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Runoff and Hydrograph

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