Safety |
system interactions, can combine to produce an undesired event, in this case, the gates failing to open sufficiently to pass the required discharge on demand. Using established reliability data together with the findings of the FMEA, the analysis calculated the Probability of Failure on Demand (PFD) for the complete system. Human factors, including operator action, remote control centre operation and access arrangements, were included within the scope of the assessment alongside the equipment itself. The calculated PFD, and the fault trees more generally, were used to evaluate the overall reliability of the system and allowed the team to evaluate where improvements might be possible.
From result to recommendation The assessment did not, at first pass, demonstrate
that the proposed design would meet its target. The calculated probability of failure on demand fell short by more than an order of magnitude. This is where a purely pass-or-fail reading of the
Paul Jones of KGAL Consulting Engineers Ltd
result would have been unhelpful. Rather than treating the shortfall as a verdict on the design, the fault tree model was used diagnostically, ranking the individual contributors to the overall PFD so that design effort could be directed at the small number of items dominating the outcome.
KGAL Consulting Engineers Ltd
KGAL Consulting Engineers Ltd is a UK-based engineering consultancy specialising in water control, hydropower and large moving structures. The company provides structural, mechanical, hydraulic, electrical and reliability engineering services, supporting projects from early concept development through detailed design, construction and commissioning. Operating from offices in Poole and Wakefield, KGAL works
internationally for owners, lenders, contractors and consultants. It is an independent subsidiary of Whessoe Sdn Bhd and has associate offices in Kuala Lumpur and Vientiane. Hydropower is one of KGAL’s core areas of expertise. Its hydropower engineers have more than 100 years of collective experience, with capabilities covering mechanical design, control systems, transient analysis and project management. The company works across the project lifecycle, from initial feasibility and detailed design to construction and commissioning, as well as providing engineering support for the refurbishment and upgrading of existing hydropower facilities. KGAL also has extensive experience in the design and construction of
hydraulic steel structures and associated water control systems. Its work includes equipment for dams and reservoirs, hydropower schemes, flood defence and river regulation projects, navigable waterways, irrigation networks, pumping stations, ports and harbours. The company says it has been involved in the design of some of the largest hydraulic steel structures currently operating worldwide. For hydropower and dam projects, its associated infrastructure expertise includes spillway and intake gates, draft tube gates, low-level outlet gates, fish passes and penstocks, together with mechanical and electrical systems required for power station operation. KGAL also provides risk and reliability engineering services for
hydropower, water control and moving structures. The company says it has assessed installations across the UK, Europe, North America, Africa and Asia, providing advice on risk management and reliability. Its multidisciplinary engineering team includes personnel with backgrounds in construction and contracting, giving the company experience of the programme, site and commercial considerations involved in delivering major infrastructure.
https://www.kgalglobal.com/
A series of sensitivity studies was then undertaken to establish the magnitude of the biasing influence exerted by particular subsystems. These identified the mechanical drive train as the dominant contributor to the calculated figure, because it is a single point of failure. The distinction matters considerably in practice: without it, a design team can expend substantial effort on improvements that barely move the overall reliability figure, while the item actually governing the result goes unaddressed. The recommendations arising from the study are
therefore focused on the top contributing items, those changes most likely to deliver a material improvement in overall reliability. Design development against those recommendations is continuing, and the reliability model provides the means to test each proposed change objectively before it is adopted.
Scope and limitations Any quantified reliability assessment rests on a
defined scope, and it is worth stating this one plainly. The analysis addressed random hardware failures and therefore assumes constant failure rates. Failures arising from equipment deterioration and wear-out are not modelled; these are assumed to be managed through maintenance and through refurbishment or replacement of equipment across the installation’s life. The assessment to date has addressed the scenario in which the outlet fails to pass sufficient water on demand during a large flood. The converse scenario, failure to stop the flow of water on demand, is to be addressed in a subsequent phase of the study. Other potential failure modes exist but were judged less critical and were not carried forward. None of this undermines the value of the exercise. It does, however, make the point that a reliability figure is a statement about a defined set of failure mechanisms, and is only as meaningful as the scope behind it is explicit.
Conclusions The methodology applied by KGAL demonstrates
how functional safety thinking can be brought to bear on the design of critical hydraulic infrastructure. By integrating hazard identification, failure modes analysis and quantified reliability assessment throughout the design process, safety considerations become an integral part of engineering decision- making rather than a final compliance exercise. Although developed for a specific low-level outlet gate project, the methodology has broader application across dams, flood defence infrastructure, navigation structures and other hydraulic steel systems where dependable operation on demand is essential. As owners and operators continue to modernise ageing infrastructure while meeting increasingly demanding safety and resilience requirements, structured, risk-based design methodologies will become an increasingly important part of engineering best practice.
Author information:
Paul Jones, CEng MIET, Associate Director, KGAL Consulting Engineers Ltd.
14 | September 2026 |
www.waterpowermagazine.com
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