Circular No. 59/2025/TT-BCT Issuing National Technical Regulations on Hydropower Projects

 

CIRCULAR

ISSUING NATIONAL TECHNICAL REGULATIONS ON HYDROPOWER STRUCTURES

On the basis of Law on Standards and Technical Regulations dated June 29, 2006 and Law Amending and Supplementing Certain Provisions of the Law on Standards and Technical Regulations dated June 14, 2025;

On the basis of Law on Issuing Legal Normative Documents No. 80/2015/QH13; Law Amending and Supplementing Certain Provisions of the Law on Issuing Legal Normative Documents No. 63/2020/QH14;

On the basis of Law on Electricity No. 61/2024/QH15 dated November 30, 2024;

Decree No. Decision No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing implementation of certain provisions of the Law on Standards and Technical Regulations and Decree No. Decision No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing implementation of certain provisions 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing implementation of certain provisions of the Law on Standards and Technical Regulations;

Decree No. Decision No. 40/2025/NĐ-CP dated February 26, 2025 of the Government stipulating functions, tasks, powers, and organizational structure of the Ministry of Industry and Trade;

At the proposal of the Department of Innovation, Green Transition, and Small and Medium Enterprise Promotion;

The Minister of Industry and Trade issues this Circular to issue National Technical Regulations on Hydroelectric Structures.

Article 1. Issuance of the National Technical Regulation

This Circular promulgates National Technical Regulations on Hydroelectric Structures.

Code: QCVN 27:2025/BCT.

Article 2. Effective Date

This Circular takes effect from June 1, 2026.

Article 3. Implementation Organization

1. The Minister, Heads of Ministries equivalent to Ministries, Heads of Government Agencies, Chairpersons of People's Committees of provinces and centrally governed cities, and organizations and individuals concerned are responsible for implementing this Circular.

2. The Directors of the Electricity Regulatory Authority and the Industrial Safety and Environmental Protection Regulatory Authority shall be responsible for guiding, inspecting compliance with the provisions of these National Technical Regulations.

3. During the implementation process, if difficulties arise, organizations and individuals shall promptly report to the Ministry of Industry and Trade (through the Electricity Regulatory Authority) for consideration, resolution, and proposals to amend and supplement these National Technical Regulations in accordance with actual conditions at each period.

 

 

QCVN 27:2025/BCT

NATIONAL TECHNICAL REGULATIONS ON HYDROPOWER STRUCTURES

National technical regulation on hydropower structures

TABLE OF CONTENTS

Foreword

Chapter 1. GENERAL PROVISIONS

1.1. Scope of Application

1.2. Applicability

1.3. Definitions

2. TECHNICAL PROVISIONS

2.1. Classification of hydroelectric structures

2.1.1. General provisions

2.1.2. Principles for determining the classification of hydroelectric structures

2.2. Main design requirements for hydroelectric structures

2.3. Main design criteria

2.3.1. Service assurance level of hydroelectric structures

2.3.2. Main design criteria for flow

2.3.3. Main design criteria for climate

2.4. Loads, effects, and their combinations

2.4.1. Loads acting on hydroelectric structures

2.4.1.1. Permanent loads

2.4.1.2. Temporary loads

2.4.2. Combinations of loads acting on hydroelectric structures

2.5. Safety factors for structures

2.6. Main technical requirements for some common types of hydroelectric structures

2.6.1. Hydroelectric reservoirs

2.6.1.1. General provisions

2.6.1.2. Requirements for calculating typical water levels of reservoirs

2.6.1.2.1 Dead water level

2.6.1.2.2 Normal high water level

2.6.1.2.3 Design maximum water level and check maximum water level

2.6.1.2.4 Flood control level

2.6.1.3 Environmental protection requirements

2.6.1.4 Tasks to be performed before reservoir impoundment

2.6.1.5 Utilization of inundation areas

2.6.2. Water-retaining dams

2.6.2.1 General requirements

2.6.2.2 Earth dams

2.6.2.3 Rockfill dams

2.6.2.4 Concrete and reinforced concrete dams

2.6.2.5 Other types of dams

2.6.3 Water discharge structures

2.6.4 Water intake structures

2.6.5 Sedimentation basins

2.6.6 Enclosed water conveyance pipelines

2.6.7 Other water conveyance pipelines

2.6.8 Hydraulic tunnels

2.6.9 Water conveyance channels and structures on channels

2.6.10 Reservoir protection structures and downstream structures of main complexes

2.6.11 Fish passage structures and aquatic life protection structures

2.7 Provisions on decommissioning of hydroelectric structures

3. MANAGEMENT PROVISIONS

4. RESPONSIBILITIES OF ORGANIZATIONS AND INDIVIDUALS

Chapter 5. ORGANIZATION OF IMPLEMENTATION

ANNEX A

Provisions on the HS Code of Terrestrial Mobile Radio Equipment and Terrestrial Radio Relay Equipment

Foreword

QCVN 27:2025/BCT was drafted by the Technical Regulation Drafting Team on Hydroelectric Structures, reviewed by the Department of Innovation, Green Transition, and Small and Medium Enterprise Promotion, examined by the Ministry of Science and Technology, and issued by the Minister of Industry and Trade pursuant to Circular No. 59/2025/TT-BCT dated December 2, 2025.

NATIONAL TECHNICAL REGULATIONS ON HYDROPOWER STRUCTURES

National technical regulation on hydropower structures

Chapter 1. GENERAL PROVISIONS

1.1. Scope of Application

These regulations specify requirements that must be met when preparing, reviewing, examining, approving new construction projects, repair, upgrade, or expansion of structures related to hydroelectric power plant construction activities during investment phases (including project preparation, project implementation, and completion) and safety inspection and evaluation of structures during construction and operation phases according to regulations, regardless of the source of investment funds.

These regulations do not apply to dike structures, inland waterway structures (except for harbor structures and ship transfer structures within hydroelectric power plant complexes), marine structures, urban water supply and drainage systems.

When designing, constructing, or demolishing hydroelectric structures, in addition to complying with these regulations, they must also comply with other national technical regulations, current legal normative documents, laws, international treaties, and agreements to which the Vietnamese State has participated or signed concerning the objects under consideration.

1.2. Applicability

These regulations apply to organizations and individuals involved in the activities specified in Point 1.1.

1.3. Definitions

1.3.1. Hydroelectric structures

Hydroelectric structures (including pumped storage hydroelectric structures) consist of human intellect, labor, building materials, and equipment installed in the structures primarily aimed at harnessing the energy of water sources for electricity generation to serve economic and social development. Hydroelectric structures may include components such as hydroelectric reservoirs, main structures, power transmission lines, water conveyance and transfer systems, and other facilities for managing and operating hydroelectric power plants.

1.3.2. Construction activities of hydroelectric structures

Includes planning studies, project investment development construction planning, construction survey, construction design of projects, construction of works, review and assessment of projects, supervision of construction work, project management for investment and construction, safety inspection of works during construction, operation phases, and other activities related to hydropower construction projects.

1.3.3. Hydropower Project

A collection of proposals related to new construction, renovation, upgrading, or expansion of existing hydropower facilities to achieve predetermined objectives.

1.3.4. Reservoir

The hydropower reservoir (or reservoir) is a structure for water storage, raising water levels, regulating flow to supply water for power generation and other purposes according to the functions and tasks of the facility.

1.3.5. Main Works

A complex of construction items concentrated at the starting point of the system for water storage, regulation, conveyance, distribution, supply, and regulation of water in hydropower projects. Main works may include one or more of the following structures:

a) A dam to store water and raise water levels;

b) Structures to release excess water from the reservoir to regulate floods and ensure safety for the dam and downstream areas;

c) Structures to draw water from the reservoir for power generation or to meet downstream water needs;

d) Other structures as required for use such as sediment discharge structures, reservoir drainage structures; waterway structures (mooring docks, ship transfer structures, ports, land transportation structures; fish passage structures, etc.);

1.3.6. Power Line

The power line is a complex of construction items from the water intake structure on the hydropower reservoir through the gate into the turbine generator to the end of the outlet channel from the hydropower plant.

1.3.7. Water Conveyance and Transfer System

Includes canals, pipelines, sluices, tunnels, bridges, or channels that have been improved for water conveyance and transfer.

1.3.8. Permanent Works

Structures that are used regularly or periodically throughout the operational period.

1.3.9. Temporary Works

Structures that are only used during the construction phase or for repairing permanent structures during the operational period.

1.3.10. Primary Works

Structures whose damage or destruction will directly affect the normal operation of the main works and the post-main works system, preventing them from fulfilling their designed tasks.

Note: Some primary works are listed in Appendix A.

1.3.11. Secondary Works

Structures whose damage or destruction will have little impact on the normal operation of the main works and the post-main works system, which can be restored within a short time.

Note: Some secondary works are listed in Appendix A.

1.3.12. Dead Water Level (DWL)

The lowest water level of the reservoir at which the hydropower project operates with the designed assurance level.

1.3.13. Normal High Water Level (NHWL)

The highest water level that must be reached at the end of the filling period to ensure sufficient water supply according to the designed assurance level.

1.3.14. Design Flood Level (DFL)

The highest water level that appears in the reservoir when a design flood occurs in the watershed of the hydropower project.

1.3.15. Check Flood Level (CFL)

The highest water level that appears in the reservoir when a check flood occurs in the watershed of the hydropower project.

1.3.16. Flood Reception Level (FRL)

Also called flood prevention level or pre-flood level, it is the highest water level allowed to be maintained before a flood to enable the reservoir to perform its flood reduction function for the downstream area.

1.3.17. Design Flood

The flood calculated to possibly occur along the construction line corresponding to the design frequency.

1.3.18. Probable Maximum Flood (PMF)

The largest flood that could occur along the project line, formed from the most adverse combination of meteorological and hydrological conditions occurring in the watershed of the hydropower project that has become saturated.

1.3.19. Check Flood

The flood calculated to possibly occur along the construction line corresponding to the check frequency or the probable maximum flood.

1.3.20. Maximum Credible Earthquake (MCE)

The earthquake of greatest intensity that can be determined based on regional tectonics.

1.3.21. Safety Evaluation Earthquake (SEE)

The largest earthquake used for safety analysis of the structure under special load combinations. The safety evaluation earthquake is selected based on the type of structure and the impact on the downstream area, for example: for a special grade water-retaining dam, SEE equals MCE or an earthquake with a recurrence interval of 10,000 years; for smaller dams than Grade I and with less impact on the downstream area, SEE may be less than 10,000 years; for hydropower plant structures, water intake structures, water conveyance tunnels, etc., independently located from the dam, SEE may be an earthquake with a recurrence interval of 475 years.

1.3.22. Operating Basis Earthquake (OBE)

An earthquake that causes minor damage to the structure, easily repairable, and does not affect the normal operation of the structure. The operating basis earthquake is defined with a recurrence interval of 475 years.

1.3.23. Reservoir-Triggered Earthquake (RTE)

An earthquake triggered by the presence of a reservoir or changes in water level in the reservoir. RTE may be smaller than, equal to, or larger than OBE, but RTE cannot be greater than MCE.

