Proceedings of the 19th IAHR-APD Congress 2014, Hanoi, Viet Nam
ISBN xxx-xxxx-xx-x
AN INITIATIVE TO IMPROVE DAM AND DOWNSTREAM COMMUNITY SAFETY IN VIETNAM
WILLIAM VEALE(1), MARK STIRLING(2), NGUYEN CANH THAI(3), PETER AMOS(1), PHAM HONG NGA(3) & TRAN KIM CHAU(3)
(1)
Damwatch Engineering Limited, Wellington, New Zealand,
bill.veale@damwatch.co.nz
(2) GNS
(3)
Science, Lower Hutt, New Zealand
m.stirling@gns.cri.nz
Water Resources University, Hanoi, Viet Nam
kimchau_hwru@wru.edu.vn
ABSTRACT
The Dam and Downstream Community Safety Initiative (DDCSI) is a three year pilot project with the objective of
improving dam safety in Viet Nam, by reducing loss of life and economic damage resulting from flooding related to dam
discharges (e.g. dam spillway releases or dam failure events). Outcomes of the DDCSI project will be a decision making
framework for identification of options to mitigate the risk of dam failure and spillway flood releases. The project
involves application of internationally recognized methods on a catchment-wide basis to identify and quantify risks to
dams and communities downstream of the dams. This includes: (i) quantifying the flood, seismic and landslide hazards
to a dam, (ii) application of potential failure modes analysis for dams, (iii) hydraulic modelling and mapping of dam
spillway release and dam break flood events, (iv) downstream consequence assessment, (v) community disaster risk
management capacity assessment and, (vi) identification of options to mitigate the risk of dam failure and spillway flood
releases. The methods used in the DDCSI project will be published in a series of guidance manuals that will be published
in English and Vietnamese at the conclusion of the project. These guidelines set out the methods required to undertake
the technical analysis of each part of the project, so that the DDCSI methodology can be applied to other dams and river
basins in Viet Nam. This paper describes the results from application of the DDCSI project methodology to one large dam
in the Hieu River catchment of Nghe An Province, Vietnam. Results have shown that promoting a river basin approach
provides the information necessary to assess mitigation measures to better protect the community.
Keywords: Dam safety, Potential Failure Modes, Hydraulic Modelling, Flood Mapping, Consequence Assessment.
1.
INTRODUCTION
Viet Nam has one of the largest dam systems in the world,
comprising more than 6,000 dams, with 750 of those
classified as medium and large dams (VNCOLD, 2012;
Dam, et al., 2012). With typography of mountainous
highlands in the west and densely populated coastal
plains, a large percentage of the Vietnamese population is
at risk from dam failure flooding (Silver, 1999). Past dam
failures have taken hundreds of lives and caused
substantial impacts on downstream property and the
environment. For example in 2013, the Ia Krel 2 dam
breached, releasing 4.5 Mm3 of water, damaging
downstream factories and inundating approximately 30
hectares of farmland. In 2012, the Dak Rong 3 dam
breached,
significantly
damaging
downstream
agricultural land.
Dam development has not considered the competing
interests of river basin communities resulting in poor
outcomes for at risk communities. In 2009, poor river
basin management during a storm event in the Ba River
led to over 100 deaths when hydro electric dams released
flood waters without warning. Damage to 5,600 houses,
the evacuation of 16,000 people, and a loss of 22 ships
were reported.
Addressing and improving dam safety has become a
priority for the Vietnamese government.
The Viet Nam – New Zealand Dam and Downstream
Community Safety Initiative (DDCSI) is a project that has
the objective of improving dam safety in Viet Nam, by
reducing loss of life and economic damage resulting from
extreme dam discharges (i.e. flood releases through the
dam spillway or dam failure events). Figure 1 provides an
overview of the DDCSI project methodology.
The DDCSI project uses internationally recognized
methods to identify and quantify natural hazards to dams
and the risk to people, property and environment
downstream of the dam (refer to Stages 1 to 3 in Figure 1).
These outputs are then used to identify improved
Community Based Disaster Response Management
(CBDRM) systems and dam safety improvements (refer to
Stage 4 in Figure 1). Implementing these improvements
will reduce the risk of extreme dam discharges to
downstream people, property and the environment.
The DDCSI project is being carried out over 2012 to 2015
by collaboration between the Water Resources University
(WRU) Hanoi, Viet Nam National Committee on Large
Dams (VNCOLD), Viet Nam Institute of Geophysics
(IGP), and GNS Science International Limited and
Damwatch Engineering Limited of New Zealand.
This paper describes the results from application of the
DDCSI project methodology to one large dam in the Hieu
River catchment of the Nghe An province, Viet Nam.
1

