Introduction to Hydrology & Precipitation - Module - 1.pptx
- 1. Sumanth A Asst Professor, Civil Engg Dep HYDROLOGY & IRRIGATION ENGINEERING 18CV63 Click to add text
- 2. Course Outcomes 1. Understand the significance of hydrology, components, precipitation measurement and analysis. 2. Identify the different losses in precipitation and its analysis. 3. Estimate runoff and develop unit hydrographs. 4. Illustrate the different systems of irrigation and compute water requirements of crops. 5. Explain reservoirs, canals and design the canal capacity by Kennedy's and Lacey's method.
- 3. Module-I Hydrology: Introduction, Importance of hydrology, Global and Indian water availability, Practical application of hydrology, Hydrologic cycle (Horton’s) qualitative and engineering representation. Precipitation: Definition, Forms and types of precipitation, measurement of rain fall using Symon’s and Syphon type of rain gauges, optimum number of rain gauge stations, consistency of rainfall data (double mass curve method), computation of mean rainfall, estimation of missing data, presentation of precipitation data, moving average curve, mass curve, rainfall hyetographs.
- 4. Module-II Losses: Evaporation: Introduction, Process, factors affecting evaporation, measurement using IS class-A Pan, estimation using empirical formulae (Meyer’s and Rohwer’s equations) Reservoir evaporation and control Evapo-transpiration: Introduction, Consumptive use, AET, PET, Factors affecting, Measurement, Estimation by Blaney- Criddle equation Infiltration: Introduction, factors affecting infiltration capacity, measurement by double ring infiltrometer, Horton’s infiltration equation, infiltration indices.
- 5. Module-III Runoff: Definition, concept of catchment, factors affecting runoff, rainfall – runoff relationship using regression analysis. Hydrographs: Definition, components of hydrograph, base flow separation, unit hydrograph, assumption, application and limitations, derivation from simple storm hydrographs, S curve and its computations, Conversion of UH of different durations
- 6. Module-IV Irrigation: Definition. Benefits and ill effects of irrigation. System of irrigation: surface and ground water, flow irrigation, lift irrigation, Bandhara irrigation. Water Requirements of Crops: Duty, delta and base period, relationship between them, factors affecting duty of water crops and crop seasons in India, irrigation efficiency,
- 7. Module-V Canals: Types of canals, Alignment of canals. Definition of gross command area, cultural command area, intensity of irrigation, time factor, crop factor, unlined and lined canals, standard sections, design of canals by Lacey's and Kennedy's method. Reservoirs: Definition, investigation for reservoir site, storage zones, determination of storage capacity using mass curves, economical height of dam.
- 8. WHY HYDROLOGY ? WHY IRRIGATION ?
- 9. HYDROLOGY Hydrology means the science of water. It is the science that deals with the occurrence, circulation and distribution of water of the earth and earth's atmosphere. Definition by Wisler and Brater The science that deals with processes governing the depletion and replenishment of water resources of the land areas of the earth.
