Nghiên cứu thiết lập mô hình thủy văn kinh tế phân bổ nước tối ưu lưu vực sông Ba Tiếng Anh

MINISTRY OF EDUCATION
MINISTRY OF AGRICULTURE
AND TRAINING
AND RURAL DEVELOPMENT
THUYLOI UNIVERSITY

NGUYEN THI THU NGA

RESEARCH ON HYDRO-ECONOMIC MODEL DEVELOPMENT FOR
OPTIMIZING WATER ALLOCATION IN BA RIVER BASIN

DISSERTATION ABSTRACT
Speciality: Hydrology
Code: 62 44 90 01

HANOI, 2017


This dissertation is completed at Thuyloi University.

Principal Advisor: Professor Ha Van Khoi

Reviewer 01: Dr. Nguyen Lan Chau
Reviewer 02: Assoc. Prof. Nguyen Tien Giang
Reviewer 03: Assoc. Prof. Ngo Le Long

This dissertation will be presented to the Evaluating Committee at
…………………………………………………………………………….
At …….. on …………….. 2017.

This dissertation could be found in the following libraries:

-

National Library
Thuyloi University Library


INTRODUCTION
1. Statement of the problem
Ba river basin is one of the largest inter-provincial river basins in Vietnam.
Based on the results of previous irrigation and hydropower planning, a series of
hydraulic structures had been built. In particular, there are two main irrigation
structures named Ayun Ha and Dong Cam, and five large hydropower plants
named An Khe, Kanak, Song Ba Ha, Song Hinh, and Krong Hnang. However,
when these projects went into operation, there had some impacts back to the
water resource system. As a result, the allocation of water resources over space
and time had been changed, which thereby affects the exploitation of water in
the whole basin. This is one of the causes leading to the conflicts between
irrigation and hydropower, upstream and downstream, economic development
and environment protection. Therefore, it is necessary to reconsider the issue of
water allocation in Ba river basin on the basis of coordination of existing
irrigation and hydropower structures to improve water use more efficiently.
In this context, "research on development of hydro-economic model for
optimizing water allocation in Ba river basin" is chosen to study to find out a
mathematical model supporting in water resources management in Ba river
basin. The model aims to improve water using in a more efficient way in the
field of economy, social balance, and environmental protection.
2. Research Objective
This research aims to address the difficult situation of water allocation problem
in Ba river basin by analyzing the relationship between relative water
availability and economic benefit from key-water using sectors. Four following

steps were taken to meet the research objective: establishing the water
allocation problem for Ba river basin; developing a hydro-economic model
applied for Ba river basin; applying the developed model to assess potential

1


policies regarding to water resource management; and proposing several water
resource management measures for Ba river basin.
3. Scope of study
Scope of study: Research on water allocation problem of Ba river basin, time
scale is a water year, time step is a month.
Research subjects: Water users to be considered are agriculture and
hydropower. The other water users including domestic, industry, fishery, and
environment are considered as constant constraints.
4. Methodology
The following methods applied in the research are including (i) inherited
method; (ii) synthetic analysis method; (iii) statistical method; and (iv)
nonlinear programming method;
5. New contributions
Study on applying an optimizing model in analysis, assessment, and allocation
of water resources in a river basin, and modifying the model for Ba river basin.
Establishment of the quantified relationship between water availability and
economic benefit from key-water using sectors.
Application of the model to evaluate several potential policies in water
resources planning and management. Based on the results, some management
measures are proposed to improve water use efficiency.
6. Structure of the thesis
The thesis consists of 113 pages, 30 tables, 19 figures and 72 references.
Besides the introduction and conclusion, the thesis consists of 4 chapters as

follows:
Chapter 1: Overview of hydro-economic model applications in water resources
planning and management

