1. GOVERNMENT ENGINEERING COLLEGE, VALSAD
SUBJECT :- HYDROLOGY & WATER RESOURCES ENGINEERING ( )
TOPIC :- MODULE 1 (INTRODUCTION)
GROUP NO :- 3
SUBMITTED TO :- PROF. KULDEEP PATEL

2. Name of group members No. Name Enrolment No. 1 Patel Nimesh R. 2
Patel Shubham R. 3
Patel Tejas R. 4
Patel Yash V.

3. INTRODUCTION:- Introduction Hydrologic cycle
Processes of Hydrologic cycle
World’s Water Resources
India’s Water Resources
Water Balance
Precipitation
Variability of precipitation
Measurement of Rainfall
Methods of calculating average rainfall over an area

4. INTRODUCTION:- Design of Rain gauge Network
Intensity of rainfall, Mean Annual Rainfall
Estimating missing rainfall data
Presentation of Rainfall data
Analysis of Rainfall data
Evaporation
Measurement of Evaporation
Transpiration
Evapotranspiration
Infiltration

5. Introduction:-
Hydrology is the science which deals with the occurance, circulation and distribution of water upon, over and beneath the earth surface.
It deals with the transportation, precipitation, evaporation, transpiration, and infiltration.

6. In a general sense, hydrology is very broad subject of an interdisciplinary nature drawing support from allied sciences such as
Metrology
Geology
Statistics
Physics
Chemistry
Fluid mechanics, etc.

7. Engineering hydrology
Scientific hydrology
Engineering hydrology
A study which is concerned with academic aspects
A study concerned with engineering applications
It deals with
Study of process in hydrological cycle
Study of problems such as floods, droughts, strategies to combat them

8. Application of Hydrology
The maximum probable flood that may occur at given site and its frequency.
The water yield from basin-its occurance, quantity and frequency, etc.
Ground water development.
The maximum intensity of storm and its frequency.
Various methods of flood forecasting and flood control.

9. Selection of suitable site for a dam, reservoir and hydroelectric power generation.
The capacity of storage structures such as reservoirs.
The interaction of flood wave and hydraulic structures like levees, reservoirs, barrages and bridges.

10. Hydrological Cycle:-
The hydrological cycle is a descriptive term applied to the circulation of water from the oceans to the atmosphere, to the ground and back to the oceans again.
Thus, hydrological cycle is the earth’s water circulation system.

12. Process of Hydrological Cycle:-
The hydrological cycle consist of the following process:-
Evaporation and Transpiration
Precipitation
Runoff

17. Evaporation and Transpiration
Due to heat of sun the water from the surface of ocean, rivers, lakes and from the moist ground surface evaporates.
The vapour are carried over the land by air in the form of clouds.
This process is called evaporation.

18. Transpiration is the process of water being lost from the leaves of the plants from their pores.
Evaporation (E)= surface evaporation
+ water surface evaporation
+ rivers, ponds surface evaporation
+ ocean surface evaporation
+ transpiration
+ atmospheric evaporation

19. Precipitation (P) Liquid precipitation Precipitation
Precipitation may be defined as the fall of moisture from the atmosphere to the earth’s surface in any form.
Precipitation
Liquid precipitation
Frozen precipitation
rainfall
Snow
Hail
Sleet
Freezing rain

20. Runoff (R)
Runoff is that part of precipitation that is not evaporated.
There are three types of runoff.
Surface runoff
Sub-surface runoff or interflow
Ground water flow or base flow.

21. Surface runoff
A large portion of the precipitation, left after infiltration , flows over the ground into the streams and rivers, which ultimately discharge the water to the sea, known as surface runoff.

22. SUB-SURFACE RUNOFF OR INTERFLOW
A Portion of the precipitation infiltrates in to soil runs as sub surface runoff and reaches the streams and rivers. This water is known as Sub Surface run off or Interflow.

23. GROUND WATER FLOW OR BASE FLOW

25. World’s water Resources

26. Per capita availability and utilization of water around various countries of the world:
World’s total land area =1,45,000 B.m³
World’s total annual precipitation that falls on total land
area =1,09,000 B.m³
Average annual precipitation depth =0.752 m
Total land evaporation = 62,000 B.m³
Average annual runoff = 47,000 B.m³
Average depth of runoff = m

27. Per Capita average annual Flow(m3)
Country
Per Capita average annual Flow(m3)
Canada
1,00,00
Egypt
1,000
India
1,700
USSR
19,500
USA
9,900
China
2,400
World
7,200

28. Water balances Catchment area:
The area of draining in to a stream or a water course at a given location is known as catchment area.
It is also called drainage area or drainage basin.
In USA, it is known as watershed.

