Nghiên cứu chế độ vận hành tích nước trong thời kỳ mùa lũ cho hệ thống hồ chứa bậc thang Hòa Bình và Sơn La Tiếng Anh

MINISTRY OF EDUCATION
MINISTRY OF AGRICULTURE
AND TRAINING
AND RURAL DEVELOPMENT
THUY LOI UNIVERSITY

VU THI MINH HUE

RESEARCH ON WATER ACCUMULATION
OPERATING MODE IN FLOOD SEASON FOR HOA
BINH AND SON LA TERRACED HYDROELECTRIC
RESERVOIRS

DISSERTATION ABSTRACT
Specialization: Water resource development
Code:

62 44 92 01

HA NOI, 2017


The project is completed at Thuy Loi University

Principle advisor 1: Associate Professor Pham Thi Huong Lan
Principle advisor 2: Professor Ha Van Khoi

Review 01: Associate Professor Nguyen Tien Giang
Review 02: Associate Professor Duong Van Tien
Review 03: Associate Professor Vu Minh Cat

The thesis will be defended in front of Thesis Evaluation Council at
…………………………………………………………………………….
At...……… on …….….…. 2017

The Thesis can be studied at libraries below:
-

National Library
Water Resources University library


PREFACE
1. The urgency of subject
Currently there are many multi-functional water reservoir projects on the
upstream area of Da river. They contribute a large proportion of hydroelectric
power output, provide water for economic development in Red river delta and
help regulate downstream flood control with extremely high efficiency. Son La
and Hoa Binh reservoirs are two lakes with highest capacity for downstream
flood control (7 billion m3) which are designed to be below normal tide rising
level. Therefore, there are severe conflicts between anti-flood mission and
electricity generation, water provision.
Inter-reservoir operation regulations on Red river basin issued on Decision no
1622/QĐ-TTg on September 17th, 2015 formed a official operation frame.
However, actual operation must be based on predictions on the process of water
running into the reservoirs. Nonetheless, two practical questions for researches
to solve are:
-

Is it allowed that the mentioned above reservoirs can accumulate water
in the beginning of flood season? If so, how are water accumulation

regulations formed to ensure downstream anti-flood safety?

-

According to the regulations, in late flood phase the reservoirs must
accumulate water up to normal water rising level. However, when
expected big floods occur, how can reservoirs function in order to
decrease downstream flood and ensure construction safety at the same
time?

Therefore, the research student chose the subject “Research on water
accumulation operating mode in flood season for Hoa Binh and Son La
terraced hydroelectric reservoirs”, hoping to study scientific foundation on
water accumulation operating mode in Hoa Binh and Son La reservoirs to
increase water accumulation efficiency for electricity generation and water
provision, ensure construction safety as well as downstream flood prevention.
1


2. Mission of thesis
-

Research on scientific and practical basis to identify water
accumulation operating mode in flood season, ensure safety in full
water accumulation for reservoirs, increase water provision and
electricity efficiency and at the same time assure safety for downstream
flood and construction flood in Hoa Binh and Son La reservoirs.

-

Research on operating mode of downstream flood restriction in late
flood period when Son La and Hoa Binh reservoirs are allowed to
accumulate full water, minimize negative impact on downstream area
in case unexpected big floods occur.

3. Object and scope of the study
Scope of the research: operation and regulation on water accumulation and
flood prevention for terraced water reservoir system of Hoa Binh and Son La in
flood season.
Object of the research: downstream flood prevention regulation is considered in
the inter-reservoir system which comprises of 4 reservoirs - Hoa Binh, Son La,
Tuyen Quang and Thac Ba. However, research on water accumulation
operating mode as the topic object focuses on Son La and Hoa Binh reservoirs
on Da river.
4. Research method
Methods used in the research are (i) Inheritance method; (ii) Integrated analysis
method; (iii) Mathematic model method.
5. New contribution of the thesis
-

Propose early conditional water accumulation mode for Hoa Binh and
Son La reservoirs. From that foundation, propose scientific basis to
identify above water level limit of water accumulation process of Son
La reservoirs in limited water accumulation period, to ensure efficient

2


water accumulation as well as downstream and construction flood
prevention safety.

-

Propose regulation operation mode to prevent flood in downstream
region and coping methods in case unexpected floods occur in full
reservoir water accumulation at the end of flood period.