2


Chapter 2: Establishment of hydro-economic problem for water allocation in Ba
river basin
Chapter 3: Simulation and solve hydro-economic problem of Ba river basin in
GAMS.
Chapter 4: Impact assessment of water exploitation scenarios to socio-economic
benefits in Ba river basin.
CHƯƠNG 1 OVERVIEW
OF
HYDRO-ECONOMIC
MODEL
APPLICATIONS IN WATER RESOURCES PLANNING AND
MANAGEMENT
1.1

Nomenclature and definitions

A hydro-economic model is the combination of a hydrology model and an
economic model, thereby it can represent hydrologic, technical, environmental,
and economic aspects of water resource system in an integrated framework
(Harou, 2009).
1.2

Introduction of hydro-economic models

In a hydro-economic model, water allocation was driven and evaluated by
economic value of water. Water is considered as a special economic good, with
the properties of both private goods and public goods. The economic value of
water varies by type of uses (consumptive uses or non-consumptive uses,
instream uses or offstream uses, uses as intermediate good or uses as final
good). Water value is also changeable over time and space. The researchers can
apply different methods to estimate the water value for certain situation. In
general, the residual method was used to estimate water value in agriculture,
producer's demand function method was used to estimate water value in
hydropower and industry, and consumer's demand function method was used to
estimate the water value in domestic uses. The hydro-economic models are
different

from

traditional

hydrological

models

by

taking

additional

consideration of "varied" water values. The hydro-economic models are
different from economic models which usually focused on economic effects of

3


projects. Therefore, hydro-economic models were developed in order to
integrate hydrologic models and economic models.
1.3

Literature review of hydro-economic models

Hydro-economic models have been widely applied in many researches in the
field of water allocation, infrastructure, groundwater and surfacewater,
institution, market and water price, transboundary conflict, water management
in climate change, flood management (Harou, 2009). The study of hydroeconomic models in the world has been implemented since 1960s. The study of
hydro-economic models in Vietnam started later, but not widely. A number of
case studies were found in Ringler et al. (2006), Vu Van Tuan (2007), IWARP
(2007), which mostly applied for large river basins like Donna, Mekong, and
Red river basins. There has been no study of hydro-economic model for Be
river basin, especially when the current situation of institution and natural
condition has changed dramatically.
1.4

Overview of integrated water resources management in Vietnam

So far, integrated water resources managment (IWRM) in Vietnam has
achieved some certain achievements, but there was still some limitation,
especially regarding to river basin management. One of the main causes of
conflictions in water uses came from water resources planning. Most of existing
plannings are sectoral or provincial. Also the procedure to issue a water
resources planning is still very complex.
1.5

The gaps have not been studied in water resources planning and
management in Ba river basin

In general, previous studies of Ba river basin were implemented basing on the
assumption that water demands were fixed at certain locations. Most of the
studies applied traditional hydrological models to simulate the process of water
allocation in the basin. The results focused on finding the regions which were
water shortage according to considered scenarios. Some hydraulic structures or
management measures would be proposed for those regions. All of the studies
4


had not considered the economic value of water which would depend on the
water users, the time and the location of withdrawal. In addition, some solutions
were not quantitative, giving decision makers difficulty to deeply understand on
the potential decisions.
1.6

Summary of chapter 1

Mathematic models were considered as very important tools supporting water
resources planning and management. These models could quantify the impacts
of potential projects and policies, thereby supporting the policy makers.
Therefore, the application of a hydro-economic model is very suitable in
current situation of river basin management in Vietnam, especially for Ba river
basin.
CHƯƠNG 2 ESTABLISHING
THE
OPTIMAL

