Luận văn Thạc sĩ Kỹ thuật: Assessment of flood control alternatives for Dong Tham Muoi Region, South Vietnam

ASSESSMENT OF FLOOD CONTROL ALTERNATIVES FOR DONG THAP MUOI REGION, SOUTH VIETNAM

Ngo Van Quan

A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Engineering

Examination Committee: Prof Ashim Das Gupta (Chairperson)

Dr Mukand Singh Babel (Co-chairperson)

Dr Roberto Sulit Clemente

Dr Sutat Weesakul

Nationality: Vietnamese

Previous Degree: Bachelor of Water Engineering

Hanoi Water Resources University Vietnam

Scholarship Donor: Government of Denmark (Danida), Vietnam

Asian Institute of Technology

School of Civil Engineering

ThaiLandMay, 2006

Dong Thap Muoi region isa hollow part of Mekong Delta in Vietnam Flood causes a large inundation area in this region every year It affects to water resources, environment, ecosystems, and socio-economic activities of people More on specific, flood inundation

affect directly to agricultural production Therefore, this study deals with the assessment of flood control alternatives in order to determine damage reducing on agricultural sector to find

the best alternative which bring securing long-term benefits in agricultural production in

Three possible alternatives are proposed, through the assessment based on the most effective net benefits and whose cost of construction is acceptable for implementation for

selection Alternatives based on critical analysis ofthe physical constraints, present situation, and in future consideration,

In order to get above purposes the determination of inundation depth, inundated area

‘and inundation time in calculation for the scenarios are very important in damage assessment,

‘Therefore, this study, the VRSAP model was applied to calibrate for the flood 1996 and to simulate forthe flood 2000, with expect to determine inundation depth and inundation time in ‘Tien riever, Vam Co river and the existing channel systems in calculation cases The GIS

tools were used to simulate and determine inundation area after getting water level from calculation of VRSAP mode.

[Benefit-cost analysis of planned Mood control alternatives indicates that scenarios Dredging An Phong - My Hoa channels and Building up Sluice at the end of channel is found

a the most effective flood control alternatives The combination flood control construction alternatives and damage reducing on agricultural production from flood inundation is

recommended for implementation, with discount rate 10% is calculation result BenelïUCost ratio of 291

Calculation results of relationship between present value (P) and interest rate (i) the

results are determined that, with change of discount rates as 6%, 8%, 12% and 14%, the corresponding Benefl/Cost ratios are 3.26, 3.08, 2.75 and 2.61, respectively and internal rate

‘of return of IRR 34.2% which is concluded that the selection is economically justified

Firsily, T would like to express my deepest gratitude to my adviser Prof Ashim Das Gupta ‘and my co-adviser Dr Mukand Singh Babel for their advices and encouragements throughout the period of this study.

Very sincere thanks and appreciation are due to Dr Sutat Weesakul and Dr Roberto Sulit Clemente who serves as the member of the examination committee for this helpful suggestions and comments

I would like to express my deep gratitude to Prof Dao Xuan Hoe, who help me a lot helpful suggestions of this study and I also gratefully acknowledges the kin cooperation and help of

Eng Nguyen Thai Quyet, who help me to understand and use VRSAP model

T thank to second base Water Resource University and my friends who help me complete data collection Dong Thap Muoi region, Mekong delta in Vietnam I also would like to thank to

my classmates in AIT and my friends in Vietnam for their kind helps during the study.

Sincere gratitude is due to WAterSPS, MARD - DANIDA - Vietnam for providing scholarship for me to study in the Water Engineering Management field, in School of Engineering Technology, at AIT

Finally, Lam profoundly grateful to my parents, my sisters, my brother, and my uncle for their love and continuous encouragement inthis study.

1.2 Rational of the Study

1.3 Statement of the Problem 1.4 Objectives of Study

1.5 Scope ofthe Study

LITERATURE REVIEW

2.1 Flood Routing Model

2.2 Geographic Information System Application in Water Resources

2.3 Approaches and Methods for Assessment of Flood Control Planning

RESEARCH METHODOLOGY 3.1 Approach for Research

3.2 Theoretical Consideration VRSAP Model

3.2.1 Schematization for hydraulic computation 3.3.5 Root mean square error

3.4 Are view GIS in Simulation of Flood Inundation,

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4.2 The Methodology of Research

RESULTS AND DISCUSSTION 5.1 Data Analysis

5.1.1 Rainfall data

5.1.2 Runoff data

5.2 VRSAP Model Setup, Calibration and Verification

5.2.1 Establish schematization of river network for VRSAP model 5.2.2 Run model, calibration and veriicat

5.2.3 The simulation for historical flood year 2000

5.3 Development of Flood Inundation

5.4 Calculation Results Inundation Area and Damage Reducing

COSTS AND BENEFITS CACULATION

6.1 Caleulation Methodology and Calculation Content

6.2 Proposed Construction Program 6.3 Construction Costs

6.4 Operation, Maintenance and Renewal Costs 6.5 Benefit Calculation

6.46 BenefityCosts Analysis,

6.7 To Compare and Select between Alternative A and Alternative B 6.8 Benefil/Codts Analysis with Other Annual Interest Rates,

CONCLUSIONS AND RECOMMENDATIONS,

REFERENCES 76

APPENDIX A 7

APPENDIX B 109

“The administration map Mekong River Delta, Vietnam and the study area ‘Schematic representation of flow systems in dong Thap Muoi region

Figure 2.1 Literature review of hydraulic and assessment flood control planning

Methodological framework for assessment analytical flood control planning

The location of all stations of study area

‘Methodological framework detail of thesis ure summarize as shown below Calculated and observed at Tan Chau station on Tie river flood 1996

Calculated and observed at Moc Hoa station on Vam Co river flood 1996 Calculated and observed at Hung Thanh station Phuoe Xuyen channel 1996

Calculated and observed at Tan Chau station on Tin river flood 1999 Calculated and observed at Moc Hoa station on Vam Co sive food 1999 Cateulated and observed at Hung Thanh station on Phuoe Xuyen channel 1999

‘Water level (Scenario 1) at some nodes along Tien river of flood 2000 Figure 5.10: Water level (Scenario 1) at some nodes along Vam Co river of flood 2000

Figure 5.11: Water level (Scenario 1) some nodes along Phuoe Xuyen channel flood 2000 Figure 5.12: Husteation of agricultural cultivation periods and water level

Figure 5.13: Hlustration to separate Field cells

Figure 5.14: Simulation flood inundation map on 30/Aug before have flood control Figure 5.15: Simulation flood inundation map on O1/Nov before have flood control

Figure 5.16: Simulation flood inundation map on 30/Aug for Sub-scenario 3 (Seenario 2) Figure 5.17: Simulation flood inundation map n 01/Nov for Sub-scenario 3 (Scenario 2) Figure 5.18: Simulation flood inundation map on 30/Aug for Sub-scenariol (Scenario 3)

Figure 5.19: Simulation flood inundation map on 01/Nov for Sub-scenariol (Scenario 3) Figure 6.1

Figure 62: Figure 6.3:

‘The stages of construction for implementation plan in Scenario?

