HYDROLOGY - BASIC CONCEPTS
HYDROLOGY - BASIC CONCEPTS
Hydrology Hydrology is the science of the waters of the earthand its atmosphere. It deals with occurrence,circulation, distribution and movements of thesewaters over the globe and their interaction with thephysical and biological environments.2
The Water Cycle3
Engineering Hydrology Engineering hydrology is the branch of hydrologywhich deals with estimation of water resources andrelated hydrologic quantities. It also investigateshydrologic problems such as floods and droughts, anddevelops strategies to mitigate them.4
Floods & Droughts5
Need for the Hydrologic Studies The need of the hydrologic studies arises from thefollowing problems: Uncertainty of precipitation and its seasonal occurrence Seasonal flow of rivers, and Population growth and rising standards of living6Continued .
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Need for the Hydrologic Studies In many countries water is the main source ofenergy and the agriculture is an important sectorfor their economic growth. Although water is vitalto life, but the precipitation which is the mainsource of water, is an uncertain phenomenon i. e.there might be plenty of rainfall when we do notneed it and no rain when it is required. So we needto plan accordingly. It is necessary to store surpluswater when and where available and to use it whenand where required. Uncertainty of precipitationmakes the study of various features of hydrologyexceedingly important, which then will be helpful inbetter planning and development of waterresources.8Continued .
Need for the Hydrologic Studies The flow in rivers varies from season toseason. There are low flows during leanperiod and high flows during floods. Thefloods although bringing fertile silts, butare hazardous to human life and property.Flood mitigation is necessary to safeguardhuman life, livestock, cash crops andagainst spread of disease. The increased population and risingstandards of living have greatly increasedthe demands of water. Hydrologic studiesare of utmost importance for planning anddevelopment of water resources to meetthese demands.9
Importance of Hydrology in CivilEngineering Hydrology has an important role in the design andoperation of water resources engineering projectslike irrigation, flood control, water supply schemes,hydropower projects and navigation. Many importantcivil engineering projects have failed because ofimproper assessment of hydrologic aspects of theprojects. Hydraulic structures which are veryimportant civil engineering projects and cost millionsof dollars may fail due to improper hydrologic design.10Continued .
Importance of Hydrology in CivilEngineering For example, a dam may fail due to inadequatespillway capacity. There may be reservoiroperational problems due to lack of hydrologic datalike probable inflows, evaporation and seepage.There might be failure of a bridge or a culvert if itsmaximum design flood is not estimated properly.Construction of a dam may cause problem forbridges upstream and downstream if properhydrologic studies regarding floods and erosiondownstream are not estimated and taken intoaccount in design. Groundwater studies areimportant for installation of tube wells andirrigation projects. These are just a few exampleswhich show the importance of hydrologic studiesfor civil engineering projects.11
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Major Aspects of Hydrology The main jobs of a hydrologist are collection andanalysis of data, and making predictions out of thisanalysis. Collection of Data The hydrologic data comprises:a. Rainfall Datab. Snowfall and Snowmelt Datac. Runoff Data (Catchment Runoff and Stream Flows), andd. Groundwater Data14Continued .
Major Aspects of Hydrology Analysis of Data Analysis of hydrologic data includes checking it forconsistency and homogeneity as well as finding itsvarious statistical parameters. Prediction Prediction means finding design values andmaximum possible floods and droughts. Variousapproaches for prediction of hydrologic valuesare: Statistical Approach Physical Approach Deterministic Approach15
Sciences Involved Hydrology is a very broad subject and it needssupport from allied sciences such as Physics,Mathematics, Geology, Geography, Meteorology,Forestry, Agriculture and Hydraulics.16
Major Hydrologic Projects Engineering Hydrology provides hydrologic dataessentially required for a variety of projects, suchas: Hydraulic Structures like Dams, Bridges, Head-works,Spillways and Culverts etc. Hydroelectric Power Generation Flood Control Projects Irrigation Projects Environmental Pollution Control, and Planning and Execution of Water ResourcesDevelopment Projects17Continued .
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Major Hydrologic ProjectsFollowing is an exhaustive list of projects dealt within Hydrology: Design of: Surface water reservoirsGroundwater reservoirsUrban storm water sewers and airport drainage systemsUrban water distribution systemsFlood control structures (Dikes, River ImprovementWorks, etc.) Navigational systems (Locks, Ports, etc.) Agricultural drainage systems Temporary construction and mining drainage systems21Continued .