ALLOCATION PROBLEM FOR BA RIVER BASIN
2.1

WATER

Current situation of water uses in Ba river basin

Ba river basin is one of the largest national river basins in Vietnam. The basin
consists of roughly 13,900 square kilometers of land of Gia Lai, Dak Lak, Phu
Yen, and Kon Tum provinces. The topography of the basin is strongly
separated by Truong Son mountains, this creates valleys from An Khe to Phu
Tuc. The northern, western, and southern mountains in downstream region
cover the Tuy Hoa delta of 24,000 hectares which is widened toward the sea.
The combination of topography and south-western and north-eastern
moonsoons made the basin has three different climate regions, West Truong
Son, East Truong Son, and the Middle Region. With these characteristics, water
resources vary unevenly over time and space. The annual rainfall depth in the
basin is about 1,740mm. The rainfall varies over space. The upstream of Ba
river and Hinh river have the annual rainfall depth of 3,000mm, while Cheo
Reo and Phu Tuc regions have around 1,300mm. The rainfall is also unevenly
distributed over time. The rainy season in upstream region is from May to

5


October or November. The rainy season in downstream region is later and last
shorter, about 3 to 4 months from September to December.
The annual flow of Ba river basin is approximate 10 billion cubic meters. The
river network includes 36 1st - level, 54 2nd - level, and 14 3rd - level tributaries.
In general, Ba river system has a very important role in hydropower generation,

irrigation, water supply, and environmental protection for Gia Lai, Dak Lak,
and Phu Yen provinces.
2.2

Developing process of water resources planning in Ba river basin

In many years, irrigation planning, hydropower planning and other sectoral
plannings had some achievements. In recent years, several provinces has issued
multi-sectoral planning. Water resources planning of Phu Yen province was
issued in 2011, and that of Gia Lai province was issued in 2015. However, the
sectoral planning or multi-sectoral plannings all have disadvantages. The
sectoral planning was not interested in other sector uses of water. Provincial
water resources planning did not consider the flow connection in river basin
scale. This would have impact on the effect of water resources planning
solutions.
2.3

Reservoir system in Ba river basin

Almost plannings regarding to water resources chose the solution of building
hydraulic structures. There are major hydropower and irrigation reservoirs,
which play very important roles in water allocation. They are Ayun Ha, Krong
Hnang, Song Hinh, Song Ba Ha and An Khe – Ka nak reservoirs. Recently, the
conflicts between hydropower and agriculture, upstream and downstream, and
economic development and environmental protection has appeared in Ba river
basin. Many researchers pointed out that the causes of these conflicts originated
from the building and operation of large reservoirs.
The large reservoirs were built without considering fully the impacts to
irrigation and environmental protection at downstream. In order to get over
these problems, a procedure of reservoir system regulation was issued in 2014.

6


This newly procedure needs time to testify the effectiveness and
reasonableness.
2.4

Establishment of optimal water allocation problem in Ba river basin

2.4.1

Objective

The allocation of water for multi-sectors in Ba river basin should have
maximized economic benefit, but also ensure the requirement of balanced
society and environmental protection.
2.4.2

Objective function

2.4.2.1

Full objective function

The most common type of objective functions in water allocation problems is to
find maximize value of overall economic benefit (Brooker and Young, 1994),
as in
max𝑧∈(𝑧) 𝐸𝐵 =

𝑖 𝐸𝐵𝑖

𝑄𝑖 , 𝑢

(2-1)

Where Q = {Qi} is the vector of water withdrawals for different sectors,
including

agriculture,

aquaculture,

domestic,

industry,

hydropower,

environment, and recreation …; EBi is the economic value, or benefit,
associated with water withdrawals Qi. The units for EBi are currency per unit
time (e.g. $/month).
There are many methods for water valuation for various economic sectors. In
general, economic benefits in agriculture, aquaculture, industry and hydropower can be calculated with production functions. However, it is usually very
difficult to determine economic benefits associated with recreational or
environmental water uses.
The objective function in water allocation problem for Ba river basin was
chosen based on previous researchs for Dong Nai river basin (Ringler, 2006),
and Red River Basin (IWARP, 2008) as followed:
𝑀𝑎𝑥 𝐟 𝐱 = (

a 𝑉𝐴𝑎

+

7

𝑚

𝑉𝑀𝑚 +

𝑖𝑛

𝑉𝐼𝑖𝑛 +

𝑝

𝑉𝑃𝑝 ) (2-3)


where VAa is water value from agriculture (including irrigation and livestock
water uses); VPp is water value from hydro-power production; VIin is water
value from industrial water use; VMm is water value from domestic water use.
2.4.2.2

