Unit 3 Hydrograph By RB 2017 - WordPress
ENGINEERING HYDROLOGYProf. Rajesh BhagatAsst. ProfessorCivil Engineering DepartmentYeshwantrao Chavan College Of EngineeringNagpurB. E. (Civil Engg.)GCOE, AmravatiM. Tech. (Enviro. Engg.)VNIT, NagpurMobile No.:- 8483003474 / 8483002277Email 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
HYDROGRAPH:1) A plot of the discharge in stream against time chronologically.2) Depending upon unit of time involved:1) Annual hydrograph2) Monthly hydrograph3) Seasonal hydrograph4) Flood hydrograph or storm hydrograph or hydrograph: it shows streamflow due to storm over catchment. It is used flooding characteristics ofstream. Above Hydrograph 1,2,3 are called long term hydrograph and are used forlonged term studies like calculating the surface potential of stream, reservoirstudies, drought studies.3
HYDROGRAPHstorm of Duration DPrecipitationPtltppeak flowDischargeQbaseflownew basefloww/o rainfall6DTEL6
WatershedUrbanization
Factors affecting Hydrograph:1)2)3)4)5)6)7)8)SizeShapeSlopeDrainage densityLand use or vegetationRainfall intensityRainfall durationDirection of storm movement9
Hydrograph:1) Hydrograph is a graphical variation of discharge against time.2) It is a response of a given catchment to a rainfall input.3) The discharge noted in hydrograph is the combined effect of surface runoff,interflow & base flow.4) If two storms occurs in a catchment such that the 2nd one doesn’t start beforethe direct runoff due to 1st one has ceased, we get a singled peakedhydrograph.10
Hydrograph:1) If however, the second storm start before the direct runoff due to 1st storm hasceased, (complex storm) then multipeak hydrograph are obtained.11
1)2)3)4)5)6)7)8)A1ABCDEE1 is called hydrograph due to isolated storm I1.AB is rising limb or concentration curve.BCD is crest curve.DE is falling curve or recession curve.C is point of crest or peak.E is end of direct runoff.EA’ is the hydrograph in the period of ground water recession.A’ is beginning of direct runoff due to 2nd storm.12
1)2)3)4)5)6)7)T is base period of 1st storm hydrograph.A1AEE1 is the base flow contribution to total discharge.ABCDE direct runoff contribution to total discharge.G1 is the centre of mass of rainfall.G2 is the centre of mass of hydrograph.TL lag time.tpk time of peak from starting point A13
Hydrograph Separation:1) In hydrological analysis it is necessary to obtain Direct Runoff Hydrograph(DRH) from Total Storm Hydrograph (TSH).2) To separate DRH from TSH, various methods are available.14
1) The flood data and base flow in a storm are estimated for a storm in acatchment area of 600 km2. calculate the effective rainfall.Time in Days0123456789Discharge (m3/s)2063151133906344292020Base flow (m3/s)2022252828262321202015
Ordinates of DRH after the separation of the base flow are:Time in Days0123456789Discharge (m3/s)2063151133906344292020Base flow (m3/s)20222528282623212020Ordinates of DRHafter the separation ofthe base flow041126105623721800Plot the DRH for given Ordinate.Volume of DRH rainfall excess x catchment areaRainfall excess (Volume of DRH / Catchment Area)16
Ordinates of DRH after the separation of the base flow are:Time in Days0123456789Discharge (m3/s)2063151133906344292020Base flow (m3/s)20222528282623212020Ordinates of DRHafter the separation ofthe base flow041126105623721800Volume of DRH rainfall excess x catchment areaRainfall excess (Volume of DRH / Catchment Area)Volume of DRH direct runoff (41 126 105 62 37 21 8) x 1 400 m3/s 34560000 m3/day 34560000 m3Rainfall excess (Volume of DRH / Catchment Area)Rainfall excess (34560000/ (600 x 106)) 0.0576 m 5.76 cm17
