Page - 1113 - in Book of Full Papers - Symposium Hydro Engineering

for all water-retaining structures and safety-critical appurtenant components of such an installation, including lateral embankments or dams within the storage area. Present structural, hydraulic, hydrogeological, geological, steel-structural and process control technology state of all above components require an assessment, as well as implemented surveillance and maintenance practices. If necessary, based on actual scientific and technical state of knowledge, improvements are recommended and may be set into practice. Two case studies of multi-technical in-depth safety assessments for run-of- river hydropower plants along the Aar river are presented in this paper. 2. LEGAL FRAMEWORK FOR THE IN-DEPTH SAFETY ASSESSMENT OF WATER-RETAINING INSTALLATIONS ALONG THE AAR RIVER The Aar river with its 295 km is the longest river that both rises and ends entirely in Switzerland by descending 1’845 m from the Swiss Alps to its junction with the Rhine river. There are more than 20 hydropower plants along its course (Fig.1). The Enforcement Guideline of Dam Safety Legislation specifically referring to the construction and operation of large run-of-river hydropower plants along the Aar river was published in 2015 [1] and covers 11 hydropower plants under the direct supervision of the SFOE. The scope of the Enforcement Guideline is to clarify and practically-deepen the legislation of water-retaining installations and to supplement the dam safety guidelines [2, 3] specifically for these types of installations in order to accomplish the in-depth safety assessment. The methodology can also be adopted to smaller installations, which are not directly SFOE-supervised but by direct supervision of the cantons. The in-depth safety assessment end-product is a report which contains multi- technical chapters based on specific qualitative and quantitative evaluations as stepwise presented in the following paragraphs. 1113