For new dams on rock foundations, it may be feasible to review sliding safety under a very stringent rules approach. However, the task of identifying the most stringent standard is not always straightforward, as different approaches are seen to apply different criteria, with different levels of stringency applied to the different components of sliding resistance. This situation can give rise to complications in less competent foundations or in the case of deteriorating foundation strength on an existing concrete dam. Therefore, the main task of this paper is to assist in the challenge of identifying the most stringent standard or practice for assessing the sliding safety of concrete dams. Computational stability tests were carried out for an existing dam in accordance with European and American standards. Then the comparison of standards was carried out based on a parameter that represents the ratio of the assumed safety factor to the safety factor determined by use of a standard. The lower the established ratio, the more stringent the standard because the safety factor value reflects stringency. The paper also demonstrates that the stringency of a standard should be characterised by the contribution of friction and cohesion to the assumed safety factor.

The accurate assessment of undrained shear strength in natural soils is essential, as these materials often form the foundation of critical geotechnical structures such as embankments, slopes, and dams. Their behaviour is complex, influenced by stress history, depositional environment, and over-consolidation ratio (OCR). Conventional analysis methods typically assume homogeneity and uniform stress conditions, which do not represent the variability of natural soils, particularly those of pleistocene origin, often leading to conservative or unreliable stability estimates. Cone penetration tests with pore pressure measurement have improved interpretation by indirectly capturing stress history and stratigraphic variability; however, challenges remain in consistently defining the transition between drained and undrained behaviour and in relating undrained shear strength to effective stress parameters. To address these limitations, this study proposes a methodological framework introducing sectorisation of undrained shear strength ratios, considering both OCR and in situ stress state. The approach was applied to a sediment retention dam, demonstrating practical value in capturing subsurface heterogeneity and refining soil behaviour interpretation. Results indicate improved accuracy in defining shear strength parameters, thereby supporting safer and more reliable geotechnical design in complex geological settings.

This briefing note summarises two bulletins currently being produced by the ICOLD (International Commission on Large Dams) Technical Committee C ‘Chutes, Stilling Basins, Upgrading and Surveillance of Spillway’, which met on 17 May 2025 in Chengdu, China. This note outlines the progress being made on the two new bulletins, one on the design and upgrading of chutes and stilling basins, and the other on surveillance of spillways.

Since 2013 it has been mandatory for incidents on statutory reservoirs in England to be reported to the Environment Agency using the incident report template. It is expected that both an initial incident report and a post-incident report will be submitted. The Environment Agency is working on the Reservoir Safety Reform programme, the purpose of which is to update reservoir legislation following the publication of the Balmforth report in 2021. As part of recommendation 9 in the Balmforth report, a new online database for reservoir incidents has been created by the Environment Agency, Natural Resources Wales, and the Institution of Civil Engineers. As part of the creation of the new reservoir incidents database, all reservoir incident data between 2004 and 2024 held by the Environment Agency was reviewed. During this task trends were identified in the historical incident data which influenced the new database. This paper will focus on the analysis of the historical reservoir incident data in England held by the Environment Agency and the lessons learnt from this.

The construction of canals in the late eighteenth and early nineteenth centuries met the industrial revolution’s needs for the bulk transport of raw materials and finished products. However, canals need a water supply, and for the Worcester and Birmingham Canal that supply was mainly from reservoirs. The canal and its reservoirs were fed by rivers, but these rivers powered mills prior to the construction of the canal. The canal proprietors were therefore obliged to build compensation reservoirs to ensure that the operation of factories relying on waterpower was not prejudiced by the diversion of river flows into the canal. The construction of these reservoirs, both to supply the canal and to provide compensation water, and the subsequent developments, through to the present day are discussed. The canal system is now used for amenity rather than freight, but many of these reservoirs survive, used for both their original and new purposes.

Current practice in risk analysis and assessment of dams in the UK, including historical development and current practice, is summarised. This includes comments on current features and areas for improvement in estimation of both consequences of failure and annual likelihood of failure. It is noted that a condition of implementation of the Reservoirs Act in 1985 was that a wide spectrum of safety criteria should be introduced to account for the wide variation of risk between individual reservoirs, a fact which appears to have been overlooked in current regulatory requirements in UK. The differences between risk-based and risk-informed approaches in dam safety management are covered; risk-based is a narrow interpretation based largely on the outcome from a risk assessment, while risk-informed considers the outcome from a risk assessment with many other factors, always including considerations such as cost to save a life of any candidate upgrades and benefits of the reservoir to society. The paper suggests features that should be considered in a risk-informed approach. The paper finally reflects on how reservoir engineers can use risk assessments to improve the safety of dams in the UK, with suggestions to improve both the regulatory regime and how to assess when the cost of candidate risk reduction measures is proportionate to the reduction in risk to the public.