tóm tắt luận án tiến sĩ tiếng anh nghiên cứu sự thay đổi một số yếu tố thủy văn - thủy lực hạ lưu hệ thống sông hương dưới tác động của các công trình thủy lợi - thủy điện và biến đổi

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT WATER RESOURCES UNIVERSITY NGUYEN DINH RESEARCH ON CHANGES OF SOME HYDRAULIC AND HYDROLOGICAL FACTORS OF THE HUONG RIVER SYSTEM’S DOWNSTREAM UNDER THE IMPACT OF IRRIGATION AND HYDROPOWER CONSTRUCTIONS AND CLIMATE CHANGE Specialization: Water resources development Code: 62 44 92 01 DOCTORAL THESIS SUMMARY HANOI–2014 Research has been completed at Water Resources University Science advisors: Associate Prof Le DinhThanh Associate Prof Hoang Minh Tuyen Reviewer No.1: Reviewer No.2: Reviewer No.3: Thesis will be defended from university thesis evaluating council of Water Resources University At(hour)(day)(month) 2014 Thesis can be found at: - National Library - Water Resources University Library INTRODUCTION The problem statement of thesis: Many irrigation and hydropower constructions have been built on the Huong river basin, which have significant impacts on the hydraulic and hydrological regimes at downstream Meanwhile climate change also impacts on water resources in the basin Therefore the research of thesis “Research on changes of some hydraulic and hydrological factors of the Huong river system’s downstream under the impact of irrigation and hydropower construction and climate change” is necessary, meeting the demand of socio-economic sustainable development in the basin, particularly helpful for the activities of restructuring the agricultural structure and developing Thua Thien Hue Province to be a municipality Purpose of research: Clarifying the change of some hydrology-hydraulic factors at downstream of Huong river system under the impacts of irrigation and hydropower constructions and climate change in order to propose adaptive measures to mitigate the negative impacts on economic-social development and environmental protection Objects and range of research: Assessing the impacts of irrigation-hydropower construction system on some hydrologyhydraulic factors at downstream of Huong river from reservoirs to Thao Long dam with climate change calculated to the year of 2030 Research methodology: Thesis has used these methods: inheriting, investigating, surveying, statistic analysing, hydrologyhydraulic mathematical modelling, GIS, system analysing, expert method and community consulting Summarizing new contributions of the thesis: 1) Assess quantitatively the impact of irrigation - hydroelectric power constructions on the Huong river basin and the impacts of climate change on hydraulic and hydrological factors in downstream of the Huong river system 2) Propose structural and non-structural measures to mitigate the negative impacts of hydropower and irrigation works on the Huong river basin to flow regime in downstream and improve the efficient operation of those constructions Chapter I LITERATURE RIVEW 1.1 OVERVIEW OF PREVIOUS RELATED STUDIES The thesis overviewed 38 related studies in the world, Vietnam and the Huong river basin 1.1.1 Research in the world There are many studies relating to the impact of reservoirs and climate change on hydrology-hydraulic regime at downstream of catchments around the world These focus mainly on catchments which have large scales and can be divided into two directions: (i) comparing and analysing environmental changes between the periods before and after constructions of reservoirs by observed data, and (ii) Applying hydrological and hydraulic mathematical models to assess the impacts on flow at downstream 1.1.2 Research in Vietnam In Vietnam, the assessment of impacts of constructions and climate change to flow regime has been concerned recently, particularly after great irrigations and hydropower constructions were built on river systems Studies about impacts of climate change focus on assessing the change of water resources on watershed without going further into detailed and quantitative assessment about impacts of irrigation and hydropower constructions and climate change on hydrology-hydraulic factors at downstream of river systems 1.1.3 Constraints of previous research on Huong river basin and corrective direction