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
Trang 1MINISTRY 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
Trang 2Research has been completed at Water Resources University
Science advisors:
Associate Prof Le DinhThanh
Associate Prof Hoang Minh Tuyen
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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 hydraulic factors at downstream of Huong river from reservoirs to Thao Long dam with climate change calculated to the year of 2030
hydrology-Research methodology: Thesis has used these methods:
inheriting, investigating, surveying, statistic analysing, hydraulic mathematical modelling, GIS, system analysing, expert method and community consulting
hydrology-Summarizing new contributions of the thesis:
1) Assess quantitatively the impact of irrigation -
Trang 4hydroelectric 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
Trang 5Corrective 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
Trang 6Figure 1.1: Research approaching diagram of thesis
Impacts of
upstream reservoirs
system
Propose oriented measures
Operating hydropower reservoirs
irrigation-hydraulic model
Hydrology-Change of some factors
Changing flow
to reservoirs
Assess changing tendency of climatic factors Rainfall-Runoff
model
Selecting climate change scenarios
Detailed climate change scenarios
Comparing with investigated result
Trang 81.2 CHARACTERISTICS OF THE HUONG RIVER BASIN 1.2.1 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 socio-economic 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 METEOROLOGY FACTORS ON HUONG RIVER BASIN 1.3.1 Data and trend assessment method
HYDRO-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 meteorology factors of Huong river basin have the changing trend that suitable to climatic conditions, in which the typical factors are the
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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 hydraulic mathematical models and integrated analyzing are chosen to
hydrology-be the major methods in assessing the impacts of main hydropower constructions in the river basin with published scenarios
irrigation-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
Trang 102.1.2 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
2.2 MAIN FACTORS AFFECTING THE HYDROLOGY -
HYDRAULIC REGIME OF HUONG RIVER
2.2.1 Rain, storms and weather phenomena causing flood
Binh Dien, Huong Dien, Ta Trach reservoirs and Thao Long dam calculated without climate changed
Binh Dien, Huong Dien, Ta Trach reservoirs and Thao Long dam calculated, climate change considered
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
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The regime of precipitation distributes irregularly in both in space and time, creates a great differentiation in hydrology-hydraulic regime of Huong River, with the flow depleted in dry season and overflow causing flooding in rain season everyyear
Storm is an important figure that have a great impact on hydrology-hydraulic regime of Huong River, particularly the flood flow Storms and tropical depressions combined with other weather phenomena often create downpour and thunderstorms, causing severe flooding at downstream delta and lagoon areas
2.2.2 Conditions of topography and land cover
Mountain and coastal direction is nearly perpendicular with main wind direction, which has the effect to block the wind, causing heavy rain The watershed has the shape of a large sink, the mountain area is very close
to the delta-lagoon area, which causes a fierce property of flood flow
Forest cover rate is quite high while the role to control flow of the vegetative cover is low due to the low rate of primary forest, which are decreasing
2.2.3 Lagoons and tide
Before Thao Long dam’s construction, Tam Giang – Cau Hai lagoon system has a significant impact on flow regime of Huong River With the property that low tide goes along with dry season and high tede come at the same time with flood season, the impact of tide makes it even more dificult to supply water in dry season due to saltwater intrusion, and flood draining in flood season
2.2.4 Socio-economic activities in the watershed
In the period of 2007-2009, Thao Long dam raised the mean annual water level of Kim Long and Phu Oc by 26-27cm, the lowest and highest water level in dry season increased by 20-31cm, the figure for flood season is 4cm at Kim Long and 22cm at Phu Oc In the period of 2010-2012, Binh Dien reservoir and Huong Dien reservoir lowered the highest annual water lever at Kim Long by 53cm and Phu
Oc by 37cm, as well as raised the lowest mean water level in dry season at Kim Long by 37cm and at Phu Oc by 22cm
Trang 122.3 MAIN IMPACTS OF IRRIGATION-HYDROPOWER
CONSTRUCTIONS ON HYDROLOGY - HYDRAULIC REGIME AT DOWNSTREAM OF HUONG RIVER
2.3.1 In flood season
In flood season, reservoirs have the impact to lower the water level and peak flow at downstream due to flood controlling However, they are also able to cause artificial flood unless reservoir operating procedure is implemented Sediment is hold in reservoirs, cause to river bed transformation at downstream, increasing incident risk…
2.3.2 In dry season
Thao Long dam controls the flow of the river and freshens Huong river, creating the potential to supply water for Truoi irrigation system and maintaining flow for environmental requirement This dam has a vital role in preventing saltwater from entering the river, even though by sea water rise
2.4 APPLYING HEC-HMS AND HEC-RAS MODEL IN
SIMULATING FLOW IN HUONG RIVER BASIN
2.4.1 General introduction of HEC-HMS and HEC-RAS model
HEC-HMS hydrological model is applied for flow simulation to reservoir and inflow from tributaries, which result is used for input data of HEC-RAS hydraulic model to calculate flow to downstream according to operating plans of reservoir which are programmed by controlling code The two models are closely connected to DSS data base
2.4.2 Applying HEC-HMS and HEC-RAS models for HRB
This thesis has used data of 278 cross sections measures and undated to the year of 2009, including: 18 sections of Huu Trach river, 24
in Ta Trach river, 59 in Huong river, 37 in Bo river and 140 in flood draining routes at downstream 27 storage cells were built, with Z-W relation calculated by HEC-GeoRAS software Precipitation, discharge and observed water level data are used in calculations
By steps of forming CN coefficients map, creating hydraulic system, calibrating and validating models, results showed that HEC-HMS’s parameters meet the requirement, with Nash coefficient is 0.90-0.92 (calibration, figures 2.17) and 0.78-0.95
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(validation, figures 2.21); the coeficient for HEC-RAS is 0.63-0.77 (figure 2.26, 2.27)
Figure 2.17: Calibration of Figure 2.21: Validation of
HEC-HMS at Binh Dien 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