Runoff and Hydrograph
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This document discusses methods of estimating evaporation and runoff. It describes different types of pans that can be used to directly measure evaporation, as well as theoretical methods like the water, energy and mass budget approaches. It also discusses factors that influence infiltration and various formulas that can be used to compute runoff, including the rational method. Hydrographs and unit hydrographs are introduced to analyze streamflow over time from rainfall-runoff events.
Runoff and Hydrograph
- 1. NUST Institute of Civil Engineering/Engr Sajjad Ahmad1
- 2. Engineering Hydrology(CE- 235)CHAPTER - 32Runoff & Hydrographs(Contd…)NUST Institute of Civil Engineering/Engr Sajjad AhmadRunoff & hydrograph - OutlineEstimation of evaporation
- 4. Indirect or theoretical method
- 5. Measurement of infiltration3Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadRunoff & hydrograph - OutlineComputation of runoff by various methods
- 7. Components of a hydrograph
- 10. S-curve4Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad5Engineering Hydrology(CE- 235)Direct measurement of evaporation by Pan There are three types of panSunken pans
- 11. Above ground or surface pans
- 12. Floating pans
- 13. NUST Institute of Civil Engineering/Engr Sajjad Ahmad6Engineering Hydrology(CE- 235)Sunken pansBuried in ground
- 14. Wall effects such as heat exchange and ration effects are neglected
- 16. NUST Institute of Civil Engineering/Engr Sajjad Ahmad7Engineering Hydrology(CE- 235)Sunken pans drawbacksDifficult 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 Ahmad8Engineering Hydrology(CE- 235)Bureau of plant industry (B. P. I) panCircular 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 Ahmad9Engineering Hydrology(CE- 235)Colorado panSquare 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 Ahmad10Engineering Hydrology(CE- 235)Young’s panCircular shape
- 29. 0.6m diameter
- 30. 0.9m deep
- 31. Covered with 6mm wire mesh screen
- 32. NUST Institute of Civil Engineering/Engr Sajjad Ahmad11Engineering Hydrology(CE- 235)Above ground or surface panMade 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 Ahmad12Engineering Hydrology(CE- 235)Floating pansFloat over surface of water
- 37. Gives accurate reading which are free from atmospheric effects
- 38. Drawbacks
- 40. Leakage cannot be detected
- 41. NUST Institute of Civil Engineering/Engr Sajjad Ahmad13Engineering Hydrology(CE- 235)Estimation by theoretical methodWater budget approach
- 44. NUST Institute of Civil Engineering/Engr Sajjad Ahmad14Engineering Hydrology(CE- 235)Water budget approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad15Engineering Hydrology(CE- 235)Energy budget approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad16Engineering Hydrology(CE- 235)Energy budget approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad17Engineering Hydrology(CE- 235)Mass transfer approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad18Engineering Hydrology(CE- 235)Mass transfer approachNUST Institute of Civil Engineering/Engr Sajjad Ahmad19Engineering Hydrology(CE- 235)Pan coefficientMeasured 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 Ahmad20Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad21Engineering 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 AhmadLysimeterA 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 calculated22Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad23Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadInfiltrationWater 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 24Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadFactors affecting infiltrationGround conditions
- 51. Type of soil
- 53. Temperature
- 54. etc…. 25Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadBy Horton’s equation26Engineering Hydrology(CE- 235)Measurement of infiltrationNUST Institute of Civil Engineering/Engr Sajjad Ahmad27Engineering Hydrology(CE- 235)The area under the curve gives the total amount of infiltration
- 55. NUST Institute of Civil Engineering/Engr Sajjad Ahmad28Engineering Hydrology(CE- 235)Infiltration indicesThey gives the average rate of loss
- 56. Φ index
- 57. W indexΦ indexNUST Institute of Civil Engineering/Engr Sajjad AhmadNUST Institute of Civil Engineering/Engr Sajjad Ahmad29Engineering Hydrology(CE- 235)The limitation for determining the infiltration indices is that the quantity of total runoff must be known30Engineering Hydrology(CE- 235)W indexNUST Institute of Civil Engineering/Engr Sajjad Ahmad31Engineering Hydrology(CE- 235)Example # 6 (from book)Example # 7 (from book)DRO1.45 cminfiltrationNUST Institute of Civil Engineering/Engr Sajjad AhmadComputation of runoffBy runoff formulae and tables
- 60. By unit hydrograph32Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadBy runoff formulas and tablesRunoff coefficient
- 62. Inglis’s formula
- 63. Lacey’s formula
- 64. Khosla formula
- 65. Parker’s formula 33Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad34Engineering Hydrology(CE- 235)Runoff coefficientNUST Institute of Civil Engineering/Engr Sajjad AhmadBarlow’s table35Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad36Engineering Hydrology(CE- 235)Inglis’s formulaFor sloping/hilly areas
- 66. For flat areas
- 67. NUST Institute of Civil Engineering/Engr Sajjad Ahmad37Engineering Hydrology(CE- 235)Lacey’s formulaNUST Institute of Civil Engineering/Engr Sajjad Ahmad38Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad39Engineering Hydrology(CE- 235)Khosla formulaNUST Institute of Civil Engineering/Engr Sajjad Ahmad40Engineering Hydrology(CE- 235)Parker’s formulaNUST Institute of Civil Engineering/Engr Sajjad Ahmad41Engineering Hydrology(CE- 235)Runoff by infiltration methodNUST Institute of Civil Engineering/Engr Sajjad Ahmad42Engineering Hydrology(CE- 235)cmNUST Institute of Civil Engineering/Engr Sajjad AhmadIt considers following factors
- 68. Catchment area ‘A’ in hectares
- 69. Impermeability factor ‘I’ of the catchment area
- 70. Intensity of rainfall ‘R’ in mm/hr43Engineering Hydrology(CE- 235)Rational methodNUST Institute of Civil Engineering/Engr Sajjad Ahmad44Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadImpermeability factorThe 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 used45Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadHydrographA hydrograph is a graph of the flow in a stream over a period of time46Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad AhmadUnit hydrographA unit hydrograph is a graph representing 1 cm or 1 inch of runoff from a rainfall of some unit duration47Engineering Hydrology(CE- 235)NUST Institute of Civil Engineering/Engr Sajjad Ahmad