SEAPORT22
Major Hydrologic Projects Design of: Tunnels and underground excavationsFlow control systems for highway developmentHydraulic structures (Bridges, Culverts, Dams, Barrages)Open channels and other river flow control structuresFlood waves propagationSoil conservationSanitary landfills and waste disposal facilitiesContaminated-soil remedial systemsPolluted-aquifer containment or restoration systems23Continued .
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Major Hydrologic Projects Management of: Rivers, lakes, wetlands,estuaries and aquifers Crops, forests andpasture lands25Continued .
Major Hydrologic Projects Prediction and Forecasting of: Contamination effects on rivers and lakesContamination propagation in soils and groundwaterEffect of drainage on flood flowsEnvironmental impact of water resources projectsEnvironmental impact of deforestationEnvironmental impact of urbanizationEnvironmental impact of chemical spillsEnvironmental impact of chemical leaks from tanksEnvironmental impact of leachates from landfillsEnvironmental impact of pesticide applicationEnvironmental impact of global climate changeFlood waves propagation26
Questions - A Hydrologist has to Answer Some of the typical questions that a hydrologisthas to answer are: Is the flow of stream sufficient to meet the needs of acity or industry seeking the water supply, or an irrigationproject, or a proposed water resource development, ornavigation, or recreation? Would a reservoir be required in connection with any ofthe proposed uses and if so, what should be its capacity? In the design of a flood protection system a barrage, aculvert or a spillway for a dam, what is the design floodthat may be expected to occur with any specifiedfrequency?27Continued .
Questions - A Hydrologist has to Answer What would be the effect of draining an upland area or amarshy region upon the flow of stream from the watershed? How would certain changes, removal of forests etc.,affect the ground water level or the stream flow fromsuch an area?28Continued .
Questions - A Hydrologist has to Answer In order to answer the above and other similarquestions work is undertaken in three phases (as alsoexplained), which are collection of data, analysis ofdata and making predictions out of this analysis. The data that must be collected includes stream flowrecords, precipitation records, topographic maps,groundwater data, evaporation data andtranspiration data.29
Hydrologic Cycle Journey of water from the ocean to atmosphere and backto the earth and ultimately to the ocean through theprocesses of evaporation, precipitation, percolation,runoff and return to the ocean is called hydrologic cycle.The importance of hydrologic cycle in hydrology is suchthat Hydrology is also briefly defined as the science ofhydrologic cycle. Figure 1.1 shows a schematic flow chart of the hydrologiccycle. Though the actual hydrologic cycle is quite complex,this figure just broadly depicts the sequence of majorevents of the cycle. The hydrologic cycle can be broadlydivided into two phases - land phase, and atmosphericphase.30Continued .
Hydrologic Cycle Before discussing the two phases of hydrologiccycle, some of the related terms are definedbelow: Infiltration Precipitation falling on the ground is, to some extent,absorbed by the land. This absorption of precipitationwater by land from the surface of earth is calledinfiltration. Interception A part of the precipitation is obstructed by vegetationand temporarily remains there. This process is calledinterception. Later the intercepted water is eitherevaporated or infiltrated.31
Hydrologic CycleAtmospherePrecipitationDirect RunoffGround e StorageSea32Continued .
Hydrologic Cycle Depression Storage A part of precipitation is stored in depressions on thecatchment area. This is called depression storage. Detention Storage When the precipitation occurs for a longer duration andat a rate greater than the rate of infiltration some wateris collected on the surface of the earth up to a certaindepth. On attaining a certain depth, the action of gravitymakes this water flow. Before it starts flowing, thewater stored on the surface of earth is called detentionstorage.33Continued .
Hydrologic Cycle Runoff After the detention storage is built up, as explainedabove, the water will start flowing over the ground andis called runoff. Inter Flow The part of infiltrated water which moves laterallythrough the upper soil layers above the groundwaterlevel and soon joins the stream is called inter flow.34Continued .
Hydrologic Cycle Total Runoff A part of infiltrated water moves in the form of interflow which soon joins the stream, the remaining portionof infiltrated water percolates to deeper layers of theground and is stored as groundwater. This groundwatersometimes also joins the stream flow through springsand seepage process. The stream flow is then called thetotal runoff i. e. it is sum of all the components ofprecipitation water. Direct runoff plus the losses givestotal runoff. The runoff can be expressed in depth units for a certainarea or it can be expressed in volume units. It can alsobe expressed in discharge units for a specified time.35Continued .
