Michael Bassett-Foss , David Bouma , Dewi Knappstein
The Wairarapa Water Use Project (WWUP) in the southern North Island, New Zealand, is investigating new water storage schemes involving large dams that will allow the community to make use of the water resources that are currently available, but not necessarily available at the time they are needed. It is estimated that the 12,000 hectares currently irrigated in the Wairarapa could be increased to about 42,000 hectares depending on actual demand. The WWUP provides for a range of possible needs, such as supply of new areas of irrigation, increased reliability for existing irrigation and frost fighting, environmental augmentation of low summer river flows, environmental flushing flows, stock drinking water, power generation, municipal water supply, and recreational use.
WWUP objectives include early engagement of stakeholders, early integration of financial, social, cultural and environmental factors in decision-making, management of uncertainty associated with the preliminary level of investigation and evolving regulatory framework, development of an equitable framework for efficiently comparing options, and balancing long and short-term considerations.
A large number of dam options were identified, storing 3 to 80 million m3 of water, and progressively narrowed to a shortlist of 2 sites through a complex process of concept development, desktop studies, site visits, hydrological analyses, cost estimates and multi-criteria analyses.
The WWUP demonstrates how sustainable new major water storage schemes can be promoted in a highly regulated environment of a developed nation.
Keywords: Dams, water storage, stakeholder engagement, environment, water allocation, multi-criteria analysis
Dr Andy Hughes
Tailings dams continue to undergo failures at an unacceptable rate compared to water storage dams, including failures at operations owned by high profile mining companies.Tailings dams have often a different form and method of construction than water storage dams in that tailings dams continue to be raised over time as part of the mine operations and rise to considerable heights. These failures are often the result of a combination of design, construction and operations actions that are controlled by humans and must be better coordinated and managed in the future. The consequence of failure can be widespread flows of tailings and water over the landscape and water courses. This can have extreme consequences in terms of life loss, environmental damage, social license to operate, company value, and mining industry sustainability. Therefore,it is necessary that the mining industry strive for zero failures of tailings facilities. Any additional technology and information that enables an owner of a tailings dam to be more certain of its condition and thereby reduce the risk of failure is of tremendous value to reliable tailings and mine water management.The Willowstick method uses low voltage, low amperage, and alternating electrical current to directly energise the groundwater by way of electrodes placed in wells or in contact with seepage or leaks. This approach has been successfully used to identify water flow paths through, under and around tailings dam in plan and elevation.The Willowstick technology provides additional information to supplement the geological, geotechnical and hydrological, evaluations analyses and designs, and to further improve tailings dam safety by more robust designs if necessary. This paper, using several tailings dam case studies, illustrates the procedure, findings, and the benefits of the Willowstick methodology. The findings of many Willowstick surveys range from tailings dams where the methodology has confirmed the design evaluations, to tailings dams where new groundwater and leakage flow paths were identified. In the latter case, the dam designers were able to update the designs, based on the new information,to mitigate the identified risks and to improve the overall safety of the tailings dams in accordance with the goal of zero failure.
Legislation specifically addressing dam safety was passed into law by the New Zealand Government on 12 August 2004 as part of the Building Act 2004.
Government, local authorities, and the dam industry have debated the need for specific dam safety legislation in New Zealand since the late 1980’s. The previous legislative framework addressing dam safety in New Zealand included civil law, the Resource Management Act 1991 and the Building Act 1991. The provisions regarding dam safety within this legislation were implied rather than specific.
In 2001, as part of the Building Act Review, various government departments reviewed current dam safety regimes in New Zealand. One of the objectives was to address issues related to lack of clarity with regard to regulatory responsibility and inconsistency in the application of the current law. The New Zealand Society on Large Dams (NZSOLD) along with owners and Local Government representatives has participated in this process. The following paper is an update on the progress of dam safety legislation, outlining the evolution and structure of the dam safety provisions within the new Act. Some brief comparisons are also made to current Australian legislation.
Mark Pearse, Peter Hill
Risk assessments for large dams and the design of upgrades are often dependent on estimates of peak inflows and outflows well beyond those observed in the historic record. The flood frequencies are therefore simulated using rainfall-runoff models and design rainfalls. The recent update of Australian Rainfall and Runoff (ARR) has revised the design rainfalls used to model floods that are of interest to dam owners. This will change the best estimate of flood frequencies for some dams. However, for most dams the impact of revised design rainfalls on flood frequencies is small compared to other factors that can change (independent of dam upgrades). These include model re-calibrations to larger floods, changes to operating procedures that affect the drawdown distribution and improvements in how the joint probabilities of flood causing factors are simulated. In this paper, we look at how the design flood frequencies for some of Australia’s large dams have changed, the reasons for this and then identify five key questions for dam owners to ask to aid assessment of whether the hydrology for a dam should be reviewed
There are many international guidelines, state regulations and technical standards relating to tailings disposal. In addition, the larger mining companies have their own in-house standards and design rules with competent personnel in charge of their operations. Sound embankment design methods can be used by most designers familiar with earth dam design.
The paper gives a listing of many of the current sources of information and guidance available, with some comments by the author on their perceived relevance to the Australian mining industry. Despite the availability of a number of other guidelines at the time, the need for Australian Guidelines was recognised in the mid 1990s and the reasons for the development of the 1999 ANCOLD Tailings Guideline are explained.
Perhaps the best recognition of the need for the original ANCOLD guideline is the degree to which it has been adopted since publishing the 1999 edition. It is in almost universal use in the Australian mining industry and is recognised as providing appropriate and acceptable standards by all state governments. Its use is recognised and sometimes even specified by a number of neighbouring countries and it is also recognised internationally when used by Australian companies with overseas operations.
The reasons for this wide acceptance are described. However, there are some areas where more recent developments have led to the Guidelines becoming dated and improved international guidelines have been published since 1999. The need for a revised ANCOLD guideline and its elevance is then described.
Keywords: Tailings, dams, mining, guidelines