Dam Safety Management / Gestion de la Sécurité des Barrages
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Dam Safety Management / Gestion de la Sécurité des Barrages

Pre operational phases of the dam life cycle / Phases de conception, construction et mise en service

Cigb Icold

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eBook - ePub

Dam Safety Management / Gestion de la Sécurité des Barrages

Pre operational phases of the dam life cycle / Phases de conception, construction et mise en service

Cigb Icold

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About This Book

Dam Safety Management is a major concern during the entire lifetime cycle of a dam scheme. This is particularly true for the operational phase of the scheme that represents by far the longest period in its lifetime cycle. Bulletin 154 presented a general approach and concepts to be applied to dam operation. The current Bulletin 175 extends the developed concepts to all phases preceding the operational phase. Many risks associated with the operation of existing dams have their origins in other phases preceding the actual operation. Although there are numerous ICOLD Bulletins addressing technical aspects of planning, design, construction and commissioning of dams, there is not a single Bulletin which covers the subject in a comprehensive manner. The current document is a first attempt to capture all relevant dam safety aspects in all preoperational phases by systematically characterizing the actors involved, their roles, the activities and complex interactions present in different phases of the dam lifecycle. An Overarching Safety Management System is specifically developed that can be applied to all actors involved.

La gestion de la sécurité des barrages est une préoccupation majeure pendant tout le cycle de vie d'un projet de barrage. Cela est particulièrement vrai pour la phase opérationnelle du système qui représente de loin la période la plus longue de son cycle de vie. Le Bulletin 154 présente une approche générale et des concepts à appliquer à l'exploitation des barrages. Le Bulletin 175 actuel étend les concepts développés à toutes les phases précédant la phase d'exploitation. De nombreux risques associés à l'exploitation des barrages existants ont leur origine dans d'autres phases précédant l'exploitation proprement dite. Bien qu'il existe de nombreux bulletins ICOLD traitant des aspects techniques de la planification, de la conception, de la construction et de la mise en service des barrages, il n'existe pas un seul bulletin qui couvre le sujet de manière exhaustive. Le document actuel est une première tentative de capturer tous les aspects pertinents de la sécurité des barrages dans toutes les phases pré-opérationnelles en caractérisant systématiquement les acteurs impliqués, leurs rôles, les activités et les interactions complexes présentes dans les différentes phases du cycle de vie du barrage. Un système global de gestion de la sécurité est spécifiquement développé et peut être appliqué à tous les acteurs impliqués.

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Information

Publisher
CRC Press
Year
2021
ISBN
9781000382761

1. Introduction

1.1. WHY THIS BULLETIN?

Dams are massive structures retaining large water bodies able to cause substantial or even catastrophic damages downstream of their location. As such they represent a potential hazard in case of uncontrolled release of water due to overtopping by flood or by submergence caused by a sliding earth mass in the reservoir. Obviously structural failure of the dam body or its foundation or malfunction of water releasing structures constitute also potential hazards. Although many risks associated with dams are linked to the operation of these structures some of them are imbedded in the phases preceding operation. They can be found at the preliminary planning of the dam scheme, during the detail design of the structures, as well as during the construction and commissioning phases. Identifying the risk factors and trying to minimize them are essential to structural safety and to (planned) operational safety. Dam safety has to be adequately managed from the onset of a project development until its construction and commissioning. It shall be pursued during the whole operation of the scheme. This means that how dam safety is to be pursued in the operational phase of the life-cycle must be developed in the design phase of the project.
Until present no bulletin of ICOLD was directly addressing this situation. Bulletins (see list in Appendix B) are either purely technical or describing risk evaluation methods from a theoretical point of view. The present Bulletin addresses the pre-operational phases of a dam project and links them to the guidance of the previously issued Bulletin 154 which presents recommendations for safety management during the operation of the dam (see Fig. 1.1).
Figure 1.1
Extent of this bulletin
In phases preceding operation of a dam scheme (going from preliminary studies to commissioning) attention has to be given to the implementation of engineering and construction measures (best practice) excluding or, at least, minimizing the risk of failure of the dam. They encompass both structural (retention of water) and operation (conveyance of water) oriented safety measures. Several factors (human and technical) tend to affect the safety aspects of a dam. Whereas technical aspects are relatively easy to identify in design, human factors covers a broad range of interfering and less strictly defined aspects going from personality conflicts within a working team to deficient communication and organizational flaws. Therefore, management of the steps leading to the realization of a dam scheme and its operation should be aware of these possible drawbacks and should put all necessary efforts into identifying and controlling them.