Previous studies on Huong river basin assessing the impact individually, while the integrated impact of constructions and climate change on hydrology-hydraulic regime at downstream is not yet comprehensive considered Approaches of these research are not of systematic and integrated, mostly based on the assumption that the hydrological condition and ground surface remain unchanged Quantitative assessments are still restricted Corrective directions of thesis: - Assessing system analysis perspective of Huong river basin, concentrating on main structures which have considerable impact on flow regime at downstream - Quantitatively assessing of impacts of constructions and climate change, initially considering the role of land use and forest layer on the basis of selecting annual flow and specific flood to study the change of some typical hydrology-hydraulic factors - Proposing measures which are scientific-based, practical, possible and effective 1.1.4 Approach of thesis - Integrated approach following the water system - Imitative approach by hydrological and hydraulic mathematical models - Approach by scenarios Gathering data of climate, hydrology and topographic Analyzing impact factors Impacts of upstream reservoirs system Impact of estuary construction Rainfall-Runoff model Changing flow to reservoirs Operating irrigationhydropower reservoirs Assess changing tendency of climatic factors Selecting climate change scenarios Detailed climate change scenarios Hydrologyhydraulic model Change of some factors Comparing with investigated result Propose oriented measures Figure 1.1: Research approaching diagram of thesis Figure 1.2: The Huong river basin in Vietnam 1.2 1.2.1 CHARACTERISTICS OF THE HUONG RIVER BASIN Physical characteristics The Huong River Basin (HRB) locates mostly in Thua Thien Hue Province (figure 1.2), including three main tributaries: Bo river, Huu Trach river and Ta Trach river, the last of which is the main source of Huong river Water resources of HRB have a vital role in socio-economic-cultural development and environmental protection of Thua Thien Hue province 1.2.2 Socio-economic characteristics In recent years on Huong river irrigation and hydropower structures have been constructed in order to meet the demand of socioeconomic development Constructions along with the change of landuse structure have considerable impacts on hydrology-hydraulic regime of Huong river 1.3 CHANGING TENDENCY OF SOME HYDROMETEOROLOGY FACTORS ON HUONG RIVER BASIN 1.3.1 Data and trend assessment method Research uses data of precipitaion, evaporation and water level gathered from stations in the area to analyse and assess the tendency of some hydrometorology factors by Mann Kendall validating method and Sen method 1.3.2 Changing tendency of some climatic factors Precipitation characteristics tend to rise but not clearly (not meet the 5% significant level) In contrast, evaporation seems to decrease The average temperature at mountain areas rises, when the figure at Hue is about to drop slightly (not meet the 5% significant level) 1.3.3 Changing tendency of some hydrological factors Water level characteristics at Kim Long and Phu Oc stations have the trend to rise, appropriate with the increasing trend of rainfall on the catchment 1.3.4 General assessment about changing tendency of some hydrometeorology factors and scenarios of climate change and sea water rise for Huong river basin Result of tendency assessment shows that some hydrometeorology factors of Huong river basin have the changing trend that suitable to climatic conditions, in which the typical factors are the increasing trend of precipitation in both rainy and dry seasons, as well as the maximum precipitation of 1, 3, 5, days continuously, which are the main factors causing flood in the basin In 2012, Ministry of Nature Resources and Environment (MONRE) published scenarios of climate change and sea water rise for Vietnam, in which data for Thua Thien Hue province ware also provided, with the average amount of change in precipitation in 2030 period increases by 2.1 percent compared with the base period of 1980-1999 1.4 CONCLUSIONS OF CHAPTER I Studies relating to Huong river basin so far have assessing the impact of construction individually