The U.S. Army Corps of Engineers (USACE) has a robust Dam Safety Program (DSP) that utilizes risk- informed decision-making to prioritize its portfolio of dams in need of further study and modifications. USACE also utilizes a two-tiered governance structure in which one body makes portfolio recommendations around risk management while the other body oversees the execution of the agency’s routine DSP and makes policy recommendations. The routine program consists of the activities required for interim risk reduction measures, inspections, instrumentation, monitoring, assessments, operations and maintenance, emergency action planning, training, and other dam safety activities. An internal program management tool exists to monitor and track all these activities and generate metrics around execution of the routine DSP, however, it does not include metrics around other aspects of the DSP like governance, asset management, public safety and security, flow controls, or audits/reviews. USACE hopes to identify gaps in its DSP that can be used to correct shortcomings, continuously improve, and to increase the resilience of its DSP, which will enable each project to deliver benefits to the Nation. The Centre for Energy Advancement through Technological Innovation (CEATI), through its Dam Safety Interest Group (DSIG), collaboratively developed a spreadsheet tool known as the Dam Safety Maturity Matrix (DSMM). The DSMM is a facilitated exercise used to help evaluate how well-developed a program is across 12 elements considered to be typical and important of most dam safety programs. Each of the elements is then deaggregated into sub-elements, each of which can be evaluated by the team. The maturity ranges across 5 levels from Needing Improvement to Leading Edge. After all sub-elements are evaluated, an aggregate maturity level is computed that gives an estimation of the overall maturity level of the program. USACE will present the results of its pilot project using the DSMM and share lessons learned regarding its implementation. The short-term goal is to identify program strengths and areas for improvement, while the long-term goal of USACE using the DSMM is to participate in bench- marking across multiple agencies and international dam owners regarding their dam safety programs, for which has never been done to the knowledge of this author.
There are currently around four new flood detention reservoirs (retarding basins) built each year in UK, which although only being modest structures with median height of 4m and reservoir capacity of 300,000m3 pose a significant risk to the community as they are located immediately upstream of the community they are protecting. These communities range from around five to several thousand households.
The cost and therefore viability of these structures can vary depending on the number of defensive features built into the design, which raises interesting conflicting issues of public safety contrasted to vulnerability to property inundation in operational (say, 1 in 100 chance) floods.
The authors have designed and supervised over 30 flood detention reservoirs in the UK in the last 20 years. This paper describes the engineering decisions which need to be made regarding defensive measures and the resilience of these structures to withstand flood loading on demand. Examples of measures to include resilience are described, with discussion of when selection of the options to increase resilience against a particular failure mode should be mandatory, and when it may be more appropriate to consider it on a case by case risk-based approach. The paper will also discuss more strategic issues of how to balance making flood detention reservoirs affordable, while at the same time maintaining high standards of public safety and compares Australian and UK approaches.
As part of the development of some dams and hydroelectric power schemes, deep infrastructure is often required which requires and understanding of the in situ stresses of the rock mass. Recent works completed in southern Australia and Europe have led to improved methodologies for conducting effective, reliable, and repeatable measurements of in situ strain and/or deformation, as well as the subsequent estimation of in situ stress.
In situ stress testing is generally an item that is specified as part of a geotechnical investigation, however it is not commonly well understood in terms of reliability, repeatability, or, in fact, what the result actually means and its implications to project design. Commonly, a handful of tests are completed, with variable results, which often generates more confusion than answers.
This paper provides a discussion of recent in situ stress testing completed for two deep Australian projects. It summarises the aim of the investigations, test selection process, laboratory testing, data review and model development. This is to illustrate how complex the estimation of in situ stress can be and some of the pitfalls that may be avoided whilst acquiring and assessing the data. It also examines several different testing methods available in the Australian and International industry and some of the analysis techniques available to dam and tunnel projects. Finally, the paper provides an update on topical developments provided at recent workshops in Europe.