1.3.24. Dead Storage Capacity

Part of the reservoir volume below the dead water level.

1.3.25. Useful Volume

Part of the reservoir volume between the dead water level and the normal high water level.

1.3.26. Flood Control Volume

Part of the reservoir volume between the flood reception level and the highest checked level for flood regulation tasks. Depending on the specific conditions of each reservoir project, the flood control volume may be arranged below the normal high water level or from the normal high water level upwards.

1.3.27

Total Volume

The part of the reservoir volume calculated up to the normal high water level.

1.3.28. Embankment Dam

Also called dam. A structure that spans across river or stream flow to retain water, raise the water level upstream or to assist in diverting the flow to another location.

1.3.29. Water Discharge Structure

A structure for discharging excess water, adjusting the discharge flow rate downstream to ensure safety for hydropower projects or structures used to actively discharge water according to management procedures: completely draining or partially draining water when repairs are needed, cleaning sediment buildup, or withdrawing water to prevent accidents.

1.3.30. Surface Discharge Structure

A surface discharge structure is a water discharge structure where the top of the flow is fully exposed to air or referred to as having an open surface.

1.3.31. Deep Discharge Structure

A water discharge structure with a sill and inlet roof submerged entirely below the normal high water level.

1.3.32. Bottom Discharge Structure

A structure with a discharge sill set low enough to drain the upstream side of the dam. A bottom discharge structure can be either a surface discharge structure or a deep discharge structure.

1.3.33. Water Intake Structure

A structure for actively drawing water from the source into the conveyance system to operate the turbine generator or to supply water to users as required by operation.

1.3.34. Ship Lock and Vessel Transfer Structures

Structures serving water transport vessels passing through the dam.

1.3.35. Fish Passage

A structure enabling certain aquatic species to move from downstream of the water-raising facility to upstream and vice versa according to their biological characteristics.

1.3.36. Reservoir Basin

The area defined from the land acquisition boundary down to the reservoir.

1.3.37. Permanent Inundation Area of the Reservoir

The ground surface area of the reservoir basin lying below the normal high water level.

1.3.38. Flood Impact Zone of the Reservoir

Calculated from the normal high water level to the highest checked level.

1.3.39. Downstream Impact Zone of Hydropower Dam

The area flooded when the hydropower reservoir releases water according to procedures, emergency flood release, or dam failure.

1.3.40. Service Assurance Level of the Project

The number of years the project ensures operation according to its design mission within a continuous 100-year exploitation period, expressed as a percentage.

2. TECHNICAL PROVISIONS

2.1. Classification of hydroelectric structures

2.1.1. General provisions

2.1.1.1. The project grade serves as the basis for determining technical requirements that must be adhered to at different levels appropriate to the scale and importance of the project. In this Standard, the project grade refers to the grade for design construction and safety assessment of the project.

2.1.1.2. Hydropower projects are classified into five grades in ascending order (Special Grade, Grade I, Grade II, Grade III, Grade IV) based on the scale of the project or its significance, and the extent of its impact on economic and social development, security, defense, etc. Projects at different grades have different technical requirements. Special Grade projects have the highest technical requirements, which decrease progressively at lower grades.

2.1.2. Principles for determining the classification of hydroelectric structures

2.1.2.1. The grade must be determined based on criteria such as installed capacity, reservoir volume, technical characteristics of structures within the main project, etc., as specified in Table 1. The hydropower project grade is the highest grade among those determined according to each criterion mentioned above.

2.1.2.2. The grade of the main project is determined based on the grade of the hydropower project. The grade of the power transmission line is determined based on the installed capacity of the hydropower plant. Components of the power transmission line located at the main project are determined based on the grade of the hydropower project.

2.1.2.3. The hydropower project grade determined according to Table 1 may be reduced by one grade (except for Grade IV projects) in any of the following cases:

a) When the grade determined based on dam height is lower than the grade determined based on reservoir volume at the normal high water level;

b) Components of Special Grade and Grade I projects not located in the pressure line (excluding hydropower plants, pressurized water pipelines, pipelines leading to turbines, pressure tanks, surge towers);

c) Power transmission structures requiring repair or maintenance without affecting the normal operation of the main project;

d) The grade of auxiliary dams within the main project, when considered independently according to Table 1, based on the maximum height criterion, is two grades lower than the main project with Special Grade, Grade I, and Grade II, and one grade lower for Grade III projects.

2.1.2.4. The hydropower project grade determined according to Table 1 may be increased by one grade (except for Special Grade projects) if any major component of the project could cause damage to important national defense, security, urban, or critical economic and political centers.

Table 1 - Classification of Hydropower Projects

Type of Project, Capacity, and Degree of ImpactType of FoundationProject GradeSpecialGrade IGrade IIGrade IIIGrade IV1. Reservoir with volume corresponding to Normal High Water Level, 10⁶ Granite, gabbro, decorative stone...³
>1000>200 ÷ 1000>20 ÷ 200≥3 ÷ 20< 32. Hydropower Plant with Installed Capacity, 10³kW
>1000300 ÷ ≤100050 ÷ ≤30010 ÷ ≤50<103. Raw Water Supply Structure for Other Water-Using Sectors with Flow Rate, m³.s
>20>10 ÷ 20>2 ÷ 10≤ 2-4. Earthwork dams, earth-rock dams with the greatest height, mA>100>70 ÷ 100>25 ÷ 70>10 ÷ 25≤ 10B->35 ÷ 75>15 ÷ 35>8 ÷ 15≤ 8C-->15 ÷ 25>5 ÷ 15≤ 55. Concrete dams, reinforced concrete dams of various types, and other hydraulic structures subject to pressure with heights, mA>100>60 ÷ 100>25 ÷ 60>10 ÷ 25≤ 10B->25 ÷ 50>10 ÷ 25>5 ÷ 10≤ 5C-->10 ÷ 20>5 ÷ 10≤ 56. Retaining walls with heights, mA->25 ÷ 40>15 ÷ 25>8 ÷ 15≤ 8B-->12 ÷ 20>5 ÷ 12≤ 5C-->10 ÷15>4 ÷ 10≤ 4NOTES:1) The foundation of the structure is divided into three typical groups in the operational state of the structure:- Type A: rock foundation (the foundation is considered as rock when the unconfined compressive strength of the dry sample is >5 MPa);- Type B: sandy soil, gravelly soil, cobblestone, clay soil in hard and semi-hard states;- Type C: saturated clay soil in plastic to flow states;2) The height of the structure is calculated as follows:- For earthwork dams, earth-rock dams: the height is measured from the lowest ground surface after excavation (excluding the height of the dam base) to the top of the dam;- For concrete dams of various types and other cast-in-place structures subject to pressure: the height is measured from the lowest base of the dam to the top of the dam or equivalent.

2.1.2.5. In the stepped development scheme, if the structure at the lower step is constructed after the upper step structure, it shall not be permitted to affect the operational capacity of the upper step structure, including the mission of the structure, safety of the structure, flood discharge capacity, etc. In case of changes, the overall efficiency of the steps must significantly increase, while still ensuring the safety of all structures within the step according to regulations, then there must be a justification, consensus among the owners of related structures, and approval by the competent authority for planning. If the structure at the upper step is constructed after the lower step structure, the operation discharge regime of the upper step structure shall not disrupt the designed operating frequency of the lower step structure (except in cases where the structure is constructed to ensure community safety as required by the competent authority under relevant laws).

2.1.2.6. Structures belonging to other specialties located within a hydropower project or a hydropower design that intersects with existing structures (roads, railways, irrigation works, etc.), their grades shall be determined separately according to the principle of ensuring the highest safety among these structures.

2.1.2.7. The grade of a hydropower structure intersecting with a flood protection dike shall be determined as the grade of a pressure-bearing structure but shall not be lower than the design grade and equivalent safety standards of that dike.

2.1.2.8. The grade of temporary structures serving construction may be raised higher than specified in Table 2 provided there is justification, but shall not exceed the grade of the main structure if failure could lead to the following consequences:

a) Loss of safety for ongoing long-term structures under construction;

b) Significant economic, social, and environmental losses downstream. Material damage caused by a major failure exceeds the additional investment cost for the temporary structure;

c) Delay in commissioning the structure, reducing investment effectiveness.

2.1.2.9. The grade of each structure within the same key structure, water conveyance system, or energy transmission line specified in Table 2. For secondary structures and temporary structures, the value specified in Table 2 is the maximum value, except in the case stipulated in point 2.1.2.8.

Table 2 - Relationship between the grade of a hydropower structure and the grade of primary, secondary, and temporary structures within the same key structure, water conveyance system, or energy transmission line

Grade of StructureSpecialIIIIIIIVGrade of Primary StructureSpecialIIIIIIIVGrade of Secondary StructureIIIIIIIVIVGrade of Temporary StructureIIIIIIVIVIV

2.1.2.10. Determination of the grade of structures as prescribed from point 2.1.2.1 to point 2.1.2.9 shall be justified and proposed by the design consultant and approved by the investment decision-making authority according to regulations.

2.1.2.11. For hydropower structures, if deemed necessary, the design consultant may recommend to the investor to request the competent authority to approve special design standards for part or all of this structure.

2.2. Main design requirements for hydroelectric structures

2.2.1. Feasibility Study Reports, Preliminary Feasibility Study Reports, Detailed Feasibility Study Reports, and Technical and Economic Construction Reports must be based on relevant plans approved by the competent authority to propose reasonable exploitation and utilization schemes for water resources.

2.2.2. The sequence of exploiting hydropower cascades must be based on the cascade development plan and construction sequence diagram approved by the competent authority. Exploitation of hydropower cascades must ensure optimal water use and minimize excess discharge.

2.2.3. It is necessary to ensure the return of appropriate flow rates and flow regimes downstream to meet environmental protection requirements and the water usage needs of current users, including future projects such as additional water supply to downstream structures and navigational requirements during the dry season.

2.2.4. When designing, the following aspects should be considered for feasibility and economic-technical rationality:

a) The possibility of combining additional functions within a single project component. There should be a phased commissioning plan to quickly realize investment benefits;

b) Reorganizing existing structures and proposing solutions to improve and adapt them to fit the new investment project;

c) Standardizing equipment layout, structural dimensions, and construction methods to accelerate progress, reduce costs, and facilitate future operation management;

d) Applying advanced technology in materials, structures, and facility layout.

2.2.5. Ensure architectural harmony and aesthetic integration of each component project within the main project with the surrounding landscape. In all cases, design must ensure the maintenance of natural protection conditions and ecological environmental sanitation. Study the possibility of combining to create tourist attractions and rest areas, ...

2.2.6. Clearly define construction conditions and methods, reasonable construction time consistent with progress, power generation operation requirements, labor supply capacity, material, equipment, construction materials, water and land transportation, and natural resources in the project area for construction purposes. Combine mechanical and manual construction reasonably. Must maximize the use of easily exploitable and available materials in the construction site area.

2.2.7. Continuously monitor the condition of the project and equipment during the construction period as well as throughout the subsequent exploitation process.

