Hydrology & Irrigation Engineering Formulas for Civil Engineering Exam | Engineering Hydrology - Civil Engineering (CE) PDF Download

 Page 1


 
 
 
  
 
MODULE – 1  
HYDROLOGY, PERCIPITATION 
1.1 INTRODUCTION: 
Hydrology is the science that treats the waters of the earth, their occurrence, circulation and distribution, 
their chemical and physical properties and their reaction with the environment, including the relation to 
living things. The domain of hydrology embraces the full life history of water on the earth.   
1.2 DEFINITIONS: 
1.2.1 Hydrology: Hydrology is defined as science dealing with the occurrence, circulation, distribution 
and properties of the waters of the earth and its atmosphere.  
(Or) 
Hydrology is defined as Hydro (Water) + Logus (Science).  
1.2.2 Hydrology is further divided into:  
1.2.2.1 Scientific Hydrology: deals with academic aspects.  
1.2.2.2 Engineering Hydrology: deals with engineering applications as estimation of water resources, 
study of precipitation, runoff, evaporation and transpiration, study of problems such as floods and 
droughts.  
1.2.2.3 Climatology: deals with the study of climate over given area within a specified period of time.  
1.2.2.4 Meteorology: is branch of science dealing with the atmospheric phenomena.  
1.3 IMPORTANCE OF HYDROLOGY: 
1.3.1 Structural and Hydraulic Design: 
? For any type of reservoir a spillway of sufficient capacity is most essential.  
? The capacity of the spillway, its height, downstream protection works etc. depend on the correct 
assessment of flood flow and routing. 
Note: Spillway means a channel that carries excess water over or around a dam or other obstruction.   
Page 2


 
 
 
  
 
MODULE – 1  
HYDROLOGY, PERCIPITATION 
1.1 INTRODUCTION: 
Hydrology is the science that treats the waters of the earth, their occurrence, circulation and distribution, 
their chemical and physical properties and their reaction with the environment, including the relation to 
living things. The domain of hydrology embraces the full life history of water on the earth.   
1.2 DEFINITIONS: 
1.2.1 Hydrology: Hydrology is defined as science dealing with the occurrence, circulation, distribution 
and properties of the waters of the earth and its atmosphere.  
(Or) 
Hydrology is defined as Hydro (Water) + Logus (Science).  
1.2.2 Hydrology is further divided into:  
1.2.2.1 Scientific Hydrology: deals with academic aspects.  
1.2.2.2 Engineering Hydrology: deals with engineering applications as estimation of water resources, 
study of precipitation, runoff, evaporation and transpiration, study of problems such as floods and 
droughts.  
1.2.2.3 Climatology: deals with the study of climate over given area within a specified period of time.  
1.2.2.4 Meteorology: is branch of science dealing with the atmospheric phenomena.  
1.3 IMPORTANCE OF HYDROLOGY: 
1.3.1 Structural and Hydraulic Design: 
? For any type of reservoir a spillway of sufficient capacity is most essential.  
? The capacity of the spillway, its height, downstream protection works etc. depend on the correct 
assessment of flood flow and routing. 
Note: Spillway means a channel that carries excess water over or around a dam or other obstruction.   
 
 
 
  
 
1.3.2 Municipal and Industrial Water Supply: 
? Due to constant increase in the urban and industrial water demands greater efforts are being made 
by hydrologists to meet the demands.  
1.3.3 Irrigation: 
? Irrigation demands are similar to municipal and industrial water supply but on a larger scale.  
? Hydrology plays an important role, to evaluate new projects in areas where the margin of safety is 
already low or to discover new source of water and its applications.  
1.3.4 Power: 
? Hydrological studies are most essential for the operation of an Hydel project. 
? For the storage plant, low seasonal flows rather than low daily flows are important and the 
reservoir draw down studies is must to determine the relative economics of various heights of the 
dam and power generating capacities.   
1.3.5 Flood Control: 
? Flood control project range from small improvements like channel straightening to large project 
involving huge budget.  
? Hence, for the large projects statistical and probabilistic flood frequency analysis are necessary.  
? These studies would yield fruitful results in proper flood controlling methods.  
1.3.6 Navigation: 
? When the stream is running through non – alluvial soils hydrological studies are relatively simple 
as the analysis involves hydraulic computation.  
? However streams carrying sediment pose much more complex problems.  
1.3.7 Erosion Control: 
? Proper hydrological investigations are necessary in the operation and maintenance of a reservoir 
increasing the life of the reservoir by reducing the silt entering it.    
1.3.8 Pollution Control: 
? With the increase in population, large scale industrialization, the streams and rivers are getting 
polluted and are posing more and more danger to the public health, water life etc.  
Page 3