Analyze existing Community Disaster Risk
Management (CDRM) and provide recommendations
for improvements (e.g. early warning systems,
improved evacuation planning and community
resilience).
The DDCSI project methodology is published in a series of
guidance manuals that will be published in English and
Vietnamese at the conclusion of the project. These
guidelines set out the methods required to undertake the
technical analysis of each stage, so that the DDCSI project
methodology can be applied to other dams and river
basins in Viet Nam.
Figure 1. Schematic of the DDCSI project methodology
2.
BACKGROUND & PROJECT OUTPUTS
A number of issues with dams in Viet Nam have
previously been identified (VNCOLD, 2012; Dam, et al.,
2012). These include:






Vulnerability of some dams to extreme weather
events, especially floods and heavy rainfall. This is
likely to be worsened by the potential future effects of
climate change.
Sub-standard engineering design and construction
for some dams, particularly those constructed over 30
years ago.
Lack of resources to manage and maintain dams,
leading to sub-standard dam safety.
Absence of risk based assessment guidelines to
understand and address dam safety issues.
Lack of understanding by dam managers of the
potential hazards to downstream people and
property in the event of dam failure or a dam
spillway flood release.
Lack of information, early warning systems and
awareness for people living downstream of dams
regarding the potential hazards posed by dam(s)
upstream of their community.
The guidelines will also provide options for varying the
level of detail, time and cost necessary to conduct the
analysis so that it is appropriate to the dam or river basin
under investigation. For example, more detailed analysis
may be warranted for dams with potentially high
downstream hazard potential as the consequences of dam
failure may impact a relatively large downstream
population. Whereas low-hazard potential dams situated
upstream of sparsely populated areas may rely on less
detailed (e.g. desktop) methods of analysis. It is also
acknowledged that availability of existing data (such as
downstream topography, dam and reservoir information,
hydrological data, etc) may influence the level of detail of
the analysis.
3.
The DDCSI project methodology is carried out in four
stages, outlined in Figure 1, and briefly described as
follows:
1.
2.
3.
4.
The DDCSI project provides solutions to a number of the
problems identified above by providing a methodology
to:



Identify and quantity the risk posed by natural
hazards to a dam (i.e. extreme floods, landslides and
seismic events).
Undertake a safety evaluation of a dam using
Potential Failure Mode Analysis (PFMA) and
recommend dam safety improvements (e.g. dam
upgrades/structural improvements, monitoring and
surveillance, emergency preparedness planning).
Generate dam failure and dam spillway flood release
inundation maps and perform downstream
consequence assessment (i.e. identifying and
quantifying people and property potentially at risk
downstream of the dam).
OUTLINE OF THE DDCSI METHODOLOGY
Hazard Identification: Quantification of natural
hazards (flood, seismic and landslide) to a dam.
Assessment of Hazard Impacts to a Dam: Performing
Potential Failure Mode Analysis (PFMA) for a dam,
which is a site specific approach to understanding the
risk that hazards pose to a dam.
Downstream Impact Assessment: Simulation of the effect
of extreme dam discharges on downstream people,
property and the environment using computational
hydraulic modelling and hazard impact risk
assessment.
Disaster
Risk
Management
and
Dam Safety
Improvements: Providing improved disaster risk
management procedures including emergency
preparedness, warnings and evacuation procedures.
Mitigation of risk to the dam and downstream
communities by identifying improvements to dam
operation/management and physical works to dam
structure.
4.
APPLICATION OF DDCSI PROJECT
METHODOLOGY
4.1
Overview of Dam and Catchment
The DDCSI project methodology has been applied to the
Bản Mồng dam, located in the Nghe An province. The
dam is located on the Hieu River (Figure 2) and is
currently under construction. Two large dams, a 44 m
high concrete gravity dam and a 35 m high earth
embankment closure dam, will create a large reservoir
(235.5 Mm3 at full supply level) to provide storage for
hydro-electric power generation (42 MW), irrigation and
water supply.
2
The dam has potentially high downstream hazard
impacts, and therefore the analysis described in the
following sections is the most rigorous approach outlined
in the DDCSI guidance Manuals.
rainfall-runoff model. Meteorological data was sourced
from three sites in the study area and hydrological data at
two stream gauging sites on the Hieu River (as described
previously). The rainfall records also extended from
approximately 1960 to the present day (i.e. approximately
50 year records).
Figure 3 compares the predicted HEC-GeoHMS discharge
hydrograph with that observed at the Quy Chau gauging
station for the largest flood on record (October 2007,
Typhoon Lekima - approximately 1 in 50 AEP flood
event). This figure indicates good agreement between the
measured and observed data.
Figure 4 summarizes the peak flood discharge estimated
into the Ban Mong reservoir for the various extreme flood
events analyzed. Flood hydrographs were developed for
the flood events listed in Figure 1 based on the largest
recorded flood event at the upstream flow gauging station
(approximately a 1:50 AEP event).
Figure 2. Schematic of the DDCSI project methodology
4.2
Stage 1: Hazard Identification
4.2.1 Introduction
Floods, earthquakes and landslides are recognized
internationally as the primary natural hazards that can
endanger the safety of dams. The impact of these natural
hazards to the Bản Mồng dam and reservoir have been
quantified, as described in the following sections.
Quantifying these hazards in terms of magnitude and
frequency of occurrence, allows informed decisions to be
made on methods to mitigate such hazards, as discussed
further in Section 4.5.
Figure 3. Validation results for HEC-GeoRAS model
4.2.2 Flood Hazard
In Viet Nam flood hazard typically receives the most
focus as the country is particularly vulnerable to extreme
rainfall during the typhoon season.
Inflows for the Bản Mồng reservoir were estimated for
1:20, 1:50, 1:100, 1:200, 1:500, 1:1,000 and 1:10,000 Annual
Exceedance Probability (AEP) flood events by carrying
out flood frequency analysis on stream flow data at two
stream gauging sites on the Hieu River. A Log-Pearson
Type III distribution (as recommended by USGS, 1982)
was adopted to extrapolate low probability flood events.
The gauging sites were located approximately 30 km
upstream (Quy Chau) and 45 km downstream of the dam
(Nghia Khanh). The stream flow statistics were
transposed to the Bản Mồng dam site using a catchment
area relationship. The stream flow data records extend
from approximately 1960 to the present day (i.e.
approximately 50 year records).
Low frequency events, such as the 1:1,000 and 1:10,000
AEP floods, have been extrapolated from a 50 year flow
record and therefore contain significant uncertainty.
The Probable Maximum Precipitation (PMP) for the
catchment was derived using both the Herschfield
Statistical method (WMO, 2009) and the Maximization of
Storm method (Khai & Ruân, 2009). The latter method
was judged to provide the most reliable estimate of the
PMP and used for subsequent analysis.
The Probable Maximum Flood (PMF) was derived by
routing the PMP through a calibrated HEC-GeoHMS
Figure 4. Summary of peak reservoir inflows
4.2.3 Seismic Hazard
The purpose of seismic hazard assessment is to determine
the seismic loadings for dam structures at various AEPs.
For a large dam, such as Ban Mong, with potentially high
downstream hazard impacts, a seismic event with a
1:10,000 AEP is often considered as the Maximum Design
Earthquake (MDE) for seismic safety (ICOLD, 2010).
Existing estimates of seismic hazard in Viet Nam are
based on the historical record of earthquakes (a record
from 1137 AD to present with largest earthquake
magnitude Mw 6.8) and probabilistic seismic hazard
analysis (PSHA) methods. An existing seismic hazard
model, developed by the Institute of Geophysics (IGP)
uses the historical record of earthquakes as the sole input
to the model, and makes the standard assumption that
seismicity is distributed according to a Gutenberg-Richter
distribution.
3