29. Water budget equation:
The hydrologic equation is simply the statement of the law of conservation of matter and is given by
I = O + ΔS ……………….( 1)
where, I = inflow
O = outflow
ΔS = change in storage, in given
time interval.

30. The expression for the water budget of a catchment for a time interval Δt is written as,
P – R – G – E – T = ΔS ….…..(2)
Where, P = precipitation
R = surface runoff
G = net ground water flow out of catchment
E = evaporation
T = transpiration
ΔS = change in storage

31. Precipitation
Precipitation may be define as the fall of moisture from the atmosphere to the earth’s surface
The water which comes back to the surface of earth in its various forms like rain, hail, snow, sleet, etc. is known as precipitation.

32. Frozen precipitation Precipitation i.e. Snow Hail Sleet Freezing rain
Liquid precipitation
i.e. Rainfall

33. For precipitation to form, it therefore necessary to have the following favorable conditions in the environment:
The atmosphere must have moisture
There must be sufficient nucleii present to aid condensation over them.
Weather condition must be favourable to condensation to water vapour.

34. Forms of precipitation
Rain
Snow
Hail
Drizzle
Glaze
Sleet
Rime
dew
Forms of precipitation

35. Types of pricipitation
Precipitation is often classified according to factors responsible for lifting.
Broadly speaking, there are four types of precipitation.
Cyclonic precipitation
Convective precipitation
Orographic precipitation
Precipitation due to turbulent ascent

36. 1. Cyclonic precipitation
Cyclonic precipitation is caused by the lifting of an air mass due to the pressure difference.
If low pressure occurs in an area, air will flow horizontally from the surrounding area, causing the air in the low pressure area to lift.
The cyclonic pressure may be divide into
(a) Frontal precipitation
(b) Non-frontal precipitation

37. FRONTAL PRECIPITATION :-
when two air masses due to contrasting temperatures and densities clash with each other , condensation and precipitation occur at the surface of contact. This surface of contact is called ‘ frontal ’ or ‘frontal surface’ and the precipitation is called frontal precipitation.
Different types of front is,
Cold front
Warm front
Stationary front

38. Non-frontal precipitation:-
In case of non- frontal precipitation, the moist warm air mass is stationary and the moving cold air mass meets it. Thus, due to lightness of the warm air mass there is passive ascent of warm air over cold air owing to the active under cutting. When the lifted warm air cools down at higher altitude precipitation occurs.

39. 2. Convective precipitation
Convective precipitation is caused by natural rising of warmer lighter air in colder, denser surroundings.
Generally, this kind of precipitation occurs in tropics, where on a hot day, the ground surface gets heated unequally, causing the warmer air to lift up as the colder air comes to take place.

41. 3. Orographic precipitation
Orographic precipitation is caused by moist air masse, which strike some natural topographic barriers like mountains, rise up causing condensation and precipitation.
The greatest amount of precipitation falls on the windward side, and the leeward side often has very little precipitation.

43. 4. Precipitation due to turbulent ascent:
Air mass is forced to rise up due to greater friction of earth surface after its travel over ocean.
The air mass rises up because of increased turbulence and friction, when it ultimately condenses and precipitation occurs.

44. Artificial rainfall (cloud seeding):
Sometimes the process of evaporation is smoothly carried and the air has sufficient amount of moisture, but it does not reach the point of saturation because there is a deficiency of hygroscopic nuclei, which are necessary to form the raindrops.

45. So artificial hydroscopic nuclei are provided in following forms:
Dry ice (solid CO2)
Silver dioxide
Frozon carbon dioxide
Sodium chloride etc.
The process of artificial simulation of precipitation by adding certain chemicals to cloud in atmosphere is known as cloud seeding.

46. Variablity of precipitation
The distribution of precipitation is not uniform in a particular region.
The precipitation regime for any region depends upon the following factors:
Location of region in the general circulation pattern.
The latitude.
Distance from moisture source
Orography of a region

47. Location of the region in the general circulation pattern:
The thermal circulation originates from the sun as a source of origin.
About 40% of radiant energy of sun is reflected back from upper surface of clouds.
The earth absorbs the remaining 60% with small losses.
This in turn increases the the heat of the surface.

48. Measurement of Rainfall
The knowledge of amount of rainfall, intensity of rainfall and the distribution of rainfall is extremely useful for the irrigation engineering.
Rainfall at a place can be measured by a rain gauge, usually in cm.

