This document provides an introduction to hydrology. It discusses the hydrologic cycle and its components like evaporation, transpiration, infiltration, etc. It also describes different types of precipitation like rain, snow, sleet and drizzle. Methods for measuring rainfall like rain gauges and types of rain gauges are explained. The concept of water balance and its application is introduced. Common methods for estimating rainfall over an area like arithmetic mean, Thiessen polygon and isohyetal methods are summarized.
This document provides an introduction to hydrology and discusses several key hydrologic concepts and processes. It defines hydrology and outlines its main applications, such as determining water balances, designing irrigation and drainage systems, and assessing impacts of environmental change. It also describes the hydrologic cycle, methods for measuring precipitation, estimating missing rainfall data, determining areal rainfall, and optimal rain gauge network densities.
This document provides an overview of hydrology and related concepts. It defines hydrology as the study of water on Earth, describes the hydrologic cycle of evaporation, precipitation, and runoff, and identifies the major sources and components of water. Measurement tools like rain gauges and types of precipitation such as orographic, convective, and cyclonic are explained. Factors affecting rainfall and important hydrologic terminology are also defined.
The document discusses key concepts in engineering hydrology including:
1. The hydrologic cycle and its components like precipitation, evaporation, transpiration, infiltration, and runoff.
2. Techniques for measuring and analyzing rainfall data like different types of rain gauges and methods to estimate average rainfall and missing data.
3. Methods to calculate runoff including classifying runoff by its source and defining concepts like surface runoff and overland flow.
This document provides an overview of engineering hydrology. It discusses key hydrological concepts like the hydrologic cycle, precipitation types, rainfall measurement techniques, analysis of rainfall records, runoff calculations, and abstraction from rainfall through processes like evaporation and infiltration. Specifically, it defines hydrology, describes the major components of the hydrologic cycle, discusses common rainfall measurement gauges and methods to estimate rainfall over a catchment. It also covers factors influencing runoff, empirical runoff calculation formulas like the Rational Method, and the major types of hydrological abstractions.
This document discusses the subject of engineering hydrology. It begins with an overview of the hydrological cycle and defines a catchment area. Next, it describes precipitation, including its types and measurement. Methods for estimating missing rainfall data from nearby stations are then outlined, including simple arithmetic averaging, normal ratio, modified normal ratio, inverse distance, and linear programming methods. Recording and non-recording rain gauges are also defined.
The term precipitation is also used to refer all forms of falling moisture viz., rainfall, snowfall, sleet, hail etc. Rainfall occurs in the form of a pattern. Atmospheric Precipitation is a wonderful process for the whole globe to use. This module explains it in general.
This document provides an introduction to hydrology and discusses several key hydrologic concepts and processes. It defines hydrology and outlines its main applications, such as determining water balances, designing irrigation and drainage systems, and assessing impacts of environmental change. It also describes the hydrologic cycle, methods for measuring precipitation, estimating missing rainfall data, determining areal rainfall, and optimal rain gauge network densities.
This document provides an overview of hydrology and related concepts. It defines hydrology as the study of water on Earth, describes the hydrologic cycle of evaporation, precipitation, and runoff, and identifies the major sources and components of water. Measurement tools like rain gauges and types of precipitation such as orographic, convective, and cyclonic are explained. Factors affecting rainfall and important hydrologic terminology are also defined.
The document discusses key concepts in engineering hydrology including:
1. The hydrologic cycle and its components like precipitation, evaporation, transpiration, infiltration, and runoff.
2. Techniques for measuring and analyzing rainfall data like different types of rain gauges and methods to estimate average rainfall and missing data.
3. Methods to calculate runoff including classifying runoff by its source and defining concepts like surface runoff and overland flow.
This document provides an overview of engineering hydrology. It discusses key hydrological concepts like the hydrologic cycle, precipitation types, rainfall measurement techniques, analysis of rainfall records, runoff calculations, and abstraction from rainfall through processes like evaporation and infiltration. Specifically, it defines hydrology, describes the major components of the hydrologic cycle, discusses common rainfall measurement gauges and methods to estimate rainfall over a catchment. It also covers factors influencing runoff, empirical runoff calculation formulas like the Rational Method, and the major types of hydrological abstractions.
This document discusses the subject of engineering hydrology. It begins with an overview of the hydrological cycle and defines a catchment area. Next, it describes precipitation, including its types and measurement. Methods for estimating missing rainfall data from nearby stations are then outlined, including simple arithmetic averaging, normal ratio, modified normal ratio, inverse distance, and linear programming methods. Recording and non-recording rain gauges are also defined.
The term precipitation is also used to refer all forms of falling moisture viz., rainfall, snowfall, sleet, hail etc. Rainfall occurs in the form of a pattern. Atmospheric Precipitation is a wonderful process for the whole globe to use. This module explains it in general.
The hydrological cycle describes the continuous movement of water on, above, and below the surface of the Earth. Water exists in three forms on Earth - liquid (oceans, lakes, rivers), solid (ice caps, glaciers, snow), and gas (water vapor in the air). The sun drives the hydrological cycle by evaporating water from the surface into the air as vapor, which rises and cools to form clouds. Precipitation occurs when clouds become heavy with water and it falls as rain or snow. Water also returns to the air through evaporation from soil and transpiration from plants. Water running on land and underground replenishes rivers, lakes, and groundwater in a constant cycle powered by energy from
Hydrology is the study of water on Earth. The hydrologic cycle describes how water circulates between the atmosphere, land, and oceans through various stages like evaporation, transpiration, precipitation, and subsurface flow. Precipitation occurs in forms like rain, snow, sleet, and hail. In India, rainfall patterns vary between the monsoon, post-monsoon, winter, and summer periods. Rainfall is measured using rain gauges, which collect water and can be non-recording or recording types like tipping buckets or weighing gauges. Factors like landscape, climate, and human activities influence the distribution and movement of water across environments.