Excess Rainfall & Effective Rainfall:1) Excess rainfall: if the initial losses and infiltration subtracted from the totalrainfall, the remaining portion of rainfall is called rainfall excess. Surfacerunoff occurs only when there is rainfall excess.Rainfall excess Total rainfall – Φ.t1) Effective rainfall: it is that portion of rainfall which cause direct runoff. Asdirect runoff includes both surface runoff and interflow, the effective rainfall isslightly greater than rainfall excess.Effective rainfall (direct runoff volume / area of catchment)Interflow is small, so direct runoff is equal to surface runoff & therefore they areused synonymously.18
Effective Rainfall Hyetograph:1) When initial losses and filtration losses are subtracted from the rainfallhyetograph, we get Effective Rainfall Hyetograph (ERH).2) It is also known as Hyetograph of rainfall excess.3) Direct Runoff Hydrograph (DRH) is the result of Effective RainfallHyetograph (ERH).4) Area under ERH x Catchment area Runoff Volume Area under direct DRH19
2) A storm over catchment of area 5 km2 had a duration of 14 hours. If the Φindex for the catchment is 0.4 cm/hr, determine the effective rainfallhyetograph and the volume of direct runoff from the catchment due to thestorm. The mass curve of rainfall of the storm are as below.Time from start of storm,Hr02468101214Accumulated rainfall, cm00.62.85.26.77.59.29.620
Hour Accumulatedrainfall, cmTimeinterval,hourDepth ofrainfall,cmΦ x (timeinterval)ER,cmIntensityof 1.70.80.90.45149.620.40.800Plot the hyetograph for above Intensity of ER against time.Area under ERH x Catchment area Direct Runoff VolumeTotal Effective Rainfall (0.7 0.8 0.35 0.45) x 2 4.6 cmDirect runoff volume (4.6 / 100 ) x 5 x 1000000) 230000m321
Unit Hydrograph:1) The Unit Hydrograph of the catchment is defined as hydrograph of directrunoff (DRH) results from 1cm depth of effective rainfall occurring uniformlyover the catchment at a uniform rate during a specified period of time (D-hr).2) Thus we can have 6-Hr Unit Hydrograph, 12-Hr Unit Hydrograph, etc.3) 6-Hr unit hydrograph will have an effective rainfall intensity of 1/6 cm/hr.22
Unit Hydrograph:1) The D-hr Unit Hydrograph, D should not be more than any of the following:1) Time of concentration2) Lag time3) Period of rise2) Volume of water contained inside the unit hydrograph (ie area of unit ofhydrograph) is equal to (1cm x catchment area)23
Unit Hydrograph:Assume that a 6-hour unit hydrograph(UH) of a catchment has been derived,whose ordinates are given in the following table and a correspondinggraphical representation is shown in e,m3/s0515501202011731309766402193.5224
Unit Hydrograph:2) Assume further that the effective rainfall hyetograph(ERH) for a given stormon the region has been given as in the following table.Time, Hrs061218Effective rainfall, cm02433) This means that in in the first 6 hours, 2cm excess rainfall has been recorded,4cm in the next 6 hour & 3cm in the next.4) Direct runoff hydrograph can then be calculated by the three separatehydrograph for three excess rainfalls by multiplying the ordinates of the 6hrunit hydrograph by corresponding rainfall amounts.25
