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Saturday, 21 Oct 2017

Vässinkoski Dam

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Seepage Evaluation from one single temperature Measurement

Installations in Vässinkoski Dam

The Vässinkoski embankment dam was built in the 1960’s and is owned by Fortum Energy. The dam is 1300m long and 25m high. In order to monitor the seepage flow of the Vässinkoski earthfill dam an optical fibre cable was installed along the downstream dam toe passing just under the drainage system of the dam.

The main purpose of this installation is to complete the seepage monitoring data set provided by conventional monitoring techniques.

Measurements and Result

Due to the nature of the local seasonal water temperature fluctuations, the gathered data would ideally be applicable for a long-term monitoring program to I nvestigate and quantify the seepage flow across the dam. However, valuable information can also be achieved after only the first measurement – this was performed in March 2006 using Sensornet’s Sentinel DTS. A total of 17 one-hour long measurements sessions were carried out to guarantee the optimal accuracy of the measurements. The system showed a reliable accuracy of ca. 0.05ºC. The measurements indicated temperatures varying between -2.0 and 4.8ºC with an average temperature of 2.5ºC. The lowest temperatures were recorded at the highest points of the dam. At three measurement points temperature values of below 0ºC were recorded. Although no water flow would be feasible in such low temperatures, especially at these points where the steep slope of the drainage channel prevents any water flow, these cold temperatures would only suggest the impact of the air surface temperature on the measurement system.

The West dam is 76m high. A support toe berm was constructed in 2004-2005 which includes a fibre optic cable. This cable has been installed at various elevations along the length of the downstream toe to provide a good quality seepage measurement.

This result agrees well with the measured flow rates, varying within a typical annual range of 1.5 to 15l/s. Based on this initial measurement it was concluded that the seepage flow in the dam was normal and no major water-leakage was detected. This also agrees with results obtained from surveillance of the dam and from conventional seepage flow measurements.