This document discusses precipitation, including its various forms, the requirements and mechanisms for its formation, and methods for measuring and estimating precipitation. It defines precipitation as water falling from the atmosphere to Earth's surface in solid or liquid form. The main forms are rain, snow, sleet, hail, and dew. Precipitation forms through the lifting of air masses, temperature gradients, water vapor saturation, and the presence of aerosol particles for condensation. Measurement methods include non-recording and recording rain gauges. Estimation of missing data uses surrounding station averages or normal rainfall ratios.
This document provides information about hydrology and the hydrologic cycle. It begins with an overview of the hydrologic cycle - how water is transferred between oceans, land, and atmosphere through evaporation and precipitation. It then discusses various components of the hydrologic cycle in more detail, including evaporation, transpiration, infiltration, groundwater, precipitation types and measurement, and runoff. Key hydrologic concepts like the infiltration capacity and rate, evapotranspiration, catchment areas, and runoff are also explained.
Hydrology_Lecture note on chapter two about precipitation occurrenceGetachew563258
Precipitation is studied to understand how amount, rate, duration, and quality are distributed in space and time to assess hydrologic responses. There are three main precipitation mechanisms: lifting and cooling of air masses, condensation of water vapor, and growth of liquid water droplets. Precipitation is measured using non-recording and recording rain gauges, which measure amount, intensity, and duration. Data from rain gauges is analyzed to understand basin rainfall averages, depth-duration-area relationships, and intensity-duration-frequency.
This document discusses hydrology and the hydrological cycle. It defines hydrology as the science dealing with the occurrence, distribution, and movement of water on Earth. The hydrological cycle involves the constant circulation of water between the atmosphere and Earth's surface through evaporation, precipitation, and runoff. Factors like precipitation characteristics, catchment shape and size, topography, and geology affect the amount of runoff from a catchment area. Accurate measurement of rainfall and runoff is important for irrigation engineering design and management.
Hydrology is the study of water on Earth, including rainfall, snowfall, streams, lakes, groundwater, and moisture in the atmosphere. It is an interdisciplinary science that draws from fields like meteorology, geology, statistics, chemistry, physics, and fluid mechanics. The key aspects of hydrology are the water cycle, which describes how water moves between the atmosphere, land, and oceans through various stages of the water process, and the water budget or hydrologic equation, which represents the continuity of water within a system. Common methods for measuring and estimating precipitation include rain gauges and calculating averages based on data from surrounding rain gauges.
chapter 2.ppt ,hydrological study of ethi0mulugeta48
hydrology ,A programme of groundwater investigations is to obtain information on the resource through systematic collection, synthesis, interpretation and compilation of data.
It seeks information on its occurrence, movement, storage, recharge, discharge, quality & quantity.
It includes the study of its geological, environmental, as well as the hydrologic and hydraulic aspects of its flow system.
Geologic Methods
A geologic investigation begins with the collection, analysis, and hydrogeologic interpretation of existing topographic map, aerial photographs, geologic maps and logs, and other pertinent records.
This should be supplemented, when possible, by geologic field reconnaissance and by evaluation of available hydrologic data on: stream flow and springs; well yields; groundwater recharge & levels; and water quality
Evaporation can be measured using lysimeters, which are devices that measure actual evapotranspiration from plants and soils. There are two main types of lysimeters - non-weighable lysimeters that measure percolation, and weighable lysimeters that directly measure weight changes. Weighable lysimeters can use mechanical scales, load cells, or hydraulic principles to continuously record the weight of the soil and calculate evapotranspiration from changes in water content over time. Lysimeters provide useful data for measuring actual evaporation and water budgets in agricultural and natural areas.
The document discusses precipitation measurement and analysis. It defines precipitation as water that reaches the earth from the atmosphere in forms such as rainfall, snowfall, hail, etc. Rainfall is the predominant form and is measured using rain gauges, which can be non-recording or recording. Rainfall data is analyzed spatially over areas using methods like Thiessen polygons to determine average rainfall over a catchment from point measurements. Temporal variation in rainfall is also examined from hourly to annual scales to understand precipitation patterns.
WATER RESOURCES ENGINEERING MODULE 1 NOTESReshmaMRaju
This document provides an overview of key concepts in hydrology and water resources engineering. It discusses the hydrologic cycle and its three main processes of evaporation, precipitation, and runoff. It describes different types of precipitation including cyclonic, convective, and orographic precipitation. Measurement of rainfall using rain gauges is also summarized, including factors to consider for the optimal number of rain gauges. Methods for estimating missing precipitation data from nearby rain gauges are outlined, such as the arithmetic mean method, normal ratio method, and inverse distance method.
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Introduction to Hydrology, Types of Rain gauges, Factors affecting evaporation and infiltration, Stream gauging, Mass curve, Hyetograph, DAD Curve, Horton's Method, Infiltrometers, fi-index, W-index, Methods of measurement of Discharge of Stream, Area-Velocity Method, Moving Boat Method, Salt concentration method, ADCP, Current meter, River staging
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This document discusses hyetographs, hydrographs, runoff, and unit hydrographs. It contains the following key points:
1. A hyetograph is a graphical representation of rainfall intensity over time, showing the relationship between rainfall amount and time. A hydrograph shows stream discharge over time.
2. Runoff is the portion of rainfall that flows into streams and rivers. It is affected by rainfall characteristics and basin properties like soil, vegetation and topography.
3. A unit hydrograph represents the runoff from 1 cm of effective rainfall uniformly distributed over a basin and duration. It can be used to estimate flood hydrographs from storm rainfall amounts and distributions.
The document discusses hydrology and its applications in water resource engineering. It defines hydrology as the study of occurrence, distribution, movement and properties of water on Earth. Some key applications of engineering hydrology mentioned are planning and management of water resources, determining water balance, and mitigating flood and drought risks. Methods for calculating average annual rainfall such as arithmetic average, isohyet and Thiessen polygon methods are summarized. Factors affecting surface runoff like soil type, topography and meteorological conditions are briefly explained. Different methods to calculate runoff including English, runoff coefficient and Strange's methods are also outlined.
