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Hydrology is the science of water on Earth. It studies the occurrence, circulation, and distribution of water, including precipitation, evaporation, soil moisture, groundwater, runoff, and flooding. There are two main types - scientific hydrology which studies physical processes, and engineering hydrology which applies scientific principles to water resources. The hydrologic cycle describes the continuous movement of water on, above, and below the surface of the Earth, including storage and transport through different physical states driven by energy from the sun.
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- 2. • Hydrology means the science of water. • It is the science that deals with the occurrence, circulation and distribution of water of the Earth & Earth`s atmosphere. • This is classified into:- A. Scientific hydrology. B. Engineering applied hydrology. Hydrology introduction HYDRO LOGOS = HYDROLOGY WATER SCIENCE baseerat
- 3. Hydrologic cycleHydrologic cycle – Cycling of water in and out of atmosphere and between all the earth’s components. – All of the water on our planet is recycled and a given molecule of water is used over and over throughout time. – The various aspects of water related to the earth can be explained in terms of a cycle known as HYDROLOGIC CYCLEHYDROLOGIC CYCLE baseera
- 4. Hydrologic cycleHydrologic cycle HORTON`S REPRESENTATION OF THE HYDROLOGICAL CYCLE
- 5. TRANSPORATION • PRECIPITATION. • EVAPORATION. • TRANSPIRATION. • INFILTRATION. • RUN OFF. STORAGE • STORAGE ON THE LAND SURFACE. • SOIL MOISTURE STORAGE. • GROUND WATER STORAGE. COMPONENTS HYDROLOGIC CYCLECOMPONENTS HYDROLOGIC CYCLE
- 7. CATCHMENT AREACATCHMENT AREA The area of land draining in to a stream or a water course at a givenThe area of land draining in to a stream or a water course at a given location is called catchment area / drainage area / drainage basin /location is called catchment area / drainage area / drainage basin / watershed.watershed. A catchment area is separated from its neighboring areas by a ridgeA catchment area is separated from its neighboring areas by a ridge called divide / watershedcalled divide / watershed
- 8. Watershed and watershed divide Watershed/ catchment Watershed/ catchment Watershed/ catchment Watershed divide
- 9. Water Budget EquationWater Budget Equation ??
- 10. WATER BUDGET EQUATION • The equation is applied in the form of water-balanceThe equation is applied in the form of water-balance equation to a geographical region, in order to establishequation to a geographical region, in order to establish the basic hydrologic characteristics of the region.the basic hydrologic characteristics of the region. For a given catchment, in an interval of timeFor a given catchment, in an interval of time ∆t, the∆t, the continuity equation for water in its various phases cancontinuity equation for water in its various phases can be given as:be given as: Mass inflow – Mass outflow = change in mass storageMass inflow – Mass outflow = change in mass storage • VVii - Inflow volume in to the catchment,- Inflow volume in to the catchment, • VVoo - Outflow volume from the catchment and- Outflow volume from the catchment and • ∆∆S - change in the water volumeS - change in the water volume (in soil or bedrock)(in soil or bedrock)
- 11. WATER BUDGET OF A CATCHMENT FOR A TIME INTERVAL ∆t∆t is written as P-R-G-E-TP-R-G-E-T= ∆S∆S P=PRECIPITATION G=NET GROUND WATER FLOW R=SURFACE RUN OFF E=EVAPORATION T=TRANSPIRATION THE STORAGE S CONSISTS OF THREE COMPONENTS AS S=Ss+Ssm+Sg Ss=Surface water storage Sg=water stored as ground water Ssm=water in storage as soil moisture RAINFALL-RUNOFF RELATIONSHIP R=P-L L=LOSSES
- 14. precipitation
- 15. definition All types of moisture reaching the surface of earth from atmosphere. Precipitation is the basic input to the hydrology.
- 16. What are the forms of ?What are the forms of ?
