Page - 1255 - in Book of Full Papers - Symposium Hydro Engineering

arises about the degree of dam and construction site safety during remedial works. Relevant dam safety can be usually achieved only through the significant reservoir level drawdown providing sufficient volume to trap potential flood arriving to the reservoir during construction period. The drawdown temporarily harms reservoir purposes like water supply, recreation, hydropower production etc. This study contains careful examination of aspects and requirements related to the dam safety during its reconstruction. The discussion on the proportion between individual purposes and benefits of the dam is also carried out. The experience with safety analysis during dam reconstruction is mentioned together with the method used. Practical examples demonstrate individual potential conflicts entering into analysis. 2. THE DEGREE OF DAM SAFETY DURING ITS RECONSTRUCTION The safety issues during the reconstruction of the dam concern two aspects: − the protection of the construction site during the flood; − dam safety against its total collapse usually due to water erosion. 2.1. THE PROTECTION OF THE CONSTRUCTION SITE The construction site protection concerns individual workplaces like spillway, chute, stilling basin, upstream slope lining, dam crest etc. In a view of safety rate these parts should be assessed individually. Some of them like repair of the dam crest or spillway directly relate to overall dam safety (Section 2.2). For other structures not influencing overall safety of the dam some guidance is given by [3]. As a rule cost-benefit analysis has to be performed in case of the threat of significant losses, terms of construction site insurance against floods should be taken into account too. Guidelines in [3] applied in the Czech Republic recommend the following return period N of the flood for preliminary construction site protection: 𝑁 =𝑇 +1, [1] where T is duration of the construction in years. 2.2. THE SAFETY AGAINST THE DAM FAILURE The safety of the dam against its collapse during the remedial works should be assessed considering: − current dam safety; − potential material losses due to dam break flood; − potential loss of life. 1255