Some research shows the assessment about the impacts to flow regime but are still quantitatively limited in changes of hydrology-hydraulic factors under the operations of reservoirs at upstream and Thao Long dam at downstream, particularly when climate change is setting out new challenges to integrated water resources management in Huong river basin Changing tendency of some climatic and hydrological factors in Huong river basin is quite suitable with the scenarios of climate change and sea water rise published by MONRE in 2012 On the base of research orientation and approach of thesis, applying hydrologyhydraulic mathematical models and integrated analyzing are chosen to be the major methods in assessing the impacts of main irrigationhydropower constructions in the river basin with published scenarios of climate change and sea water rise No.B2 Chapter II ANALYSIS AND CALCULATIONS 2.1 IRRIGATION AND HYDROPOWER CONSTRUCTION SYSTEM IN HUONG RIVER BASIN 2.1.1 Irrigation – hydropower constructions Directly related to the main streams in the basin, there are irrigation and hydropower constructions, weirs and dams for irrigation combined with preventing saltwater intrusion and controlling flood and flood drainage constructions at estuaries of Huong river and its branches Characteristics of irrigation – hydropower constructions The constructions system is diverse, including upstream reservoirs which have the function to control flood, supply water and generate electricity and constructions at estuary for salt water prevention and flood drainage 2.1.3 Selection of researched constructions in the thesis Criteria for selection: Volume of reservoir ≥ 100.106m3, Installed capacity ≥ 30MW for hydropower reservoirs, ≥ 10MW for combined function reservoirs, Thao Long dam at estuary of Huong River has a great impact on dry season flow of the whole system, therefore the reservoirs of Binh Dien, Huong Dien, Ta Trach and Thao Long dam are put in research 2.1.4 Impact assessment framework Based on the analysis and selection of researched constructions, the impact assessment framework and researching situations are indicated in figure 2.2 Binh Dien, Huong Dien, Ta Trach reservoirs and Thao Long dam calculated, climate change considered Impact of constructions Impact of constructions and climate change 2.1.2 Binh Dien, Huong Dien, Ta Trach reservoirs and Thao Long dam calculated without climate changed No construction calculated, Propose measures to mitigate Figure 2.2: Impact assessment framework of irrigation-hydropower constructions and climate change to some hydrology-hydraulic factors of Huong River 2.2 2.2.1 MAIN FACTORS AFFECTING THE HYDROLOGY HYDRAULIC REGIME OF HUONG RIVER Rain, storms and weather phenomena causing flood 11 (validation, figures 2.21); the coeficient for HEC-RAS is 0.63-0.77 (figure 2.26, 2.27) Figure 2.17: Calibration of HEC-HMS at Binh Dien Figure 2.21: Validation of HEC-HMS at Duong Hoa Figure 2.26: Calibration of Figure 2.27: Validation of HEC-RAS at Kim Long HEC-RAS at Phu Oc 2.5 CONCLUSIONS OF CHAPTER II Upstream reservoirs, including Ta Trach, Binh Dien and Huong Dien and Thao Long dam at downstream hold an important role in impacting the hydrology-hydraulic regime at downstream Huong river These construction are included in research of thesis Operations of Thao Long, Binh Dien and Huong Dien constructions are not so long However results from analysis have shown that there are significant impacts on some hydrology-hydraulic factors in Huong river Therefore quantitative assessment in specific situation is necessary, especially when Ta Trach reservoir went in active and climate change considered 12 HEC-HMS and HEC-RAS models are applied in Huong River for daily flow, flow in flood season and dry season Results for calibration and validation of models are acceptable for assessing change of hydrology-hydraulic factors under the impact of constructions and climate change Chapter III RESULTS AND DISCUSSION 3.1 RESEARCH SITUATIONS AND OPERATING PLANS FOR CONSTRUCTION SYSTEM 3.1.1 Research situations This thesis considers scenarios: (1) Natural condition, with no construction calculated; (2) Binh Dien, Huong Dien, Ta Trach reservoirs and Thao Long dam are constructed, with none climate