Following the failure of Paloona Dam’s intake trashrack during the 2016 floods in northern Tasmania, a replacement trashrack and support structure was designed, manufactured and installed (by diver) within five months. This was a remarkable feat and hailed as a success at the time.
The euphoria, however, was short lived. A routine dive inspection in January 2018 revealed cracked
trashrack bars on one of the panels and this was after less than twelve months’ operation. This prompted a rigorous investigation where it was determined that the bars suffered fatigue due to flow induced vibration. Indeed it is possible that the bars cracked within a few weeks of returning to service.
The science of flow induced vibration is relatively mature, having been extensively researched over several decades. Its application to trashracks is well documented. However, this experience has shown that the common design approach overly simplifies the fluid-structure interaction. For Paloona, the result was a trashrack design which has proven to be inadequate, not having the resilience required for a dam outlet works component.
This paper revisits flow induced vibration theory as it pertains to trashracks, outlines the findings of vibration testing at Paloona, and suggests a design approach which will avoid similar issues. It is hoped that similar failures can be prevented and the design life expected of trashracks achieved.
A new operating arrangement at Hume Dam is being developed to improve the transition from flood operations to the release of water set aside for delivering environmental flow demands. The arrangement also aims to help manage inherent downstream flood risks associated with this transition and with the requirement to fill the storage.
This paper describes particular flood risks and environmental impacts resulting from the current approach required to meet asset and water resource security priorities during airspace management operations at Hume Dam. It then considers how the new environmental demands have interacted with long-standing operating objectives and airspace management during high inflow periods in ways that have altered the dam operations required to meet operating priorities and manage flood risks.
Critically, requests by environmental managers to start releases can arise sooner and with greater uncertainty compared with releases for meeting irrigation demand following a period of flood operations or airspace management. This difference has led to a more rapid storage filling curve to maximise water resource during periods when inflow rates remain relatively high and catchments are still responsive to rainfall.
The paper details how the new operating arrangement provides greater volumes and more flexible flood mitigation airspace using a discretionary volume of ‘held’ environmental water without otherwise impacting on the flood operations decision-making process. A number of challenges in defining the potential level of benefit and risk, and in understanding trade-offs were faced in negotiating the arrangement. However, the successful development of the approach and agreement to trial it were ultimately achieved by framing the issue as an opportunity to adjust dam operations in a way that seeks mutual benefits for dam operators and environmental managers.
Full adoption of the arrangement would result in greater airspace flexibility during flood operations to better manage risks without affecting water resource. Simultaneously, it provides environmental benefit due to changes in the pattern of releases during the transition period from flood operations to the commencement of environmental water releases as well as during the pre-spill release period.
Failure modes of seepage and internal erosion have been identified as one of the key issues for the
ongoing safety of dams and canals in New Zealand. Accordingly, many dams and canals have had
improvement works carried out to mitigate this issue. This paper examines the long-term performance of these measures including three case studies. It is concluded that the performance of these measures has been variable, but ongoing monitoring and periodic review has identified deterioration in performance. There are a number of technical areas where uncertainties on long-term performance may still remain, such as geotextiles in important filter functions and waterstops of various types.
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.
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.
New Zealand’s economy is heavily dependent on export revenues generated by primary industries such as dairy, meat, agriculture, horticulture and viticulture. For these sectors, securing water for irrigation has been a key factor for growth. New Zealand has a temperate climate with generally wet winters and dry summers. The availability of water in the dry summer period is very important for these sectors to maximise production. A considerable amount of investment has already been made in the construction and operation of reservoirs for irrigation purposes. However, because climate change effects (more frequent occurrences of extreme events such as droughts and flash floods) have been observed around the world and the need for restrictions imposed on the use of water resources by regulators for environmental reasons, the need for developing water storage reservoirs has become more essential than ever. Climate change effects are already being factored into current practice. Drawing on the author’s experience, this paper discusses the potential impacts of climate change, with an emphasis on the effects of drought, on the design, construction and operation of water storage facilities with changes necessary to improve the resilience of new dams in
response to climate change. The paper also aims at raising awareness among the farming community so they can appreciate the associated risks and issues with climate change and be more cautious about planning and budgeting for their future investments in dam and irrigation projects.