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Saturday, 21 Oct 2017

Näs hydropower plant

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Näs hydropower plant is situated in the Dalälven River about 110 kilometres upstream the outflows in the Baltic Sea. At 2007 a new earth fill embankment dam was built for safety reasons. The dam is about 155 meters long and has a height of about 12 meter.

 Installation

Fibre optic cables were installed inside the dam during the construction. Cables were installed on both sides of the impervious till and at several levels. By measuring temperature along the fibres the seepage in- and outflow can be detected.

Another fibre optic cable was installed in the crest in between the impervious till and the isolating material. This was made for the possibility to detect movements inside the dam.

Beyond the measurements of temperature and movement two geophysical methods, resistivity and self potential (SP) were installed in the new dam aiming detection of flow and material changes. These two installations have not yet been evaluated.

Result

Temperature data have been collected at different times in between the period of September 2007 and august 2008. A temperature interpolation between the measuring dots gives a vertical temperature profile of the upstream filter. The figure represents a measurement made the 17th of April 2008 when the reservoir water temperature is rising, which means that a higher temperature in the upstream filter indicates a higher seepage. Overall the temperature is almost constant in the upstream filter, but as can seen the temperature is a bit higher in chainage 0/118 at level +62,5 m, the right abutment and in the connection between the underground and the dam. These areas are indicating a slightly higher seepage.

Temperature data measured at different dates have been plotted for the cable at level +62,6 m in the upstream filter. As can see the temperature is homo¬genous along the dam except for dam chainage 0/118 where a temperature anomaly occurs and indicates a higher seepage. http://www.lwr.kth.se/Publikationer/PDF_Files/LWR_EX_08_21.pdf