Nội dung

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 1 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 - 2 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 3 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 4 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 5 6 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 7 increasing trend of precipitation in both rainy and dry seasons, as well as the maximum precipitation of 1, 3, 5, 7 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. 8 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