2.2.8. Design and construct hydropower projects on river and stream sections related to inland waterway infrastructure planning approved by competent authorities must ensure necessary conditions for water transport means to pass through.

2.2.9. Resolve resettlement, compensation, and support issues for production losses, property, economic, cultural, and social infrastructure in flooded areas for project construction sites according to environmental principles and living conditions of affected residents at new locations that are equal to or better, increasingly stable and developing.

2.2.10. For major special grade, grade I, and grade II projects, monitoring equipment must be installed to assess the durability of the project, promptly detect any damage or defects to decide repair measures, prevent accidents, and improve operational conditions. For grade III and grade IV projects, depending on specific circumstances regarding project type, working conditions, and foundation, monitoring equipment should be arranged for key project components when there is sufficient justification and approval from the investor. The number of monitoring devices must be adequate to evaluate the state of the project in heavily loaded areas and critical structural positions or at locations where the load impact on the project changes such as underground water pressure, reverse pressure, etc. During the design phase and operation period, safety criteria based on monitoring results must be established in accordance with the characteristics of the project.

2.2.11. When designing and constructing special grade and grade I projects, certain experimental studies must be conducted to verify, calibrate, and accurately determine technical parameters and increase reliability of documentation such as foundation studies, construction materials, hydraulic regimes, seepage, complex structure performance, thermal conditions in concrete, equipment operating conditions, effectiveness of applying new scientific and technological advancements, etc. The subjects and scope of experimental research depend on specific circumstances of each project and are proposed by the design consultant in the early stages of the project. This can also be applied to lower-grade project components when there are no similar construction models in practice.

2.2.12. When designing and constructing large-scale hydropower projects, the allocation of materials within the project body must be considered reasonably, in line with stress states, deformations, waterproofing requirements, etc., to reduce costs while ensuring technical requirements.

2.2.13. When designing repairs, restoration, upgrades, and expansions of hydropower projects, the following additional requirements must be met:

a) Clearly define the objectives of repairing, restoring, upgrading, and expanding the project, such as repairing to allow normal operation or extending the operational life based on existing hydropower projects, improving management and operation conditions, increasing assurance levels, enhancing service capacity, improving the environment, etc.;

b) During the renovation, repair, and upgrade process, adverse impacts on current water users must not exceed acceptable limits, and the reuse of old facilities should be maximized;

c) Collect all available documentation of the project to be repaired, restored, or upgraded, including surveys, designs, constructions, management, monitoring, past incidents, and specialized surveys to accurately assess quality, technical status, equipment, foundations, and structures, etc., serving as a basis for selecting appropriate solutions.

2.2.14. Water regulation projects (reservoirs, regulating gates/weirs, etc.) must have an approved operation regulation procedure by competent authorities. The content of the procedure must meet the following requirements:

a) Water supply must balance the interests of corresponding water users during surplus, normal, and deficient water years;

b) Ensure flood control regulation for reservoirs and downstream flood control for reservoirs with flood control tasks.

2.3. Main design criteria

2.3.1. Service assurance level of hydroelectric structures

2.3.1.1. The service assurance level of hydropower projects shall not be lower than the values specified in Table 3.

2.3.1.2. Lowering the service assurance level of hydropower projects is only permitted with reliable justifications and approval from the investment decision-making authority.

2.3.1.3. When exploitation and utilization adversely affect current water users or the environment, the project proposal agency must provide evidence of these impacts, propose remediation measures, and clarify the superiority of adding a new project to present to the approving authority and relevant specialized government management agencies for joint consideration and decision.

2.3.1.4. Multi-purpose projects must be designed so that the service assurance level for each purpose does not fall below the provisions set out in Table 3.

2.3.1.5. For reservoirs with additional flood control tasks, flood storage volume shall not affect the water supply operation of the reservoir according to the assurance level specified in Table 3.

Table 3 - Service Assurance Levels of Hydropower Projects

Objectives of Project ServiceAssurance Level According to Project Grade, %Other RequirementsSpecialGradeIIIIIIIVAgricultural Irrigation8585858575
2 Power Generation





a) Independent household9090858080Level of hydropower capacity ensuring work throughout the year (guaranteed capacity)b) Household using irrigation water to generate electricityAccording to the irrigation scheduleWhen there is a difference in water usage for electricity generation and irrigation during the day, additional daily reservoirs must be constructed to regulate water levels3. Water supply:





a) Not allowed to interrupt or reduce water supply requirements9595959595The calculated supply flow rate may be the largest flow rate, average daily flow rate, or average monthly flow rate, etc., prescribed by the competent authority and provided to the design agency. It is permissible to increase the level of assurance above the specified level if sufficient water supply sources are available and approved by the investment decision-maker.b) Not allowed to interrupt but reduction of water supply requirements is permitted9090909090The degree of water shortage and the allowable duration of water supply interruption shall be based on specific requirements of water users as prescribed by the competent authority and provided to the design agency. It is permissible to increase the level of assurance above the specified level if sufficient water supply sources are available and approved by the investment decision-maker.c) Short-term interruptions and reduction of water supply requirements are allowed8585858580It is permissible to increase the level of assurance above the specified level if sufficient water supply sources are available and approved by the investment decision-maker.

2.3.1.6. The boundary for land clearance for the reservoir area is determined as follows:

For agricultural land, residential land, construction land for public works, production land, and non-agricultural business land, the elevation above the corresponding floodwater level should be higher by 0.3 meters for agricultural land, residential land, and construction land for public works, and 0.5 meters for production and non-agricultural business land. The frequency of floods and water levels are defined as follows:

- Central urban areas, concentrated residential areas, and special category and Category I industrial zones: 1%;

- Central urban areas, concentrated residential areas, and Category II, III, and IV industrial zones: 2%;

- Central urban areas, concentrated residential areas, and Category V industrial zones: 10%;

- Special category and Categories I, II, III, and IV parks, sports facilities: 10%;

- Category V parks, sports facilities: 50%;

- Rural residential land: 10%;

- Agricultural production land: 10%;

- Forest land and vacant land, at the normal water level;

NOTE:

Urban construction projects, concentrated residential areas, industrial zones, parks, and sports facilities are classified according to the National Technical Regulations on Urban Planning.

2.3.2. Main design criteria for flow

2.3.2.1. The frequency of maximum flow rates and water levels for design calculations and stability checks, structural integrity, foundation, and discharge capacity of hydroelectric projects built on rivers and riverbanks, projects along pressure lines, and irrigation and drainage systems upstream without flow regulation structures shall not exceed the values specified in Table 4.

Table 4 - Frequency of Maximum Flow Rates and Water Levels for Design Calculations and Stability Checks of Hydroelectric Projects

Type of ProjectDesign LevelSpecialIIIIIV1. Main projects of all types; energy line projects:




- Design frequency, %0,100,501,001,502,00Corresponding recurrence period, years10002001006750- Inspection frequency, %0,020,100,200,501,0Corresponding recurrence period, years50001000500200100- Exceedance inspection frequency0,010,020,100,200,50Corresponding recurrence period, years10000500010005002002. Related water conveyance systems in agricultural irrigation and drainage systems (excluding water conveyance systems across rivers and streams in agricultural irrigation and drainage systems):




- Design frequency, %0,200,501,001,502,00Corresponding recurrence period, years5002001006750- Inspection frequency, %0,100,200,501,001,50Corresponding recurrence period, years100050020010067NOTES:1) The maximum flow rate and water level in the statistical set are the highest values that occur each year. The quality of the statistical series (length, representativeness, time of statistics, etc.) must meet the requirements stipulated in relevant standards. Data must be processed under the same conditions before calculation;2) If there are impacts upstream that alter the formation of flow or there are flow regulation structures, when determining the factors specified in this provision, the ability to adjust the flow of these structures must be considered;3) If there are flow regulation structures downstream, the model must not destroy or exceed the regulation capacity of the downstream structure;4) For special category hydroelectric projects in Group 1 of this table, with reliable justification and approval from the Investment Decision Maker, the flood inspection can be calculated with a frequency of 0.01% (corresponding to a recurrence period of 10,000 years) or extreme floods.

2.3.2.2. When determining key indicators of flow using statistical data or calculations, it is necessary to forecast the future development of these indicators after construction to ensure appropriate technical solutions and decisions to guarantee the safety of the project and enhance investment efficiency.

2.3.2.3. Minimum flow rates and water levels for calculating the stability of project structures and foundations are specified in Table 5.

Table 5 - Minimum Flow Rates and Water Levels for Calculating the Stability of Project Structures and Foundations and Equipment Layout

Type of ProjectProject LevelMinimum Flow Rate, Water Level Frequency (%)DesignInspection1. ReservoirSpecial, I, II, III, and IVDead water levelLowest drawdown water level for repair, dredging, etc.2. River ProjectSpecial99Lowest water level occurred at the construction lineI97II95III95IV90NOTES:1) The minimum flow rate and water level in the statistical set are the lowest values that occur each year;2) If downstream water users require a minimum flow rate greater than that specified in Table 5, the lowest flow rate will be selected based on the required minimum flow rate. The lowest water level calculated at this point corresponds to the aforementioned minimum flow rate;3) When designing projects of Class I and above, the possibility of this water level being lowered due to scouring of the downstream channel or the impact of flow regulation by subsequent cascade structures must be considered.

2.3.2.4. The lowest water level at the intake for calculating the operation mode of the hydropower plant project is defined as the dead water level.

2.3.2.5. The frequency of the highest water level and flow rate for designing temporary works to serve construction diversion (such as cofferdams, diversion channels, etc.) shall not exceed the value specified in Table 6.

2.3.2.6. The frequency of the largest designed flow rate for blocking flow shall not exceed the value specified in Table 7.

2.3.2.7. When using the main structure under construction as a construction diversion channel, the diversion frequency must be equal to the design frequency of the main structure corresponding to the construction diversion period.

2.3.2.8. The form, cross-section, elevation during the construction process (or phased construction) of long-term projects need to be decided based on specific conditions considering the construction schedule, meteorological and hydrological conditions, supply capacity of construction materials, especially local materials, construction site, construction capacity and speed of the contractor, measures to handle floods larger than the construction frequency to minimize damage to the project.

Table 6 - Frequency of the largest flow rate and water level for designing temporary works serving construction diversion

Project LevelMaximum Flow Rate and Water Level Frequency for Designing Temporary Works Serving Construction Diversion, Not Exceeding (%)Diversion During One Dry SeasonDiversion Over Two Dry Seasons or MoreSpecial52I105II, III, IV1010NOTES:1) The maximum flow rate and water level in the statistical set are those corresponding to the largest values among the maximum flow rates occurring during the construction diversion period. The diversion season is the time within the year when the temporary works serving construction diversion must exist reliably when the design flood occurs;2) If there is a structure upstream discharging a flow rate larger than the design frequency during the construction period, the impact of the discharge from the upstream structure on the construction flood flow rate must be assessed;3) For projects requiring construction diversion for two years or more, if there is solid evidence that designing temporary construction diversion works with the frequency specified in Table 6 may cause significant damage to the already constructed main structure, delay progress, cause losses downstream, etc., the consulting design agency must recommend increasing the safety assurance level accordingly for this project;4) For gravity concrete structures with good foundation conditions allowing overtopping, the design agency may recommend reducing the safety level of temporary works to reduce investment costs. The reduction level depends on the number of years of temporary diversion use and is determined by the competent authority;5) Measures to prevent actual diversion frequency exceeding the design frequency should be anticipated to proactively address such situations if they occur;6) All recommendations to increase or decrease the design frequency of temporary works serving construction diversion must be supported by solid economic and technical arguments and must be approved by the competent authority for the investment project.

