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THÔNG TIN LUẬN ÁN ĐƯA LÊN MẠNG Tên luận án: Nghiên cứu chế độ vận hành tích nước trong thời kỳ mùa lũ cho hệ thống hồ chứa bậc thang Hòa Bình và Sơn La Chuyên ngành: Phát triển nguồn nước Mã số: 62 44 92 01 Họ và tên NCS: Vũ Thị Minh Huệ Người hướng dẫn: PGS.TS Phạm Thị Hương Lan; GS. TS. Hà Văn Khối, Trường Đại học Thủy lợi, Việt Nam Cơ sở đào tạo: Trường Đại học Thủy lợi Tóm tắt những đóng góp mới của luận án: Đề xuất được chế độ tích nước sớm có điều kiện cho 2 hồ chứa Sơn La và Hòa Bình. Trên cơ sở đó, đề xuất cơ sở khoa học xác định mực nước giới hạn trên của quá trình tích nước hồ chứa Sơn La trong thời kỳ tích nước hạn chế, đảm bảo tích nước hiệu quả mà vẫn an toàn chống lũ hạ du và công trình. Đề xuất được chế độ vận hành điều tiết chống lũ cho hạ du và phương thức ứng phó khi xảy ra lũ bất thường trong thời kỳ tích nước đầy hồ ở cuối thời kỳ mùa lũ. Hà Nội, ngày tháng năm Người hướng dẫn khoa học Nghiên cứu sinh (đã ký) (đã ký) Phạm Thị Hương Lan Vũ Thị Minh Huệ (đã ký) Hà Văn Khối
MINISTRY OF EDUCATION MINISTRY OF AGRICULTURE AND TRAINING AND RURAL DEVELOPMENT THUY LOI UNIVERSITY VU THI MINH HUE RESEARCH ON WATER ACCUMULATION OPERATING MODE IN FLOOD SEASON FOR HOA BINH AND SON LA TERRACED HYDROELECTRIC RESERVOIRS DISSERTATION ABSTRACT Specialization: Water resource development Code: 62 44 92 01 HA NOI, 2017 The project is completed at Thuy Loi University Principle advisor 1: Associate Professor Pham Thi Huong Lan Principle advisor 2: Professor Ha Van Khoi Review 01: Associate Professor Nguyen Tien Giang Review 02: Associate Professor Duong Van Tien Review 03: Associate Professor Vu Minh Cat The thesis will be defended in front of Thesis Evaluation Council at …………………………………………………………………………… At ……… on …….….… 2017 The Thesis can be studied at libraries below: - National Library Water Resources University library PREFACE The urgency of subject Currently there are many multi-functional water reservoir projects on the upstream area of Da river They contribute a large proportion of hydroelectric power output, provide water for economic development in Red river delta and help regulate downstream flood control with extremely high efficiency Son La and Hoa Binh reservoirs are two lakes with highest capacity for downstream flood control (7 billion m3) which are designed to be below normal tide rising level Therefore, there are severe conflicts between anti-flood mission and electricity generation, water provision Inter-reservoir operation regulations on Red river basin issued on Decision no 1622/QĐ-TTg on September 17th, 2015 formed a official operation frame However, actual operation must be based on predictions on the process of water running into the reservoirs Nonetheless, two practical questions for researches to solve are: - Is it allowed that the mentioned above reservoirs can accumulate water in the beginning of flood season? If so, how are water accumulation regulations formed to ensure downstream anti-flood safety? - According to the regulations, in late flood phase the reservoirs must accumulate water up to normal water rising level However, when expected big floods occur, how can reservoirs function in order to decrease downstream flood and ensure construction safety at the same time? Therefore, the research student chose the subject “Research on water accumulation operating mode in flood season for Hoa Binh and Son La terraced hydroelectric reservoirs”, hoping to study scientific foundation on water accumulation operating mode in Hoa Binh and Son La reservoirs to increase water accumulation efficiency for electricity generation and water provision, ensure construction safety as well as downstream flood prevention Mission of thesis - Research on scientific and practical basis to identify water accumulation operating mode in flood season, ensure safety in full water accumulation for reservoirs, increase water provision and electricity efficiency and at the same time assure safety for downstream flood and construction flood in Hoa Binh and Son La reservoirs - Research on operating mode of downstream flood restriction in late flood period when Son La and Hoa Binh reservoirs are allowed to accumulate full water, minimize negative impact on downstream area in case unexpected big floods occur Object and scope of the study Scope of the research: operation and regulation on water accumulation and flood prevention for terraced water reservoir system of Hoa Binh and Son La in flood season Object of the research: downstream flood prevention regulation is considered in the inter-reservoir system which comprises of reservoirs - Hoa Binh, Son La, Tuyen Quang and Thac Ba However, research on water accumulation operating mode as the topic object focuses on Son La and Hoa Binh reservoirs on Da river Research method Methods used in the research are (i) Inheritance method; (ii) Integrated analysis method; (iii) Mathematic model method New contribution of the thesis - Propose early conditional water accumulation mode for Hoa Binh and Son La