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.
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The purpose of this paper is to document a limited review of the existing concrete chute spillways in the United States Army Corps of Engineers (USACE) portfolio of dams. This internal review was undertaken in response to the partial spillway failure of the Oroville Dam concrete chute spillway in February 2017, the partial spillway failure of the Guajataca Dam concrete chute spillway as a result of Hurricane Maria in September 2017, and to address the request by the United States Congress for USACE, United States Bureau of Reclamation (USBR), and the Federal Energy and Regulatory Commission (FERC) to review their respective portfolios for similar spillway vulnerabilities as Oroville Dam. The intent was to screen for existing concrete chute spillways within the USACE portfolio that may be susceptible to damage/failure during operation.
Many numerical simulations have tried to model the failure-induced displacements of earth structures due to liquefaction. In this paper, the challenges in modelling such as the large displacement and non-immediate failure of earth structures due to liquefaction are discussed. An advanced bounding surface plasticity model is used to simulate the dynamic behaviour of saturated porous media. A series of benchmark welldocumented seismic events are analysed, and the results are compared to the reported laboratory and field observations. These analyses consist of one centrifuge test on liquefiable sand (Model #12 of the VELACS project) and one earthfill dam (Lower San Fernando Dam in California) subjected to seismic loading that leads to liquefaction. The capability of the model to capture the flow failure due to liquefaction is demonstrated and results are compared with other attempts in the literature to capture similar responses.
The waters that feed the Nyamwamba River in western Uganda start as meltwater from the glaciers high up in the Rwenzori Mountains. A small scale run-of-river hydropower plant, equipped with a low height tyrolean type intake weir, is now operating just upstream of the town of Kilembe, the first large community along this river. History has seen floods cause realignments of the river through the town and major damage to property and loss of life.
A devastating flood occurred during the design phase for the scheme prior to any construction commencing, which caused loss of life and significant damage to roads, bridges and buildings within the town, including the hospital. Design changes to improve resilience of all riverine connections were made, including relocation of the diversion weir to a stronghold point within the basic protection zone of a natural island. A flood diversion dyke was constructed across one of the river branches that flows around the island, with its alignment, type and height optimised to capture low flows for energy generation while deflecting large flows away from the weir to mitigate flood damage.
Another major flood arrived three months after completion. No damage was sustained which provided confidence in the resilience of the headworks. A major river dredging program contributed to the overall resilience of this reach of river through the town.
This paper describes the challenges for the development of the project site in terms of physical considerations to work with the river, adopting some lessons learned from the pre-construction floods.
The ANCOLD Guidelines (2019) require that active and neotectonic faults which could significantly
contribute to the ground-shaking or ground-displacement hazard for a dam should be accounted for in seismic hazard assessments. While geological and geomorphological field investigations along suspected active fault structures are undertaken as a matter of course in New Zealand, this practice is relatively uncommon in Australia. Granted, rates of tectonic processes are greater in New Zealand than in intraplate Australia. However, moderate to large and damaging earthquakes are not uncommon in the Australian record; there have been ~26 earthquakes of magnitude >M6 in the last 150 years (~1 event every ~6 years) and similar events might be expected in the future. We present examples of investigations undertaken to better understand earthquake hazard for two faults – previous studies on the Wellington Fault, New Zealand, and new data from recent investigations of the Avonmore Scarp, southeast Australia. We report the results from these studies and discuss how the collection of similar data on faults proximal to Australian dams would allow dam owners and operators to better quantify seismic hazard and, thereby, more meaningfully comply with the ANCOLD guidelines.
Otago Regional Council (ORC) own and operate the Lower Taieri, Lower Clutha, and Alexandra Flood Protection Schemes. Collectively the schemes comprise over 220 km of earthfill levees, together with numerous appurtenant structures, such as major spillways, flood gates and pumping stations. The schemes provide flood protection to significant and varied communities and infrastructure adjacent to the Clutha and Taieri rivers, for example Dunedin Airport, and towns such as Balclutha and Outram. The works were constructed at various times since the 19th century to a range of standards, and assets are at various lifecycle stages.
Regular and systematic condition and structural integrity assessment is a key aspect of operating flood protection schemes for resilient communities. This can be challenging due to the large spatial extent of multiple schemes. Efficient and effective on-the-ground visual inspection of the entire network is key. A field assessment methodology was developed which combined on-the-ground visual assessment with innovative use of GIS technology, for field data capture, recording, analysis and presentation.
The structural assessment methodology used LiDAR-derived digital elevation models (DEMs) integrated with the field data to screen the levee networks based on geometry condition, to identify critical locations for analysis. Levee susceptibility to hazards such as overtopping scour, piping, seismic performance and slope instability was assessed utilising a semi-quantitative multi criteria analysis. Subsequent efforts were focused on critical locations enabling analysis which would not be efficient on a scheme-wide scale. An outcome included a GIS database to enable rapid future review of asset information and condition.
The assessment coincided with the July 2017 Taieri River flood – the largest event in almost forty years, and a timely reminder of the importance of flood protection infrastructure for community resilience. This event also highlighted the importance of making use of such events to field-truth assessment results and test assumptions about scheme performance and vulnerable locations.