Reduced objective functions

The amount of water withdrawal for agriculture in Ba river basin took about
more than 90% of water consumption. The largest reservoir (Song Ba Ha) in
the Ba river system is located near to the downstream region. With these
reasons, the thesis's author proposed to reduce the original objective function to

following ones:
𝑀𝑎𝑥 𝐟𝟏 𝐱 = (

a 𝑉𝐴𝑎

𝑀𝑎𝑥 𝐟𝟐 𝐱 = (
2.4.3

+

𝑝

a 𝑉𝐴𝑎 )

𝑉𝑃𝑝 )

(2-4)
(2-5)

Decision variables and state variables

Decision variables are independent. For full objective function, the decision
variables include irrigated areas (ha) for every crop in all regions; number of
cattles in seven regions; flows through turbines of hydropower plants; water
demands for industry, domestic, and aquaculture. For reduced objective
function, the number of decision variables is reduced according to the economic
components to be considered.
State variables are dependent variables. The state variables include inflows of
irrigation and livestock nodes, storages and water levels of reservoirs, inflows
and outflows of river nodes, power generation yields, and ouflows of reservoirs.

2.4.4
2.4.4.1

Constraints
Simulation of hydro- systems

The hydrologic component of the hydro-economic model included simulation
of water balance of the system. (Simulation of water balance of the system was
included in the hydrologic component of the hydro-economic model). The
operation of each node in the system had to be simulated considering the
relationship with other nodes.
8


2.4.4.2

Bound of variables

Bounds of variables are classified as "static" or "dynamic" bounds, In which,
the "dynamic" bounds could be described as follow:
-

The flow to water supply nodes is not greater than the flow in the river at
the moment of calculation
Qcapi,t Qghi,t

(2-13)

Where Qghi,t is the flow of node i, at time t. Note that Qghi,t is not static but
changing depending on water allocation alternative of the system. The variables

have static bounds such as water level and storage of the reservoirs.
2.4.5

Nonlinear programming problem and solving methods

Water allocation problem for Ba river basin is non-linear programming problem
with constraints.
2.4.5.1

Nonlinear programming problem
min 𝒇 𝒙
𝑠𝑢𝑏𝑗𝑒𝑐𝑡 𝑡𝑜 𝑔𝑖 𝒙 = 0, 𝑖 = 1, … , 𝑚

(2-24)

𝑥𝑗 ≤ 𝑥𝑗 ≤ 𝑥𝑗 , j=1, …, n
2.4.5.2

Solving methods

There are many solving methods for nonlinear programming problems, but
none of them can be always effective. To solve nonlinear programming
problem with constraints, it is usually to be transferred to nonlinear
programming problem without constraints (by Lagrange method). Maximizing
problems are often to be transferred to minimizing problems. In very few
problems, the solution can be found directly. The most frequently method is
applying searching algorithm.
2.4.5.3

Generalized Reduced Gradient (GRG)

The main concept of GRG method is separating the variable vector (x) into
basic vector (xB) and nonbasic vector (xN). In theory, m basic variables can be
9


expressed as function of (n-m) nonbasic variables. The reduced objective
function will be:
𝑭 𝒙𝑁 = 𝒇 𝒙𝐵 𝒙𝑁 , 𝒙𝑁

(2-27)

The original problem will be reduced as nonlinear programming problem
without constraints:
Min F(𝒙𝑁 )

(2-28)

Subject to 𝑥𝑁 ≤ 𝑥𝑁 ≤ 𝑥𝑁
GRG method was developed by Abadie and Carpenter, based on GRG method
by Wolfe. This method was available in solver CONOPT integrated in GAMS
and would be applied to solve the optimized water allocation problem for Ba
river basin.
2.4.6

Selection of mathematical tool

There are a lot of tools solving optimizing problems in water resources
planning and management. In fact, they are computer languages that can
develop mathematical models connecting with a library of opimizing solvers.