reservoirs From that foundation, propose scientific basis to identify above water level limit of water accumulation process of Son La reservoirs in limited water accumulation period, to ensure efficient water accumulation as well as downstream and construction flood prevention safety - Propose regulation operation mode to prevent flood in downstream region and coping methods in case unexpected floods occur in full reservoir water accumulation at the end of flood period Structure of the thesis The thesis consists of 118 pages, 30 tables, 40 figures and 67 reference materials Aside from the introduction and conclusion, the thesis has chapters: Chapter 1: Overview of researches on multi-functional reservoir operation Chapter 2: Scientific and practical basis to identify water accumulation operation mode in flood season in Hoa Binh and Son La reservoir system Chapter 3: Research results on operation mode in water accumulation period of Hoa Binh and Son La terraced reservoirs CHAPTER OVERVIEW OF RESEARCHES ON MULTIFUNCTIONAL RESERVOIR OPERATION 1.1 Reservoir and reservoir operation To utilize integrated reservoirs for optimal benefit, scientists in the world focus to find out suitable operation rules, resolve conflicts among different objectives to reach higher operation efficiency Those researches range from Rippl’s work on simplifying water storage (1883) to recent complex researches on optimal reservoir operation in real time for multiple purposes of Mehdipour and nnk (2012) Despite systematic and specific research efforts from different investment organizations and various methods applied by scientists to form operation rules for reservoir system, successful applications are mostly related to typical features of each system There is no common methodology and tool that can be applied for all systems 1.2 Managing method and operating principles for multi-funtional reservoir system Each reservoir system in the operating phase must comply with an existing operation procedures, in which there are operation procedures for each period that the operating manager must follow Operating procedures of reservoirs are established in technical design period via imitation model or optimization model Operational procedures are presented in graphs or instruction tables according to water level (water capacity) or the reservoir in each year (Yeh, 1985) (Long, N.L, Madsen, H., and Rosbjerg, D., 2007) demonstrated in coordination chart are primary foundations for decision making in reservoir operation Operation procedure curves are one of the most popular and simple management methods in order to support decision making of the manager in reservoir operation For multi-functional reservoirs there are two ways of management: (i) water provision coordination and (ii) real time operation management Multi-functional terraced reservoirs operation procedures: (i) for purpose of flood prevention, store full water capacity in upstream reservoir in advance when flood needs avoiding, when empty water capacity is needed to prepare for flood regulation afterwards, downstream reservoir needs to be flushed in advance, (ii) for purpose of water provision, it is more simple - higher reservoirs need to store water before and lower reservoirs afterwards 1.3 Overview on method to establish multi-functional reservoirs operation process Reservoir system operation is always a complex and diverse subject which attracts attention of experts in the world as well as organizations and scientists in Vietnam Research on establishing a procedure for operation procedures mainly uses mathematical models such as imitation theory or optimization theory Optimization technique is primarily used to establish frame operation procedures, set up coordination chart for each reservoir in the system Imitation method helps the operation of reservoir system more specific with different scenarios to select a suitable an operation method, resolve conflicts and optimize objectives of the reservoir system Therefore, in researching the subject of operating multi-functional reservoir, even though optimization method is becoming more popular, there are still challenges in finding the best operating procedures (Labadie, 1997) Because of that, imitation method is still applied widely to identify suitable and flexible operation procedures 1.4 Overview of Red river Reservoir system Red river basin is the biggest basin in Northern Vietnam The Red river system originates from Yun Nan, China with 05 big tributaries which unify into 03 main branches- Da, Thao and Lo 100°0'0"E 24°0'0"N 102°0'0"E 104°0'0"E 106°0'0"E Ü 24°0'0"N CHINA 22°30'0"N "& & * # 22°30'0"N & & " Lai Chau Reservoir " &" " NOTE National boundary * # 21°0'0"N Reservoir & LAO " & Son La Reservoir " * # " & " River & & & " && & Meteorological station Hydrological station Basin boundary 100°0'0"E & 45 90 180 Km 102°0'0"E 21°0'0"N "& * # Hoa Binh Reservoir 104°0'0"E 106°0'0"E Picture 1-1: Map of Da Basin Thanks to favorable terrain conditions, Red river basin is increasingly benefited from upstream