Topographic maps: Regional topographic maps at
scales of 1:100,000 or 1:50,000 scale.
This information was used to assess the ground surface
morphology for large landslide-related landforms and
deposits. The main conclusions from a reconnaissance
assessment of large landslides with valley-blocking
potential in the study area of Hieu River catchment in
Nghe An province were:
1.
2.
3.
4.
Figure 5. Preliminary seismic hazard map for Hieu River
catchment and surrounding areas. The map shows the peak
ground acceleration (PGA) expected for a 10,000 year return
period on soft rock or stiff soil site conditions (McVerry et al.
2006). Fault sources are shown as red lines.
The current study has developed a PSH model with IGP
to determine seismic hazard for Nghe An province. The
new PSH model (Figure 5) includes the existing historical
earthquake catalogue, but also combines geological data
defining the location and activity of faults, along with a
new Global Positioning System (GPS) strain rate model
developed by the Global Earthquake Model project
(GEM, 2013). These three datasets have strengths and
weaknesses in terms of spatial coverage, temporal
coverage, and data uncertainties, but if used together in a
multidisciplinary model they can produce a more
complete source model than the existing seismic hazard
model.
4.2.4 Landslide Hazard
The area is underlain by “hard rock” geology, often
with steep slopes and deep weathering.
Few large landslides were recognized in the area.
The main areas of landslides were in the western
high country where alluvial basins are also present.
Landslide hazards, with reservoir blocking potential,
at the Ban Mong reservoir are not a significant issue,
especially where Quaternary terraces are present.
Smaller landslides, while not blocking reservoirs can
disrupt dam operation and affect infrastructure and
communities. Monitoring of landslide hazards, post dam
construction, is therefore recommended.
4.3
Stage 2: Potential Failure Modes Analysis
Potential Failure Modes Analysis (PFMA) is a tool that
informs dam designers of the wide range of potentially
catastrophic means that the dam could fail. The form and
nature of the resulting breach is an important parameter
in the consequential flood that discharges from the dam.
The PFMA also helps identify priorities for rehabilitation
as well as improvements to operation, maintenance and
surveillance of a dam. This is accomplished by looking
systematically at all of the potential ways a dam could fail
and the likelihood that this failure could happen. PFMA is
adopted internationally as a dam safety evaluation tool
(see e.g. FERC, 2005; EA, 2013).
PFMA methodology is summarized in FERC (2005) and
involves gathering and reviewing all relevant information
to the dam and reservoir; site inspection; and a workshop
with a facilitated team of experts to identify, evaluate and
screen potential failure modes for the dam.
Large landslides into a reservoir, typically with volumes
greater than 10 Mm3, can generate a seiche which may
endanger the dam due to wave run-up or overtopping of
the dam crest. Additionally large landslides in tributary
catchments upstream of the dam can form a natural
landslide dam. Because of the unconsolidated nature of
landslide debris and absence of controlled spillway,
landslide dams frequently fail catastrophically and can
also endanger dams constructed downstream.
Two PFMA workshops held at the Water Resources
University, Hanoi drew on information assembled which
included; data and information on natural hazards (refer
to Section 4.2), dam design and operation reports and
construction drawings. Workshop attendees included
dam experts from VNCOLD, Vietnamese dam design
consultants, WRU, Damwatch Engineering and GNS
Science.
An investigation into the likelihood of large reservoir
blocking landslides upstream of the Bản Mồng dam was
based on examination of geomorphic (landscape) features.
The main data sources were:
The failure modes are used to identify breach outflows
(Section 4.4) and help to identify potential risk reduction
actions (as described in Section 4.5), monitoring
enhancements, and additional data or analyses that would
be helpful in better defining the risks.



