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.
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Junction and Clover Dams are central spillway slab-and-buttress dams located in Victoria. Previous safety reviews and assessments of the dams concluded that neither dam met modern dam design standards and remedial works were recommended, including infilling the slab-and-buttress dams with mass concrete to sustain seismic loadings. These conclusions were based largely on the assessed seismic hazard at the site, the results of response spectrum analyses and observed conditions of the dams including alkali-aggregate reaction of the concrete. AECOM used current seismic hazard assessment techniques, conducted concrete investigations and testing, assessed long term surveillance monitoring results and used modern finite element techniques to demonstrate that no upgrade works were required at either dam resulting in a significant saving for AGL.
Extreme flood analyses are routinely used as inputs to dam risk assessments, spillway adequacy assessments and spillway designs. Estimation methods applied in Australia using rainfall-runoff models in combination with a Probable Maximum Precipitation (PMP) estimate are consistent with the current best practice applied around the world. The estimation methods can, however, result in substantial variability in peak flow estimates depending upon the practitioner and the methods used to quantify model parameters. Around the world, validation procedures are commonly applied to combat this variability, but no such techniques are routinely applied in Australia. A method is proposed for application across Australia which may variously be applied to validate and constrain extreme flood estimates and also provide quick estimates.
Earthquakes are a well-known threat to the safety of dams. While this threat is subdued for Australian Dams, the potential for earthquake induced failure of a dam requires risk minimisation in the downstream community through monitoring and emergency response procedures. This paper details WaterNSW’s approach to their development of a Seismic Monitoring Strategy which was to align the business and ensure an appropriate post-seismic response.
The strategy also identifies that a proactive approach to seismic instrumentation can be taken to reduce business risk by aiding decision making should a dam be in a damaged post-seismic state.
The interim outcome of implementing the Seismic Monitoring Strategy resulted in a fast emergency
response time and less overreaction/distraction of dam safety resources in insignificant seismic events. There is opportunity for other Australian dam owners to implement similar systems to = WaterNSW and achieve similar results.
For hydropower dam projects, design and construction of the temporary works including cofferdams are very important. Improper selection, design and/or construction of temporary works may cause delay of major construction works and increase construction cost.
The authors worked on the preparation of the Engineering, procurement and construct EPC tender (based on International Federation of Consulting Engineers (FIDIC) contract-yellow book) for a 20 MW Hydro Power Plant (HPP) project in the Balkans Region. The scheme involved the design and construction of three cofferdams to enable construction of the main dam, intake and powerhouse. The basis for tendering, as a part the contract documents, was the preliminary design of the HPP scheme. The tenderers were allowed to deviate from the solutions presented in the preliminary design as long as the proposed solutions fulfilled the Employer’s Requirements.
As a part of a winning strategy, the preliminary design cofferdams were changed and modified, providing significant saving and facilitating quicker and safer construction. This paper presents the development of the design and challenges faced during construction work.
For intraplate regions such as Australia, identifying and quantifying activity on tectonic faults for inclusion in probabilistic seismic hazard assessments can be challenging due to the typically long return period for ground-rupturing earthquakes associated with these structures. Return periods of 10,000’s to 1,000,000’s of years mean that surface displacement evidence is prone to degradation through erosion and burial, and paleoseismological ‘trench’ excavations may not uncover geology old enough to reveal previous events. As a consequence, there is often little or no preserved evidence of past ground rupturing events on these structures. Rather than ignoring faults which show no evidence of neotectonic displacement, we present an alternative approach; in addition to considering active faults (movement in the last 35,000 years) and neotectonic faults (movement in the last 10 Myr) in seismic hazard assessments, we also consider faults which otherwise show no evidence of neotectonic activity but which are aligned favourably with the current stress regime and are therefore potential sources of earthquakes and accompanying strong ground motion.