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.
R. Dawson, J. Grimston, R. Cole, D. Bouma
The authors have been involved in the design and construction of several embankment dams in New Zealand over the past decade, and have considerable corporate knowledge from dams designed by the company in its 47-year history. This paper examines four dams which are relatively small to medium, ranging in height from 10 to 19 m with moderate storage volumes. Three of the dams service landfills and the fourth a wood processing mill. Such dams may provide the designer with considerable challenges due to their relatively low capital cost resulting in limited investment in geotechnical investigation at the front end of the project, with varying levels of change often required during construction due to unforeseen conditions as a result of the limited investigations.
The general arrangement and conceptual design principles for each of the dams is described followed by the field investigation and laboratory testing undertaken for each dam, together with the interpreted ground conditions.
The experiences from construction have helped to develop techniques for a balance between preliminary design, investigation, and evolution of the design and specification during construction. It is imperative to develop a sufficiently detailed preliminary design, on the basis of readily available information such as visual and geological assessment, to allow the investigation to be thoughtfully designed to allow the major assumptions to be verified. This needs to be followed by a skilfully executed geotechnical investigation with the designer advising on findings and changing direction as necessary through the investigation. An investigation trench along the full alignment of the cutoff trench (if envisaged in the design) is warranted. Earthworks specifications should be evolved early in the construction phase through compaction trials using specific plant for the site, and backed up by insitu and laboratory testing.
Resource consents for Christchurch’s existing solid waste disposal facility at Burwood expire in May 2005 and the landfill must close. A new, state-of-the-art regional landfill is under construction at Kate Valley, which will accept solid waste from Christchurch and surrounding districts. Investigations and studies for the landfill have attracted considerable public attention, engaging public groups in discussions through resource consent hearings in 2002 and 2003.
The proposed landfill includes two embankment dams in a cascade arrangement below the landfill. The first is a 19m high sedimentation dam designed to retain silt runoff from the earthworks associated with landfill construction and operation, protecting the health of the stream and environment below the dam. The second is a 9m high dam performing dual roles of storing and supplying water for the landfill earthworks activities, and providing an additional safety buffer for silt control and containment of any accidental release of leachate at the landfill.
While the dams are relatively modest in size, they are being built to very high standards with strict peer review as a result of their association with the landfill project, and to minimise any community and environmental impacts. The design and construction of the landfill and dams is being completed using an innovative modified alliancing arrangement which provides the close working relationship that alliances are renowned for, while minimising up-front financial risk to the owner.
This paper deals with key aspects related to the landfill dams, such as community consultation and expectations, environmental impacts as well as the technical features. Construction is underway for the dams and the landfill at the time of writing of this paper.
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.
The Wai-iti Valley is located in the northern region of New Zealand’s South Island. Water demand during summer in the Wai-iti Valley is greater than the available supply, resulting in water allocation restrictions and pressure on in-stream habitat and uses. Further, the summer water resource in the Wai-iti Catchment is currently over-allocated. Thus, since the mid 1980s, Tasman District Council (TDC) has been unable to grant new water permits to take water from either rivers or
groundwater in the Wai-iti Catchment. Existing water permit quotas have been reduced where they were not being used, but despite this agricultural, horticultural and domestic use is frequently restricted during dry years.
Recently, the need for a community solution was identified for the Wai-iti Valley area. The Wai-iti Water Augmentation Committee (comprising representatives from the local community and TDC) was set up in 1995 to find the best option for the northernmost extent of the Wai-iti valley. A feasibility study for a community dam was completed in 2001 identifying small off-river storage dams as options. The proposed scheme is located in a tributary of the Wai-iti River and is essentially a water harvesting project where winter flows in the stream would be impounded and stored, and gradually released on a regular basis back into the stream and Wai-iti River system during dry summer periods.
The paper will cover the project’s economic objectives as well as community and environmental impacts and the consenting process under the Resource Management Act. Dam construction is planned to start in October 2004.