change applied and (3) Those constructions are calculated, with climate change to 2030 considered according to scenarios No.B2 published by Ministry of Natural Resources and Environment in 2012 3.1.2 Operating plans of constructions for impact assessment Table 3.1: Calculating plans No Plan name Calculating condition TH1 Natural flow, no construction calculated TH2-PAI Binh Dien, Huong Dien Ta Trach reservoirs and Thao Long dam constructed and operated by individual procudures TH2-PAII Binh Dien, Huong Dien Ta Trach reservoirs and Thao Long dam constructed and operated according to downstream alerted level TH2-PAIII Constructions calculated and operated according to downstream alerted level, with flood control pool added to reservoirs TH3-PAI Constructions calculated and operated by individual procedures, with climate change considered to 2030 in B2 scenarios TH3-PAII Constructions calculated and operated according to downstream alerted level, with climate change considered to 2030 in B2 scenarios 13 3.1.3 Specifying typical year and rainfall according to scenarios to year of 2030 By the work of considering hydrometerology data, this thesis chose the year 1984, which is an average water year, to assess annual flow and dry weather flow To assess impacts on flood flow, the thesis chose the historical flood in the year 1999, which rainfall had in delta area greater than in mountain area, and in 1983, which had rainfall in mountain area greater than in delta area The calculated rainfall in climate change condition is identified by the amount of change in precipitation according to B2 scenarios (MONRE, 2012) 3.2 THE IMPACTS OF CONSTRUCTION SYSTEM AND CLIMATE CHANGE ON SOME HYDROLOGY-HYDRAULIC FACTORS AT DOWNSTREAM OF HUONG RIVER 3.2.1 Locations for validating and assessing flow changes at Huong River downstream The locations for validating and assessing change of hydrologyhydraulic factors at downstream of Huong river are Kim Long station and Phu Oc station These are the two most important level controlling point for flood alert for Hue city and the downstream delta 3.2.2 Impact on daily flow Results of simulating mean daily water lever in average water year at Kim Long for each scenario with operating plan No.1 are shown in figure 3.2 and table 3.4 Figure 3.2: Water level change at Kim Long in average water year 14 Table 3.4: Chane in mean water level in average water year Point TH1 TH2-PAI TH3-PAI H0 (m) H1 (m) H1-H0 H2 (m) H2-H0 Kim Long 0.04 0.68 +0.64 0.69 +0.01 Phú Ốc 0.42 1.02 +0.60 1.06 +0.04 When climate change is not considered, the mean annual water level at downstream of Huong river in an average water year under the impact of constructions has a rising trend, about 0.60 m compared with none-construction situation With climate change calculated, water level of Huong river rises insignificantly with the impact of constructions This shows that the change of flow at downstream is greater affected by irrigation-hydropower system than by climate change according to research scenarios Before the existence of constructions, water stage in dry season fluctuated by the tide, in flood season the level changed abruptly with high peak of flow After having constructions, water level in dry season maintained stably without fluctuating with the tide; in flood season, the peak flow has been lowered, the period of over second-grade warning stage at Kim Long has reduced from days to days while the period of over first-grade warning stage has increased from days to 47 – 53 days 3.2.3 Impacts on flood flow Results of calculating flood flow at Huong river downstream for each plan are shown in figures 3.4, 3.6 and tables 3.6, 3.8 Table 3.6: Calculated peak water level change in 1999 at downstream of Huong river for each plan (m) Point TH1 TH2- PAI TH2-PAII TH2-PAIII Kim Long Phú Ốc H0 (m) H1 (m) H1-H0 6.09 5.81 -0.28 4.68 4.60 -0.08 H2(m) 5.13 4.48 H2-H0 -0.96 -0.20 H3 (m) 5.10 4.47 H3-H0 -0.99 -0.21 15 Figure 3.4: Graph of calculated Figure 3.6: Graph of calculated flood stage in 1999 at Kim Long flood stage in 1983 at Kim Long When climate change is not calculated, analysis of some flood properties in 1999 at Kim Long station shows that the flood regime has changed considerably under the impacts of reservoirs