Hydrologic Cycle Atmospheric Phase of Hydrologic Cycle Atmospheric phase of hydrologic cycle starts with the formationof clouds after vaporization from water bodies and ends afterthe occurrence of precipitation. Land Phase of Hydrologic Cycle After occurrence of precipitation, water comes in contact withthe earth surface and hydrologic cycle enters the land phase.Part of precipitation is infiltrated and a part of it, depending uponcircumstances, is intercepted by trees and vegetation. If thereare depressions in the surface upon which precipitation falls, apart of precipitation will be stored in the depressions in the formof depression storage. All of these parts are liable tovaporization. Rainwater stands on the surface of earth where itfalls, after various losses, depending upon the rate of rainfall36Continued .
Hydrologic Cycle When the depth of standing water becomes sufficient itstarts flowing over the ground surface in the form ofsurface runoff. During the travel of surface runofftowards streams, again a part of water is infiltrated and apart of it is evaporated. A part of infiltrated water moveslaterally through the upper soil layers above thegroundwater level, in the form of interflow which soonjoins the stream flow. The remaining portion of infiltratedwater percolates to deeper layers of the ground and isstored as groundwater. Sometimes this ground waterjoins the stream flow through spring or seepage process.The stream flow is then called the total runoff. The totalrunoff from the streams goes back to the oceanssubjected to vaporization throughout its travel. Thedepression storage is either evaporated or infiltrated intothe ground and similar is the case of interception. Theground water also may go to oceans after a long time.37Continued .
Hydrologic Cycle Example 1.1 A precipitation measuring 125 mm occurred over a catchment. Ifthe infiltration, interception, depression storage and otherlosses are 50 mm, find direct runoff and total runoff.SolutionPrecipitation PLosses LDirect runoff (DRO)Total runoff 125 mm 50 mm P – L 125 – 50 75 mm DRO L 75 50 125 mm Note that ‘x’ inches of runoff means that water is spreaduniformly over the catchment having ‘x’ inches depth. Runoff involume units can be obtained by multiplying the depth with thearea of the catchment.38
Hydrologic Equation The hydrologic equation states that for a given time interval,difference of inflow to and outflow from a system is equal tochange of storage of the system. In its differential form it statesthat rate of volume inflow minus the rate of volume outflow is equalto the rate of change of storage. MathematicallyI - O S/ tEq.1.1Where,I Rate of volume inflow (volume/time), measured inm3/sec, ft3/sec, etc.O Rate of volume outflow (volume/time) measured inm3/sec, ft3/sec, etc. S/ t Rate of change of storage in time (‘S’ representsstorage and ‘t’ represents time i.e. Volume/time) The above equation is a storage equation which only approximatessome hydrologic processes.39Continued .
Hydrologic Equation Components of Inflow There are two components of inflow, viz. precipitation over the catchment and reservoir, and surface or groundwater flow from other catchment areas. Components of Outflow Three components of outflow are: surface evaporation groundwater seepage, and direct runoff i.e water taken for irrigation or to spill waysfor producing power40Continued .
Hydrologic Equation If we fix the time and take the volume units, thenthe hydrologic equation can be written as,Total volume inflow – The volume outflow Total change in volume ofthe system This is hydrologic or storage equation. It is used inmany different ways. If, for example, assuminginflow changes linearly from ‘I1’ to ‘I2’ in time ‘ t’,the outflow changes linearly from ‘O1’ to ‘O2’ andstorage changes from ‘S1’ to ‘S2’ in this time, theequation can be written as:( I1 I2 ) / 2 - ( O1 O2 ) / 2 ( S2 – S1 ) / t- - - - 41Eq. 1.2Continued .
Hydrologic Equation If we fix time ‘ t’ and talk about total inflow in certain time‘ t’, total outflow and total change in storage in that time,the hydrologic equation can be written as:Volume inflow-Volume outflow Total change in storage If further, we fix the area of the system (for example, wetalk of a catchment) and assume inflow as precipitation ‘p’,the outflow as the losses ‘L’ and runoff ‘R’ then theequation can be written as:P – L – R D - - - - - - - - - - - - - - - - - - - - - - - - -Eq. 1.3Where ‘D’ is the depression storage. This concept is further applied to discuss the water budgetof a catchment.42Continued .
Example 1.2 Flow of River Chenab at Marala Barrage varied linearlyfrom 34 cumec (m 3/sec) to283 cumec in 10-hours during a flood. The flow variationat Khanki Barrage, downstream of Marala was observedto be from 28 to 255 cumec during the above mentionedtime. Assuming no lateral flow in or out of the reach,find out the rate of change of storage of the river reachbetween Marala and Khanki. What is total change instorage of the reach in this period?43Continued .