Although the effort needed to develop the code, these tools allow users
describing system in detail. GAMS is a suitable tool for solving nonlinear
programming problem and was chosen in this thesis. The solver CONOPT 3
with GRG algorithm was chosen to solve the problem of Ba river basin.
2.5

Summary of Chapter 2

In this chapter, water resources characteristics and existing exploitation
situation Ba river basin have been analyzed. An optimized water allocation
planning problem was established. The objective function, decision variables,
state variables, and the constraints were described in details. Because of the
large nonlinear programming problem, GAMS was chosen to develop a hydroeconomic model for Ba river basin.

10


CHƯƠNG 3 SIMULATING AND SOLVING HYDRO-ECONOMIC
PROBLEM IN GAMS
3.1

Introduction of GAMS

GAMS (General Algebraic Modeling System) is high-level language to solve
optimizing problem. GAMS includes a compiler and many solvers. The general
form of nonlinear programming problem in GAMS/CONOPT is as follow:
min or max
subject to
lo< x < up

f(x)
g(x) = b

(1)
(2)
(3)

where f(x) is the objective function; x is the variable vector; g(x) are the
constraints; b is right hand side vector; lo and up are lower and upper bounds of x.
Objective function
The user has to create a variable without domain (scalar). Then, the user will
use an equation to take it as the objective function.
Decision variables
All the variables in GAMS have to be declared by the statement Variables.
Example3-2Decision variable in GAMS
POSITIVE VARIABLES
declare the decision variable
ar(n)
the area of irrigated spring rice at node n

Domain
Description

name
Constraints

The constraints are declared in GAMS by the statement Equations.
Bounds
The lower and upper bounds of a variable can be described in two ways: using
equations or using lower bound (lo) and upper bound (up).

11


3.2

Developing a hydro-economic model in GAMS

The structure of hydro-economic model is the integration of hydrology and
economic components. The links between these two components are the
allocated flows to different users. The solution of the economic component will
be the optimizing allocated water withdrawals. Then, these allocated water
withdrawals will decide the state of the whole system at each time step in
hydrology model. In contrary, water balance equations in hydrology component
will change the "dynamic" constraints of economic model. Basically, the hydroeconomic model is an optimize model with a simulation component. The model
is to find the maximize value of total net benefit from all water uses. The
details of the model program are shown in the Annex 1.
3.3

Combination of scenarios for application of the hydro-economic
model

Some scenarios related to policy management of water resources were
developed on the basis of considering the natural, economic, social and
environmental conditions. The results from these scenarios can assist policy
makers to take measures of planning, construction or management accordingly,
improve the efficiency of water utilization.
Base scenarios (KBCS) reallocate water resources in 2009-2010 to assess the
economic efficiency of optimizing water allocation alternative compared to
actual water uses. The other scenarios are adjusted from the base scenarios with

some changes in input data. Scenarios of Group A were set up to assess the
impact of natural flow changes to optimizing water allocation. Scenarios of
Group B refered to the effectiveness of economic policies in water management
through changing economic inputs of the model. Scenarios of Group C studied
a number of water-saving measures in the management of water resources.
Scenarios of Group D reviewed the water allocation of Ba river basin in case of
drought (with the flow of 1982-1983) by proposing decrease minimum capacity
of hydropower plants. Combination of scenarios are presented in Table 3.3. In

12


addition, all adjusted scenarios considered minimum flow requirements and
food security (food crop acreage minimum).
Table 3.3 Combination of scenarios
Group