Table 7 - Frequency of the largest flow rate for designing flow blocking

Project LevelMaximum Flow Rate Frequency for Designing Flow Blocking, Not Exceeding (%)Special, I, II5III, IV10NOTES:1) The flow in the statistical set is the daily average flow rate with the largest value for non-tidal flows or hourly average flow rate with the largest value for tidal flows appearing during the planned blocking period of each year. The blocking period is divided into ten-day intervals in the month planned for blocking, corresponding to the period when the flow rate is decreasing;2) Based on actual measurement data before the scheduled blocking date (usually continuous measurements are conducted from the end of the flood season to the scheduled blocking date), the blocking plan can be adjusted to fit the actual flow, weather, tide schedule, and submitted to the Investment Decision Maker for approval.

2.3.3. Main design criteria for climate

2.3.3.1. When there is insufficient reliable flow measurement data to determine the amount of water entering the reservoir, the rainfall-runoff relationship calculation method of the project watershed or similar watershed shall be used with the assurance level specified in Table 3.

2.3.3.2. Calculation criteria and methods for other climatic factors are stipulated by the competent authority depending on the specific object and calculation case.

2.4. Loads, effects, and their combinations

2.4.1. Loads acting on hydroelectric structures

2.4.1.1. Permanent loads

Permanent load is the load continuously acting on the structure throughout the construction and operation period, including:

a) The weight of the structure and fixed equipment placed on and inside the structure;

b) Direct pressure of water on the surface of the structure and foundation; seepage pressure (including seepage force and buoyancy force in saturated parts of the structure and foundation) corresponding to the highest water level during the design flood when the filtration and drainage equipment is operating normally. For components within the reservoir's pressure line and the raised dam, additional pressures as mentioned herein corresponding to the normal reservoir water level must also be considered;

c) Weight of soil and its lateral pressure; rock pressure (on tunnels);

d) Load caused by prestressed structural elements.

2.4.1.2. Temporary loads

2.4.1.2.1. Temporary load is the load acting on the structure but which may not act at certain points or periods during the construction and operation period.

2.4.1.2.2. Loads with relatively long duration of action are called long-term temporary loads, including the following loads:

a) Soil pressure generated by foundation and structure deformation or by external loads;

b) Silt deposition pressure during operation.

2.4.1.2.3. Loads with short duration of action are called short-term temporary loads, including the following loads:

a) Pressure generated by shrinkage and creep effects;

b) Load caused by excess pore water pressure in saturated soil at the normal water level, when filtration and drainage equipment is operating normally.

c) Thermal effects on the structure and foundation during construction and operation periods with average monthly air temperature fluctuations being moderate;

d) Loads from ships, boats, and floating objects (mooring, impact, etc.);

e) Loads from lifting, loading, unloading, and transportation equipment, and other machinery and structures (such as cranes, hoists, winches, etc.), taking into account the possibility of over-design loading;

g) Pressure from waves (determined according to the maximum long-term average wind speed);

h) Wind loads;

i) Water impact pressure during normal operation period;

k) Dynamic loads generated in pressurized and non-pressurized pipelines when conveying water at normal reservoir level;

l) Loads caused by excavation during foundation construction;

m) Loads due to the impact of an Operational Basis Earthquake (OBE);

NOTE:

When considering OBE loads during the operation period of the project, the reservoir water level is taken as the normal water level;

2.4.1.2.4. Loads that appear in special working conditions called special temporary loads. Special temporary loads that may affect hydropower projects include:

a) Loads due to the impact of a Seismic Excitation Earthquake (SEE) or explosion;

b) Water pressure corresponding to the water level during a test flood;

c) Loads caused by excess pore water pressure in saturated soil before full consolidation, corresponding to the largest test water level under normal operation conditions of drainage and filtration equipment or normal water level but with damaged drainage and filtration equipment;

d) Increased seepage pressure when drainage and filtration equipment does not operate normally;

e) Thermal effects during construction and operation periods with the highest average monthly air temperature fluctuation;

g) Wave pressure when the design maximum wind speed occurs;

h) Water pressure and when all loads are suddenly cut off;

i) Dynamic loads generated in pressurized and non-pressurized pipelines when conveying water at the design maximum water level;

k) Loads generated in earth embankments due to sudden increases and decreases in water levels (rapid drawdown);

l) High wave loads caused by earthquakes in reservoirs and tsunamis for coastal structures;

2.4.2. Combinations of loads acting on hydroelectric structures

2.4.2.1 When designing hydropower projects, calculations must be made based on basic load combinations and special load combinations;

2.4.2.2. Basic load combination includes loads and impacts: permanent loads, long-term temporary loads, and short-term temporary loads that the designed object may have to accept simultaneously;

2.4.2.3. Special load combination still includes loads and impacts considered in the basic load combination, but one of them is replaced by a special temporary load. If there is solid evidence, two or more special temporary loads can be used for verification. The most adverse basic load combination and special load combination that may occur during the construction and operation period of the project must be selected;

2.5. Safety factors for structures

2.5.1. Safety factors are used to evaluate the degree of stability, strength, stress, overall and local deformation for each component of the project and its foundation. The safety factor is the ratio between the general calculated resistance, deformation, or other parameters of the subject under consideration and the general calculated load (force, moment, stress), deformation, or other parameters acting upon it. Other methods of safety assessment may be used to assess the safety of the project, but they must ensure at least equivalent safety factors;

2.5.2. When calculating stability, strength, stress, overall and local deformation for hydropower projects and their foundations, limit state method must be applied. Calculations must be carried out according to two limit states:

a) First limit state: the project, structure, and foundation work under the most adverse operating conditions including: calculations of overall strength and stability of the project-foundation system; overall seepage resistance of the foundation and earth structures; strength of parts whose failure would cause the project operation to cease; calculations of stresses and displacements of structural components on which the overall strength or stability of the project depends, etc.;

b) Second limit state: the project, structure, and foundation work under adverse conditions during normal operation including: calculations of local strength of the foundation; calculations of displacement and deformation limitations, formation or expansion of cracks and construction joints; destruction of local seepage resistance or strength of structural components not considered in the first limit state;

2.5.3. To ensure the safety of the structure and foundation of the project, calculations must comply with the conditions specified in formula (1):

where: is the load combination factor, determined as follows:

- Calculating according to the first limit state:

Basic load combination: = 1,00;

Special load combination: = 0,90;

Load combination during construction and repair: = 0,95;

- Calculating according to the second limit state: = 1,00;

F is the general calculated load (force, moment, stress), deformation, or other parameter serving as the basis for evaluating the limit state, F determined taking into account the load factor γ_f. The load factor is determined according to Table B.3 of Appendix B;

R is the general calculated resistance, deformation, or other parameter established according to standard design documents. Determining R must take into account material deviation factors γ_{Granite, gabbro, decorative stone...}, soil γ_g and working condition factors γ_of.

γ_of is the working condition factor considering the type of project, structure, or foundation, material type, approximate design scheme, limit state group, and other factors specified in current standard design documents for different types of projects, structures, and foundations. Working condition factors for some typical hydropower projects are specified in Table B.2 of Appendix B;

Values of material deviation factors γ_{Granite, gabbro, decorative stone...} and soil γ_gused to determine the calculated resistance of materials and soil properties, these factors are established according to design standards for certain types of projects, structures, and foundations.

γ_n is the guarantee factor considered based on scale, mission, and type of project. When calculating the project according to the first limit state. γ_n refer to Table B.1 in Appendix B. When calculating the project according to the second limit state, take γ_n = 1.

NOTE:

When applying other calculation methods, the safety results must not be lower than those obtained from the aforementioned limit state methods.

2.6. Main technical requirements for some common types of hydroelectric structures

2.6.1. Hydroelectric reservoirs

2.6.1.1. General provisions

2.6.1.1.1. In addition to complying with the provisions of point 2.3, when designing reservoir projects, the following requirements must also be met:

a) Ensuring sufficient water supply at the designed assurance level;

b) Providing adequate flood storage capacity for downstream areas if the reservoir has flood control requirements for downstream areas and ensuring the safety of the project itself during design floods and check floods. The annual flood discharge process must pay attention to minimizing damage to the downstream area.

c) Warning about the potential for reservoir-induced earthquakes (RTE) for reservoirs located in regions with earthquake activity of magnitude VII or higher, affecting residential areas within the earthquake impact zone.

2.6.1.1.2. The sedimentation volume of the reservoir is considered filled when the elevation of the sediment surface before the pressure line reaches the elevation of the main intake gate threshold. The operating period is calculated from the first year of water accumulation until the sedimentation volume of the reservoir is filled with sediment but does not affect the ability to draw water, under normal operating conditions, it shall not be less than the provisions in Table 8:

Table 8 - Allowable Time for Reservoir Sedimentation Volume to be Filled

Level of Reservoir ProjectSpecial, IIIThree, IVTime specified for the intake gate threshold not being buried by sediment during the operating period after water accumulation shall not be less than years1007550NOTES:1) The sedimentation process of special-level and level I reservoirs needs to be determined through hydraulic calculations or model tests;2) If there is reasonable economic and technical justification, a shorter time for sedimentation volume can be selected compared to the provisions in Table 11. In this case, measures to limit sedimentation in front of the intake gate by constructing additional sediment discharge structures or regular dredging must be implemented. The location and scale of sediment discharge structures for special-level and level I reservoirs are determined through hydraulic model tests.

2.6.1.1.3. In cases where the flood flow has abundant excess water, consideration should be given to arranging sediment discharge structures to reduce sedimentation volume and increase the lifespan of the reservoir. This structure should also serve the function of guiding construction flows and draining the reservoir when there is a risk of failure.

2.6.1.2. Requirements for calculating typical water levels of reservoirs

2.6.1.2.1. Dead Water Level

The dead water level of the reservoir must ensure normal operation conditions, storing sedimentation volume during the operating period as specified in Table 8, having a stable hydraulic regime through water intake structures, providing sufficient water according to requirements for water users:

a) For reservoirs primarily for power generation, the dead water level must ensure that the sedimentation volume during the operating period is not lower than the provisions in point 2.6.1.1.2, ensuring normal water supply for water users under normal conditions, and meeting the technical requirements of hydropower equipment, allowing turbines to operate normally and within the permissible efficiency range at this water level. The dead water level may be higher through optimal economic energy calculation;

b) If the reservoir has additional tasks (such as aquaculture, tourism, recreation, inland navigation, etc.), the dead water level must consider meeting the requirements of these additional tasks.

2.6.1.2.2 Normal high water level

Ensuring that the reservoir has the necessary volume of water to meet the water demand of water users according to the assured water supply level.

