Lecture 3: Flood Routing CEM001 Hydraulic Structures, Coastal and River Engineering Dr Md Rowshon...

Lecture 3: Flood RoutingCEM001 Hydraulic Structures, Coastal and River

Engineering

Dr Md Rowshon Kamal

[email protected]

H/P: 0126627589

1School of Computing, Information Technology & Engineering

School of Civil Engineering/Linton

mailto:[email protected]








Hydrologic Routing: Application

Analyse the effects of conduit modifications••

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•

•

•

•

•

Stormwater detention

Flood mitigation

Reservoir storage

Spillway sizing

Pumping stations

pond storage

Changes in land use and

Overtopping of highway embankments

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School of Computing, Information Technology & Engineering


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 aknown amount of rainfall.

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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 aflood wave) as it moves down a channel

• Physical/Hydraulic:momentum

Conservation of mass and

• Conceptual/Hydrologic:(continuity), but inexact

Somerepresentations

physics

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Routing and Types

Routing is the process of predicting temporaland spatial variation of a flood wave as it

ortravels through a river (or channel reachreservoir.

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Two types of routing can be performed:

• Hydraulic Routing

• Hydrologic Routing

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 wateraccurately described

or flood wave movement be more

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Use of Manning Equation

• Stage is also related to the outflow via arelationship such as Manning's equation

3 2

h fn

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Q 1.49 AR

2

S 1

Hydrologic RoutingHydrologic routing techniques involve the

balancingofof

inflow, outflow and volume of storage through usethe continuity equation.

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School of Computing, Information Technology & EngineeringSchool 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

Bukit Merah Reservoir, Malaysia9


Lake Livingston, USA 10


Lake Conroe, USA 11


Detention Ponds

Detention ponds store and treat urban runoff and alsoprovide flood control for the overall development.

Ponds constructed as amenities for the golf courseand other community centers that were built uparound them.


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Detention Pond, AUSTIN, TX13


Hydrologic Routing

Continuity

Where

Equation: t

I = Inflow

O= Outflow

S/t = Rate of change of storage

Problem:

You

You

Need:

have a hydrograph at one location (I)

have river characteristics (S=f(I,O))

A hydrograph at different location (O)14


I O S

Hydrologic Routing

The hydrograph at B is attenuated due tostorage characteristics of the stream reach.

Assumption: no seepage, leakage, evaporation, or inflow from the sides.

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Hydrograph at point B

Hydrograph at point A

Level pool reservoir

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River Reach

Comparisons: River vs. Reservoir Routing

Hydrological RoutingCombine the continuity equation with some

•relationship between storage, outflow, andpossibly inflow

• These relationships are usuallynature

assumed,empirical, or analytical inAn of example of such a• relationship mightbe a stage-discharge relationship

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Inflow Characteristics

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Inflow-Storage-Outflow Characteristics

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Inflow-Storage-Outflow Characteristics

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Inflow-Outflow Characteristics

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Storage-Water Level Characteristics

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Outflow Determination

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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

–

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Reservoir Routing

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Required Information

••

•

Inflow hydrographOutflow hydrograph

Surcharge Storage vs Water Level graph

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Inflow-Storage-Discharge (ISD)Step 1: At first, a suitable time interval t is chosen

and acurve is prepared+ O] as abscissa. to 0.40 times the

between elevation as Ordinate and [2S/tThe 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 andelevation 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,vsthe value of elevation is determined from [2S/t + O]

Elevation curve and O2 from Outflow vs Elevation curve.

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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 isdetermined from [2S2/t + O2]

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

Step 6: The above procedures are repeatedinflow hydrograph is routed.

till the entire

Step 7: Finally, the maximum water level andoutflow rate are determined. Also the outflow drawn.

the maximumhydrograph is

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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 riverrouting for certain channel situationsThe Modified Puls method is also referred toas the Storage-Indication method

•

• As a hydrologic method, the Modified Pulstheequation is described by considering

discrete continuity equation...

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Storage Indication or ModifiedMethod

Puls

S n I n Qn S n1 I n1 Qn1 t 2 2

Re-writing (substituting O for Q to follow convention)

2S n 2S n1 I I O On1

n1n nt t

The solution to the Modified Puls method isaccomplished 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

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Modified Puls Exampleand 2S/tGiven

curve,the following inflow hydrograph + Ofind the outflow hydrograph for the reservoir

assumingstorm.

it to be completely full at the beginning of the

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Dis

ch

arg

e (

cfs

)

Hydrograph For Modified Puls Example

180

150

120

90

60

30

0

0 2 4 6 8 10

T ime (hr)

able time inter v

Storage Indication or Modified PulsMethod

t al t is chosen and a

Step 1: At first, a suicurve is prepared between Elevation as Ordinate and[2S/t + O] as Abscissa. The time interval is usually takenas 0.20 to 0.40 times the time of the rise of the inflowhydrograph. From the same plot, a curve between outflowrates 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 Step2, the value of Elevation is determined from [2S/t + O]vs Elevation curve and O2 from Outflow vs Elevationcurve.

