Nghiên cứu xác định quy mô và hình thức bố trí hợp lý hồ điều hoà cho vùng hỗn hợp nông nghiệp đô thị

Thus, the theme: "The research on determining optimal size and layout of detention pond for the mixed urban and agricultural areas" very meaningful to reality and science.. Objectives P

THUY LOI UNIVERSITY

LUU VAN QUAN

THE RESEARCH ON DETERMINING OPTIMAL SIZE AND LAYOUT OF DETETION POND FOR THE MIXED URBAN

AND AGRICULTURAL BASINS

Major: Planning and management of water resources

The thesis was completed at the Thuy loi University

Supervisors1: Assoc Prof Dr Tran Viet On

Reviewer 01: Prof Dr Duong Thanh Luong

Reviewer 02: Prof Dr.Tran Huu Uyen

Reviewer 03: Dr Nguyen Van Tuan

The thesis will be presented to the Doctoral Evaluation Council at Room 123-A1 buiding, Thuyloi University

………

………

Time of presentation: ………

If you would like to get more information on this thesis, please feel free to visit:

- The national Library

- Thuyloi University Library

INTRODUCTION

1 The necessity of thesis

In recent decades, due to the demands of the development, constructing the urban areas and industrial zones have shifted the soil structure of many agricultural regions to urban - agriculture mixed regions This change has increased flooding in these areas Using detention pond to regulate stormwater and reduce flooding is an effective solution However, there are no researches on the effects of detention pond to the construction cost of the drainage system for the mixed areas Thus, the theme: "The research on determining optimal size and layout of detention pond for the mixed urban and agricultural areas" very meaningful to reality and science

2 Objectives

Proposing a methodology to determine optimal size and layout of detention pond

to reduce the construction cost of the drainage system for the mixed areas

3 The scope of work and object of study

The thesis focused on determining optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas, applying

to the Western Hanoi

Object of study: the drainage system for the mixed areas, applying to the

Western Hanoi

The scope of work:

- The optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas in terms of ditermining topography, ground, slope of canal as well as location of constructions

- Regardless of sewage or water quality as well as other costs such as operating costs and maintenance of drainage system

- Applying to the western Hanoi

4 Research methods and approaches

4.1 Approaches: Approaching the system, inheriting available researches 4.2 Research methods and used techniques

Inherited methods, modeling and simulation methods, analysing system and optimization, statistical methods

5 Scientific and practical significance

Scientific Significance: The thesis provides scientific methodology for

determining the optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas

Practical Signigicance: The thesis proposed the percentage of area and form of

rationl layout of detention pond in the Western Hanoi This result can be applied

in planning of detention pond for the Western Hanoi and other areas with similar conditions

6 New contributions of the thesis

1 This thesis provided a scientific method to determine the capacity and layout form of detention ponds for the mixed urban and agricultural drainage to reduce the construction cost The new method includes: constructing objective functions, identifying components of the objective function, solving optimization problems, suggesting a decision alternative (i.e instead

of proposing and calculating each of available alternatives in detail, these alternatives were compared, and then the best alternative was selected) The new method overcomes a limitation of the existing method which limits quantity of alternatives, hence the new method is considered more appropriate than the old one

2 The thesis has applied the new method successfully for a case study- a basin

in Western Hanoi This area is currently being urbanized, and industrialized with the combination of agricultural land and urban land The thesis used SWMM5.0 (Storm Water Managament Model of EPA, USA) to analyze and evaluate 500 options including centralized detention ponds at the headworks or decentralized ponds at major channels and at minor channels The results show that: i) For this study area: The appropriate ratio of detention pond area to total drainage basin area fluctuates from 2% to 3.82% depending on two factors: (1) layout form of detention ponds (i.e decentralization or centralization) The more dispersive the detention ponds are, the higher the ratio is; (2) land acquisition cost The more the land

acquisition cost is, the smaller the ratio is and vice versa; ii) With the same ratio, the more dispersive the detention ponds are, the less the land acquisition is and vice versa This result (first time) proved (through specific data) the effectiveness of the motto "spraying water, burying water" proposed long time ago by water resources experts of Viet Nam

The research results can be applied for other similar drainage areas

7 The layout of thesis

There are three main chapters:

Chapter 1 Overview of detention pond, effect of detention pond to drainage

system for the composite areas

Chapter 2 Methodology and research tools

Chương 3 Researching and determining the optimal size and layout of

detention pond for the Western Hanoi

CHAPTER 1 OVERVIEW OF DETENTION POND, EFFECT OF DETENTION POND TO DRAINAGE SYSTEM FOR THE COMPOSITE

1.1.2 The function of detention pond

The detention ponds in drainage system simultaneously perform multiple functions such as regulating stormwater, reducing flood, storing water for irrigation, aquaculture, improving the microclimate, creating good ecological environment

