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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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.
Luke Toombes and Rob Ayre
Many large dams are built as multi-purpose structures, providing both flood mitigation and bulk water storage, but requiring a trade-off in functionality between those purposes. In response to the Millennium Drought (2001 to 2009) closely followed by devastating floods in 2011, the State of Queensland initiated a comprehensive review of the operation of its flood mitigation dams. Part of this study involved development of an Integrated Assessment Methodology to provide an informed and unbiased assessment of the competing factors affecting dam operations. The methodology assessed the primary variables of flood damage and other impacts, future bulk water infrastructure and water security requirements in the form of a net present cost/benefit. The study concluded that modification of the dam flood release strategy to reduce flood damage during large events would come at the expense of increased frequency of minor flooding, or vice versa, with minimal net benefit. Similarly, reducing bulk water storage to increase flood mitigation would increase water supply costs by a similar magnitude to the flood damage prevented.
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.
Lyndon Johnson and Jamie Campbell
Data presentation is an important and much discussed aspect of Dam and asset safety worldwide. We rely on drawings and graphs of instrumentation data to tell us things about our assets that are hidden from the eye and to monitor changes linked to failure modes. It’s common that we look at data gaps for our assets, data quality and data processing but how often do we rethink the fundamentals of data presentation?
Engineers and data analysts, as humans, have evolved in a 3D world with our senses to match match. According to Keller GB, et al (2012) almost 20% of the human brain is dedicated to processing vision with up to 60% involved when locating, scaling and referencing objects in 3D space. As a result, 3D is an extremely efficient platform from which to display and disseminate information.
This paper discusses methods to efficiently transfer asset information into 3D and how to present animated surveillance data against asset models. The paper discusses how these methods work, benefits and limitations in the context of modern dam asset portfolio management and presents some key case studies of where and how these methods have assisted with asset diagnoses.
This paper outlines lessons learned from 8 years of regular operations and testing of 111 gates at 22 sites. It points out that the implementation challenges involved are not only technological in nature, but also encompass human factor and organizational issues. This is perhaps understandable since the initiative is part of the cultural shift to sustain gate reliability long-term.
An increase in gate testing frequency has led to the identification of more performance anomalies, ranging from deficiencies to operational failures. This finding may not be unique to a single dam owner. It leads to the following question to the general dam owner community: Are we testing our gates enough?