water flow In the upstream area of Da river (LyTien river) of China territory, 11 reservoirs are already planned, of which reservoirs are operated In Vietnam territory, in addition to water provision and electricity generating in flood season, Son La and Hoa Binh reservoirs (in Da river) spent billion m3 combined with 1,0 billion m3 of Tuyen Quang (on Gam river) and 0,45 billion m3 of Ba waterfall (on Chay river) to ensure safety of Hanoi not to exceed water level of 13,4 m with periodic flood repeated every 500 years Operating procedures of reservoir system in Red river basin Realizing the importance of these reservoirs, as soon as Hoa Binh reservoir comes to operation, many scientists have researched to support management agencies in setting up legal documents for an operation procedure in line with the system development The process has issued reservoir operation regulations in water accumulation period quite flexibly while maintaining reservoir water level above flood level However, there are no clear regulations about the moment of water accumulation and solutions to cope with flood when water level in reservoirs is high The subject of reservoir operation in water accumulation period still faces some challenges causing difficulties for operation decision makers (this subject is analyzed further in Chapter 2) and needs more research to improve operation efficiency Flood prediction subject Prediction on water flowing into a reservoir is one of the most critical tasks in operating the reservoir Prediction quality in forecast news has a big impact on efficiency of inter-reservoir operation, especially prediction of water flow in water accumulation period Flood forecast in Red river is a complicated subject with many challenged as more upstream reservoirs are constructed, lack of information from measurement stations in China territory, unreliable quality of numerical rain forecast Nevertheless, flood forecast for the system has drawn attention of many scientists (Trinh Quang Hoa and nnk, 1994) (Nguyen Van Diep, 2013) (Bui Dinh Lap, 2016) who utilize modern and progressive technology in the world to improve forecast quality and increase efficiency of operating reservoir in Red river basin Flood flow forecast with estimated time of 72 hours for “good” forecast is one of conditions to resolve conflicts between water accumulation and flood prevention for reservoir system in Red river basin system 1.5 Research orientation Considering Son La and Hoa Binh reservoir system, there have been many researches as scientific basis in constructing procedures for operating reservoir system in Red river, in addition to a lot of reports analyzing operating facts using many modern technology Yet, operational decision makers still face many challenges in periods with no clear regulations As a result, the thesis chooses the research as the scientific basis for operating reservoir system in Red river basin in water accumulation period The research model is illustrated in Figure 1-7 as below Figure 1-7: Flow chart researching water accumulation operating mode for Hoa Binh and Son La reservoir system Current reservoir operation procedure in Red river basin (QT1622) suggests a solid operation frame for the reservoir operation management Therefore, the thesis chooses imitation method with different advantages and disadvantages to make the operation of the reservoir system more specific with various scenario From those chosen scenario, a suitable water accumulation method is chosen to resolve conflicts and optimize objectives of the system CHAPTER SCIENTIFIC AND FACTUAL BASIS TO IDENTIFY WATER ACCUMULATION OPERATION MODE IN FLOOD SEASON FOR HOA BINH AND SON LA RESERVOIR SYSTEM 2.1 Comments on published procedures and suggesting research direction on water accumulation operation mode Downstream flood prevention mission QT 1622 provides that Son La and Hoa Binh reservoirs spend a big enough volume to constrict the above limits so that when floods occur, the design can cope with highest level in Hanoi according to 13,1 meter level of 300 year recurring flood and 13,4 meter of 500 recurring flood in Son Tay (see Table 21) Table 2-1: Regulations on distributing flood prevention volume for downstream flood demolition following restricted water level in Hanoi of Son La and Hoa Binh reservoir in QT1622 Water level to Volume spent for flood prevention following restricted be restricted level in Hanoi (billion m3) in Hanoi ZHN 11,5 m ZHN > 13,1 m to 13,4 m Son La reservoir Hoa Binh reservoir Total 1,00 1,13 (reservoir water level (reservoir water level 2,13 from 197,3÷203 m) from 101÷107m) 3,00 1,87 (reservoir water level (reservoir water level 4,87 from 203 ÷217,2 m) from 107 ÷117 m) Some limits of operation procedures In early phase and primary phase of flooding, operation procedures mainly focus on flood prevention when Hanoi water level may exceed 11,5 meter There are no specific operation procedures when Hanoi water level goes below this yet Calculate in technical profiles, establish procedures using Research