MINISTRY OF EDUCATION AND TRAINING
MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
WATER RESOURCES UNIVERSITY NGUYEN DINH

RESEARCH ON CHANGES OF SOME HYDRAULIC
AND HYDROLOGICAL FACTORS OF THE HUONG
RIVER SYSTEM’S DOWNSTREAM UNDER THE
IMPACT OF IRRIGATION AND HYDROPOWER
CONSTRUCTIONS AND CLIMATE CHANGE

Specialization: Water resources development
Code: 62 44 92 01

DOCTORAL THESIS SUMMARY
HANOI–2014 Research has been completed at Water Resources University

Science advisors:
Associate Prof. Le DinhThanh
Associate Prof. Hoang Minh Tuyen Reviewer No.1:

municipality.
Purpose of research: Clarifying the change of some
hydrology-hydraulic factors at downstream of Huong river system
under the impacts of irrigation and hydropower constructions and
climate change in order to propose adaptive measures to mitigate the
negative impacts on economic-social development and environmental
protection.
Objects and range of research: Assessing the impacts of
irrigation-hydropower construction system on some hydrology-
hydraulic factors at downstream of Huong river from reservoirs to
Thao Long dam with climate change calculated to the year of 2030.
Research methodology: Thesis has used these methods:
inheriting, investigating, surveying, statistic analysing, hydrology-
hydraulic mathematical modelling, GIS, system analysing, expert
method and community consulting
Summarizing new contributions of the thesis:
1) Assess quantitatively the impact of irrigation -
2

hydroelectric power constructions on the Huong river basin and the
impacts of climate change on hydraulic and hydrological factors in
downstream of the Huong river system.
2) Propose structural and non-structural measures to mitigate
the negative impacts of hydropower and irrigation works on the
Huong river basin to flow regime in downstream and improve the
efficient operation of those constructions.

Chapter I
LITERATURE RIVEW


hydrological condition and ground surface remain unchanged.
Quantitative assessments are still restricted.
Corrective directions of thesis:
- Assessing system analysis perspective of Huong river basin,
concentrating on main structures which have considerable impact on
flow regime at downstream.
- Quantitatively assessing of impacts of constructions and climate
change, initially considering the role of land use and forest layer on
the basis of selecting annual flow and specific flood to study the
change of some typical hydrology-hydraulic factors.
- Proposing measures which are scientific-based, practical,
possible and effective.
1.1.4 Approach of thesis
- Integrated approach following the water system
- Imitative approach by hydrological and hydraulic mathematical
models
- Approach by scenarios

4
-
hydraulic model
Change of
some factors
Changing flow
to reservoirs
Assess changing
tendency of
climatic factors

Rainfall
-
Runoff
model
Selecting
climate change
scenarios

Detailed climate
change scenarios
Impact of estuary
construction
Analyzing
impact factors
Gathering data of
climate, hydrology
and topographic
Comparing with
investigated
result


Figure 1.2
:
The
Huong river basin in Vietnam

6

1.2 CHARACTERISTICS OF THE HUONG RIVER BASIN
1.2.1 Physical characteristics
The Huong River Basin (HRB) locates mostly in Thua Thien Hue
Province (figure 1.2), including three main tributaries: Bo river, Huu Trach
river and Ta Trach river, the last of which is the main source of Huong river.
Water resources of HRB have a vital role in socio-economic-cultural
development and environmental protection of Thua Thien Hue province.
1.2.2 Socio-economic characteristics
In recent years on Huong river irrigation and hydropower
structures have been constructed in order to meet the demand of socio-
economic development. Constructions along with the change of
landuse structure have considerable impacts on hydrology-hydraulic
regime of Huong river.
1.3 CHANGING TENDENCY OF SOME HYDRO-
METEOROLOGY FACTORS ON HUONG RIVER BASIN
1.3.1 Data and trend assessment method

impact of construction individually. Some research shows the
assessment about the impacts to flow regime but are still quantitatively
limited in changes of hydrology-hydraulic factors under the operations
of reservoirs at upstream and Thao Long dam at downstream,
particularly when climate change is setting out new challenges to
integrated water resources management in Huong river basin.
Changing tendency of some climatic and hydrological factors
in Huong river basin is quite suitable with the scenarios of climate
change and sea water rise published by MONRE in 2012. On the base
of research orientation and approach of thesis, applying hydrology-
hydraulic mathematical models and integrated analyzing are chosen to
be the major methods in assessing the impacts of main irrigation-
hydropower constructions in the river basin with published scenarios
of climate change and sea water rise No.B2.

