MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMENT

VIET NAM ACADEMY FOR WATER RESOURCES SOUTHERN INSTITUTE OF WATER RESOURCES

RESEARCH _________________

LE VAN TUAN

STUDY ON MECHANISM FOR BENDS RIVER REGULATION

UNDER TIDAL AREA

Specialization: Hydraulic Structure Engineering

Code No: 62 5802 02

SUMMARY OF DOCTORAL DESSERTATION

HO CHI MINH CITY, 2017

The work was completed at: SOUTHERN INSTITUTE OF WATER RESOURCES RESEARCH

Advisor 1: Assoc.Prof.Dr. Hoang Van Huan

Advisor 2: Prof. Dr.Luong Phuong Hau

Reviewer No.1: ……………………………………………….

Reviewer No.2: ……………………………………………….

Reviewer No.3: ……………………………………………….

This dissertation will be defended at the meeting of State level Doctoral assessement Council in Southern Institue of Water Resources Research No. 658- Vo Van Kiet Street – District 5 – Ho Chi Minh city on……………/2017 This dissertation is available at: - Naitional Libary of Viet Nam - Library of Viet nam Academy for Water Resources - Library of Southern Institute of Water Resources Research

1 PREFACE

0.1 THE PRACTICAL IMPLICATIONS OF DISSERTATION In the plains, moderate meandering rivers has the most stable type of river and most favorable for targets of exploitation. However as the meandering river develop exceedily, it creates sharply curved river. The stretch of the sharply curved river significantly affect the economic development of the fields related to integrated exploitation from river, regulating curved river to meet the actual requirements for: (1) flood control by resistance in the curved river section as rising water levels, minimizes the ability of flood drainage. It can be seen that the East Southern delta with a lot of sharply curved river networks and poor flood drainage capacity has caused severe flooding when occuring tides, especially in Ho Chi Minh City (HCMC); (2) to prevent bank erosion due to large circulation intensity and high flow impact to bank at sharply curved sections. Typically, the phenomenon of serious bank erosion at bends of the river cause many losses at the sharply curved river at the southern Delta (DBNB) on the Tien River (Tan Chau and Hong Ngu, Sa Dec, An Hiep ...); Hau river (the Vinh Loi and Binh Trach, An Phu, Ong Ho islet ...); Dong Nai River (Bien Hoa, Pho Isle ...); Saigon River (Thanh Da, Cape Red light, Hiep Phuoc ....) (3) Development of waterway because of longer distance due to sharply meandering river, obscuring vision, causing difficulties for the return of ships, strongly horizontal flow becoming unsafe to ship transportation, in addition to sharply meandering sections also creates serious shallow thresholds with deep creek such as the Go Dau section, Nhon Trach on the Thi Vai River [24]; An Thon Hiep section on the Long Tau River [25]; Binh Khanh section on Soai Rap river [24], [25]; Rach La section on Cho Gao canal [34]; (4) the landscape, the environment, building the city: The meandering river sections of the city are always the landscape with attractive environment. Due to complicated movements, the meandering river can endanger the safety of residents and public works. Regulating sharply meandering river is always urgent demand in the city, such as Thanh Da, Thu Thiem-Ho Chi Minh City, Tan Chau, Sa Dec in the Tien River ...; (5) designing regulation works at sharply meandering river: the sharply meandering river always creates unexpected hapennings. If occurring naturally chute cutoff, it would be able to create a passive situation, uncontrol the flow of new river, causing erosion, serious unwanted damages, leading to large losses for

2 the population. Only creating new chute cutoff favorable to go through meandering river basically improve from the disadvantage of the old river caused economic - engineering sectors. In Southern delta, a number of chute cutoff works as follows:

1) Thanh Da in the Sai Gon river; 2) Go Dau in the Thi Vai river; 3) Ly Nhon in the Vam Sat river; 4) My An in the Vam Co Tay river; 5) Binh Phu in the Rach La river of Cho Gao; 6) Dong Thanh in the Rach La river of Cho Gao; 7) Bui Huu Nghi in the Lang The river; 8) Chua Ba So in the Ben Chua river; 9) Can Chong in the Cau Quan river; 10) Long My in Nuoc Duc river of Hau Giang.

Due to the chute cutoff works have not been studied fully, the efficiency of above mentioned projects are severely constrained. The requirements of sustainable development of economy and society, there would be many more projects of chute cutoff in the future. From that fact, it is necessary for the in-depth study on issues of sharply meandering river aiming to meet the urgent need for regulations works in this kind of river.

0.2 SCIENTIFIC IMPLICATIONS OF DISSERTATION Research on regulating sharply meandering river in tide affected

areas has to solve a series of difficult and complex issues in the river dynamics because of variation in the three dimensions of space and time of both flow and river bed, leading to its continuous impact on the river system. The dissertation has to consider the physical phenomena which has not yet been accurately described by mathematical equations so far such as activities generating bed river by flow in the tidal area, the flow characteristic in estuaries and the sediment distribution at the mouth of the river into the chut cutoff, relationships of stable shape of canal in the southern delta, calculating transformation of bed river in the chute cutoff...

To establish a scientific basis for the design of the chute cutoff canal in the river, it is necessary to study the morphological relationship of canal’s stability in the tidal regioin of southern delta, representative level of flow for creating flow of stable chute cutoff has not yet studied as well. In calculating developments for river bed of chute cutoff, the distribution for volume of accretion and erosion could not be divided

3 equally across the cross-section wet perimeter at the present, it should be based on the morphological rules.

