pan<br /><ul><li>Circular shape
  29. 29. 0.6m diameter
  30. 30. 0.9m deep
  31. 31. Covered with 6mm wire mesh screen
  32. 32. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>11<br />Engineering Hydrology(CE- 235)<br />Above ground or surface pan<br /><ul><li>Made from galvanized sheet
  33. 33. Placed on wooden floor
  34. 34. Easy operation and maintenance
  35. 35. Correction factors are applied
  36. 36. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>12<br />Engineering Hydrology(CE- 235)<br />Floating pans<br /><ul><li>Float over surface of water
  37. 37. Gives accurate reading which are free from atmospheric effects
  38. 38. Drawbacks
  39. 39. Difficulty in measurement
  40. 40. Leakage cannot be detected
  41. 41. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>13<br />Engineering Hydrology(CE- 235)<br />Estimation by theoretical method<br /><ul><li>Water budget approach
  42. 42. Energy budget approach
  43. 43. Mass transfer approach
  44. 44. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>14<br />Engineering Hydrology(CE- 235)<br />Water budget approach<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>15<br />Engineering Hydrology(CE- 235)<br />Energy budget approach<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>16<br />Engineering Hydrology(CE- 235)<br />Energy budget approach<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>17<br />Engineering Hydrology(CE- 235)<br />Mass transfer approach<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>18<br />Engineering Hydrology(CE- 235)<br />Mass transfer approach<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>19<br />Engineering Hydrology(CE- 235)<br />Pan coefficient<br /><ul><li>Measured evaporation is always greater than the actual value
  45. 45. The coefficient multiplier of 0.6 or greater is used to get actual reading
  46. 46. This coefficient is termed as pan coefficient
  47. 47. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>20<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>21<br />Engineering Hydrology(CE- 235)<br />Example # 1 (from book)<br />Example # 2 (from book)<br />Example # 3 (from book)<br />Example # 4 (from book)<br />Example # 5(from book)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Lysimeter<br /><ul><li>A lysimeter is a measuring device which can be used to measure the amount of actual evapotranspiration which is released by crops or trees. By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated</li></ul>22<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>23<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Infiltration<br /><ul><li>Water loss due to absorption of water by the ground surface
  48. 48. Horizontal movement of absorbed water is called interflow
  49. 49. Vertical movement of absorbed water is called percolation </li></ul>24<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Factors affecting infiltration<br /><ul><li>Ground conditions
  50. 50. Presence of vegetation
  51. 51. Type of soil
  52. 52. Storm characteristics
  53. 53. Temperature
  54. 54. etc…. </li></ul>25<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li><ul><li>By Horton’s equation</li></ul>26<br />Engineering Hydrology(CE- 235)<br />Measurement of infiltration<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>27<br />Engineering Hydrology(CE- 235)<br /><ul><li>The area under the curve gives the total amount of infiltration
  55. 55. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>28<br />Engineering Hydrology(CE- 235)<br />Infiltration indices<br /><ul><li>They gives the average rate of loss
  56. 56. Φ index
  57. 57. W index</li></ul>Φ index<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad<br />29<br />Engineering Hydrology(CE- 235)<br /><ul><li>The limitation for determining the infiltration indices is that the quantity of total runoff must be known</li></li></ul><li>30<br />Engineering Hydrology(CE- 235)<br />W index<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>31<br />Engineering Hydrology(CE- 235)<br />Example # 6 (from book)<br />Example # 7 (from book)<br />DRO<br />1.45 cm<br />infiltration<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Computation of runoff<br /><ul><li>By runoff formulae and tables
  58. 58. By infiltration method
  59. 59. By rational method
  60. 60. By unit hydrograph</li></ul>32<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>By runoff formulas and tables<br /><ul><li>Runoff coefficient
  61. 61. Barlow’s coefficient
  62. 62. Inglis’s formula
  63. 63. Lacey’s formula
  64. 64. Khosla formula
  65. 65. Parker’s formula </li></ul>33<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>34<br />Engineering Hydrology(CE- 235)<br />Runoff coefficient<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Barlow’s table<br />35<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>36<br />Engineering Hydrology(CE- 235)<br />Inglis’s formula<br /><ul><li>For sloping/hilly areas
  66. 66. For flat areas
  67. 67. NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>37<br />Engineering Hydrology(CE- 235)<br />Lacey’s formula<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>38<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>39<br />Engineering Hydrology(CE- 235)<br />Khosla formula<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>40<br />Engineering Hydrology(CE- 235)<br />Parker’s formula<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>41<br />Engineering Hydrology(CE- 235)<br />Runoff by infiltration method<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>42<br />Engineering Hydrology(CE- 235)<br />cm<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li><ul><li>It considers following factors
  68. 68. Catchment area ‘A’ in hectares
  69. 69. Impermeability factor ‘I’ of the catchment area
  70. 70. Intensity of rainfall ‘R’ in mm/hr</li></ul>43<br />Engineering Hydrology(CE- 235)<br />Rational method<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>44<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Impermeability factor<br /><ul><li>The percentage of storm water that is available in the form of runoff is known as impermeability factor
  71. 71. It varies with respect to the type of surface
  72. 72. If more than one type of area is included the average factor is used</li></ul>45<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Hydrograph<br /><ul><li>A hydrograph is a graph of the flow in a stream over a period of time</li></ul>46<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>Unit hydrograph<br /><ul><li>A unit hydrograph is a graph representing 1 cm or 1 inch of runoff from a rainfall of some unit duration</li></ul>47<br />Engineering Hydrology(CE- 235)<br /><ul><li>NUST Institute of Civil Engineering/Engr Sajjad Ahmad</li></li></ul><li>

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