‘The stages of construction for implementation plan in Secnario3 “The relationship between present & interest rates

LIST OF FIGURES

Figure 6.4: Cash flow graph of not benefits and costs

Figure 5.20: Flood inundation map on 30/Aug before flood control (Scenario!)

Flood inundation map on 01/Noy before flood control (Scenario 1) Flood inundation map on 30/Aug for Sub-1 (Scenario 2)

Flood inundation map on O1/Nov for Sub-l (Scenario 2) Flood inundation map on 30/Aug for Sub-2 (Scenario 2) Flood inundation map on OL/Nov for Sub-2 (Scenario 2)

Flood inundation map on 30/Aug for Sub-3 (Scenario 2) Flood inundation map on O1/Nov for Sub-3 (Scenario 2)

Flood inundation map on 30/Aug for Sub-4 (Scenario 2) Flood inundation map on OL/Nov for Sub-4 (Scenario 2) Flood inundation map on 30/Aug for Sub-1 (Scenario 3)

Flood inundation map on O1/Nov for Sub-l (Scenario 3) Flood inundation map on 30/Aug for Sub-2 (Scenario 3)

Flood inundation map on 01/Noy for Sub-2 (Scenario 3) Flood inundation map on {O/Aug for Sub-3 (Scenario 3) Figure 5.35 Flood inundation map on 01/No for Sub-3 (Scenario 3)

Flood inundation map on 30/Aug for Sub-4 (Scenario 3) Flood inundation map on O1/Nov for Sub-4 (Scenario 3)

Flood inundation map on 30/Aug for Sub-5 (Scenario 3) Flood inundation map on O1/Nov for Sub- (Scenario 3) Flood inundation map on 30/Aug for Sub-6 (Scenario 3)

Flood inundation map on O1/Nov for Sub-6 (Scenario 3) Flood inundation map on 30/Aug for Sub-7 (Scenario 3)

Flood inundation map on O1/Nov for Sub-7 (Scenario 3)

LIST OF TABLES

Table Title Page ‘Table 4.1: The data collection of stations in study area "

Table 42: The information of agricultural production in region 19 ‘Table $.2: The area of field cells 31

‘Table 5.7: Flood water level at 30/August (Summer-Autumn) before and after have flood control alternatives in (Scenario 2) 35 ‘Table 5.8: Flood water level at O1/Nov (Spring-Winter) before and after have flood controL

alternatives in (Scenario 2) 35 ‘Table 5.9: Flood water level at 30/August (Summer-Autumn) before and after have flood.

control alternatives (Scenario 3) 36 ‘Table 5.10: Flood water level aLĐ1/Nov (Spring-Winter) before and after have flood control alternatives (Scenario 3) 36

Table 5.11: Summarize calculation results of inundation area in Summer-Autumn season after completed flood control construction (Scenario2) 4

‘Table 5.12: Summarize caleuladion results of inundation area in Winter-Spring season after completed flood control construction (Scenario 2) 46

Table 5.13: Calculation results of inundation area in Summer-Autumn season after completed

Food control construction (Scenario 3) 47 ‘Table 5.14: Calculation results of flood inundation area in Winter-Spring season after

completed flood control construction (Seenario 3) 48 ‘Table 6.1: The stage for construction in scenatio 2 50 Table 6.2: The stage for construction in scenario 3 30

Table 6.3: Scenario3: Alternatives for floodwater drainage in field internal by horizontal channel systems 3

‘Table 64: Seenario3: Alternatives for floodwater drainage in internal field by channel

systems parallel with Tien river 35 Table 6.5: Investment throughout the stages for scenario 2 38

Table 6.6: Investment throughout the stages for scenario 3 38

‘Table 6.7: Calculation results of flood inundation area in Summer-Autumn season of Sub-scenariol (Scenario 2) before and afler have stages construction 6

LIST OF TABLES

Table Title Page ‘Table 6.8: Calculation results of flood inundation area in Winter-Spring season of Sub.

scenario! (scenario 2) before and after have stages construction “ ‘Table 6.29: Summarize calculation results Initial investment cost and economic damage

reducing on scenario? after have stages construction 65 ‘Table 6.30: Summarize calculation results initial investment cost and economic damage ‘reducing on scenatio3 after have slages construction 66

Table 6.31: Summarize calculation results of Economic Benefits and Costs Analysis forall scenarios as mentioned above contents as shown below 6

‘Table 6.32: Shows the cash flow in Investment, Operation and Maintenance (O&M), and Benefits of Alternative A 6s

Table 6.33: Shows the cash flow in Investment, Operation and Maintenance (O&M), and

Benefits of Altemative B “ ‘able 6.43: Comparison and select between alertative A and altemative B 0

‘Table 6.4: Sensitivity analysis or different interest rate for alternative A 10 ‘Table 6.45: Summarize calculation results benefilveosts analysis for alternatives n Table 6.54: Summarize calculation and comparisons results for alternative A & alternative B

n ‘Table 5.3: Max water level calculation results along rivers and channels before & after have

flood control (Scenario 2) 81 ‘Table 54: Max water level calculation results along rivers and channels before & after have

flood control (Scenario 3) 2

Table 5.5: Max flood water level at field cells before and after have flood control alternatives (Scenario 2) 83

‘Table 5.6: Max flood water level at field cells before and after have flood control alternatives (Scenario 3) 84

Table 6.9: Calculation results of flood inundation area in Summer-Autumn season of

Sub-scenario 2 (Scenario 2) nô

‘Table 6.10: Calculation results of flood inundation area in Winter-Spring season of

‘Table 6.11: Calculation results of flood inundation area in Summer-Autumn season of

LIST OF TABLES

Table Title Page ‘Table 6,12: Calculation results of flood inundation area in Winter-Spring season of Sub.