These are intensive scientific problems that this disertation need to solve. After unraveling these issues on a scientific basis, the development of a calculation program using the knowledge of mathematics, informatics technology for programming for automated calculations, manipulating for reality of chute cutoff in southern delta will also be a significant scientific contribution.

0.3 OBJECTIVE AND MAIN CONTENTS OF DISSERTATION 0.3.1. The objective of dissertation (1)- On the basis of analyzing the current situation and the actual requirements, proposing mechanism of appropriate effect to adjust the chute cutoff in sharply meandering river. (2)- Studying to determine the relationship values of chute cutoff morphology and affected factors to serve designing chute cutoff. (3) – Building scientific, simple and easily applied methodology of calculating design chute cutoff for southern delta. 0.3.2. The main contents of the dissertation (1) - Overview of research achievements in the domestic and world in the adjustment of sharply meandering river and proposing research problem of the desertation; (2) – Base of theory and research methods of the desertation; (3) - The results of study on the mechanism of impact for adjustment of sharply meandering river; (4) - Research results applied into practical projects.

0.4. INNOVATIVE CONTRIBUTION OF THE DISSERTATION - The thesis indicated that adjusting sharply meandering river

in Southern delta is small, slow progress and mostly employing bypass means which means creating channel suitable for demand of operation and keeping original channel route. Cutoff regime with pilot channel is difficult to implemented because developing canal and filling old river last a hundreds years. In order to speeding, it is necessary to use auxiliary solutions such as dam on the old river, diversion dam in upstream flow of the canal

- The thesis established relationship of canal’s cross section shape B /h for three areas under different tidal regime in southern

4 delta. This finding is used to design and calculate channel’s transformation for bends river regulation by chute cutoff methods.

- The thesis proposed the function of “critical discharge” Qkđ is multiplication between cross section area and velocity for initiation of motion Vkđ of sediment d50. This kind of discharge is employed for designing chute cutoff and relative to river parameters of B, h, V as below functions:

- The thesis developed software of CASO-2015 which will be

applied to design chute cutoff roughly by shortcut channel and pilot channel mechanism suitable for southern delta of Viet Nam.

CHAPTER 1. OVERVIEW OF THE STUDY ON ADJUSTING SHARPLY MEANDERING RIVER 1.1. ITEMS OF RESEARCH The adjusting sharply meandering river comes from requirements of navigation, erosion and flood drainage. Concerning adjusting meandering river sections, the research contents mainly include: 1.Cause and conditions forming meandering river; 2. Flow pattern in the meandering river; 3. Morphological relationship and developing river bed of chute cutoff; 4. Mechanism of river cutoff; 5. A hydraulic modeling and morphological changes in the adjusting works of meandering river sections. 1.2. ACHIEVEMENTS OF THE RESEARCH METHODOLOGY Three common methods to study adjusting meandering river is applied include: - Methods of analysing documents of measurements: high accuracy - Methods of physical modeling: simulation and good forecast; - Mathematical modeling method: developed and improved. 1.3. RESEARCH ACHIEVEMENTS IN THE WORLD 1.3.1. Flow pattern in the meandering river These important studies focused on the flow of three issues: Determine the horizontal slope of water level [85], the Packman A.I. [70];

5 explaining and describing the circulation pattern of Zhang R.C [86] and Xie Jian Heng [87]; determine the horizontal velocity and its distribution in depth from Rozopski experiments [85] according to measurements in natural river Zhang R.C [86] ... 1.3.2. Morphology of meandering river sections The study of morphological rule have 5 rules of L.Fargue from survey and measurements data on the Garona river (France), called the Fargue’s law. Cross-section morphology relations of basic river bed: Research about parameters and exponent coefficient of the relationship between the elements of bed (B, h, V, J) and the flow to create bed river based on a theoretical and empirical matters as Lacey. G, Leopoll, Simons, Hancu S. Levi ... The relationship between the width and depth by the Hydrographic Institute of the USSR (former) recommended 1.3.3. The adjusting sharply meandering river At the end of the eighteenth century, the Germans had carried out cutting the Elbe river to serve for irrigation and flood control; Mississippi River in the US in the early 30s of the twentieth century implemented by the Committee on the Mississippi River; in the twentieth century in Europe many works had done as the Meuse River Crossing (France), Elbe, Havel (Germany), Rhine (Germany, France, the Netherlands), Ijssel (Netherlands) vv..In China, river cutoff was done simultaneously on Giang Ha chanel (Hubei) of the Yangtze river in the 40-50 years of the twentieth century. The research of river cutoff projects mainly include: 1.Specification of channel; 2.Study on at the withdrawal and the entrance channel; 3. Defining the rate of river cutoff; 4. Designing the pilot channel. 1.3.4. Flows and developments affecting the tidal river: The dissertation defines the research works related to the flow and development of bed level in the tidal river, classification theory of estuary, segmentation characteristics of estuaries and flow characteristic of estuarine under tidal influence. 1.4. RESEARCH ACHIEVEMENTS IN VIETNAM 1.4.1. The study of the tidal river

6 The study of the tide of the authors in Vietnam and the prominent research of the authors about river under tidal areas in southern delta. 1.4.2. The research and implementation of chute cutoff works There are not many the actively river cutoff works in tidal are of southern delta, typically river cutoff to serve waterway in Thanh Da Peninsula (1905), Saigon River; Recent cutoff works in sharply meandering river in Go Dau area (Ba Ria - Vung Tau) on the Thi Vai channel. Upgrade project for Cho Gao canal at La section... Several sharply meandering rivers occurring natural or semi-natural river cutoff are taking place complicatedly as Ong Con isles (District 9- Dong Nai river) or Cha River (Binh Khanh) on the Soai Rap river.