- 17. PRECIPITATION PROCESSPRECIPITATION PROCESS EVAPOURATION SETTLEMENT ON NUCLEII PASSING THROUGH ATMOSHPHERE CONDENSE WATER DROPLET PRECIPITATION
- 18. What are the forms ofWhat are the forms of precipitation?precipitation? • RAIN • SNOW • HAIL • FOG • DEW • MIST • GLAZE • SLEET basi
- 19. Forms of PrecipitationForms of Precipitation RainRain - liquid deposits falling from the atmosphere- liquid deposits falling from the atmosphere to the surfaceto the surface - with a diameter > 0.5 mm- with a diameter > 0.5 mm - < 0.5 mm: drizzle- < 0.5 mm: drizzle - max. size: about 5 - 7 mm- max. size: about 5 - 7 mm (too large to remain suspended)(too large to remain suspended) basi
- 20. Snow • Snow is the second most common precipitation in the North East. • Snow forms when water vapor turns directly into ice without ever passing through a liquid state. This happens as water condenses around an ice crystal.
- 21. Hail Hail is created when moisture and wind are together. Shapes of hail particles 1.Spherical 2.Conical 3.Irregular Diameter range 5 to 125 mm Specific gravity = 0.8 Average density (specific gravity) = 0.1
- 22. Fog • There are four main types of fog, • radiation fog • advection fog • upslope fog • evaporation fog There is really no different between fog and the clouds that are high in the sky. In simple terms fog is; a cloud that has formed near the surface of the Earth.
- 23. Dew • The small drops of water which can be found on cool surfaces like grass in the morning. • This is the result of atmospheric vapor condensing on the surface in the colder night air. • Dew Point is the temperature in which condensation starts to take place or when dew is created.
- 24. Mist / Drizzle Mist is a bunch of small droplets of water which are in the air. This occurs with cold air when it is above a warm surface, for example water. Fog and mist are very similar, the only difference is their visibility. If you cannot see 1 kilometer or less you know you're dealing with fog. You can see visuals through mist and it is more haze looking than a thicker substance. Diameter range between 0.1 and 0.5 mm/hr
- 25. Glaze • Glaze is the ice coating, generally clear and smooth, formed on exposed surfaces by the freezing of super cooled water deposited by rain or drizzle. Specific gravity may be as high as 0.8-0.9
- 26. Sleet Sleet consists of transparent, globular, solid grains of ice formed by the freezing of raindrops or freezing of largely melted ice crystals falling through a layer of sub freezing air near the earth’s surface.
- 27. TYPES OF PRECIPITATION • ACCORDING TO THE FACTOR`S RESPONSIBLE FOR LIFTING &SUBSEQUENT COOLING .BROADLY THERE ARE THREE TYPES OF PRECIPITATION. CYCLONIC PRECIPITATION CONVENTION PRECIPITATION OROGRAPHIC PRECIPITATION
- 28. FRONT PRECIPITATION • A front is the Interface between two distinct air masses. • The lifted air mass cools, converts into clouds & subsequently precipitates. • Front precipitation exists in following types a)Cold front . b)Warm front . c)Stationary front .
- 29. CYCLONIC PRECIPITATION • A cyclone is a large low-pressure region with circular wind motion. • Two types of cyclones are recognised A.Tropical cyclones . B.Extra tropical cyclones.
- 30. Tropical cyclones& Extra tropical cyclones • Tropical cyclone, also called Typhoon or Hurricane in USA and CYCLONE In INDIA • Drawing energy from the sea surface and maintaining its strength as long as it remains over warm water, a tropical cyclone generates winds that exceed 119 km (74 miles) per hour. In extreme cases winds may exceed 240 km (150 miles) per hour, and gusts may surpass 320 km (200 miles) per hour.
- 31. CONVECNTIVE PRECIPITATION • Convective precipitation is generally more intense, and of shorter duration, than strati form precipitation. • In this type precipitation, a packet of air which is warmer than the surrounding air due to localised heating rises because of its lesser density air from the cooler surroundings flows to take up its place, thus setting up a convention cell. • The warm air continues to rise and hence undergoes cooling resulting in precipitation.
- 32. OROGRAPHIC PRECIPITATION • Orographic precipitation, rain , snow, or other precipitation produced when moist air is lifted as it moves over a mountain range. As the air rises and cools, orographic clouds form and serve as the source of the precipitation, most of which falls upwind of the mountain ridge. Some also falls a short distance downwind of the ridge and is sometimes called spill over. On the lee side of the mountain range, rainfall is usually low, and the area is said to be in a rain shadow. • Very heavy precipitation typically occurs upwind of a prominent mountain range that is oriented across a prevailing wind from a warm ocean
- 33. MEASUREMENT OF RAIN FALL • Rainfall is expressed in terms of the depth to which rainwater would stand on an area, if all the rain were collected on it. • The instrument used to collect and measure the precipitation is called rain gauge.
