Barton Maher, Richard Rodd
Changes to the estimation of extreme rainfall events resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the dam to meet these new requirements, SEQWater (owner and operator) formed an Alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.
The option selected for the upgrade works included the construction of a new secondary spillway, upgrade of the existing gravity section, radial-gated spillway, and strengthening of the dam crest.
Value management was key throughout the project ensuring the Alliance was continually looking to
improve practices, increase cost-effectiveness and create innovative solutions for design elements of the project.
On numerous occasions when the design was challenged, the Alliance made ‘best for project’ decisions to carry out additional investigations or design work to pursue alternatives. As an example, the powerful tool of Computational Fluid Dynamics was used in the analysis and design of flow deflector plates on the existing spillway, which were an alternative to the originally designed gate locking pins. The investigation and development of this alternative resulted in significant cost savings and a more effective design solution.
This paper presents aspects of the design carried out by the Wivenhoe Alliance, lessons learned, and the way continual investigations during construction provided value for money solutions.
Robert Virtue, Deryk Forster, Jon Williams and Sabina Fahrner
Basic pre-construction foundation investigations for the Ross River Dam were done in the late ‘60s to early ‘70s but a more detailed hydrogeological assessment was carried out to investigate and manage water logging and salinity, which developed immediately downstream in the late 1970s.
As part of the 2005 Stage 2 to 5 upgrade design, detailed conceptual and numerical hydrogeological modelling was required to predict aquifer response along the embankment and downstream. This required “data mining” and additional drilling and aquifer testing to fill in data gaps, with the filtered and re-interpreted data used to build a 3D conceptual model of the embankment and underlying geology, by a design team comprising specialist hydrogeologists, geologists, geotechnical and damsengineers. This was converted to a 10-layer, 2-million cell numerical model, to enable high-resolution modelling of groundwater behaviour for a range of aquifer properties, flood hydrographs and seepage management options. As well as a design tool, the model is a valuable monitoring tool in confirming the performance of seepage management systems and to provide early warning of seepage management failures.
The study emphasised the need to capture data for a wide range in aquifer stress, to have simple preliminary spreadsheet models to provide a “sanity check” and to collect data away from the embankment to allow a 3D interpretation of the geology, to the assumption of “layer cake” models.
This paper presents a number of innovative hydrologic investigations undertaken for the recent
detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating
extreme floods in the tropics is the estimation of flood events of long critical durations. The
implication is that there is an increased focus on estimating the correct volume (not only the peak
flow). This paper describes the regional analysis of flow volumes that was used to validate the
estimated flood volumes.
Another issue of considerable importance is the assumed relationship between inflows and initial
reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works.
Jon Williams and Chi Fai Wan
The Ross River Dam was first commissioned in 1974 and raised in 1976. The 8200 m long embankment was not fitted with chimney filters and has suffered extensive desiccation cracking since it was raised. A significant component of the dam upgrade is the retrofitting of filter zones to ensure the embankment meets current dam safety guidelines.This paper describes the process of investigation of the existing desiccation cracks and the use of Hole Erosion Tests (HET) and No Erosion Filter (NEF) tests to validate the design of the retrofitted filter.
A significant challenge in the design is to provide a cost effective solution given the 7500 m length of embankment requiring treatment. Assessment of flow rates within cracks and expected piping erosion along the cracks was used to assess the required drainage capacity. This assessment of expected flow capacity allowed the deletion of the coarse filter inthe design reducing the filter requirement from a triple filter to a single fine filter. Results of this assessment were incorporated into the Risk Assessment based design validation process
Ian Cordery, Peter S. Cloke
Scientists advocate more hydrological monitoring but in most regions publicly funded monitoring is in
steady decline. The lack of measured data at dam sites means there are many designs for new dams and remedial work that are insufficiently supported by factual information. Unfortunately data –free modelling exercises will usually produce favourable results – favourable to the modeller’s purposes, but not necessarily favourable to the determination of physical reality or truth. In these days of the popularity of modelling it is common to find decisions being made based on model studies for which little or no local data were available for model calibration or verification. How can the ‘large dam’ fraternity encourage (ensure) more data use? Causes of lack of data are many. For example governments fund data collection but others need the data, and data collection is a long-term activity that produces few benefits in the short term. Some years ago it was shown that hydrological data collection and archiving provided benefits to the community of at least nine times the costs of the data.
The real costs of comprehensive data collection are not large but examples will be given of the huge
costs, mainly due to the need to allow for uncertainty, that result from unavailability of data. Those
who understand this problem need to explain it to their communities, politicians and CEOs in a clear,
unmistakably persuasive manner, and to demand an increase in data collection. If we do not, no one
Changes to the Regulatory and legal environment have resulted in an increased focus on the
importance of proficient management of dams. Operation and maintenance manuals are now a
Regulatory requirement in Tasmania for all but very low hazard dams and are also required to ensure that dams are managed efficiently and safely. To meet these requirements Hydro Tasmania has developed the ‘Smart’ operations and maintenance manual.
Hydro Tasmania has a large portfolio of dams and as a result requires a large number of operations and maintenance manuals. This would result in an overwhelming array of information that is subject to evolving change if the traditional approach to the manual was adopted. To overcome this burden, a controlled electronic manual was developed to enable:
• Critical operation and maintenance information to be collated with minimal effort;
• Electronic hyperlinks to key existing operation and maintenance documents, reference
materials, and portals into operational data bases; and
• A means of updating and controlling information that is subject to change.
This paper will discuss how Hydro Tasmania developed its user-friendly operation and maintenance manuals in an innovative, unique and controlled manner to ensure prudent management of dams and to comply with Regulatory change.