Name

CS

KBCS1
KBCS2

2009-2010

A

A1
A2

…
A25

B

C

D

3.4

Water
year

Irrigation
demand

Other
water
demands

Water
demand
for
Hydropower
generation

Economic
data

Minimum
flow
requirement

3.3.1.4

3.3.1.4

3.3.1.4

3.3.1.5

No

No

3.3.1.6

1978-1979
1979-1980
…
2009-2010

KBCS

KBCS

KBCS

KBCS

Yes

Yes

KBCS

B1a
B1b
B1c

1980-1981
1984-1985
2003-2004

KBCS

KBCS

KBCS

Yes

Yes

KBCS

B2a
B2b
B2c

1980-1981
1984-1985
2003-2004

KBCS

KBCS

KBCS

Yes

Yes

KBCS

B3a
B3b
B3c

1980-1981
1984-1985
2003-2004

KBCS

KBCS

KBCS

Yes

Yes

KBCS

C1a
C1b
C1c

1980-1981
1984-1985
2003-2004

Irrigation
efficiency:
0,8

KBCS

KBCS

KBCS

Yes

Yes

KBCS

C2a
C2b
C2c

1980-1981
1984-1985
2003-2004

KBCS

Domesti
c water
demand
increase
100%

KBCS

KBCS

Yes

Yes

KBCS

C3a
C3b
C3c

1980-1981
1984-1985
2003-2004

Changing
crops

KBCS

KBCS

KBCS

Yes

Yes

KBCS

D1
D2
D3

1982-1983

KBCS

KBCS

Nmin=0.55Nđb
Nmin=0.45Nđb
Nmin=0.35Nđb

KBCS

Yes

Yes

KBCS

Crop
price
increase
20%
Power
cost
increase
20%
Crop
yield
increase
to
maximu
m value

Food
security
require

ment

Reservoirs

Input data of the hydro-economic model

The thesis inherited the regions of water use after IWARP, with the scheme in
Figure 3.2. Each region required input data of inflows, water demands, and
hydraulic structures.

13


Figure 3.2 Map of water use regions in Ba river basin (after IWARP)
14


Figure3.3 Ba river basin network

15


Ba river system was described in GAMS by nodes and links. There were 7
boundary nodes, 20 flow nodes, 6 reservoir nodes (besides 7 quasi-irrigation
reservoirs), 6 hydropower plant nodes, 42 diversion nodes, and 4 environmental
control nodes. The whole system of Ba river basin is shown in Figure 3.3. The
thesis inherited inflows of boundary nodes phase 1978-2010 from IWARP.
Water demands in domestic, industry, aquaculture, hydropower and agriculture
are also inherited from the research of IWARP. The quantity and cost are
referenced from existing documents and market prices with adjustment. The

information of hyraulic structures, hydro-power plants, and minimum flow
requirements are referenced from the Operating Procedure of reservoir-system
in Ba river basin. Besides that, the thesis also considered requirement of food
security in adjusted scenarios.
3.5

Summary of chapter 3

Contents of Chapter 3 focuses on the introduction of GAMS system and how to
set a hydro-economic model in GAMS to describe the optimization problem of
water allocation of Ba River Basin. The full program of the model is presented
in Annex 1 of the thesis. In chapter 3, a combination of scenarios was also be
set up for model application, with detailed descriptions of the input data.
CHƯƠNG 4 EVALUATION OF ALTERNATIVE SCENARIOS
SOCIO-ECONOMIC CONDITION OF BA RIVER BASIN
4.2
4.2.1

TO

Result analysis of base scenario
Evaluate the reasonableness of hydrology simulation

The hydro-economic model of Ba river basin was applied to reallocate water
use in the water year 2009-2010, aiming to increase the benefits from multisectoral water uses. The application of the model was implemented for two base
scenarios, KBCS1 and KBCS2, corresponding to two objective functions f1(x)
and f2(x).

16

Figure 4.1 Simulated and observed flow at Cung Son station in 2010

Figure 4.2 Water levels of Song Hinh reservoir indifferent scenarios
4.2.2

Solution of the optimizing problem

In scenario KBCS1, the solutions are the flow through turbines and the crop
areas. In scenario KBCS2, the decision variables are crop areas at each region.
17


The values of objective functions in two senarios are compared with the
estimated value of the year 2010 and shown in Figure 4.2.