Vertical aerial photography: Supplied by the
Department of Mapping and Surveying of Ministry of
the Natural Resources and Environmental
Engineering (MONRE). Ground scales were
approximately 1:35,000.
Satellite imagery: Supplied by GoogleEarth and USGS
Landsat.
Geological maps: Regional geological map sheets at a
scale of 1:200,000 published by the General
Department of Geology and Minerals of Viet Nam
(GDGMV) of MONRE.
4.4
Stage 3: Downstream Impact Assessment
Flood hazard assessment and consequence analysis is a
primary element of dam safety management and is used
for a wide variety of purposes, including:




Classifying hazard potential of dams
Developing an Emergency Action Plan (EAP)
Emergency response planning
Hazard mitigation planning
4

Communicating the hazard potential of dams to those
outside the industry
A detailed flood hazard assessment and consequence
analysis was carried out for Ban Mong dam.
Consideration was given to both the hazard and
consequences of spillway flood releases as well as
hypothetical breach of the dam. The process is outlined as
follows:
1.
Evaluation of the dam spillway outflow hydrographs:
Hydraulic modelling with HEC-RAS (USACE, 2013)
to route the inflow design floods for the Ban Mong
reservoir (refer to Section 4.2.2) through the reservoir
and spillway to determine the spillway outflow for
various extreme flood events. Spillway rating curves
were developed based on gate operation rules
developed to pass extreme flood events.
2.
Evaluation of dam break outflow hydrographs:
Estimation of hypothetical dam breach outflow
hydrographs for the Ban Mong dam based on current
international methodologies (e.g. FEMA, 2013). For
the Ban Mong earthen embankment closure dam
breach outflow hydrographs were developed by (i)
estimating breach geometry and development time
from using empirical equations derived from
regression analysis of historic dam failures (e.g.
Froehlich, 1995a and 2008; Xu & Xhang, 2009). These
breach parameters are used as inputs into a
parametric breach model, which models the outflow
through the breach over time due to erosion of the
embankment by the breach outflow. Sensitivity
testing to key parameters was also carried out.
3.
Routing of the dam spillway outflow and dam break
hydrographs through the downstream catchment:
Prediction of the arrival, depth and extent of flooding
resulting from a dam break flood wave or spillway
release with a HEC-RAS computational hydraulic
model. The hydraulic model extended 130 km
downstream of the dam site to the confluence with
the Ca River (refer to Figure 3). Cross-sectional data
for the model was based on a river cross-section
survey of the Hieu and Con Rivers in 2007. The
model was validated against stage-discharge rating
curves at the Nghe Khan gauging station,
approximately 40 km downstream of the dam, for
two historic flood events – refer to Figure 6.
Sensitivity testing to key model parameters was also
carried out.
4.
Flood inundation mapping:
High-quality flood inundation maps were generated
with ArcGIS from the results of hydraulic modelling
and a DEM for the catchment, developed from
1:10,000 scale topographic map contours, spaced at
2.5 to 5.0 m vertical intervals. A sample of the flood
inundation map is provided in Figure 7. For dam
break scenarios, time to initial and peak flood arrival
is plotted on the flood maps.
Figure 6. Comparison of measured and predicted discharge on
the Hieu River at the Nghe Khan gauging station for the October
2007 flood event
Figure 7. Sample flood inundation map
5.
Downstream consequence assessment:
The impact to people, houses, infrastructure and
agricultural land downstream of Ban Mong dam was
evaluated using RiskScape software, developed by
GNS Science (RiskScape, 2014). This software is a GIS
based package that combines inputs flood hazard,
assets in the flood hazard area and the resilience of
buildings and infrastructure to withstand the flood
hazard to determine the overall impact of the flood –
refer to Figure 8. Flood hazard layers for the model
were developed from hydraulic modelling described
previously. An asset database was gathered from
inspection of land use maps and field inspections to
determine the buildings and infrastructure in the
flood hazard area downstream of the dam. Damage
and fragility functions that describe the resilience of
buildings and infrastructure as a function of flood
hazard were developed specifically for buildings and
infrastructure in the catchment based on data derived
from site inspection. RiskScape was used to
determine the potential losses (casualties,
displacement, costs of repair and rebuild) for the Ban
Mong dam spillway release and break flood events.
5
improvements that can be made to the dam. These may
include:




Figure 8. Overview of the RiskScape modelling process
4.4.1 Summary of Outputs from Stage 1 to 3
The following lists the main outputs from Stage 1 to 3 of
the DDCSI project methodology.