Chapter II
ANALYSIS AND CALCULATIONS
2.1 IRRIGATION AND HYDROPOWER CONSTRUCTION
SYSTEM IN HUONG RIVER BASIN
2.1.1 Irrigation – hydropower constructions
Directly related to the main streams in the basin, there are
irrigation and hydropower constructions, weirs and dams for irrigation
combined with preventing saltwater intrusion and controlling flood and
flood drainage constructions at estuaries of Huong river and its branches.
8

2.1.2 Characteristics of irrigation – hydropower constructions
The constructions system is diverse, including upstream
reservoirs which have the function to control flood, supply water and
generate electricity and constructions at estuary for salt water
2.2 MAIN FACTORS AFFECTING THE HYDROLOGY -
HYDRAULIC REGIME OF HUONG RIVER
2.2.1 Rain, storms and weather phenomena causing flood
Impact of constructions

Impact of constructions and climate change
No construction
calculated,

Binh Dien, Huong Dien, Ta Trach
reservoirs and Thao Long dam
calculated without climat
e changed
Binh Dien, Huong Dien, Ta Trach
reservoirs and Thao Long dam
calculated, climate change
considered

Propose measures to mitigateFigure

2
.2
:
Impact assessment framework of irrigation
-

annual water level of Kim Long and Phu Oc by 26-27cm, the lowest
and highest water level in dry season increased by 20-31cm, the figure
for flood season is 4cm at Kim Long and 22cm at Phu Oc. In the
period of 2010-2012, Binh Dien reservoir and Huong Dien reservoir
lowered the highest annual water lever at Kim Long by 53cm and Phu
Oc by 37cm, as well as raised the lowest mean water level in dry
season at Kim Long by 37cm and at Phu Oc by 22cm.

10

2.3 MAIN IMPACTS OF IRRIGATION-HYDROPOWER
CONSTRUCTIONS ON HYDROLOGY - HYDRAULIC
REGIME AT DOWNSTREAM OF HUONG RIVER
2.3.1 In flood season
In flood season, reservoirs have the impact to lower the water
level and peak flow at downstream due to flood controlling. However,
they are also able to cause artificial flood unless reservoir operating
procedure is implemented. Sediment is hold in reservoirs, cause to river
bed transformation at downstream, increasing incident risk…
2.3.2 In dry season
Thao Long dam controls the flow of the river and freshens
Huong river, creating the potential to supply water for Truoi irrigation
system and maintaining flow for environmental requirement. This
dam has a vital role in preventing saltwater from entering the river,
even though by sea water rise.
2.4 APPLYING HEC-HMS AND HEC-RAS MODEL IN
SIMULATING FLOW IN HUONG RIVER BASIN
2.4.1 General introduction of HEC-HMS and HEC-RAS model
HEC-HMS hydrological model is applied for flow simulation to
reservoir and inflow from tributaries, which result is used for input data of

constructions are not so long. However results from analysis have
shown that there are significant impacts on some hydrology-hydraulic
factors in Huong river. Therefore quantitative assessment in specific
situation is necessary, especially when Ta Trach reservoir went in
active and climate change considered.
12

HEC-HMS and HEC-RAS models are applied in Huong River
for daily flow, flow in flood season and dry season. Results for
calibration and validation of models are acceptable for assessing
change of hydrology-hydraulic factors under the impact of
constructions and climate change.

Chapter III
RESULTS AND DISCUSSION
3.1 RESEARCH SITUATIONS AND OPERATING PLANS
FOR CONSTRUCTION SYSTEM
3.1.1 Research situations
This thesis considers 3 scenarios: (1) Natural condition, with
no construction calculated; (2) Binh Dien, Huong Dien, Ta Trach
reservoirs and Thao Long dam are constructed, with none climate
change applied and (3) Those constructions are calculated, with
climate change to 2030 considered according to scenarios No.B2
published by Ministry of Natural Resources and Environment in 2012.
3.1.2 Operating plans of constructions for impact assessment
Table 3.1: Calculating plans
No

Plan name


according to downstream alerted level
4

TH2
-
PAIII

Constructions calculated

and operated according
to downstream alerted level, with flood control
pool added to reservoirs
5