Figure 4.2 The net benefits from water users (Base Scenarios)
4.2.3

Selection of the reduced objective function

The reservoirs in Ba river basin have been located in quite special places. The
An Khe – Kanak hydropower plants are located at the upstream of the main
river. Water is transferred from Ba river basin to Con river basin for
hydropower generation. Another large reservoir Song Ba Ha is located at the
downstream of the main river.

Table 4.3 The optimal irrigated areas after KBCS 2
Unit: ha

Crops

North &
South
An Khe

Upper
Ayun

Ayun
Pa

Krong
Pa

Krong
Hnang

Upper
Dong cam

Downstream

Spring rice

8800

0

0

4400

0

3740

24200

Winter rice

8800

3921.9

0

4400

7700

3740

24200

Spring maize

27500

2750

5054.7

8800

20388.2

4950

820

Winter maize

27500

2116.2

0

8800

22000

4950

820

Coffee

1100

16500

6050

0

24200

2200

330

Sugar cane

9900

0

242.7

1100

2970

11800

4680

18

Table 4.4 The actual irrigated areas in 2009-2010
Unit: ha
North&
South An
Khe

Crops

Upper
Ayun

Ayun
Pa

Krong
Pa

Krong
Hnang

Upper
Dong cam

Downstream

Spring rice

2364

7810

12240

2000

1729

1525

19560

Winter rice

5500

9114

16540

3000

4059

1846

2440

25000

2500

10400

8000

20000

4500

740

987

14577

5112

0

20957

1845

285

9000

0

9229

1000

2700

10725

4250

Maize (2 crops)
Coffee
Sugar cane

Since the water value per one cubic meter in hydro-power generation is much
higher than in irrigation, then water from upstream regions (such as Thuong
Ayun) and middle regions (such as Ayun Pa) will be transferred to downstream
regions for optimized benefit of the whole basin. To avoid this situation, the
objective function f2(x) would be chosen.
The minimum flow requirement was referenced from the Procedure of reservoir
system, in which the values were transferred to one- month time step.
4.3

Assessment of variant boundary flow impacts

The relationship of the total net economic benefit and the total water
availability is nonlinear as shown in Figure 4.3. More water is available, more
benefit is generated. Upto a certain threshold of water availability (about 15
billion m3), the growth rate of benefit will decline. This may be due to all water

demands in the basin have been satisfied, or all the reservoirs and other
structures have been fully operated.
Variability of inflows in Ba river basin have an impact on water allocation in
space. Annually, the North and South An Khe region has highest ratio of water
withdrawal, showed that this region has very high economic value of water use.
The group of hydro-power plants Ka Nak - An Khe with a total capacity of
173MW in this region transfers a large amount of water to the Con river.
19


Downstream region takes advantage from upstream reservoir operation,
especially Song Ba Ha reservoir. Thereby, the downstream region is usually
fully water supplied. Besides that, the Downstream region also has the
advantage of convenient location should lower production costs, and higher
yields. Upper Dong Cam has two large hydropower projects are Song Hinh and
Song Ba Ha, featuring non-consumptive water use. If the authorities want to
allocate water more for the remaining areas include Upper Ayun, Ayun Pa,
Krong Pa and Krong Hnang, they should adopt policies to invest in new or
enhanced capacity for the reservoir in these areas.