Table 6.20: Calculation results of flood inundation area in Winter-Spring season of Sub: scenario 3 (Scenario 3) tại

‘Table 6.21: Calculation results of flood inundation area in Summer-Autumn season of

‘The Cash flow in Investment, (OM), and Benefits of Sub-L

The cash flow in Investment, (OM), and Benefits of Sub-2 The cash flow in Investment, (OSM, and Benefits of Sub-+ ‘The Cash flow in Investment, (O&M), and Benefits of Sub-2

The cash flow in Investment, (ORM), and Benefits of Sub-3 The canh flow in Investment, (O&M), and Benefits of Sub-#

The cash flow in Investment, (OM), and Benefits of Sub-S The cash flow in Investment, (OM), and Benefits of Sub-6 ‘The cash ow in Investment, (O&M), and Benefits of Sub-7

Calculation result of benefiscosts of altemative A, with Calculation result of benefitscosts of alermatixe B, with

Calculation result of benefits/coss of alternative A, with Calculation result of benefits/eosts of alternative B, with Calculation result of benefitscosts of alternative A, with i=

Calculation result of benefits/costs of alternative B, with i Calculation result of benefitsleosts of alternative A, with

Calculation result of beneffs/eosts of alternative B, with i

INTRODUCTION 1.1 Background

“The Mekong River (Figure 1.1) is one ofthe histori rivers of Asia, ranking twelfth inthe list (of Tongest rivers of the world It flows along the borders of six countries: China, Myanmar,

Laos, Thailand, Cambodia and Vietnam A large delta in South of Vietnam, the Vietnam's ‘Mekong delta comprise of provinees: Long An, Dong Thap, Tien Giang, Ben Tre, Tra Vinh,

‘Vinh Long, An Giang, Can Tho, Kien Giang, Hau Giang, Soe Trang, Bac Lieu and Ca Mau as shown Figure 1.3 This dela is subdivided into four main regions: (a) Dong Thap Muoi, (b) Long Xuyen Quadrangle, (c) Bassac and Mekong (the region located between the Mekong

and Bassac river), and (d) west Bassac River region (the area on the westside of Bassac River between Long Xuyen and Mekong River) as shown in Figure 1.2.

T T T ~

Map of ubided Region Mong iver Celta, Vietnam

asice

T T

MAP OF PROVINCES IN MEKONGRIVER DELTA, VIET NAN

, EaaRiver

Figure 1.3: Schematic representation of flow systems in dong Thap Muoi region

‘A large area in the northern part of Viet Nam's Mekong Delta (Dong Thap Muoi) is flooded ‘annually when the water level in the main channels rises above the river, canal banks and

particularly, the floodwater overflow border Vietnam-Cambodia Flooding has serious negative impacts on production and livelihood of the people In the past, the flooded areas were almost unproductive or planted with floating rice of low yield Since the 1980s, as the

result of many projects funded by the Government to exploit the Dong Thap Muoi area, water control structures have begun to promote development with a new perspective Double or

triple cropping patterns using high yielding varieties are new concept and have practiced in the flooded area.

Annually, floods still cause serious losses in terms of production, infrastructure damage and

hhuman lives In recent years, 1994, 1995, 1996, more than hundreds of people were flood ‘victims Particularly flood in 2000 is still vivid memory Total losses amounted to hundreds

Of million dollars This results as permanent threat to the communities, where people are living in low-lying lands, The low-lying land in the delta is usually fertile that has been exploited for the agricultural purposes Inundation occurs causing great damage for the

lowland inhabitants whose economy mainly depends on agriculture activities from flooding,

‘This is a flood plain (closed floodplain systems) and contains agricultural atea, which

accounts about 72% of Dong Tháp Muoi region where agriculture is the mainstay of economy, Nevertheless, flood has positive effects, for example, floodwaters carry sediments

40 enrich the rice fields, increase aquaculture production, and leach toxic ions from acidic soils,

Flood controls in the Mekong Delta in general have been the focus of many studies by various

Vietnamese and international agencies particularly in Dong Thap Muoi region While the main problem is to minimize the impact and maximize benefits of flood and inundation using

flood control planning still in obscure

According to Vietnam's atlas, the Dong Thap Muoi region is located between 10°35-11°00N latitude and 105°20-106'00E longitude Its surrounded by Cambodia in North, Tien River in the West and South, Van Co River in the East It covers the land of Long An, Dong Thap and Tien Giang Provinces as shown in Figure 1.3 The slope is from North-West to

South-East, the land surface of 1.0 to 3.5m Total area ofthe region is 7,088.6 km’, with agricultural area of 510,379.2 ha (72%) and it includes three provinces as

Long An: districts including are Tan Hung, Vinh Hung, Moc Hoa, Tan Thanh, Thanh

Hoa, Due Hue, Ben Lục, Thu Thua Total area of this province is 3,205.3 km*

‘Tien Giang: districts including are Cai Be, Cai Lay, Chau Thanh, Tan Phuoe, Total

area of this province is 1401.3 km”

Dong Tháp: district, one City including Hong Ngu, Tan Hong, Tam Nong, Thanh Binh, Cao Lanh, Thap Muoi, city Cao Lanh Total area of this province is 2,482 km’ (Source

statistical yearbook)

‘Some of the characteristics ofthese regions are described as follows

48) Water quality: Fresh water is available for the whole year Tidal effect inthe dry season: “The semi diurnal tidal (twice daily) is dominant with amplitude of 1.0m and a high tidal water level of 1.5m and coming along some main tives as Tien riever and Vam Co river

») Flooding: Annual inundation for periods of up to five months (from July to November) High flood occurs at the end of September and first of October, with water level from 3.7 to

5.12m compared with Hon Dau datum (at Vung Tau beach) During that time, 90% of the area is submerged.

«) Existing channels and hydraulic structures: except for the main rivers namely the Tien

river, Vam Co river and Phuoc Xuyen channel, the horizontal channel systems and the

parallels channel system with Tien rives,

1.2 Rational of the Study

“The natural limitations are deciding factors to exploit land resources of this region such as ‘lood inundation, alum soil and salt intrusion particularly in coastal belt Recognizing the high

potential for agricultural development in the region, the Government of Vietnam accorded a

high priority to this region for the design and construction of flood protection and flood

drainage project, These activities for flood control and potential development in region have

been partially implemented, based on caleulaion results om historic flood 1996 The

purposes ofthese projects are to minimizing the flood effect on agricultural sector in Dong

‘Thap Muoi region.

Although they brought economic benefit due to agricultural productions and improved <rainage in region However, it has been observed that there are many limitations, after the particularly historical flood 2000.

