RATING OF DAM SAFETY DEFECTS

Svenska Kraftnät (the central authority on dam safety in Sweden) in co-operation with Svensk Energi (the Swedish electricity production, transmission and distribution industry association) have established a proposal for a standardized rating scheme for dam safety defects. The system is intended to be utilized by dam owners in their own monitoring of dam safety in conjunction with activities such as dam safety evaluations (design reviews) and in-depth inspections. This system could furthermore be utilized to evaluate defects, malfunctions, and other changes detected outside regular monitoring activities. The scheme provides a common terminology that should, among other things, facilitate communications between various parties concerned with dam safety. This paper provides a description of the structure and utilization of the rating scheme. When observing a functional defect, the obvious question is whether it affects dam safety. The rating scheme is based on four established evaluation criteria: A – The extent to which the defect results in a discrepancy between the existing condition and the desired or intended condition, B – The importance of the component/subsystem for the proper performance of the dam, C – Frequency of loading, and D – Possibility to monitor the deterioration process and to take measures against progression to dam failure. Each of the evaluation criteria should be assessed according to 5-grade rating scales for each dam safety defect. The rating of a defect, based on A1-A5, is then combined with the supplementary criteria ratings, B1-B5, C1-C5 and D1-D5, to produce a dam safety rating BK1-BK5 (in Swedish; “BedömningsKlass”). The rating BK5 is the most serious from a dam safety point of view and BK1 the least serious. This scheme is to be utilized when evaluating defects related to a dam facility. Application instructions and guiding examples have been produced for this purpose. Full documentation of the scheme including application examples can be downloaded from the website www.svk.se. An evaluation of the rating scheme itself will be carried out in the winter of 2005, before the inspections of 2006 begin.