Figure 4.5 Correlation between water availability and total net benefit from
water usein Ba river basin

Figure 4.7
Annual regional
water
withdrawals

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Annually, the amount of water withdrawals for irrigation took 83.7% of total
water withdrawals, for power generation (by transferring to Con river) took
9.5%. The water demands for domestic uses, industry, aquaculture and
livestock production accounted for only a very small proportion.
Rice was a kind of special water consumption crop in Ba river basin (near 50%
of total water withdrawals). The economic value of rice was very low.
However, to ensure required food crop areas, the amount of water allocated for
rice crop was still very high. In order to manage water in a more efficient and
economical way, rice acreage should be reduced in future. This is probably true
not only for the Ba river basins, but also for many other river basins in the
country.
4.4

Impact assessment of economic factors

The economic value of water in agriculture has always been considered to be
lower than in other sectors, such as industry, hydropower, and aquaculture.
Some economic policies such as subsidies or tax can be applied, are reflected in
the changing economic inputs of the hydro-economic model. For example, the
inputs were considered in the thesis including agricultural product prices,
power-generation costs, and crop yields. Of these, the first two factors did not
affected much the water allocation rates in the basin. Conversely, when the crop
yields increased, significantly changes of the irrigated areas in the middle area
could be found in the calculation results.
The economic factorsbeing

under consideration includecrop prices, power

generation cost, and crop yields. While the first two factors did not affect to the

total net benefit of the basin but the last one had a significant effect. The
changing yields had reallocated water to irrigated areas of middle regions.
4.5

Impact assessment of other factors

The other input factors having been adjusted include: increasing irrigation
efficiency from 70% to 80%, increasing domestic and industrial demands
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100%, and changing crop patterns. Water demands in domestic and industry
are very small, mostly have no affect on

water allocation in the basin.

Irrigation efficiency improvement had increased the irrigated areas. Scenarios
to consider changing the crop pattern are not effective due to lack of water
areas in the middle (Ayun Pa, Krong Pa, Krong Hnang) were dehydrated for all
crops.
4.6

Research on reasonable allocation of water in times of drought

Upon the occurrence of droughts, the adjustment of hydropower reservoirs
tasks by reducing the average minimum capacity of only 0.3 to 0.5 times of
guaranteed capacity can ensure other requirements for minimum food crop
areas and minimum flow requirements. Of course, the adjustments would affect
to the total power generation of the hyro-power plants.
4.7

Summation of calculation results and proposal of water resource
management measures for Ba river basin

Based on the initial calculated results of the hydro- economic model, many
alternatives of water allocation in Ba river basin had been proposed to improve
the efficiency of water uses. The priority policies in water resource
management of Ba river basins should be investing in regions of North & South
An Khe, Upper Dong Cam, and Downstream; cutting cultivated crops from two
to one in regions of Ayun Pa, Krong Pa, and Krong Hang. The policy makers
may consider to raise taxes for sectors having high economic value of water
like industry and hydropower, or to reduce input costs for food production in
agriculture by subsidies. Although the later measures would have little impact
on water allocation, but they would be somehow supporting social stability. A
technical measure to increase the irrigated water value significantly that is to
increase yield of crops in the upper and middle regions.
4.8

Summary of Chapter 4

With a total of 48 scenarios, the hydro-economic models have been applied in
many different natural, economic, social, and environmental conditions. It
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shows that hydro-economic models are high flexible. The input and the output
of the model can be adjusted up to the expectation of users. The results of
models allows rapid assessment of potential policies or management practices.

CONCLUSIONS AND FUTURE RESEARCH

New contributions
1. Study on applying an optimizing model in analysis, assessment, and
allocation of water resources in a river basin, and modifying the model for
Ba river basin.
2. Quantifying correlation between hydrology and economic factorsinBa river
basinwith consideration of natural, infrastructural, environmental, and social
conditions.
3. Evaluating economic benefits of some proposed policies in water resources
planning and management, and proposing measures in order to
improvewater use efficiency for Ba river basin.
Future research
The hydro-economic model of Ba River Basin is a tool with high flexibility, is
ideal for optimal water allocation problem of Ba River Basin. The model has
some drawbacks such as shortened the objective function, streamlining some
physical relations, or economic data input. This limitation is mainly due to the
limited scope of the thesis. For more complete model, further studies may
develop additional components of economic value in the objective function,
detailed input data including hydrological and economic.

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