1.3 Statement of the Problem

Flood and inundation are annual events, which might affect the infrastructure, house, and specifically agricultural production, It not only interrupts socio-economic activities but also bring negative impact in natural environment

The flood inundation in the Dong Thap Muoi region is mainly due to overflow across the Vietnam ~ Cambodia border In addition, a part of the floodwater in the Dong Thap Muoi

originates from the rainfall within the region itself The floodwater in the Dong Tháp Muoi is, being drained out to the Tien River and Vam Co River Also, the flood drainage system is not ‘adequate enough to drain effectively that results high inundation depth causing permanent

threat to the communities, Some sluices have improved the flood control, but now their effects are limited because of development efforts to date, and their physical conditions do not

‘permit stable and effective operation Specially, the historical flood of 2000 was very high, so they were not fully effective as they planned In addition, the Government of Vietnam built ‘Tan Thanh-Lo Gach Dyke in order to conteol the overflow across Vietnam-Cambodia border

to protect the agricultural field from severe

Inecent years with climatic variability and extremity, the flow and water level upstream of ‘Vietnam Mekong River Delta and Cambodia border is increasing during the rainfall season and in addition, the Dyke (Tan Thanh-Lo Gach) is seriously downgraded and the bed level of

natural channel systems is raised due to siltation These factors impact the agricultural development in the region, To address this, the project has been implemented with the flood

control alternatives based on flood year 1996 The flood event of year 2000 was severe with

discharge of floodwater across the border of 12,000 m'/s compared to 8,270 m'fs (1996

event) (Vietnam yearbook 2001) and the resultant damages were higher,

With the limitations shown after historical flood 2000, the Government of Vietnam have assigned the Ministry of Agricultural and Rural Development to establish flood control

alternatives in Dong Thap Muoi region with purpose of economie potential development in this region in order to secure cultivation of two rice crops per year The objectives are

1) To control and reduce the water level for early floods in August ensuring safe

hharvesting of the Summer-Autumn erop.

2) To improve the floodwater drainage conditions at the end of the flood season to

advance sowing of theWinter-Spring crop This allows sufficient time forthe eropping cycle, “The proposal for the lood control alternatives ate given in detail in the next section In order 40 know the economic effectiveness of each alternative, an assessment and analysis of cost

and benefit of each alternation is needed,

1.4 Objectives of Study:

The main objective of study is to ass the effectiveness of flood control altematives in reducing inundation of region, The specific objectives areas follows:

To simulate flooding (VRSAP model).

tation using Vietnam River System and Plain Model

‘To determine depth, area of inundation and the damage to agricultural sector for

different flood control alternatives.

To compare and assess the economic effectiveness of the proposed flood control alternatives

‘Conclusion and recommendations for implementation of flood control alternatives

1-5 Scope of the Study

“The scope of the study includes:

Collection of relevant data and information mainly from the secondary sources

Development of spatial database for the study area, using Geographie Information ‘System tool

Calibration and verification of VRSAP model using flood year 1996 and flood

1999 respectively.

‘Simulation for flood year 2000 u 1g calibrated VRSAP model

Estimation of depth, area and duration of inundation, with/without flood control

Calculation of investment cost for flood control construction scenarios.

Calculation of economic losses reduction in agricultural sector corresponding to

different flood control scenarios.

Recommendations for alternatives to solve the problem of inundation in Future

Chapter 2

LITERATURE REVIEW

‘The literatures relevant to flood inundation and its impact on society were studied and discussed in this chapter This chapter is sub-divided into three sections according to the

‘proposed objectives oÏ the study as shown in figure 2.1

Literature Review

‘Studies of flood control inthe etudy

acea and related basin

‘New approaches of GIS application in

Water Resource

‘Approaches and methods for assessment of

flood control planning

Figure 2.1 Literature review of hydraulic and assessment flood control planning 2.1 Flood Routing Model

“The VRSAP model has been used in a number of water control studies in Viet Nam on both

low flow saltwater intrusion, and flood flow, such as: salinity intrusion studies in the Mekong Delta supported by the Australian Government through the Interim Mekong Committee from

1981 to 1991; eco-development planning and pre-feasibility studies of water control in the ‘Quan Lo - Phung Hiep area of the Mekong Delta supported by the Mekong Secretariat and Canada’s CIDA! the UNDP-supported Mekong Delta Master Plan project studied by

NEDECO of the Netherlands, 1990-1993 In this project the VRSAP model was used to simulate the flood flow and the low flow including salinity intrusions the study of flood

control planning for the Mekong Delta, a high priority study of the Vietnamese Government; flood flow and low flow-salinity intrusion studies in the Saigon-Dong Nai Basin; the drainage studies of stom-generated rain water in the Nhieu Loc Thi Nghe canal system and water resources development projects in the Mekong Delta and the Saigon-Dong Nai Basi.

Khue (1978) developed VRSAP model based on the solution of the full Saint-Vernant

equations using the implicit Finite difference scheme that take the cross-sectional data in average of the segment Later in 1980s, VRSAP model was added with a subroutine that calculated salinity intrusion, This model has been widely used in recent water resources

planning projects, especially in recent topographic and hydraulic data and calibration for the

flood, 1996 in Vietnam part of Delta

Lya, D.A and Goodwin, P (1987) examined stability and convergence characteristics of the

{our point implicit finite difference schemes due to Preissmann which has been wisely used in ‘open channel flow modeling The analysis is made for a general linear hyperbolic system of n

first order equations but is resrieted to the homogeneous or frictionless case In particular the effects of a Weighting factor in space, as well as in time was considered.

‘Nien (1998) developed KOD model for flood computation in the Vietnam Mekong River

Delta, The model is based on the full St.Vernant equations for unsteady flow in the river channel and equations for flow over structure, The solution is based on explicit scheme.

Dutta (2000) applied Distributed Hydrologic model for the simulation of the flood inundation parameters and for flood warnings for any predicted rainfall event in Japan The physically based distributed hydrologic model considers five major components of hydrological cycle,

they are interception, and evapotranspiration, River flow, Overland flow, Subsurface flow and Ground water flow, In this model, for river flow, diffusive approximation of St enant's

momentum equation is considered and an implicit finite difference scheme is used to solve the equation for river network Similarly, for overland flow also diffusive approximation of the St.Venant's momentum equations ae considered and the equations ate solved by using an

implicit finite difference scheme,

Nhan (2000) developed HYDROGIS model, and used for flood and salinity intrusion

forecasting in the Mekong Delta The model is based on the full Saint Vernant equations Upstream boundary conditions was based on the forecasted Mow at Pakse Downstream conditions was forecasted tidal wate level in the river mouth, A comprehensive interface was

developed for data entry and presentation

‘Suphat and Nguyen (2000) developed a hydrologic-hydraulic modeling approach to simulate

the rainfall-runoff process and the flow in the large river basin, The rainfall-runoff models was first developed for the subeatchment of the river basin, which are combined to form a large river basin This model was used to generate the runoff being modeled as lateral flow to

the hydrodynamic model in which the main streams in the basin are schematized,

Gupta, Babel and Ngoc (2003) used VRSAP model to simulate the flood phenomena in the

Mekong Delta Information on depth, duration, and spatial extent of inundation and estimation of damages caused by floods are needed for planning proper flood mitigation

2.2 Geographic Information System Application in Water Resources

Recently, as a results of development of technological science, many flood damage estimation models were developed with aid of flood simulation models based on high techniques such as

Geographical Information System (GIS) These models simulate a flood event with spatial distribution of extent of flood, a criterion of new approach by aid of GIS and RS Spatial

information management and spatial analysis help managers for making decisions on structural, non-structural floods mitigation measures.