- 34. TWO TYPES OF GAUGE`S • SymonS'S gauge . • SyPHon gauge .
- 35. SymonS'S gauge . • METALLIC CYLINDER IS USED FOR SNOW FALL • IMD HAS CHANGED OVER THE USE OF FIBER GLASS REINFORCED GAUGE, WHICH COMES IN DIFFERENT SIZES LIKE 100CM,4200CM CACH AREA AS IN I(IS5225-1969) • THE RAINFALL IS MEASURED EVERDAY AT 8.30AM (IST) &IS RECORDED AS THE RAINFALL OF THAT DAY.
- 36. SyPHon gauge . • The rainfall collected in the funnel shaped collector is led into a float chamber, causing the float to rise. • As the float rises, a pen attached to the float through a lever system records the rainfall on a rotating drum driven by a clockwork mechanism. • A syphon arrangement empties the float chamber when the float has reached a present maximum level.
- 37. SymonS'S gauge vS SyPHon gauge SYMON`s GaugeSYMON`s Gauge • Necessity of an attendant arise. • Non recording gauge gives only total rainfall. • It is not economical. • It will contain dust particles. SYPHON GaugeSYPHON Gauge • Necessity of an attendant does not arise. • Intensity of rainfall at anytime as well as total rainfall is obtained. • Only initial cost is more. • Doesn’t not contain any particles.
- 39. Selection of rain gauge station ?Selection of rain gauge station ? • 1. The spot at which rain-gauge is to be installed should be truly representative of the area, of which it is supposed to give depth of rainfall. • 2. The gauge should be erected on level ground, not upon a slope or a terrace and never on a wall or a roof. • 3. All other conditions satisfied, a position sheltered from the wind is preferable to an exposed one. In mountains and near sea coasts it is very essential to ensure that the gauge is not un-dully exposed to the swept of wind. • 4. The gauge should be properly secured by a barbed wire fencing and locking arrangement.
- 40. 40 Adequacy of Rain gauge Stations where N = optimal number of stations, ε = allowable degree of error in the estimate of the mean rainfall and Cv = coefficient of variation of the rainfall values at the existing m stations (in per cent) 2 C N = v ε
- 41. Adequacy of Rain gauge Stations P CV = 100σ m−1 2 m −1 (P − P) m ∑ i m−1σ = 1 = standard deviation Pi = precipitation magnitude in the ith station m m P = ∑Pi = meanprecipitation1 1 σ = standard deviation.
- 42. m CvEex = Eex=Expected error (%) is the estimation of the mean P
- 43. EXAMPLE A catchment has six rain gauge stations. In a year, the annual rainfall recorded by the gauges are as follows:- Station A B C D E Rainfall (cm) 82.6 102.9 180.3 98.8 136.7 For a 10% error in the estimation of the mean rainfall, calculate the optimum number of stations in the catchment Solution:- from first data m = 6 P = 118.6 σ m−1 = 35.04 ε = 10 10 118.6 2 Cv = 8.7, say9 29.54 N = = 100*35.04 = 29.54
- 44. Methods of computing average rainfall Apoint sampling of the area distribution of a storm However hydrological analysis requires a knowledge of the rainfall over an area such as over a catchment or over watershed. s indicated earlier,raingauge readings are the The methods used to calculated are as follows a)Arithmetical mean method b)Thiessen –polygon method c)Isohyetal method
- 45. 34 MEAN PRECIPITATION OVER AN AREA 1. Arithmetical—Mean Method ∑= = ++++ = N I i ni P N N PPPP P 1 21 1 ......
- 46. 35 MEAN PRECIPITATION OVER AN AREA 2. Thiessen-Mean Method )....( ... 621 662211 AAA APAPAP P +++ +++ = A A P A AP P i M i i M i ii ∑ ∑ = = == 1 1
- 47. 36 MEAN PRECIPITATION OVER AN AREA 3. Isohyetal Method A PP a PP a PP a P nn n + ++ + + + = − − 2 ..... 22 1 1 32 2 21 1
- 48. Example 2
- 51. Rain gauge network • Rainfall data is the most important and fundamental data required for all hydrological investigations. • Catch area of a raingauge is very small compared to the aerial extent of a storm. Hence to get a representative picture of a storm over the entire drainage basin, the number of raingauges should be as large as possible (drainage area/raingauge should be small). • The raingauge network should consist of adequate number of raingauges evenly distributed all over the drainage basin. • However the number of raingauges is many a time restricted by economic considerations as well as topography, accessibility etc. • Desired density would also depend on the purpose.