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Sample calculation for the example solved graphically is given tableTime,HrsUHOrdinates,m3/sDirect runoffdue to 2cmexcess rainfallin first 6hrsDirect runoff dueto 4cm excessrainfall in second6hrsDirect runoff due Direct runoffto 3cm excesshydrograph,rainfall in 3.5736631068424142745900810.518.596006629
3) The ordinates of 6 hr unit hydrograph of a catchment is given below:Time,Hr03691215182430364248546069Ordinatesof 6 hr UH02550851251601851601106036251680Derive the flood hydrograph in the catchment due to the storm given below:Time from start of storm (hr)061218Accumulated Rainfall03.51116.5The storm loss rate for the catchment is estimated 0.25 cm/hr. The base flowcan be assumed to be 15 m3/s at the beginning and increasing by 2.0 m3/sfor every 12 hours till the end of the direct runoff hydrograph.30
Time interval of storm (hr)61218Accumulated Rainfall3.51116.5Rainfall3.57.55.5Loss @ 0.25cm/Hr for 6 Hrs1.51.51.5Effective Rainfall, cm264Due to unequal time interval of UH ordinates, a few entries have to be interpolatedto complete the table.31
Time,HrOrdinatesof UHDRH dueto 2cm ERDRH due to6cm ERDRH due to4cm EROrdinates ofFinal DRHBase Flow,m3/sOrdinates ofFloodHydrograph,m3/sABC (B x 2)D (B x 6)E (Bx4)F (C D E)GH (G 3529349237137592732
Derivation Unit Hydrograph from Flood Hydrograph of IsolatedStorm:4) The following are the ordinates of the flood hydrograph from a catchmentarea of 780 km2 due to 6 hr storm. Derive the 6 hr unit hydrograph of ,m3/s4064215360405350270205145100705040Assume the base flow of 40 m3/s.Direct Surface runoff (64-40) (215-40) (360-40) (405-40) (350-40) (270-40) (205-40) (145-40) (100-40) (70-40) (50-40)Direct Surface runoff 1794 m3/sDRH in depth ((1794 x 6 x60 x 60) / (780 x 106)) x 100 4.968 cm (Rain Excess)33
Derivation Unit Hydrograph from Flood Hydrograph of IsolatedStorm:4) The following are the ordinates of the flood hydrograph from a catchmentarea of 780 km2 due to 6 hr storm. Derive the 6 hr unit hydrograph of ,m3/s4064215360405350270205145100705040Therefore the ordinates of UH are obtained by dividing the ordinates of DRHhydrograph by rain excess 4.968 cm to get ordinates of 1753203653102301651056030100(Ordinatesof 121.1312.0776.042.01340
5) The peak of flood hydrograph due to a 3 Hr duration isolated storm in acatchment is 270 m3/s. The total depth of rainfall is 5.9cm. Assuming anaverage infiltration losses of 0.3 cm/hr and a constant base flow of 20 m3/sestimates the peak of the 3 hr unit hydrograph of this catchment. If the areaof catchment is 567 km2 determine the base width of 3 hr unit hydrographby assuming it to be triangular in shape.Duration of Rainfall Excess 3 HrTotal Depth of Rainfall 5.9 cmLoss @ 0.3 cm/Hr for 3 hours 0.3 x 3 0.9 cmRainfall Excess 5 cmPeak Flood Hydrograph 270 m3/sBase flow 20 m3/sPeak of DRH 270 – 20 250 m3/s35Peak of 3 Hr Unit Hydrograph (peak of DRH / Rainfall Excess) 250 / 5 50 m3/s
5) The peak of flood hydrograph due to a 3 Hr duration isolated storm in acatchment is 270 m3/s. The total depth of rainfall is 5.9cm. Assuming anaverage infiltration losses of 0.3 cm/hr and a constant base flow of 20 m3/sestimates the peak of the 3 hr unit hydrograph of this catchment. If the areaof catchment is 567 km2 determine the base width of 3 hr unit hydrographby assuming it to be triangular in shape.Let B base width of 3 hr Unit HydrographVolume represented by the area of UH Volume of 1 cm depth over the catchmentArea of UH Area of catchment x 1 cmPeak of 3 Hr Unit Hydrograph 50 m3/sArea of catchment 567 km2(1/2) B x 50 x 60 x 60 567 x 106 x (1/100)B 63 Hours36
