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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Millions of dollars are spent on dam upgrade works which are often undertaken to meet the flood security requirements. Prioritisation of the dam upgrade work is based on portfolio risk assessments in which dambreak modelling is an integral part. Concurrent design flow hydrographs of tributaries downstream of dam are required for the assessment of the incremental effect of a dam break scenario. The Annual Exceedance Probability (AEP) neutral concurrent tributary flows can be estimated using a bivariate-normal distribution approach.
This paper examines the underlying assumptions made in the application of the bivariate normal distribution approach using observed and design rainfall data for Avon Dam and its downstream tributary catchments. Synthetically generated data was used to illustrate the impact of the log-normal distribution assumption on the AEP neutral concurrent tributary rainfalls. This paper suggests a modification to the bivariate-normal distribution approach to estimate more unbiased AEP neutral concurrent design rainfalls. The use of historical gridded rainfall in the estimation of inter-catchment rainfall correlation is also demonstrated.
The U.S. Army Corps of Engineers (USACE) is responsible for flood risk management across the United States. USACE has more than 710 dams and is responsible for more than 24,000 kilometres of levees. Since 2008, USACE projects have prevented more than AU$1.2 Trillion (in 2017 dollars) in damages from flooding. Although some of this came as a result of dozens of smaller floods, much of that protection came during three events within the last five years. From 2010 through 2017, the U.S. has had three major inland floods and two coastal events where federal flood protection exists: in 2010 on the Cumberland River, in 2011 on the Missouri, Ohio, White, and Mississippi Rivers, in 2015 on several rivers in Texas and Oklahoma, and in 2017 along the Gulf Coast of the U.S. and its territories in the Caribbean. For many of these locations, these events produced record rainfall and the flood of record. USACE operated many large facilities on these systems and those systems overall performed as expected. However, USACE also experienced some operational issues, did a substantial amount of flood fighting, had several incidents, and several failures. This paper will describe the flooding experienced in those events, the operations of the flood protection systems, the performance overall, and some of the lessons learned.
New technology and outputs from flood forecasting systems can raise issues for dam safety managers in how they use uncertain information to make critical dam safety decisions. In particular, making operational decisions around pre-releases based on forecast inflow presents challenges. In this case dam safety risk needs to be weighed up with other risks such as increasing downstream flooding, or being able to supply water into the future. The process of developing a flood forecasting system should be a close collaboration between the developers and the users. This ensures that outputs provide meaningful information that can be used to support operational decision-making in a flood or emergency response situation.
Investigations into the core material of earth fill dams are undertaken reluctantly due to the potential to cause damage to the embankment. Where investigations are required, Cone Penetration Testing (CPT) is increasingly used to assist with the geotechnical assessment of dam embankments. The risk of hydraulic fracture within embankment core material is well known and procedures are typically adopted to minimise the risk of hydraulic fracture during remediation of the holes. Backfilling is typically done in stages allowing for an initial set of the cement/bentonite grout mixture prior to subsequent lifts.
While the risk of hydraulic fracture is well understood, the lesser known risk of pneumatic fracture is a possibility where certain conditions exist. This paper discusses CPT investigations at Fairbairn Dam, operated by Sunwater in Central Queensland, and the challenges faced in undertaking the remediation of the CPT holes. The potential for pneumatic fracture of the embankment core was highlighted during the investigations and details of alternative techniques adopted for reinstatement of the holes are presented. Recommendations are made to appropriately manage the risk of pneumatic fracture when undertaking CPT’s through embankment core.
Dams leak! But only some of the leaks require investigation and remediation. When they do, finding the pathway of the leak becomes an expensive and slow process, often characterised by drilling “trial and error” boreholes that further impair the integrity of the structure. A much better alternative is to collect specialised data with highly sensitive instruments along all relevant points, map the data using the latest groundwater geophysics technology or hydrogeophysics technology, create 3D models of the subsurface including the flow path of the leak in question, and finally use software filters and algorithms to predict ongoing effects of the water problem. In this paper three case studies are presented including the Bartley Dam, King George Dam, and the Samanalawewa dam. All of the dams had leaks that concerned the dam owners. The method was applied to determine the location of the seepage paths passing through the dam. Remediation was completed at the Bartley Dam and King George Dam confirming the results from the method. And there are plans for remediation at the Samanalawewa dam. The method saved the clients a significant amount of money because they had a focused remediation. Knowing the dam has been repaired and there are no other leaks provides peace of mind to the dam owners.