This is the first of the inspection galleries and the only one open to the public. Along the length of the gallery we may contemplate several devices used by the technicians to take readings on the proper functioning of the dam. These devices include:
Red cabinets for measuring temperature. The technicians plugged a thermometer into the cabinet to obtain a reading from the thermometers in the dam. The listening points were installed at strategic places during the construction of the dam to enable these measurements to be taken. It was highly important to know the temperature of the concrete expansion blocks. There are some five hundred measuring devices in the dam.
Expansion joint. The internal and external joints must be measured with a device called a manometer. A needle shows the size of the gap between each block, which may become wider or narrower. In winter, for example, the cold makes them contract, creating very small openings between the blocks.
The other hole is to see whether the blocks have moved, as one may be displaced in relation to another. These internal and external joints measure thousandths of a millimetre. These readings of apertures and movement are taken every 15 days.
Load bearing tests. At this point we can explain the test process for load bearing of a dam. Once built - in this case it was completed in February, when the cold weather makes the blocks shrink and the gaps between them expand - concrete was injected under pressure to seal each block with those around it. When all the blocks had been treated in this way, the dam could be filled. This was not done at once but by stages, filling and draining while observing response. The process began after its inauguration, in 1976. In the case of Baells, this process took four years, depending on the rainfall at the time.
Drainage shafts These are sloping shafts running along all the galleries. They were set 5 metres apart when the dam was already built. They are used for visual observation of water filtering, as any water in the structure would emerge from these holes.