SolutionI1 34 cumecI2 283 cumecO1 28 cumecO2 255 cumecI ( I1 I2 ) / 2 ( 34 283 ) / 2 158.5 cumecO ( O1 O2 ) / 2 ( 28 255 ) 141.5 cumec S/ t ?According to hydrologic equation( I1 I2 ) /2 - ( O1 O2 ) / 2 S/ t158.5 - 141.5 S/ t 17 cumec t 10 hours 10 x 60 x 60 36,000 secTotal change in storage S ( S/ t) x t 17 x 36,000 612 x 10³ m344Continued .
Example 1.3 Water at a constant rate of 370 cumec was observed tobe entering into Tarbela Reservoir in a certain season. Ifoutflow from the reservoir including infiltration andevaporation losses is 280 cumec, find out the change instorage of reservoir for 10 such days. Also convert youranswer into Hectare-Meter.45Continued .
SolutionI 370 cumecO 280 cumecΔS ?According to hydrologic equation,I - O ΔS / Δt370 – 280 ΔS / Δt 90 cumecΔt 10 x 24 240 hours 240 x 60 x 60 864x10³ secTotal change in storage ΔS (ΔS / Δt) x Δt 90 x 864x10³ 777.6x104 m3 777.6x10 4/10 4 777.6 Hectare-m46
Water Budget in a Catchment The water budget of a catchment is similar to budget of acountry. The water budget in a catchment can be given byhydrologic equation. If we take the inflow as theprecipitation ‘P’ on the ground surface , outflow asinterception losses ‘Li’, surface runoff ‘R’ and evaporation‘Le’ and the change in storage due to Infiltration ‘F’ andDepression storage ‘D’, the hydrologic equation isexpressed as:P - ( Li R Le ) D For R P - ( Li Le D F )R P- The Losses.R P-L47Continued .
Water Budget in a Catchment If all the quantities on right-hand-side of the aboveequation could be measured, the surface runoff of agiven catchment as result of a known precipitationcould easily be determined. But unfortunately, it isvery difficult to get these values directly. Thehydrologists have therefore evolved a number ofdirect and indirect techniques to find the rainfall runoff relationship described by the above equation.48Continued .
Example 1.4 A part of catchment area of Hub River measuring 78 km²received 100 mm of rainfall in 3 hours due to a storm. Adrainage stream joins this part of catchment to the HubRiver. The stream was dry before rainfall and there wasflow in the stream for a period of 2.5 days with anaverage discharge of 10 cumec. After the storm runoff,the stream again became dry. Find the losses, directrunoff and total runoff in cumec and Hectare-meter.49Continued .
SolutionAccording to hydrologic equation,Area of catchmentA 78 km2 78x106 m2P 100 mm 0.1 mQ 10 m3/sect 2.5 days 2.5 24x60x60 secTotal runoff PxA ( 0.1 ) x 78 x 106 7.8x106m3 7.8x106 / 104 780 Hectare-mDRO 10x2.5x24x60x60 2.16x106 m3 216Hectare-mL P - R 7.8x106 - 2.16x106 5.64x106m3 564 Hectare-m50Continued .
Example 1.5 Assume that Mangla Reservoir has surface area of 39 sq.km in the beginning of a certain month and the waterdepth is 76.20 m for this whole surface of the lake.Further assume that sides of reservoir are nearlyvertical. Now in that month the reservoir received anaverage inflow of 226.50 cumec as a direct runoff, anddirect precipitation of 125 mm. The outflow from thereservoir was 170 cumec and evaporation and seepagelosses were estimated to be 113 mm during that month.Find out depth of reservoir at the end of that month andtotal increase or decrease in the storage.51Continued .
SolutionThe hydrologic equation will be applied to solve this water budgetrelated problem.Δt 1 month 30 x 24 x 60 x 60 2.592x106 sec.Total inflow as direct runoff I x Δt 226.50 x 2.592x106 m3 587.088x106 m³Addition from precipitation precipitation x surface area ofreservoir (125/10³)x39x106 4.875x106 m3Total outflow O xΔt 170 x 2.592x106 440.64x106 m3Losses ( Evaporation Seepage ) x Surface area of reservoir (113/10³)x39x106 4.407x106 m352Continued .
Now the total change in volume of storage total volume of inflow total volume of precipitation – ( total volumeof outflow total volume of losses ) 587.088x106 4.875x106 – ( 440.64x106 4.407x106 ) 146.916x106 m3Change in depth of reservoir change in storage / surface area 146.916x106/ 39x106 3.77 mDepth at the end of month depth in the beginning change in depth 76.20 3.77 79.97 m53
Application of Hydrology toEnvironmental Problems Most of environmental aspects are directly orindirectly related to water. Floods haveenvironmental effects, droughts affect theenvironment, constructing a dam or a barrage hasenvironmental effects, groundwater pollutionaffects environment. All forms of life are waterdependent. Land, air and water are interrelated. Asworld’s population is increasing, living standardsare rising and the recreational demands aregrowing, as a result of which, there are newdevelopments in industry and food production.54Continued .
