2.FLOOD RISK ANALYSIS _PRADYUMNA MACHHKHAND - Copy

Confidential Restricted Public Internal A company of
10 December 2016
Flood Risk Analysis
by Hydrologic
Routing and
Hydraulic Modelling:
A Comparative Study

Confidential Restricted Public Internal A company of
10/12/2016 FLOOD RISK ANALYSIS BY HYDROLOGIC ROUTING AND HYDRAULIC MODELLING: A COMPARATIVE STUDY
10 December 2016
Flood Risk Analysis by Hydrologic
Routing and Hydraulic Modelling: A
Comparative Study
Author and Presenter : Pradyumna Machhkhand
Deputy General Manager (Hydropower & Water Resources)| Lahmeyer International (India) Pvt. Ltd. (A company of
Tractebel Engie) | Gurgaon-122002| Tel. +91 124 4712260 Extn. 574| Mob: +919999326876 | Fax: +91 124 6697601|
Email: pmachhkhand@lahmeyer.in

Chapter 1
Chapter 2
Chapter 3
Chapter 4
OUTLINES OF THE PRESENTATION
10/12/2016 FLOOD RISK ANALYSIS BY HYDROLOGIC ROUTING AND HYDRAULIC MODELLING: A COMPARATIVE STUDY 3
Introduction
- Project location
- Overview of probable maximum flood (PMF)
- Scope of study
Determination of PMF hydrographs
- At Dulhasti HEP
- At Drangdhuran HEP
Hydrologic routing
- Muskingum’s method
- Routing parameters
- Routing co-efficients
Hydraulic modelling
- Model setup
• River geometry, calibration, initial condition and boundary conditions

Chapter 5
Results
- Muskingum’s method
- Hydraulic modelling
- Comparative study
Chapter 6
Conclusions
OUTLINES OF THE PRESENTATION

Introduction
10/12/2016 DAM BREAK MODELLING OF PHOUPHONG DAM, LAO PDR AND FLOOD INUNDATION MAPPING OF POST DAM BREAK SCENARIO 5

PROJECT LOCATION

PROJECT LOCATION
Particulars Name/Coordinates
Country India
Stream/River Chenab River
Latitude 33° 10' 43”N
Longitude 75° 48' 26”E

CATCHMENT AREA
Ratle catchment area =14209 Sq Km

 Hydro-meteorological approach
 PMP (Source: Indian Meteorological Department (IMD)
— Estimated PMF at Ratle > PMF of Baglihar, which is located on the downstream; Unrealistic.
 PMP of Baglihar
— Estimated PMF at Ratle = 11100 m3/s; Unconcluded.
— To be validated; How??!
 PMFs of upstream HEPs to be routed between upstream HEPs and Ratle.
 For accuracy, both hydrologic routing and hydraulic modelling are to be compared.
OVERVIEW OF PROBABLE MAXIMUM PRECIPITATION (PMP)
AND PROBABLE MAXIMUM FLOOD (PMF) VALUES AT RATLE

 PMF hydrographs determination of upstream projects, Dulhasti HEP and Drangdhuran HEP;
 hydrologic flood routing by Muskingum method;
 hydraulic modelling of river reaches initiating at the locations of Dulhasti HEP and Drangdhuran
HEPs through Ratle on the downstream with an objective to find out the outflow at Ratle Dam site;
and
 comparative study.
SCOPE OF STUDY

Determination of PMF
hydrographs

 Catchment delineations
 Dulhasti Catchment:
Hydro-meteorological,
Snyder’s unit hydrograph
 Drangdhuran Catchment:
Hydro-meteorological,
Snyder’s unit hydrograph
Approaches for PMF
estimation
Unit hydrograph:
Dulhasti HEP
Unit hydrograph:
Drangdhuran HEP
APPROACHES
0
50
100
150
200
250
300
350
0 10 20 30 40 50 60Discharge(m3/s/cm)
Time (Hrs)
Unit Hydrograph by Snyder'sMethod: Dulhasti HEP
Actual
Ordinates
Adjusted
Ordinates
0
50
100
150
200
250
300
0 5 10 15 20 25 30 35
Discharge(m3/s/cm)
Time (Hrs)
UnitHydrograph by Snyder'sMethod:DrangdhuranHEP
Actual
Ordinates
Adjusted
Ordinates

DERIVED PMF HYDROGRAPHS
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0 10 20 30 40 50 60 70 80 90 100
Discharge[m3/s]
Time [hour]
PMF Hydrpgraph : Dulhasti HEP
Flood (m3/s)
0
1000
2000
3000
4000
5000
0 10 20 30 40 50 60 70 80
Discharge[m3/s]
Time [hour]
PMF Hydrograph : Drangdhuran HEP
Flood (m3/s)
PMF hydrograph: Dulhasti HEP PMF hydrograph: Drangdhuran HEP

Hydrologic routing

Routing
Parameters
Value Unit Remarks
x 0.2 -- weighing factor;
0<x<0.5
K 1.0 hour travel time of flood
wave between
channel reach
Δt 1.0 hour duration
MUSKINGUM ROUTING PARAMETERS

