Asst. Professor, CED, YCCE, B. E. (Civil Engg.) M. Tech. (Enviro. Engg .

Water Resources Engineering (Engineering Hydrology)Prof. Rajesh BhagatAsst. Professor, CED, YCCE, NagpurB. E. (Civil Engg.)GCOE, AmravatiM. Tech. (Enviro. Engg.)VNIT, NagpurAchievement: Selected Scientist, NEERI-CSIR, Govt. of India. GATE Qualified Three Times. UGC - NET Qualified in First Attempt. Selected Junior Engineer, ZP Washim. Three Times Selected as UGC Approved Assistant Professor. Assistant Professor, PCE, Nagpur. Assistant Professor, Cummins College of Engg. For Women, Nagpur Topper of PhD Course Work at UGC-HRDC, RTMNU NagpurMobile No.:- 8483002277 / 8483003474Email ID :- rajeysh7bhagat@gmail.comWebsite:- www.rajeysh7bhagat.wordpress.com

Unit-III1) Runoff: Runoff, sources and component, classification of streams, factorsaffecting runoff, Estimation Methods. Measurement of discharge of a stream by Areaslope and Area-velocity methods.2) Hydrograph: Flood hydrographs and its components, Base flow & Base flowseparation, S-Curve technique, unit hydrograph, synthetic hydrograph. InstantaneousUnit hydrograph.2

Runoff: Flowing off of precipitation from catchment area through a surface channel. It is normally expressed as volume per unit time. It is defined as that portion of precipitation which is not absorbed by the deepstrata but find its way into the stream after meeting the demands of losses. Types of runoff:- (Based on time delay between precipitation and runoff)1) Direct runoff: part of runoff, which enters the stream immediately after theprecipitation. Includes surface runoff, prompt interflow and precipitation onchannels surface. Also called storm runoff.2) Interflow: the delayed flow that reaches a stream essentially as groundwater flow. Includes ground water flow & delayed interflow.3

Runoff: Runoff may be referred to as a stream flow, river discharge or catchment yield. Types of runoff:-1) Surface runoff: the flow of water over land or surface before joining openchannel. Open channel finally reaches the catchment outlet. Laminar &turbulent regime.2) Interflow: part of precipitation that infiltrates and moves laterally throughupper crust of the soil or above GWT and returns to the surface at somelocation. Through flow or storm seepage or subsurface flow or quick returnflow.3) Ground water flow: part of precipitation that undergo deep percolation,reaches the ground after some time (usually delayed flow)4

Sources of runoff or stream flow

1) The infiltrated water which percolates deeply and reaches theground water storage in the soil which follows a complicated andlong path of travel and ultimately reaches the surface is calledground water run-off.2) The ground water movement is very slow.3) Based on the time delayed, runoff is classified as direct runoffand base flow.4) Base flow consists of delayed interflow & ground water runoff.6

TranspirationEvaporationSoil waterOverland flowInterflowGroundwater accreditationEvapotranspirationDirect runoff

Water FlowRunoff Processes:Horton overland flowSubsurface storm flow,Return flowGroundwater flow

Water balance of drainage basins

Factors affecting distribution of runoff in time:1) Type of precipitation: rain contributes directly to runoff. Hail & sleet takestime to melt.2) Rainfall intensity: heavy rainfall contribute directly & rapidly towardsstream than lower intensity rainfall3) Rainfall duration: if rainfall duration is equal to or greater than time ofconcentration, runoff will be more. Also at the starting infiltration capacity ismore.4) Rainfall distribution: a uniformly distributed rainfall volume may lead todelayed runoff.5) Catchment factors: shape, roughness, storage, topography & soil type.6) Slope: if slope is more, water moves faster.7) Geology: fined grained compacted soil will yield more surface water.8) Vegetation: vegetation slow down the movement of water.9) Drainage network: closely spaced stream allow efficient drainage ofprecipitated water.10

Types of Streams:1) Perennial stream: always carries some flow, ground water flow occursduring non precipitation period.2) Intermittent: streams remain dry for most of dry month, limited contributionfrom the ground water.3) Ephemeral: does not have any base flow contribution, streams becomes drysoon after the end of storm flow. Annual hydrograph shows series of shortduration spikes marking flash flow.11

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Types of Streams:1) Influent stream : If the ground water below the bed of stream, the seepagefrom the stream feeds the ground water such a streams are called influentstreams. Ephemeral streams.2) Effluent stream : When GWT is above the water surface elevation in thestream , ground water feeds the streams such a stream is called effluent stream.Perennial streams.15

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Antecedent Precipitation:1) If due to previous rain, soil is already saturated, runoff will be more due to nextrainfall. The previous rainfall is called Antecedent precipitation.2) Antecedent Precipitation Index (API) is taken as a measure of the soil moistureconditions existing on the day of storm under consideration.It K x I t-1 PtIt API of any Day t.K constant known as Recession Factor.I t-1 API of the day (t-1).Pt the precipitation of t th day.19

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Determination of Runoff :1) Using Empirical Formulae such as Lacey, Inglis, Khosla, etc.2) Using Curves & Tables.3) Using Runoff Coefficient Method.4) Using Infiltration Curves.5) Using Water Shed Simulation Method.6) Using Rainfall Runoff Correlation.21

