1.dam break modelling of phouphong dam_pradyumna machhkhand

Confidential Restricted Public Internal A company of

10 December 2016

Dam Break Modelling of Phouphong Dam, Lao PDR and Flood Inundation Mapping of Post Dam Break Scenario

Confidential Restricted Public Internal A company of

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

10 December 2016

Dam Break Modelling of Phouphong Dam, Lao PDR and Flood Inundation Mapping of Post Dam Break Scenario

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: [email protected]

mailto:[email protected]

Chapter 1Introduction- Project location

- Project background

Chapter 2

Data organization- River geometry

- Storage area

Chapter 3

Model set up- Convention and calibration

- Initial and boundary conditions

- Critical condition for dam break modelling

- Breach parameters

Chapter 4Results and discussions- Partial breach scenario

- Full breach scenario

OUTLINES OF THE PRESENTATION

10/12/2016 DAM BREAK MODELLING OF PHOUPHONG DAM, LAO PDR AND FLOOD INUNDATION MAPPING OF POST DAM BREAK SCENARIO 3

Chapter 5 Conclusions

OUTLINES OF THE PRESENTATION


Introduction


PROJECT LOCATION


Project

Location

Phouphong Dam

Phouphong

Reservoir

Particulars Name/Coordinates

Country Lao PDR

Stream Phouphong/Katan

Latitude 15° 08' 30"

Longitude 106° 06' 10"

PROJECT LOCATION


Phouphong Dam is an integral structure of the

Namphak Hydropower Project (Namphak HPP)

Located at the south-western corner of Bolaven

Plateau of Laos PDR

Namphak HPP is planned to collect the runoff from

a number of streams on the plateau that flow

generally north-west and south-west and convey this

via two diversions to the Phouphong Reservoir

Run-of-river scheme with generating facility sited

on the banks of Houay (River) Namphak at the

base of the plateau escarpment and has a total

installed capacity of 150MW

PROJECT BACKGROUND


Upstream view of Phouphong Dam

Phouphong River : a tributary of Bangliang

River

Phouphong Dam in the proximity of the

confluence

PROJECT BACKGROUND


Ray diagram of Phouphong River network

Particulars Values/Type Unit

Dam Type Rockfill --

Crest Elevation 914.5 m a.s.l.

Stream Bed (Thalweg) Level 863 m a.s.l.

Embankment width at crest 6 m

Embankment length at crest 230.668 m

Upstream slope 2:1 [H:V]

Downstream slope 2:1 [H:V]

CHARACTERISTICS OF PHOUPHONG DAM


CHARACTERISTICS OF PHOUPHONG DAM


Particulars Values Unit

Full Supply Level/FSL 909 m a.s.l.

Minimum Drawdown Level/MDL 905 m a.s.l.

Maximum Water Level (PMF Level) 912.5 m a.s.l.

Total Storage Volume 22.66 MCM

Live Storage Volume 12.36 MCM

Dead Storage Volume 10.30 MCM

RESERVOIR CHARACTERISTICS


Modelling theory


Conservation of mass (continuity):

...(1)

Conservation of momentum equation:

...(2)

MODELLING THEORYPhysical laws governing the flow of water


01

q

x

Q

t

A

0

fS

x

zgA

x

QV

t

Q

where,

MODELLING APPROACHFlowchart of dam break analysis for the project

10/12/2016 PRESENTATION TITLE ( FOOTER CAN BE PERSONALIZED AS FOLLOW: INSERT / HEADER AND FOOTER") 15

Boundary Conditions for Steady State Model

Input : River Geometry, Reservoir Geometry, Inline Structure (Dam) et al

Model Calibrated ?

Initial and Boundary Conditions for Unsteady State Model

Run Unsteady State Model

Analyze and Prepare Flood Inundation Map

Run Steady State Model

No

Define Breach Parameters of Dam

Yes

Data organization


Chainage of River

Cross-sections (m)

River Remarks

0.00 Phouphong Phouphong Dam at Ch 0.00

0.00 to 4250.00 Phouphong Cross-sections interval 250m to 500m.

Confluence of Phouphong River and

Bangliang River at Ch 4250.00

4250.00 to 46391.00 Bangliang Cross-sections interval 250m to 500m.