1.5. GENERAL COMMENTS 1.5.1. The achievements

- The greatest achievement related to adjusting sharply meandering river is the description and explanation of the pattern in the maendering river circulation and its impact on developmentof river bed.

- The affected mechanism to adjust sharply meandering river introduced on the materials is to usepilot channel in design of river cutoff.

- The methods of hydraulic calculation for distributed computing application store has been modernized by the model of numerical method. 1.5.2. The exist problems a- Exists in basic research

- Circulation pattern in the meandering river only have qualitative descriptions, there are no good mathematical model for this problem.

- There is no study on how to handle discharge elements generating flow to design river cutoff in tidal areas.

- Mophological relationships which is studied only on cross-section of natural river without researching for this kind of canals is essential to design chanel of the river cutoff works.

-The mechanism of water and sediment distribution in distributary points still have to use the assumed diagram which is not consistent with reality.

b-Exist issues in the method of calculation.

7 - There are no more study on the method of calculation for river cutoff in tidal area. - Several studies were conducted and published on the river bed morphology relations in southern delta. They are the parameters corresponding to the flow generating bed river, but it does not clarify how to determine the value of that flow. - The calculation for morphological process of pilot channel and adjacent river segments are important in designing the river cutoff, but so far there is no research achievement in this issue. Jian Xie Heng [115] has proposed a method of simplified calculation to estimate transformation of river bed after river cutoff through 1D equations of sediment balance used to calculate it manually that there is no automatic calculation model. The expression of stability morphological relations of canal, sediment, geology in river bed and bank, the surface water gradient in the river and the impact of tidal factors are completely in appropriate to apply southern delta. The current mathematical model unresolved issues in relation to the horizontal erosion patterns according to morphology. - Measurement data on river cutoff projects in Vietnam are few and unsystematic. c Exist issues in solution of works

- The study in the world mainly introduces uninterrupted river cutoff or works of sharply meandering river cutoff by mechanism of pilot channel, but in Vietnam, especially in southern delta, it is inappropriate the mechanism of this effect. - In southern delta, the transforming sharply meandering river to tributary flow section is quite popular solution. Which means that it is only a share of the flow into the channel and continue to maintain old river section, but there is no in-depth study of the mechanism of this effect. - In southern delta, most canals are straight-line and fairly stable, but there are no studies on the relationship of forming a straight canal. 1.6. THE QUESTION OF THE DISSERTATION 1.6.1. Research Issues

8 1. Analysis and selection for mechanism of effect consistent with

natural conditions and economic - social areas for adjusting sharply meandering river in southern delta.

2. Analysis of morphological relations for stable canal cross-section as the basis for designing the canal in tidal affected area.

3. From chute cutoff morphological relations, the dissertation studies and proposes a parameter of flow used for designing chute cutoff.

4. Building a simple program of calculation and easy to use for the problem under 2 mechanism as chute cutoff and pilot channel. 1.6.2. Research scope

- The dissertation focuses on chute cutoff as the main object of study, not extended to other ancillary works.

- The dissertation does not study the mechanisms of adjustment with chute cutoff.

- The scope of research in space is divided in three regions with specific natural conditions, mainly tidal amplitude and time difference between the tides and low tides.

Chapter 2. THEORY BASIS & RESEARCH METHODOLOGY 2.1. THEORY BASIS OF ADJUSTING SHARPLY MEANDERING RIVER 2.1.1. Interaction flow – river bed in estuarine under tidal influence: Research by Wang Y.H. [109] has clarified the relationship and the direction of flow at high tide –low tide for shape of bed river. 2.1.2. Flow generating bed river and morphological relation of bed river The dessertation states that the concept and the way to determine the flow generating bed river by the authors. It analyzed the stable morphological relation of river bed according to regime theory. It analyses reseach result of morphological relation by Dou Gouren (Dau Quoc Nhan) for the estuary. In detail, average falling tide flows in many years is flow of calculation. 2.1.3. Hydraulic calculations of distributary There are a lot of modern computational models of hydraulic distributaries. To be consistent with the calculation method of transform

9 of the canal bed, the dissertation refers calculation method of distributary introduced by Prof.Luong Phuong Hau in "Technical Instructionof adjusting river works" [21] to solve simultaneous equations consisting of equations of motion and continuity equations of steady flow and one way. 2.1.4. Velocity for initation of motion of sediment: The formula for calculating velocity for initation of motion according Mirkhulavar selected after comparison with some other formulas. 2.1.5. Caculation of bed river transformation To calculate bed transformation after sharply meandering river cutoff, the dissertation uses the method of calculation from Xien Jian Heng (China) to calculate the evolution of the bed river of chute cutoff and old sharply meandering river. 2.2. DATA BASE 2.2.1. Data on the tide in southern delta It is stated on the characteristics of tidal propagation in South Eastern area and the Mekong Delta through outstanding research projects in these areas. Features include: Discharge of flow sources, tidal flow, the propagation of tide, velocity of tidal current, time of falling tide and spring tide, the limit of tidal propagation. 2.2.2. Measurement data on morphology, hydrology, sediment of the river, canal.