Introduction, hydrologic cycle, climate and water m1Bibhabasu Mohanty
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Precipitation: Forms, Classification, Variability, Measurement, Data analysis, Evaporation and its measurement, Evapotranspiration and its measurement, Penman Monteith method. Infiltration: Factors affection infiltration, Horton’s equation and Green Ampt method.
This document discusses hydrologic processes and the hydrologic cycle. It begins with definitions of hydrology and explains that hydrology studies the occurrence and movement of water on Earth. It then describes the hydrologic cycle, in which water is circulated between the atmosphere, land, and oceans through various processes. The document provides details on precipitation formation mechanisms, precipitation measurement techniques, and concepts like hydrologic abstractions. It aims to explain the basic framework of hydrology and hydrologic cycle.
This document provides an introduction to engineering hydrology. It discusses key hydrological concepts like the hydrological cycle, precipitation types and measurement, and mechanisms of precipitation. Engineering hydrology deals with water resource estimation, processes like precipitation and runoff, and problems like floods and droughts. Precipitation is measured using non-recording rain gauges and recording rain gauges like tipping buckets, weighing buckets, and float gauges. Site selection for rain gauges and data preparation are also outlined.
Introduction to Hydrology & Precipitation - Module - 1.pptxsurekha1287
This document provides information about a course on hydrology and irrigation engineering. It outlines the key modules to be covered in the course, including hydrology concepts like the hydrologic cycle, precipitation measurement, losses from precipitation, runoff, and hydrographs. Other modules cover irrigation water requirements, canal design, reservoirs, flood and drought management, and water harvesting. The goal is for students to understand hydrological processes and their measurement, develop unit hydrographs, compute crop water needs and irrigation systems, and analyze water resource management topics like floods and conservation.
Precipitation occurs when moisture from the atmosphere reaches the Earth's surface. There are several types of precipitation including rain, snow, hail, fog, dew, mist, glaze, rime, and sleet. Precipitation forms through convectional, orographic, and cyclonic/frontal mechanisms. Rainfall and snowfall are most commonly measured using non-recording and recording rain gauges, which collect precipitation and allow measurement of amount, intensity, and duration. Proper siting and placement of rain gauges is important to obtain accurate precipitation measurements.
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The hydrological cycle describes the continuous movement of water on, above, and below the surface of the Earth. Water exists in three forms on Earth - liquid (oceans, lakes, rivers), solid (ice caps, glaciers, snow), and gas (water vapor in the air). The sun drives the hydrological cycle by evaporating water from the surface into the air as vapor, which rises and cools to form clouds. Precipitation occurs when clouds become heavy with water and it falls as rain or snow. Water also returns to the air through evaporation from soil and transpiration from plants. Water running on land and underground replenishes rivers, lakes, and groundwater in a constant cycle powered by energy from
Hydrology is the study of water on Earth. The hydrologic cycle describes how water circulates between the atmosphere, land, and oceans through various stages like evaporation, transpiration, precipitation, and subsurface flow. Precipitation occurs in forms like rain, snow, sleet, and hail. In India, rainfall patterns vary between the monsoon, post-monsoon, winter, and summer periods. Rainfall is measured using rain gauges, which collect water and can be non-recording or recording types like tipping buckets or weighing gauges. Factors like landscape, climate, and human activities influence the distribution and movement of water across environments.
This document discusses precipitation, including its various forms, the requirements and mechanisms for its formation, and methods for measuring and estimating precipitation. It defines precipitation as water falling from the atmosphere to Earth's surface in solid or liquid form. The main forms are rain, snow, sleet, hail, and dew. Precipitation forms through the lifting of air masses, temperature gradients, water vapor saturation, and the presence of aerosol particles for condensation. Measurement methods include non-recording and recording rain gauges. Estimation of missing data uses surrounding station averages or normal rainfall ratios.
This document provides information about hydrology and the hydrologic cycle. It begins with an overview of the hydrologic cycle - how water is transferred between oceans, land, and atmosphere through evaporation and precipitation. It then discusses various components of the hydrologic cycle in more detail, including evaporation, transpiration, infiltration, groundwater, precipitation types and measurement, and runoff. Key hydrologic concepts like the infiltration capacity and rate, evapotranspiration, catchment areas, and runoff are also explained.
Hydrology_Lecture note on chapter two about precipitation occurrenceGetachew563258
Precipitation is studied to understand how amount, rate, duration, and quality are distributed in space and time to assess hydrologic responses. There are three main precipitation mechanisms: lifting and cooling of air masses, condensation of water vapor, and growth of liquid water droplets. Precipitation is measured using non-recording and recording rain gauges, which measure amount, intensity, and duration. Data from rain gauges is analyzed to understand basin rainfall averages, depth-duration-area relationships, and intensity-duration-frequency.
This document discusses hydrology and the hydrological cycle. It defines hydrology as the science dealing with the occurrence, distribution, and movement of water on Earth. The hydrological cycle involves the constant circulation of water between the atmosphere and Earth's surface through evaporation, precipitation, and runoff. Factors like precipitation characteristics, catchment shape and size, topography, and geology affect the amount of runoff from a catchment area. Accurate measurement of rainfall and runoff is important for irrigation engineering design and management.
Hydrology is the study of water on Earth, including rainfall, snowfall, streams, lakes, groundwater, and moisture in the atmosphere. It is an interdisciplinary science that draws from fields like meteorology, geology, statistics, chemistry, physics, and fluid mechanics. The key aspects of hydrology are the water cycle, which describes how water moves between the atmosphere, land, and oceans through various stages of the water process, and the water budget or hydrologic equation, which represents the continuity of water within a system. Common methods for measuring and estimating precipitation include rain gauges and calculating averages based on data from surrounding rain gauges.
chapter 2.ppt ,hydrological study of ethi0mulugeta48
hydrology ,A programme of groundwater investigations is to obtain information on the resource through systematic collection, synthesis, interpretation and compilation of data.