After the constructions of reservoirs, the peak flow has lowered, maximum flood intensity has decreased from 0.54m/hour to 0.24 – 0.52 m/hour, average flood intensity has also decreased from 0.2 m/hour to 0.1 – 0.15 m/hour depending on operating plans The period of over third-grade warning stage has also been reduced by – hours Table 3.8: Change of simulated peak flood stage in 1983 at Huong river downstream according to operating plans (m) Point TH1 TH2- PAI TH2- PAII TH2- PAIII H0 (m) H1 (m) H1-H0 H2(m) H2-H0 H3 (m) H3-H0 Kim Long 5.00 4.70 -0.30 3.81 -1.19 3.56 -1.44 Phu Oc 4.73 4.43 -0.30 4.41 -0.32 4.30 -0.43 For the 1983 flood, result shows that characteristics at Kim Long witnessed a significant change Without the apperance of reservoirs, the maximun flood intensity reached 0.35 m/hour, and dropped to 0.14 – 0.33 m/hour after reservoirs are constructed The average flood intensity decreased from 0.09 m/hour to 0.05 – 0.07 m/hour depending on the operating plan The period of over third-grade warning stage was reduced by – hours Flood is more regulated With climate changed considered, results of calculation for the historical flood in 1999 are shown in figures 3.8, 3.9 and table 3.10 16 Figure 3.8: Graph of calculated Figure 3.9: Graph of calculated flood stage in 1999 at Kim Long, flood stage in 1999 at Kim Long, plan I, climate change considered plan II, climate change considered Table 3.10: Change of peak flood stage in 1999 at Huong River downstream with climate change calculated (m) Point TH1 PA I PA II H0 TH2 TH3 H2-H1 TH2 TH3 H4-H3 (m) (H1) (H2) (m) (H3) (H4) (m) Kim Long 6.09 5.81 6.15 + 0.34 5.13 5.32 + 0.29 Phu Oc 4.68 4.60 4.71 + 0.11 4.48 4.56 + 0.08 Generally, research has shown that the change of flood flow regime at downstream of Huong river flow depends greatly on flood controlling operation mode of upsream reservoirs, particularly Ta Trach reservoir Both plans PAII (combined operating) and PA III (combined operating + increasing flood control volume) decreased the peak flood stage by 1.2 – 1.4m, guaranting 1983 flood controlling criteria for Hue city Also in research, the impacts of climate change for each plan of operation on change of peak flood stage at downstream in are inconsiderable compared to the impacts of reservoirs 3.2.4 Impacts on dry season flow Results of calculation for dry flow stage (Jan-Aug) in an average water year for individual operating plan are shown in table 3.11 17 Table 3.11: Change of dry flow stage in average water year TH1 TH2-PAI TH3-PAI Point H1 (m) H2 (m) H2-H1 H3 (m) H3-H2 Kim Long -0.11 0.52 +0.63 0.52 0.00 Phu Oc 0.17 0.74 +0.57 0.75 +0.01 Result shows that in dry season, the role of Thao Long dam and reservoirs is essential They increase mean water level at downstream to about 0.6m In case of climate change considered, calculation shows that mean water level in dry season to the year of 2030 at Kim Long and Phu Oc remain nearly unchanged At Kim Long, after existences of constructions, the lowest mean stage in dry season is +0.44m, that can ensure water supply for Huong river delta area and transporting water for Phu Loc area (supporting Truoi reservoir) 3.2.5 Impacts on sediment issue at downstream Research has shown that water level at Binh Dien station falls significantly along with flow levels With the same discharge, the stage dropped by about 40cm compared to when reservoir is not yet constructed Due to the limited data of only ome year of investigating after Binh Dien operation, this thesis could not fully and correctly indicate the reason of this drop However it can tell that Binh Dien reservoir has certain impacts of change of sediment at downstream, being one of the reasons for riverbed erosion and changes of hyrology-hydraulic relations When Ta Trach reservoir is in operation, progress Q-H relation will have more changes 3.3 PROPOSING ORIENTED MEASURES TO MITIGATE NEGATIVE IMPACTS AND IMPROVING EFFICIENT OPERATION OF IRRIGATION-HYDROPOWER CONSTRUCTIONS 3.3.1 Purposes and basis of proposing solution 18 - Mitigate the negative impacts of irrigation-hydropower constructions to downstream in flood and dry season for socioeconomic development and environmental protection - Improve the efficiency of constructions in order to