Application of Hydrology toEnvironmental Problems Due to these man-made activities, water demands areincreasing and the environment is changing day byday. Planning and development of sustainable waterresources has become a challenging job forhydrologists. It is very important to understand thehydrologic process in order to develop waterresources with least harm to the environment.55
Questions Write a note on importance of Hydrology in CivilEngineering. Explain “Hydrologic Cycle”. What is Hydrologic Equation? What is meant by Catchment Area, Why is it studied?Do Basin and Watershed mean the same? Explain. Define the term Runoff and describe various units toexpress runoff.56
Exercise During July, 1996 monthly inflow to TarbelaReservoir was 20 billion cubic meters andoutflow was 18.70 billion cubic meters. Find therate of change of storage and change instorage during the period.At Basha Reservoir the storage volume is 11,410million cubic meters at elevation of 1,180 m. Ifinflow is 11,500 cubic meters per second. Findthe time to fill the reservoir up to mentionedelevation. Assume that losses are negligible.57
Exercise Mangla Lake had a water surface level of 650 m above adatum at the beginning of a certain month. In that monththe lake received an average inflow of 250 cumecs. Therewas an outflow of 150 cumecs. In the same month, thelake received a rainfall of 150 mm and the evaporationfrom the lake surface was 5 cm. Using hydrologicequation, estimate the water surface elevation of thelake at the end of the month. Assume the lake surfacearea as 450 hectares and that there was no contributionto or from the groundwater storage.A catchment area of 100 Sq. Km. in Gilgit received arainfall of 12 cm from a 3-hours storm. At the outlet of thecatchment, a natural stream had a steady flow of 10cumecs before the storm and experienced a runofflasting for 20 hours with an average discharge value of 90cumecs. The stream was again to its original steady statewith a flow of 10 cumecs. Estimate the losses and ratio ofrunoff to precipitation.58
The Water Cycle 3 Engineering hydrology is the branch of hydrology which deals with estimation of water resources and related hydrologic quantities. It also investigates hydrologic problems such as flood
Physical Hydrology Second Edition S. Lawrence Dingman University of New Hampshire . Introduction to Hydrologic Science 1.1 Definition and Scope of Hydrology 1 1.2 Development of Scientific Hydrology 1 1.3 Approach and Scope of This Book 5 Basic Hydrologic Concepts 2.1 Physical Q
Stanford University, the University of Arizona and Wisconsin. The Hydrology Program at NM Tech now offers an on-line 15-Credit Graduate Certificate and a 30-Credit coursework only Professional Masters Degree Hydrology. The hydrology faculty who teach distance education classes are listed below in Table 1.
Chapter 7 HYDROLOGY 7.1 HYDROLOGIC DESIGN GUIDELINES Manual, hydrology will address estimating flood magnitudes as The following sections summarize ODOT practices that relate to hydrology.
with the LACDPW Hydrology Manual. The soil type used is No. 10 and the 50year, 24hour ‐‐ isohyet is 5 inches per Appendix B Sheet 1H1.7 of‐ LACDPW Hydrology Manual (2006). The isohyets for WQV and 25year storms are converted by multiplication factors per Table 5.3.1 of ‐ LACDPW Hydrology Manual.
This edition includes new sections on wetlands hydrology and snowmelt hydrology, an expanded section on arid lands hydrology, corrections of minor errors, and inclusion of dual units. 17.
Hydrology- Madan Mohan Das, Mim Mohan Das-PHI Learning private Ltd. New Delhi-2009 3. A Text Book Of Hydrology- Jayarami Reddy, Laksmi Publications, New Delhi-2007 (Ed) 4. Irrigation, Water Resources and water power Engineering- P.N.Modi- standard book house, New Delhi. 5. Irrigation and Water Power Engineering-Madan Mohan Das & Mimi Das Saikia .
Syllabus for ERTH 3701.03, Fundamentals of Hydrology, Fall 2019 Dalhousie University. S. Sterling Page 1 of 7 Faculty of Science Course Syllabus Department of Earth and Environmental Sciences ERTH/ENVS 3701.03 – Fundamentals of Hydrology Fall, 2019 Instructor: Dr. Shannon
Catalog Description: An elementary introduction to logical thinking. One-third of the course is devoted to problems of language and semantics. Section Description: The study of logic attunes us to the structure of our thoughts and judgments about the world. The brick and mortar of this structure is argument and reason. We will learn the rules of constructing good arguments, better understand .