- 10. Hydrology is a interdisciplinary science Hydrology Physics, Chemistry, Biology, Geology, Fluid Mechanics, Mathematics, Probability, Statistics Surface Water Ground Water Water affects plants and animals
- 16. DESCRIPTIVE REPRESENTATION OF THE HYDROLOGIC CYC
- 17. Hydrologic cycle consists of various complicated processes • Precipitation • Interception • Evaporation • Transpiration • Infiltration • Percolation • Storage • Runoff
- 18. QUALITATIVE REPRESENTATION OF THE HYDROLOGIC CYC
- 19. ENGINEERING REPRESENTATION OF THE HYDROLOGIC CYCLE
- 21. Importance of hydrology Maximum probable flood that may occur at a given site. Water yield from the basin. Groundwater development Maximum intensity of storm and its frequency for the design of drainage system
- 22. Practical application of hydrology Design of hydraulic structures Municipal and industrial water supply Irrigation Hydropower Flood control Erosion and sediment control Navigation
- 26. Indian water availability Rain gauge station : 3000 (IMD) Indian Average rainfall : 120cm Geographical area of the country : 3.28x106 km2 Total available water : 3916 km3 ≈ 4000 km3 Lost to atmosphere 700km3 Groundwater 2150km3 Surface runoff 1150km3 Total 4000km3 According to irrigation commission of India the total surface water in the country is about 1800 km3 Depression storage 150km3 Diversion works and pumping 150km3 Towards sea 1500km3 Total 1800km3
- 30. Precipitation All forms of moisture that reaches the earth surface from the atmosphere. Usual forms are rainfall, snowfall, hail, frost, dew Of all these, only the first two contribute significant amount of water. Rainfall being the predominant form causing stream flow and flood flow
- 31. Formation of precipitation Atmosphere must have moisture There must be sufficient nuclei present to aid condensation Weather conditions must be good for condensation of water vapour to takes place Products of condensation must reach the earth
- 33. Forms of precipitation Rain : Size of the drop 0.5 to 6mm Light rain – 2.5mm/h Moderate rain – 2.5-7.5mm/h Heavy rain - >7.5mm/h Snow : consist of ice crystals, density – 0.06-0.15g/cm3 Drizzle : fine sprinkle of numerous water droplets Glaze : type of ice coating Sleet : precipitation of snow and rain simultaneously Hail : irregular pellets or lumps of size more than 8mm Dew : it forms directly by condensation on the ground mainly during night when the surface has been cooled by the outgoing radiation
- 43. Types of precipitation 1 Cyclonic precipitation 2 Orographic Precipitation 3 Convective precipitation
- 44. Cyclonic precipitation A cyclone is a large low pressure region with circular wind motion. It is caused by the lifting of the air mass due to the pressure difference.
- 45. Cold front : when cold air mass drives away a hot air mass. Heavy rainfall Warm front : if the hot air mass replaces the cold air mass Distributed rainfall over a large area Stationary front : Cold and warm air masses drawn simultaneously to a low pressure area
- 46. Orographic Precipitation Air masses which strikes some natural topographic barriers like mountains and can not move forward and hence rise up causing condensation and precipitation. Heavy rainfall in the windward side
- 47. Convective precipitation Air which is warmer than the surrounding air due to localized heating rises because of lesser density. The warm air continues to rise undergoes cooling and results in precipitation.
- 48. Measurement of precipitation 1) Non recording rain gauges ( Symons gauge) : it records the amount of rainfall only. 2) Recording rain gauges(Automatic rain gauges) : it records the amount of rainfall and also provide the information regarding when exactly the rain commenced, when the rain ended, intensity of rainfall. a) Tipping bucket type b) Weighing bucket type c) Float type ( Siphons gauge)
- 49. Non recording rain gauge ( Symons gauge) :
- 50. Recording rain gauge (Siphons gauge)
- 51. Rainfall chart
- 55. Adequacy of rain gauge stations : As per Indian standard recommendation 1. One gauge per 520km2 in plain areas. 2. One gauge per 260 - 390km2 in regions with an average elevation of 1km above the sea level. 3. One gauge per 130km2 in predominantly hilly regions with heavy rainfall. Optimum number of rain gauge stations
- 56. Computation of average rainfall 1. Arithmetic mean method 2. Thiessen polygon method 3. Isohyetal method
- 58. Thiessen polygon method gauge rain gauge rain gauge rain gauge rain gauge rain gauge
- 60. Isohyetal method
- 70. consistency of rainfall data (double mass curve method) It is used to test the consistency of rainfall record at any raingauge stations. P’ = (tan’/tan) x P Where, P – observed rainfall at station X in the same year tan’ – slope of the adjusted mass curve tan - slope of the unadjusted mass curve P’ – adjusted rainfall of station X in any year
- 71. Assignment problem Refer Jaya Ramy Reddy Text book Page No. : 138
- 74. Moving Average Curve Used to identify the long term trend or patterns in the rainfall