disentangle the conflict between electricity generation and flood control, mitigate losses to downstream 3.3.2 Nonstructural measures (1) Enforcing the vegetative cover on the basin: Based on CN coefficient of land use and vegetative cover scenarios, the applying of HEC-HMS model has estimated flood flow to reservoirs in 1983 It is estimated correlation function between CN coefficient to flood volume that comes into the reservoirs: y= 13.19x +2676, R2 =0.994 Result of peak flow and stage of 1983 flood at Kim Long and Phu Oc according to land cover scenarios is shown in table 3.16 Table 3.16: Influence of change of land use and vegetative cover to flood flow in 1983 at downstream of Huong River Kim Long Phu Oc Year Hmax ΔH Qmax ΔQ Hmax ΔH Qmax ΔQ 3 (m) (m) (m /s) (m /s) (m) (m) (m3/s) (m3/s) 1983 5.00 5907 4.73 1801 2020 5.00 0.00 5898 -9 4.73 0.00 1797 -4 2030 5.00 0.00 5891 -16 4.71 -0.02 1776 -25 2050 4.98 -0.02 5880 -27 4.69 -0.04 1759 -42 As can be seen, forest cover and landuse have impacted the flood flow but this differs for each area, with the impact at upstream being more significant than one at downstream Forestation needs to be enforced in these critical areas: - Upstream areas of reservoirs(including small reservoir) - Afforest at the belts along the downstream river and coastal strip - Planting and protecting the forest is integrated river basin 19 management, in which water resources management is the key factor (2) Planing, buliding and protecting the protecting corridor of reservoirs, river, lagoon (3) Building inter-reservoir operating procedures cooperated with Thao Long dam This thesis proposes the Combined operating procedure of irrigation-hydropower constructions in Huong river basin as below: (1) For upstream reservoirs a)- Binh Dien reservoir: - Flood control elevation: +80.6m - With incoming flood, store inflow to the eleveation of +85.0 m then discharge with Qdischarge ≤ Qinflow and cooperate with downstream flood control requirement Amount of discharge depend on warning stage at Kim Long - After flood, reservoir keeps on dischaging to drop the water elevation to +80.6m in order to engage the following flood b) Huong Dien reservoir: - Flood control elevationL +56.0m - When flood come, store inflow to the elevation of +58.0m the discharge with the flow smaller than inflow and coperate with warning stage at Phu Oc - After flood, continue on discharging opeartion to drop the water elevetion to +58.0m c) Ta Trach reservoir: - Before flood season, keep the water elevation of reservoir at +25.0m for flood controlling - When flood comes and water elevation rise from +25 m to +46.97 m, discharge with the flow lower than inflow and coperate with warning stage at Kim Long - After flood, continue water elevation to +45.0 m discharging operation to drop the 20 (2) For Thao Long dam at downstream In flood season, Thao Long dam should be totally open in order to maximize flood draining In case of high tidal elevation, lift the floodgate to prevent saltwater intrusion (by small flood, high tide, ) The efficiency to flood control by cooperated plan compared to individual operation is shown in table 3.17 Table 3.17: The efficiency to flood control by coopearated plan compared to individual operation (m) 1983 Flood 1999 Flood Point PA I PA II Reduced PA I PA II Reduced Kim Long 4.70 3.81 -0.89 5.81 5.13 -0.68 Phú Ốc 4.43 4.41 -0.02 4.60 4.48 -0.12 3.3.3 Structural measures (1) Increase flood control storage of Binh Dien and Huong Dien reservoirs Table 3.18: Proposed flood control storage of reservoirs Now Proposed Reservoir VFC (10 m ) % VE VFC (106m3) % VE Ta Trach 435.9 125.8 435.9 125.8 Binh Dien 70 20.3 150 43.6 Huong Dien 0 200 57.0 Total 505.9 48.6 785.9 75.4 Table 3.19: The efficiency to flood control at downstream by integrated operation and flood control storage increase of reservoirs in comparision with keeping flood control storage constant and individually operation (m) Point Kim Long Phu Oc 1983 Flood 1999 Flood TH2- TH2- Reduction TH2- TH2- Reduction PAI PAIII level PAI PAIII level 4.70 3.56 -1.14 5.81 5.10 -0.71 4.43 4.30 -0.13 4.60 4.47 -0.13 21 As can be seen, increasing total flood storage and integrated operation of upstream reservoirs would have led to greatly