Regular assessment of dam stability is essential to ensure safe and reliable operation of these structures throughout their service life. In some cases, monitoring of the surrounding environment can be as important as monitoring carried out over the dam itself. Risk management programs should therefore look at the entire site and nearby terrain to ensure any and all possible geohazards which may impact dam integrity are identified and tracked over time.
InSAR is a type of remote sensing that uses radar satellite imagery to measure surface movement occurring over time, often achieving millimetric levels of precision. This approach does not require fieldwork or the installation of equipment, measurements are instead obtained from reflections of the satellite radar signal off infrastructure, rocks and bare ground. Furthermore, as the measurements are obtained from satellite images that extend over regions thousands of kilometres squared in size, they can provide information on stability over dams, surrounding reservoirs, even entire regions.
The main advantage of InSAR technology for dam monitoring is two-fold. First, in addition to monitoring the dam itself, stability of the surrounding area (including slopes around dam reservoirs) can be tracked. Second, both long- and short-term displacement trends can be captured (including historical analyses) providing a more complete picture of dam behaviour over time.
Several examples of InSAR results obtained over different dam sites are presented.
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Many mapped faults in the south-eastern highlands of New South Wales and Victoria are associated with apparently youthful topography, suggesting that faulting may have played a role in shaping the modern landscape. This has been demonstrated to be the case for the Lake George Fault, and may reasonably be inferred for the poorly characterised Murrumbidgee, Khancoban, Tantangara, Berridale Wrench and Tawonga faults. More than a dozen nearby major faults with similarly youthful topography are uncharacterised. In general, fault locations and extents are inconsistent across different scales of geologic mapping, and rupture lengths, slip rates and other fault behaviours remain largely unquantified. A more comprehensive understanding of these faults is required to support safety assessments for communities and large infrastructure in the region.
The evaluation of the maximum instantaneous uplift force produced by turbulent pressure fluctuations plays a key role in designing concrete slab protection in spillway chutes and stilling basins. Recent incidents involving damage to chute linings have highlighted the significance of this issue. To evaluate the stability of spillway stilling basin slabs, it is necessary to determine the statistical structure of the turbulent pressure fluctuations in the spillway chute and stilling basin. This can be defined by an extensive experimental work with a scale Physical Hydraulic Model (PHM). This exercise can be prohibitively expensive in terms of time and cost and it is proposed that the use of Computational Fluid Dynamics (CFD) in this application could become a cost effective alternative. A new approach using Detached Eddy Simulation (DES) was applied to the case of a scale physical hydraulic model representing a real-world prototype and the results of the simulation were compared with the direct laboratory measurements. Here the forces and pressures acting on the slabs are evaluated using both CFD and physical hydraulic modelling results. In conclusion, some considerations on the design of slabs with unsealed joints are reported and discussed.
The U.S. Army Corps of Engineers (USACE) Risk Management Center (RMC) developed the Reservoir Frequency Analysis software (RMC-RFA) to facilitate, enhance, and expedite flood hazard assessments within the USACE Dam Safety Program. RMC-RFA is a stochastic flood modeling software that employs advanced statistical and computing techniques, allowing a user to perform a screening-level stage-frequency analysis on a desktop PC with runtimes on the order of seconds to a few minutes. RMC-RFA utilizes an inflow volume-based stochastic simulation framework that treats the seasonal occurrence of the flood event, the antecedent reservoir stage, inflow volume, and the inflow flood hydrograph shape as uncertain variables rather than fixed values. In order to construct uncertainty bounds for reservoir stage-frequency estimates, RMC-RFA employs a two looped, nested Monte Carlo methodology. The natural variability of the reservoir stage is simulated in the inner loop defined as a realization, which comprises many thousands of events, while the knowledge uncertainty in the inflow volume-frequency distribution is simulated in the outer loop, which comprises many realizations.
Stage-frequency curves derived with RMC-RFA are compared to those derived with more complex, precipitation-based simulation frameworks, such as the Monte Carlo Reservoir Analysis Model (MCRAM), the Stochastic Event Flood Model (SEFM), and the Watershed Analysis Tool (HEC-WAT). The inflow volume-based framework employed by RMC-RFA produces stage-frequency curves that strongly agree with the more complex, precipitation-based methods. Furthermore, the results from the alternative methods fall within the RMC-RFA uncertainty bounds, demonstrating its robustness. In this sense, the RMC-RFA simulation framework lends itself to a value of information approach to risk management, where knowledge uncertainty can be efficiently quantified at a screening-level assessment, and then the value of performing more complex and sophisticated studies to reduce uncertainty can be considered.
Yarrawonga and Torrumbarry Weirs; located on the Murray River bordering Victoria and New South
Wales, are operated by Goulburn Murray Water on behalf of the Murray Darling Basin Authority.
The electrical and control systems that operate both structures were nearing 20 years of age, resulting in risk associated with equipment nearing the end of its useful working life and hardware obsolescence, driving this upgrade program. These control systems are critical in the monitoring and management of river levels and flows that extensively affect Victorian and New South Wales irrigation supplies and recreational users on the Murray River and Lake Mulwala.
Considerable effort was required to update and develop the control philosophy before proceeding to the design phase of the projects. The requirement to work on these brownfield sites, while maintaining operational ability and minimising dam safety and water delivery risks, resulted in a significant implementation and commissioning process. During the course of these works, the opportunity was also taken to enhance and update remote monitoring capability.
The lessons learnt on these projects are being incorporated into current Electrical and Control System Upgrade projects at Cairn Curran Reservoir and Dartmouth Dam.
This paper will explore the differences in pore pressures resulting from saturated and unsaturated seepage (pore pressure) analysis. It will also evaluate some conventional recommendations, such as the inclusion of essential components of the embankment dam and omission of inessential components. In addition, the identification of inessential components will be discussed.
Finally, pore pressures obtained from these analyses will be compared to monitoring data in order to identify the most appropriate seepage (pore pressure) model.
In conclusion, advantages and disadvantages of each method will be discussed and recommendations will be provided in order to gain the most appropriate results.
The results of this paper can be used for designing new embankment dams or safety reviews of existing dams, particularly when there is lack of reliable monitoring data.