Stage 1: A quantitative understanding of the natural
hazards (floods, seismic and landslides) that have the
potential to endanger the dam.
Stage 2: An understanding, based on expert evidence,
of the site specific vulnerabilities to the dam which
may not otherwise have been foreseen from
traditional design approaches.
Stage 3: Knowledge of the location of people,
infrastructure and agricultural land that could be
impacted in both dam spillway release and dam
break flood events through flood inundation maps. A
detailed breakdown of the likely casualties,
displacement and economic costs of extreme flood
events with RiskScape hazard impact and risk
assessment modelling software.




5.
This paper has described the results from application of
the DDCSI project methodology to one large dam in the
Hieu River catchment of the Nghe An province, Viet Nam.
Current outputs from the project include:


4.5

4.5.1 Introduction
This stage of the DDCSI project is in progress at the time
of writing and is intended to be completed in late 2014.
However the following sections outline the anticipated
direction for this work and some preliminary results.
4.5.2 Community Disaster Risk Management
The intention of the project is that the Province is able to
instigate a warning system that includes detection of damrelated flood events through to correct action by dam
owners and the community to reduce loss and casualties.
For the Hieu River catchment, this will be achieved by
firstly assessing the current state of CDRM downstream of
the Ban Mong dam. With knowledge of population,
agriculture and structures at risk from the results of Stage
1 to 3, the project team will work collectively with
Provincial representatives to improve existing CDRM
systems and downstream community resilience.
This will involve collaboration between downstream
communities, dam operators and authorities charged with
alerting the public during flood events. This will include
undertaking drills or exercises to test communications and
response and update plans if necessary.
4.5.3 Structural and Dam Safety Improvements
Using accurate knowledge of the dam, downstream flood
path and vulnerable communities and infrastructure it is
possible to determine the most cost effective
CONCLUSIONS
Addressing and improving dam safety has become a
priority for the Vietnamese government. The Viet Nam –
New Zealand Dam and Downstream Community Safety
Initiative (DDCSI) is a project that has the objective of
improving dam safety in Viet Nam, by reducing loss of
life and economic damage resulting from extreme dam
discharges (i.e. flood releases through the dam spillway or
dam failure events).
These outputs are used to identify and coordinate
CBDRM and dam safety improvements as outlined in the
following sections.
Stage 4: Community Based DRM and Structural and
Dam Safety Improvements
Dam structural improvements
Upstream flood warning systems
Dam operational improvements such as pre-flood
reservoir drawdown.
Dam communication improvements such as warnings
of flood release.
Multiple reservoir operation rules
Downstream protective measures (e.g. dykes)
Improved evacuation escape routes
Community resilience measures
Identification of flood, seismic and landslide hazards
to the dam
Potential failure modes analysis for the dam has
identified vulnerabilities not otherwise foreseen from
traditional design standards
Downstream impact assessment has provided flood
inundation maps for dam break and dam spillway
flood events. The impact of these flood events on
people, houses, infrastructure and agricultural land
downstream has been identified using the loss
modelling tool RiskScape.
The next phase of the project will identify community
disaster risk management (CDRM) improvements that can
be made based on informed knowledge of the risks and
impacts of dam failure and dam spillway floods. In
addition, improvements to the dam and operation will be
identified. Implementing these improvements will
significantly reduce the risk of the dam to downstream
people, property and the environment.
Following this pilot study, the objective is to see the
DDCSI project methodology implemented at other
dammed catchments throughout Viet Nam. The
framework outlined in this paper will provide an
internationally benchmarked guideline that can be
practically applied to achieve appropriate dam safety in
Viet Nam.
ACKNOWLEDGMENTS
This study has been carried out within the framework of
Project "The Dam and Downstream Community Safety
Initiative (DDCSI)". The project is sponsored by the New
Zealand Government and approved by the Vietnamese
Ministry of Agriculture and Rural Development (MARD).
The project is a partnership between the Water Resources
University (WRU) of Viet Nam, Damwatch Engineering
and GNS Science of New Zealand, supported by the
Vietnamese Committee on Large Dams (VNCOLD). We
6
have also collaborated closely with Viet Nam Institute of
Geophysics (IGP) in the hazard identification stage of the
project.
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