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Saturday, 21 Oct 2017

Temperature

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Seepage Monitoring and Internal Erosion Detection Using Temperature

Temperature measurements for seepage monitoring is gaining rapid acceptance in order to investigate the seepage flow in embankment dams. This method has been used successfully especially in Sweden, where HydroResearch has introduced and improved the required method including the evaluation procedure. Temperature measurements have successfully been used in more than 30 Swedish dams since 1987, both for limited monitoring/investigations and for long-term monitoring. The method is now recommended in the Swedish Guidelines for dam monitoring. One of the key tools for the measurement of temperature is the introduction of fibre optic distributed temperature measurements that started in 1998.

The seepage monitoring method uses the natural seasonal temperature variations that occur in all surface water (such as lakes, reservoirs and rivers). The seepage flow causes a seasonal temperature variation inside the dam. This seasonal temperature variation can be measured in the dam and used to evaluate the seepage flow through the dam. Temperature measurements can detect seepage flow changes, i.e. internal erosion.

The fundamentals for the methods are:

  • - Seasonal temperature variation in the water creates seasonal temperature variation inside the dam.
  • - Larger seasonal temperature variations and shorter time lag between the temperature in the water and inside the dam indicate higher seepage.
  • - Increasing seepage causes increased annual temperature variation, and shorter time lag between the temperature in the water and inside the dam

Generally, a constant temperature will be a sign of a small seepage, while large seasonal variations may be sign of significant seepage. At increasing seepage flows the temperature in the dam will be changed, and the seasonal variation will increase. This variation is dependent on seepage flow, the seasonal variation at the inflow boundary, and the distance from the boundary to the measuring point.

Evaluation can made by FEM simulations of the temperature field, or by using DamTemp software, which provides a more efficient way of seepage evaluation, appropriate for most dam applications.