“Thapa er al (1992) described about the GIS assisted watershed management in the upper

Pokhara Valley in Nepal They studied the deteriorating condition of the watershed and

performed the spatial analysis using GIS as a tool The spatial analysis focused on the

identification ofthe locations under severe threat to environmental degradation and zoning of the land unit's were done in accordance with their physical suitability

Leipnik et al (1993) explained about the implementation of GIS for water resources planning

and management GIS is designed to store information about the location, topology and attributes of spatially referenced objects and many data base queries are performed through it,

‘They have described in detail about the stages in the implementation of GIS, and understanding ofthese stages help in using GIS in water resources planning and managemer effectively

Dutta er al, (1998) presented the methodology for flood damage assessment using GIS and Distributed Hydrology model and a case study in Ichinimiya River Basin, Chiba, Japan, The

IIS Distributed Hydrologic Model (Tha etal, 1996); which include four major component such as overland flow, river flow, unsaturated zone flow, and saturated zone flow, was used in this study for flood modeling He also deseribed the method to develop flood damage

assessment model with consideration of three categories in term of land use pattern as urban «damage and damage to service by using various hypothetical damage functions which were

developed by Bhavnagri ea (1965), Beraden (1973) and Beggs (1974)

Heping et al (1998) presented the implementation of GIS technology on Urban Flood Dynamic Simulation Model The main characteristics of Urban Flood Dynamic Simulation

‘Model are simulation of the detailed flood process, therefore, the results can be applied in many aspects such as flood loss calculation, flood hazard map, regional planning, flood

insurance, lood control planning, ee

2.3 Approaches and Methods for Assessment of Flood Control Planning

‘The Red Commission for Flood control and Management (1973) made a study on the flood

control planning in Red River Delta and concluded that to protect Hanoi and downstream, areas from flooding in case do historical flood as occurred in 1971 itis necessary to divert

flood in to the sea through Day River Basin, Based on the land use condition on the basin as well as structural conditions such as barrage and dikes and sluices along the floodways, the study indicated that the maximum discharge that the Fay Basin can carry tothe sea is 4800

Horn (1987) Use an approach to establish priorities for future flood control planning and

applied to hydrologic sub basins in the New Jersey Data on historical flood losses, flood potential, and current and prior flood control planning efforts were compiled and entered into Flood control database, accessed through a computer database management system The

selection of indicator variables, characterizing flood control planning need, was considered along with a system of the ranking and weighting these variables for assignment of planning

priority numbers to the sub basins, This approach provided an adequate sereening mechanism for establishing an initial list of planning candidates, although more subjective factors must then be used for further evaluation,

Ouellette, Leblane and Roussell (1988) The economic yield of ä floodplain zoning program ‘was measured by cost-benefit analysis The methodology entails the use of a probabilistic

hydro economic model to evaluate expected flood damages with and without zoning The application showed that this type of program, albeit cost-effective overall, may be unacceptable for various reasons tothe various parties involved.

'Nefeco (1993) curred out the study on optimal use of resources of Mekong Delta in Vietnam,

The study defined the water abstractions and their distribution over the delta and the low flow

period for different land use scenarios The study looked at surface and ground water

resources as well as consumptive use of water for drinking water supply and for irrigation of agricultural land, The water Fequirement was calculated for the dry season only

‘Ty (1995) developed a new perspective of sustainable development for the Mekong Basin

development plan This repor listed five key issues of development planning: (1) Active

participation of the riparian countries, (2) Continuity and consistency of the basin planning

‘work, (3) Advanced technology and latest achievements in basin natural planning, (4) A soil foundation of the basin development knowledge, and (5) Core human resoure

the basin development planning

elements for

Lund (2002) Economical integration of permanent and emergency flood control options is a long-standing problem in water resources planning management, A two-stage linear

programming formulation of this problem was proposed and demonstrated, which provides as explicit economie basis for developing integrated floodplain management plan The approach ‘minimized the expected value of flood damage and costs, given a flow or stage frequency

distribution A variety of permanent and emergency floodplain management options can be ‘examined in the method, and interactive effects of options on flood damage reduction can be

represented The approach was demonstrated and discussed for a hypothetical example Limitations of the method in terms of forecast uncertainty and concave additive damage function forms was discussed along with extensions for addressing these more difficult situations.

Braden and Douglas (2004) assessed the downstream economic consequences of development

designs lesing benefit transfer method to promote greater once-site water retention It concluded that once-site retention provides many services For residential properties, the economic value of those service was on the order of 0-0.5% of the market value depend on

the difference that retention makes to downstream flood exposure, For water quality improvements, the increases range up to 15% of the market value for waterside residences

‘where clarity of the water quality was greally improved The increases were much less for improvements that are much less visible, properties that property value on average for all properties in the flood plain The public sector realized additional benefit theough smaller

bridges, culverts, and other drainage infrastructure and through increased recharge Cities and industries may avoid costly upgrades to waste water treatment facilities if low flow increase,

Hayes, Amasce (2004) An interdisciplinary team consisting of representatives from state {government and academia has developed an innovative flood tisk management plan that combines a large-scale nonstructural hazard mitigation plan with portions of a federally

authorized plan previously developed by the U.S Army Corps of Engineers Separate elements of the federally authorized plan were considered for inclusion inthe alternative plan

bbaved on the estimates of each element's marginal benefil/ cost ratio, potential environment impacts, and level of consistency with current policy, The plan involved retrofitting approximately 1,500 residential and nonresidential structures in the 100- year floodplain and

require development of a structure-by-structure flood proofing benefiv/cost analysis computer program, At less the half the cost, the alternative plan achieved flood risk management goals,

ina significantly more cost-effective manner for an environmentally sensitive area.