TH3
-
PAI

Constructions calculated and operated by
indi
vidual procedures, with climate change
considered to 2030 in B2 scenarios
6

TH3
-
PAII

Constructions ca
lculated and operated according
Figure 3.2: Water level change at Kim Long in average water year
14

Table 3.4: Chane in mean water level in average water year
Point

TH1

TH2
-
PA
ITH3
-
PA
I

H
0


calculated, water level of Huong river rises insignificantly with the
impact of constructions. This shows that the change of flow at
downstream is greater affected by irrigation-hydropower system than by
climate change according to research scenarios.
Before the existence of constructions, water stage in dry season
fluctuated by the tide, in flood season the level changed abruptly with
high peak of flow. After having constructions, water level in dry season
maintained stably without fluctuating with the tide; in flood season, the
peak flow has been lowered, the period of over second-grade warning
stage at Kim Long has reduced from 4 days to 2 days while the period
of over first-grade warning stage has increased from 9 days to 47 – 53
days.
3.2.3 Impacts on flood flow
Results of calculating flood flow at Huong river downstream
for each plan are shown in figures 3.4, 3.6 and tables 3.6, 3.8.
Table 3.6: Calculated peak water level change in 1999 at downstream
of Huong river for each plan (m)
Point

TH1 TH2- PAI TH2-PAII TH2-PAIII
H
0
(m) H
1
(m) H
1
-H
0
Figure 3.4: Graph of calculated Figure 3.6: Graph of calculated
flood stage in 1999 at Kim Long flood stage in 1983 at Kim Long
When climate change is not calculated, analysis of some flood
properties in 1999 at Kim Long station shows that the flood regime has
changed considerably under the impacts of reservoirs. After the
constructions of reservoirs, the peak flow has lowered, maximum flood
intensity has decreased from 0.54m/hour to 0.24 – 0.52 m/hour, average
flood intensity has also decreased from 0.2 m/hour to 0.1 – 0.15 m/hour
depending on operating plans. The period of over third-grade warning
stage has also been reduced by 4 – 8 hours.
Table 3.8: Change of simulated peak flood stage in 1983 at Huong
river downstream according to operating plans (m)
Point

TH1

TH2
-

PAI


(m)

H
2
-
H
0

H
3

(m)

H
3
-
H
0Kim Long

5
.
00

4
.
7
0

73

4
.
4
3

-
0
.
3
0

4
.
4
1

-
0
.
3
2

4
.
3
0

-


TH1

PA I

PA II

H
0

(m)
TH2

(H
1
)
TH3

(H
2
)
H
2
-
H
1
(m)
TH2

(H

.
34

5
.
13

5
.
32

+ 0
.
2
9

Phu Oc

4
.
68

4
.
60

4
.
71



17

Table 3.11: Change of dry flow stage in average water year

Point
TH1

TH2
-
PAI

TH3
-
PAI

H
1

(m)

H
2

(m)

H
2
-
H

0
.
52

0
.
00

Ph
u Oc

0
.
17

0
.
74

+0
.
57

0
.
75

+0
.
01

economic development and environmental protection.
- Improve the efficiency of constructions in order to disentangle the
conflict between electricity generation and flood control, mitigate
losses to downstream.
3.3.2 Nonstructural measures
(1) Enforcing the vegetative cover on the basin:
Based on CN coefficient of land use and vegetative cover
scenarios, the applying of HEC-HMS model has estimated flood flow to
reservoirs in 1983. It is estimated correlation function between CN
coefficient to flood volume that comes into the reservoirs: y= 13.19x
+2676, R
2
=0.994. Result of peak flow and stage of 1983 flood at Kim
Long and Phu Oc according to land cover scenarios is shown in table 3.16.
Table 3.16: Influence of change of land use and vegetative cover to
flood flow in 1983 at downstream of Huong River
Kim Long Phu Oc
Year H
max