 
 
 
  
 
MODULE – 1  
HYDROLOGY, PERCIPITATION 
1.1 INTRODUCTION: 
Hydrology is the science that treats the waters of the earth, their occurrence, circulation and distribution, 
their chemical and physical properties and their reaction with the environment, including the relation to 
living things. The domain of hydrology embraces the full life history of water on the earth.   
1.2 DEFINITIONS: 
1.2.1 Hydrology: Hydrology is defined as science dealing with the occurrence, circulation, distribution 
and properties of the waters of the earth and its atmosphere.  
(Or) 
Hydrology is defined as Hydro (Water) + Logus (Science).  
1.2.2 Hydrology is further divided into:  
1.2.2.1 Scientific Hydrology: deals with academic aspects.  
1.2.2.2 Engineering Hydrology: deals with engineering applications as estimation of water resources, 
study of precipitation, runoff, evaporation and transpiration, study of problems such as floods and 
droughts.  
1.2.2.3 Climatology: deals with the study of climate over given area within a specified period of time.  
1.2.2.4 Meteorology: is branch of science dealing with the atmospheric phenomena.  
1.3 IMPORTANCE OF HYDROLOGY: 
1.3.1 Structural and Hydraulic Design: 
? For any type of reservoir a spillway of sufficient capacity is most essential.  
? The capacity of the spillway, its height, downstream protection works etc. depend on the correct 
assessment of flood flow and routing. 
Note: Spillway means a channel that carries excess water over or around a dam or other obstruction.   
 
 
 
  
 
1.3.2 Municipal and Industrial Water Supply: 
? Due to constant increase in the urban and industrial water demands greater efforts are being made 
by hydrologists to meet the demands.  
1.3.3 Irrigation: 
? Irrigation demands are similar to municipal and industrial water supply but on a larger scale.  
? Hydrology plays an important role, to evaluate new projects in areas where the margin of safety is 
already low or to discover new source of water and its applications.  
1.3.4 Power: 
? Hydrological studies are most essential for the operation of an Hydel project. 
? For the storage plant, low seasonal flows rather than low daily flows are important and the 
reservoir draw down studies is must to determine the relative economics of various heights of the 
dam and power generating capacities.   
1.3.5 Flood Control: 
? Flood control project range from small improvements like channel straightening to large project 
involving huge budget.  
? Hence, for the large projects statistical and probabilistic flood frequency analysis are necessary.  
? These studies would yield fruitful results in proper flood controlling methods.  
1.3.6 Navigation: 
? When the stream is running through non – alluvial soils hydrological studies are relatively simple 
as the analysis involves hydraulic computation.  
? However streams carrying sediment pose much more complex problems.  
1.3.7 Erosion Control: 
? Proper hydrological investigations are necessary in the operation and maintenance of a reservoir 
increasing the life of the reservoir by reducing the silt entering it.    
1.3.8 Pollution Control: 
? With the increase in population, large scale industrialization, the streams and rivers are getting 
polluted and are posing more and more danger to the public health, water life etc.  
 
