A brief overview of dam surveillance is given from a South African perspective and more specifically the perspective of the Department of Water Affairs and Forestry (DWAF). DWAF’s Ten Commandments for the design of dam monitoring systems serve as introduction and this is followed by a summary of the design steps. The various parameters that can be measured and the South African preferences are discussed briefly followed by a synoptic description of crack and joint monitoring in South Africa. This provides the background for DWAF’s recent developments in 3-D Crack-Tilt gauges. Some of DWAF’s achievements as well as some of the blunders made by the author during the past 30 years are illustrated by means of a few case histories.
We can all learn by our mistakes and the experience of others. This paper seeks to look at three
incidents/accidents which recently occurred in the UK so that others can learn from them. The
paper then seeks to answer the question as to whether we are improving in looking after our dams
in the UK in respect of reservoir safety.
In Austria, special procedures for ensuring dam safety apply to dams higher than 15 m or reservoirs with a capacity of more than 500,000 m³. There are at present about 90 dams which belong to this category. The largest one is the 200 m high Kölnbrein arch dam.
In general, it is the task of the dam owner to provide for the safety of a dam. For that, he has to appoint qualified engineers, the “Dam Safety Engineers”, which are in charge of dam surveillance and maintenance. The Water Authority verifies that the owner makes the necessary provisions for dam safety. Water Authorities are the Provincial Governor and the Federal Minister of Agriculture and Forestry. The Water Authorities are supported by a governmental advisory board, the “Austrian Commission on Dams”.
Projects for new dams or for reconstruction of existing dams are examined by the Austrian Commission on Dams. Approval by the Water Authority is based on the findings of this commission. A group of a few experts of the commission accompanies the project during construction, first impounding and the final acceptance procedure. In normal operation, dam attendants carry out visual inspections and measurements. The most important instruments are measured automatically and the data are transmitted to a permanently manned control centre. The Dam Safety Engineer has to inspect the dam at least once a year. His annual report to the Water Authorities must contain an assessment of the safety of the dam. The Federal Dam Supervisory Department of the ministry checks the annual reports and carries out an in-depth inspection of the dam at least every five years.
In the case of extraordinary events, the Dam Safety Engineer has to assess the situation and he has to set appropriate measures. An Emergency Action Plan is available for all dams of the said category.
C Lake and J Walker
Meridian Energy is the owner and operator of a chain of hydro dams on the Waitaki River in the South Island of NZ. It operates a Dam Safety Assurance Programme which reflects current best practice; consequently it has focused primarily on managing civil dam assets. Advances in plant control technology have allowed de-manning of our power stations, dams and canals through centralised control. The safety of our hydraulic structures is increasingly reliant on the performance of Dam Safety Critical Plant (DSCP) – those items of plant (eg water level monitoring, gates, their power and control systems, and sump pumps) which are required to operate automatically, or under operator control, to assure safety of the hydraulic structures in all reasonably foreseeable circumstances.
Recent dam safety reviews have highlighted that the specification and testing of our DSCP is based on the application of ‘rules of thumb’ which have been established through engineering practice (eg. “monthly tests”, “third level of protection”, “backup power sources”, “triple voted floats”). The adequacy of these engineering practices is difficult to defend as they are not based on published criteria. The realisation that such rules may not be relevant to the increased demand on, and complexity of, DSCP led us to ask “Which belts and braces do we really need?”
The current NZSOLD (2000) and ANCOLD (2003) Dam Safety guidelines give little guidance regarding specific criteria for the design and operation of DSCP. Meridian has identified the use of Functional Safety standards (from the Process industry, defined in IEC 61511) as a tool which can be applied to the dams industry to review the risks to the hydraulic structures, the demands on the DSCP, and utilise corporate “tolerable risk” definitions to establish the reliability requirements (Safety Integrity Levels) of each protection, and determine lifecycle criteria for the design, operation, testing, maintenance, and review of those protections.
This paper outlines the background to identifying Functional Safety as a suitable tool for this purpose, and the practical application of Functional Safety Analysis to Meridian’s DSCP.
G. L. Sills, N. D. Vroman, J. B. Dunbar, R. E. Wahl
In August 2005, Hurricane Katrina made landfall just east of New Orleans and inflicted widespread damage on the Hurricane Protection System (HPS) for southeast Louisiana. Subsequent flooding was a major catastrophe for the region and the Nation.
The response to this disaster by the U.S. Army Corps of Engineers included forming an Interagency
Performance Evaluation Taskforce (IPET) to study the response of the system and, among many lines of inquiry, to identify causes of failure of levees and floodwalls.
Beginning in September 2005, the IPET gathered geotechnical forensic data from failed portions of levees and floodwalls. Major clues discovered at the 17th Street break, including clay wedges dividing a formerly continuous layer of peat, led to an explanation of the failures. Field data from the failure sites were interpreted within the regional geologic setting of the New Orleans area to identify geologic and geotechnical factors that contributed to the catastrophe. The data gathered provided a method that resulted in the “IPET Strength Model.” This strength was used in analyses of the I-walls and levees using limit equilibrium stability analyses, physical modeling using a powerful centrifuge, and finite-element analyses.
The results of all three types of studies revealed a consistent mode of failure that included deformation of the I-walls and foundation instability. The IPET also studied non-failed I-walls at Orleans and Michoud Canals, to identify geotechnical, structural, and geologic distinctions between failed and non-failed reaches.
Performance of the HPS during Hurricane Katrina offered many lessons to be learned. These lessons learned include: the lack of resiliency in the HPS; the need for risk-based planning and design approach; the need for the examination of system-wide functionality; and knowledge, technology, and expertise deficiencies in the HPS arena. In addition, understanding of the failure mechanisms and related causes of the levee and floodwall breaches provides a new direction for future designs of hurricane protection systems.