orientation on water accumulation operation mode of Hoa Binh and Son La reservoir From analysis on procedures and operation reality, the thesis’s orientation comprises of two main themes: - Research water accumulation operation mode in flood season to increase water generating efficiency, ensure full reservoir water accumulation and still maintain flood prevention safety for downstream areas and constructions - Research to establish flood prevention regulating mode, minimize negative impact for downstream areas in case of unexpected big floods in water accumulation period after annual August 21st or after annual August 10th when it is allowed to accumulate water early 2.2 Scientific basis to identify water accumulation operation mode Point of view The thesis’ research orientation proposes to apply early conditioned water accumulation (medium method) for Hoa Binh and Son La reservoirs However, the fact that reservoirs are allowed to accumulate water early does not mean that water accumulation up to normal water rising level right after flood season finishes should be done Water should only be accumulated up to a certain limit so that when there is forecast of big flood, reservoir water level can be brought back to pre-flood level, ready to prevent flood as design Water accumulation mode is called “conditional” because in each water accumulation time, accumulated water level in the reservoir depends on factors (1) reservoir water level and downstream water level (in Hanoi) in water accumulation time; (2) flood forecast scale and water progress flowing into the reservoir and downstream water level in forecast time; (3) Restrictions on flood flushing regulation via flood flushing constructions Based on that, flood season is divided into operation periods: Restricted water accumulation period (before annual August 21st): restricted water accumulation operation period including early flood and main flood period This is the period that flood flushing for downstream area is primary, therefore reservoirs only allow accumulating water up to a certain water level 11 called restricted water level Hgh Hgh is identified so that when there is big flood forecast reservoir water level can be turned to pre-flood level to safely flush flood for downstream area Full reservoir water accumulation period (after annual August 21st): water accumulation period that requires reservoirs to store water up to normal rising water level In this case, an operation procedure to flush flood must be established to minimize damage for downstream areas when reservoirs are not capable to flush flood following downstream flood prevention standards Method to establish operation mode in restricted water accumulation period In restricted water accumulation period, Hoa Binh and Son La reservoir system operate in accordance with Hgh From that base, establish Hgh relationship called “water accumulation operation principle chart” to apply in water accumulation process To identify water accumulation operation principle chart, calculations need to be done Subject 1: With each scenario on Hanoi water level in the time to identify water accumulation, consider restricted water level Hgh when there is forecast of big flood equivalent to designated flood in flood prevention zone (recurring 500 year flood in Son Tay) From that base, identify Hgh plans following Hanoi water level The value of restricted water level Hgh depends on estimated time of applied forecast method In Red river basin, estimated forecast time is in 3-5 days range (will be analyzed in 2.3) Subject 2: Calculate and check big floods in reality From that base, select Hgh method to establish “operation principle chart” If downstream flood prevention requirements are not met, Hgh needs re-identifying following steps in Subject Establish operation mode to cope in case of unexpected floods in water accumulation time 12 Within scope of the research, the thesis only focuses on analyzing unexpected floods in water accumulation time of reservoirs which means when reservoirs are not capable of preventing flood for downstream area following designated floods Research orientation is illustrated in figure 2-7 Figure 2-7: Research approach model suggesting operation solutions to cope with unexpected floods 2.3 Analyzing factual basis and feasibility of identifying restricted water level Hgh for Son La and Hoa Binh reservoirs 2.3.1 Reality of downstream water level change in flood season Red river downstream water level’s state is becoming increasingly complicated with gradual decrease trend, especially in Hanoi According to flow statistics in Hanoi hydrological stations from 1960 to 1988 and reverting flow from 1989 to 2013, it can be seen that: - Highest water level in flood season is in peak phase and there are 09 years when highest Hanoi water level exceeds 11,5m, so that only 16% of the years upstream reservoirs had to flush flood for downstream area - Following the trend, the lowest water level decreases over time Water level was usually above 6,0m before 2002 and decreases in