6) Determine the ordinates of flood hydrograph of 3 successive storms of 4hr duration, each producing rainfall of 3 cm, 4 cm and 2 cm respectively.Φ-index 0.25 cm/hr and base flow is 10 m3/sec.Time (T)(Hrs.)Ordinates of 4IIIIIIDRHhr. UHstorm storm stormOR 2cmR 3cmBaseflowOrdinates FloodhydrographR 11920032321042222020103024001010
6) A storm produces rainfall intensities of 0.75, 2.25 and 1.25 cm/hr on a drainagearea in 3 successive time period of 4 hr. Φ-index 0.25 cm/hr and base flow is 10m3/sec.Time (T) Ordinates of 4(Hrs.)hr. UHABIStormCIIstormDIIIstormER 2cmR 8cmR 4cmDRHOF B C D EBaseflowOrdinatesFloodhydrographGH F 0.48200.0610210.061012.1824.36188.32 8.721058.72200010100
7) Determine the ordinates of unit hydrograph from flood hydrograph.Neglect base flow. Area 405 hectare.Time (T) (Hrs.)Ordinates of Flood hydrograph, m3/s0020.341.762.685.4104122.6141.1160.6180
7) Determine the ordinates of unit hydrograph from flood hydrograph.Neglect base flow. Area 405 hectare.Excess rainfall x Catchment area runoff volume Area of HydrographExcess rainfall (runoff volume) / Catchment areaExcess rainfall (131760) / 4050000 0.0325m 3.25 cm
7) Determine the ordinates of unit hydrograph from flood hydrograph.Neglect base flow. Area 405 hectare.Time (T) (Hrs.)AOrdinates of Flood hydrograph, m3/sBOrdinates of 2 hr. UHC B 41.231122.60.800141.10.338160.60.1851800.000
8) Determine the ordinates of flood hydrograph of 3 hr rainfall resultinginto total rainfall of 15 cm. initial loss is 0.5 cm and Φ-index 1 cm/hr.Sol: Excess rainfall 15 – 0.5 – (1 x 3) 11.5 cmTime (T) (Hrs.)AOrdinates of 3 hr UHBOrdinates of Flood hydrographC B x 5036557.5042446.0048223.0054111.506000.00
S-CURVE METHODS-curve or the summation curve is the hydrograph of direct surface discharge that wouldresult from a continuous succession of unit storms producing 1 cm in time (T) hrs.
Time(T)(Hrs.)Ordinatesof 4 hrUHOrdinates of 4 hrUH lagged by4hrS-CurveordinateS-Curve laggedby 12 hrDifferenceOrdinates of12 hr UHABCD B CEF D-EG 46996524715.67440699699679206.67
Q.9 The ordinates of 4-hr unit hydrograph are given below. Determine the ordinates of 3-hr UH using SCurve technique.Ordinates of OrdinatesOrdinates of 4-hr U.H.of 4-hrTime334-hr U.H.(m /s)U.H. (m /s)(Hours)3(m /s)lagged by 4- lagged byhr8-hrCDS-Curveordinates3(m /s)S-Curveordinates3(m /s)lagged by3-hrDifferenceOrdinates of 33hr U.H. (m /s)E B C DFG E-FH 3.0017.33
Q.10 The ordinates of surface runoff of 4-hr duration from a catchment area of 357 km2 are measured at 1 hr intervalare given below. Determine the ordinates of 6-hr UH using S-Curve technique.Ordinates Ordinates OrdinatesSurfaceof 4-hrof 4-hrof 4-hrTimeOrdinatesRunoffU.H.U.H.U.H.(Hourof 4-hr333Ordinates3(m /s)(m /s)(m /s)s)3U.H. (m /s)(m /s)lagged by lagged by lagged by4-hr8-hr12-hrABC B/0.8160.000.000.001.00 15.0018.362.00 25.0030.613.00 36.0044.074.00 38.0046.525.00 48.0058.776.00 69.0084.487.00 91.00111.418.00 113.00138.349.00 101.00123.6510.00 88.00107.7411.00 71.0086.9212.00 54.0066.1113.00 31.0037.9514.00 21.0025.7115.00 tes3(m /s)G C D E inates3Ordinates of 6-hr(m /s) Difference3U.H. (m /s)lagged 4.87200.78I H-G J .2555.5063.6642.4452.6435.10
Q.11. The ordinates of 4-hr UH are given below. Determine the ordinates of 2-hrUH using S-Curve technique and plot the same.33Time (Hours)Ordinates of 4-hr U.H. (m /s)Ordinates of 2-hr U.H. (m 0351330A B*(4/2)025125260350360280180100702660