In this research, detention pond (called HDH) focuses only on the function of regulating stormwater and reducing flood

1.1.3 The connecting forms between detention pond and chanel

There are two connecting forms: detention pond is on channel and detention pond is beside of channel (1) Pond on channel is construction connected from pond to channel by spillway, culvert or channel or combination between channel and spillway, channel and culvert (2) Pond beside channel is part of channel extended with function of regulating water

1.2 Overview of using detention pond

1.2.1 On the world

Detention pond used to reduce flood in urban areas have built widely since 06’s

of 20th century all around the world However, the uneven contribution of pond area with total drainage area is diffirently divieded among cities as well as continents

1.2.2 In the Vietnam

The detention pond in urban drainage system have area ratio from 1% to 5%, most natural lakes, and scattered distribution Some detention ponds use less efficient due to the location, area ratio, capacity, operation or connecting system between pond and channel

1.3 Overview of researches on detention pond

1.3.1 On the world

There have been many researches on the effect of detention pond to the flooding, environment and landscape Some studies which have figured out the approaching method by using detention pond to store the rainfall for other purposes is very effective either technique and economy Some studies shown that the concentrating pond reduce peak discharge and flooding better than dispersing pond

1.3.2 In the Vietnam

Some studies on sustainable drainage have considered the detention pond under the aspect of dispersion, rainfall reducing at source (stored in households and increased permeability) The studies about the influence of the detention pond to the drainage headworks were also considered In addition, studies of other fields (environment, landscape, ecology) were also announced

In conclusion, either worldwide and Vietnam doesn’t have any research on relationship between size and layout form of detention pond to the construction cost of the drainage system for the composite areas

1.4 Conclusions of chapter 1

The results of research show that: 1) Area ratio of detention pond in cities on the world and in the Vietnam are very different 2) Most of the research focused on the function of environmental improvement and storing water for many different purposes 3) Concentrating pond has good efficiency for reducing the peak discharge, flooding area and the flooding depth depends on the scale and layout form of detention pond 4) Detention pond in agricultural drainage system have researched at the simple level: aquaculture pond, storage water in fields 5) Effect of detention pond to headworks is very clear

There are no researches on relationship between size and layout form of detention pond to the construction cost of the drainage system for the composite areas

According to above reasons, the thesis: “The research on determining the size

and form of rational layout for the composite area” is sponsored to research

CHAPTER 2 METHODOLOGY AND RESEARCH TOOLS

2.1 The detention pond in the drainage system

2.1.1 The detention pond in the urban drainage system

The detention pond is one of terms of urban drainage system The detention pond originated from either nature or artificiality is distributed in residential areas or park to store rainfall, reduce flooding, improve the environment and provide water for irrigation

2.1.2 The detention pond in agricultural drainage system

The detention ponds in agricultural drainage systems are natural ponds or lakes existing before headworks were built The natural ponds are sparsely distributed and the artificial pond has function on aquaculture or irrigation These detention ponds have function to store rainfall, reduce the peak discharge for downstream constructions, and provide water for irrigation

2.1.3 The detention pond for composite areas

The drainage system for composite area includes simultaneously drainage construction for urban areas and for agricultural areas Constructions in drainage system are characterized by incharge area is urban or agricultural

2.2 Making the problem to determine the size and layout of detention pond

Figure 2.7 Drainage system layout for the composite areas

The problem is applied to the composite areas The initial conditions of the problem stated that the drainage ground, land using and infrastructure need to be planned in the researching area (determing location of the drainage headworks, regulating culvert and canals) Therefore, the detention pond area may be reached to a certain rate

Requirement: Determing the size and layout form of detention pond in order to minimize the construction investment cost and ensure no waterlogging corresponding the design storm

b New method

The author proposes a new method to determine the size and form of rational layout for detention pond (Figure 2.8) including building objective function, solving the optimization problem by regression method, proposing a reasonable solution

Figure 2.8 New method Figure 2.9 Traditional method (Diagram of determining steps of the reasonable layout of the detention pond) The basic advantage of this proposed method is to increase the considered cases (more than 500 cases), regardless of the experience of proposer Thus, the rationality of the proposed method is very high

2.3.2 Facility to determine the size and layout form of detention pond

The construction area should take advantage of the natural ponds and farmland and are not coincided to the technical infrastructure already planned

Proposing some different

solutions: (canal,

Establishing methods (hydraulic,

hydrological calculating –

determining designing flow rate and

method scale by modelling)

Establishing regression

function

Studing basin characteristic:

Topography, geology, land

Proposing selected method

Proposing some solutions: (channel, detention pond) Determining the designing flow rate of each method Economy, technical calculating of

The calculating scenarios are created from the combination of size and layout form of the detention ponds (concentrated or dispersed) in the determined region under the plane containing thescale and layout form axis (Figure 2.10)

n n

n n

n

KB KB

VT Nm VT

Ni VT

N VT N VT

KC

VT Nm VT

Ni VT

N VT N VT

KC

VT Nm VT

Ni VT

N VT N VT

KC

m Branch i

Branch Branch

Branch cannal

Main

.