6. Structure of the thesis
The thesis consists of 118 pages, 30 tables, 40 figures and 67 reference
materials. Aside from the introduction and conclusion, the thesis has 3 chapters:
Chapter 1: Overview of researches on multi-functional reservoir operation.
Chapter 2: Scientific and practical basis to identify water accumulation
operation mode in flood season in Hoa Binh and Son La reservoir system.
Chapter 3: Research results on operation mode in water accumulation period of
Hoa Binh and Son La terraced reservoirs.
CHAPTER 1 OVERVIEW OF RESEARCHES ON MULTIFUNCTIONAL RESERVOIR OPERATION
1.1

Reservoir and reservoir operation

To utilize integrated reservoirs for optimal benefit, scientists in the world focus
to find out suitable operation rules, resolve conflicts among different objectives
to reach higher operation efficiency. Those researches range from Rippl’s work
on simplifying water storage (1883) to recent complex researches on optimal
reservoir operation in real time for multiple purposes of Mehdipour and nnk
(2012). Despite systematic and specific research efforts from different
investment organizations and various methods applied by scientists to form
operation rules for reservoir system, successful applications are mostly related
to typical features of each system. There is no common methodology and tool
that can be applied for all systems.

3


1.2

Managing method and operating principles for multi-funtional
reservoir system

Each reservoir system in the operating phase must comply with an existing
operation procedures, in which there are operation procedures for each period
that the operating manager must follow. Operating procedures of reservoirs are
established in technical design period via imitation model or optimization
model. Operational procedures are presented in graphs or instruction tables
according to water level (water capacity) or the reservoir in each year (Yeh,
1985) (Long, N.L, Madsen, H., and Rosbjerg, D., 2007) demonstrated in
coordination chart are primary foundations for decision making in reservoir
operation. Operation procedure curves are one of the most popular and simple
management methods in order to support decision making of the manager in
reservoir operation. For multi-functional reservoirs there are two ways of
management: (i) water provision coordination and (ii) real time operation
management.
Multi-functional terraced reservoirs operation procedures: (i) for purpose of
flood prevention, store full water capacity in upstream reservoir in advance
when flood needs avoiding, when empty water capacity is needed to prepare for
flood regulation afterwards, downstream reservoir needs to be flushed in
advance, (ii) for purpose of water provision, it is more simple - higher
reservoirs need to store water before and lower reservoirs afterwards.

1.3

Overview on method to establish multi-functional reservoirs
operation process

Reservoir system operation is always a complex and diverse subject which
attracts attention of experts in the world as well as organizations and scientists
in Vietnam. Research on establishing a procedure for operation procedures
mainly uses mathematical models such as imitation theory or optimization
theory. Optimization technique is primarily used to establish frame operation
procedures, set up coordination chart for each reservoir in the system. Imitation
method helps the operation of reservoir system more specific with different
4


scenarios to select a suitable an operation method, resolve conflicts and
optimize objectives of the reservoir system. Therefore, in researching the
subject of operating multi-functional reservoir, even though optimization
method is becoming more popular, there are still challenges in finding the best
operating procedures (Labadie, 1997). Because of that, imitation method is still
applied widely to identify suitable and flexible operation procedures.
1.4

Overview of Red river

Reservoir system
Red river basin is the biggest basin in Northern Vietnam. The Red river system
originates from Yun Nan, China with 05 big tributaries which unify into 03
main branches- Da, Thao and Lo.
100°0'0"E

24°0'0"N

102°0'0"E

104°0'0"E

106°0'0"E

Ü

24°0'0"N

CHINA

22°30'0"N

"&

&

*
#

22°30'0"N

&
&

"

Lai Chau Reservoir

"
&"

"

NOTE
National boundary

*
#
21°0'0"N

Reservoir

&

LAO

"

&

Son La Reservoir
"
*
#
"

&
"

River
&

&
&
"
&&

&

Meteorological station
Hydrological station
Basin boundary
100°0'0"E

&

0

45

90

180
Km

102°0'0"E

21°0'0"N

"&
*
#

Hoa Binh Reservoir
104°0'0"E

106°0'0"E

Picture 1-1: Map of Da Basin
Thanks to favorable terrain conditions, Red river basin is increasingly benefited
from upstream water flow. In the upstream area of Da river (LyTien river) of
China territory, 11 reservoirs are already planned, of which 9 reservoirs are
operated. In Vietnam territory, in addition to water provision and electricity
generating in flood season, Son La and Hoa Binh reservoirs (in Da river) spent
7 billion m3 combined with 1,0 billion m3 of Tuyen Quang (on Gam river) and
5