It seeks information on its occurrence, movement, storage, recharge, discharge, quality & quantity.
It includes the study of its geological, environmental, as well as the hydrologic and hydraulic aspects of its flow system.
Geologic Methods
A geologic investigation begins with the collection, analysis, and hydrogeologic interpretation of existing topographic map, aerial photographs, geologic maps and logs, and other pertinent records.
This should be supplemented, when possible, by geologic field reconnaissance and by evaluation of available hydrologic data on: stream flow and springs; well yields; groundwater recharge & levels; and water quality
Evaporation can be measured using lysimeters, which are devices that measure actual evapotranspiration from plants and soils. There are two main types of lysimeters - non-weighable lysimeters that measure percolation, and weighable lysimeters that directly measure weight changes. Weighable lysimeters can use mechanical scales, load cells, or hydraulic principles to continuously record the weight of the soil and calculate evapotranspiration from changes in water content over time. Lysimeters provide useful data for measuring actual evaporation and water budgets in agricultural and natural areas.
The document discusses precipitation measurement and analysis. It defines precipitation as water that reaches the earth from the atmosphere in forms such as rainfall, snowfall, hail, etc. Rainfall is the predominant form and is measured using rain gauges, which can be non-recording or recording. Rainfall data is analyzed spatially over areas using methods like Thiessen polygons to determine average rainfall over a catchment from point measurements. Temporal variation in rainfall is also examined from hourly to annual scales to understand precipitation patterns.
WATER RESOURCES ENGINEERING MODULE 1 NOTESReshmaMRaju
This document provides an overview of key concepts in hydrology and water resources engineering. It discusses the hydrologic cycle and its three main processes of evaporation, precipitation, and runoff. It describes different types of precipitation including cyclonic, convective, and orographic precipitation. Measurement of rainfall using rain gauges is also summarized, including factors to consider for the optimal number of rain gauges. Methods for estimating missing precipitation data from nearby rain gauges are outlined, such as the arithmetic mean method, normal ratio method, and inverse distance method.
Introduction to Hydrology, Stream GaugingAmol Inamdar
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Module 2 ch-1 heytograph and hydrology analysisAnkit Patel
This document discusses hyetographs, hydrographs, runoff, and unit hydrographs. It contains the following key points:
1. A hyetograph is a graphical representation of rainfall intensity over time, showing the relationship between rainfall amount and time. A hydrograph shows stream discharge over time.
2. Runoff is the portion of rainfall that flows into streams and rivers. It is affected by rainfall characteristics and basin properties like soil, vegetation and topography.
3. A unit hydrograph represents the runoff from 1 cm of effective rainfall uniformly distributed over a basin and duration. It can be used to estimate flood hydrographs from storm rainfall amounts and distributions.
The document discusses hydrology and its applications in water resource engineering. It defines hydrology as the study of occurrence, distribution, movement and properties of water on Earth. Some key applications of engineering hydrology mentioned are planning and management of water resources, determining water balance, and mitigating flood and drought risks. Methods for calculating average annual rainfall such as arithmetic average, isohyet and Thiessen polygon methods are summarized. Factors affecting surface runoff like soil type, topography and meteorological conditions are briefly explained. Different methods to calculate runoff including English, runoff coefficient and Strange's methods are also outlined.
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This document provides an introduction to engineering hydrology. It discusses key hydrological concepts like the hydrological cycle, precipitation types and measurement, and mechanisms of precipitation. Engineering hydrology deals with water resource estimation, processes like precipitation and runoff, and problems like floods and droughts. Precipitation is measured using non-recording rain gauges and recording rain gauges like tipping buckets, weighing buckets, and float gauges. Site selection for rain gauges and data preparation are also outlined.
Introduction to Hydrology & Precipitation - Module - 1.pptxsurekha1287
This document provides information about a course on hydrology and irrigation engineering. It outlines the key modules to be covered in the course, including hydrology concepts like the hydrologic cycle, precipitation measurement, losses from precipitation, runoff, and hydrographs. Other modules cover irrigation water requirements, canal design, reservoirs, flood and drought management, and water harvesting. The goal is for students to understand hydrological processes and their measurement, develop unit hydrographs, compute crop water needs and irrigation systems, and analyze water resource management topics like floods and conservation.
Precipitation occurs when moisture from the atmosphere reaches the Earth's surface. There are several types of precipitation including rain, snow, hail, fog, dew, mist, glaze, rime, and sleet. Precipitation forms through convectional, orographic, and cyclonic/frontal mechanisms. Rainfall and snowfall are most commonly measured using non-recording and recording rain gauges, which collect precipitation and allow measurement of amount, intensity, and duration. Proper siting and placement of rain gauges is important to obtain accurate precipitation measurements.
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Syllabus
Chapter-1
Introduction to objective, scope and outcome the subject
Chapter 2
Introduction: Scope and Specialization of Civil Engineering, Role of civil Engineer in Society, Impact of infrastructural development on economy of country.
Chapter 3
Surveying: Object Principles & Types of Surveying; Site Plans, Plans & Maps; Scales & Unit of different Measurements.
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Levelling: Instrument used Object of levelling, Methods of levelling in brief, and Contour maps.
Chapter 4
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Chapter 5
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Chapter 6
Environmental Engineering: Environmental Pollution, Environmental Acts and Regulations, Functional Concepts of Ecology, Basics of Species, Biodiversity, Ecosystem, Hydrological Cycle; Chemical Cycles: Carbon, Nitrogen & Phosphorus; Energy Flow in Ecosystems.