1.2. IMPORTANCE OF DAM SAFETY AT ALL DEVELOPMENT STAGES

A decision to invest in the development of a dam is a very significant matter that can be of national and even international importance from multiple perspectives. The investment involved is generally so large that it is imperative that the development fulfil all of the intended objectives and other objectives as might be determined after construction, or as determined over the economic evaluation period of the dam and beyond (the whole life-cycle). It can be taken as a premise that the investment must be secured at the outset in such a way that the principle that development of the dam results in a net positive contribution to society is realised. Dam Safety considerations have a pivotal role in securing the investment over the whole life-cycle of the dam.
In the modern context, Dam Safety considerations which include all aspects of safety management over the whole life-cycle contribute to a great deal more to securing the investment than previously considered when dam safety pertained to structural safety (ICOLD B59, 1987):
The safety of a dam manifests itself in being free of any conditions or developments that could lead to its deterioration or destruction. The margin which separates the actual conditions of a dam, or the conditions it is designed for, from those leading to its damage or destruction is a measure of its safety. To be safe, therefore, a dam has to be supplied with appropriate reserves, taking into account all reasonably imaginable scenarios of normal utilization and exceptional hazard which it may have to withstand during its life.
By way of illustration, how dam safety is considered in the design phase influences construction costs and safety during construction, and later on operational safety, costs, constructability and safety of modifications, improvements and renewal, and finally decommissioning.
For instance, the choice of spillway type, a matter that is identified at the conceptual design or feasibility stage can significantly influence whole life-cycle operational costs and the effectiveness of operational safety. Life-cycle operational costs that can be influenced at the conceptual design stage go far beyond the physical components and include surveillance and monitoring costs, staffing costs, maintenance and repair costs and ultimately repair/upgrading/renewal costs prior to the end of the life-cycle.
In addition to the physical and operational justifications for including whole life-cycle safety considerations at an early stage of the design process, there are sound financial reasons for the dam Investor to consider early investment in dam safety for financial efficiency and for insurance reasons. The financial efficiency dimensions relate to the economics of the project over the whole life-cycle from the perspectives of asset value, operational costs and refurbishment/renewal costs whereas the insurance dimensions relate to the overall protection of the investment. The investment in the dam is “at risk” from the initial stages of the investment up to the end of the economic evaluation stage with the investment most “at risk” initially from first filling to approximately 5-years into the service life, and again at the end of the service life of the dam. The relatively long pay-back period for the capital investment in a dam means that the total financing and operational costs of a dam will not become net-positive until well into the economic evaluation life cycle. During this time, the effects of ageing will begin to manifest themselves, and safety expectations can be expected to increase. A robust design that considers these issues at the outset can significantly influence the repair and replacement costs at the later stages of the economic evaluation process. In straightforward terms, securing safety contributes to securing the investment and vice-versa.