0,45 billion m3 of Ba waterfall (on Chay river) to ensure safety of Hanoi not to
exceed water level of 13,4 m with periodic flood repeated every 500 years.
Operating procedures of reservoir system in Red river basin
Realizing the importance of these reservoirs, as soon as Hoa Binh reservoir
comes to operation, many scientists have researched to support management
agencies in setting up legal documents for an operation procedure in line with
the system development. The process has issued reservoir operation regulations
in water accumulation period quite flexibly while maintaining reservoir water
level above flood level. However, there are no clear regulations about the
moment of water accumulation and solutions to cope with flood when water

level in reservoirs is high. The subject of reservoir operation in water
accumulation period still faces some challenges causing difficulties for
operation decision makers (this subject is analyzed further in Chapter 2) and
needs more research to improve operation efficiency.
Flood prediction subject
Prediction on water flowing into a reservoir is one of the most critical tasks in
operating the reservoir. Prediction quality in forecast news has a big impact on
efficiency of inter-reservoir operation, especially prediction of water flow in
water accumulation period. Flood forecast in Red river is a complicated subject
with many challenged as more upstream reservoirs are constructed, lack of
information from measurement stations in China territory, unreliable quality of
numerical rain forecast. Nevertheless, flood forecast for the system has drawn
attention of many scientists (Trinh Quang Hoa and nnk, 1994) (Nguyen Van
Diep, 2013) (Bui Dinh Lap, 2016) who utilize modern and progressive
technology in the world to improve forecast quality and increase efficiency of
operating reservoir in Red river basin. Flood flow forecast with estimated time
of 72 hours for “good” forecast is one of conditions to resolve conflicts between
water accumulation and flood prevention for reservoir system in Red river basin
system.
6


1.5

Research orientation

Considering Son La and Hoa Binh reservoir system, there have been many
researches as scientific basis in constructing procedures for operating reservoir
system in Red river, in addition to a lot of reports analyzing operating facts
using many modern technology. Yet, operational decision makers still face

many challenges in periods with no clear regulations. As a result, the thesis
chooses the research as the scientific basis for operating reservoir system in Red
river basin in water accumulation period. The research model is illustrated in
Figure 1-7 as below.

Figure 1-7: Flow chart researching water accumulation operating mode for Hoa
Binh and Son La reservoir system
Current reservoir operation procedure in Red river basin (QT1622) suggests a
solid operation frame for the reservoir operation management. Therefore, the
thesis chooses imitation method with different advantages and disadvantages to
make the operation of the reservoir system more specific with various scenario.
From those chosen scenario, a suitable water accumulation method is chosen to
resolve conflicts and optimize objectives of the system.
7


CHAPTER 2 SCIENTIFIC AND FACTUAL BASIS TO IDENTIFY
WATER ACCUMULATION OPERATION MODE IN FLOOD
SEASON FOR HOA BINH AND SON LA RESERVOIR SYSTEM
2.1 Comments on published procedures and suggesting research direction
on water accumulation operation mode
Downstream flood prevention mission
QT 1622 provides that Son La and Hoa Binh reservoirs spend a big enough
volume to constrict the above limits so that when floods occur, the design can
cope with highest level in Hanoi according to 13,1 meter level of 300 year
recurring flood and 13,4 meter of 500 recurring flood in Son Tay (see Table 21).
Table 2-1: Regulations on distributing flood prevention volume for downstream
flood demolition following restricted water level in Hanoi of Son La and Hoa
Binh reservoir in QT1622
Water level to

Volume spent for flood prevention following restricted

be restricted

level in Hanoi (billion m3)

in Hanoi
ZHN

11,5 m

ZHN > 13,1 m
to 13,4 m

Son La reservoir
Hoa Binh reservoir Total
1,00
1,13
(reservoir water level (reservoir water level
2,13
from 197,3÷203 m)
from 101÷107m)
3,00
1,87
(reservoir water level (reservoir water level
4,87
from 203 ÷217,2 m)

from 107 ÷117 m)

Some limits of operation procedures
In early phase and primary phase of flooding, operation procedures mainly
focus on flood prevention when Hanoi water level may exceed 11,5 meter.
There are no specific operation procedures when Hanoi water level goes
below this yet. Calculate in technical profiles, establish procedures using 3
8


flood models with disadvantage rate of 0,33% and 0,2% when flood stage level
in Hanoi reaches 10,5 till 11,5 meter without considering cases when big floods
do not occur. Therefore, procedures QT198 and QT1622 generally provide that
in case of non- flood and depending on the changes of the weather and the
water level in Hanoi, it is allowed to raise reservoir water level above pre-flood
water level and in the forecast of flood, flush water to bring reservoir water
level back to pre-flood water level. Consequently, it is necessary to identify the
limit of above water level and in which forecast that water level is allowed to be
raised above? On the other hand, according to 56-year statistic documents (from
1959-2015), only in 9 years (16%) Hanoi water level in natural conditions may
exceed 11,5m did reservoirs take part in downstream flood prevention. Hence,
specifying operation mode for reservoir in flood season when floods do not
occur (Hanoi water level <11,5m) is highly critical.
There have not yet been any specific regulations on downstream flood
prevention operation mode in water accumulation period (late flood) as
unexpected floods happen. When there if forecast that flood season ends early,
reservoirs are allowed to accumulate water since August 10th which means Hoa
Binh reaches 110m level and Son La reaches 209m level (according to
QT1622), downstream flood prevention remains only 2,65 billion m3, unable to
cope with downstream flood with 300 year recurring flood in Son Tay. In
technical profiles for establishing operation procedures, there are not yet

