Richard Herweynen, Robert Montalvo, John Ager
The choice of materials used in the construction of a dam is one of the most critical decisions in the design process. Our natural behaviour as engineers is to adopt materials which have proven performance, and which conform to Australian or international standards, which sometimes causes us to overlook the specific conditions and demands of the project at hand. In an environment where the majority of concrete produced is for structural purposes, the properties of these concretes is often vastly different to those desired for mass concrete structures such as dams and spillways.
The big question at Wyaralong Dam was could onsite aggregate be used in the Roller Compacted Concrete (RCC)? The Wyaralong Dam is located in the Gatton Sandstone (early Jurassic), predominantly feldspathic to lithic‐feldspathic sandstones with a clay matrix. Early analyses and tests suggested that the Gatton Sandstone was not suitable for RCC aggregate due to a 68% wet/dry strength reduction, high water absorption (5.2 – 7.5%) and petrographic interpretation that clay content was mainly swelling clay, leading to durability concerns.
Due to significant community, safety and cost issues with importing aggregate, Wyaralong Dam Alliance (WDA), during the development of the RCC mix design for Wyaralong Dam, chose to pursue the use of onsite quarried sandstone aggregate instead of importing aggregate. Additional petrographic and XRD analyses and extensive durability tests were undertaken on cores of sandstone and RCC samples, including wet‐dry cycles, soak tests in ethylene glycol, soaks in sodium hydroxide, and heating and cooling cycles. These tests indicated that, if swelling clays are present, they do not impact the durability behavior of the RCC aggregate.
The substantial effort put into testing the sandstone aggregate has paid off for WDA. Not only have the results indicated that the RCC mix performs remarkably well in terms of durability, but the very low modulus of elasticity of the mix has provided exceptional performance in terms of thermal loading; with all the related benefits in reduced restrictions to placement schedule and cooling requirements. Onsite sandstone was not only proven to be a feasible option, it has been demonstrated that it is the best option for the project. Details of the study are provided in this paper.
Keywords: Roller Compacted Concrete (RCC), Sandstone, Aggregate, Clay, Mix, Durability
Monique de Moel, A/Professor Jayantha Kodikara, Dr Gamini Adikari
All embankment dams have some seepage as the impounded water seeks paths of least resistance through the dam and its foundation. Seepage must, however, be controlled to prevent internal erosion of the embankment or foundation and avoid damage to surrounding structures. Embankment dams are designed to operate under controlled steady state seepage, which over time may change due to movement in the foundation and the dam, chemical actions and other forms of deterioration. Effective monitoring of seepage within embankment dams is therefore essential in regards to management of dam safety and prevention of failure.
Traditional methods of seepage monitoring have involved measurement or visual monitoring on the downstream side of the dam after the seepage has occurred. Effective, early detection of seepage in embankment dams has been difficult as it originates and develops in the subsurface. Infrared Thermal Imaging is such a technique that is non-contact, non-intrusive, simple and flexible. The analysis draws on the temperature behaviour and the heat capacity of materials within the body of the dam and consequently allows the user to identify and isolate temperature variations along the surface of interest. This paper describes the method, application and feasibility of infrared thermal imaging for the detection of seepage in earth and rockfill embankment dams. The value of this technique as an additional tool in the surveillance of dams is discussed.
Infrared thermal imaging has been in use in other fields of engineering for condition monitoring and defect detection of structures. It has shown great potential in identifying variations in surface characteristics, which may not be evident through visual inspection alone. In this paper, reliability of this technique for seepage detection in embankment dams has been analysed using 8 case studies in order to arrive at a fair understanding of the best conditions under which Infrared Thermal Imaging field inspections should be carried out. The results of field investigations undertaken at these dams suggest that Infrared Thermal Imaging is a useful and effective tool for detection of seepage and an aid in identifying seepage behaviour.
Keywords: Seepage Detection, Infrared Thermal Imaging, Dam Surveillance, Monitoring
An essential criterion for any new dam project in Australia is to provide for passage of fish past the structure in both the upstream and downstream direction. In recent projects with a relatively high barrier this has been provided by mechanised systems such as locks, lifts or a combination of both.
A nature-like fishway provides for passage of fish past a barrier by applying some of the features of natural streams. The concept has been increasingly applied to fishway designs in North America and Europe. A nature-like fishway will provide variable flow depths, velocities and turbulence across its width and along its length and is constructed using natural materials to simulate the natural stream characteristics. The variable flow conditions coupled with the use of natural materials inherently result in different channel substrates that support the passage of a large range and size of fish species as well as other aquatic species. Where fish habitat has been depleted, a nature-like fishway can also supplement and enhance aquatic habitat.
The performance of nature-like fishways can be difficult to quantify due the very nature of the system. However, qualitative assessments in North America are indicating that a wide range of species are using such fishways and that fish species that were previously extirpated from rivers are again migrating.
The nature-like fishway concept has been applied to in-stream structures up to four metres high in the eastern states of Australia. However, the substantial progress made with this design in North America and Europe has not as yet been applied in this country.
