Earthquake design of a dam and associated appurtenant structures is a key aspect of dam design in the modern era. This paper outlines the design process undertaken to address potential earthquake loading for the 32m high outlet tower to be constructed as part of the new Eurobodalla Southern Storage project on the NSW South Coast. The driver for the project is to provide increased water supply security to communities on the South Coast, an area that is currently serviced by a single reservoir and is subject to frequent water restrictions. Construction is planned to commence for the project in early 2021.
This paper presents the design methodology undertaken to meet the requirements for earthquake design and presents a novel defensive design solution to improve the reliability of the outlet works for post-earthquake operation. The Authors contend that utilising this approach in design of future outlet towers will provide a greater level of confidence in the ability to undertake intervening measures following a severe earthquake. Moreover, the technology has the potential to serve as a relatively inexpensive interim upgrade measure for existing outlet towers expected to sustain an unacceptable degree of damage under earthquake loading.
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 development of geological, engineering geological and geotechnical models is essential for all dams. These models provide the basis for understanding the engineering characteristics of foundation materials and geological structures that are critical to the safe design, construction and operation of the dam.
The use of digital three dimensional (3D) engineering geological modelling techniques is becoming more common for civil infrastructure projects. In addition to established design applications, 3D engineering geological models can be utilised by dam owners, operators and stakeholders for ongoing management of the dam.
The recent option studies at North Pine Dam in Brisbane, Australia, provides an example of collaboration between the owner (Seqwater) and the designer (GHD) to maximise the use of existing information and to enable future information to be efficiently integrated and utilised.
The initial North Pine Dam 3D engineering geological model was developed using historical records dating from the design and construction of the dam in the 1950’s and 1960’s. These records had been carefully stored, collated and digitised by the owner, so that they could be easily georeferenced and incorporated into the 3D engineering geological model.
The initial model was interrogated to identify data gaps and to plan targeted and cost-effective investigations that addressed critical geotechnical issues. The 3D engineering geological model was further refined using the newly acquired data, to develop a comprehensive “3D database” that can be used to visualise and interrogate all existing records as high- resolution georeferenced images and embedded data.
This provides an asset for the dam owner to maximise the use of existing information and reduce the cost of future safety reviews or design.
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.
Australasian and global need and demand for water resilience often changes reservoir use from single purpose to multipurpose. These changes are affecting existing dam and reservoir structures and operations, as well as those planned or under construction. The International Commission on Large Dams (ICOLD) recognised this issue and established a working group to investigate and prepare Bulletin 171 titled Multipurpose Water Storage “Essential Elements and Emerging Trends”, which is now and available on the ICOLD website.
The Bulletin’s scope was to provide a global view on the dynamics of multipurpose water schemes (MPWS) by presenting essential elements and emerging trends for planning and managing reservoir and dam infrastructure, with source data collected from 52 global case studies including five from New Zealand and two from Australia.
Water storage design and implementation has evolved significantly in recent decades, and further
development is expected as innovative approaches emerge in search of optimal sustainable solutions. The focus of Bulletin 171 is therefore not on what should be done, but rather what is being done, how, and by whom. Essential elements represent a recommended checklist for implementing MPWS storage, while emerging trends is a snapshot of the current state-of-the-art for MPWS projects.
This paper presents a summary of Bulletin 171 and its findings, and a brief overview of the new and
complementary ICOLD Committee ‘T’ which is assessing emerging challenges and needs for dams in the 21st century.
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.