material to calculate and check flood prevention capacity and solutions in
reservoir regulating operation in case of unexpected floods in this water
accumulation period.
Operation mode regulations to prevent downstream floods in case of big
floods are reasonable and not yet comprehensive. In regulations, reservoirs
can prevent downstream floods when Hanoi water level may exceed 11,5 meter,
however there is no reservoir volume distribution between two restricted levels
of 13,1 m and 13,4 m. This causes many challenges for reservoir system
operator in factual downstream prevention.
9


Dividing flood season into 3 periods with fixed timeline to establish
regulation and operation mode for each period. Published procedures, the
mode to operate reservoir in flood season is always divided into 3 periods: early
flood, main flood and late flood. In regulations, the starting time to accumulate
water into reservoirs is regulated to be in the beginning of late flood period
(after August 21st every year) and early water accumulation since annual
August 10th is only allowed if flood season is predicted to end early.
Even though procedures provided highest water level in flood season, in factual
operation system, the operation is proceeded via water accumulation before
allowed time. Specifically, 4 years (2012-2015) after Son La reservoir’s
operation followed QT198 providing that flood prevention water level of Son
La is 194 m and Hoa Binh as 101 m, water accumulation time is not earlier than
August 10th and yet, all reservoirs remain water level higher than regulations
despite no flood (Figure 2-1). Especially, in 2012, the highest water level of
Son La reservoir reached 201,84 m with 5,84 m increase and highest water
level of Hoa Binh reservoir reached 201,84 m with 5,76 m increase. Even
though reservoirs accumulate water early, at the end of flood season when
water flow in rivers decrease fast, there are times when these reservoirs reduce

water generation capacity to ensure water is accumulated fully in reservoirs to
safely provide water for downstream areas in dry season.

Figure 2-1: Chart illustrating water level in Son La reservoir in flood season in
2012-2015
10


Research orientation on water accumulation operation mode of Hoa Binh
and Son La reservoir. From analysis on procedures and operation reality, the
thesis’s orientation comprises of two main themes:
- Research water accumulation operation mode in flood season to increase
water generating efficiency, ensure full reservoir water accumulation and still
maintain flood prevention safety for downstream areas and constructions.
- Research to establish flood prevention regulating mode, minimize negative
impact for downstream areas in case of unexpected big floods in water
accumulation period after annual August 21st or after annual August 10th when
it is allowed to accumulate water early.
2.2 Scientific basis to identify water accumulation operation mode
Point of view. The thesis’ research orientation proposes to apply early
conditioned water accumulation (medium method) for Hoa Binh and Son La
reservoirs. However, the fact that reservoirs are allowed to accumulate water
early does not mean that water accumulation up to normal water rising level
right after flood season finishes should be done. Water should only be
accumulated up to a certain limit so that when there is forecast of big flood,
reservoir water level can be brought back to pre-flood level, ready to prevent
flood as design. Water accumulation mode is called “conditional” because in
each water accumulation time, accumulated water level in the reservoir depends
on 3 factors (1) reservoir water level and downstream water level (in Hanoi) in
water accumulation time; (2) flood forecast scale and water progress flowing

into the reservoir and downstream water level in forecast time; (3) Restrictions
on flood flushing regulation via flood flushing constructions. Based on that,
flood season is divided into 2 operation periods:
Restricted water accumulation period (before annual August 21st): restricted
water accumulation operation period including early flood and main flood
period. This is the period that flood flushing for downstream area is primary,
therefore reservoirs only allow accumulating water up to a certain water level
11


called restricted water level Hgh. Hgh is identified so that when there is big flood
forecast reservoir water level can be turned to pre-flood level to safely flush
flood for downstream area.
Full reservoir water accumulation period (after annual August 21st): water
accumulation period that requires reservoirs to store water up to normal rising
water level. In this case, an operation procedure to flush flood must be
established to minimize damage for downstream areas when reservoirs are not
capable to flush flood following downstream flood prevention standards.
Method to establish operation mode in restricted water accumulation
period.
In restricted water accumulation period, Hoa Binh and Son La reservoir system
operate in accordance with Hgh. From that base, establish Hgh relationship called
“water accumulation operation principle chart” to apply in water accumulation
process. To identify water accumulation operation principle chart, 2
calculations need to be done.
Subject 1: With each scenario on Hanoi water level in the time to identify
water accumulation, consider restricted water level Hgh when there is forecast of
big flood equivalent to designated flood in flood prevention zone (recurring 500
year flood in Son Tay). From that base, identify Hgh plans following Hanoi
water level. The value of restricted water level Hgh depends on estimated time