‘This chapter describes systematic procedures for achieving the objectives ofthe study Figure

Sen aed retort of food conto“asesoment fhe preniriesim l nấy area

ni vỏ inodaien potions

nai in apc octor Spent

Flood Control Planning

3.1 Approach for Research

The proposed methodological framework is comprised of two main components

‘+ Application of Vietnam River System and Plain Model (VRSAP model) for flood routing

‘+ Application of tool for development of flood inundation maps by using Acrview

GIS software, and simulating flood inundation from results of the VRSAP model

‘+ Estimation of damage and economic effectiveness to agricultural sector for different flood control alternatives

3.2 Theoretical Consideration VRSAP Model

Khue (1978) developed VRSAP model, for simulation one-dimensional motion of water and substance (salinity, bio-chemical material, etc) An implicit finite difference scheme for solving one-dimensional Saint-Vernant equations and advection dispersion equation are

applied for complex network of rivers and canals

3.2.1 Schematiz jon for hydraulic computation

In VRSAP model, river, canal and floodplain system are divided into segments, nodes, and

storage cells for hydraulic computation,

River segments link together at nodes Nodes are intersection points of one or several river

‘segments Fach segment links two nodes: the upstream node (4) and the downstream node (c) ‘Segments are described by representative cross section while plain cell by area corresponding to land level

{In the network, nodes are code by natural numbers, form 1 to NN (NN are total number of nodes) The coding is principally arbitrary and free from the place of nodes on the plane One

node may accept either given discharge Q,, inflow (+) or out flow (-) or given water level as boundary The edge of an amputated branch is also one normal node, where the inflow discharge is Q

‘Segments are basic finite difference elements ofthe problem, the Saint - Vernant equation system will be used to every segment, the water balance condition at nodes links them to form

aan equation system forthe whole network,

3.2.2 Governing equations

For a general network flow may exist in river network, flow in, or out or storage cells, So, one hhas to deal with three types of equation; Partial differential equations for a main river

branches, ordinary differential equations for storage cells and equation for hydraulic structures, Apart from these, itis also needed to add junction conditions in some location of the network to keep the flow continuity

a) Main river

Unsteady flow can be expressed by the two governing equations, they are continuity and momentum equations, and are non-linear, VRSAP model is based on the solution of the full

fedge Saint - Vernant equations The governing equations are used as follow:

-anal width at free surface (),

Be = canal width, including storage area, averaged over the segment (m), or storage width

«= lateral flow per unit length

(C= Chezy's resistance coefficient (m'"/s)

1b) Equation for storage cells:

‘This isthe continuity equation for storage cells

w G4)

‘Where V is the water volume, Q is in and out going discharges.

‘©) Equation for hydraulic structures and junction conditio

The flow must be conservative, so at confluences or tributaries the sum ofall discharges must be zero, At hydraulic structure, flow rate is defined by the empirical formula:

Q=fi2u.zhha) 65)

Where Zi, Zh? are the upstream and downstream water levels and a is characteristic parameter of structures A structure may be modeled by one of two ways as a spillway and a sluice The discharge, passing through a spillway is calculated as:

QemoY2e(Z,-2,)" for feetow G6

Q=#b,[2g(Z,—Z,À(Z,—Z, tor submerged flow G7

The discharge through sluices can be determined as flows:

Q= po2g JZ, —Z, for free flow G8)

=poy2g \Z,-Z, for submerged flow 69)

Where m,@,1,.H, are empirical coefficients for the structure; ở is the width of the

spillway; QD is the wet area of the sluice

3.2.3 Method of solution

To get numerical solutions, the considered river network is split into river branches, separated

by nodes A node is point in a river system A confluence or tributary is a node For a hydraulic structure in river, it is associated with two nodes Upstream and downstream nodes

are defined due to different water levels

“The numerical method is based on the implicit 4 points method for river branches instead of high-resolution numerical methods, implicit finite difference scheme for storage cells and

linking discharge of hydraulic structures,

4) Finite difference scheme for river branch’s equation:

‘A branch with length [a,b] is split so that: nel

=4, <5, <0<4 5b, Ất =

at eT

Where 2X, (ik, l) are location of cross section Using difference scheme for any function f

are given below equations.

For cell& with wate level Z, surface area F Q, the discharge between nodes k andj

¢) The exchange of water between river, channel and plain cell

VRSAP distinguished two types of the exchange ofthe river flow and flood plain area, ‘Separated, conditionally connected cell:

‘This type is applied for the exchange, limited by small canal system or structure, There

‘water level difference between canal system and plain so that equation can be writen as:

r= Opn V2 V2 ~ZE oy

Qe discharge of rice-ietd

Z2 wate level inrice-feld

Z« water level in channel Opened Adjacent Cell:

‘This type is applied for the cells freely connected with a segment of river or canal, Water

level in the plain equals to that in the canal system Submerged area of cell affect directly to flow atea in governing equations for this case, equation is

'B,= canal width, including storage area, averaged over the segment (m), or storage width;

total submerged area of cells along the river

Ax length of river segment where cell is connected (m)

3.3 Statistical Criterion

The degree of accuracy in calibration of any mathematical model can be checked by statistical evaluation of the observed and computed data, The following criterion are used to check the

model efficiency.

and G9)

= represent the computed vals

presen the observed vals he sample size

333 Standard deviation

or] so =[~L¬‡(øi 2] G20)

‘STDP is the standard deviation of the computed data,

‘STDO is the standard deviation of the observed data,

3.33 Correlation coefficient

Correlation coefficient r measures the linear relation between the computed and observed data The range of its value is from - to 1 A value r=-1 indicates a perfect negative linear

relation between them, while a value r= 1 indicates a perfect positive linear association of them, I's = Ö no linear relationship exists between them.

3.34 Coefficient of efficiency

Feor-or- oir

Kĩ TT

‘The coefficient of efficiency is commonly used for measurement of the degree of association

between computed and observed data, The value ofthis coefficient approaches to | for perfect

3.3.5 Root mean square error

E (Oi pi) 5

rn — =

Root mean square error can be regarded as measure of absolute error between the computed and observed data It tends to be zero for perfect agreement

34 Are view GIS in Simulation of Flood Inundation.

A GIS, a system that is capable of assembling, storing, manipulating and displaying ‘geographically referenced information A GIS can perform complex operations on ‘geographical information, This technology are used in this thesis to simulate for quick

estimation of effected depth inundation, duration and area inundation in different flood control alternatives scenarios during flood time, GIS spatial analysis technique are used for

this work as using the GIS tool for development of flood inundation maps by using Acrview GIS software, from simulation results of the VRSAP model

‘The application tools of Acrview GIS software are shown detail in chapter five,

Chapter 4

DATA COLLECTION AND METHODOLOGY

4.1 Data Collection

1 Hydrology dat

‘The all available hydrological data in the study area are collected and shown in the table 4.1

‘below and location ofall station is described in igure 4.1 below ‘Table 41: The data collection of stations in study area

No | Measurement factors | Station Location Collected data

Teena | Tan Chow Tien River | bang Hood eon 2 Nha | Cho Moi Tien River | PANE Mood seman

3 | Watertevel (hourly) | Cao Lanh Tien River | Pung Heed sen * ein mgs | Mỹ Than | Tien River te NMẾC

5 | Water level (hourly) | My Tho Tien River During food season

6 [Wasrfet eas] oc ton West Vam Corner | Pung Hod season 7 Meine att | KienBih | LagBangechumel Paving Roe sven

8 Màn daly) Hung Thanh | Dong Tien Channel "na 9 | Rainfall (daily) | VinhHung | West Vam Co river eae

10 | Rainfa ityy | Tan An | West Vam Coriver | Pune fond sco

It | Discharge (daily) Kratie MeKong "”.

