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.
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.
Suraj Neupane, Paul Southcott, and Tung Hoang
Conglomerate Dam has multiple cracks along the asbestos cement outlet conduits running through the embankment. The reservoir level has been maintained at 2m below the full supply level to reduce the amount of seepage, emerging on the downstream face, until the conduits are repaired and protect the embankment from slope instability and piping. Several methods were investigated under an options study to determine the most suitable internal lining method. Slip lining with polyethylene pipe was found to be the most suitable method in terms of technology as well as cost.
Stephen Newman, Rod Jacobs, and Dr John Yeates
Independence Group (IGO) is assessing the feasibility of re-commissioning a closed copper-zinc mine in Victoria. Due to the acid producing potential of the mine tailings if exposed to oxygen they are to be contained in a saturated condition not only during the life of the mine but well beyond closure and effectively in perpetuity. The tailings are to be stored in a saturated condition underground in the mining void however due to the limited volume available approximately half of the tailings produced over the mine life will require containment in a purpose built surface Tailings Storage Facility that would need to perform as a water retaining structure.
This paper describes key challenges with tailings management including demonstrating the viability of maintaining permanent saturation of the tailings and the long term integrity of the structure. Excessive poor quality seepage, piping and other failure modes have also been considered in the long term design of the closed Tailings Storage Facility. A surveillance program to provide early identification of potential issues has also been developed.
The design is consistent with ANCOLD guidelines and used a risk based approach to assess key issues associated with the extended design life.
Wark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
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.