of applied forecast method. In Red river basin, estimated forecast time is in 3-5
days range (will be analyzed in 2.3)
Subject 2: Calculate and check big floods in reality. From that base, select Hgh
method to establish “operation principle chart”. If downstream flood prevention
requirements are not met, Hgh needs re-identifying following steps in Subject 1.
Establish operation mode to cope in case of unexpected floods in water
accumulation time

12


Within scope of the research, the thesis only focuses on analyzing unexpected
floods in water accumulation time of reservoirs which means when reservoirs
are not capable of preventing flood for downstream area following designated
floods. Research orientation is illustrated in figure 2-7.

Figure 2-7: Research approach model suggesting operation solutions to cope
with unexpected floods.
2.3 Analyzing factual basis and feasibility of identifying restricted water
level Hgh for Son La and Hoa Binh reservoirs
2.3.1 Reality of downstream water level change in flood season
Red river downstream water level’s state is becoming increasingly complicated
with gradual decrease trend, especially in Hanoi. According to flow statistics in
Hanoi hydrological stations from 1960 to 1988 and reverting flow from 1989 to
2013, it can be seen that:
- Highest water level in flood season is in peak phase and there are 09 years
when highest Hanoi water level exceeds 11,5m, so that only 16% of the years
upstream reservoirs had to flush flood for downstream area.
- Following the trend, the lowest water level decreases over time. Water level
was usually above 6,0m before 2002 and decreases in recent years. Especially,

in 2006, 2011, water level decreased down to 2,6m in peak flood season and
there was a moment it decreased down to below 2,0m.
13


- Flood foot water level in Hanoi lies below 6,0m and gradually rises from the
beginning of the season till pea of the season. Afterwards, it decreased.
- On the other hand, according to analysis materials (Ha Van Khoi, 2010), when
Hanoi water level is lower than 7m, the riverbed can carry an addition of 1300
m3/s to increase water level up to 1,0m. The river bed can load an addition of
2000 m3/s when Hanoi water level increases from 8,0m to 9,0m. In the whole
flood season, in 50% of the time of flood season, Hanoi water level is lower
than 8,0m.
2.3.2 Analysis of flood characteristics and big flood formation in the basin
Big flood in a vast area is often caused by the combination of primary weather
patterns with other weather patterns. The majority of big floods on Red river in
Hanoi have peak flood water level (Hmax) exceeding alert point III (11,5m)
caused by continuous occurrence of weather patterns mentioned above. Big
floods in Red river in the years: 1968, 1969, 1971, 1986, 1996 (Hmax > 12,0m)
are caused by 02 or more weather patterns happening respectively or at the
same time. There is not yet the most negative combination causing Red river
flood when there are major floods on all 3 rivers – Da, Thao, Lo. However,
especially big floods 1969, 1971 and 1996 are caused by big rain in 3
tributaries. The rain is not the same reason why there were big floods in 3
rivers.. Especially big floods in Hanoi happen when there are especially big
floods on 01 or 02 rivers. Especially big floods in Hanoi are usually caused by
01 to 03 continuous floods which last 08-10 days with average rain volume
between 100-300mm, some place up to 500-700mm and rain peak between 700800mm.
2.3.3 Capacity to forecast and identify big flood in Red river basin
Forecast lasting for an average time (5 days) is very important for inter

reservoir operation subject. According to estimation of national weather
forecast center, long-term forecast quality in Hanoi station and towards Son La
14


reservoir is of good quality (80%); the rate towards Hoa Binh, Tuyen Quang
and Thac Ba reservoirs reach above 70%. Guaranteed level in short term
forecast in recent years reached 80% with estimated time more than 24h, above
80% with estimated time of 36h and above 75% with estimated time of 48h.
Flood forecast quality has been improved because major floods in Northern
area are mainly caused by continuous or respective occurrence of two or more
weather patterns. Therefore, Red river area flood forecast quality totally ensures
the standards of water accumulation operation requirements of the thesis, which
means analysis on big rain causal patterns can be received pretty early.
This is the basis that there is enough time to lower water level of Hoa Binh and
Son La reservoirs back to pre-flood water level when there is forecast result.
2.4 Calculation tool
2.4.1 Apply MS Excel to calculate water flow regulation through reservoir
Establish calculation tool to regulate water flow through Red river reservoir
system in Red river in MS Excel. The calculation principle is as below:
Calculation principle to regulate water flow through reservoirs: based on
water balance equation and dynamics equation along with typical lines,
parameters to describe characteristics of construction system.
River flow illustration: apply Muskingum method to illustrate flow in a natural
river pattern is a classic yet very effective method.
2.4.2 MIKE 11 model
Water flow state for whole Red river basin of previous researches using Mike
11 model produce very practical flow demonstration results. Therefore, the
researcher uses the total system of rivers, sections and statistics of MIKE 11
established for Red river basin as calculation tool to imitate water flow from the

back of reservoirs to downstream area. Total river system comprises of 25 main
rivers divided into 52 tributaries, established in measured sections in 2012.
15


