Phillip Jordan, Alan Seed, Rory Nathan, Peter Hill, Eva Kordomenidi, Clive Pierce, Michael Leonard
This paper discusses the stochastic framework that was used to generate the 5449 sets of inflow hydrographs, to develop and stress test a dam operations model. The stochastic simulations were driven by 600 different space-time patterns of rainfall generated using a stochastic space-time multiplicative cascade model. Eight significant storms were identified in the radar archive to identify parameter sets for the stochastic generation algorithm and 600 replicates of space-time rainfall were generated. The statistical properties of spatial patterns of 48-hour rainfall bursts on eight major subcatchments of the Brisbane River catchment from the 600 stochastic replicates were verified against the same statistics derived from 38 major flood causing rainfall events observed in the catchment. The hydrographs were generated using an URBS rainfall runoff routing model of the Brisbane River catchment, which was calibrated to 38 historical flood events (between 1955 and 2013) and tested on a further 10 historical flood events (between 1887 and 1947).
The stochastically simulated sets of inflow hydrographs were then used to assess the impact of variations in flood operation rules for Wivenhoe and Somerset dams. The stochastically generated events exhibit substantial variability in runoff hydrographs but with variability that is statistically consistent with observed events. The stochastically generated hydrographs provide a considerably more realistic basis for testing the outcomes for different flood operations strategies than the single design event approaches that have previously been adopted.
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Peter F Foster and Peter K Silvester
Clyde Dam, the largest concrete gravity dam in New Zealand, was constructed in the 1980’s on the Clutha River in New Zealand. Lake Dunstan, which is the reservoir formed by the dam, reached its full operating level in 1993, some 21 years ago.
This paper summarises the performance of the dam over this period, the changes in operations that have been undertaken and looks to future challenges. The performance and management of the landslides around Lake Dunstan that were remediated prior to lake filling is outlined. The large floods experienced in the Clutha River in the 1990’s highlighted aspects of the flood management procedures that needed amending to capture lessons learned and some modifications to appurtenant structures have been completed. Changes to the environmental management in moving from water rights to consent conditions under the Resource Management Act are addressed.
Over the last 21 years a sediment delta has progressed down Lake Dunstan, as expected, and a long term sediment management plan has been developed for both Lake Dunstan and Lake Roxburgh which is downstream of Clyde Dam. A summary of the plan is discussed. The seismic hazard at the dam site is currently under study to update the seismic assessment parameters for the dam.
Peter Allen and Kevin Bartlett
One of the recommendations of the Queensland Flood Commission of Inquiry was for the introduction of a legislative requirement for all referable dams in Queensland to have Emergency Action Plans (EAPs) formally approved by the Dam Safety Regulator. Prior to this EAPs were required under the dam safety conditions applied to each referable dam and they were not formally approved. This recommendation has now been implemented as a requirement of the Water Supply (Safety and Reliability) Act 2008. This paper summarizes the emergency action planning system now applicable to Queensland’s referable dams and details the actions involved in implementing this system. It involves significant consultation between dam owners and local disaster managers and gives local disaster managers an opportunity to formally comment on EAPs prior to them being submitted for approval. Development of associated regulatory guidelines to cover all aspects of EAPs was done in order to make EAPs more consistent and more readily understood by users and other stakeholders in emergency situations. Once the guidelines had been developed, the Regulator undertook a state-wide series of seminars to raise the level of awareness of local disaster management groups and dam owners of the new requirements. The legislation also requires the publication of the approved EAPs on the department’s website to raise the public’s awareness of the risks involved and improve their responses in advance of emergency events. This represents a challenge from a public relations perspective because people will become more aware of the risks to which they are exposed. The paper summarises the Regulator’s experience in reviewing and considering the EAPs submitted for approval and it indicates some of the benefits and challenges of the ongoing program.
Gavan Hunter, David Jeffery and Chris Kelly
Laanecoorie Reservoir, located in central Victoria, passed 3 significant floods in late 2010 to early 2011; the last flood being the highest on record since 1909. Significant cracking and deformation of this 100 year old puddle core earthfill embankment occurred. A series of longitudinal cracks up to 25 mm in width opened up in the crest over a length of 70 m and crest settlements were up to 70 mm; very large for a dam of this age. A significant difference at Laanecoorie compared to other similar dams is that it experiences high tail water levels during major flooding.
Investigations into the embankment following the January 2011 flood encountered several defects
including a decomposed tree root hole (large void up to 90 mm) that almost fully penetrated the raised section of puddle core, permeable gravel layers within the puddle core and transverse cracks up to 2 mm wide. The encountered defects and performance of the embankment many years after construction highlighted the deterioration that can occur with aging of these older embankments and the issues associated with poor past practices in tree management adjacent to dam embankments.
Dam safety upgrade works were undertaken in 2013 to address the identified piping and stability risks.
The works included construction of a filter buttress, replacement of a length of the raised puddle core and construction of a buried gabion wall on the left abutment to provide protection against scour should the secondary spillway fail or overtop.
GMW implemented a series of actions during the flood events in accordance with the Dam Safety
Emergency Plan (DSEP) to address cracking and deformation. Once aware of the dam safety risks, interim actions were implemented including increased frequency of monitoring, together with set up and measurement of crack pins, and temporary survey markers on the embankment.
Behrooz Ghahreman Nejad
In recent years, dam designers have become increasingly interested in application of the geomembrane sealing systems (GSS) in design of tailings storage facilities around the world. The main reasons for this have been the deformation characteristics, environmental aspects (ie seepage minimisation), speed of construction and constructability of geomembrane liners in most climatic conditions. This paper reports the design and application of two types of geomembrane sealing system in Angas Zinc (AZ) and Sarcheshmeh Copper (SC) tailings dams. The former is a 25m high zoned earthfill embankment with an HDPE liner system, located in an environmentally sensitive site in South Australia. The latter is a 94m high zoned rockfill embankment with a PVC liner system, located in a region of high seismicity in central Iran.
The designs of the AZ and SC geomembrane sealing systems including geomembrane liner, drainage layer, anchoring, leak detection system and drains, and instrumentations are discussed in detail. The performance of the liner systems during operation is also presented.
Robert Kingsland, Andy Noble and Dr Eric Lam
Engineering design is necessarily context specific. However, engineering design produced in industrialised nations often comes encumbered with design methods, standards and construction process familiarities that can result in inappropriate design solutions for developing nations. This is no more apparent than with the design of small hydropower projects where budgets are small and the implications of poor decisions can easily threaten the viability of schemes.
In this paper we explore the challenges and opportunities for the scheme’s developer and designer, in striking an appropriate balance on engineering solutions that remain appropriate for the local construction practices. In most cases, based on our experiences from small, run-of-river developments, the available methods for feasibility study data collection, including geotechnical investigations and hydrology assessments, are in themselves a challenge. Consequently, the designer needs to work with what is readily available and often has to reset the established thinking to incorporate practical constructability into the designs, while giving special attention to the operation and maintenance aspects. More labour-intensive methods are not uncommon.
The stakeholders in small hydropower schemes are many: the community, the approval agencies, the lenders, the developers, the local construction industry, the government. Design decisions cannot be made in a vacuum. However, designers are often distant from the social, political, environmental and commercial context of their project. This separation can present significant challenges which, without due attention, can result in poor design outcomes.
This paper will, with reference to examples of good and poor design, discuss various facets of small hydropower development from a civil engineering perspective including, the scale of development, design methods, stakeholder engagement, local content involvement, constructability and financing. The paper concludes with suggestions for improving design outcomes for small hydropower projects.