2024 – An Evidence Based Rapid Reliability Assessment Method for Gated Control Structures and Outlet Works

Jackson Wilson, Richard Mannix, Nick Cartledge, Glen Hobbs

Existing methods of assessing the reliability of spillway gate systems and outlet works in dams and other major water control systems tend to adopt a simplistic single-value judgement-based approach for screening and intermediate risk assessments or comprehensive fault tree analysis (FTA) for advanced risk assessments. This paper presents a semi-quantitative alternative, the Rapid Reliability Assessment Method (RRAM), that aims to fill a gap between single-value subjective assessment and fault tree analysis. The proposed method is a suitable and technically defensible reliability assessment approach and is best suited to portfolio level risk assessments and operational risk
assessments.

The paper presents the risk analysts perspective on the theory and application of the RRAM, detailing the rationale behind the method. The paper outlines how the RRAM produces reasonable and defensible failure model outputs when applied to spillway gate systems (e.g. Any Gate, All Gate and Single and Multi-Gate failure models) that are contextually consistent with the output models from FTA while significantly reducing the effort required to produce these models. Limitations of reliability assessment approaches adopted in the dams industry is also discussed citing paucity of collected and collated data on the reliability of electromechanical equipment commonly utilised in dam spillway gate systems and outlet works.