Boundary of lower area and above area: the process in which flushing
volume from Hoa Binh reservoirs (Da river), Thac Ba (Chay river), Tuyen
Quang (Gam river). The process that volume and water level in hydro station
(Yen Bai, Ham Yen, Quang Cu, Thac Huong, Cau Son, Chu, Chi Thuy, Hung
Thi, Nhu Tan, Phu Le, Ba Lạt, Định Cu, Đong Xuyen, Quang Phục, Kien An
and Cua Cam)
Middle area boundary: Middle areas are identified based on terrain
documents and hydro-meteorological documents. Middle areas provide a
considerable water flow for river system comprising of 6 areas.
2.5 Chapter 2 conclusion
The thesis analyzes flaws of operation process, challenges in operation reality
from which perspectives on researching water accumulation operation process
to align with conditional early water accumulation. According to this research
direction, the thesis proposes calculation method for restricted water level Hgh
(for restricted water accumulation period) and establish operation method in
case of unexpected floods. The thesis analyzes conditions forming big floods
and rain, flood flow quality and flood forecast quality, proving feasibility of the
research direction.
CHAPTER 3 RESEARCH RESULTS OF OPERATION MODE IN
WATER ACCUMULATION PERIOD OF TERRACED
RESERVOIRS HOA BINH AND SON LA
3.1 Establish problem
Establish operation principle chart, the thesis gradually identifies Hgh,
measurement chart illustrated in Figure 3-2 in which Hanoi water level ranging
in 3 levels: (i) from 6,0-8,0 m; (ii) from 4,0-6,0 m; (iii) and below 4,0 m; with

water level above 8,0m, maintain reservoir water level equivalent to pre-flood
water level .
Choosing safe restricted water level in Hanoi as 10,5 m (due to prediction
errors). The early state of Tuyen Quang and Thac Ba reservoirs are equal to
16


pre-flood water level. Flood model of 1996 is not favourable for regulation
operation of reservoir in Da river (peak flood flow into Son La reservoir is
31.863 m3/s, total flood volume in 20 days of Da river tributaries account for
more than 50% of total downstream flood). As a result, this thesis chooses this
flood model to calculate. Flood flow process three previous days in boundaries
are identified from early state of the system connected to starting point of the
designated flood.
To simplify calculating process, choose a fixed water level of Hoa Binh
reservoir as 101m, gradually increase water level of Son La reservoir.
Afterwards, modify based on total volume preservation principle. The
calculation results are illustrated in Table 3-1 and Table 3-3.

Figure 3-2: Calculation model to establish operation principle chart
Table 3-1: Results to calculate Hgh of Son La reservoir
Water level (m)/ Flow(m3/s)
In the
beginning
In water level
of SonLa equal
MNTL

Hanoi water level (m)
Hgh of Son La reservoir

(m)

207,5

205,5

200,5

Hanoi water level (m)

8,3

9,67

9,75

Qmax Hoa Binh (m3/s)

8.270

11.289

11.126

17

197,3


Table 3-2: Total solutions to adjust Hgh

Hanoi water level (m)
Z Sơn La (m)
Solution 1
Z Hòa Bình (m)
Z Sơn La (m)
Solution 2
Z Hòa Bình (m)
Z Sơn La (m)
Solution 3
Z Hòa Bình (m)
Z Sơn La (m)
Solution 4
Z Hòa Bình (m)