Specifing the source of documents and research materials for the dissertation; data of collection, measurement, remote sensing. The content of the document data including topography, geology, hydrology and sediment. 2.3. RESEARCH METHODOLOGY 2.3.1. Survey methodology, fieldwork, analysis of measured data

Data sources are mainly of the author collected through field survey on 10 cases of river cutoff and 27 stable canal connecting with river in all 3 research areas. The content of measurements are: (1) Measurements of cross-section parameters of canal bed: Using survey measurements in the field with synthetic flow instrument of ADCP including flow velocity, flow, bed shape and sonar; (2) bottom sediment sampling in canal

10 2.3.2. Research Methodology on mathematical model

Depending on the mechanism of effect, the dissertation sets up 3 problems and on the basis of the presented findings and the proposing some schemes of calculation, the dissertation has developed a calculated method based on the model of one way steady flow but acceptable reliability of science to solve above problems.

CHAPTER 3. THE RESEARCH RESULTS 3.1. CLASSIFICATION OF STUDY AREA 3.1.1. The basis for classification The dissertation was based on the following criteria for classification of study area including tidal regime; tidal magnitude; rising tide, falling tide and factors of geography, geomorphology: In addition to the above factors, it should have further consideration of classification of geography, major river systems and the topography, geomorphology as the classification of upper and lower in the Mekong delta ... 3.1.2. Results of area classification:

Region Tidal regime

Tide magnitude

(m)

TD / TR at upstream boundary

Province

I Irregular Semi diurnal tide in East Dea

2,0m ÷ 1,0m

-Tien river at Tân Châu: 5g30ph / 9g00ph -Hau river at Châu Đốc: 4g15ph / 9g30ph.

Dong Thap and An Giang

II Irregular Semi diurnal tide in East Dea + Diurnal tide in West Sea

3,0m ÷ 2,0m

-Tien river at My Thuan 5g45ph/7g15ph. -Hau river at Can Thơ: 4g30ph/8g30ph

Tien Giang, Ben Tre, Tra Vinh, Soc Trang, Bạc Lieu, Ca Mau, Hau Giang, Tien Giang, Can Tho, Kien Giang

11 III Irregular

Semi diurnal tide in East Sea

3,0m ÷ 2,0m

- at Vung Tau: 6g 00ph/6g45ph. - Dong Nai river at Bien Hoa: 5g 45ph/7g15ph.

Ho Chi Minh city; Ba Ria-Vung Tau; Dong Nai; Binh Duong; Long An.

3.2. THE ANALYSIS OF AFFECTED MECHANISMS FOR ADJUSTING SHARPLY MEANDERING RIVER IN SOUTHERN DELTA Based on studies of the existing works for adjusting sharply meandering river were conducted in southern delta, the dissertation identified the principal mechanism of effect to adjustment of sharply meandering river include: (1) Mechanism of increasing in radius of curvature; (2) The mechanism of bypass canal (bypass) and (3) Mechanism of opening channel, closing the river. From which some comments as follow: - Works of artificial or natural river cutoff were conducted in Region II and Region III. There is no any case of river cutoff carried out in Region I but with importance of its economy - society, a number of bends in the upstream of the Hau River (An Giang province), can will be studied on cutoff to improve flood drainage and waterway conditions in the future. The sharply meandering section with a large curvature radius such as Tanchau, Sa Dec ... can also implement adjustment of 1 mechanism to mitigate the erosion and improve conditions for sailing. - In the 4 mechanisms of effecting the world used to adjust sharply meandering river as increasing the radius of curvature, bypass canal to distributary, river cutoff by canals to the final cross – section, chute cutoff by pilot canal, the first three mechanisms have used in southern delta, little or no use mechanisms of pilot channel. In particular, mechanisms of pass-by canal without removing the old river used more (7/10 cases). - In the southern delta, the works of adjusting meandering river are small-scale and it is not a great impact on the river's shape in the region.

12 - Three cases of river cutoff creating a new line and removing the old river to serve irrigation works have been performed on Lang The River, the Ben Chua river and Can Chong river of Tra Vinh. - Most of the canals have a straight line, with unfavorable connection in upstream and downstream of the river, so the bypass canal develop slowly. - Measures of increasing in radius of curvature only solve temporary without long-term effectiveness. Thus, the bypass cannal is the main solution for the mechanism adjusting meandering river in southern delta. However, in order to expand the range of applications in the future, the dissertation indicated that depending on specific conditions it can be used one of the 4 following mechanisms of effect: mechanism of increasing the radius of curvature; mechanism of passby canal; mechanisms of digging canal, fill the river and mechanism of pilot canal. Because mechanism of increasing in radius of curvature and mechanisms of digging canal, fill the river are relatively simple, so the dissertation only studies in depth on mechanism of bypass canal and mechanism of pilot canal. Some scientific questions to be addressed when determining the mechanism of effect: The main object to research in works of sharply meandering river is to design chute cutoff. In the mechanism of pass- by canal or mechanism of digging canal of last cross section are related to issues of stable morphology for the canal. It means that it is designed to canal with stable cross section under designed flow. In the southern delta, most canals are river cutoff canal with a straight line. Therefore, it is necessary to solve the problem of stable morphology relations of straight canal in southern delta. In the river cutoff by pilot canal, issues of morphological relation are also important in determining the size of horizontal erosion, deep erosion in the process of canal development, unable to equally divide through the whole of cross section. Concerning the issue of relation of canal morphology, that is to determine flow corresponding to generate stable cross section.

