Eric Lesleighter, Erik Bollaert
Abstract: Many of the dams in Australia, and other countries, are potentially unprotected from the occurrence of extreme floods which would discharge either over the dam and/or the abutments due to inadequate spillway capacity.
The paper commences with the presentation of the evaluation procedure that has been applied by the first author for a number of dams in Queensland, initially with a detailed description of dams, the original hydraulics studies, the current hydrology, and the geological information. The procedure then comprises analysis of the extreme flood hydraulics and an erodibility assessment which leads to an estimate of the possible erosion of the rock for a range of flood magnitudes. A description of the components of the final evaluation and the typical conclusions is presented with reference to the Julius Dam in Queensland.
The paper includes a description of an alternative or complementary procedure that comes from the work of the second author. Comparison is made with the Comprehensive Scour Model (CSM) developed by Bollaert (2002, 2004). This model is physically based and allows estimating scour formation in rock or concrete as a function of time duration of discharge. The model compares the resistance against fracturing of concrete or rock layers with the hydrodynamic pressure fluctuations exerted by a turbulent aerated jet impacting in the plunge area. Once the fracture network is formed, dynamic uplift of single rock or concrete blocks in computed. Based on fracture mechanics and air-water hydrodynamics, a detailed time-evolution of scour formation is obtained. The model is generally used for projects involving plunge pool floors, ski-jump spillways, fractured rock and so on, where sufficient data are available on both rock quality and duration and intensity of spill from the dam. In the present paper, the CSM has been used to model scour of non-overflow abutment sections when there is overtopping flows.
Keywords: dams, spillways, extreme floods, rock scour, erosion, dam safety
Andrew Shields, Dr Mark Bailey, Graeme Hannan
Abstract: In recent years, water resources have declined markedly under the effects of long-term drought and climate change. Resource planning has turned from a process of routine allocation to the specialised management of a limited and highly valued commodity. Probabilistic outlooks of water availability based on historical inflows have proven an important component of the drought communication strategies used by Goulburn-Murray Water. In turn, Goulburn-Murray Water has examined alternative means of securing additional water for its customers, including revised operating criteria and pumping from the dead storage of its dams.
With the focus on meeting essential domestic water needs and boosting irrigation supplies, Goulburn-Murray Water has used the opportunity afforded by water levels to review the capacity of its storages. The regular, but unwelcome, outcome of reduced storage capacities from these studies, and the predictions of continuing drought, present Goulburn-Murray Water and its customers with an ongoing challenge.
Keywords: water resources, allocation outlook, capacity table, dead storage, resource position
Jeffrey A. Schaefer
Abstract: The U.S. Army Corps of Engineers (USACE) has numerous dams built on limestone foundations that are susceptible to solutioning (karst). Significant dam safety issues related to the karst foundation have developed in many of these projects. Screening risk assessments of the USACE portfolio of dams has shown that defects related to karst foundations is one of the largest contributors to our risk. To better evaluate this risk, a method to estimate the probability of failure from piping into karst foundations has been developed by team of experts from the University of New South Wales, URS, the US Bureau of Reclamation, the US Army Corps of Engineers. This paper summarizes the major failure modes associated with dams on karst foundations and the methodology developed to perform risk analysis. A summary of USACE case histories with karst foundation issues and recent projects to remediate the foundations are also included.
KEYWORDS: Dam, Seepage, Karst, Solution Feature, Risk
Abstract: Recent studies in SE Queensland for existing and proposed dams and other flood studies have highlighted a number of issues with respect to the design event approach in deriving and applying design rainfalls to calibrated runoff routing models.
The estimation of design rainfall depths for frequent to large events is usually done by the intensity-frequent-durations (IFD) methods outlined in Australian Rainfall and Runoff (AR&R) or CRC-Forge.
The design temporal patterns applied to these rainfall depths are critical in the estimation of design floods as are the adopted loss rates.
This paper describes the methods used to derive the design rainfall and some of the issues which arose in their application in the design event approach to assessing design floods. It uses examples at several locations in studies undertaken by SunWater and refers to similar issues encountered in other studies.
Implications for flood studies are outlined.
Keywords: design rainfall, design floods, CRC-FORGE, IFD, temporal patterns, SunWater, Queensland.
Brunner Wolfgang G, Bi Arthur, Chang William, Zong Dung Feng
ABSTRACT: In the South of the Sichuan province the 240 MW Yeleh hydroelectric power project is under construction by Sichuan Nanya River Basin Hydraulic Power Development Company Limited, a state-owned enterprise, and China Gezhou Ba Water & Power Group Company Ltd.. This project sets out to develop the mountain cascade of the Nanya river, a tributary of the Dadu River, provide superior electricity and adjust flood peak and frequency. The specialist contractor Foundation Engineering Company of China Water Resource and Hydropower (FEC) was awarded the contract of foundation treatment at the right bank, which included the construction of a 75 m deep concrete cut-off wall inside a 6.0 m x 6.5 m tunnel. The requirement for 19 317 m3 cut-off wall to be constructed in permeable and very dense gravel/cobble formations and a demanding project program led FEC to adopt the BAUER Low Headroom Cutter CBC25/MBC30 in conjunction with the overlap cutter joint.
Keywords: hydroelectric project, dam, dam tunnel, cut-off wall, trench cutter
Abstract: A number of SunWater’s dams are in the process of being upgraded to the acceptable flood capacity (AFC) to ensure the highest level of safety. The Fred Haigh Dam upgrade was completed in September 2006 and the Bjelke Petersen Dam upgrade was completed in October 2007. Borumba Dam is the latest upgrade being undertaken with construction commencing in April 2008 and is expected to be completed by December 2008. Each dam underwent a comprehensive risk assessment to identify and evaluate all risks with respect to the ANCOLD tolerability limits to ensure risks satisfied ALARP. The assessment identified the most cost effective upgrade solutions for detailed design.
The upgrade at Fred Haigh, Bjelke Petersen and Borumba Dams will enable them to pass an extreme flood equivalent to 50% of the Acceptable Flood Capacity (AFC). This is Stage 1 of a two stage upgrade to ultimately achieve 100% of the ANCOLD “Fallback” AFC which is the standard SunWater has adopted for its major dams. SunWater has prioritised spillway capacity upgrades to achieve a minimum dam portfolio standard of passing 50% Acceptable Flood Capacity inflow by 2015 and full Acceptable Flood Capacity inflow by 2025.
The most economic Stage 1 upgrade option for Fred Haigh, Bjelke Petersen and Borumba Dams was to maintain the existing spillway width and to raise the dam crest with a concrete parapet wall. For the Bjelke Petersen and Borumba Dams the spillway training wall heights were raised to allow for increased flow though the spillway. From the hydraulic model studies and flood routing a height of each different dam crest wall was obtained.
This paper will describe the different methods and considerations used for upgrading Fred Haigh, Bjelke Petersen and Borumba Dams to the 50% AFC.
Keywords: dam safety, spillway, Fred Haigh Dam, Bjelke Petersen Dam, Borumba Dam, SunWater, Queensland.