 
 
  
 
? Hence a complete stream pollution control study including an investigation of stream, particularly 
the magnitude and duration of low flows are found to be more useful.  
1.4 GLOBAL WATER DISTRIBUTION: 
? The total water available on the earth is about 140 x 10
16
 meter
3
. 
? Out of this 97% is contained in the oceans and sea as salt water, the remaining 3% is fresh water.   
? Table from World Water Balance and Water Resources of the Earth, UNESCO, 1978.  
Item 
Area  
(10
6
 km
2
) 
Volume  
(km3) 
Percent of Total 
Water 
Percent of Fresh 
Water 
Oceans 361.3 1,338,000,000 96.5 - 
Ground Water 
Fresh  134.8 10,530,000 0.76 30.1 
Saline 134.8 12,870,000 0.93 - 
Soil Moisture 82.0 16,500 0.0012 0.05 
Polar Ice 16.0 24,023,500 1.7 68.6 
Other Ice and Snow 0.3 340,600 0.025 1.0 
Lakes 
Fresh 1.2 91,000 0.007 0.26 
Saline 0.8 85,400 0.006 - 
Marshes 2.7 11,470 0.0008 0.03 
Rivers 148.8 2,120 0.0002 0.006 
Biological Water 510.0 1,120 0.0001 0.003 
Atmospheric Water 510.0 12,900 0.001 0.04 
Total Water 510.0 1,385,984,610 100 - 
Fresh Water 148.8 35,029,210 2.5 100 
1.5 WATER RESOURCES OF INDIA: 
? It is a fact that Asia’s Water Supply is the lowest with an average annual runoff of only 17 cm.  
? However India is well placed with 16.83 x 10
11
 meter
3
 running off a total area of 369 million 
hectares, yielding an overall runoff 457 mm, almost same as the richest continent which gets 450 
mm. 
? But, the water supply in India is not well distributed as can be seen from table.  
? Table shows the Surface water potential of India.     
? Table gives the run off data of the Indian Rivers.  
Page 4


 
 
 
  
 
MODULE – 1  
HYDROLOGY, PERCIPITATION 
1.1 INTRODUCTION: 
Hydrology is the science that treats the waters of the earth, their occurrence, circulation and distribution, 
their chemical and physical properties and their reaction with the environment, including the relation to 
living things. The domain of hydrology embraces the full life history of water on the earth.   
1.2 DEFINITIONS: 
1.2.1 Hydrology: Hydrology is defined as science dealing with the occurrence, circulation, distribution 
and properties of the waters of the earth and its atmosphere.  
(Or) 
Hydrology is defined as Hydro (Water) + Logus (Science).  
1.2.2 Hydrology is further divided into:  
1.2.2.1 Scientific Hydrology: deals with academic aspects.  
1.2.2.2 Engineering Hydrology: deals with engineering applications as estimation of water resources, 
study of precipitation, runoff, evaporation and transpiration, study of problems such as floods and 
droughts.  
1.2.2.3 Climatology: deals with the study of climate over given area within a specified period of time.  
1.2.2.4 Meteorology: is branch of science dealing with the atmospheric phenomena.  
1.3 IMPORTANCE OF HYDROLOGY: 
1.3.1 Structural and Hydraulic Design: 
? For any type of reservoir a spillway of sufficient capacity is most essential.  
? The capacity of the spillway, its height, downstream protection works etc. depend on the correct 
assessment of flood flow and routing. 
Note: Spillway means a channel that carries excess water over or around a dam or other obstruction.   
 
 
 
  
 
1.3.2 Municipal and Industrial Water Supply: 
? Due to constant increase in the urban and industrial water demands greater efforts are being made 
by hydrologists to meet the demands.  
1.3.3 Irrigation: 
? Irrigation demands are similar to municipal and industrial water supply but on a larger scale.  
? Hydrology plays an important role, to evaluate new projects in areas where the margin of safety is 
already low or to discover new source of water and its applications.  
1.3.4 Power: 
? Hydrological studies are most essential for the operation of an Hydel project. 
? For the storage plant, low seasonal flows rather than low daily flows are important and the 
reservoir draw down studies is must to determine the relative economics of various heights of the 
dam and power generating capacities.   
1.3.5 Flood Control: 
? Flood control project range from small improvements like channel straightening to large project 
involving huge budget.  
? Hence, for the large projects statistical and probabilistic flood frequency analysis are necessary.  
? These studies would yield fruitful results in proper flood controlling methods.  
1.3.6 Navigation: 
? When the stream is running through non – alluvial soils hydrological studies are relatively simple 
as the analysis involves hydraulic computation.  
? However streams carrying sediment pose much more complex problems.  
1.3.7 Erosion Control: 
? Proper hydrological investigations are necessary in the operation and maintenance of a reservoir 
increasing the life of the reservoir by reducing the silt entering it.    
1.3.8 Pollution Control: 
? With the increase in population, large scale industrialization, the streams and rivers are getting 
polluted and are posing more and more danger to the public health, water life etc.  
 