13 .3. STUDY ON STABLE MORPHOLOGICAL RELATIONS OF CANAL BED Findings on stable morphological relation of the cross section of the canal types in the southern delta are presented in Tables 3.1, 3.2, 3.3, 3.4 and 3.5. 3.3.1. Morphological relationship of canal from works of chute cutoff implemented in the southern delta. From the measured data in the field for 10 projects of river cutoff in 2 areas II and III, the calculated results of stable cross-section of river cutoff canal shown in Table 3.1. 3.3.2. Canal morphological relation connecting the rivers in the southern delta. Based on the average cross-sectional shape of the canal linking the two rivers (canals) in the three studied regions, the determining the relationship of B /h, from which to find the maximum and minimum values and the in each subarea I, II and III. See Table 3.2, 3.3 and 3.4. Based on the summary sheet as Table 3.5

Bảng 3.5: The summary Sheet of critical and avergage values in relationship of cross-sectional shape of the canal in Southern Delta

Region (area)

Style of canal case

Max Min Average

I Chute cutoff 0 Canal linking two rivers

10 2,49 1,42 1,95

II

Chute cutoff 4 1,80 1,62 1,71 Canal linking two rivers

9 1,89 1,35 1,62

III Chute cutoff 6 1,78 1,60 1,69 Canal linking two rivers

7 1,99 1,80 1,90

3.3.3 Reviews of calculation results (1) Value of cross morphological relations (δ) of the river cutoff canal or canal connecting the river in various areas are substantially smaller than natural river (except the Saigon River). According to the reference,

hB

14 the morphological relationship of the natural river is valuable δ = 3 ÷ 4 on the Tien River and Hau (Le Ngoc Bich [59]); δ = 3.76 ÷ 6.02 on Tien and δ = 4.87 on Hau River in Region II (Hoang Van Huan [64]); δ = 3.35 ÷ 5.14 on Dong Nai River (Le Ngoc Bich Hoang Van Huan [62], [55]); δ = 1.2 ÷ 1.6 on the Saigon River region Thanh Da (Le Van Tuan [57]). Above values of δ are consistent with research on the ratio B / h of Le Manh Hung and Dinh Cong San [44], [31] with the value of B / h (bankfull) ranging from 150 -: - 70 on Tien river and 270 -: - 50 on the Hau river in the range of estuaries (Km0) toward the upstream with a distance of 200km. (2) In the region II, the value of stable morphological relationship of river cutoff canal and the river connected canal are approximately the same (1.62 versus 1.71), it can be caused by hydraulic gradient of the two types of canal different in much. (3) In the region III, the river cutoff canal has average value δ = 1.69, while the river connected canal has larger values δ (1.90), nearly 10% larger than the river cutoff canal (i.e river connected canal is relatively wide and shallower than the river cutoff canal). It is also due to the difference in the hydraulic gradient between the river cutoff canal and river connected canal (river cutoff canal by natural river have larger curve, then length of cutoff canal is significantly shorter. (4) In the region I, there is no data on the river cutoff canal, but only have the data of river connected canal δ. The river connected canal of region I with δ value approximates the river connected canal in region III. So, in case ofriver cutoff in region I, it can be accepted with the value δ = 1.69 as Region III. Thus, the value of morphological relations for cross section of river cutoff canal in region 3 is recommended as Table 3.6.

Bảng 3.6.Giá trị quan hệ hình thái mặt cắt ngang kênh đào cắt sông Region I II III

δ 1,69 1,71 1,69

3.4. DISCHARGE FOR INITIATION OF MOTION OF CANAL BED 3.4.1. Interaction of flow and river bed in estuaries

15 Velocity of falling tide has great and period of falling tide is larger than rising time, thus creating river bed is done mainly during falling tide. Flow of falling tide have the straight line, so the effect of creating river cutoff canal’s bed usually depends on the flow of falling tide. This is also consistent with the research of Dau Quoc Nhan in relational formulas of bed morphology in estuary using average flow component during falling tide as mainly calculated parameter. 3.4.2. The concept of discharge for initiation of motion of Canal Qkđ.

Based on the theoretical basis of flow creating bed presented in Chapter 2, the dissertation indicated that stable cross section of the canal is the product of the effect of natural flow in a long time and representative is flow creating canal bed.

Stemming from the inference be able to stabilize the canal morphology, without erosion and sedimentation, the discharge for initiation of motion has to create velocity value equal booting speed of sediment. The author indicated that the discharge for initiation of motion is the multiplication of the volume of the wet cross area of the channel with velocity for initiation of motion of sediment with diameter d50. If velocity for initiation of motion of sediment d50 is Vkđ, the corresponding flow to ensure stable canal morphology is Qkđ:

Qkđ = Bk.hk.Vkđ (3-1)

In which: Qkđ- Discharge for initiation of motion of canal, (m3/s); Bk-Width of cross section, (m); hk - The average depth of the canal cross section, (m); Vkđ- Velocity for initiation of motion of sediment d50, (m/s); d50- Sediment particle diameter corresponding to the sieve proportion of 50%, (m).

