Tim Gillon and Grant Murray
Chelsea Estate is located on the edge of the Waitemata Harbour, and is only ten minutes drive from Auckland central business district. Within Chelsea Estate are four ‘low’ potential impact classification (PIC) dams, which cascade along Duck Creek. Three of the dams are over 100 years old and all dams were built from 1884 to 1917. The dams and the reservoirs have served, and continue to serve, several purposes including stormwater retention, recreational use and water supply for the adjacent sugar factory. In 2008 Auckland Council (AC) purchased the Chelsea Estate from the New Zealand Sugar Company (NZSC) and in 2009 the Estate was registered in the New Zealand Historic Places Trust (NZHPT). This paper discusses the history and functionality of the multi-function Chelsea Estate dams, the development of the site and how it impacts our understanding of the dams today.
Keywords: Chelsea Estate, multi-function dams, heritage dams.
Now showing 1-12 of 36 2977:
Kinchant Dam is a zoned earth and rockfill embankment situated on the north branch of Sandy Creek, approximately 30 km southwest of Mackay in central Queensland. Kinchant Dam was constructed in stages. The ‘Initial Development Stage’ which consisted of an embankment length of approximately 3.3 km and full supply level (FSL) of EL 49.21 m AHD was completed in 1977. Further development completed in 1986 (Stage I) increased the FSL to EL 57.21 m AHD with an embankment length of 5.5 km and a maximum embankment height of 22.3 m. The dam has a storage capacity of 62,800 Ml and a 60 m wide emergency spillway with a fixed crest level of EL 58.21 m AHD, one metre higher than the FSL.
A series of investigations have been carried out since its construction as a consequence of both regulatory safety reviews and observed excessive pore pressures within the foundation that have led to wet patches developing at the toe of the dam. In one area at the toe, pore pressures were such that artesian conditions developed. This paper outlines the history of various stages of construction of the dam, the foundation investigations since construction and the safety review and comprehensive risk assessment process that lead to the upgrade design and construction of remedial works. The remedial works include the extension of the downstream filter material adjacent to the clay core and the provision of additional pressure relief wells at the downstream toe of the dam.
Lyndon Johnson, Alan White and Chris Topham
The integrity of foundation drainage systems is a key factor in minimising uplift pressures under concrete gravity dams. Contemporary industry practice for foundation drainage systems (and modern criteria presented in the imminent release of the concrete gravity dam guidelines) will lead owners with older concrete dams to consider enlarging foundation drainage systems via borehole drilling in the foundation. This paper presents the cautionary tale of a dam owner that undertook foundation drilling works in the gallery of a 67-m high concrete gravity arch dam and experienced borehole “blowout” in one of the drilled holes. Water under 90% of full reservoir head issued from the borehole and needed to be controlled. The context of the works is presented, followed by a description of the blowout, the risk mitigation measures that were planned prior to the work, and which ultimately had to be initiated. Management of the incident is discussed, including the use of blowout protection collars and valves, subsequent investigatory drilling, and pressure grouting programme. Dam safety concerns associated with the incident and their management are presented. The paper concludes with some recommendations to manage these risks for other owners considering a drilling programme in a concrete dam foundation.
Jeong Yeul, Lim
For various historical reasons and some technical reasons, the safety of dams has been evaluated using an engineering standards-based approach, which was developed over many years. It was used initially for the design of new dams, but increasingly has been applied over the past few decades to assess the safety of existing dams. Some countries have carried out risk assessments of existing dams that included both the structural and hydraulic safety of the dam and social risk. These methods developed by other countries could be adapted to assist in decision-making for dam safety management. Unfortunately, methods for risk assessment of dams were not established in Korea. This study outlines a beginning risk analysis for structural safety management. The first stage consisted of research on the present domestic dam safety guidelines and reviewing operations for management systems of dam safety abroad. Also, dam risk analysis requires reliable data on dam failure, past construction history and management records of existing dams. A suitable risk analysis method of dams for structural safety management in Korea is use of event tree, fault tree and conditioning indexes methods. A pilot risk assessment was carried out for two dams. The dam risk assessment process was thus established, and we learned the importance of risk assessment. The future includes additional research and risk analysis to develop the system.
As the Panama Canal is upgraded to accommodate larger vessels, hydrological and ecological elements of the project are being closely monitored, along with the effects of the increased usage that is projected to accompany the upgrade when it opens to traffic in 2015. Each of the 14,000 ships that annually pass through the Panama Canal requires 200 ML of fresh water – drawn from Gatun Lake and other Chagres River reservoirs – to navigate through the locks. The reliability of a sustainable water supply is thus vital to the canal’s operation and, by extension, to the world’s economy.
Hydrologic, hydraulic, and sedimentation studies are providing baseline data for comparison with projected operational scenarios. Several projects are currently being undertaken to restore and protect the widely recognised and highly valued biodiversity within Gatun Lake’s catchment area. Efforts to promote biodiversity conservation during the construction and operation of the expansion project are being coordinated with the concurrent efforts of a variety of academic, scientific, and private institutions, including the Smithsonian Tropical Research Institute, which is located on the largest island in Gatun Lake.
This paper examines the implications of growth and expansion on Gatun Dam and Lake. Current studies are assessing the impacts of deforestation on sedimentation and temporal flow distribution into Gatun Lake. Methodologies and results are presented for the USAID-funded Panama Canal Watershed Biodiversity Conservation Project, an undertaking that engages public and private sector partners in an effort to improve the management and conservation of critical areas through the implementation of sustainable practices and engagement of local stakeholders.
John Duder, David Bouma and Paul McCallum
The authors have been involved in the safety inspection and remediation of many older (pre-dating the 2004 Building Act) farm dams over the past decade coupled with considerable corporate knowledge from dams inspected by Tonkin & Taylor Ltd in its 50+ year history. This paper presents a summary of the varied benefits and risks of these older dams and the difficulties encountered in bringing them into alignment with current practice.
The many farm dams around New Zealand provide considerable benefit to the owners and often to the environment and wider community including the obvious stock water and irrigation, but also micro hydro, recreation, flood detention, release of environmental flows and flows for downstream users, and wetland habitat.
However, when applying current dam safety practice, and looking forward to the implementation of the Dam Safety Regulations, some of the older farm dams have significant dam safety issues that are often challenging to address. Although there is a high degree of variability, typical issues include:
Little or no documentation of geotechnical investigations, design or construction,
Design standards, particularly for spillway capacity have generally increased,
Little or no formal surveillance or maintenance carried out or recorded since commissioning,
Many farm dam owners have a poor understanding of their obligations under the Building Act and the Conditions of their Resource consents,
Consent conditions may not require dam safety related monitoring and maintenance, and/or the conditions may not have been historically enforced.
Many of these farm dams have been constructed by small contractors at the request of the farmers, often with only “standardised” engineering design and little specific geotechnical investigation. Typically there are no as-built records and the dam owners have been left with a general lack of understanding of owner’s responsibilities to monitor and maintain the dam.
Given that there are often very limited funds available for upgrade work, it has proved important to apply sound engineering judgement and a high degree of pragmatism to realise the greatest possible reduction in dam safety related risk for the available funds. Good cooperation between the Regional Authority, the Building Consent Authority for dams (often they are different organisations), the dam owner, and the dam engineer, together with a pragmatic approach is vital in moving toward current best practice for management of these dams.
Case studies are presented for the Northland Region, where the farm dams are typically homogenous earth fill dams in the order of 8 to 12 m high, fulfilling functions as irrigation, stock water supply, recreation and flood detention structures. The findings are considered relevant to earth fill farm dams across the country.