2.6.1.2.3 Design maximum water level and check maximum water level

Ensuring that during the design flood and check flood discharge, the reservoir water level does not exceed the maximum design water level and the maximum check water level. The maximum design water level and check water level of reservoirs are determined based on flood regulation in the volume above the normal water level. If the reservoir has flood storage volume, this level is determined based on flood regulation in the volume above the flood storage level. The amount of water discharged and drained through the pressure line structures of the reservoir must be calculated based on the worst flood peak or total flood volume considering the possibility of compound floods due to typhoons (if they have occurred in the project area).

2.6.1.2.4 Flood control level

Ensuring that the reservoir has sufficient volume to perform flood regulation tasks for the project and downstream areas according to the design frequency. Depending on specific conditions, this water level may be equal to or lower than the normal water level, even equal to the dead water level.

2.6.1.3 Environmental protection requirements

2.6.1.3.1. The design and construction of reservoir projects must comply with current environmental protection requirements.

2.6.1.3.2. It is necessary to analyze and assess adverse impacts and implement protective or mitigating measures for the following adverse impacts:

a) Material losses caused by flooding such as loss of land, especially agricultural land, loss of nature reserves, special forests, mineral resources, economic and social infrastructure, cultural sites, historical and cultural landmarks, scenic spots, decline leading to extinction of certain species of flora and fauna, etc.;

b) Risk of narrowing or losing settled residential areas that have existed for hundreds of years, adverse effects on security, society, defense, and consequences of dam failures that could occur;

c) The affected downstream area due to changes in flow regime, sediment, etc., predicting the impact of these changes on riverbeds, levees, estuaries;

d) Evaluating the economic, social, and environmental benefits after the construction of the project.

2.6.1.3.3. Measures must be taken to ensure water quality in the reservoir during management and operation, such as limiting the intrusion of harmful substances into the reservoir, developing protective forests, increasing the area and quality of vegetation cover in the watershed.

2.6.1.4 Tasks to be performed before reservoir impoundment

2.6.1.4.1. Complete land clearance work in the reservoir basin.

2.6.1.4.2. Complete reservoir basin cleaning as prescribed.

2.6.1.4.3. Create necessary conditions to meet the requirements for inland waterway transportation (if applicable).

2.6.1.4.4. Anticipate measures to address floating blocks of coal slurry and other material masses (if any) when the reservoir fills with water.

2.6.1.4.5. Adhere to legal regulations on the safety of hydropower projects as follows:

a) The project components and the water-retaining structures have been officially notified by the competent state management agency regarding the inspection results for acceptance and commissioning;

b) The operation procedures for the reservoir, emergency response plans, and dam protection plans have been approved by the authorized authority;

c) Complete investment and installation of equipment for water discharge warning systems, surveillance cameras, water level monitoring devices, and direct information transmission systems to disaster prevention and control agencies, industry and trade departments, and water resource management agencies;

d) Ensure a system to maintain minimum flow downstream in compliance with legal provisions on water resources;

đ) Fulfill other responsibilities and obligations as stipulated by relevant laws.

2.6.1.5 Utilization of inundation areas

Allow research and design for utilizing flooded areas in accordance with flooding regimes without altering the reservoir's primary functions and without affecting its safety and stability.

2.6.2. Water-retaining dams

2.6.2.1 General requirements

2.6.2.1.1. Design calculations for the dam must ensure safety concerning the strength and stability of the dam body, foundation, and abutments under both design and inspection conditions. Safety factors for stability, strength, overall and local deformations of the dam and foundation shall comply with the provisions of point 2.5.3. Values for stability and permeability strength must fall within permissible ranges.

2.6.2.1.2. The type and structure of the dam should be selected based on economic-technical comparisons of various options, taking into account the tasks, parameters of the project, local natural conditions (climate, hydrology, topography, geology, regional tectonics and seismicity, local construction materials, etc.), overall layout of the complex, construction organization plan, construction period, operational conditions of the dam, human resources, construction materials, and equipment.

2.6.2.2 Earth dams

2.6.2.2.1. When designing an earth dam, the following basic technical requirements must be met:

a) Adequate height (including settlement allowance for the foundation and dam body) to ensure no overtopping occurs under all operating conditions;

b) Sufficient protective works and equipment to withstand the effects of waves, wind, rain, temperature, and other destructive factors;

c) Permeation through the foundation, dam body, abutments, and interface zones between the dam and foundation, banks, and structures within the dam must not affect the stored water volume, cause internal erosion, damage the dam, or reduce the lifespan of the structure;

d) If water release and water intake structures are located within the dam body, they must ensure safety and stability, and measures to prevent longitudinal seepage along the contact surface between the embankment fill and these structures must be implemented, ensuring that the dam toe is not eroded during flood releases;

e) The interface zone between non-homogeneous fill sections in an earth dam must prevent excessive seepage-induced soil destruction from one section to another, avoid crack formation, and prevent sudden stress and deformation changes within the dam and foundation;

f) Segmental and phased construction designs must not create continuous earthfill construction joints from upstream to downstream. When designing additional loading sections to enhance foundation and downstream toe stability, they must be considered part of the main cross-section of the dam. In cases where the project is divided into operational phases, the crest of the additional loading section downstream must be above the saturation line of the construction phase 1 cross-section;

g) Compaction factor k (compaction coefficient) and dry unit weight of the fill material for compacted earth dams must be specified in the design documentation.

2.6.2.2.2. The shape and size of the dam cross-section at design stage must meet the following requirements:

a) The crest elevation of the dam must comply with the provisions of point 2.6.2.2.1, clause a;

b) The width of the dam crest depends on the project grade, traffic conditions, construction, and operation management but must not be less than 10 meters for special-grade and Grade I dams. When used as a traffic route, the dam surface must comply with traffic regulations but must not be narrower than the aforementioned requirement;

c) The dam slope must be protected against destructive impacts from waves, rain, and other factors, ensuring stability under all dam operating conditions;

d) Dams higher than 15 meters must have steps. The height difference between adjacent steps on the same slope must not exceed 15 meters. The width of each step must not be less than 3.0 meters. If the downstream dam step is used as a traffic route, its width and structure must comply with traffic regulations. The upstream slope must place the step at the lower limit of the main reinforcement layer to form a necessary support cushion.

2.6.2.2.3. When calculating seepage and permeability strength, determine the basic cross-section to calculate the following seepage parameters in the dam body, foundation, and abutments:

a) The position of the seepage surface (saturation line) at typical cross-sections in the dam body and abutments;

b) Pressure gradient (or water column pressure) of the seepage in the dam body and foundation: at locations where seepage enters drainage facilities or exits the dam crest, abutment slopes, and at interfaces between different soil layers and anti-seepage structures;

c) Seepage flow rate through the dam body, foundation, and abutments;

d) If the geological structure of the foundation or fill material is heterogeneous or anisotropic, additional characteristics must be considered when determining seepage parameters.

2.6.2.2.4. Design of dam slope protection must meet the following requirements:

a) The protective structure and materials used for slope reinforcement must ensure stability and durability under wave pressure; resist corrosion and deformation in continuously wet-dry environments;

b) A reverse filter structure must be provided to prevent dam body material and small filter particles from being drawn out.

2.6.2.3. Rockfill Dam

2.6.2.3.1. Follow the provisions of clauses a, b, and c of point 2.6.2.2.2; clauses a, b, c, and d of point 2.6.2.2.1, and clause a of point 2.6.2.2.3.

2.6.2.3.2.3. Parts related to waterproofing structure such as core waterproofing, foundation slab, core wall, etc., must be placed on a good soil base.

2.6.2.3.3. The foundation of the rock prism must be placed at least on a geological layer with a modulus of deformation not lower than that of the filled mass.

2.6.2.3.4. If there is a section of the dam foundation consisting of gravel and cobblestones that are difficult to thoroughly remove, it may be used as a dam foundation when appropriate structural, waterproofing, compaction measures, and suitable construction methods have been implemented. The relative density of the gravel and cobblestone foundation must not be less than 75%. Settlement and deformation must be monitored to prevent cracking and core lifting.

2.6.2.3.5. It is allowed to arrange temporary spillways for flood discharge through partially constructed rock-fill dams, but safety measures for the dam and reservoir must be in place.

2.6.2.3.6. Technical requirements for designing earth-rockfill dams shall comply with the provisions set forth in Points 2.6.2.2.1, 2.6.2.2.2, 2.6.2.2.3, 2.6.2.3.2, 2.6.2.3.3, 2.6.2.3.4, and 2.6.2.3.5.

2.6.2.4 Concrete and reinforced concrete dams

2.6.2.4.1. Stability and durability calculations for the dam must also consider the operation of the reservoir-dam-foundation system, ensuring safety for the dam, its structural components, and the foundation.

2.6.2.4.2. The crest of the non-overtopping dam must have sufficient height above the maximum water level before the dam and must not allow water to overtop. The width of the crest must meet construction, management, operation, traffic, and other requirements (if applicable). When used for traffic purposes, the dimensions and structure of the crest must comply with traffic regulations.

2.6.2.4.3. Seepage and seepage durability calculations shall be carried out according to the provisions of Subpoint c of Point 2.6.2.2.1. When the dam foundation is not rock, a seepage boundary under the ground (the interface between watertight parts of the dam and the foundation) including the dam footing, apron, vertical water barriers (sheet piles, toe boards, berms, seepage cut-off walls, etc.) must be long enough to ensure overall seepage durability of the foundation and local seepage durability at critical locations.

2.6.2.5 Other types of dams

Research and application of new types of dams and new construction technologies currently being applied in advanced countries to overcome the shortcomings of traditional dams are permitted. Regardless of the type of dam, when applied to specific projects, they must ensure safe and stable operation (strength stability, anti-slide, anti-toppling, seepage stability) in design and inspection conditions.

2.6.3. Water discharge structures

2.6.3.1. These structures must operate safely and stably in design and inspection conditions. Water discharge and drainage must be actively managed according to operational procedures to ensure that the water level in the reservoir does not exceed the specified limit.

2.6.3.2. The overall layout and structure of water discharge and drainage facilities, and the connection solutions with downstream areas must ensure that when they operate, they meet the following requirements:

a) Not affecting the safety and stability of the reservoir structure as well as the normal management and operation conditions of the reservoir itself;

b) During design flood discharge operations, they do not destroy the natural regime of the downstream riverbed, minimize impacts on economic and social activities, do not affect the operation mode of hydropower plants of equivalent or higher grade in the cascade below, and do not cause damage to other construction works of equivalent or higher protection levels or grades in the downstream area. When there are water transport works, ensure that the flow and velocity in the downstream do not adversely affect the established operation mode of vessels;

c) When operating at the check water level condition, the following is allowed:

- Water discharge structures can operate under different conditions from normal operation without leading to emergency situations for water users;

- Drainage through closed conduits with changing hydraulic regimes (from non-pressure to pressure and vice versa) without causing conduit damage;

- The downstream channel and slope may suffer erosion but this damage does not threaten the destruction of major components of the main structure nor reduce the safety of downstream residential, industrial areas, and infrastructure;

- There may be damage to the emergency discharge structures but this damage does not affect the safety of the main structure.