This paper analyses the advantages and disadvantages of nature-like fishways over mechanised systems, such as locks and lifts, and makes an assessment of the suitability of the concept to dams in Australia with relatively high walls.
After a period of drought for many years, inflows during May and June 2009 resulted in releases from North Pine Dam. These releases resulted in deaths of fish downstream of the dam wall including lungfish. The Australian Lungfish is a protected species under the Environmental Protection and Biodiversity Conservation Act 1999 (Australian Government). The events of 2009 have shown, however, that a proactive response supported by sound knowledge is required to minimise lungfish losses from flood events and other dam operations activities. A framework has been developed for the management of lungfish populations in Seqwater storages. The framework centres on a Seqwater Fish Management Policy, and four broad strategies that are considered necessary for addressing fish management in Seqwater storages: Fish Management, Storage Operations, Communication, and Research. These strategies are being used as a basis for identifying, planning and managing a range of actions designed to ensure that impacts to lungfish are minimised. Seqwater intends to develop the framework further to include long term management initiatives such as implementing viable technologies for preventing lungfish strandings, habitat protection and restoration activities that support viable lungfish populations, as well as establishing priorities for managing risks to other aquatic vertebrates in Seqwater storages, including other protected species, recreationally and commercially important species; e.g. turtles , carp, mullet, etc.
M. Tooley, N. Anderson, N. Vitharana, G. McNally, C. Johnson and D. Moore
There is a significant stock of aging concrete dams in Australia which would not meet the requirements of the current recognised dam safety practices applicable to concrete gravity dams.
In this paper, field and laboratory investigations undertaken for two concrete gravity dams are presented, these being Middle River Dam and Warren Dam both owned and operated by the South Australian Water Corporation. The field investigations included a comprehensive drilling program recovering core samples ranging in diameter from 61mm (HQ) to 95mm (4C), continuous imaging (RAAX) of the drilled holes and installation of piezometers. Geological logging of the holes and mapping of the unlined spillway were also undertaken. The laboratory program included the testing of concrete lift joints and concrete samples in direct tension, shear and compression.
Concrete in Middle River Dam is suffering from extensive Alkali Aggregate Reaction (AAR), and consequently a suite of laboratory testing is being undertaken to determine the current level of deterioration and residual reactivity so that potential future AAR-induced expansion can be incorporated into any upgrade design solution.
The main purpose of the study is to determine whether site-specific parameters can be used to re-assess the stability of these two dams as calculations, based on the current standards, have shown that the dams have exceeded the allowable factors of safety values at the storage water levels experienced to date.
The findings may be useful to dam designers and owners faced with the upgrading of concrete dams, where traditional assumptions can result in no upgrade or an upgrade costing several million dollars.
Aric Torreyson, Krey Price, Bob Hall
In a 2004 feasibility study, the U.S. Army Corps of Engineers (Corps) and Ventura County Watershed Protection District (VCWPD) recommended decommissioning Matilija Dam, a concrete arch dam originally constructed to a 60-metre height in 1948. A decade after its completion, the United States Bureau of Reclamation (USBR) constructed the Ventura River Project, comprising additional facilities designed to meet the growing water demand of Ventura County. Robles Diversion Dam, a 7-metre high by 160-metre long diversion structure located downstream of Matilija Dam, was built under the Ventura River Project to feed Lake Casitas, a water supply reservoir that serves as an integral part of the overall project.
Due to extreme sedimentation, Matilija Dam no longer serves its intended water supply and flood control purposes. In addition to the loss of storage capacity, other issues surround the dam, including adverse environmental impacts from its continued operation, seismic considerations, and structural concerns. These concerns led to the decision to decommission the dam as an essential step in rehabilitating key ecosystems in the Ventura River Catchment and reducing future risks to public safety. According to current estimates, 5 million cubic metres of sediment has accumulated behind the dam and will need to be removed in conjunction with the dam decommissioning; minimising the associated downstream impacts has been the subject of additional government studies.
The USBR determined through detailed hydrologic, hydraulic, and sediment transport analyses, including numerical and physical modelling, that the existing Robles Diversion Dam was not capable of passing the increased sediment load expected to result from the removal of Matilija Dam. To increase the sediment transport capacity across its spillway, the existing diversion dam requires modification. Under contract with the Corps, Tetra Tech and its subcontractors are completing the design plans for the Robles Diversion Dam modifications.
This paper presents unique aspects of the Robles Diversion Dam modifications, including sediment management procedures guided by numerical and physical model results and issues associated with the design of a rock ramp spillway and high-flow fishway, expansion of the existing spillway gate structure, and raising of the dam embankment. The rehabilitation efforts reduce impacts to the migration of endangered fish species and allow for the eventual removal of Matilija Dam, which is the ultimate goal in the effort to balance engineered structures with a natural river setting. When completed, the project will provide fish passage to the upper catchment for the first time in over sixty years.