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CEM001 Hydraulic Structures, Coastal and River Engineering

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CEM001 Hydraulic Structures, Coastal and River Engineering
Lecture 3: Flood Routing CEM001 Hydraulic Structures, Coastal and River Engineering Dr Md Rowshon Kamal H/P: 1 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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

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 hydrograph from a watershed subjected to a known amount of rainfall. 3 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Routing Simulate the movement of water through physical components of watershed (e.g., channels) Commonly used to predict the magnitudes, volumes, and temporal patterns of flow (often a flood wave) as it moves down a channel Physical/Hydraulic: momentum Conservation of mass and Conceptual/Hydrologic: (continuity), but inexact Some representations physics 4 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

or Routing and Types Routing is the process of predicting temporal and
spatial variation of a flood wave as it or travels through a river (or channel reach reservoir. Two types of routing can be performed: • Hydraulic Routing • Hydrologic Routing 5 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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 hydraulic routing analysis, it is intended that the dynamics of the water accurately described or flood wave movement be more 6 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Use of Manning Equation
Stage is also related to the outflow via a relationship such as Manning's equation Q  1.49 AR2 S 1 3 2 n h f 7 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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

Bukit Merah Reservoir, Malaysia
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Lake Livingston, USA 10 School of Civil Engineering/Linton School of Computing, Information Technology & Engineering

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

Detention Ponds  Detention ponds store and treat urban runoff
and also provide flood control for the overall development.  Ponds constructed as amenities for the golf course and other community centers that were built up around them. School of Civil Engineering/Linton 12 School of Computing, Information Technology & Engineering

Detention Pond, AUSTIN, TX
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Hydrologic Routing I  O  S Continuity Where Equation: I = Inflow
O= Outflow S/t = Rate of change of 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 Civil Engineering/Linton School of Computing, Information Technology & Engineering

Hydrologic Routing Hydrograph at point A Hydrograph at point B The
is attenuated due to 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

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

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

Inflow Characteristics 18
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Inflow-Storage-Outflow Characteristics
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Inflow-Storage-Outflow Characteristics
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Inflow-Outflow Characteristics 21
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Storage-Water Level Characteristics 22
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Outflow Determination 23
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Hydrological Routing River or Channel Routing • Reservoir 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

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

Required Information • Inflow hydrograph Outflow hydrograph Surcharge
Storage vs Water Level graph 26 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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. 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. Eq. (3) are known and [2S2/t + O2] is computed. of Step 3: For the value of [2S2/t + O2] computed in Step 2, vs the value of elevation is determined from [2S/t + O] Elevation curve and O2 from Outflow vs Elevation curve. 27 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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(I2 + I3) + [2S2/t - O2] = [2S3/t + O3]
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

Modified Puls • The Modified Puls routing method is most
often applied to reservoir routing – storage related to outflow The method may also be applied to river routing for certain channel situations The Modified Puls method is also referred to as the Storage-Indication method As a hydrologic method, the Modified Puls the equation is described by considering discrete continuity equation... 30 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

S n1  S n I n  I n1 Qn  Qn1 Storage Indication or Modified
Method Puls S n1  S n I n  I n1 Qn  Qn1 t 2 2 Re-writing (substituting O for Q to follow convention) 2S n 2S n1 I  I  O On1 n n1 t n t The solution to the Modified Puls method is accomplished by developing a graph (or table) of O vs [2S/Δt + O]. In order to do this, a stage-discharge- storage relationship must be known (outlet works). (rules) or derived 31 School of Civil Engineering/Linton School of Computing, Information Technology & Engineering