Water Pollution: Water Quality standards, Introduction to Treatment & Disposal of Waste Water. Reuse and Saving of Water, Rain Water Harvesting. Solid Waste Management: Classification of Solid Waste, Collection, Transportation and Disposal of Solid. Recycling of Solid Waste: Energy Recovery, Sanitary Landfill, On-Site Sanitation. Air & Noise Pollution: Primary and Secondary air pollutants, Harmful effects of Air Pollution, Control of Air Pollution. . Noise Pollution Harmful Effects of noise pollution, control of noise pollution, Global warming & Climate Change, Ozone depletion, Greenhouse effect
Text Books:
1. Palancharmy, Basic Civil Engineering, McGraw Hill publishers.
2. Satheesh Gopi, Basic Civil Engineering, Pearson Publishers.
3. Ketki Rangwala Dalal, Essentials of Civil Engineering, Charotar Publishing House.
4. BCP, Surveying volume 1
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3. HYDROLOGY | applications
Determining the
water balance
for a region
Determining
agricultural
water balance
Designing buffers
Predicting
floods
Designing
irrigation
schemes
Designing
drainage
systems Designi
ng
Urban
drinking
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and
sewer
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Assessing
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Assessing
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5. 1) Evaporation of water from the (a) surface sources like
river, lakes, oceans, (b) from the surface of soil (c) plants
through transpiration. By this process water is converted
into vapour.
2) Condensation :- It is the process by which vapour is
converted into solid form. (Clouds)
3) Precipitation in the form of rain, snow, sleet, drizzle etc.
4) Interception :- When precipitation occurs it is intercepted
by vegetation . So, this part do not contribute to the
surface water.
6. 6) Infiltration :- After water reaches the ground it infiltrates
into the ground.
7) Surface Detention :- Some part of the water is stored in
depression present on the ground.
8) Surface runoff :- The remaining water which flows on
ground or surface and joins channel is called surface
runoff.
9) Ground water flow or inter flow :- The water which
infiltrated into the ground joins the stream on the later
stage is called inter flow.
7.
8. Rain – It is the main form of precipitation in India. When the size of
the drop is larger than 0.5 mm, it is called rainfall.
The rainfall is classified into
Light rain – if intensity is trace to 2.5 mm/h.
Moderate rain – if intensity is 2.5 mm/hr to 7.5 mm/hr.
Heavy rain – above 7.5 mm/hr.
Snow- Snow is made up of one or more tiny ice crystals that come
together to form the unique shapes of a snowflake.
Drizzle- Drizzle is a light liquid precipitation consisting of liquid
water drops smaller than those of rain generally smaller than 0.5 mm
in diameter and having intensity less than 1mm/hr.
9.
10. Sleet- a mixture of rain and snow, when the temperature of
atmosphere and that near the ground is near 0 degree Celsius than
precipitation will be mixture of rain and snow.
Dew - forms by condensation on the ground during night when the
surface has been cooled by outgoing radiation.
11. The main phenomenon responsible for the precipitation
is lifting of air mass.
Based on the factors responsible for lifting, precipitation
is classified as follows :
1. Cyclonic precipitation
2. Convective precipitation
3. Orographic precipitation
12. Cyclonic precipitation is caused by lifting of air mass due
to the pressure difference created in an area.
It is responsible for most of the winter rain in Haryana
and Punjab.
Cyclonic precipitation may be of two types.
13. 1. Frontal Precipitation – When the moving warm moist air
mass is obstructed by the zone of cold air mass , the
warm air mass rises up to higher altitude where it gets
condensed and heavy rainfall occurs.
2. Non-Frontal Precipitation – When air mass rushes into
low pressure area , the air mass from low pressure area
rises to the higher altitude. At higher altitude this air
mass gets condensed and heavy rainfall occurs.
14.
15.
16. In a tropical countries where on a particular hot day
ground surface heated unequally , the warm air is lifted
to the higher altitude and cooler air takes its place.
The warm moist air is condensed at higher altitude and
rainfall of heavy intensity and of short duration.
17.
18. Orographic precipitation is the most important
precipitation and is responsible for most of the
precipitation in India.
It occurs when air masses laid with moisture strikes any
topographic barriers and cant move further so rises up
and condensed at higher altitude and cause precipitation.
20. In hydrology water balance equation describes the flow of
water in and out of a system.
A system can be one of several hydrological systems such
as column of soil or a whole drainage basin.
The water balance equation can be used for many basic
analysis of water availability in the area. For example how
much water is available for various purposes from the
system.
21. The water balance equation for a basin states that all the
water that enter in a system in specified period of time
must be consumed, stored or go out as surface or sub-
surface flow.
Inflow = Outflow + Change in storage
I = O + ΔS
Where,
I= Inflow in system
O= Outflow in system
Δ = Change in storage in a given time period
22. The inflow into the system includes :
Precipitation
Surface inflow
Subsurface inflow
The outflow from the system includes :
Surface outflow
Subsurface outflow
Evaporation
Transpiration
Evapo -transpiration
23. The change in storage includes :
Change in soil moisture storage
Change in groundwater storage
Snow cover
Surface Storage
Depression storage
Channel storage
24. For a specified area and for specified period of time , the
water balance equation can be written as,
P = Q + E+ ΔS
Where,
P= Precipitation
Q = Runoff
E= Evapotranspiration
ΔS = Change in storage
25. The measurement of rainfall is generally done by instrument
called rain gauge.
Rainfall and other forms of precipitation are measured in
terms of depth, the values being expressed in millimeters.
It works on the principle that amount of rainfall collected in a
small area will represent the total amount of rainfall in large
area provided the meteorological conditions of the both areas
are identical.
26. Non-Recording type Rain gauges
Recording/ Automatic Rain gauges
1) Weighing bucket type
2) Tipping bucket type
3) Float- type rain gauge
27. It is also known as Symon’s rain gauge.
It is used for all Government rain gauge stations throughout
India.
The capacity of the glass bottle is 100 mm of rainfall which
is placed in the casing.
A funnel with brass rim is placed in the top of the bottle.
The rainfall collected in the bottle is measured at every 24
hours.
It is generally taken at 8 am in India.
29. In this type of rain gauges the rainfall is automatically
recorded on a graph paper by some mechanical
arrangement.
It records the cumulative rainfall over the specified
period of time.
30. It is the most common type of self-recording
gauge.