recent years Especially, in 2006, 2011, water level decreased down to 2,6m in peak flood season and there was a moment it decreased down to below 2,0m 13 - Flood foot water level in Hanoi lies below 6,0m and gradually rises from the beginning of the season till pea of the season Afterwards, it decreased - On the other hand, according to analysis materials (Ha Van Khoi, 2010), when Hanoi water level is lower than 7m, the riverbed can carry an addition of 1300 m3/s to increase water level up to 1,0m The river bed can load an addition of 2000 m3/s when Hanoi water level increases from 8,0m to 9,0m In the whole flood season, in 50% of the time of flood season, Hanoi water level is lower than 8,0m 2.3.2 Analysis of flood characteristics and big flood formation in the basin Big flood in a vast area is often caused by the combination of primary weather patterns with other weather patterns The majority of big floods on Red river in Hanoi have peak flood water level (Hmax) exceeding alert point III (11,5m) caused by continuous occurrence of weather patterns mentioned above Big floods in Red river in the years: 1968, 1969, 1971, 1986, 1996 (Hmax > 12,0m) are caused by 02 or more weather patterns happening respectively or at the same time There is not yet the most negative combination causing Red river flood when there are major floods on all rivers – Da, Thao, Lo However, especially big floods 1969, 1971 and 1996 are caused by big rain in tributaries The rain is not the same reason why there were big floods in rivers Especially big floods in Hanoi happen when there are especially big floods on 01 or 02 rivers Especially big floods in Hanoi are usually caused by 01 to 03 continuous floods which last 08-10 days with average rain volume between 100-300mm, some place up to 500-700mm and rain peak between 700800mm 2.3.3 Capacity to forecast and identify big flood in Red river basin Forecast lasting for an average time (5 days) is very important for inter reservoir operation subject According to estimation of national weather forecast center, long-term forecast quality in Hanoi station and towards Son La 14 reservoir is of good quality (80%); the rate towards Hoa Binh, Tuyen Quang and Thac Ba reservoirs reach above 70% Guaranteed level in short term forecast in recent years reached 80% with estimated time more than 24h, above 80% with estimated time of 36h and above 75% with estimated time of 48h Flood forecast quality has been improved because major floods in Northern area are mainly caused by continuous or respective occurrence of two or more weather patterns Therefore, Red river area flood forecast quality totally ensures the standards of water accumulation operation requirements of the thesis, which means analysis on big rain causal patterns can be received pretty early This is the basis that there is enough time to lower water level of Hoa Binh and Son La reservoirs back to pre-flood water level when there is forecast result 2.4 Calculation tool 2.4.1 Apply MS Excel to calculate water flow regulation through reservoir Establish calculation tool to regulate water flow through Red river reservoir system in Red river in MS Excel The calculation principle is as below: Calculation principle to regulate water flow through reservoirs: based on water balance equation and dynamics equation along with typical lines, parameters to describe characteristics of construction system River flow illustration: apply Muskingum method to illustrate flow in a natural river pattern is a classic yet very effective method 2.4.2 MIKE 11 model Water flow state for whole Red river basin of previous researches using Mike 11 model produce very practical flow demonstration results Therefore, the researcher uses the total system of rivers, sections and statistics of MIKE 11 established for Red river basin as calculation tool to imitate water flow from the back of reservoirs to downstream area Total river system comprises of 25 main rivers divided into 52 tributaries, established in measured sections in 2012 15 Boundary of lower area and above area: the process in which flushing volume from Hoa Binh reservoirs (Da river), Thac Ba (Chay river), Tuyen Quang (Gam river) The process that volume and water level in hydro station (Yen Bai, Ham Yen, Quang Cu, Thac Huong, Cau Son, Chu, Chi Thuy, Hung Thi, Nhu Tan, Phu Le, Ba Lạt, Định Cu, Đong Xuyen, Quang Phục, Kien An and Cua Cam) Middle area boundary: Middle areas are identified based on terrain documents and hydro-meteorological documents Middle areas provide a considerable water flow for river system comprising of areas 2.5 Chapter conclusion The thesis analyzes flaws of operation process, challenges in operation reality from which perspectives on researching water accumulation operation process to align with conditional early water accumulation According to this research direction, the thesis proposes calculation method for restricted water level Hgh (for restricted water accumulation period) and establish operation method in case of unexpected floods The thesis analyzes conditions