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Lecture 3: Flood Routing CEM001 Hydraulic Structures, Coastal and River Engineering Dr Md Rowshon Kamal H/P: School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Hydrologic Routing: Application Analyse the effects of conduit modifications Stormwater detention Flood mitigation Reservoir storage Spillway sizing Pumping stations pondstorage Changes in land useand Overtopping of highway embankments 2 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Hydrological Flood Routing The movement of flood wave down to a channel or through a reservoir and associated change in timing or attenuation of the wave constitute an important topic in floodplain hydrology. It is essential to understand the theoretical and practical aspects of flood routing to predict the temporal and spatial variations of a flood wave through a river reach and/or reservoir. Flood routing is also used to predict the outflow hydrographfromawatershedsubjectedtoa known amount of rainfall. 3 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Routing Simulate the movement of water through physical components of watershed (e.g., channels) Commonlyusedtopredict the magnitudes, volumes,andtemporalpatternsofflowflow(oftena flood wave) as it movesdown a channel Physical/Hydraulic: momentum Conservation ofmassand Conceptual/Hydrologic: (continuity), but inexact Some representations physics 4 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Routing and Types Routingistheprocess of predictingtemporal andspatialvariationofafloodwaveasit or travelsthroughariver(orchannelreach reservoir. 5 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Two types of routing can be performed: Hydraulic Routing Hydrologic Routing

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Hydraulic Routing Hydraulic routing method combines the continuity equation with a more realistic relationship describing the actual physics of the movement of the water The equation used results from conservation of momentum, assuming – In uniform velocity distribution (depth averaged) hydrostatic pressure small bottom slope hydraulicroutinganalysis, it isintended thatthethe dynamics of the water accurately described or flood wave movement be more 6 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Use of Manning Equation Stage is also relatedto the outflow via a relationshipsuch asManning'sequation 3 2 hf n 7 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Q 1.49 AR 2 S 1

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Hydrologic Routing Hydrologic routing techniques involve the balancing of inflow, outflow and volumeofstoragethroughuse thecontinuityequation. 8 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Application: Flood predictions Evaluation of flood control measures Assessment of effects of urbanization Flood warning Reservoir design and operation Spillway design for dams

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Bukit Merah Reservoir, Malaysia 9 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Lake Livingston, USA 10 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Lake Conroe, USA 11 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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DetentionPonds Detention ponds store and treat urban runoffand also provide flood control for the overall development. Ponds constructed asamenities forthe golf course andothercommunitycentersthatwerebuiltup around them. School of Civil Engineering/Linton 12 School of Computing, Information Technology & Engineering

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Detention Pond, AUSTIN, TX 13 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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HydrologicRouting Continuity Where Equation: tt I= Inflow O= Outflow S/ t = Rate of changeof storage Problem: You Need: have a hydrograph at one location (I) have river characteristics (S=f(I,O)) A hydrograph at different location (O) 14 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton I O SI O S

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HydrologicRouting ThehydrographatBisattenuateddueto storage characteristics of the stream reach. Assumption: no seepage, leakage, evaporation, or inflow from the sides. 15 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Hydrograph at point B Hydrograph at point A

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Levelpoolreservoir 16 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton River Reach Comparisons: River vs. Reservoir Routing

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Hydrological Routing Combine the continuity equation with some relationshipbetween storage,outflow,and possibly inflow Theserelationshipsareusually nature assumed, empirical, or analytical in An of example of such a relationshipmight be a stage-discharge relationship 17 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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InflowCharacteristics 18 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Inflow-Storage-OutflowCharacteristics 19 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Inflow-Storage-OutflowCharacteristics 20 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Inflow-OutflowCharacteristics 21 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Storage-WaterLevelCharacteristics 22 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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OutflowDetermination 23 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Hydrological Routing River or Channel Routing – Muskingum method – Muskingum-Cunge Method Reservoir Routing –Inflow-Storage-Discharge Curve (Puls Method) Storage-Indication Method (Modified Puls Method) Method – 24 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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ReservoirRouting 25 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Required Information Inflow hydrograph Outflow hydrograph SurchargeStoragevsWaterLevelgraphgraph 26 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Inflow-Storage-Discharge (ISD) Step 1: At first, a suitable time interval t is chosen and a curve is prepared + O] as abscissa. to 0.40 times the between elevation as Ordinate and [2S/ t The time interval is usually taken as 0.20 time of the rise of the inflow hydrograph. Fromthethesame plot,acurvebetweenoutflowratesandand elevation can be drawn. Step 2: At the start of the routing, the terms on the L.H.S. Eq. (3) are known and [2S 2 / t + O 2 ] is computed. of Step 3: For the value of [2S 2 / t + O 2 ] computed in Step 2, vs thevalueof elevationis determined from [2S/ t +O] Elevation curve and O 2 from Outflow vs Elevation curve. 27 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Inflow-Storage-Discharge (ISD) Step 4: Step 3: For the value of [2S2/ t + O2] computed in Step 2, the value of elevation is determined from [2S/ t + O] vs Elevation curve and O2 from Outflow vs Elevation curve. Step 5: Then the value of [2S2/ t + O2] by deducting 2O2 is determined from [2S2/ t + O2] (I2 + I3) + [2S2/ t - O2] = [2S3/ t + O3] Step 6: The above procedures are repeated inflow hydrograph is routed. till the entire Step 7: Finally, the maximum water level and outflow rate are determined. Also the outflow drawn. the maximum hydrograph is 29 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Modified Puls TheModifiedPulsroutingmethodismost often applied to reservoir routing – storage related to outflow Themethodmay alsobeappliedtoriver routing for certain channel situations The Modified Puls method is also referred to as the Storage-Indication method Asahydrologicmethod,thetheModifiedPuls the equationisdescribedbyconsidering discrete continuity equation School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Storage Indication or Modified Method Puls S n S n I n Q n S n1S n1 I n1I n1 Qn1Qn1 tt 22 Re-writing (substituting Ofor Q to follow convention) 2S n2S n 2S n12S n1 I I I O O On1On1 n1n1 nn tt tt TheThesolutiontotheModifiedPulsmethodis accomplished by developing a graph (or table) of O vs [2S/Δt+O].O].Inordertodothis,astage-discharge- storage relationship must be known (outlet works). (rules) or derived 31 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Modified Puls Example and 2S/ t Given curve, thethefollowinginflowhydrograph+O findtheoutflowhydrographforthereservoir assuming storm. ittobecompletelyfullatthethebeginningofthe 32 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Discharge (cfs) Hydrograph For Modified Puls Example T ime (hr)