2.6.3.3. The discharge volume calculated during long-term operation through the discharge-drainage-transfer structures of the main project must be determined based on the design flood volume specified in Point 2.3.2 and Table 4, taking into account changes due to the regulation effect of existing or planned reservoirs and changes in flow formation conditions caused by economic and social activities in the watershed.

2.6.3.4. When determining the maximum design and check discharge volumes of the main project on a cascaded river, consideration must be given to the grade of the project's upper part, its position in the cascade, the discharge-drainage-transfer capacity of the upper cascade's main project structures corresponding to normal and high water levels, operational rules for hydropower and reservoir projects in the cascade, inflow flows of tributaries upstream of the designed main project, to avoid affecting the discharge capacity of the upper cascade project.

2.6.3.5. Reservoirs of Grade I and above, in addition to the main spillway, must have solutions to handle cases exceeding the check flood. Reservoirs of Grade II and below may consider exceeding the check flood if there is reasonable justification and approval by the competent authority:

a) The main spillway must always have the capacity to discharge the design flood and the check flood;

b) If the solution involves arranging a secondary spillway, the combined capacity of the secondary spillway and the main spillway must be able to discharge the flood exceeding the check flood, ensuring that the reservoir water level does not overtop the local material dam crest. The frequency of the flood exceeding the check flood is defined as follows:

- For special-grade structures: a flood with a return period of 0.01% (equivalent to a recurrence interval of 10,000 years) or extreme floods;

- For structures of Grade I and below: equal to the check flood frequency corresponding to the project grade increased by one level (see Table 4);

c) The safety grade of the secondary spillway structure may be lower than that of the main spillway structure.

d) When there are no conditions to arrange separate emergency flood discharge facilities, it is allowed to study expanding the main discharge facility or changing the pre-flood water level or raising the dam to increase the regulating capacity of the reservoir or combining the above solutions to ensure that the emergency flood discharge facility can handle floods exceeding the design flood.

e) The determination of the model for the flood exceeding the design flood and the grade of the emergency flood discharge facility proposed by the design consultant shall be approved by the investment decision-making authority in accordance with the regulations.

2.6.3.6. Reservoirs equipped with emergency flood discharge facilities through flood drainage wells or tunnels must be arranged with over-design emergency flood discharge facilities (emergency spillway).

2.6.3.7. In addition to the main flood discharge spillway, it is allowed to study the possibility of using other facilities within the complex of primary structures to participate in flood discharge, discharge construction flow rates, and sediment discharge during operation.

2.6.3.8. It is allowed to arrange emergency flood discharge facilities at the top of the dam and within the dam body but must ensure the safety of the dam during construction and operation.

2.6.3.9. Emergency flood discharge facilities for projects from Grade I upwards or Grade II projects but with complex hydraulic conditions must undergo physical model testing to demonstrate the rationality of their layout and hydraulic design.

2.6.3.10. The structure of the emergency flood discharge facilities, water release facilities, and their subsequent components must be designed and calculated for basic operational cases and must be rechecked under abnormal conditions to ensure the safety of the facilities and prevent water from overflowing the crest line under pressure. The calculation cases include:

a) Operating with the largest upstream water level according to the design: All water release, drainage facilities when encountering the design flood are fully opened, all turbines operate, and other drainage and water transfer facilities work in normal operating mode. Under this condition, all parts of the primary structure including the upper and lower connecting sections and equipment must function normally without damage. Loads and impacts corresponding to this case are calculated based on the basic load combination. For drainage facilities with gates, if there is reasonable evidence, the possibility of one or several gates being jammed may be considered;

b) Operating with the largest upstream water level according to the test flood: All drainage, water release, and water transfer facilities mentioned in paragraph a of point 2.6.3.10 and the emergency flood discharge facilities when encountering the test flood are fully opened. The possibility of gates being jammed is not considered. Loads and impacts corresponding to this case are calculated based on the special load combination;

c) Considering additional gate opening combinations to meet both design objectives and ensure the safety of the facilities during flood regulation or potential accidents;

d) Considering the possibility of encountering a flood exceeding the test flood.

NOTE:

If the situation described in paragraph a of point 2.6.3.10 occurs where a main discharge gate is jammed and cannot operate, it should be classified as a special load combination calculation case.

2.6.3.11. When determining unit discharge rate (specific discharge), downstream channel velocity, downstream flow connection mode, main structure configuration, energy dissipation measures, and downstream reinforcement, the results of comparing economic and technical indicators of various options must be taken into account.

2.6.3.12. Drainage and deep-water discharge facilities must have main gates and repair gates meeting the following requirements:

a) Repair gates - accident gates are located in front of the main gates;

b) When it is impossible to drain completely to expose the entrance of the deep-water discharge facility, in addition to the main gate and repair gate - accident gate, another repair gate must be arranged in front or repaired;

c) When the threshold of the drainage and deep-water discharge facility is lower than the downstream water level, a movable repair gate or repair gate must be arranged behind the outlet section of the culvert;

d) Establish operating procedures for the aforementioned gates according to typical operational diagrams.

2.6.3.13. When selecting the type of gate and lifting machinery, the speed of the rising flood, the water storage capacity upstream and downstream, and the requirement to ensure minimum downstream flow rate, including the sudden reduction or complete shutdown of part or all of the hydropower plant's load, must be taken into account.

2.6.3.14. When the gate of the deep-water discharge facility is a flat gate with an area greater than 60 square meters but requires a smaller discharge volume significantly less than the discharge capacity of a single culvert hole, a separate smaller discharge hole must be designed to meet this requirement.² 2.6.4.1. The design calculation of water intake structures must meet the following requirements:

2.6.4 Water intake structures

a) Safe and stable operation in design and test cases;

b) Ensuring sufficient flow and total water volume according to the requirements of water users;

c) Having the ability to adjust the water supply volume and proactively stop supply when necessary for inspection, maintenance, or accident handling;

d) Must be equipped with a trash rack; arrange trash collection equipment or facilities, steps at the entrance, sedimentation tanks, grass washing channels, etc., if necessary, to prevent and remove sediment, debris, and floating objects from entering the conveyance route;

e) Facilitating construction, management, inspection, maintenance, repair, and application of scientific and technological progress such as electrification and automation.

2.6.4.2. The structural type and overall layout of the water intake structure must be selected in accordance with the project's mission and depend on the type of conveyance route (pressurized, non-pressurized, or mixed; regulated or unregulated); characteristics of the water intake structure (dam-type or non-dam-type); natural conditions such as hydrological regime, sediment flow, bank morphology, presence of aquatic vegetation, floating objects, operational mode, and sedimentation upstream of the structure. When operating to draw water into pressurized conveyance routes, it must ensure no air suction and minimal head loss. Water intake structures should be designed with multiple units so that individual units can be separated for repair or dredging when necessary.

2.6.4.3. Water intake structures from reservoirs, in addition to complying with the provisions of point 2.6.4.1, must also meet the following requirements:

a) During the specified operation period in Table 8, the threshold of the water intake gate is not silted up by sediment. When the process of bank regeneration occurs, it does not affect the water conveyance route.

a) During the exploitation period specified in Table 8, the intake water threshold shall not be silted up with sand and gravel. When the process of bank regeneration occurs, it shall not affect the water conveyance line;

b) For underground culverts serving as water intake structures:

- The body of the underground culvert placed directly on the ground foundation must ensure structural stability and permeability, satisfying the load-bearing capacity conditions of the foundation;

- The flow regime within the culvert may be pressurized, non-pressurized, or semi-pressurized. It is not allowed for the culvert to have a semi-pressurized flow regime where both the inlet and outlet are submerged (pressurized), while the middle section remains unpressurized;

- Underground culverts taking water from earth or rock dams of reservoirs with a volume of 20 x 10^6 cubic meters or more must be located within the dam's substructure corridor to facilitate inspection, repair work, and ensure safe working conditions for the culvert and the dam;⁶ Granite, gabbro, decorative stone...³ c) For water intake structures that are pipelines embedded in concrete or reinforced concrete dams, they must meet the requirements specified in the construction of concrete and reinforced concrete dams.

2.6.4.4. The type of water intake structure from rivers should be selected based on the design water levels on the river and the required water level elevation in the main conveyance channel, considering hydrological, topographical, and geological conditions at the site. Non-dam water intake structures can be used when the river water level always ensures it is higher than the required water level elevation of the main conveyance channel. If the water level at the water intake structure site is lower than the required water level elevation of the main conveyance channel, a water intake structure with a dam must be used.

2.6.4.5. The calculation water level for checking the stability, structure, and foundation upstream of the water intake structure is defined as follows:

a) For non-dam water intake structures: the water level corresponding to the largest designed discharge flow rate and checked along the water intake structure line, determined in accordance with the requirements specified in point 2.3.2.1;

b) For dam water intake structures: the water level upstream of the dam when discharging the largest designed discharge flow rate and checked.

2.6.4.6. To ensure operational conditions and prevent accidents for the water intake structure itself, the conveyance channel, and the technological equipment of subsequent structures, appropriate gate valves must be installed at the water intake points. The type, quantity, and location of the gate valves are determined according to the specific tasks of each structure.

2.6.4.7. To ensure that the water entering the conveyance channel has the necessary clarity, the sedimentation pond and related equipment must be designed and decided upon based on economic and technical calculations.

2.6.4.8. When designing water intake and conveyance structures for urban water supply systems and other production water needs, the requirements of the regulations on external network design and corresponding water supply structures must be followed.

2.6.5.1. Sedimentation ponds and related equipment must meet the following requirements:

a) Retain particles larger than the permissible size in the pond to obtain water with turbidity suitable for quality requirements. The size of particles allowed to enter the conveyance channel is determined based on maximizing the utilization of beneficial silt; minimizing or preventing channel silting or erosion; and not reducing the lifespan of technological equipment below the prescribed level, etc.;

2.6.5 Sedimentation basins

b) Actively remove settled sediment from the settling chamber when necessary.

2.6.5.2. Design calculations for sedimentation ponds on water conveyance channels must be based on the sediment composition of the year with average turbidity and tested under the year with the highest turbidity, considering the operation mode of the channel.

2.6.5.3. The location of sedimentation ponds should be within the cluster of primary facilities or at the beginning of the main conveyance channel, considering the following conditions:

a) Local topography and geology allow for the layout of water conveyance channels to the sedimentation pond with appropriate dimensions and flow regimes to settle harmful sediment particles in the pond;

b) There is the ability to discharge settled sediment from the settling chamber or accumulate it in the pond for periodic mechanical dredging.

2.6.5.4. Selecting continuous or periodic cleaning methods for settling chambers using hydraulic or mechanical means must be based on economic and technical comparisons and the following criteria:

a) Hydraulic cleaning settling chambers are applicable in areas with abundant excess water and sufficient hydraulic slope for cleaning lines;

b) When there is insufficient water head difference to wash away the entire deposited layer in the pond, a mixed cleaning method must be used: small particle sediment is removed by hydraulic means, while large particle sediment is cleaned mechanically;

c) Settling ponds with periodic single-chamber cleaning can only be applied if complete water supply shutdown or raw water supply (unprocessed) during cleaning is permitted.

