Klavže na Idrijci (Water barriers on Idrijca river) (KA2 Erasmus+ project Roots)

KLAVŽE
The Klavže – water barriers! Wood was an essential resource for the mine’s activities. In order to ensure safety in the mine, the tunnels had to be supported with wood beams. The mining equipment and tools were made from wood, as was the hoist. Wood was also used as fuel in heap smelting of mercury ore.
The mine’s administrators opted for felling of trees along the Idrijca, Belca and Zala, later also along the Kanomljica creeks.
A special rake mechanism was built in the Idrijca stream in Idrija. Wood obtained along the banks of the creeks was floated on the water, which carried it to Idrija, where it was caught in the rake. The wood was then lifted from the river and taken to the Lenštat depot, which supplied the mine and the smelting plant. The mine’s administrators also established a special forestry management service that was put in charge of felling and reforestation.
This was one of the first examples of forest management in the Slovenian lands. The predicament was overcome in the early 17th century with the construction of dams made of wood, stone and soil. The dams had a special opening that was closed with a large door. The dams were closed to allow water to build up.
Around a quarter of a million cubic metres of water accumulated behind each barrier. When enough water accumulated and enough wood had been floated, the door was opened to allow the water to carry the wood to Idrija (up to 30 km away). The first klavže were built predominantly of wood. The frames lasted for around 50 years before rotting caused them to fall apart. In order to reduce costs associated with their building, the mine decided in the late 18th century to construct all klavže using stone. Jožef Mrak led the efforts to build stone klavže. His constructions were so solid that they still exist today. The klavže were in use all until 1926.
The biggest of all the preserved klavže is that on the Idrijca river. It was built in 1772 and had walls of average breadth of 10.8 metres. The breadth at the base was 18 metres. The dam spans 41.4 metres and is about 15 metres high. The structure has two openings of size 3.8 by 5.6 metres through which water flowed when the barriers were lifted. In the second half of the 1980s Soške elektrarne electric company below the klavže water barrier built a dam for the accumulation lake; it is used for its small hydro power plant.