forming big floods and rain, flood flow quality and flood forecast quality, proving feasibility of the research direction CHAPTER RESEARCH RESULTS OF OPERATION MODE IN WATER ACCUMULATION PERIOD OF TERRACED RESERVOIRS HOA BINH AND SON LA 3.1 Establish problem Establish operation principle chart, the thesis gradually identifies Hgh, measurement chart illustrated in Figure 3-2 in which Hanoi water level ranging in levels: (i) from 6,0-8,0 m; (ii) from 4,0-6,0 m; (iii) and below 4,0 m; with water level above 8,0m, maintain reservoir water level equivalent to pre-flood water level Choosing safe restricted water level in Hanoi as 10,5 m (due to prediction errors) The early state of Tuyen Quang and Thac Ba reservoirs are equal to 16 pre-flood water level Flood model of 1996 is not favourable for regulation operation of reservoir in Da river (peak flood flow into Son La reservoir is 31.863 m3/s, total flood volume in 20 days of Da river tributaries account for more than 50% of total downstream flood) As a result, this thesis chooses this flood model to calculate Flood flow process three previous days in boundaries are identified from early state of the system connected to starting point of the designated flood To simplify calculating process, choose a fixed water level of Hoa Binh reservoir as 101m, gradually increase water level of Son La reservoir Afterwards, modify based on total volume preservation principle The calculation results are illustrated in Table 3-1 and Table 3-3 Figure 3-2: Calculation model to establish operation principle chart Table 3-1: Results to calculate Hgh of Son La reservoir Water level (m)/ Flow(m3/s) In the beginning In water level of SonLa equal MNTL Hanoi water level (m) Hgh of Son La reservoir (m) 207,5 205,5 200,5 Hanoi water level (m) 8,3 9,67 9,75 Qmax Hoa Binh (m3/s) 8.270 11.289 11.126 17 197,3 Table 3-2: Total solutions to adjust Hgh Hanoi water level (m) Z Sơn La (m) Solution Z Hòa Bình (m) Z Sơn La (m) Solution Z Hòa Bình (m) Z Sơn La (m) Solution Z Hòa Bình (m) Z Sơn La (m) Solution Z Hòa Bình (m) 197,3 101,0 197.3 101,0 197,3 101,0 197,3 101,0 200,5 101,0 200.5 101,0 200,5 101,0 200,5 101,0 205,5 101,0 203 103,5 202,4 104,0 201,5 105,0 207,5 101,0 205 103,5 204,4 104,0 203,5 105,0 To measure feasibility of Hgh water level solutions of Son La and Hoa Binh reservoirs, the thesis operates reservoir system experimenting 10 big floods in reality 1969, 1970, 1971, 1972, 1996, 1999, 2000, 2002, 2006 2008 Result of regulation operation following Hgh solutions proposed are all feasible Adjusting reservoir water level following Hanoi water level is flexible and not leading to artificial floods for downstream area Hoa Binh reservoir opens maximally flushing gates in two big floods 1971 and 1996 In calculated floods, water level of reservoirs are brought back near pre-flood water level as regulations to prepare for downstream flood prevention and Hanoi water level does not exceed 10,5m The thesis chooses method to only increase Son La reservoir above pre-flood water level (197,3 m) and proposes water accumulation principle table (Table 3-5) to be active in factual operation and safe when flood happens in middle area Table 3-5: Water accumulation operation principle Hanoi water level (m) Hgh of Son La reservoir (m) Hgh of Hoa Binh reservoir (m) 207,5 205,5 200,5 197,3 101,0 101,0 101,0 101,0 18 Table 3-6: Comprehensive table of water level in Son La, Hoa BInh and Hanoi reservoirs operated based on solution and Oder Flood Beginning of Hanoi water level (m) Beginning of waterb level in Son La reservoir Lowest water level in Son la reservoir (m) (m) Highest water level in Son La reservoir when flushing flood Beginning of waterb level in Hoa Binh reservoir (m) (m) Highest water level in Hoa Binh reservoir when flushing flood Highest number of flusing gates of Hoa Binh reservoir Highest water level in Hanoi (m) (m) 8/1969 6,43 200,49 197,18 205,33 100,99 108,33 11,79 7/1970 4,43 205,49 197,52 202,19 101,01 101,96 10,25 7/1970 4,43 202,49 197,31 201,76 104,01 103,21 10,23 8/1971 6,12 200,5 197,52 211,93 101,00 113,19 12,02 7/1972 4,41 205,49 196,97 198,27 101,01 103,34 10,91 7/1972 4,41 202,39 197,25 198,66 104,01 102,38 10,91 8/1996 6,32 200,5 197,05 201,88 101,00 106,63 11,67 9/1999 4,47 205,49 197,32 200,01 101,09 101,84 10,28 9/1999 4,47 202,37 197,33 201,11 101,09 102,37 10,04 7/2000 4,63 205,51 197,03 200,16 101,06 101,86 11,22 7/2000 4,63 202,39 197,21 200,6 103,99 102,77 11.02 8/2002 7,15 200,45 197,81 201,61 101,00 106,9 11,61 7/2006 5,84 205,50 197,41 201,88 101,04 104,56 11,25 7/2006 5,84 202,37 197,22 202,73 104,02 105,07 11,41 8/2008 6,48 200,57 197,43 201,29 100,96 104,25 11,91 10 19 3.2 Research results on operation solutions in case of unexpected floods in water accumulation period The thesis only researches operation mode in case of unexpected floods in water accumulation period (Case 1: from 10/8 to 22/8; Case 2: from 22/08 to 15/09) following below steps: - Analyze solutions which can be used in urgent situations along with researching characteristics