The weighing bucket rain gauge essentially
consists of a receiver bucket supported by a spring
or any other weighing mechanism.
The movement of the bucket due to its increasing
weight is transmitted to a pen, which traces the
record on a clock-driven chart.
31.
32. It consists a sharp edge receiver.
At the end of the receiver is provided a funnel.
A pair of buckets are pivoted under the funnel in
such a way that when one tipper bucket receives
2.54 mm of precipitation it tips, discharging its
contents into a reservoir bringing the other bucket
under the funnel.
Tipping of bucket completes an electric circuit
causing the movement of pen to mark on clock
driven revolving drum, which carries a record sheet.
33.
34. The working of a Float type rain gauge is similar to the weighing bucket
type gauge.
A funnel receives the rainwater, which is collected in a rectangular
container.
A float is provided at the bottom of the container. The float is raised as
the water level rises in the container, its movement being recorded by a
pen moving on a recording drum actuated by clockwork.
When the water level in the container rises so that the float touches the
top, the siphon comes into operation, and releases the water; thus the
entire box is drained out.
35. Float type Raingague
The graphic rain gauge
1-receiver
2-floater
3-siphon
4-recording needle
5-drum with diagram
6-clock mechanism
36. 1. Arithmetic Average Method: Normal annual precipitation of the
adjacent stations are within 10% of the normal annual
precipitation of the station under consideration
2. Normal Ratio Method:
• Px = missing precipitation of station X
• P1, P2, P3,… Pm = precipitation values at m neighboring
raingauges.
• Nx = normal annual precipitation at station X.
• N1, N2, N3,…, Nm,= normal annual precipitation at m surrounding
raingauges
Estimation of Missing Rainfall Data
m
x P
P
P
m
P
...
1
2
1
m
m
x
x
N
P
N
P
N
P
m
N
P ...
2
2
1
1
37. Sometimes a significant change may occur in and around
a particular rain gauge station.
Then it becomes necessary to check the rainfall data from
that particular station.
Causes of inconsistency of records are:
1. Shifting of rain gauge to a new location
2. Change in instrument
3. Change in surrounding of the rain gauge
38. 1. Let X be the station where inconsistency in rainfall records is observed.
2. Select a group of about 10 or more base stations in the neighbourhood of station X.
3. Data of annual or monthly mean rainfall of station X as well as the average rainfall of the
group of base stations over a long time period is arranged in reverse chronological order
i.e. the latest record is the first entry and the oldest record is the last entry in the list.
4. Accumulated precipitation at station X (∑Px) and the accumulated values of the average
precipitation of the group of base stations (∑Pav) are computed from the latest records.
5. A plot of (∑Px) v/s (∑Pav) for various consecutive time periods is prepared.
6. A break in the slope of this plot indicates a change in the precipitation of station X.
7. Precipitation values at X beyond the period of change of regime is corrected as shown in the
next slide.
39. Pcx – corrected precipitation at any time period t1 at station X
Px – Original recorded precp. at time period t1 at station X
Mc – corrected slope of the double mass curve
Ma – original slope of the mass curve
Double Mass Curve Analysis
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.5 1 1.5 2 2.5
Accumulated annual rainfall of neigbouring stns in 10^3 cm
accumulated
annual
rainfall
of
X
stn
in
10^3
cm
c
a
a
c
M
M
a
c
a
c
x
cx
M
M
P
P
40. Rain gauges rainfall represent only point sampling of the
areal distribution of a storm.
The important rainfall for hydrological analysis is a rainfall
over an area, such as over the catchment.
To convert the point rainfall values at various stations in to
average value over a catchment, the following methods are
used:
◦ Arithmetic mean method
◦ Thiessen polygon method
◦ Isohyets method
41. This is the simplest method of computing the average rainfall
over a basin.
As the name suggests, the result is obtained by the division of
the sum of rain depths recorded at different rain gauge stations
of the basin by the number of the stations.
Where,
Pi : rainfall at the ith rain gauge station
N : total no of rain gauge stations
N
i
i
n
i
P
N
N
P
P
P
P
P
1
2
1 1
.....
.....
42. This is the weighted mean method.
The rainfall is never uniform over the entire area of
the basin or catchment, but varies in intensity and
duration from place to place.
Thus the rainfall recorded by each rain gauge station
should be weighted according to the area, it
represents.
For the construction of the polygon, the following
procedure is to be followed:
43. Step 1: Draw the area concerned to a suitable scale, showing its
boundary, locations of the rain gauges in the area and outside
but close to the boundary
44. Step 2: Join location of the rain gauges to form a network of
triangles
45. Step 3: Draw perpendicular bisectors to the triangle sides. These
bisectors form polygons around the stations
46. Step 4: Delineate the formed polygons and measure their areas
using a planimeter or by converting them into smaller regular
geometric shapes (i.e. triangles, squares, rectangles, etc.)
47. Step 5: compute the average rainfall using following formula:
Where,
A= total area of basin
Ai = area of the particular polygon
Pi = rainfall data of particular rain gauge
m
m
m
A
A
A
A
P
A
P
A
P
P
.....
.....
2
1
2
2
1
1
M
i
i
i
total
i
M
i
i
A
A
P
A
A
P
P
1
1
The ratio is called the weightage factor of station i
A
Ai
48. An Isohyetal is a line joining places where the rainfall amounts are
equal on a rainfall map of a basin.
An Isohyetal map showing contours of equal rainfall is more
accurate picture of the rainfall over the basin.
Isohyets are drawn on the map by the method of interpolation, after
the rainfall at each station is marked.
The area between the adjacent Isohyets are measured using
planimeter.
Let, A1, A2, A3...... An are the area between each pair of Isohyets.
P1, P2, P3......Pn are the Average precipitation for each pair of
adjacent isohyets.
49.
50. Let, A1, A2, A3...... An are the area between each pair of
Isohyets.
P1, P2, P3......Pn are the Average precipitation for each pair of
adjacent isohyets.