A definition of "discharge for inition of motion, Qkđ " as follows: discharge for inition of motion of canal (Qkđ) is discharge in falling tide through the canal creating sectional average velocity equal to or greater than the velocity for inition of motion of sediment in the canal. 3.4.3. Qkđ value calculations for the study area a- Formula of calculating velocity for inition of motion

16 To calculate Vkđ, the dissertation examined through 3 different

formulas: Formula Zhang R.C (1989); formula of Civil Engineers Association United States ASCE (1967) - Mehrota (1983) and the formula of Mirkhulava (Mirtskhulava, 1967) [19]. After calculated and compared with some same work in tidal area of southern delta [25], [59], [31], the dissertation used formula of Mirkhulava. Table for calculating to define Vkđ for 3 formula presented in Appendix B. b- Calculate discharge for inition of motion of the canal

Mirkhulava formula is used to obtain Vkd, then calculate Qkđ for canal based on formula (3-1) for river cutoff canal and river connected canal corresponding to the 3 research sub-areas I, II and III. Calculation results are presented in Table 3.7. 3.4.4. Buiding the relation of Bk,hk and Qkđ

Based on factors of Bk, hk, Vkđ and Qkđ in Table 3.7, it can be found out empirical relationship between the width of the canal in the cross section at water level Bk, average depth hk, velocity Vkđ with Qkđ as Figure 3.13 to Figure 3:24.

Figure 3.13: Relationship curve Bk vs Qkd in case of cutoff cannals

Figure 3.14: Relationship curve hk vs Qkd in case of cutoff cannals

Figure 3.15: Curve Bk vs Qkd in case of connecting cannals in I

Figure 3.16: Curve hk vs Qkd in case of connecting cannals in I

17

Figure 3.17: Curve Bk vs Qkd in case of connecting cannals in II

Figure 3.18: Curve hk vs Qkd in case of connecting cannals in II

Figure 3.19: Curve Bk vs Qkd in case of connecting cannals in III

Figure 3.20: Curve hk vs Qkd in case of connecting cannals in III

Figure 3.15: Curve Vkd vs Qkd in case of cutoff cannals

Figure 3.16: Curve Vkd vs Qkd in case of connecting cannals in I area

18

Figure 3.15: Curve Vkd vs Qkd in case of connecting cannals in II

Figure 3.16: Curve Vkd vs Qkd in case of connecting cannals in III

The empirical expression obtained in different areas can be generalized in the form of the following formula:

(3-2)

(3-3)

(3-4)

With hydraulic relations Q = B.h.V, we can infer Vk = Kv. Α + β + Qγkd and γ = 1; KB.Kh. KV = 1. Where: The values of the correlation coefficient (KB, Kh, KV) and the exponent (α, β, γ) shown in Table 3.8.

Table 3.8: Results of the determining coefficients and exponents in the relational formula canal cross section morphology

Vùng KB Kh KV α β γ Cắt

sông 2,458 0,885 0,459 0,601 0,307 0,091

I 2,647 0,714 0,528 0,571 0,332 0,097 II 2,642 0,775 0,488 0,566 0,33 0,102 III 3,069 0,738 0,441 0,562 0,322 0,116

The results of calculation show that: Relation between Qkđ and Bk, hk in the canal (including river cutoff

canal and river connected canal) is affected by tide in southern delta, there is a general form similar to formula of the morphological relation under the "Regime theory "(section 2.1.1, the formula 2-1 ÷ 2-5) and it shows the relationship between factors of stable river bed and the flow creating river bed. The form of formula is exponential and the exponent of the flow corresponding to the elements of B, h and V are the same

19 approximately. Only the coefficients of KB, Kh, KV is different from AB, Ah and AV.

This proves that discharge for initiation of motion is a flow level representing the process of canal bed change. The flow creating natural bed river in tidal area of southern need to be examined further with measured data.

If the relationship of morphology is a necessary condition, the discharge for initiation of motion will be sufficient condition for the stability of the canal. If the flow in canal is greater than Qkđ, the canal can be eroded, inversely the canal flow is smaller than Qkđ, the canal may be sedimentation. 3.5. CALCULATION PROGRAM FOR SHARP MEANDERING RIVER CUTOFF CANAL 3.5.1. General scheme for the calculation program of river cutoff: Block diagram of calculation by pilot canal: See Figure 3.25. 3.5.2. The automatic program of calculation for chute cutoff under mechanism of pilot canal - CASO-2015 a- Software of Computing: The algorithm and the application diagram are shown, the program of automatic calculation is built by Fortran language. Structure of calculation is presented fully in Appendix C. This program was named CASO-2015. Due to be used many simplified diagram, this program is only estimated level. b Input data for program of CASO-2015:

- Documents of topography, geology, hydrology, sediment in study area. - The requirement of the economy - society for the river. - Planning on canal line and river cutoff mechanism. c Output obtained:

- Cross section of design canal and estimation of its development process; - Flow, water surface in channel lower designed flow. d- Application range of CASO-2015:

Due to the use of empirical formula on mrophology relation and starting flow in tidal area of southern delta. Its application range is also limited in the Southern Delta in Viet Nam.

20 CHAPTER 4: PRACTICAL IMPLEMENTIONS AND IMPLICATIONS: STUDY ON RIVERBED MANIPULATION CALCULATION IN UTILISATION OF PILOT CHANNEL MECHANISM ADJUSTMENT OF SHARPLY MEANDERING THANH DA RIVER SEGMENT WITHIN SAI GON RIVER

4.1 INTRODUCTION The implementation of the study's results for a river cutoff construction in reality proves its feasibility and validity for CASO-2015 calculation program. Due to the limitation of the input of those river cutoffs which need to be adjusted, this thesis used fully worked-out data of Thanh Da river cutoffs on Sai Gon river as the study's subject. Because Thanh Da river section has cut the river in accordance with chute cutoff mechanism (calculation 1), the utilisation of pilot channel mechanism for the implementation of CASO-2015 program is just a hypothesized calculation.