49. The following are the main types of rain gauges used for measurement of rainfall.
Non recording type
Symon’s rain gauge
IMD
Recording type
Weighing bucket type
Tipping bucket type
Float type rain gauge

50. Symon’s rain gauge: The symon’s rain gauge consist of
It can measure up to 12.5 cm of rainfall.
Metal case internal dia.
127 mm
Base dia.
210 mm
Metal casing size
600*600*600 mm
Funnel with circular rim
Height of metal casing
305 mm above G.L.
Receiving bottle
75 to 100 mm dia.

51. The following points should be kept in mind while selecting the site for a rain-gauge station:
The rain gauge should be an open place
The distance between the rain gauge and the nearest object should be at least twice the height of the object.
The rain gauge should be at least 30m away from the near by obstruction.
The rain gauge should never be situated on the side or top of a hill.

53. I.M.D. standard rain gauge:
The symon’s rain gauge was used by Indian Metrology Department upto 1969 when the IMD standard rain gauge was adopted.
The IMD consist collector which surface area is either 100 cm² or 200 cm² .
The collector is fitted over the base which is fixed to a concrete masonry.

54. IMD standard rain gauge

55. Weighing bucket type rain gauge:
This is self recording type or automatic type rain gauge.
In weighing bucket type rain gauge, the rain water is collected by a receiver bucket.
The rainfall record produced by this gauge is in the form of a mass curve of rainfall.
The mass curve gives the intensity of rainfall.

57. Tipping bucket type rain gauge:
The tipping bucket type rain gauge consist of two small bucket placed below the funnel fitted in a 30 cm diameter receiver.
The buckets are so designed that when 0.25 mm of rainfall collects in one bucket, it tips and empties its water into the measuring tube below it.

59. Float type rain gauge:
The working of float type rain gauge is similar to the weighing bucket type rain gauge.
A funnel receives the rain water which is collected in rectangular, float chamber.
A float is provided at the bottom of the float chamber.

60. Float type or syphon type rain gauge

61. Methods of calculating average rain fall over an area:
The rain fall is recorded by a rain gauge represent the rain fall at that station.
In many hydrological studies, the average depth of rainfall over a specified area due to a storm is required.

62. Number of rain gauge station is required
The number of rain gauge stations required in particular climate area depends upon the size of the catchment as given in table.
Area of catchment sq. km
Number of rain gauge station is required
0 to 80 1
80 to 160 2
160 to 320 3
320 to 560 4
560 to 800 5
800 to 1200 6

63. The average rainfall over an area can be computed by the following methods:
Arithmetic average method
Thiessen polygon method
Isohyetal method

64. Arithmetic average method:
In this method the average depth of rain fall over an area is obtained by dividing the sum of depths of rainfall recorded at the gauge stations located in the area by the number of stations.

65. Thus, if P1, P2, P3, …… Pn are the depths of rain fall recorded at various rain gauge stations.
n = number of rain gauge stations

66. Thiessen polygon method:
This method is better then the arithmetic mean method which gives equal weightage of to all the stations.

67. Procedure:
Join the adjacent rain gauge stations A, B, C, D etc. by straight lines, forming triangles.
Construct the perpendicular bisectors of each of these sides of triangles.
A thiessen network is thus created.

68. Let P1, P2, P3, ……Pn are the details of rainfall
A1, A2, A3, ……An area represented by various rain gauge stations.

69. Isohyetal method: Isohyetal are the contours of equal rainfall.
An isohyetal map showing contours of equal rainfall represent a more accurate picture of the rainfall distribution over the basin.

71. Estimating missing rainfall data:-
The prediction of the missing data can be made with the help of available data of nearby measuring stations, using the following methods :
Arithmetic mean method
Normal ratio method
Inverse distance method
station-year method.

72. Arithmetic mean method

73. Inverse distance method
In this method a set of rectangular co- ordinates axes are passed through the missing station so that its co – ordinates are (0,0). The co-ordinates (x,y) of each index surrounding the missing station are found.

74. STATION YEAR METHOD
In this method , the records of two or more rain gauge stations record are independent and areas of stations are climatologically the same. The missing record at a certain station in a particular year may be found out by the ratio of the average or by graphical comparison. o

75. Evaporation :
Due to heat of sun the water from the surface of ocean, rivers, lakes, and from the moist ground surfaces evaporates.
The vapour are carried over the land by air in the forms of clouds.
This process is called evaporation.

76. U.S. weather bureau class a pan
This is perhaps the most commonly used evaporation pan. The pan consists of a shallow vessel 1.2 m dia. And 25 cm deep the pan is made of unpainted galvanized iron sheet. Where there is corrosion problem, it is made of Monel sheet.
Evaporation is computed as the difference between observed water levels on two consecutive days. Pan coefficient is about 0.6 to 0.8 , generally taken as 0.7 .

