FIBRE INSTALLED IN THE CORE OF THE LÖVÖN DAM DURING DAM REPAIR WORK
Two sinkholes have occurred in the dam and during the summer of 1998 the upper part of the dam was repaired along about 80m. Two optical fibre loops were then installed to measure the temperature upstream, above and downstream from the core. The optical fibres are located on eight levels (see figure 3). The first measurements were carried out from mid November 1998 to mid February 1999 using a different company’s DTS. In 2004 once the Sentinel DTS was available a second measurement was made.
igure 2: Temperatures in the estimated saturated part of the dam at EL 273.8m to 276m in 1999 (solid line) and in 2004 (dotted line). Measurements indicate concentrated seepage at 0/028, and between 0/045 and 0/060m.
This project was carried out by HydroResearch using Sensornet’s technology. The embankment dam at Lövön was built between 1972 and 1973 and has a total length of 1500m, and a height of 25m. Leakage water cannot be collected and measured by conventional leakage systems, due to a high downstream water level.
The measurements using the sentinel dts has an accuracy ten times better and are also much more stable and reliable than the system used in 1998. Measurements were made during six days and showed that a relative accuracy better than 0.1ºc, can be achieved. Calculated temperature trends (in the order of 0.01ºc/day) agree well with those obtained from the very accurate vibrating wire temperature sensors. Evaluation using damtemp (a software developed by hydroresearch with support from the dam safety interest group) and based on short-time dts measurements and continuous temperature measurements in temperature sensors indicated maximum seepage flow rates about 20-30 ml/(s,m).
A concentrated seepage flow about 0.05 l/s was detected at chainage 0/028. A wider seepage area was also detected between chainage 0/045 and 0/060 with total flow of about 0.5 l/s.
Figure 3: Installation of fibre in dam
To discuss your particular requirements please contact Sensornet or visit HydroResearch at www.hydroresearch.se or call them on +46 8 756 4950.