Computational Fluid Dynamics (CFD) is the science of predicting momentum, mass and heat transport, and can aid in design and safety issues for dam resilience in modern settings. Applications of CFD have historically been in the aerospace, automotive and chemical process industries with limited application in the hydraulic engineering field; possibly due to the associated computational intensity that is typically required. However, over the past two decades the cost of computing power has decreased substantially while the processing speed has increased exponentially. These developments have now made the application of CFD in the commercial environment feasible. CFD is particularly valuable in complex flow situations where the outputs required cannot be provided by a traditional hydraulic assessment approach and where there are stakeholder drivers such as service life, insurance cover and safety implications of infrastructure. The need for CFD when these drivers and complex flow situations arise, are demonstrated by means of a case study.
In the case study, CFD was used to investigate the flow patterns and the predicted performance of the outlet pipework from Massingir Dam in Mozambique. Three flow scenarios with appropriate pressure and flow boundary conditions were analysed for the outlet pipework, which included bifurcations for power generation from the main discharge conduits. Specific concerns addressed were, firstly, the possible excessive negative pressure in the region of the offtake for power generation and the potential for cavitation effects and, secondly, unacceptable velocity gradients in the power offtake pipework. Results showed that although some negative pressures were possible in one flow scenario, mitigation measures based on the CFD outputs could be considered and designed before construction.
The implementation of CFD in the above case study displays how risk in design can be reduced to ensure safety issues are addressed effectively.
The use of simulation models to assess dam failure consequences has progressively advanced in Australia over the past few years. For example, it is now common for HEC-LifeSim to be used to estimate potential loss of life from the failure of large dams with large populations at risk downstream. Since its introduction to Australia, numerous presentations and papers have been provided by USACE and industry professionals that highlight the benefits of using HEC-LifeSim for a range of different case studies.
Whilst the majority of the literature published to date have focused on the benefits of simulation modelling, this paper identifies some of the technical challenges that can arise, particularly in the evacuation modelling component of HEC-LifeSim. The techniques that have been used to overcome these challenges are also discussed using three case studies.
The first case study demonstrates the sensitivity of the life loss to changes in cell size and the output interval of the gridded hydraulic data. This is done by comparing the differences in life loss between high-resolution and low-resolution models for three dambreak models. The second case study illustrates the importance of the road network representation in HEC-LifeSim because the resolution of the road network is important to achieve plausible estimates of the fatalities along roads, and logical animations of the mobilisation. The final case study demonstrates the implications of coincident flow modelling on the life loss, and therefore the importance of understanding the hydrology of the target and neighbouring catchments.
This paper provides a checklist that prompts practitioners to consider some of the lessons learnt over the last few years and is envisaged to be a working document that improves the defensibility and robustness of HEC-LifeSim estimates throughout the industry.
Flood inundation consequence and emergency evacuation assessment using advanced numerical modelling tools such as HEC-LifeSim is progressively emerging as accepted best practice, due in part to the growing ease in obtaining the necessary datasets and hydraulic numerical modelling results and the increasing computational power readily available to perform analyses. In turn, these tools are being applied to assess dam failure consequence and the effectiveness of emergency response procedures.
An essential resource is an approved Emergency Action Plan (EAP, also known as a Dam Safety Emergency Plan), which describes how dam owners and disaster management groups notify and warn persons at risk of harm during an emergency event. There have been progressive improvements in the effectiveness of EAPs through a series of reviews and lessons learnt from emergency events, legislative and regulatory amendments and general improvements in communications, monitoring, alerts and public awareness. Effectiveness is measured through feedback from training exercises and expert reviews, however a more quantitative measure is not presently available. This limitation can challenge decision makers who need to balance costs associated with emergency preparedness with anticipated reductions in life safety risks.
The paper explores the feasibility of providing a quantitative assessment of the effectiveness of an EAP using advanced consequence modelling (HEC-LifeSim). Using consequence models for two dams in Queensland, EAP effectiveness is assessed for a range of emergency response measures. The accuracy and reliability of the model parameters applied to each simulation and their impact upon the reliability of predictions of potential loss of life (PLL) are analysed and discussed. The feasibility of the approach is discussed and recommendations to be considered for future applications made.