12 | Discharge (daily) Bien Ho Tolesap ee

13 | Discharge daily) | Bast Vam Co | Bast Vam Co river DU load season

14 | Discharge ail) | West Vam Co | West Vam Cover | Paving load gen 15 | Tidal tevel hourly) | VamKenh Tiensiver DỰ lod seus

16 | Tidal level (hourly) | Binh Dai Ham Luong river eee 19892000

17 | Tidal level (hourly) | Ben Trai Co Chien river "dẻ

Figure 4.1: The location of all stations of study area

2 Bathymetric data: Cross section data, which are measured along the rivers of Tien river,

‘Van Co river and Channel systems are collected from the Institute Water Planning in South Vietnam.

3 Map: The collection Topography map (1/50.000) (use to develop DEM) and Land Use

‘map (1/50.000), are collected from secondary sources as; Water Resources University and also download to get DEM 90m from free Internet

4 Agricultural documents: Collected Agricultural report of Dong Thap Muoi region in 2001 and agricultural damage of region in flood 2000, are collected from the Institute Water

Planning in South Vietnam and second based Water Resources University The information of agricultural production in region as given able 4.2 below.

‘Table 42: The information of agricultural production in region

Item Total Unit 1 Natural land area 7.088,60.0 ha

2, Agricultural land area 5103792 hà 3 Average yield rice two seasons 485 tonha

4 Yield rice of Summer-Autumn season 63 tonha

5 Yield rie of Spring-Winter season 339 tonha 6 Rice price 1668 USS/lon

7 Input for rice growth 40% of rice production

(Sources: Agricultural report in 2001 for provinces in Dong Thap Muoi region)

4.2 The Methodology of Research

‘Summary of esearch methodology ate shown in the flowchart 4.2 below:

Figure 4.2: Methodological framework detail of thesis are summatize as shown below yéaudic model (VRSAP Moda)

Input data RH, Q, Cros ection data

‘Model elitration fond 1996 Node venison 8oed 1999

‘mulation ofhistarcal ood 2000

or change commrios in Afferent food contrlalleratver

(Output ens by simulation vate evel

Wate depth eid ftom DEM and Hyératlic mose

(G1 tod (map query, map calculation, image dassScsion, đc

loodarea đape fle wih change allematives Tender areas wh comespanding

Chapter S

RESULTS AND DISCUSSTION

5.1 Data Analysis

5.11 Rainfall data

‘There are 8 stations measuring rainfall in Dong Thap Muoi region, all these are daly rainfall data, specially Tan Chau station with long observation period about 34 years (from 1970 to

date) Dong Thap Moue region is high rainfall, the average annual rainfall from 1800 to 2200mm, in which 70% fall in the flooding season Flood-caused by rainfalls normally occur

in September and October 5.1.2 Runoff data

“There are four stations measuring daily discharge in region, E stations hourly observed data of

‘water level and 3 stations hourly of tidal level

2 VRSAP Model Setup, Calibration and Verification

Like other hydrod) VRSAP model requires data at boundaries: Flow data at upstream, rainfall data, tidal level and water

availablity of the data for flood 1996, 1999 and historical 2000, data using flood 2000 for simulation, flood in 1996 are used for model calibration and the data of the flood 1999 are used for verification,

tamie model

level at station and cross section, Due to

‘5.2.1 Establish schematization of river network for VRSAP model.

In VRSAP model, river, canal and floodplain system are divided into segments, nodes, and storage cells for hydraulic computation

River segments link together at nodes Nodes are intersection points of 1, 2, 3 or several river ‘segments Fach segment links wo nodes: the upstream node (4) and the downstream node (©) ‘Segments are described by representative cross section while plain cell by area corresponding to land level One node may accept either given discharge Q,, inflow (+) or out flow (-) or siYen water level Z as boundary The edge of an amputated branch is also one normal node, ‘where the inflow discharge is Q, = 0.

‘There was a schematization of the Mekong rive systems in Vietnam Mekong delta, which was set up and this schematization is now accepted and is sued broadly for simulation the river system of Mekong river system,

Based on above large schematization inthis study also will be used but it have to added and developed some nodes as well as segments of main channel system to meet with requirement of thị study region (Dong Tháp Muoi)

“The Establish Schemazation of river network for VRSAP model in Dong Thap Muoi region is shown in Figure 5.1 in (Appendix A)

) Boundary conditions:

Upstream boundary conditions: The upstream boundary conditions of the model are the flow

discharges at Kratie (Qt) Bien Ho (Q2), Vam Co Dong (Q-0, and Vam Co Tay (Q4)

Downstream boundary conditions: The Downsteam are the tidal water levels at Vam Kenh

(H+, Binh Dai (Ht) and Ben Trai (HE),

Intermediary itself include: Rainfall within the region: Tan Chau, Cho Moi, Hung Thanh, Moc Hoa, Vinh Hung, Kien Binh, My Thuan, and Tan An.

) Initial conditions

Initial conditions of flow discharge and water level ate required atthe first time step for every

node of the model, when the model is stable, the errors in the initial conditions would decay and have no effect on the model results after several time steps So tht, the initial conditions

‘of the model are chosen such a way as to achieve the model stability 5.22 Run model, calibration and verifieation

4) After completing input data for model, run model and output to compute results are carried

‘out The Model calibration is carried out to find the model parameters, The model parameters are considered in VRSAP model as channel roughness The data of floods in 1996 are used

for model calibration and the data ofthe flood 1999 are for model verification

‘The model calibration is carried out firstly with the investigation on the channel bottom roughness, Different values of roughness ate applied the same to all channel sections to find ‘out the most suitable value After that, difference channel sections are fine turned with the

variations of bottom roughness to get the best fit with observation data at the check points, ‘which are Tan Chau on the Tien river (node 1), Moe Hoa on Vam Co river (node 93) and

Hung Thanh on Phuoe Xuyen river (node 235) The bottom roughness that gives the best fit for computed and observed water levels at checkpoints, is found to be range from 0.024 to (0405, which are suitable with experiment values of roughness of rivers.

b) The results for calibration of flood 1996 and verification 1999 from run VRSAP model is shown the below.