Then, mean rainfall on whole basin is given by,
A
P
P
A
P
P
A
P
P
A
P
n
n
n
2
...
2
2
1
1
3
2
2
2
1
1
The isohyetal method is superior to the other two methods
especially when the stations are large in number.
51. To obtain the reliable rainfall data, the rain gauges in the
catchment area should be evenly and uniformly distributed.
Their number should be neither too many nor too less as to
give unreliable results.
Optimum numbers of rain gauges are required in catchment
area to give correct average rainfall.
However the density of rain gauge may vary from region to
region.
52. According to Indian Standard (IS :4987-1968) the following
terrain gauge density is required.
1) In plain terrains, 1 station / 520 km2
2) In region of average elevation of 1000 m , 1 station /
260-360 km2
3) Hilly areas with heavy rainfall , 1 station / 130 km2
Optimum Numbers of Rain gauges
N = (Cv / E)2
Cv = Coefficient of variation of rainfall values at the existing
station
E = Allowable percentage error in the estimate of basic mean
rainfall.
53. A rainfall at a place can be described if its intensity, duration
and frequency are known.
The intensity of the rainfall is the rate at which it is falling.
The duration is the time for which rain is falling with given
intensity.
Frequency is the number of times the rainfall is falling.
54. It is a plot of accumulated precipitation against time,
plotted in chronological order.
It gives information on duration and magnitude of a storm.
Intensity at various time intervals in a storm = slope of the
curve.
55. It is a plot of rainfall intensity against time interval.
Hyetograph can be derived from the mass curve of rainfall.
To draw the hyetograph, a convenient time period is chosen and
corresponding accumulated rainfall is noted from the mass curve of the
rainfall.
From it, the intensity for that time period is computed and it is plotted
against the time period to get the hyetograph.
The area under the hyetograph represents the total rainfall received in that
period.
It is useful in estimation of design storm for predicting extreme floods.
56.
57. Point rainfall, also known as station rainfall refers to the rainfall
data of a station.
It can be in the form of daily, weekly, monthly, seasonal or
annual of rainfall.
These are also represented graphically in the form of bar
diagrams.
58.
59. EVAPORATION
■ Evaporation is the
process whereby liquid water is converted to
water vapour by the transfer of water molecules
to the atmosphere.
■ Evaporation (and Transpiration) are small for a
runoff event and can be neglected.
■ The bulk of these abstractions take place during
the time between runoff events, which is usually
long.
■ Hence, these are more important during this time
interval.
60. Factor Affecting Evaporation
Vapor pressure between the water surface and air above
Temperature
Atmospheric pressure
Wind
Depth of water in the water body
Water quality
Size of the water body
Radiation
Humidity
61. Vapor-pressure difference
The rate of evaporation is proportional to the difference
between the saturation vapour pressure at the water
temperature, ew and the actual vapour pressure in the air, ea
EL = C(ew-ea)
Where;
EL= rate of evaporation (mm/day)
C= constant
ew and ea are in mm of mercury
Evaporation continues till ew= ea
Dalton’s law of evaporation
Temperature
Other factors remaining the same, the rate of evaporation
increases with an increase in the water temperature.
Increase in evaporation rate with increasing temperature
Atmospheric pressure
A decrease in the barometric pressure, as in high altitudes,
increases evaporation.
62. Wind speed
Wind aids in removing the evaporated water vapour from the zone
of evaporation and consequently creates greater scope for
evaporation.
Water depth/ Heat storage in water Bodies
Deep water bodies have more heat storage than shallow ones.
A deep lake may store radiation energy received in summer and
release in winter causing less evaporation in summer and more
evaporation in winter compared to a shallow lake exposed to a
similar situation.
More exposed area leads to more evaporation and vice-versa.
Size of water body
63. Water quality
When solute is dissolved in water, the vapour pressure of
solution is less than that of pure water.
Hence causes reduction in the rate of evaporation.
Thus, under identical condition evaporation from sea water is about
2-3 % less than that from fresh water.
Turbidity also affects the rate of evaporation by affecting the heat
transfer within the depth of water body.
64. Measurement/ Estimation of Evaporation
The amount of water evaporated from a water surface is
estimated by the following methods:
■ Empirical evaporation equation
■ Water budget method
■ Energy budget method
■ Mass transfer method
■ Actual observations
■ Pan observations
65. Empirical
Formulae
Various empirical formulae have been developed by different
investigators to estimate the evaporation.
Most of them are dependent on wind velocity, temperature and
atmospheric pressure.
Fitzgerald’s equation (1886):
E =( 0.4 + 0.124 V ) (es - ea)
Rohwer’s equation (1931):
E = 0.771 (1.465 – 0.000732 Pa) ( 0.44 + 0.0733 V ) (es - ea)
Meyer’s equation (1915):
E =C ( 1 + V10 / 16 ) (es - ea)
Lake Mead’s equation:
E = 0.0331 V (es - ea) [1-0.03 (T a-T w)]
66. The various variables used in the formulae are as follows:
E = Evaporation in mm/day
es = Saturated vapor pressure in mm Hg
ea = Actual vapor pressure in mm Hg
Pa = Mean atmospheric pressure in mm Hg
V = Wind velocity at the water surface in km/hr
Ta = Average air temperature in °C
Ta = Average water temperature in °C
67. Surface runoff - Qr
Subsurface
runoff - Qs
Inflow- Q
Outflow- Q0
Evaporation- E
Subsurface seepage losses- Qd
E
E
Q
Q
Q
Q
Q
P
t
S
d
s
r 0
Precipitation - P
68.
69. When wind flows on the surface, a boundary is formed.
This method is based on turbulent mass transfer in the
boundary layer to calculate the mass of water vapor
transferred from surface to the surrounding atmosphere.
The evaporation is expressed as
E =
Where
E = Evaporation in mm/h
z1 & z2 = Arbitrary levels above water surface
e1 & e2 = Vapor pressure at z1 & z2 in km/h
v1 & v2 = wind velocity at in km/h
T = Average temperature in C between z1 & z2.
