Page - 1116 - in Book of Full Papers - Symposium Hydro Engineering

accordance with the Enforcement Guideline, all water-retaining and safety-critical appurtenant structures of the installation are inspected and evaluated, which include: - Structural inspection of the weir, powerhouse and gates - Geological inspection: foundation, lateral embankments or dams and potential slope instabilities within the storage area, natural hazards and groundwater - State of the monitoring instrumentation and safety-critical appurtenant structures such as drives, control technology, power supply and emergency diesel generators. 3.3. INSTRUMENTATION AND MONITORING PROGRAM The aim is to assess whether the existing monitoring instrumentation is adequate for the facility. As there are no binding rules on the required type and number of instruments, the judgment is left to an experienced engineer. For both plants, the deformation monitoring relies mainly on geodetic measurements. It was checked that sufficient monitoring points are available, the points are situated well distributed over the plant and that sufficient fix points are available on both abutments and at appropriate distance from the structures to be monitored. The number of fix points shall guarantee a redundancy in case a fix point is lost e.g. due to construction works. In Ruppoldingen, piezometers are installed under the weir and the powerhouse. As a result of the assessment, it was recommended to consider the installation of additional piezometers in the right abutment to monitor a possible flow around the weir and underlying sheet pile wall through the abutment. In Flumenthal currently no piezometers are available. Based on conservative structural stability calculations, it was assessed whether this state can be further tolerated or the installation of piezometers must be recommended to monitor the uplift pressure for both the weir and the powerhouse. For both plants, the water level monitoring instruments are assessed as complete, with redundant measurements of the head and tail water levels with both, automatic readings and staff gauges. This is considered as a basic installation for any run-of-river plant. The instrumentation monitoring is complemented with regular bathymetric surveys which focalize in the downstream area on potential scouring of the weir’s stilling basin, in the upstream area on possible sediment depositions. With these surveys and with regular opening of the weir gates for checking its functionality it is ensured that the gates can be opened anytime required. In addition to the instrumentation array installed, the frequency of the measurements and treatment of the read values was evaluated. It was concluded that the implemented procedures including the back-up of the data is well organized. 1116