Rainfall Runoff Relationship:1) In hydrological analysis & design, it is necessary to develop relations betweenprecipitation & runoff.2) Such relations are important & useful for extrapolation or interpolation ofrunoff records from the precipitation records which are generally available forlonger periods.3) These relations may estimates runoff of ungauged catchments.The equation between runoff & precipitation isR a x P bThe values of coefficient a & b are given bya ( N ( P x R ) - ( P ) ( R ) ) / ( N ( P2 ) - ( P2 ))b (( R)-(ax P))/ NN number of observation sets for R & P22

Rainfall Runoff Relationship:The equation between runoff & precipitation isR a x P bThe values of coefficient a & b are given bya ( N ( P x R ) - ( P ) ( R ) ) / ( N ( P2 ) - ( P)2 )b (( R)-(ax P))/ NN number of observation sets for R & PThe coefficient of correlation ‘r’ can be calculated byr ( N ( P x R ) - ( P ) ( R ) ) / ((( N ( P2 )) - ( P)2 ) x ( N ( R2 ) – ( R)2))23

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Empirical Equation: Empirical runoff estimation formulae:1) Binnie’s Percentages: developed for small catchment near to Nagpur.2) Barlow’s Tables: developed for small catchment in UP.3) Strange’s Table : developed for border areas of maharashtra and karnataka.4) Inglis’s formula : developed for western India.5) Khosla’s formula: developed for time period of the month.Khosla’s relationship for runoff estimation is given byRm Pm – LmLm 0.48 Tm ( Tm 4.5OC )Rm monthly runoff in cmPm monthly rainfall in cmLm monthly losses in cmTm monthly temp. of catchmentAnnual runoff coefficient annual runoff / annual rainfall.26

Empirical Equation:1) Khosla’s formula: developed for time period of the month.Khosla’s relationship for runoff estimation is given byRm Pm – LmLm 0.48 Tm ( Tm 4.5OC )Rm monthly runoff in cmPm monthly rainfall in cmLm monthly losses in cmTm monthly temp. of catchmentAnnual runoff coefficient annual runoff / annual rainfall.If Tm 4.5OCTOC4.5-1-6.5-12-18Lm(cm)2.171.781.521.251.027

1) For a catchment in UP, India, the monthly rainfall and temperature aregiven. Calculate the annual runoff coefficient by Khosla’s Formula.MonthTemp. OCRainfall in er191December14228

the annual runoff coefficient by Khosla’s Formula.Rm Pm – Lm & Lm 0.48 Tm ( Tm 4.5OC )If the loss Lm is higher than Pm then Rm will be zero.MonthTemp. OC(Tm)Rainfall(Pm) in cmMonthly Loss(Lm) in cmRunoff(Rm) in r29213.920November1919.120December1426.72029

MonthTemp. OC(Tm)Rainfall(Pm) in cmMonthly Loss(Lm) in cmRunoff(Rm) in r29213.920November1919.120December1426.720 10634.8Annual Runoff coefficient (annual runoff / annual rainfall) 34.8 / 106.0 0.32830

Runoff Coefficients for the Rational MethodType Of Drainage AreaRunoffCoefficient,CSteep, bare rock0.90Rock, steep but wooded0.80Plateaus lightly covered, ordinary ground bare0.70Densely built up areas of cities with metal led roads & paths0.70-0.90Residential areas not densely built up, with metal led roads0.50-0.70Residential areas not densely built up, with unmetalled roads0.20-0.50Clayey soils, stiff and bare0.60Clayey soils lightly covered0.50Loam, lightly cultivated or covered0.40Loam, lightly, largely cultivated0.30Suburbs with gardens, lawns and macadamized roads0.30Sandy soil, light growth0.2031

Area Velocity Method of Flood Measurement in River: Most accurate method to measure discharge.Q AxVA Cross sectional are of flow & V Average velocity of flow. Involves obtaining information at a number of points over the cross section. Points selected in a such way that the measurement are completed withinreasonable quick time. Dividing the flow area into a number of strips by means of verticals selected alongthe width of the river & measuring the depths at these verticals. The velocities are also measured at one or more points on the verticals to obtainthe mean velocity for any vertical. The velocity at any point in the river is measured by inserting the current meter atthat point facing the flow.Current Meter:- Cup type current meter & Propeller type current meter Principle involved in meter is that the water flowing past the rotating element ofthe meter makes it revolve due to the unbalanced drag force acting on it and thespeed of the rotating elements is directly proportional to the velocity of water. 32

Catchment: Quantitative assessment of hydrological parameters like precipitation,evaporation, infiltration, runoff & their use in water balance studies or inproblems of design and forecasting will be rational only when they are applied toan area with well defined boundaries. Drainage basin or drainage area or catchment or watershed or river basin. The area enclosed by the boundaries of the surface runoff system. The line which divides the surface runoff between two adjacent river basins iscalled the topographic water divide or the watershed divide or simply the divide. Based on area the watershed are classified as small, medium & large. Small watershed is less than 250km2, Medium 250 to 2500 km2 & Largewatershed exceeds 2500 km2. Depending on the land use the watershed may be referred as urban, agricultural,mountainous, forest, desert, coastal or marsh watershed or combination of two ormore of them.33

2 Unit-III 1) Runoff: Runoff, sources and component, classification of streams, factors affecting runoff, Estimation Methods. Measurement of discharge of a stream by Area-slope and Area-velocity methods. 2) Hydrograph: Flood hydrographs and its components, Base flow & Base flow separation, S-Curve technique, unit hydrograph, synthetic hydrograph.