)
ln(
)
273
(
)
)(
(
08
.
46
2
1
1
2
2
1
z
z
T
v
v
e
e
70. Atmometers are provided with special surface which
are kept wet from where the evaporation takes place.
There is continuous supply of water to the surface
for measuring the evaporation.
A variety of Atmometers are used in the world. The
most frequently used one are Piche and Bellani
Atmometer.
The different types of atmometers indicate different
amount of evaporation under different meteorological
conditions
However, they are not common because of their
small size.
71. The previous methods are not directly applicable in design
problems.
In most design problems, evaporation is measured by
evaporation pans which are called evaporimeters.
A pan is a metal container (square or circular) with diameter
varying from 300 – 1500 mm.
It is filled water and the water loss is measured in a specified
period.
The rate of evaporation is then correlated to the evaporation
from a reservoir.
The most commonly used evaporimeter in India is US Weather
Bureau Class A Pan.
73. Advantages:
Cost of installation is reasonably low.
It is easy for measurement.
Disadvantages:
The pan gives higher rate of evaporation than that of large free water
surface.
Effects of wind and radiation are more which overestimate the
evaporation rate.
75. Environmental factors that
affect the rate of transpiration
1. Light
Plants transpire more rapidly in the light
than in the dark. This is largely because
light stimulates the opening of the stomata
(mechanism). Light also speeds up
transpiration by warming the leaf.
76. 2. Temperature
Plants transpire more rapidly at
higher temperatures because water
evaporates more rapidly as the
temperature rises. At 30°C, a leaf
may transpire three times as fast
as it does at 20°C.
77. 3. Humidity
At high humidity (moist air), the
stomata tends to close and thus limit the
exit of water vapour from the plant. In
addition, at high humidity the
atmosphere contains more water and
has low atmospheric demand, meaning
that it has limited capacity to absorb
more water.
78. 4. Wind
When there is no breeze, the air
surrounding a leaf becomes increasingly
humid thus reducing the rate of
transpiration. When a breeze is present,
the humid air is carried away and replaced
by drier air.
79. 5. Soil water
A plant cannot continue to transpire
rapidly if its water loss is not made up by
replacement from the soil. This
immediately reduces the rate of
transpiration (as well as of
photosynthesis).
80. 6. Stage of plant development
Transpiration depends upon plant
growth as the water requirement is
different at different stage of its growth.
83. Evapotranspiration or consumptive use of water is the depth of
water consumed by evaporation and transpiration during crop
growth, including water consumed by accompanying weed growth.
Consumptive use of water includes the water deposited by rainfall
and subsequently evaporating without entering the plant system.
Its study is important in the design of reservoir, irrigation canals,
water balance on earth surface and projects relating to water.
The value of consumptive use of water varies from crop to crop
and also for the same crop it varies with time as well as place.
84. Factors Affecting Evapotranspiration
Meteorological factors:
It increases with the increase in temperature,
sunshine and wind velocity but decreases with
humidity.
Plant and soil factors:
• Greater the density of vegetation, greater is the
evapotranspiration.
• When the vegetative surface becomes dry and the
soil moisture decreases, the evaporation decreases.
• Evapotranspiration depends upon the stage of the
plant growth.
85. Measurement (or Estimation) of Evapotranspiration (or Consumptive use)
The various methods adopted are broadly classified into:
a) Direct measurement of consumptive use of water.
o Lysimeter Method
o Field Experimental Method
o Soil Moisture Studies
o Integration Method
b) Empirical formula
86. Lysimeter
Method
Lysimeter is an evapotransporimeter, which is a circular tank
with pervious bottom whose diameter may be extended to 5m.
Tanks are watertight cylindrical containers open at one end and
are set into ground with their rim flush with the surface.
Consumptive use is determined by the difference of the total
water applied to the tank and that draining through the pervious
bottom and collected in a pan.
This method is time consuming and expensive.
87. Field Experimental
Plots
In this method the irrigation water is applied to the selected
field experimental plots.
In the plot, all the elements of water budget are measured in a
known time interval and the evapotranspiration is determined as
Evapotranspiration = Precipitation + Irrigation input –
Runoff – Increase in soil storage – Groundwater loss
Since it is difficult to determine the ground water loss due to
deep percolation so it can be neglected by maintaining the
moisture condition in the plot at the field capacity.
88. In this method the consumptive use of water is determined by
the summation of the products of
i. Consumptive use of water for each crop times its area.
ii. Consumptive use of water for natural vegetation time its
area.
iii. Evaporation from water surface times water surface area.
iv. Evaporation from bare land times its area.
Note: It is necessary to know the division of total area under
irrigation crops, natural vegetation, water surface area bare land
area.
89. 1. Blaney-Cridddle Equation:
It is based on the data collected from the arid Western Zone
of the United States.
It is based on the assumption that the potential
evapotranspiration depends only on the mean monthly
temperature and the monthly daylight hours.
ET = evapotranspiration (cm).
t = mean monthly temperature (°C).
p = monthly percentage of hours of bright day.
k = monthly consumptive use coefficient.
90. 2. Thornthwaite Equation:
The equation was derived from the data obtained from the eastern
USA.
The monthly heat index i:
The monthly heat indices for a year I:
Potential evapotranspiration (cm/month) is calculated from
Where, a = (67.5 x 10-8) I3 – (77.1 x 10-6) I2 – (0.01791) I + 0.492
91. 3. Christiansen Equation:
The Christiansen equation for estimation of potential
evaporation
PET = 0.473 Qo C
Where
Qo = Solar radiation at the top of the atmosphere
converted to mm of equivalent evaporation.
C = Coefficient derived from series of climatic
measurements like temperature, humidity, wind,
sunshine, elevation etc.
92. The Penman-Monteith equation requires daily mean
temperature, wind speed, relative humidity, and solar
radiation to predict net evapotranspiration.
In addition to weather uncertainties, this equation is
sensitive to vegetation specific parameters (stomatal
resistance).