Confluence of Phouphong River and

Bangliang River at Ch 4250.00

RIVER GEOMETRYCross-sections of Phouphong River and Bangliang Rivers


Storage-area curve of reservoir

PMF hydrograph at Phouphong Dam site

PMF hydrograph of Bangliang River at

confluence

DATA FROM HYDROLOGICAL STUDYStorage-area curve of reservoir and PMF hydrohraphs


0 10000 20000 30000 40000 50000 60000 70000860

870

880

890

900

910

920

Volume (1000 m3)

Ele

vatio

n (

m)

Legend

Vol-Elev

0.0 0.2 0.4 0.6 0.8 1.00

100

200

300

400

500

600

700

SA: PhouphongReserv

Simulation Time (days) La

tera

l Inf

low

(m

3/s)

Legend

Lateral Inflow

0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800

1000

1200

1400

River: Phouphong R iver Reach: Upper RS: 170.000 to 168.75*

Simulation Time (days)

La

tera

l In

flow

(m

3/s

)

Legend

Lateral Inflow

Model setup


Dam break scenarios at the dam are hypothesized at PMF event as well as at stage flowing over

dam conditions.

Bangliang at confluence: additional boundary condition

PMF events at Phouphong Dam and Bangliang River at confluence are simultaneous.

Failure of Phouphong Dam is due to overtopping.

Time series data chosen for hydrographs starts from 1 June 2014 1200hours to 2 June 2014

1100hours, which is merely relative of flood event and universally applied for the simulation.

CONVENTION ADOPTEDAssumptions


MODELLIING SOFTWAREHEC-RAS


Phouphong

Reservoir

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.

Phouphong

Reservoir

Model is calibrated by using the stage-discharge data at the confluence of Bangliang River and

Phouphong River

Global parameter Manning’s n = 0.04

CALIBRATION


Model No.

Flood

routing

event

description

Initial condition Boundary condition

Stage

Elevation

Upstream

(m)

Reservoir

Min

Elevation

(m)

Flow

(m3/sec)

Upstream

End

Downstream

End

Model 1

Dam break at

PMF or at

Overtopping

Stage

909 909 676

PMF

hydrographs,

Elevation-

Storage

Curve

Normal

depth

INITIAL AND BOUNDARY CONDITIONS


(PMF) is impinged when reservoir level is at FRL

(PMF) is impinged when reservoir level is greater than FRL

Impinging a PMF hydrograph at a level higher than FRL has been selected based on optimization

and the dam breach has been initiated when the dam is overtopped.

CRITICAL CONDITIONS


Case No Breach

level (m)

Breach

width (m)

Breach

slope

Breach

time(hr)

Remarks

Initial Final Initial Final

Case 1 914.5 897.3 120 120 0 0.2

Breach to start from EL 914.5 in the

proximity of left overbank down to

EL 897.3

Case 2 914.5 863 154.5 154.5 0 0.2

Breach to start from EL 914.5 in the

proximity of left overbank down to

EL 863

BREACH PARAMETERS


Results of dam break cases


RESULTS Case1: Partial breach of Phouphong Dam


-400 -300 -200 -100 0 100 200 300 400860

880

900

920

940

960

980

1000

Dam Break Model_Phouphong Dam Plan: DB Unsteady Phouphong Dam

Station (m)

Ele

vation

(m

)

Legend

EG 01JUN2014 1400

WS 01JUN2014 1400

Ground

Ineff

Bank Sta

.04

1200 1400 1600 1800 2000 2200 2400 0200 0400 0600 0800 100001Jun2014 02Jun2014

0

1000

2000

3000

4000

5000

6000

7000

Time

FL

OW

(M

3/S

)

Legend

188.000

1.000

RESULTS Case 2: Full breach of Phouphong Dam


-400 -200 0 200 400860

880

900

920

940

960

980

1000

Dam Break Model_Phouphong Dam Plan: DB Unsteady Phouphong Dam

Station (m)

Ele

vation

(m

)

Legend

EG 01JUN2014 1400

WS 01JUN2014 1400

Ground

Ineff

Bank Sta

.04

1200 1400 1600 1800 2000 2200 2400 0200 0400 0600 0800 100001Jun2014 02Jun2014

0

500

1000

1500

2000

Time

FL

OW

(M

3/S

)

Legend

188.000

1.000

RESULTS Flood inundation map for full breach scenario


The dam break analysis predicts the flood inundation plan, which is vital in resource management

and catastrophe management.

Flood warning system - ESSENTIAL

ADVISABLE - Discourage the inhabitation encroachment towards Phouphong River and Bangliang

River so that mitigation measures against post dam break flood on the downstream reaches of the

project are cost effective.

The modeled breach levels and progressions considered in the model are hypothetical. A deep

prognosis of breach progression, however, encourages further research on the topic.

CONCLUSIONS


QUESTIONS


1.dam break modelling of phouphong dam_pradyumna machhkhand

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