Dam owners manage many complex activities to maintain and operate their dams safely and resiliently. Identifying, and continually improving, the key elements of an effective dam safety program and associated practices can be challenging but are essential to support resilient dams and resilient communities; using the Dam Safety Maturity Matrices (DSMM) is an efficient and thorough way to do this. A maturity matrix is a tool to evaluate how well-developed and effective a process or program is. The matrices were developed within CEATI’s Dam Safety Interest Group (DSIG) for owners to assess the effectiveness of their dam safety program against industry practice, and to assist with identifying improvement initiatives.
This paper will present the matrices and demonstrate how they are used to evaluate the effectiveness (or maturity) of a dam safety program. It will also highlight the benefits associated with using the matrices as an assessment tool, including the identification of improvements that can be made to a dam safety program, and the prioritization of efforts across multiple facets of a dam safety program.
User case studies from dam owners in both New Zealand and overseas will be presented to elaborate on the tool and the process.
Now showing 1-12 of 53 3220:
Dam spillway gate collapse may have fatal consequences and cause severe structural damage due to flooding, additionally the dam owner will suffer substantial business losses. The repair work required to put a gate back in service can be time consuming, challenging, dangerous and costly. To ensure the reliability of radial gate operation, and depending on the type of trunnion bearing and the structural capacity of the gate arms, the bearing friction should be carefully monitored and gate performance evaluated to confirm the gate’s ability to withstand increases in friction over time. The frequency of monitoring requires careful consideration.
Radial gate arms are normally designed to withstand bending moments from nominal bearing friction. An inappropriate bearing, or a bearing in poor condition, might have friction sufficiently high to cause a gate arm to fail due to the excessive bending moment during gate operation.
An easy and non-invasive way of analysing the condition of the bearing, to ensure safe operation of radial gates where the arms might be prone to increased bending moment, is through friction measurement with the use of strain gauges. This paper briefly presents common radial gate design and some failure modes as a consequence of increased bearing friction, and a method of determining the bearing friction coefficient through strain gauge measurements and experience from the field is presented.
The ANCOLD (2003) Guidelines on Risk Assessment contain criteria regarding the tolerable level of individual risk from dam failure. Maslin et al. (2012) describe an approach to estimating individual risk from dam failure, using exposure factors, warning and evacuation factors, and fatality factors. These factors vary according to the people at risk, the anticipated warning time, the flood severity and the shelter people are likely to be in. Maslin et al. (2012) provide step-by-step instructions, which means their approach can be applied in a consistent manner from dam to dam. However, the recommended fatality factors are based on Graham (1999) and DHS (2011) definitions of high, medium and low severity flooding which have been superseded by the Reclamation Consequence Estimating Methodology (RCEM). Therefore, in this paper modifications to the Maslin et al. (2012) approach are proposed, so that estimates of individual risk from dam failure are consistent with RCEM-based estimates of societal risk. The paper then concludes with two predictions about how the assessment and use of individual risk in Australian dam safety management may change in future.
Trustpower’s Mahinerangi Dam in New Zealand’s South Island is a concrete arch and gravity abutment dam built in 1931, subsequently raised in 1946 and strengthened with tie-down anchors in 1961.
This paper discusses a 3D finite element analysis of the dam and the predicted performance of the arch section under Safety Evaluation Earthquake (SEE) loading against identified potential failure modes.
Current guidelines and recent seismic hazard assessments recommend earthquake loadings higher than what was originally accounted for in previous decades. A Comprehensive Safety Review identified stability under SEE loading as a potential deficiency, so a programme of works was commenced to evaluate and better understand the seismic risk by using modern day tools and technology to evaluate the dam against current performance standards.
The final model incorporated the results of extensive laboratory testing, high-resolution LiDAR survey data and dynamic calibration using ambient-vibration monitoring. Motion recordings across the face of the dam during the 2016 Kaikōura earthquake were also used to validate the model. The reservoir has been explicitly modelled together with the opening, closing and sliding of contraction joints and the foundation interface. This allowed the modelling of permanent displacements and the redistribution of loads within the dam under SEE loading, which had been shown to be an important behaviour from the previous stages of analysis.
Many quantified risk assessments finish the failure mode event tree at the estimated occurrence of an embankment breach leading to dam failure outflows and downstream consequences. In some situations, for dams with multiple embankments with potentially different consequences downstream of each embankment, the possibility for further breaches may be pertinent if there may potentially be higher consequences for a multiple breach scenario. The location of an initial breach and sequence of subsequent breaches could also result in different contributions to total risk.
This paper discusses a method applied to investigate the conditional probability of flood overtopping breaches for multiple earth-fill embankments with grass covered downstream slopes.
For the subject dam, preliminary modelling identified that for a flood overtopping breach of an embankment the breach’s development may not be sufficient to reduce the lake level and sustained overtopping flow over the remaining embankment crests could lead to further embankment breaches.
A Monte Carlo dam breach simulation modelling approach was used with a large number of flood events. The simulation modelling considered erosion initiation for a grass slope due to the combination of velocity and duration of flow, and erosion continuing to breach based on duration of flow after erosion initiation. Potential uncertainty of erosion initiation and erosion continuing to breach were represented with probability distributions in the Monte Carlo modelling.
The results from the large number of dam breach simulations were then analysed with post processing to derive conditional probabilities for single or multiple breaches and breach sequence.
This paper discusses the current regulatory requirements and guidelines, which address to varying degrees the need for recovery controls and the engagement of Owners with Impacted Communities (ICs) within a Dam Safety Emergency Response Plan. The planning and application of appropriate recovery controls, which are applicable from the moment of failure, help to build resilience and reduce the ultimate consequence of TSF failure. The application of such controls, developed with close engagement with impacted communities has a strong precedent, being recommended as a result of the International Council on Mining and Metals (ICMM) review of good practice for emergency preparedness (Emery, 2005).
This paper presents a simple method to assess various recovery controls, with risk minimisation as its basis, and the use of existing risk assessment techniques such as bow-tie diagrams or the inclusion of recovery controls to other qualitative assessment methods. This will be illustrated through application to some relevant historical TSF failures.