Q.12 The ordinates of S-Curve Hydrograph are given below. Determine the ordinates of 3-hrUH. Effective rainfall is 1 cm/hr.Ordinates of STime Ordinates of S33Curve (m /s) lagged(Hours) Curve (m /s)by 3-hrABC00DifferenceDOrdinates of 3-hr U.H. (m3/s)E D x 2.33852341311036.6795384637525.00105465014515.00
Q.13 The ordinates of 6-hr UH are given below. Determine the ordinates of 4-hr UH usingS-Curve technique and plot the same.Time Ordinates of S-Curve S(Hours 6-hr U.H. addition Curve)(m3/s)ordinates3(m 02303604405105605906004 2 2364044S-Curveordinates3(m /s) 4hrduration6 3393.33400.00400.000.00S-Curve Difference Ordinatesordinatesof 4-hr3(m /s)U.H.3lagged by(m 33393.33400.00400.008 6-7 9 6.677033.335020.00306.67100.000-400.00-600
Unit Hydrograph: 1) The Unit Hydrograph of the catchment is defined as hydrograph of direct runoff (DRH) results from 1cm depth of effective rainfall occurring uniformly over the catchment at a uniform rate during a specified period of time (D-hr). 2) Thus we can have 6-Hr Unit Hydrograph, 12-Hr Unit Hydrograph, etc.
2009]. A synthetic unit hydrograph is a unit hydrograph derived using an established formula, without a need for analysing the rainfall-runoff data [Ponce 1989]. This includes Snyder’s method, Soil Conservation Service (SCS) method, Gray’s method and Clark’s Instantaneous Unit Hydrograph method.Cited by: 7Page Count: 10File Size: 325KBAuthor: A Wale
of unit hydrograph and its linear systems theory. Furthermore, Viessman et al [1989], Wanielista [1990] and Arora [2004] presented the history and procedures for several unit hydrograph methods. Ramirez [2000] reported that the synthetic unit hydrograph of Snyder in 1938 was based on the study of 20 watersheds located in the Appalachian .Cited by: 7Publish Year: 2017Author: Wahab Adebayo Salami, Solomon Olakunle Bilewu, Biliyamin Adeoye Ibitoye, Mufutau Ayanniyi Ayanshola
and no average unit hydrograph would be obtained. There fore, HEC-1 was used to compute a unit hydrograph and Snyder's coefficient (CP) for each storm (see Table 2). The mean value of CP was 0.40 with a standard deviation
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.
166 MODERN SEWER DESIGN The post-development 10-year runoff hydrograph from the watershed is given in Figure 6.3. 1. On the hydrograph, plot a straight line from the zero intercept to a point on the hydrograph at the 0.43 m3/s point. The area between these two curves is the approximate volume of storage required. The planimetered area 9832 mm2
Average Several UHG’s It is suggested that several unit hydrographs be derived and averaged. The unit hydrographs must be of the same duration in order to be properly averaged. It is often not sufficient to simply average the ordinates of the unit hydrographs in order to obtain the final unit hydrograph. A numerical average o
7. Time-to-peak for the Snyder unit-hydrograph method estimated with the method of Singh (1981) compared with the minimum, mean, and maximum values determined from calibration for all storms on selected watersheds in Lake County, 111., utilized to develop and verify the equations for estimation of Cited by: 11Publish Year: 1997Author: Charle
AutoCAD 2D Tutorial - 166 - Creating Local Blocks (BMAKE) 19.1 1. Choose Draw, Block, Make. or 2. Click the Make Block icon. or 3. Type BMAKE at the command prompt. Command: BMAKE or BLOCK 4. Type the name of the block. 5. Pick an insertion point. 6. Select objects to be included in the block definition. 7. Click OK