2.6.6.1. Closed conduits (with enclosed cross-sections) must ensure adequate water conveyance under all anticipated operating modes in the design.

2.6.6.2. In all operating conditions, the flow regime within the conduit must be stable (either stable pressurized or stable non-pressurized). If operating in a pressurized mode, vacuum formation within the water conduit must be prevented. If operating in a non-pressurized mode, measures must be taken to introduce air into the water conduit. Short-term transitions between pressurized and non-pressurized flow regimes are allowed if justified.

2.6.6 Enclosed water conveyance pipelines

2.6.6.3. When designing water conduits and related structures, hydraulic calculations must be based on. For complex-shaped closed conduits of special and Class I projects, hydraulic model testing must be conducted to determine water column losses, maximum and minimum water levels in non-pressurized conduits during uneven and unstable flows, and maximum and minimum pressures along pressurized conduits due to water impact.

2.6.6.4. At the intake point of pressurized conduits that are partially open or fully open along the water supply line, repair gates must be installed ahead and separate emergency gates for each pipeline to ensure maintenance conditions and quick isolation when the pipeline breaks. After the emergency gate, measures must be taken to provide sufficient air for pipe maintenance. Additionally, protective measures against damage to structures in the affected area due to pipeline rupture must be considered.

2.6.6.3. When designing water conveyance channels and related structures, the hydraulic calculation results must be taken into account. For enclosed water conveyance channels of special grade and Grade I with complex shapes, hydraulic model testing must be conducted to determine head loss, the highest and lowest water levels in the non-pressure channel during uneven and unstable flow, the maximum and minimum pressures along the length of the pressure channel when water impact occurs.

2.6.6.4. At the water intake point of pressurized water conveyance channels where partial or full-line openings are set, repair valves must be arranged ahead and emergency valves for each individual pipeline to ensure maintenance conditions and quick disconnection when the pipeline bursts. After the emergency valve, measures must be taken to supply sufficient air for pipe maintenance. Additionally, protective measures to prevent damage to structures in the affected area due to pipeline rupture must be anticipated.

2.6.6.5. When determining the largest calculated water level in non-pressure conduits, consideration must be given to positive waves generated during rapid load shedding at fault conditions or simultaneous shedding of the largest load during operation.

2.6.6.6. The impact water calculation for conduits leading to turbines and pump stations' push pipes shall consider the following cases:

a) Sudden complete shedding of all plant loads;

b) Gradual loading according to operational procedures until the plant reaches full capacity.

2.6.6.7. Repair and emergency valves shall operate in a fully automatic mode. Additionally, they must be designed with remote control and local control modes for necessary operations.

2.6.7 Other water conveyance pipelines

2.6.7.1. The selection of conduit type and structure must be based on an economic-technical comparison of options, taking into account the conduit's mission, head value, foundation soil, installation, and operational conditions. Conduits passing through subsiding wet ground, saturated soil, mud, or areas prone to softening must be designed above ground, and if necessary, measures to reinforce the foundation soil must be implemented.

2.6.7.2. When designing exposed conduits on the ground, expansion joints must be arranged along their length, including at sections connecting to cast-in-place structures, etc., to ensure that settlement and thermal deformation of each section are independent; or placed on continuous reinforced concrete foundations to ensure uniform settlement. Steel conduits without expansion joints may be designed when there are reasonable grounds and under suitable conditions, and protective measures against corrosion and erosion must be provided.

2.6.7.3. Observation gates, equipment for gradually filling the conduit with water, and air supply or release devices must be installed at both ends and along the conduit route.

2.6.7.4. The design of reinforced concrete conduits must specify crack limitation standards based on corrosion and waterproofing conditions.

2.6.8 Hydraulic tunnels

2.6.8.1. Hydraulic tunnels must be designed to meet the requirements of one or more different purposes such as water conveyance for power generation, flood discharge, sediment discharge, reservoir drainage, construction flow diversion, water supply, etc.

2.6.8.2. The selection of tunnel alignment, type (pressurized or unpressurized), and cross-sectional shape must be based on the tunnel's mission, economic-technical comparison of criteria, and consideration of the following factors:

a) Overall layout of the complex, mutual influence between the tunnel and surface and adjacent underground structures;

b) Depth below ground, head value, and hydraulic regime of the tunnel;

c) Geological and hydrogeological conditions of the project;

d) Construction conditions.

2.6.8.3. The tunnel alignment should be straight with the shortest possible length. Curved alignments may be applied but must meet the following requirements:

a) At curved sections, the turning angle of the tunnel must not be less than 60° (for flow velocities below 10 m/s) and the radius of curvature must not be less than five times the depth of water in the tunnel;

b) For flow velocities exceeding 10 m/s in the tunnel, hydraulic model testing must be conducted to determine the values of the turning angle and radius of curvature.

2.6.8.4. The minimum thickness of the overlying rock layer for unpressurized tunnels without a lining must be greater than three times the diameter of the circular tunnel or three times the equivalent diameter of non-circular tunnels. For pressurized tunnels, this thickness must also be determined based on the condition of avoiding hydraulic fracturing.

The safety factor to avoid hydraulic fracturing is taken as follows:

For basic force combinations: 1.3;

For special combinations (with impact water): 1.1.

2.6.8.5. Tunnel alignments passing through expansive soil layers must be avoided.

2.6.8.6. Measures must be taken to address energy dissipation in the downstream area after the tunnel outlet to prevent scouring and landslides of downstream structures.

2.6.8.7. The cross-sectional dimensions of the tunnel must meet the requirements for usage, construction, maintenance, and repair, but must not be smaller than the following: height not less than 2.0 m and width not less than 1.5 m.

2.6.9 Water conveyance channels and structures on channels

It must meet usage requirements and ensure safety and stability during construction and operation.

NOTE:

For channels on embankments with significant heights, stability and durability considerations must be made similar to those for dams.

2.6.9.1. The selection of channel alignment, channel type, technical parameters, and head loss must be justified through a comparison of options considering water transfer capability, ability to accommodate waterway traffic (if applicable), construction workload and equipment, water regulation operation methods, operating costs, environmental protection requirements, etc.

2.6.9.2. If there are no high water level restrictions, the channel should be located within excavated or half-excavated half-embanked sections. When determining the radius of curvature of the channel alignment, it must ensure navigability (if applicable) and prevent scouring of the channel bed.

2.6.9.3. Measures to prevent flooding and siltation of the land adjacent to the channel and the development of aquatic vegetation within the channel must be anticipated.

2.6.9.4. In complex conditions such as passing through subsiding wet ground, expansive soil, salt-bearing soil, steep slopes prone to collapse, or where the channel may intersect with mud flows, changes in foundation and embankment characteristics during future operation must be considered. Appropriate structural and construction technology solutions may be applied if necessary.

2.6.9.5. The water velocity in the channel must be determined based on the condition of preventing scouring or deposition in the channel bed. Measures to prevent blockage due to debris, algae, and floating vegetation must be anticipated.

2.6.9.6. To prevent scouring and mechanical damage to the channel from rain, flow, and seepage losses, appropriate protective structures must be provided.

2.6.9.7. The slope of the channel bank must be determined based on the stability of the slope.

2.6.9.8. To ensure the water quality standard, sedimentation works or expanding the initial section of the channel must be planned. The form of sedimentation and treatment of deposited sediment in the channel will be decided through economic-technical justification calculations.

2.6.9.9. Channels should be divided into several sections to facilitate regular inspection and maintenance. The length of each section shall be determined based on specific conditions, taking into account natural characteristics and operational and repair requirements.

2.6.9.10. When designing channels, the possibility of using additional water sources from intersecting rivers and streams must be considered. The additional flow volume is the basic amount of water from the river or stream after deducting the required discharge for maintaining environmental flow downstream.

2.6.9.11. Alongside the channel, management paths should be arranged to regularly check the condition of the channel. Studies should be conducted to build isolation barriers at locations where the channel passes through dangerous areas, residential clusters, and civilian structures.

2.6.9.12. When utilizing additional water sources from rivers and streams, the following conditions must be adhered to:

a) Water quality criteria at the intake point must meet the requirements of the water usage standard;

b) The quantity and particle composition of the solid flow must be compatible with the channel's transport capacity.

2.6.9.13. In hydraulic calculations for the channel, unstable flow regimes caused by changes in flow rate and water level, as well as the effects of wind-induced water surges, waves, and those generated during gate operation, turbine operation, regulating structures, pump stations, and ship basins, etc., must be taken into account.

2.6.9.14. For sections of the channel passing through areas with unfavorable topographical and geological conditions, such as locally dissected terrain or easily erodible soils, alternative solutions like appropriate connecting structures (culverts, siphons, etc.) should be considered.

2.6.9.15. The design of multi-purpose channels must be based on forecasts of water demand and water quality requirements for users within the project area that the channel serves.

2.6.9.16. The potential for combining rural transportation development should be maximized when designing water conveyance channels. If consistent with transportation planning, the channel banks can be designed according to road standards. When designing channels for combined waterway transport, the type and structure of vessels must be considered to determine the calculation water levels and channel dimensions, while also considering the requirements of ship basins. Waterway transport channels are typically designed for two-way vessel navigation. Along the channel, suitable berthing sites should be arranged.

2.6.9.17. When designing underground structures passing under the channel bottom, the overlying cover layer must ensure subsidence and uneven settlement of the channel bottom within permissible limits.

2.6.9.18. Design of structures on the channel, such as spillways, regulating works, water conveyance structures, etc., must comply not only with the requirements of Article 2.6.9 but also with the requirements specified in Articles 2.6.3, 2.6.4, 2.6.5, 2.6.6, and 2.6.7 of this Standard.

2.6.10 Reservoir protection structures and downstream structures of main complexes

2.6.10.1. Protective works for reservoirs and downstream areas of primary structures, such as embankments and bank reinforcement structures, must be planned to protect valuable land areas and national economic objects like cities, industrial facilities, agricultural lands, and improve the hygiene conditions of ponds and lakes from flooding and bank erosion. The design of protective works shall be carried out in accordance with relevant design regulations prescribed by competent authorities.

2.6.10.2. When reinforcing banks, predictions of bank migration and channel scouring (if applicable), bank regeneration, and overall stability of the protected section must be forecasted.

2.6.10.3. In areas protected from flooding, a network of boreholes for monitoring groundwater dynamics should be established.

2.6.11 Fish passage structures and aquatic life protection structures

2.6.11.1. The design of hydropower projects on rivers and lakes in areas of significant aquatic resources value must include provisions for fish passage structures and aquatic resource protection measures. Design documentation for these structures must comply with requirements and regulations for protecting aquatic resources.

2.6.11.2. Fish passage structures must ensure continuous or seasonal passage routes for protected aquatic species that align with their biological characteristics.

2.7 Provisions on decommissioning of hydroelectric structures

2.7.1. Consideration and evaluation for the demolition of hydropower structures shall only be made in the following cases:

a) Reservoir sedimentation capacity is fully filled;

b) The structure is severely damaged;

c) Comprehensive inspection of the structure no longer ensures efficient and safe operation as per current regulations.

d) The structure no longer has its original mission or has been replaced by more effective structures.