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Modified Puls MethodStep 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 fromthe values of [2S2/t - O2] and (I2 +

(I2 + I3) + [2S2/t - O2] = [2S3/t +I3), thus

O3]

Step 6: The above procedures areinflow hydrograph is routed.

repeated till the entire

Step 7: Finally, the maximum water level and themaximum outflow rate are determined. Also the outflowhydrograph is drawn.

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Modified Puls Example• 2S/t + O curve:

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Modified Puls Example•A table may be created as follows:

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Time In In+In+1 2Sn/t - On 2Sn/t + On+1 On+1

(hr) (cfs) (cfs) (cfs) (cfs) (cfs)

0123456789

101112

Modified Puls Example

•Next, using the hydrograph and interpolation,inflow (discharge) values.

insert the

•For example at 1 hour, the inflow is 30 cfs.

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Dis

ch

arg

e (c

fs)

Hydrograph For Modified Puls Example

180

150

120

90

60

30

0

0 2 4 6 8 10

Time (hr)



0 01 302 603 904 1205 1506 1807 1358 909 45

10 011 012 0

Modified Puls Example•The next step is to add the inflow to the inflow in thenext time step.•For the first blank the inflow at 0 is added to the inflowat 1 hour to obtain a value of 30.

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0 0 301 302 603 904 1205 1506 1807 1358 909 45

10 011 012 0


•This is then repeated for the rest of the values in the column.

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0 0 301 30 902 60 1503 90 2104 120 2705 150 3306 180 3157 135 2258 90 1359 45 45

10 0 011 0 012 0 0

Modified Puls Example2S n 2S n1

I I O On1

n n1 nt t•The 2Sn/t +equation:

On+1 column can then be calculated using the following

1 2 1 2t t

Note that 2Sn/t - On and On+1 are set to zero.

30 + 0 = 2Sn/t + On+1

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I + I + 2 S1 - O =

2 S 2 + O

Time In In+In+1 2Sn/

(hr) (cfs) (cfs)

(c

t - On 2Sn/t + On+1 On+1

fs) (cfs) (cfs)

0 0 30 0 01 30 90 302 60 1503 90 2104 120 2705 150 3306 180 3157 135 2258 90 1359 45 45

10 0 011 0 012 0 0


• 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

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0 0 30 0 01 30 90 30 52 60 1503 90 2104 120 2705 150 3306 180 3157 135 2258 90 1359 45 45

10 0 011 0 012 0 0


• To obtain the final column, 2Sn/t - On, two times the outflow issubtracted from 2Sn/t + On+1.

• In this example 30 - 2*5 = 20

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0 0 30 0 01 30 90 20 30 52 60 1503 90 2104 120 2705 150 3306 180 3157 135 2258 90 1359 45 45

10 0 011 0 012 0 0

Modified Puls Example2S n 2S n1

I I O On1 n n1 nt t • The same steps are repeated for• First 90 + 20 = 110.

the next line.

• From the graph, 110 equals an• Finally 110 - 2*18 = 74

outflow value of 18.

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0 0 30 0 01 30 90 20 30 52 60 150 74 110 183 90 2104 120 2705 150 3306 180 3157 135 2258 90 1359 45 45

10 0 011 0 012 0 0


•This process can then be repeated for the rest of the columns.•Now a list of the outflow values have beenproblem is complete.

calculated and the

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0 0 30 0 01 30 90 20 30 52 60 150 74 110 183 90 210 160 224 324 120 270 284 370 435 150 330 450 554 526 180 315 664 780 587 135 225 853 979 638 90 135 948 1078 659 45 45 953 1085 65

10 0 0 870 998 6411 0 0 746 870 6212 0 0 630 746 58

End

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Lecture 3: Flood Routing CEM001 Hydraulic Structures, Coastal and River Engineering Dr Md Rowshon...

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Transcript of Lecture 3: Flood Routing CEM001 Hydraulic Structures, Coastal and River Engineering Dr Md Rowshon...