Routing
Co-efficients
Equation Value of
Co-
efficients
Remarks
C0 C0={(Δt/K)-2x}/{2(1-x)+(Δt/K)} 0.231
C0+C1+C2 =1; OkayC1 C1={(Δt/K)+2x}/{2(1-x)+(Δt/K)} 0.538
C2 C2={2(1-x)-(Δt/K)}/{2(1-x)+(Δt/K)} 0.231
MUSKINGUM ROUTING CO-EFFICIENTS

 Arrange the flood ordinates of both the stations,
Dulhasti and Drangdhuran in the order of time;
 Start time = 0 hr;
 For a corresponding duration, sum up the flood
ordinates of both Dulhasti and Drangdhuran to
from a combined hydrograph as inflow; and
 Apply Muskingum method to route the combined
hydrograph as inflow to obtain outflow
hydrograph at Ratle on the downstream.
HYDROLOGIC ROUTING STEPS
Dulhasti HEP
DRANGDHURAN
HEP
Ratle HEP
Marusudar River
ChenabRiver
Ray diagram of river network system

Hydraulic modelling

 Conservation of mass (continuity):
...(1)
 Conservation of momentum equation:
...(2)
MODELLING THEORY
Physical laws governing the flow of water
01 





q
x
Q
t
A
0














fS
x
z
gA
x
QV
t
Q
where,

 The software, HEC-RAS is designed to perform
one-dimensional hydraulic computations
numerically for a full network of natural and
constructed channels.
 The HEC-RAS model comprises two major
components; steady flow and unsteady flow.
 HEC-RAS software can model inline structures,
such as dams, weirs, spillways, and structures
with sluice gates, radial gates, and overflow
gates.
MODELLIING SOFTWARE
HEC-RAS

MODELLING SCHEME

RIVER GEOMETRY
Cross-sections of Phouphong River and Bangliang Rivers
Chainage of River
Cross-sections (m)
River Remarks
0.00 to 10400.00 Chenab Cross-sections interval 100m. Cross-sections
interval 100m.
10400.00 to 24700.00 Chenab Cross-sections interval 100m. Confluence at Ch
10500.00 m
0.00 to 29000.00 Marusudar Cross-sections interval 100m. Confluence
at Ch 29000.00 m

 The available historical inflow data at Dulhasti, Drangdhuran, and Premnagar (Gauge and discharge
station located on the downstream of Ratle) have been utilized to calibrate the model. The
roughness parameter (Manning’s n) has been found to be sensitive in the model and therefore, with
a number of iterations, the optimum value n = 0.04 has been observed to exhibit less errors while
comparing the modeled outflow hydrograph and the observed hydrograph at Premnagar.
 Manning’s n =0.04 has been applied globally in the model.
CALIBRATION

 Dulhasti and Drangdhuran HEPs being in the proximity, the PMF events at these catchments are
simultaneous.
ASSUMPTIONS

Station ID Station
name
Initial
condition
Upstream
boundary
condition
Downstream
boundary
condition
XS ID – 72 Dulhasti Base flow PMF
hydrograph
-
XS ID – 6.7 Drangdhuran Base flow PMF
hydrograph
-
XS ID – 1 Ratle - - Normal depth
INITIAL AND BOUNDARY CONDITIONS

Results

HYDROLOGIC ROUTING RESULTS
2000
4000
6000
8000
10000
12000
0 2 4 6 8 101214161820222426283032343638404244464850525456586062646668707274767880828486889092949698100
Discharge(m3/s)
Duration (hours)
Muskingum Hydrologic Routing
Combined Inflow from
Drangdhuran and
Dulhasti
Outflow at Ratle

HYDROLOGIC ROUTING RESULTS
1200 2400 1200 2400 1200 2400 1200
19Sep2011 20Sep2011 21Sep2011 22Sep2011
0
2000
4000
6000
8000
10000
12000
Time
FLOW(M3/S)
Legend
1
72
6.7
Ratle
Dulhasti
Drangdhuran

 The outflow peak flood from the method of Muskingum routing is 10562 m3/s, whereas from
hydraulic modelling; the outflow peak flood is 10589 m3/s.
 The results indicate that models have least difference in terms of peak flow magnitude validating
the methods to be appropriate and good measures to check if the results are consistent.
 The roots of the PMF hydrographs are same for both the tested methods.
 For project planning, the study also exhibits the performance of the models developed.
COMPARATIVE STUDY

 The intent of the paper is to describe the methods, hydrologic routing and hydraulic modelling, as an
important part of study in order to establish consistency in the project flood estimation.
 The comparison of both the methods is as equally important as the estimation of flood itself. The
hydrologic routing exercise only includes the fluvial storage losses and gain processes, whereas the
hydraulic modelling takes all possible losses, such as friction loss, head loss et al into
considerations. Therefore, one method may be graded better than the other. However, both the
methods, in principle, are assumptions based. The important is to evaluate the assumptions based
on comparative judgments so that the qualities of results remain not negotiable. The results from the
applied models validate the same.
 In the project planning of the study, due to availability of peak flood data in the vicinity of the project
site it has been possible to apply other methods and to do numerous comparisons additionally.
However, the availability of data is often scarce. Therefore, in such scenarios, the best possible
comparisons may be made from the methods discussed in this paper. The extent of application may
be wide and it blossoms the possibility of future research.
CONCLUSIONS

QUESTIONS

2.FLOOD RISK ANALYSIS _PRADYUMNA MACHHKHAND - Copy

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