 
 
  
 
? Hence a complete stream pollution control study including an investigation of stream, particularly 
the magnitude and duration of low flows are found to be more useful.  
1.4 GLOBAL WATER DISTRIBUTION: 
? The total water available on the earth is about 140 x 10
16
 meter
3
. 
? Out of this 97% is contained in the oceans and sea as salt water, the remaining 3% is fresh water.   
? Table from World Water Balance and Water Resources of the Earth, UNESCO, 1978.  
Item 
Area  
(10
6
 km
2
) 
Volume  
(km3) 
Percent of Total 
Water 
Percent of Fresh 
Water 
Oceans 361.3 1,338,000,000 96.5 - 
Ground Water 
Fresh  134.8 10,530,000 0.76 30.1 
Saline 134.8 12,870,000 0.93 - 
Soil Moisture 82.0 16,500 0.0012 0.05 
Polar Ice 16.0 24,023,500 1.7 68.6 
Other Ice and Snow 0.3 340,600 0.025 1.0 
Lakes 
Fresh 1.2 91,000 0.007 0.26 
Saline 0.8 85,400 0.006 - 
Marshes 2.7 11,470 0.0008 0.03 
Rivers 148.8 2,120 0.0002 0.006 
Biological Water 510.0 1,120 0.0001 0.003 
Atmospheric Water 510.0 12,900 0.001 0.04 
Total Water 510.0 1,385,984,610 100 - 
Fresh Water 148.8 35,029,210 2.5 100 
1.5 WATER RESOURCES OF INDIA: 
? It is a fact that Asia’s Water Supply is the lowest with an average annual runoff of only 17 cm.  
? However India is well placed with 16.83 x 10
11
 meter
3
 running off a total area of 369 million 
hectares, yielding an overall runoff 457 mm, almost same as the richest continent which gets 450 
mm. 
? But, the water supply in India is not well distributed as can be seen from table.  
? Table shows the Surface water potential of India.     
? Table gives the run off data of the Indian Rivers.  
 
 
 
  
 
No. River Basins 
Water Potential 
million Cubic meters 
1 
West Flowing Rivers  
(Rivers of Kerala, Tamil Nadu, Tapi Basin and Narmada Basin and the 
basins above Narmada) 
305471.3 
2 
East Flowing Rivers 
(Kaveri Basin, Mahanadi Ganga, Godavari, Krishna, Pennar and between 
Kaveri and Pennar) 
355599.9 
3 Indus Basin 79473.1 
4 
Ganga Basin  
(Chambal, Yamuna, Ramganga, Gomti, Ghagra and Main Ganga Basins) 
550082.7 
5 Brahmaputra and Barak Basins 590713.6 
Total 1881340.6 
 
No. Region 
Catchment 
area 1000 km2 
Annual Runoff 
cm 
1 Rivers falling into Arabian Sea (except the Indus system) 481 63 
2 Indus Basin in India 354 22 
3 
Rivers falling into Bay of Bengal (except Ganga and 
Brahmaputra) 
1210 34 
4 Ganga System 978 50 
5 Brahmaputra System 506 75 
It may be interesting to note that out of the 16.83 x 10
11
 meter
3 
of water, only 20% is utilised at present, 
giving considerable scope for further development of water resources.  
1.6 WATER RESOURCES OF INDIA: 
Success of any water resources development project depends on timely and sufficient availability of 
water. Hence proper assessment of this natural resource assumes great importance. Therefore, 
Hydrological investigation from the first step in any water resources development scheme involving 
design construction and operation of hydraulic structures is of importance. An engineer is supposed to 
have an idea of the practical applications of Hydrology. The applications of hydrology are:  
? Hydrology is used to estimate the probable maximum flood at a proposed site of dam, bridge etc. 
Page 5