Figure 4.1: Map of Thanh Da peninsula within Sai Gon river

Figure 4.2: Map of Thanh Da canal in 1962 (Internet)

4.2 DATABASE Terrain materials: topography of Thanh Da peninsula region in 1998, 2003, 2011 [12]; hydrology materials - muds and sands; water level material, flow and mud and sand in 2003, 2013, 2014 [12]

4.3 CONSTRUCTION ARRANGEMENT AND INPUT DATABASE 4.3.1 Construction arrangement map and calculated section a) Channel alignment The former channel alignment was reused: the entrance position is at point A and the exit is at point G in figure 4.2. The channel alignment is a straight line connecting 2 points B and G, 1850 metres long.

21 b) The channel alignment's cross section Inrespect to breaking the river by pilot channel mechanism, utilising the study's results of the relationship between channel alignment and river cutoffs on Thanh Da, the initial cross section of channel alignment is trapezium cross section, bottom 37 metres wide, depth 5,75 metres, surface 60 metres wide, coefficiency of bank slope equal 2. The channel's cross section is simulated in rectangle shape, 60 metres wide, 4,66 metres deep, in accordance with real complexion measured at the channel crossing Thanh Da river, with = 1,66 (figure 4.1)

Figure 4.1: Cross – section shape of pilot canal and rectangular

changing shape c) Calculated section In respect to topography and the features of the flow, all the curved sections are divided into 8 sections, in which the former cutoff section is divided into 5 sections, as shown in figure 4.2:

Figure 4.2: Diagram of divided segment- number

Thanh Da Peninsula

22 4.3.2 Input database The input database is mainly topographical data, hydrology, mud and sand of the former curved river section (before calculation or before cutting off). See table 4.1, input statistics. 4.4 CALCULATED RESULTS In order to run the analysis, bed river transformation and distributary within the former river section at certain time were calculated. The program had been being run until the channel was fully developed and the former river was exterminated. 4.4.1 Calculating, auditing and adjusting procedure - After completing to inform the input data, errors were controlled and the program was being run on the base of topographical form in 1998, mud and sand intrinsic measurement conducted in 2003. - If the river section had been adjusted in accordance with pilot channel mechanism (calculation 1), after calculating the channel's distributary with the initial cross section, water level and flow distribution would have been examined in order to test whether they satisfy the criteria of exploitation. If the flow of Qk is different from Qkđ, the hypothesis of channel cutoff needs to be recalculated from the beginning until Qk is equal to Qkđ. In order to stabilize the channel system, bank improvement should be conducted. - If the river is broken up with pilot channel mechanism (calculation 3), bed river change at t1 needs to be conducted. Erosion condition of the channel requires to be investigated. If it is not eroded, the pilot channel's cross section must be rehypothesized or accomodating subsidiary construction is required in order to increase the flow to the channel until the erosion condition is satisfied; then, calculation at T2 time can be carried out. - In the following period, calculations and investigations were conducted for the development of the pilot channel. - Calculations can be ceased when the channels have gone through 75% Q0. - When the calculations finish, topographical condition of the channel needs to be examined at the flow of Qkđ. 4.4.2 Exporting result output

23 With the time t=15 of hands-on days calculating (equipvalent to one tidal period), the program has calculated the development of the channels in 7200 intervals, equal to 300 years. Due to the limitation of time and calculating condition, this study only regards to the development of the channels, not exporting results of the changes of other sections. The result database of the program was exported as Excel output and was attatched to the result calculating appendix of hydraulic power and distributary forecast and topography of the channel - former river within Thanh Da Peninsula on Sai Gon river. The statistical result database was displayed in the form of Excel file in the Appendix. Table 4.2 showed the statistical output of the calculating program of hydraulic changes and mud and sand after river cutoff. The major results were analyzed and displayed through the charts from figure 4.3 to figure 4.6. The final result indicated that for the channel's development to the last cross section (via 98% of distributary), the entrance to the former river was closed; it takes 222 years. Cross section of canal after 222 years has sise of B=283m and h=12m. Calculated result of distributary ratio is shown in Figure saved 4.3 and Figure 4.4 with greater value and when the canal becomes the main river, the rate reaches at 100%. Figure 4.5 and Figure 4.6 show the process of canal erosion in the process of development.The first time is very powerful, when the canal erosion reaches at certain level, canal goes to the stability.

Figure 4.3: Correlated curve between the former river flow and cutoff canal

Figure 4.4: Curve show the process of ratio of yearly canal inflow

24

Figure 4.5: Curve show the volume of canal erosion in the process development

Figure 4.6: Curve show the process of the width and the height of the cutoff canal

4.5. ANALYSIS OF RESULTS AND COMPUTATIONAL PROGRAM 4.5.1. Rationality and reliability of calculation results Figure 4.3 shows the correlation between chute cutoff canal and the old river, the canal will grow in time and overwhelm the old river and time for canal completely replace old river is the 222 year. This figure reflects fairly accurately the development of canal in the southern delta such as since 1907 to date Thanh Da canal is only about 12% in flow; Cho Gao canal (dug from 1876, now it is still relatively strong bank erosion); Quan Chanh Bo canal was dug in 1856, now it is relatively stable); An river cutoffof My An in Vam Co Tay, Thu Thua, Long An is only 55% of the flow after spending nearly 100 years... The phenomenon of slow growing canal is affected strongly by tide in southern delta, hydraulic gradient and terrain slope is very small and flow from upstream declines due to reservoir construction. The size of the final section of the canal Bk = 283m, hk = 12m have shown quite well about morphological relation of B, h with Q as the research results presented in Chapter 3. Therefore, the southern area not very suitable for application for mechanism of pilot canal. 4.5.2. Comments on the automaticprogram of calculation From general basic theory on works in river cutoff, the dissertation has built successfully initially programs of CASO-2015 which is automatic, computational applications for sharply meandering cutoff works in southern delta.