- 52. WMO recommendations on rain gauge density •Flat regions of temperate, Mediterranean and tropical zones •Ideal – 1 station for 600-900 sq.km. •Acceptable – 1 station for 900-3000 sq.km. •Mountainous regions of temperate, Mediterranean and tropical zones •Ideal – 1 station for 100-250 sq.km. •Acceptable – 1 station for 250-1000 sq.km. •Arid and polar zones •Ideal – 1 station for 1500-10000 sq.km. Depending on the feasibility. •10% of rain gauge stations should be equipped with self recording rain gauges BIS recommendations on rain gauge density •In plains – 1 station for every 520sq.km. •In regions with average elevation 1000m – 1 station per 260-390 sq.km. •In hilly areas with heavy rainfall – 1 station for every 130 sq.km.
- 53. 30 Ni = Normal Precipitation in i station. Estimation of Missing Data If the normal precipitations vary considerably (>10%) +++= Nm Pm N P N P M N P x x ...... 2 2 1 1 ANALYSIS OF PRECIPITATION DATA
- 54. PREPARATION OF DATA Estimation of missing data procedure 1.Statement is missing data estimation 2.Procedure +++= Nm Pm N P N P M N P x x ...... 2 2 1 1 Px=1/m (P1+P2+…………Pm
- 55. Example
- 57. 32 PREPARATION OF DATA Test for Consistency of Record – use : DMC Accumulated Annual Rainfall of 10 stations Mean ΣP in units of l03 cm Accumulated ΣPinunitsofl0 a c xcx M M PP =
- 58. 33 PRESENTATION OF RAINFALL DATA Hyetograph
- 59. EVAPORATION
- 60. Definition:- Theoretically, • “Evaporation is the process in which a liquid changes to the gaseous state at the free surface ,below the boiling point through the transfer of heat energy .” • Thus, no boiling occurs and the rate of vaporization depends on the diffusion of vapor through the boundary layers above the liquid. 60
- 62. Factors affecting the Evaporation • There are SIX factors to affect evaporation.There are SIX factors to affect evaporation. 1.1. TemperatureTemperature 2.2. SATURATIONSATURATION 3.3. WIND VELOCITYWIND VELOCITY 4.4. QUALITY OF WATERQUALITY OF WATER 5.5. ATMOSPHERE PRESSUREATMOSPHERE PRESSURE 6.6. SIZE IF WATER BODYSIZE IF WATER BODY
- 63. Temperature: The rate of evaporation is directly proportional to the temperature. SATURATION VAOUR PRESSURESATURATION VAOUR PRESSURE:-:-The rate of the evaporation is directlyThe rate of the evaporation is directly proportional to the difference between saturation vapor pressure at theproportional to the difference between saturation vapor pressure at the water temperature and the actual vapor pressure in the air .water temperature and the actual vapor pressure in the air . WIND VELOCITY:-Wind velocity enhances evaporation rate as theWIND VELOCITY:-Wind velocity enhances evaporation rate as the vapor particles are driven out of place creating more space forvapor particles are driven out of place creating more space for further evaporation.further evaporation. ATMOSPHERE PRESSUREATMOSPHERE PRESSURE:-With other factors remaining constant, the decrease in pressure (at higher altitude) increase the rate of evaporation.
- 64. QUALITY OF WATERQUALITY OF WATER:-The rate of evaporation depends on the specific gravity of the water . That means the presence soluble salts reduce the evapouration rate as compared units with fresh/pure water. SIZE IF WATER BODY:-Deep water bodies (depth>3.0m)storeSIZE IF WATER BODY:-Deep water bodies (depth>3.0m)store more heat energy than shallow once .more heat energy than shallow once .