effective flood reduction in both 1983 and 1999 floods Particularly the peak water level at Kim Long been lowered by 1.14m for 1983 flood and 0.71 for 1999 in comparison with keeping flood control storage constant and individually operation Both PAII and PAIII plans reduced peak water stage in 1983 by 1.19 – 1.44m Consequently, peak elevation at Kim Long reachs +3.69m (PAII) and +3.44 m (PAIII), that meet the requirement of flood control in 1983 for Hue city Research has shown that the measure to increase total flood control storage for upstream reservoirs is acceptable However, it is necessary to have deeper and more detailed research to smoothly disentangle the conflict of flood control and electricity generation of private hydropower constructions for stronger and more pratical foundations for later implementation (2) Improving and upgrading flood drainage and sea dike Improve and extend downstream rivers and creeks such as Dien Hong, An Xuan, Kim Doi in the northen area of Huong river; silted section of Nhu Y, Pho Loi, Dai Giang river; improve and upgrade drainage, pump station and overflow dike lines on Tam Giang – Cau Hai lagoon Dike routes that need to be upgraded include east and west routes of Tam Giang lagoon and routes of Sam – Thuy Tu – Cau Hai lagoon in order to prevent sea water rising 3.4 CONCLUSIONS OF CHAPTER III Impacts of irrigation-hydropower constructions in Huong river basin on downstream flow regime is considerable It is necessary to concern with (i)-Binh Dien and Huong Dien reservoir operating procedures in flood season; and (ii)- main role in flood reduction of flood control storage, typically Ta Trach reservoir and tide prevention role of Thao Long dam Impact of climate change (B2) to the year of 2030 on annual flow and dry season flow at downstream is insignificant compared to impacts of constructions For flood flow, in case of extreme flood 22 (1999), impacts of climate change become more apparent The oriented measures to mitigate the negative impacts include the group of nonstructural solutions: Enforcing afforestation in watershed, constructing water preservation corridor and building inter-reservoir operating procedures in cooperation with Thao Long dam The group of structural solutions includes increasing total flood control storage of reservoirs, improving and upgrading flood drainages and sea dikes CONCLUSION AND RECOMMENDATION Conclusions Main results of thesis in assessing the impact of irrigationhydropower constructions system and climate change on some hydrology-hydraulic factors at downstream of Huong river based on integrated and systematic approach perspective and advanced calculations, particularly hydrology-hydraulic mathematical models, has shown that: 1) Changing tendency of some hydrometerology factors in Huong river basin to the year 2030 has been researched and identified that it is available with scenarios of climate change of Ministry of Natural Resources and Environment 2) Impacts of irrigation-hydropower constructions on some hydrology-hydraulic factors at downstream are transparent and considerable, which are presented in specific quantitative results: -Regardless of mean annual water level of typical year (1984): Thao Long dam and Binh Dien, Huong Dien, Ta Trach reservoirs system have leveled up mean annual water level at downstream significantly, with the figure at Kim Long raised by 0.64 m, at Phu Oc by 0.6 m -Regardless of peak flood stage: All three operating plans of constructions system (individual operating, integrated operating with warning stage at downstream considered, integrated operating and increasing flood control storage) drop sharply the peak flood stage at downstream of Huong river In term of the 1983 flood, peak stage 23 dropped by 0.30 – 1.44 m at Kim Long, 0.3 – 0.43 m at Phu Oc; in term of the 1999 flood, the figures are 0.28 – 0.99 m at Kim Long and 0.08 – 0.21 m at Phu Oc -Regardless of mean dry season water stage (Jan-Aug): The role of constructions with mean water level is significant, particularly for Thao Long dam Water level at downstream in dry season is stable without influence of tide and rise significantly (about 0.60 m) at both Kim Long and Phu Oc 3) Impacts of climate change on Huong river basin according to