of proponents of water volume used for downstream and construction flood prevention of reservoir system Son La and Hoa Binh to propose a reasonable operation solution in case of unexpected floods - Analyze feasibility of proposed operation method via experimental operation in case of unexpected floods normally occurring in different phases of water accumulation period Proposing operation solution In this research, choose a solution to consider using part of flood prevention for the construction to prevent downstream flood in necessary conditions and still ensure safety for the construction This solution has many advantages such as reducing damages for downstream areas (thanks to non-flood splitting); increasing water accumulation efficiency and economic and societal damages are decreased thanks to flood non-splitting The thesis proposes specific solutions as below: When HHN< 6,0 m and there is likelihood of big floods within 72 hours, reservoirs in the system gradually opens flushing gates to bring reservoir water level back to regulated water level, QHoa Binh flushing does not exceed 12.000 m3/s and HHN12,5 m and it is predicted that Da river water level continually rises, Z Son La reservoir>215,0 m and ZHoa Binh reservoir >115,0 m, consider allowing Son La reservoir accumulate above 217,83m when flood volume in Da river is smaller than 20.000 m3/s and decreasing 20 Table 3-7: Lowest water level in reservoirs is allowed to reduce to cope with flood based on QT 1622 Reservoir Period From 10/8-22/8 From 22/8 – end of flood season 209 Sơn La 197,3 Hoà Bình 101 110 Tuyên Quang 105 110 thấp Calculation proposal Statistics on Hanoi flood level in Hanoi in flood seasons shows that flood foot in Hanoi is always below 6m and decreases over time during water accumulation period (Ha Van Khoi, 2010) Therefore, the initial conditions of water level in Hanoi can be considered as 6m Choose unexpected flood scenarios as natural type with recurring period respectively of 500 years and 300 years happening in main flood period (before 22/8); late flood period is only applied with flood scenario with recurring period of 300 years and real floods based on flood models of 1969, 1971 and 1996 Analysis results In scenario when unexpected flood happens with recurrence time of 500 years, upstream reservoirs are capable of flushing flood to ensure downstream safety if a portion of flood prevention volume for the construction is used The time to maintain Hanoi water level above 13m lasts 5-8 days In scenario 2, when floods with recurrence time is 300 years, upstream reservoirs must use part of construction flood prevention volume (Son La increases water level up to 200m) to protect Hanoi The time to maintain Hanoi water level above 13m is from to days Two reservoirs are always safe and can protect downstream area from big floods whose intensity equivalent to historical big floods in Red river during 21 water accumulation period without using flood protection water volume of the construction 3.3 Propose water accumulation operation mechanism of terraced reservoir system Hoa Binh and Son La 3.3.1 Restricted water accumulation period (from June 15th to August 21st ) In this period, the thesis proposes operation mechanism when Hanoi water level is below 11,5 m as below: operate upstream reservoirs based on flood forecast results with estimated time of days and Hanoi water level condition, Son La water reservoirs range from 197,3m to 207,5m Hoa Binh reservoir maintains pre-flood water level (101,0 m) as specifically provided in Table 3-5 When water level forecast in Hanoi in days is lower than 4,0m, regulate so that Son La reservoir water level maintains not higher than 207,5m and Hoa Binh reservoir water level maintains not being higher than 101,0m When water level forecast in Hanoi in days ranges within 4,0 m ÷6,0 m, regulate so that Son La reservoir water level maintains not higher than 205,5m and Hoa Binh reservoir water level maintains not being higher than 101,0m When water level forecast in Hanoi in days ranges within 6,0 m ÷ 8,0 m, regulate so that Son La reservoir water level maintains not higher than 205,5m and Hoa Binh reservoir water level maintains not being higher than 101,0m When water level forecast in Hanoi in days ranges higher than 8,0 m, regulate so that Son La reservoir water level maintains not higher than 205,5m and Hoa Binh reservoir water level maintains not being higher than 101,0m 3.3.2 Method to operate Son La and Hoa Binh reservoirs to cope in case of unexpected floods in water accumulation period When Hanoi water level is lower than m, predicting likelihood of big flood in the next 72 hours (equivalent to 300 year or 500 year recurring floods or more) 22 Reservoirs in Red river system starts to open flushing gates to bring reservoir water level back to the level regulated in Table 3-7 depending on different periods, but downstream safety must be ensured The volume being flushed down to Hoa Binh town can not exceed 12.000 m3/s and restricting Hanoi water level always below 11,5m