4 From simulation results of model calibration for flood 1996, as shown in Figure %2, Figure 5.3 and Figure 5.4 below Based on evaluation statistical ctiteria or of calculated and observed water level at check points such as Peak difference (AHmax)

and Efficiency Index (EI) their errors results are evaluated: AHimax at Tan Chau is

903m and El is 0.95, AHmax at Moc Hoa is 0.016m and EI is 0.97, AHmax at Hung “Thanh is 0.107m and Elis 0191

‘Similarly, for evaluation of simulation results for verification by flood 1999 is carried out ‘The calculated and observed water levels at checkpoints for flood 1999 are shown in Figure

5.5 to Figure 5.7 below.

Evaluation of statistical erteria (food 1999) such as Peak difference (AHmax) and

Efficiency Index (ED are calculated AHmax at Tan Chau is 0.045m and El is 0.89,

AHmax at Moc Hoa is 0025m and El s 0.96, and AHmax at Hung Thanh is 0.077m

and EL is 093 Looking at the flood hydrograph at three stations and based on calculation statistical criteria error, the verification result is suitable in Dong Thap ‘Muoi region, thus the calibration and verification results of VRSAP model for flood in

1996 and 1999 are acceptable The evaluation statistical criteria are represented in Table 5.1 {Appendix A)

Figure 5.2: Calculated and observed at Tan Chau station on Tien river flood 1996

Observed and calculated water level at Moc Hoa station flood 1996

eae ae — Tớ in mh

Figure 5.4: Calculated and observed at Hung Thanh station Phuoe Xuyen channel 1996 Result of calibration for flood depth showed that the peaks are fitted well with observed valu

at three stations, though the shapes of the graphs are not the matches properly, especially at ‘Hung Thanh siaion However, ooking atthe flood hydrograph at three stations und based on calculation statistical criteria error, the results are seems in acceptable limit

Observation and calculation water level at Tan Chau station flood 1989

1199 S97 595 79 91 116012671585 178 1912179 277 ars 273 a7 sts sr aes en TH)

bse Gdedaion

Figure 5.6: Calculated and observed at Moc Hoa station on Vam Co river flood 1999

Observed and calculated water level at Hung Thanh station flood 1999

52.3 The simulation for historical flood year 2000 in flood control alternatives

‘With the expected damage, reduction by annual flood inundation, and in order to increase the agricultural production of region, options are flood control alternatives, having main purpose as protection against early floods in August to ensure the safe harvest of the Summer-Autumn

crop Improvement of the drainage conditions al the end of the flood season to advance sowing of the Winter-Spring crop This allows sufficient time for the eropping cycle.

1 The proposed flood control alternatives are considered as table below

Scenario! Without flood control measures,

Scenario 2: Alternatives for floodwater drainage in field internal by Horizontal

‘channel systems

Sub- Scenario || Dredging of the Hong Ng channel with bed width B=40m, H=-4m,

‘and building up Sluice to remoxe floodwater at the end of channel

Dredging and Widening of the Dong Tien-Lagrange channel with bed widih tim, H=-3.5m, m=l.5 and building up Sluice for both of blocking the ‘saline waier intrusion and removingfloodwater at he

Dredging and Widen of the An Phong My How-Bac Dong_chumels with bed

Sub- Scenario 3 Ì iinh B=Lậm, H=-3m, m=1.5 and building up Sluice gate for both of blocking

the saline water intrusion andremoving floodwater atthe end of channel Dredging and Widening of the Nguyen Van Tiep channel with bed widih

L3m, H=-3m and building up Sluice gate for both of blocking the saline water intrusion and removing floodwater atthe end of channel

Scenario3 | Alternatives for floodwater drainage in internal field by channel

systems parallel with Tien river.

Building up the lood preventing Dyke Tan Thank-Lo Gach (elevation+6.5m at

Sub Scenario ! | Hong Nu and +55 a Vink Hung) Dredging and Widening [thế Tan Thanh Lo Gach channe 33m at Hong Neu Vink Hung, Hm, m= 1.0)

Sub: Scenario 2

Sub- Scenario 4

Sub- Scenario 2 | Dredging and Widening of the 2Thang 9 channel with bed width B=30m, H: im m=1.0 and building up Sluice at head of channel for flood control ‘Sub- Scenario 3 | Dredging and Widening of the Khang Chien channel with bed wit B=30m,

“im, m=1 and building up Sluice at head of channel

Sub- Scenario 4 Dredging and Widening ofthe Bình Than channel with bed wit B=20m, mand building up Sluice at head of channel

Sub- Scenario S| Dredging and Widening ofthe Thong Nhat channel with bed wit B=20m, 3m, m=T and building up Sluice at head of channel

Sub- Scenario 6 | Dredging and Widening of the Song Trang channel with bed widih B=20m, cảm, n=] and building up Slice at head of channel

‘Sub- Scenario 7 | Dredging and Widening ofthe Hai Tam channel with bed width 3m and building up Sluice at head of charmel

“The proposal o building up of sluice at head and the end of channel

Site of Sluice Width (ay Height aa Bottom (m)

[Based on these calibration and verification suitable result, this study simulate water level along river channels for historical flood year 2000, when there were no such alternatives to

‘know information regarding flood peak and peak time to concer for cultivation period Then simulation water level correlative with each scenario (after have alternatives) to identify

ability of floodwater drainage of region.

‘This simulation result of flood 2000 for each sub-scenario is used for development of the flood inundation maps to estimate depth, area and time of inundation and determine the

damage to agricultural sector.

‘Also, to assess the economic effectiveness ofthe different flood control alternatives based on

‘costs that have to invest in flood control with a value to reduce economic damage of flood in Dong Thap Muoi region

‘The hydraulic modeling would provide information for water levels at different locations

throughout the study area; correspond with different flood control alternatives This information would be used lo assess the damage-cost related to the different inundation

scenarios based on land use data and value of agricultural products,

2 The caleulation results

With purpose: Protection against early floods in August and to ensure the safe harvest of ‘Summer-Autumn crops Improvement of the drainage conditions at the end of the flood ‘season to advance sowing of the Winter-Spring crop This allows sufficient time for the

cropping cycle

Determine the maximum water level in that region in order to get information of flood peak and peak time to concern to cultivation period, On the other hand, also rely on this simulation result and some characteristic as: terrain, main channel route, road route to separate field cells in study region (as given below)

Determine water level at the end of August and first of November in order to

determine damage for Summer-Autumn crop and Winter-Spring crop against before

and after have flood contol alternatives.

4) Results of simulation WL at nodes on main rivers (before have flood control)

The simulation resis at some nodes before have flood contelateratives

“The simulation results at nodes along rivers as Figure 58 above before flood control construction are shown Figures: 5.9, 5.10, and 5.11