197,3
101,0
197.3
101,0
197,3
101,0
197,3
101,0

200,5
101,0
200.5
101,0
200,5
101,0

200,5
101,0

205,5
101,0
203
103,5
202,4
104,0
201,5
105,0

207,5
101,0
205
103,5
204,4
104,0
203,5
105,0

To measure feasibility of Hgh water level solutions of Son La and Hoa Binh
reservoirs, the thesis operates reservoir system experimenting 10 big floods in
reality 1969, 1970, 1971, 1972, 1996, 1999, 2000, 2002, 2006 và 2008. Result
of regulation operation following Hgh solutions proposed are all feasible.
Adjusting reservoir water level following Hanoi water level is flexible and not
leading to artificial floods for downstream area. Hoa Binh reservoir opens
maximally 7 flushing gates in two big floods 1971 and 1996. In calculated
floods, water level of reservoirs are brought back near pre-flood water level as
regulations to prepare for downstream flood prevention and Hanoi water level

does not exceed 10,5m.
The thesis chooses method to only increase Son La reservoir above pre-flood
water level (197,3 m) and proposes water accumulation principle table (Table
3-5) to be active in factual operation and safe when flood happens in middle
area.
Table 3-5: Water accumulation operation principle
Hanoi water level (m)
Hgh of Son La reservoir (m)
Hgh of Hoa Binh reservoir (m)

207,5

205,5

200,5

197,3

101,0

101,0

101,0

101,0

18


Table 3-6: Comprehensive table of water level in Son La, Hoa BInh and Hanoi

reservoirs operated based on solution 1 and 3

Oder

Flood

Beginning
of Hanoi
water
level
(m)

Beginning
of waterb
level in
Son La
reservoir

Lowest
water
level in
Son la
reservoir

(m)

(m)

Highest
water

level in
Son La
reservoir
when
flushing
flood

Beginning
of waterb
level in
Hoa Binh
reservoir
(m)

(m)
1

Highest
water
level in
Hoa
Binh
reservoir
when
flushing
flood

Highest
number
of

flusing
gates of
Hoa
Binh
reservoir

Highest
water
level in
Hanoi
(m)

(m)

8/1969

6,43

200,49

197,18

205,33

100,99

108,33

7

11,79

7/1970

4,43

205,49

197,52

202,19

101,01

101,96

6

10,25

7/1970

4,43

202,49

197,31

201,76

104,01

103,21

6

10,23

8/1971

6,12

200,5

197,52

211,93

101,00

113,19

5

12,02

7/1972

4,41

205,49

196,97

198,27

101,01

103,34

6

10,91

7/1972

4,41

202,39

197,25

198,66

104,01

102,38

6

10,91

8/1996

6,32

200,5

197,05

201,88

101,00

106,63

7

11,67

9/1999

4,47

205,49

197,32

200,01

101,09

101,84

6

10,28

9/1999

4,47

202,37

197,33

201,11

101,09

102,37

6

10,04

7/2000

4,63

205,51

197,03

200,16

101,06

101,86

6

11,22

7/2000

4,63

202,39

197,21

200,6

103,99

102,77

6

11.02

8/2002

7,15

200,45

197,81

201,61

101,00

106,9

6

11,61

7/2006

5,84

205,50

197,41

201,88

101,04

104,56

6

11,25

7/2006

5,84

202,37

197,22

202,73

104,02

105,07

6

11,41

8/2008

6,48

200,57

197,43

201,29

100,96

104,25

5

11,91

2
3
4
5
6

7
8
9
10

19


3.2 Research results on operation solutions in case of unexpected floods in
water accumulation period

The thesis only researches operation mode in case of unexpected floods in
water accumulation period (Case 1: from 10/8 to 22/8; Case 2: from 22/08 to
15/09) following 2 below steps:
- Analyze solutions which can be used in urgent situations along with
researching characteristics of proponents of water volume used for downstream
and construction flood prevention of reservoir system Son La and Hoa Binh to
propose a reasonable operation solution in case of unexpected floods.
- Analyze feasibility of proposed operation method via experimental operation
in case of unexpected floods normally occurring in different phases of water
accumulation period.
Proposing operation solution
In this research, choose a solution to consider using part of flood prevention for
the construction to prevent downstream flood in necessary conditions and still
ensure safety for the construction. This solution has many advantages such as
reducing damages for downstream areas (thanks to non-flood splitting);
increasing water accumulation efficiency and economic and societal damages
are decreased thanks to flood non-splitting. The thesis proposes specific
solutions as below:
When HHN< 6,0 m and there is likelihood of big floods within 72 hours,
reservoirs in the system gradually opens flushing gates to bring reservoir water
level back to regulated water level, QHoa Binh flushing does not exceed 12.000 m3/s
and HHN<12,5 m.
When HHN>12,5 m and it is predicted that Da river water level continually rises,
Z Son La reservoir>215,0 m and ZHoa Binh reservoir >115,0 m, consider allowing Son La
reservoir accumulate above 217,83m when flood volume in Da river is smaller
than 20.000 m3/s and decreasing.
20