When Hanoi water exceeds 11,5m and flood forecast in Da river continues to increase, Son La reservoir water level exceeds 215m, Hoa Binh level exceeds 115m, allow Son La reservoir accumulate water below 217,83m Only use construction flood prevention volume of Son La and Hoa Binh reservoirs when flood volume in Da river is below 20.000 m3/s and decreasing However, restrict Son La reservoir water level below 228 m and Hoa Binh reservoir not above 122 m (equal to tested water level) However, when there is a sign of flood more seriously than 500 year flood, especially floods with form such as 1969 or worse, combine with flood-splitting method into Day river according to the Decree 04 of the Prime Minister 3.4 Chapter conclusion Chapter presents calculation results to gradually identify Hgh of reservoirs and experimentally operate with some of 10 floods which happened From that foundation, feasibility of the research direction to find out conditional early water accumulation method for Son La and Hoa Binh reservoirs during flood season Early research results on feasibility of the method using part of construction flood prevention volume of Son La and Hoa Binh reservoir systems to cope with downstream floods in case of unexpected floods in water accumulation period (with flood scale equivalent to 300 year flood) CONCLUSIONS- RECOMMENDATIONS Conclusions 1) The latest operation procedures QT1622 still contains some shortcomings The thesis has researched, analyzed operation procedures and 23 factual process of system operation From that foundation, orient water accumulation operation research for Hoa Binh and Son La terraced reservoirs following condition water accumulation perspective with water accumulation period: restricted water accumulation period and full reservoir water accumulation period Based on that, system operating decisions depend on flood forecast results in days and Hanoi water level conditions 2) The thesis established scientific basis to identify above limit of water accumulation process of Hoa Binh and Son La terraced reservoir system The results identifying Hgh according to each Hanoi water level assessed feasibility of experimental operation for 10 big floods that happened Operating following the mechanism proposed by the thesis helps increase efficiency in accumulating water to fill reservoirs and at the same time, ensure safety of downstream flood prevention (Son La reservoir water level can increase 10m compared to preflood water level when Hanoi water level stays below 4,0m) 3) Propose using part of flood volume for construction taking part in downstream flood prevention to cope with cases of unexpected floods when Son La reservoir’s water level is above 209m and Hoa Binh reservoir is above 110m Eventually, bring out a back-up solution in operation process of factual reservoirs and foundation for researches to establish operation procedures in emergency cases Recommendations Recommendations on water accumulation operation mechanism of terraced reservoirs Hoa Binh and Son La along with coping solutions of the thesis need verification in a period of time Methodology on scientific basis in the thesis can be a research direction to help managers adjust and add to inter-reservoir operation procedures in Red river to increase efficiency of reservoir water accumulation, increase electricity generating efficiency and downstream flood prevention 24 PUBLICATIONS Vu Thi Minh Hue “Research on proposing plan for operating terraced hydropower reservoir system in Hoa Binh and Son La to cope with unexpected downstream floods in accumulated water period”, Annual science conference collection, Thuy Loi University, 2016 Vu Thi Minh Hue “Study on water storing operating rules of Hoa Binh and Son La reservoirs”, Scientific and technical journal on Environment and Water Resources, vol.54, pp 81-88, Sept.2016 Vu Thi Minh Hue, Ha Van Khoi “Research on pre-flood water level raising for developmental operation stage”, Annual science conference Collection, Thuy Loi University, 2015 Ngo Le An, Vu Thi Minh Hue, “study on flood forecasting for Son La, Hoa Binh and Tuyen Quang reservoirs in Red river”, Scientific and technical journal on Environment and Water Resources vol.49, pp 7379, Jun.2015 Ha Van Khoi, Vu Thi Minh Hue “Research the effect of upstream reservoirs on China to flow regime of Da river and Thao river”, Scientific and technical journal on Environment and Water Resources vol.38, pp 3-8, Sep.2012 ... Hgh Hanoi water level (m) Z Sơn La (m) Solution Z Hòa Bình (m) Z Sơn La (m) Solution Z Hòa Bình (m) Z Sơn La (m) Solution Z Hòa Bình (m) Z Sơn La (m) Solution Z Hòa Bình (m) 197,3 101,0 197.3... accumulation period In restricted water accumulation period, Hoa Binh and Son La reservoir system operate in accordance with Hgh From that base, establish Hgh relationship called “water accumulation... Son La reservoirs back to pre-flood water level when there is forecast result 2.4 Calculation tool 2.4.1 Apply MS Excel to calculate water flow regulation through reservoir Establish calculation