- 65. Types of Evaporimeters • Class A evaporation pan ✔ • ISI STANDARD PAN ✔ • Colorado Sunken pan
- 66. • Class A evaporation pan • In the United States, the National Weather Service has standardized its measurements on the Class A evaporation pan, a cylinder with a diameter of 47.5 in (120.7 cm) that has a depth of 10 in (25 cm). The pan rests on a carefully levelled, wooden base and is often enclosed by a chain link fence to prevent animals drinking from it. Evaporation is measured daily as the depth of water (in inches) evaporates from the pan. The measurement day begins with the pan filled to exactly two inches (5 cm) from the pan top. At the end of 24 hours, the amount of water to refill the pan to exactly two inches from its top is measured. • The Class A Evaporation Pan is of limited use on days with rainfall events of >30mm (203mm rain gauge) unless it is emptied more than once per 24hours. Analysis of the daily rainfall and evaporation readings in areas with regular heavy rainfall events shows that almost without fail, on days with rainfall in excess of 30mm (203mm Rain Gauge) the daily evaporation is spuriously higher than other days in the same month where conditions more receptive to evaporation prevailed. • The most common and obvious error is in daily rainfall events of >55mm (203mm rain gauge) where the Class A Evaporation pan will likely overflow.
- 68. ISI STANDARD PAN • This evaporation pan should confirm to IS 5973:1976 and is also called Class A pan. It consists of a circular copper vessel of 1220 mm effective diameter, 255 mm effective depth and a wall thickness of 0.9 mm. A thermometer is assembled to record the variation in temperature. A wire mesh cover with hexagonal openings is provided at the top to prevent entry of foreign matter. A fixed gauge housed in a stilling well as shown in figure • is provided. During evaporation measurement a constant water level is maintained at the top level of fixed gauge. For this purpose water has to be added or removed periodically. • The water level measurements are done using micrometre hook gauge. The entire assembly is mounted on a level wooden platform.
- 70. Colorado Sunken pan •The Colorado Sunken pan • is square, 1 m (3 ft) on a side and 0.5 m (18 in.) deep and made of unpainted galvanized iron. As the name suggests, it is buried in the ground to within about 5 cm (2 in.) of its rim. Evaporation from a Sunken Colorado Pan can be compared with a Class A pan using conversion constants. The pan coefficient, on an annual basis, is about 0.8.
- 71. ESTIMATION USING EMPIRICALESTIMATION USING EMPIRICAL METHODSMETHODS Meyer’s Formula (1915) •EL = KM (ew – ea) (1 + u9/16) •In which, u9 = monthly mean wind velocity in km/h at bout 9 m above ground and •KM = coefficient accounting for various other factors with a value of 0.36 for large deep and 0.50 for small shallow waters.
- 72. • Example :- A reservoir with a surface area of 250hectares had the following average values of parameters during a week : water temperature = 20o C, relative humidity = 40% wind velocity at 1.0 m above ground = 16km/h. Estimate the average daily evaporation from the lake and volume of water Evaporated from the lake during that one week. • Solution : ew = 17.54 mm of Hg • ea = 0.40 x 17.54 = 7.02 mm of Hg • u9 = wind velocity at a height of 9.0 m above ground • u1 = 16 km/h • u9 = ? • uh = C (h) 1/7 • uh = C (1) 1/7 = 16 km/h • u9/u1 = C ((9) 1/7) / C ((1) 1/7) • u9 = u1 (9) • 1/7 = 16 (9) 1/7 = 21.9 km/h • By Meyer’s formula E = 0.36 (17.54 – 7.02) (1 + 21.9/16) • = 8.97 mm/day Evaporated volume in 7 days • = 7 x 8.97/1000 x 250 x10000 • = 157,000 m3
- 73. Rohwer’s Formula (1931) • EL = 0.771(1.465 – 0.000732 Pa) (0.44 + 0.0733 uo) (ew – ea) • Pa = mean barometric reading in mm of mercury • Uo = mean wind velocity in km/h at ground level, which can be taken to be the velocity at 0.6 m height above ground. • The wind velocity can be assumed to follow the 1/7 power law Uh = C h 1/7 Where, • Uh = wind velocity at a height h above the ground and • C = constant. This equation can be used to determine the velocity at any desired level.
- 74. Methods of reduction of evaporation • The following methods are employed to reduce evaporation losses:- • Reduction of surface area:-Selection of wide spread reservoirs . • Mechanical corers :-Permanent /temporary roofs or floating roofs such as rafts, lights –weight floating body can be used particularly for small bodies . • Chemical films :-Apply this chemical film over the surface such as cetyl alcohol and stearyl alcohol. basi