B2 scenarios on some hydrology-hydraulic factors of downstream is generally inconsiderable compared to impacts of irrigationhydropower constructions system in the period to 2030 In case of extreme flood (1999), impacts of climate change become more transparent 4) Based on results of reseach, analysis, scientific assessment and pratice, this thesis proposes two groups of solutions in order to mitigate disadvantageous impacts and improve efficiency of constructions: -Nonstructural solutions include: (i)”Enforcing vegetative cover in watershed”; (ii)”Planning, building and protecting preservation corridor of water in rivers, reservoirs, lagoons”; and (iii)”Building inter-reservoir operating procedures in cooperation with Thao Long dam” -Structural solutions include: (i)”Increasing flood control storage of Binh Dien and Huong Dien reservoirs”; and (ii)”Improving and upgrading flood draining routes and sea dikes” These measures are possible and suitable with requirements and sustainable developing direction of Thua Thien Hue Province New contributions of the thesis The thesis has been new contributions (see introduction) Recommendations 1) In fact, irrigation-hydrology constructions system that put in research include three main reservoirs (Binh Dien, Huong Dien, Ta Trach) and Thao Long dam, in which two hydropower reservoirs Binh 24 Dien and Huong Dien and Thao Long are actually activated, while Ta Trach reservoir will be implemented and operated by 2014 Therefore, there is not enough operational statistics to fully assess Consequently, it is proposed that the Government should give the permission of governing the synchronous observation of topographic, meteorology, hydrology, and oceanographic factors, combined with upgrading equipment, build extra rain gauge and flow measurement station which meet high reliable basis for completion of inter-reservoir operating procedures in Huong River basin as soon as possible 2) In order that operation of irrigation-hydropower constructions system for flood and drought control and electricity generation is effective, it is necessary to enhance the quality of forecast and hydrometeorology forecasting technology in the watershed 3) The issue of operating the irrigation-hydropower system in a watershed is extremely complicated due to binding conditions of nature and techno-economy Therefore Huong river basin needs to be researched more comprehensively, particularly in the period of solving the conflict of increasing flood control storage, supplying water in dry season and electricity generating efficiency LIST OF AUTHOR’S PUBLISHED SCIENCE RESEARCHES Nguyen Dinh (2013), “Studying the Effects of the main irrigations, hydroelectricPowersto Huong River Downstream Flow, Hue City”, Scientific and Technical Hydro – Meteorological Journal, (634), pages -6 Nguyen Dinh, Nguyen Hoang Son, Le DinhThanh (2013), “Application of HEC-HMS and HEC-RAS for flood flow simulation of Huong river basin”, Journal of Water Resources & EnvironmentalEngineering, (42), pages 12-17 Nguyen Dinh, Le DinhThanh, Ngo Le An (2013), “Study on impacts of climate change to hydrological regime of Huong river”, Journal of Water Resources & Environmental Engineering, (40), pages 15-22 Nguyen Dinh, Le DinhThanh (2012), “Current status of exploitation and management of surface water resources on Huong river basin”, Scientific and Technical Hydro – Meteorological Journal, (613), pages 7-13 Nguyen Dinh, Le DinhThanh (2011), “Hydropower development on Huong river basin, limitations and the measures to improve the benefits”, Journal of Water Resources & Environmental Engineering, (32), pages 3-10 ... (m) Point TH1 TH 2- PAI TH2-PAII TH2-PAIII Kim Long Phú Ốc H0 (m) H1 (m) H1-H0 6.09 5.81 -0 .28 4.68 4.60 -0 .08 H2(m) 5.13 4.48 H2-H0 -0 .96 -0 .20 H3 (m) 5.10 4.47 H3-H0 -0 .99 -0 .21 15 Figure 3.4:... Point TH1 TH 2- PAI TH 2- PAII TH 2- PAIII H0 (m) H1 (m) H1-H0 H2(m) H2-H0 H3 (m) H3-H0 Kim Long 5.00 4.70 -0 .30 3.81 -1 .19 3.56 -1 .44 Phu Oc 4.73 4.43 -0 .30 4.41 -0 .32 4.30 -0 .43 For the 1983 flood,... 1983 5.00 5907 4.73 1801 2020 5.00 0.00 5898 -9 4.73 0.00 1797 -4 2030 5.00 0.00 5891 -1 6 4.71 -0 .02 1776 -2 5 2050 4.98 -0 .02 5880 -2 7 4.69 -0 .04 1759 -4 2 As can be seen, forest cover and landuse