Modified Puls Example Given curve, the following inflow hydrograph
and 2S/t + O find the outflow hydrograph for the reservoir assuming storm. it to be completely full at the beginning of the Hydrograph For Modified Puls Example 180 150 120 90 60 30 T ime (hr) Discharge (cfs) 32 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Storage Indication or Modified Puls
Method t al t is chosen and a able time inter v Step 1: At first, a sui curve is prepared between Elevation as Ordinate and [2S/t + O] as Abscissa. The time interval is usually taken as 0.20 to 0.40 times the time of 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 [2S2/t + O2] is computed. Step 3: For the value of [2S2/t + O2] is computed in Step 2, the value of Elevation is determined from [2S/t + O] vs Elevation curve and O2 from Outflow vs Elevation curve. 33 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Step 4: Then the value of [2S2/t + O2] by deducting 2O2
Modified Puls Method Step 4: Then the value of [2S2/t + O2] by deducting 2O2 is determined from [2S2/t - O2] Step 5: Then, the value of [2S3/t + O3] is computed from the values of [2S2/t - O2] and (I2 + (I2 + I3) + [2S2/t - O2] = [2S3/t + I3), thus O3] Step 6: The above procedures are inflow hydrograph is routed. repeated till the entire Step 7: Finally, the maximum water level and the maximum outflow rate are determined. Also the outflow hydrograph is drawn. 34 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Modified Puls Example 35 • 2S/t + O curve:
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Modified Puls Example 36 •A table may be created as follows:
Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 1 2 3 4 5 6 7 8 9 10 11 12 36 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Modified Puls Example •Next, using the hydrograph and interpolation,
inflow (discharge) values. insert the •For example at 1 hour, the inflow is 30 cfs. Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) Hydrograph For Modified Puls Example 18 0 150 120 90 60 30 Time (hr) 1 30 2 60 3 90 4 120 5 150 Discharge (cfs) 6 180 7 135 8 90 9 45 10 11 12 37 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

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 0 is added to the inflow at 1 hour to obtain a value of 30. Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 30 1 30 2 60 3 90 4 120 5 150 6 180 7 135 8 90 9 45 10 11 12 38 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Modified Puls Example 39 •This is then repeated for the rest of
the values in the column. Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 30 1 30 90 2 60 150 3 90 210 4 120 270 5 150 330 6 180 315 7 135 225 8 90 135 9 45 45 10 11 12 39 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Modified Puls Example 2S n 2S n1     On1 •The 2Sn/t + On+1
2S n 2S n1 I  I  O On1 n n1 n t t •The 2Sn/t + equation: On+1 column can then be calculated using the following I + I +  2 S1 - O  = 2 S 2 + O t 1 t 2 Note that 2Sn/t - On and On+1 are set to zero. Time In In+In Sn/ (hr) (cfs) (cfs) (c t - On 2Sn/t + On On+1 fs) (cfs) (cfs) 30 1 30 90 30 2 60 150 3 90 210 = 2Sn/t + On+1 4 120 270 5 150 330 6 180 315 7 135 225 8 90 135 9 45 45 10 11 12 40 School of Civil Engineering/Linton School of Computing, Information Technology & Engineering

Modified Puls Example • In this case, since 2Sn/t + On+1 41
• Then using the curve provided outflow can be determined. • In this case, since 2Sn/t + provide (darn hard to see!) On+1 = 30, outflow = 5 based on the graph Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 30 1 30 90 30 5 2 60 150 3 90 210 4 120 270 5 150 330 6 180 315 7 135 225 8 90 135 9 45 45 10 11 12 41 School of Computing, Information Technology & Engineering School of Civil Engineering/Linton

Modified Puls Example • To obtain the final column, 2Sn/t - On, two times the outflow is subtracted from 2Sn/t + On+1. • In this example 30 - 2*5 = 20 Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 30 1 30 90 20 30 5 2 60 150 3 90 210 4 120 270 5 150 330 6 180 315 7 135 225 8 90 135 9 45 45 10 11 12 42 School of Civil Engineering/Linton School of Computing, Information Technology & Engineering

Modified Puls Example 2S n 2S n1 On1   I  I    O     t 
• The same steps are repeated for • First = 110. the next line. • From the graph, 110 equals an • Finally *18 = 74 outflow value of 18. Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 30 1 30 90 20 30 5 2 60 150 74 110 18 3 90 210 4 120 270 5 150 330 6 180 315 7 135 225 8 90 135 9 45 45 10 11 12 43 School of Civil Engineering/Linton School of Computing, Information Technology & Engineering

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 Time In In+In Sn/t - On 2Sn/t + On On+1 (hr) (cfs) (cfs) (cfs) (cfs) (cfs) 30 1 30 90 20 30 5 2 60 150 74 110 18 3 90 210 160 224 32 4 120 270 284 370 43 5 150 330 450 554 52 6 180 315 664 780 58 7 135 225 853 979 63 8 90 135 948 1078 65 9 45 45 953 1085 65 10 870 998 64 11 746 870 62 12 630 746 58 44 School of Civil Engineering/Linton School of Computing, Information Technology & Engineering

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