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able time interv Storage Indication or Modified Puls Method t al t is chosen and a Step 1: At first, a sui curve ispreparedbetween ElevationasOrdinateand [2S/ t + O] as Abscissa. The time interval is usually taken as0.20 to0.40 times the timeof the rise of the inflow hydrograph. From the same plot, a curve between outflow rates and elevation can be drawn. Step 2: At the start of the routing, the terms on the L.H.S. of Eq. (3) are known and [2S 2 / t + O 2 ] is computed. Step 3: For the value of [2S 2 / t + O 2 ] is computed in Step 2, the value of Elevation is determined from [2S/ t + O] vsElevationcurveand O 2 from OutflowvsElevation curve. 33 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Modified Puls Method Step 4: Then the value of [2S 2 / t + O 2 ] by deducting 2O 2 is determined from [2S 2 / t - O 2 ] Step 5: Then, the value of [2S 3 / t + O 3 ] is computed from the values of [2S 2 / t - O 2 ] and (I 2 + (I 2 + I 3 ) + [2S 2 / t - O 2 ] = [2S 3 / t + I 3 ), thus O 3 ] Step 6: The above procedures are inflow hydrograph is routed. repeatedtill the entire Step7:7:Finally, the maximumwaterlevelandandthe maximum outflow rate are determined. Also the outflow hydrograph is drawn. 34 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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ModifiedPulsExample 2S/t + 2S/t + O curve: 35 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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Modified Puls Example A table maybecreated as follows: 36 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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Modified Puls Example Next, using the hydrograph and interpolation, inflow (discharge) values. insertthethe Forexampleat1hour,hour,thetheinflowis30cfs. 37 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Discharge (cfs) Hydrograph For Modified Puls Example Time (hr) Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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Modified Puls Example The next step is to add the inflow to the inflow in the next time step. For the first blank the inflow at 0isaddedtotheinflow at1hourtoobtainavalueof School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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Modified Puls Example This isthen repeated for the rest ofthe values in the column. 39 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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Modified PulsExample 2S n2S n 2S n12S n1 I I I O O On1On1 n n1n1 n tt tt The 2S n / t + equation: O n+1 column can thenbe calculated using the following tt tt Note that 2S n / t - O n and O n+1 are set to zero = 2S n / t + O n+1 40 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton I + I + 2 S 1 - O = 2 S 2 + O Time I n I n +I n+1 2S n / (hr) (cfs) (cfs) (c t - O n 2S n /t + O n+1 O n+1 fs) (cfs) (cfs)

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Modified Puls Example Then using the curve provided outflow can be determined. In this case, since 2S n / t + provide (darn hard to see!) O n+1 = 30, outflow = 5 based on the graph 41 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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Modified Puls Example To obtain the final column, 2S n / t - O n, two times the outflow is subtracted from 2S n / t + O n+1. In this example 30- 2*5 = School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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ModifiedPulsExample 2S n2S n 2S n12S n1 I I I O O On1On1 n n1n1 n tt tt The same steps are repeated for First = 110. the next line. From the graph, 110 equals an Finally *18 = 74 outflow value of School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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Modified Puls Example This process can then be repeated for the rest of the columns. Now a list of the outflow values have been problem is complete. calculated and the 44 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton Time I n I n +I n+1 2S n /t - O n 2S n /t + O n+1 O n+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs)

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End 45 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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