Joseph Thomas, Peter Thomson, John Grimston, Sally Marx
The Waimea Basin is located in the South Island of New Zealand. The area has an acute water shortage with recent studies showing the water resources to be over-allocated by 22% for a 1 in 10 year drought security. The current area irrigated is about 3,700 ha and there is additional productive land that could potentially be irrigated if more water were available. Water users have suffered severe restrictions on their water use over recent years through drought management measures imposed to meet critical environmental flow requirements and coastal salinity buffering. This has caused significant production cutbacks for irrigated crops resulting in regional economic loss, affected major urban water supplies resulting in water supply cut-backs affecting domestic and industrial users and also affecting the important environmental values of the Wairoa/Waimea Rivers and the coastal springs that are highly valued by the community and local iwi (Maori).
The principal objective of this project is to carry out a study into the feasibility of water storage in the upper parts of the catchment for enhancing water availability for both consumptive and environmental/community/ aesthetic benefits downstream. The outcome from this feasibility study will provide the community with the necessary information to make an informed decision on proceeding with potential storage options. The Waimea Water Augmentation Committee is overseeing this feasibility study. The study will be completed byJune 2007.
The Waimea Plains area is also quite unique as to the interest and values relating to the water resource as it has multi stakeholder interest. Being close to urban centres, the water resource not only caters for irrigation use but also public water supplies as well as recreational, community interest and cultural values.
This paper sets out the project’s aim, general methodology being followed, and summarises the progress to June 2005.
Brian Simmons, Glen Hobbs, S Muralitharan, Udaya Peeligama
Warragamba Dam supplies up to 80% of Sydney’s water needs and is currently undergoing a range of major infrastructure upgrades. The outlet works upgrade is one of these projects. The outlet works of the dam were constructed in the 1950s and consisted of four 2100mm pipes with isolating gate valves and needle control valves feeding two large aboveground pipelines running 27 kilometres east to Prospect Reservoir in Sydney’s western suburbs.
In the 1990s the then dam owner (Sydney Water) undertook a detailed and extensive risk analysis of the outlet works. The study resulted in a recommendation to remove the existing valves and replace them with a combination of emergency closure (guard) valves and isolating valves. Under the Sydney Catchment Authority (the present dam owner) work subsequently proceeded in 2004 as a design and construct contract with all aspects of construction and water supply risks identified. Stringent controls were developed and placed on work programs and pipeline shutdowns to ensure the safety of all involved and the integrity of the supply to Sydney.
The four outlets required eight large valves, which were manufactured in Germany and were required to meet stringent operational requirements.At the time of writing three of the four outlets have been successfully upgraded and commissioned.Work has commenced on upgrading the fourth outlet, which is due for completion by the time of the conference, approximately 20 months ahead of schedule.
This paper discusses the project from the initiation of the risk analysis study, through the consideration of options, development of the contract, and the supply, installation and commissioning of the large valves and pipe work. It highlights the role of risk assessment in selection of the preferred option and addresses some of the engineering challenges faced during the project.
Construction of the Lake Buffalo Dam was completed in 1965. It was to be a temporary dam, required to operate for several years, then act as a cofferdam for the construction of a much larger dam downstream. This larger dam was never built and a risk assessment completed by Goulburn Murray Water (G-MW) in 2001 identified several dam safety deficiencies at Lake Buffalo were among the highest priorities for risk reduction measures across the G-MW dams portfolio. Specifically it identified Lake Buffalo as having inadequate flood capacity and there were also concerns about transverse cracking within the embankment.
This paper describes the detailed investigation and analysis of the embankment cracking including assessing the potential for piping through an embankment having deficient filters and known transverse cracking. The design features of the upgrade are also described including the design of the a filter buttress, a parapet wall raise, Computational Fluid Dynamics (CFD) modelling and spillway anchoring. Construction was completed in 2003.
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.
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.
A risk assessment was performed for the Sacramento District of the U.S. Army Corps of Engineers to explore the justification for imposing an operating restriction on Lake Success to reduce the
probability and consequences of an Earthquake-induced dam failure. The potential for both a sudden overtopping failure and a delayed “seepage erosion through cracks” failure were considered.
The risk assessment focused on the seismic performance of the dam, the potential life loss and
economic consequences of Earthquake-induced dam failure, and the estimated residual risk and
degree of risk-based justification for the Existing operating regime, a range of Potential Operating
Restrictions, and an Indicative Improved Warning and Evacuation System. Risk assessment inputs
were supported by seismic deformation analyses under various Earthquake loadings and pool
elevations, dam break-inundation modelling, and reservoir simulation.
Evaluations against tolerable risk guidelines from the USBR, ANCOLD, and the UK HSE, together
with insights into the relationship between pool elevation and dam failure risk, provided important
inputs for the decision to implement an operating restriction.