Dam safety review process
A dam safety review requires an understanding of the dam design, the methods and practices used for its construction and the surrounding conditions. Ideally, a complete set of records would be available for every existing dam, including the following:
- Reports from previous dam safety inspections and reviews
- Any relevant information on planning, field investigations, laboratory testing, design decisions, construction and quality control, first reservoir filling, operation and maintenance, repairs and modernization or expansion
- Design calculations, drawings and reports
- Equipment specifications
- As-built drawings, reports and documents
- Updated drawings
- Hydrological and structural data (including seismic)
- Instrumentation and operational monitoring data
- All safety inspection reports
- Dam operation, maintenance and surveillance manual
- Dam emergency preparedness and response plan
Analysis of internal and external hazards
Dam safety analysis is a combination of considering hazards, failure modes and mechanisms as well as consequences of functional dam failure. The dam system safety analysis should include internal and external hazards, failure modes and effects, operating reliability, dam response and emergency scenarios.
External hazards are hazards or threats to the proper functioning of the dam that are beyond the owner’s control and originate outside the boundary of the dam and its reservoir system, such as meteorological events, seismic events, reservoir environment (potential landslide), terrorist attacks and vandalism.
Internal hazards are those related to errors and omissions in the dam design and water conveyance structures, construction errors or design compromises, maintenance procedure errors and errors in developing and maintaining operating rules or means of verifying adequate operation. Internal hazardous sources can be classified in water barriers, hydraulic structures, mechanical and electrical subsystems, infrastructures and plans.
Failure mode analysis
A failure mode describes how element or component failures must occur to cause loss of the subsystem or system function. At a very general level, there are two main dam failure modes:
- The overtopping failure mode is related to inadequate freeboard, causing water to flow over the crest of the dam in a manner not intended or provided for in the dam design, construction, maintenance and operation.
- The collapse failure mode is related to the inadequate internal resistance to the hydraulic forces applied to the dam, foundations and abutments while being hydraulically operated in accordance with the design intent.
There are different functional failure mode characterizations that can cause dam overtopping or collapse failures, and they should be reviewed in detail separately in failure mode analysis.
A safety review report is an assessment of dam safety, based on data, analysis and professional engineering interpretation in accordance with generally accepted engineering practices involved in determining the currency and adequacy of the physical performance capacity of a dam and in managing its operational integrity.
BBA’s team is experienced in this field and can advise you on the best approach to adopt. Contact us to discuss your projects!