78. COLORADO SUNKEN PAN
It is 90 cm square with a depth ranging from 30 to 90 cm and buried in the ground within about 10 cm of the top. the water should be within 2.5 cm of ground level.
Pan coefficient is 0.75 to 0.86 generally taken as

79. U.S. GEOLOGICAL SURVEY FLOATING PAN
This is 90 cm square in plan and 45 cm deep pan by drum floats in the center of a raft 14’ *16’ .
The pan coefficient is generally taken as
U.S. GEOLOGICAL SURVEY FLOATING PAN

80. TRANSPIRATION

81. FACTORS AFFECTING TRANSPIRATION
All the factors that affect the evaporation from the free water surface also affect transpiration, that is follows:
temperature of air
wind velocity
atmosphere pressure
humidity
solar radiation
soil moisture
physiologic factors

82. Dalton’s law of evaporation:
According to Dalton’s law “ The rate of evaporation depends upon the difference between the saturation vapour pressure and the vapour pressure in the air above.”
where E = evaporation loss (mm/day)
C = coefficient

83. Factors Affecting Evaporation :
Temperature of air
Wind velocity
Atmospheric pressure
Area of water surface
Depth of water body
Humidity
Impurities in water
Nature of evaporating surface

84. Measurement of evaporation :
The rate of evaporation from large water surfaces can be determined by following methods :
1. Pan Measurement method
2. Using Empirical formula
3. Water budget method
4. Energy budget method

85. Pan measurement method :
The most reliable method for the estimating of evaporation from large water bodies is that by measurements from evaporation pans.
Different shapes of pans have been designed by different designers, and different values of pan coefficient have been suggested.

86. The more important of these pans are described below.
U.S. Weather Bureau class A pan
Colorado sunken pan
U.S. Geological Survey Floating pan
I.S. Standard pan

87. Using Empirical formula
Evaporation from lakes and reservoirs is usually estimated by empirical methods based on metrological data.
There are a number of empirical formulae available in the literature.
Most of these equations are based on Dalton’s law of evaporation.

88. 1. mayer formula It states that Where, E = evaporation (mm/day)
es = saturation vapour pressure
ea = actual vapour pressure
V9 = mean wind velocity at 9 m
above G.L.
km = coefficient

89. 2. Rohwer’s Formula :
It states that

90. Lake Hefner formula :
It states that

91. WATER BUDGET METHOD

92. Evapotranspiration :
Evapotranspiration is the sum of the water lost to the atmosphere by the plants through transpiration, and the water evaporated from the soil or water body surrounding the plant.
Evapotranspiration = Evaporation +Transpiration

93. If sufficient moisture is always available to completely meet the needs of the plants, the resulting evapotranspiration is called Potential evapotranspiration (PET).
The real evapotranspiration occuring in a specific situation is called Actual evapotranspiration.

94. Factors affecting evapotranspiration
Metrological factors
Density of vegetation
Soil moisture
Stage of plant growth
Adjoining joint
Surface of leaves

95. Measurement of evapotranspiration (consumptive use) :
Measurement of consumptive use of water
direct measurement method
Use of empirical formula
Tank and lysimeter method
Field experimental plots
Inflow and out flow studies
Penman method
Jensen-Haise method
Hargreaves method
Blaney-criddle method

96. Penman’s method :
For shorter periods, it is necessary to use calculation methods to estimate evapotranspiration.
This can done by penmen’s method. The penman’s equation is a equation is a combination of energy balance and wind transfer approach, which reads:

97. Where,
PET = daily potential evapotranspiration
A = slope of the saturation pressure versus temperature curve at mean air temperature
Hn = net incoming solar radiation (mm/day)
Ea = Parameter including wind velocity and
saturation deficit.
= Psychometric constant

99. Infiltration :
Infiltration may be defined as the downward movement of water from soil surface, into the soil mass through the pores of the soil.
The process of downward movement of water into soil, once water enters into the soil, is known as percolation.

100. The maximum rate at which a soil in any given condition is capable of absorbing water is called its infiltration capacity.
The infiltration rate at any instant is the rate at which water actually enters the soil during a storm and is equal to the infiltration capacity or rainfall rate, whichever is less.

101. Factors affecting infiltration:
Thickness of saturated layer
Permeability characteristics of soil formation
Soil moisture
Temperature
Intensity and duration of rainfall
Vegetation cover

102. Compaction due to men and animals Washing of fines Quality of water
Human activities
Quality of water
Size and characteristics
Pressure of ground water table

103. Horton’s equation :
The maximum rate at which the soil in any given condition is capable of absorbing water is called its infiltration capacity.
Infiltration often begins at a high rate (20 to 25 cm/hr) and decreases to a fairly steady state rate as the rain continues, called ultimate fp.

107. Green – Ampt method :

113. Thank you