.

02

01

.

.

.

.

.

.

.

02

01

.

02

01

_

_

02 _ 01

_

2 1 2

2 2

2 2

1 1

1 1

Figure 2.10 The determining method of layout form scenario

2.3.3 Determining the size of the drainage system in scenarios

After proposing the scenarios on size and layout of detention ponds, it is period

to determine the construction scale in system by following steps:

1 st Step: Determining the preliminary dimensions of channels, pumping stations

according to the current regulations, namely follow to the formula in TCVN 7957: 2008, TCVN 4118-85

2 nd Step: Using Storm Water Management Model 5.0 (SWMM 5.0, EPA USA),

to simulate and to check the system determined from the 1st Step This problem suggests for the urban drainage system and appling “on-farm detention pond” method for the agricultural area The calculating result of on-farm detention pond method is outflows and they are entered into the SWMM 5.0 model as

inflows at Nodes

2.3.4 Establishing the objective function and the constraint conditions

a General objective function

General objective function for reasonable design problem is only minimum the construction investment cost The general objective function form:

Min C

C C

C C C

C

j

T

1 hdh m

1 thkj n

1 đmi j

hdh j htk j

With: C j ht: The total construction investment cost of drainage system for the

scenario j, C j đm: The total construction investment cost for drainage headworks

for the scenario j, C j htk: The total construction investment cost for conveying line

(conveying cannal) for the scenario j, C j hdh: The total construction investment

cost for the detention ponds for the scenario j, J: Number of scenario J = 1, 2,

3, , n: Number of cannals in system, T: Number of detention pond in system

b Constraint condition

The constraint conditions in the simulation: 1) Fngập = 0; no flooding in the case

of calculating rain 2) Fhồ < (a%* Flưu vực); detention pond area is smaller than a% total drainage area 3) Construction the detention ponds are workable 4) Assuming the studing field has defined boundaries, planned ground of canal and pipepline, identified the slope of each channel segment, and fixed the structure form and the detention pond work in the gravity form 5) The scenarios are siminar in work structure, unit price and calculating period

c Establishing the objective function for studying area

The identification of the objective function for the studying area is done on the basis of determining the regression function’s components Following as 02 methods below:

Method 1: Calculating directly the construction cost, establishing the regression function between construction cost and discharge

Method 2: Construction costs are taken from the project in the region Establishing of regression function between the construction costs and discharge

or area is to determine the objective function’s components

In this study, both of two ways has chosen to build the specific objective fundtion to studying areas

The order of elaboration of the regression function for each item is implemented

as follows:

* Drainage headwork is pumping station

The headwork of system is pumping station The regression function corresponding to each pumps forming:

C đm = f 1 (Q đm ); (2.30)

* Drainage channel system

Drainage channel system including multi-channel grade, each channel considers

a representative length segment L (m)

C htk = ΣC kênh cấp 1 + ΣC kênh cấp 2 + ΣC kênh cấp 3 … (2.31)

* Grade 1 and 2 channels: Assuming the grade 1 and 2 channels have trapezoidal cross-section with earth channel and earth channel with embankment The regression functions of grade 1 and 2 channels:

* Grade 3 channel: Most grade 3 channels’s common structure is prefabricated reinforced concrete culverts or box reinforced concrete culverts and buried underground

The regression functions of grade 3 channel:

C k3 = f 3 (Q k3 ); (2.33a)

* Detention pond: In this studying, the detention pond has function of regulating

rainfall and reducing flooding The regession function of detention pond:

* The specific objective function:

Regarding to (2.25) and (2.30, 2.31, 2.32, 2.33a, 2.33b) established, the specific objective function has following formula:

C = f 1 (Q đm ) + f 2 (Q k1,2 ) + f 3 (Q kc3 ) + f 4 (F h ); (2.34)

2.3.5 Applying the objective function to choose an optimal scenario

a The relationship between discharge and area of the detention pond

The relationship between total peak discharge on the drainage headwork, total peak discharge on channel system and pond area is the inverse relationship

b The relationship between total cost and pond area

According to the above relationships, the figure 2.26 has summersized the relationship between construction investment cost and pond area or pond’s area ratio

In where: Cđm Construction investment cost in headwork, Chtk Construction investment cost for channel system, Chdh Construction investment cost for detention pond, Cht Construction investment cost for whole system

Figure 2.26 The relationship form between construction investment cost and

to back away from the origin (Figure 2.26)

The methodology also presents a problem description and resolution procedures With the method described, this methodology can be applied to all the basins where have the composite area

The Storm Water Management Model 5.0 is selected to simulate the hydrology, hydraulics for urban area, on the other hand, the on-farm pond is selected to