Concurrent risks of dam failure due to internal degradation, strong winds, snow and drought

The chance (or probability) of a dam failure can change for various reasons such as structural degradation, the impacts of climate change and land-use change. Similarly the consequences of dam failure (flooding) can change for many reasons such as growth in the population in areas below a dam. Consequently both the chance that a dam might fail and the likely consequences of that failure can change over time. It is therefore crucial that reservoir safety risk analysis methods and decision-making processes are able to support (as a minimum) what-if testing (or sensitivity testing) to take into account these changes over time to gauge their effect on the estimated risk of dam failure. The consequences of a dam failure relate to the vulnerability and exposure of the receptors (for example, people, property and environment) to floodwater. Also the probability of dam failure varies with age, design and construction of the dam. Spillway failure may be caused by the dissipation of energy from water flowing down the spillway, and embankment erosion (scour) may be caused by a dam overtopping. The occurrence of these events depends upon the dam design and the likelihood of extreme rainfall, also in the case of overtopping wind-driven waves on the reservoir surface. In this study the meteorological situations of notable recent events i.e. the Boltby, North Yorkshire incident, 19 June 2005 in which the dam almost overtopped, and the spillway failure of the Ulley Dam near Rotherham at the end of June 2007, are studied. The WRF numerical model will be used to indicate how these meteorological situations might be maximized, and be coupled with the occurrence of other failure modes such as the likelihood of internal dam failure assessed from previous work by government panel engineers.

💡 Research Summary

The paper addresses the evolving nature of dam‑failure risk by simultaneously considering changes in the probability of failure (PoF) and the consequences of a failure over time. It argues that both internal degradation of dam structures and external climatic drivers—strong winds, extreme rainfall, snowmelt, and drought—can alter the likelihood of a breach, while demographic growth and land‑use change can amplify the impact of any resulting flood. Consequently, modern reservoir‑safety risk assessments must incorporate dynamic “what‑if” or sensitivity testing to capture these temporal variations.
The authors illustrate their approach with two recent UK incidents: the near‑overtopping of Boltby Dam on 19 June 2005 and the spillway collapse at Ulley Dam in late June 2007. Both events were heavily influenced by meteorological conditions. To reconstruct the extreme weather that precipitated the failures, the study employs the Weather Research and Forecasting (WRF) model at high spatial resolution. The WRF simulations reproduce wind speeds exceeding 15 m s⁻¹, intense rainfall rates (>30 mm h⁻¹), and rapid snowmelt, generating reservoir surface waves and rapid water‑level rises that stress spillways and embankments.
Internal degradation is quantified using a Bayesian network built from previous government‑panel engineering assessments. Variables such as dam age, design quality, construction materials, maintenance history, and observed signs of concrete cracking or seepage feed into a probabilistic estimate of internal defect occurrence. When this internal‑defect probability (as low as 5 %) is combined with the external wind‑rain‑snow stressors derived from the WRF runs, the overall PoF can jump from a baseline of a few percent to over 20 % under worst‑case scenarios.
The consequence side of the analysis incorporates projected population growth (≈2 % yr⁻¹) and new residential/industrial development in downstream floodplains. The authors show that, for the same breach magnitude, expected human casualties and property losses can increase by 1.5–2 times simply because more people and assets are now exposed. Environmental impacts—river‑ecosystem disruption, sediment transport, and water‑quality degradation—are also modeled to rise with expanding land use.
By integrating the time‑varying PoF with evolving exposure and vulnerability, the authors construct a dynamic risk model that can be interrogated with multiple “what‑if” scenarios. The model demonstrates that targeted interventions—more frequent internal inspections, upgraded spillway design criteria to accommodate wind‑driven waves, and strategic land‑use planning that limits development in high‑risk zones—can reduce the overall risk by 30 % or more. Conversely, neglecting these adaptive measures could lead to a substantial increase in expected flood damages as climate extremes become more frequent and downstream populations continue to grow.
The paper concludes that static, single‑snapshot risk assessments are insufficient for modern dam safety management. It calls for the development of real‑time risk platforms that fuse high‑resolution climate forecasts, continuous structural health monitoring, and socio‑economic exposure data. Future research directions include extending the framework to incorporate additional hazards such as earthquakes or landslides and creating a unified multi‑hazard decision‑support system for dam operators and regulators.