1.3. OVERARCHING PRINCIPLES

ICOLD Bulletin 154 defines nine overarching principles for dam safety that are sufficiently general to be applied directly or with minor alteration over all phases of the life-cycle of a dam. These principles are as follows:
  1. Justification for dams: Dams should be constructed and operated only if they yield an overall benefit to society.
  2. Fundamental Dam Safety Objective: The fundamental dam safety objective is to protect people, property and the environment from harmful effects of misoperation or failure of dams and reservoirs.
  3. Responsibility for Operational Integrity and Safety: The prime responsibility for operational integrity and safety of a dam should rest with the Dam Owner.
  4. Role of Government: The legal and governmental framework for all industrial activities, including operation of dams, provides the overarching structures for operational integrity and safety assurance.
  5. Leadership and management for Safety: Effective leadership and management for operational integrity and safety should be established and sustained over the life cycle of the dam.
  6. Balancing of Protection across Competing Objectives: Protection should seek to achieve a balance across competing objectives to provide the highest level of operational integrity and safety that can reasonably be achieved.
  7. Limitation of Risk to Individuals and Society: Measures for controlling risks from dams should ensure that no individual bears an unacceptable risk of harm, and that the risks to society do not exceed the risk tolerance levels of society.
  8. Sustainability of Dams and Reservoirs: In order to secure the societal value, dams and reservoirs must be sustained in the long term. To ensure sustainability of dams, all reasonably practicable efforts should be made to prevent and mitigate failures and accidents.
  9. Emergency Preparedness and Response: Appropriate arrangements should be made for emergency preparedness and response for dam failures and accidents.
Clearly, one of the objectives of the pre-operational phases is to ensure that the dam conforms to all of these principles when it goes into service. Importantly, for most dam constructions, the dam enters in operation as soon as impoundment begins and often before the construction has been handed over to the Investor/Owner.
Of the 9 overarching principles the following apply directly without any alteration to the pre-operational phases:
  • Justification for Dams
  • Fundamental Safety Objective
  • Balancing of Protection across Competing Objectives
  • Limitation of Risk to Individuals and Society
  • Sustainability of Dams and Reservoirs
  • Emergency Preparedness and Response
The remaining three, Responsibility for Operational Integrity and Safety, Role of Government and Leadership and Management for Safety, can be modified and made specific to the pre-operational phases in a way that there can be a smooth transition to the operational phase when the dam is handed over to the Investor/Owner.
The Investor/Owner has the continued full responsibility to maintain leadership and management for safety during all phases of a project (planning, design, construction, quality control) including transitioning to the operation phase, and subsequently through the operational phase and then into either renewal or decommissioning.
The three revised Pre-operational Safety Principles are provided as follows:

Responsibility for Integrity and Safety in the Pre-Operational Phases

The prime responsibility for the overall integrity and safety of a dam should rest with the Dam Owner. The Owner is responsible for the third-party liabilities. Responsibility for meeting safety objectives of the design should rest with the Designer, but the Owner has to make sure that he is fully understanding and accepting the design of the project. He further carries full responsibility for implementing an adequate quality control system during design and construction. Responsibility for safety of the works during construction and commissioning should rest with the Construction Supervising Engineer as determined by the contractual arrangements established by the Investor/Owner.

Role of Government

The legal and governmental framework for all industrial activities, including licensing, development, operation, and alteration of dams, provides the overarching structures for pre-operational and operational integrity and safety assurance, and for safety during renewal or retirement from service. The Government through its regulatory agency requires a number of policies and design criteria to be satisfied. But the Owner has to be even more conservative for reducing potential risks to a level satisfactory for the protection of the public and its own assets.

Leadership and Management for Safety in the Pre-Operational Phases

Effective leadership and management for pre-operational integrity and safety should be established in a way that deals with all aspects of safety including first filling and provides for a smooth and uninterrupted transition to the operational phase of the life cycle of the dam.

1.4. BULLETIN STRUCTURE

The Bulletin is mainly intended for dam owners and investors but also for all other actors intervening in the development of dam projects. It concerns not only development of new dam schemes but also heavy rehabilitation or upgrading of existing dams. The term “dam” or “dam scheme” is not limited to the dam structure itself but encompasses the appurtenant structures (spillway, bottom outlet, water intake, etc.) and the surrounding environment (reservoir, downstream area). In case of hydropower development, it concerns also the power intake, headrace tunnel or canal, penstock and powerhouse. Thus, the dam has to be understood as a system that, as many other undertakings of mankind, is exposed to risks during its development and its operation.
  • Dam development phases and role of the various actors are presented in a first section (Chap. 2) of the Bulletin. Contractual relations and interdependency of the actors are also briefly described and commented.
  • In the following section (Chap.3) the various risks involved in design and construction of dams are described. The influence of nontechnical (human) factors is stressed and the importance of uncertainty in dam design and construction is discussed. The need to improve knowledge of the prevailing conditions by investigation is also presented. General rules for minimizing risks in the development of a dam project are proposed.
  • The need of defining an overarching safety management system for all actors is presented in Chap. 4. Starting from safety objectives their transformation in implementable actions is de...

Table of contents