1. 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
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2. 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
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3. 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
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4. 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
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5. 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
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6. 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
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7. 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
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8. Hydrologic routing techniques involve the balancingof
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
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9. Bukit Merah Reservoir, Malaysia9
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10. Lake Livingston, USA 10
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11. Lake Conroe, USA 11
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12. 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.
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13. Detention Pond, AUSTIN, TX13
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14. 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
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15. Hydrologic Routing Hydrograph at point A Hydrograph at point B Theis
attenuated
due to
storage characteristics of the stream reach.
Assumption: no seepage, leakage, evaporation, or inflow from the sides. 15
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16. Comparisons: River vs. Reservoir Routing
River Reach
Level
pool
reservoir 16
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17. 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
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18. Inflow Characteristics 18
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19. Inflow-Storage-Outflow Characteristics19
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20. Inflow-Storage-Outflow Characteristics20
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21. Inflow-Outflow Characteristics 21
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22. Storage-Water Level Characteristics 22
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23. Outflow Determination 23
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24. 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
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25. Reservoir
Routing 25
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26. Required Information • Inflow hydrograph Outflow hydrograph Surcharge
Storage vs
Water
Level
graph 26
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27. 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
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28. 28 School of Computing, Information Technology & Engineering
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29. (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
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30. 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
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31. 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
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32. 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
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33. 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
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34. 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
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35. Modified Puls Example 35 • 2S/t + O curve:
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36. 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
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37. 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
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38. 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
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39. 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
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40. 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
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41. 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
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42. 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
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43. 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
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44. 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
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