25 Because of many simplifying assumptions and the accuracy not high, program ensure reasonable results and the confidence level is acceptable.This is possible to apply in the basic design reports of the stage of pre-feasibility study or feasibility report of the project adusting sharply meandering river by river chute cutoff. The river form is common in the souther delta.

CONCLUSIONS AND RECOMMENDATIONS

A. RESULTS OF THE DISSERTATION 1. The dissertation studied morphological characteristics of the river system in southern delta, divided sharply meandering river into 2 main types: V shaped type and Ω shaped type. The sharply meandering river concentrated in regions III (Southeast region) and Region II (the Lower Mekong River Delta) on the small and medium rivers. 2. Based on the analysis of measured data, the dissertation clearly shows works of adjusting meandering river in southern delta are small, slow process. Therefore here primarily use mechanism bypass canal, which means canal is dug once to the size of exploitation satisfactory, not removing the old river. Mechanism of river cutoff by pilot canal only consider applications in the works on the big river in the weakly tide affected areas. The mechanism of river cutoff by pilot is difficult to apply in southern delta because the new river development period lasts very long, only consider applicationfor the works on the big river, strong flow or small tide. Mechanism of river cutoff by diging canal until last cross section and filling the river, removing the old river routes may consider in region III to improve flood drainage, reduce flooding for Ho Chi Minh City. 3. The dissertation has studied the establishment of morphological relations of cross sectionvalues B /h of river cutoff canal and river connected canal in the three studied regions with various tidal level in southern delta. The value of morphological relations for the river cutoff canal in 3 areas shown in Table 3.6. The results are used to serve the designing and calculating transformation of channel in works of adjusting meandering river by river cutoff. 4. The dissertation proposed the expression "starting volume" Qkđ by the multiplication between the cross-section area and starting velocity of the particle sediment of canal bed d50 (formula 3-1). This is the type used in

26 the design of river cutoff canal, it is related to the function of B, h and V of the canal such as the formula (3-2), (3-3), (3 -4) and Table 3.8 shown. 5. The dissertation proposed hydraulic calculation program CASO-2015 used in the design and estimating the technical efficiency of the the river cut off canal under the mechanism of pass-by canal and pilot canal. CASO-2015 program is simple, easy application, suitable for the planning period, report of a pre-feasibility study, feasibility reports for projects of adjusting meandering river in cutoff direction under the tidal area of southern delta. 6. The dissertationwas successfully applied program for CASO-2015 for problem of chute cutoff by supposed pilot canal for Thanh Da on Saigon river.

B. RECOMMENDATION 1. Continuing to improve the concept of "discharge for initiation of motion, Qkd" and expand the applications for "flow generated bed river in tidal areas." 2. Continue to study and complete CASO-2015 software. 3. Continue to study the mechanism for mechanism of river cutoff continuously towards many sharply meandering adjacent segments.

27 PUBLISHED PROJECTS RELATED TO THE DISSERATION

1.Hoang Van Huan, Le Van Tuan, "The scientific basis of the measurements to protect the river, coast in Southern region", Proceedings of the scientific and technology in 2003, the Southern Institute of Water Resouces Research, p.346. 2. Le Van Tuan, "Study on the characteristics of Saigon river erosion at Thanh Da peninsula", Proceedings of the scientific and technology in 2005, the Southern Institute of Water Resouces Research, p.328-336. 3. Le Van Tuan, Tran Thu Tam Hoang Van Huan, "Evaluation of the impact of loads at the peak of bank and water level to stabilize the banks of the Saigon River - Thanh Da peninsula region", Proceedings of the scientific and technology in ninth, HCMC University of technology, 2005, p.553. 4. Le Van Tuan, "Analysis of the impact of geological factors to change of bed in the downstream of Dong Nai river system - Saigon", Proceedings of the scientific and technology in 2006, the Southern Institute of Water Resouces Research, p.370 -390. 5. Le Van Tuan, Hoang Van Huan, Luong Phuong Hau, "Study morphological characteristics of the river bed in sharply meandering river under the tidalarea", Proceedings of the national scientific conference of Atmospheric, Hydro mechanism in 2010, the Vietnam Mechanics Association, p.443-452. 6. Nguyen Thanh Minh, Le Van Tuan, Mai Duc Tran, Nguyen The Border, "Study on the cause of river bank erosion in An Hoa and propose prevention solutions", Proceedings of the national scientific conference of Atmospheric, Hydro mechanism in 2011, p.459-469. 7. Le Van Tuan, Hoang Van Huan, Luong Phuong Hau, "Study on some of the achievements for adjusting meandering river by river cutoff in the worldand Vietnam and the exist problems ", Proceedings of the national scientific conference of Atmospheric, Hydro mechanism in2015, Vietnam Mechanics Association. 8. Le Van Tuan, "Study on morphological relations of stable cross section for canal in tidal area of southern delta ", Proceedings of the of Science and Technology, 2015, the Southern Institute of Water Resouces Research. 9. Le Van Tuan, "Research on completed calculation methods and developing calculation program of transformingcross section of canl by pilot canal under tide regime in southern delta ", Journal science and technology of water resources, Vietnam academy for water resources.