2.7.2. A comprehensive safety and efficiency assessment project for the structure under consideration for demolition must be prepared.

2.7.3. Demolition of the structure shall not proceed if the assessments result in meeting at least one of the following criteria:

a) The structure still has the ability to operate safely and effectively;

b) The structure can be rehabilitated to ensure safety and continued effective operation;

c) The structure can be upgraded or expanded to continue operating effectively;

d) The structure remains safe and can be repurposed for continued effective use.

2.7.4. Structures not requiring demolition according to points b, c, and d of Article 2.7.3 must have a design prepared; the sequence and steps of the design will depend on the scale of rehabilitation, upgrading, or new mission.

2.7.5. The design for demolishing hydropower structures must include measures to ensure safety during the demolition process and downstream safety; the demolition design must include sustainable restoration and re-establishment of the flow direction harmonious with the environment, and measures to handle waste dumps in compliance with environmental protection requirements. Based on economic and technical solutions, safety for both the structure itself and the downstream area, full or partial demolition of the hydropower structure to be demolished may be allowed.

3. MANAGEMENT PROVISIONS

3.1. Management of construction, demolition, repair, upgrade, or expansion activities of hydropower structures shall be carried out in accordance with this Standard and relevant laws and regulations on electricity, construction, water resources, environment, and other related laws and regulations.

3.2. This Technical Standard shall be mandatorily applied to organizations and individuals related to construction, demolition, repair, upgrading, or expansion activities of hydropower projects on the territory of Vietnam. For hydropower projects that have commenced construction prior to the effective date of this Technical Standard, they must apply this Standard when carrying out renovation, upgrading, expansion, or demolition.

3.3. In cases where Vietnam participates in or signs bilateral or multilateral agreements, such agreements shall be implemented according to their provisions.

4. RESPONSIBILITIES OF ORGANIZATIONS AND INDIVIDUALS

4.1. When using other scientific and technical methods for hydropower projects, they must comply with the requirements set forth in the clauses of this Technical Standard.

4.2. Organizations and individuals involved are responsible for implementing the provisions of this Technical Standard and are subject to inspection by state management agencies in accordance with current regulations.

4.3. The Electricity Regulatory Authority, the Agency for Industrial Safety and Environmental Protection under the Ministry of Industry and Trade, within their functions, tasks, and assigned authorities, are responsible for disseminating and guiding the implementation of this Technical Standard for Provincial Departments of Industry and Trade; organizations and individuals participating in power activities and using electricity for production nationwide.

4.4. People's Committees of provinces and centrally governed cities are responsible for disseminating and guiding the implementation of this Technical Standard for organizations and individuals participating in power activities within their jurisdiction in accordance with their assigned functions, tasks, and levels of authority as stipulated in current regulatory legal documents.

Chapter 5. ORGANIZATION OF IMPLEMENTATION

5.1. This Technical Standard shall take effect from July 1, 2026.

5.2. During the implementation of this Technical Standard, if organizations and individuals encounter difficulties or obstacles, they should report them to the Electricity Regulatory Authority under the Ministry of Industry and Trade for consideration, guidance, and resolution within its authority.

ANNEX A

List of Main and Secondary Projects

A.1. Main Projects

The following hydropower projects are classified as main projects:

a) Dams of various types;

b) Boundary walls, retaining walls, and structures in pressure lines;

c) Water intake, water extraction, drainage, and discharge structures;

d) Various types of canals and structures on canals;

e) Pump stations, water conduits, and hydraulic tunnels;

f) Pressure tanks and regulating towers;

g) Hydropower plants;

h) Riverbank reinforcement and river regulation structures;

i) Navigation structures (mooring basins, ship lifts, flow-regulating dams);

k) Slopes of primary structures and energy transmission lines.

A.2. Secondary Projects

The following hydropower projects are classified as secondary projects:

a) Partition walls;

b) Boundary walls and retaining walls not located in pressure lines;

c) Emergency discharge structures;

d) Riverbank reinforcement structures outside the primary structure complex;

e) Fish protection structures;

f) Logging and wood floating channels;

g) Houses and roads for managing structures;

h) Natural slopes.

NOTE:

Depending on the potential losses that could be caused by damage or the difficulty in rebuilding, some secondary projects may be reclassified as main projects in specific circumstances with appropriate justification.

Provisions on the HS Code of Terrestrial Mobile Radio Equipment and Terrestrial Radio Relay Equipment

Provisions on Design Calculation of Structures

B.1. Values of material deviation coefficients used to determine the calculated resistance of materials and characteristics of soil specified in design standards for each type of project, structure, and foundation, and prescribed by competent authorities for application. When projects use large quantities of local materials including earth fill, rock fill, etc., the calculated resistance of materials is determined through statistical processing of laboratory test results and field experimental studies. γ_{Granite, gabbro, decorative stone...} and d) The tax authority shall base on the document issued by the competent state agency permitting the extension of the land use period to determine and notify the additional amount payable by the land user as prescribed in Points a and b of this Clause within fifteen days from the date of receipt of the land use period extension document from the competent state agency." γ_g B.2. First limit state calculation is performed with calculated loads. Calculated loads equal standard loads multiplied by load deviation factors (Table B.3). Standard loads are specified in design investigation standards for each type of project, structure, and foundation, and prescribed by competent authorities for application.

B.3. Second limit state calculation for projects, structures, and foundations is carried out with load deviation factors and material deviation factors both set at 1.0, except for specific cases prescribed in design investigation standards by competent authorities. γ_f B.4. Necessary calculations, assumptions for calculation scenarios, and calculation diagrams for projects and foundations must be consistent with possible occurrences, fully comply with design investigation regulations prescribed by competent authorities, and ultimately find the least favorable solution. Additional considerations must also be made in necessary cases:

a) Construction sequence and loading sequence of project components; γ_f, b) Influence of temperature effects, shrinkage, and sudden seepage pressure impacts; γ_{Granite, gabbro, decorative stone...} and soil γ_g c) Non-linear elastic and plastic deformations, as well as material properties of project components and foundation rocks;

d) Discontinuity of project body and foundation structures (cracks, etc.);

e) Heterogeneity of construction materials, foundation rocks, and their anisotropy.

B.5. When calculating the structures of foundations that settle, the internal forces generated due to foundation deformation must be considered. Settlements and differential settlements must remain within permissible limits without adversely affecting operation, durability, and deformation of the project, structure, or between individual components.

B.6. Physical model tests for hydraulic performance must be conducted for water conveyance, discharge, and release structures of Class I and above to determine their water conveyance capacity, check hydraulic regimes, water velocity, water pressure on structures, connection solutions with upstream and downstream sections, erosion protection measures, etc., determine the shape and size of components, and select the most reasonable and economical overall layout of primary structure complexes. This work may also be applied to Class II structures with complex channel shapes where conventional hydraulic calculation guidelines do not achieve the required reliability, and there are no similar construction models in practice without adequate justification.

Table B.1 - Safety Factor

of Structures

Type of Project and ComponentSafety Factor

B.6. Water conveyance, drainage, and discharge works from Grade I and above must undergo physical hydraulic model testing to determine water conveyance and drainage capacity, check hydraulic regimes, velocities, and water pressures on the structure, connection solutions between the structure and upstream/downstream sections, erosion protection measures, etc., determine the shape and size of components, and select the most reasonable and economical overall layout plan for the main structure cluster. This work may also be applied to Grade II works with complex channel shapes where conventional hydraulic calculation guidelines do not achieve the necessary reliability, and there are no similar construction models in practice without adequate justification.

Table B.1 - Safety Factor γ_n of Works

Type of Work and ComponentSafety Factor γ_n According to the level of construction project, for Special Class II, III, IV: 1. Concrete and reinforced concrete structures, natural sloping roofs, sloping roofs made of stone fill, excavated slopes. 1.25 1.20 1.15 1.15 2. Artificial sloping roofs made of soil fill 1.5 1.35 1.3 1.25

Table B.2 - Coefficient of working conditions γ_of for some types of hydropower projects

Type of project and type of foundationCoefficient of working conditions (γ_of) 1. Concrete and reinforced concrete structures on soil and semi-hard rock foundations 1.00 2. Concrete and reinforced concrete structures on rock foundations: - When the slip surface passes through cracks in the rock foundation 1.00 - When the slip surface passes through the contact surface between concrete and rock or through part of the rock foundation with cracks and part of intact rock 0.95 3. Arch dams and other flood control structures on rock foundations 0.75 4. Natural and artificial slopes 1.00 NOTE: In necessary cases, when there is appropriate justification, supplementary coefficients of working conditions may be taken into account to consider the specific characteristics of the structures and their foundations, in addition to those listed in the table.
- When the sliding surface passes through cracks in the rock foundation1,00- When the sliding surface passes through the contact surface between concrete and rock or through rock foundation with part passing through cracks and part through intact rock0,953. Arch dams and other anti-erosion works on rock foundations0,754. Natural and artificial slopes1,00NOTE: In necessary cases, when appropriate justifications are provided, additional working condition factors outside those listed in the table may be considered to take into account the specific characteristics of the structural works and their foundations.

Table B.3 - Load factor γ_f

Name of load and effectLoad factor (γ_f) 1. Self-weight of the structure (excluding the weight of soil and tunnel lining) 1.05 (0.95) 2. Weight of the tunnel lining 1.20 (0.80) 3. Vertical pressure due to soil weight 1.10 (0.90) 4. Lateral pressure of soil 1.20 (0.80) 5. Pressure of sand and silt 1.20 6. Rock pressure: - Weight of rock forming an arch 1.50 - Horizontal pressure of rock 1.20 (0.80) 7. Total weight of soil and rock over the tunnel or destroyed area (vertical pressure due to soil weight) 1.10 (0.90) 8. Direct water pressure on the surface of the structure and foundation, wave pressure, backwater pressure, seepage pressure, and void pressure 1.00 9. Static underground water pressure on the tunnel lining 1.10 (0.90) 10. Water pressure inside the tunnel (including impact water) 1.00 11. Dynamic water pressure 1.20 12. Pressure of sprayed concrete grout 1.20 (1.00) 13. Vertical and horizontal loads from lifting, loading, transportation machines, and fixed technological equipment 1.20 14. Storage loads within the range of loading and unloading berths, operation of roller bridges 1.30 15. Wind loads 1.30 16. Ship loads 1.20 17. Effects of temperature and humidity 1.10 18. Earthquake loads 1.10 19. Bulk cargo handling loads 1.30 (1.00) NOTE: 1) The load factor for trains running on railways and vehicles running on roads must be taken according to bridge design standards; 2) A load factor of 1.00 may be applied for the self-weight of the structure and vertical pressure due to the weight of the fill soil mass if the weight of that mass is determined from characteristic values of soil (unit weight and strength characteristics), while concrete is determined from material characteristics (unit weight of concrete and other characteristics) consistent with current testing and foundation design standards; 3) The load factors in parentheses should only be used when the calculation results indicate a less favorable condition for the structure.