(m)
ΔH
(m)
Q
max

(m
3
/s)


be enforced in these critical areas:
- Upstream areas of reservoirs(including small reservoir)
- Afforest at the belts along the downstream river and coastal strip.
- Planting and protecting the forest is integrated river basin
19

management, in which water resources management is the key factor.
(2) Planing, buliding and protecting the protecting corridor
of reservoirs, river, lagoon.
(3) Building inter-reservoir operating procedures co-
operated with Thao Long dam
This thesis proposes the Combined operating procedure of
irrigation-hydropower constructions in Huong river basin as below:
(1) For upstream reservoirs
a)- Binh Dien reservoir:
- Flood control elevation: +80.6m.
- With incoming flood, store inflow to the eleveation of +85.0
m then discharge with Q
discharge
≤ Q
inflow
and cooperate with
downstream flood control requirement. Amount of discharge depend
on warning stage at Kim Long.
- After flood, reservoir keeps on dischaging to drop the water
elevation to +80.6m in order to engage the following flood.
b) Huong Dien reservoir:
- Flood control elevationL +56.0m.
- When flood come, store inflow to the elevation of +58.0m
the discharge with the flow smaller than inflow and coperate with

Table 3.18: Proposed flood control storage of reservoirs
Now Proposed
Reservoir V
FC
(10
6
m
3
) % V
E
V
FC
(10
6
m
3
) % V
E

Ta Trach 435.9 125.8 435.9 125.8
Binh Dien 70 20.3 150 43.6
Huong Dien 0 0 200 57.0
Total 505.9 48.6 785.9 75.4
Table 3.19: The efficiency to flood control at downstream by integrated
operation and flood control storage increase of reservoirs in comparision with
keeping flood control storage constant and individually operation (m)
1983 Flood 1999 Flood
Point
TH2-
PAI

control storage for upstream reservoirs is acceptable. However, it is
necessary to have deeper and more detailed research to smoothly
disentangle the conflict of flood control and electricity generation of
private hydropower constructions for stronger and more pratical
foundations for later implementation.
(2) Improving and upgrading flood drainage and sea dike
Improve and extend downstream rivers and creeks such as
Dien Hong, An Xuan, Kim Doi in the northen area of Huong river;
silted section of Nhu Y, Pho Loi, Dai Giang river; improve and
upgrade drainage, pump station and overflow dike lines on Tam Giang
– Cau Hai lagoon. Dike routes that need to be upgraded include east
and west routes of Tam Giang lagoon and routes of Sam – Thuy Tu –
Cau Hai lagoon in order to prevent sea water rising.
3.4 CONCLUSIONS OF CHAPTER III
Impacts of irrigation-hydropower constructions in Huong
river basin on downstream flow regime is considerable. It is necessary
to concern with (i)-Binh Dien and Huong Dien reservoir operating
procedures in flood season; and (ii)- main role in flood reduction of
flood control storage, typically Ta Trach reservoir and tide prevention
role of Thao Long dam.
Impact of climate change (B2) to the year of 2030 on annual
flow and dry season flow at downstream is insignificant compared to
impacts of constructions. For flood flow, in case of extreme flood
22

(1999), impacts of climate change become more apparent.
The oriented measures to mitigate the negative impacts include the
group of nonstructural solutions: Enforcing afforestation in watershed,
constructing water preservation corridor and building inter-reservoir
operating procedures in cooperation with Thao Long dam. The group of


dropped by 0.30 – 1.44 m at Kim Long, 0.3 – 0.43 m at Phu Oc; in
term of the 1999 flood, the figures are 0.28 – 0.99 m at Kim Long and
0.08 – 0.21 m at Phu Oc.
-Regardless of mean dry season water stage (Jan-Aug): The
role of constructions with mean water level is significant, particularly
for Thao Long dam. Water level at downstream in dry season is stable
without influence of tide and rise significantly (about 0.60 m) at both
Kim Long and Phu Oc.
3) Impacts of climate change on Huong river basin according
to B2 scenarios on some hydrology-hydraulic factors of downstream
is generally inconsiderable compared to impacts of irrigation-
hydropower constructions system in the period to 2030. In case of
extreme flood (1999), impacts of climate change become more
transparent.
4) Based on results of reseach, analysis, scientific assessment
and pratice, this thesis proposes two groups of solutions in order to
mitigate disadvantageous impacts and improve efficiency of
constructions:
-Nonstructural solutions include: (i)”Enforcing vegetative
cover in watershed”; (ii)”Planning, building and protecting
preservation corridor of water in rivers, reservoirs, lagoons”; and
(iii)”Building inter-reservoir operating procedures in cooperation with
Thao Long dam”.
-Structural solutions include: (i)”Increasing flood control
storage of Binh Dien and Huong Dien reservoirs”; and (ii)”Improving
and upgrading flood draining routes and sea dikes”.
These measures are possible and suitable with requirements
and sustainable developing direction of Thua Thien Hue Province.
New contributions of the thesis