 
 
 
  
 
MODULE – 1  
HYDROLOGY, PERCIPITATION 
1.1 INTRODUCTION: 
Hydrology is the science that treats the waters of the earth, their occurrence, circulation and distribution, 
their chemical and physical properties and their reaction with the environment, including the relation to 
living things. The domain of hydrology embraces the full life history of water on the earth.   
1.2 DEFINITIONS: 
1.2.1 Hydrology: Hydrology is defined as science dealing with the occurrence, circulation, distribution 
and properties of the waters of the earth and its atmosphere.  
(Or) 
Hydrology is defined as Hydro (Water) + Logus (Science).  
1.2.2 Hydrology is further divided into:  
1.2.2.1 Scientific Hydrology: deals with academic aspects.  
1.2.2.2 Engineering Hydrology: deals with engineering applications as estimation of water resources, 
study of precipitation, runoff, evaporation and transpiration, study of problems such as floods and 
droughts.  
1.2.2.3 Climatology: deals with the study of climate over given area within a specified period of time.  
1.2.2.4 Meteorology: is branch of science dealing with the atmospheric phenomena.  
1.3 IMPORTANCE OF HYDROLOGY: 
1.3.1 Structural and Hydraulic Design: 
? For any type of reservoir a spillway of sufficient capacity is most essential.  
? The capacity of the spillway, its height, downstream protection works etc. depend on the correct 
assessment of flood flow and routing. 
Note: Spillway means a channel that carries excess water over or around a dam or other obstruction.   
 
 
 
  
 
1.3.2 Municipal and Industrial Water Supply: 
? Due to constant increase in the urban and industrial water demands greater efforts are being made 
by hydrologists to meet the demands.  
1.3.3 Irrigation: 
? Irrigation demands are similar to municipal and industrial water supply but on a larger scale.  
? Hydrology plays an important role, to evaluate new projects in areas where the margin of safety is 
already low or to discover new source of water and its applications.  
1.3.4 Power: 
? Hydrological studies are most essential for the operation of an Hydel project. 
? For the storage plant, low seasonal flows rather than low daily flows are important and the 
reservoir draw down studies is must to determine the relative economics of various heights of the 
dam and power generating capacities.   
1.3.5 Flood Control: 
? Flood control project range from small improvements like channel straightening to large project 
involving huge budget.  
? Hence, for the large projects statistical and probabilistic flood frequency analysis are necessary.  
? These studies would yield fruitful results in proper flood controlling methods.  
1.3.6 Navigation: 
? When the stream is running through non – alluvial soils hydrological studies are relatively simple 
as the analysis involves hydraulic computation.  
? However streams carrying sediment pose much more complex problems.  
1.3.7 Erosion Control: 
? Proper hydrological investigations are necessary in the operation and maintenance of a reservoir 
increasing the life of the reservoir by reducing the silt entering it.    
1.3.8 Pollution Control: 
? With the increase in population, large scale industrialization, the streams and rivers are getting 
polluted and are posing more and more danger to the public health, water life etc.  
 