Table 3-7: Lowest water level in reservoirs is allowed to reduce to cope with

flood based on QT 1622
Reservoir

Period

From 10/8-22/8

From 22/8 – end of
flood season
209

Sơn La

197,3

Hoà Bình

101

110

Tuyên Quang

105

110 hoặc thấp hơn

Calculation proposal
Statistics on Hanoi flood level in Hanoi in flood seasons shows that flood foot
in Hanoi is always below 6m and decreases over time during water

accumulation period (Ha Van Khoi, 2010). Therefore, the initial conditions of
water level in Hanoi can be considered as 6m. Choose unexpected flood
scenarios as natural type with recurring period respectively of 500 years and
300 years happening in main flood period (before 22/8); late flood period is
only applied with flood scenario with recurring period of 300 years and real
floods based on flood models of 1969, 1971 and 1996.
Analysis results
In scenario 1 when unexpected flood happens with recurrence time of 500
years, upstream reservoirs are capable of flushing flood to ensure downstream
safety if a portion of flood prevention volume for the construction is used. The
time to maintain Hanoi water level above 13m lasts 5-8 days.
In scenario 2, when floods with recurrence time is 300 years, upstream
reservoirs must use part of construction flood prevention volume (Son La
increases water level up to 200m) to protect Hanoi. The time to maintain Hanoi
water level above 13m is from 6 to 8 days.
Two reservoirs are always safe and can protect downstream area from big
floods whose intensity equivalent to historical big floods in Red river during
21


water accumulation period without using flood protection water volume of the
construction.
3.3 Propose water accumulation operation mechanism of terraced
reservoir system Hoa Binh and Son La
3.3.1 Restricted water accumulation period (from June 15th to August 21st )
In this period, the thesis proposes operation mechanism when Hanoi water level
is below 11,5 m as below: operate upstream reservoirs based on flood forecast
results with estimated time of 3 days and Hanoi water level condition, Son La
water reservoirs range from 197,3m to 207,5m. Hoa Binh reservoir maintains
pre-flood water level (101,0 m) as specifically provided in Table 3-5.

When water level forecast in Hanoi in 3 days is lower than 4,0m, regulate so
that Son La reservoir water level maintains not higher than 207,5m and Hoa
Binh reservoir water level maintains not being higher than 101,0m.
When water level forecast in Hanoi in 3 days ranges within 4,0 m ÷6,0 m,
regulate so that Son La reservoir water level maintains not higher than 205,5m
and Hoa Binh reservoir water level maintains not being higher than 101,0m.
When water level forecast in Hanoi in 3 days ranges within 6,0 m ÷ 8,0 m,
regulate so that Son La reservoir water level maintains not higher than 205,5m
and Hoa Binh reservoir water level maintains not being higher than 101,0m.
When water level forecast in Hanoi in 3 days ranges higher than 8,0 m, regulate
so that Son La reservoir water level maintains not higher than 205,5m and Hoa
Binh reservoir water level maintains not being higher than 101,0m.
3.3.2 Method to operate Son La and Hoa Binh reservoirs to cope in case of
unexpected floods in water accumulation period
When Hanoi water level is lower than 6 m, predicting likelihood of big flood in
the next 72 hours (equivalent to 300 year or 500 year recurring floods or more).
22


Reservoirs in Red river system starts to open flushing gates to bring reservoir
water level back to the level regulated in Table 3-7 depending on different
periods, but downstream safety must be ensured. The volume being flushed
down to Hoa Binh town can not exceed 12.000 m3/s and restricting Hanoi water
level always below 11,5m. When Hanoi water exceeds 11,5m and flood
forecast in Da river continues to increase, Son La reservoir water level exceeds
215m, Hoa Binh level exceeds 115m, allow Son La reservoir accumulate water
below 217,83m. Only use construction flood prevention volume of Son La and
Hoa Binh reservoirs when flood volume in Da river is below 20.000 m3/s and
decreasing. However, restrict Son La reservoir water level below 228 m and
Hoa Binh reservoir not above 122 m (equal to tested water level). However,

when there is a sign of flood more seriously than 500 year flood, especially
floods with form such as 1969 or worse, combine with flood-splitting method
into Day river according to the Decree 04 of the Prime Minister.
3.4 Chapter 3 conclusion
Chapter 3 presents calculation results to gradually identify Hgh of reservoirs
and experimentally operate with some of 10 floods which happened. From that
foundation, feasibility of the research direction to find out conditional early
water accumulation method for Son La and Hoa Binh reservoirs during flood
season.
Early research results on feasibility of the method using part of construction
flood prevention volume of Son La and Hoa Binh reservoir systems to cope
with downstream floods in case of unexpected floods in water accumulation
period (with flood scale equivalent to 300 year flood).

CONCLUSIONS- RECOMMENDATIONS
Conclusions
1)

The latest operation procedures QT1622 still contains some

shortcomings. The thesis has researched, analyzed operation procedures and
23