 
 
  
 
? Hence a complete stream pollution control study including an investigation of stream, particularly 
the magnitude and duration of low flows are found to be more useful.  
1.4 GLOBAL WATER DISTRIBUTION: 
? The total water available on the earth is about 140 x 10
16
 meter
3
. 
? Out of this 97% is contained in the oceans and sea as salt water, the remaining 3% is fresh water.   
? Table from World Water Balance and Water Resources of the Earth, UNESCO, 1978.  
Item 
Area  
(10
6
 km
2
) 
Volume  
(km3) 
Percent of Total 
Water 
Percent of Fresh 
Water 
Oceans 361.3 1,338,000,000 96.5 - 
Ground Water 
Fresh  134.8 10,530,000 0.76 30.1 
Saline 134.8 12,870,000 0.93 - 
Soil Moisture 82.0 16,500 0.0012 0.05 
Polar Ice 16.0 24,023,500 1.7 68.6 
Other Ice and Snow 0.3 340,600 0.025 1.0 
Lakes 
Fresh 1.2 91,000 0.007 0.26 
Saline 0.8 85,400 0.006 - 
Marshes 2.7 11,470 0.0008 0.03 
Rivers 148.8 2,120 0.0002 0.006 
Biological Water 510.0 1,120 0.0001 0.003 
Atmospheric Water 510.0 12,900 0.001 0.04 
Total Water 510.0 1,385,984,610 100 - 
Fresh Water 148.8 35,029,210 2.5 100 
1.5 WATER RESOURCES OF INDIA: 
? It is a fact that Asia’s Water Supply is the lowest with an average annual runoff of only 17 cm.  
? However India is well placed with 16.83 x 10
11
 meter
3
 running off a total area of 369 million 
hectares, yielding an overall runoff 457 mm, almost same as the richest continent which gets 450 
mm. 
? But, the water supply in India is not well distributed as can be seen from table.  
? Table shows the Surface water potential of India.     
? Table gives the run off data of the Indian Rivers.  
 
 
 
  
 
No. River Basins 
Water Potential 
million Cubic meters 
1 
West Flowing Rivers  
(Rivers of Kerala, Tamil Nadu, Tapi Basin and Narmada Basin and the 
basins above Narmada) 
305471.3 
2 
East Flowing Rivers 
(Kaveri Basin, Mahanadi Ganga, Godavari, Krishna, Pennar and between 
Kaveri and Pennar) 
355599.9 
3 Indus Basin 79473.1 
4 
Ganga Basin  
(Chambal, Yamuna, Ramganga, Gomti, Ghagra and Main Ganga Basins) 
550082.7 
5 Brahmaputra and Barak Basins 590713.6 
Total 1881340.6 
 
No. Region 
Catchment 
area 1000 km2 
Annual Runoff 
cm 
1 Rivers falling into Arabian Sea (except the Indus system) 481 63 
2 Indus Basin in India 354 22 
3 
Rivers falling into Bay of Bengal (except Ganga and 
Brahmaputra) 
1210 34 
4 Ganga System 978 50 
5 Brahmaputra System 506 75 
It may be interesting to note that out of the 16.83 x 10
11
 meter
3 
of water, only 20% is utilised at present, 
giving considerable scope for further development of water resources.  
1.6 WATER RESOURCES OF INDIA: 
Success of any water resources development project depends on timely and sufficient availability of 
water. Hence proper assessment of this natural resource assumes great importance. Therefore, 
Hydrological investigation from the first step in any water resources development scheme involving 
design construction and operation of hydraulic structures is of importance. An engineer is supposed to 
have an idea of the practical applications of Hydrology. The applications of hydrology are:  
? Hydrology is used to estimate the probable maximum flood at a proposed site of dam, bridge etc. 
 
 
 
  
 
? The variation of water production from a catchment can be calculated and described by hydrology.  
? Engineering hydrology helps in determining the relation between a catchment surface water and 
ground water resources.  
? The expected flood flows over a spillway at a highway culvert, or in an urban storm drainage 
system can be known through hydrology.  
? Hydrology helps us to know the required reservoir capacity in order to assure adequate water for 
irrigation or municipal water supply in drought conditions.  
? Hydrology helps in the design of river training works.  
? Dependable yields from the stream for generation of hydroelectric power can be calculated.  
? Water supply to township and sewerage schemes can be properly designed.  
? Water resources account of a river basin can be prepared.  
? Operation of reservoirs can be done in an efficient manner.  
1.7 HYDROLOGIC CYCLE: