500 years of mining in Idrija Mercury Mine needed vast quantities of timber for mine architecture, supporting pillars, machines, smelting ore, Idrija inhabitants supply etc. So forestry was besides the mining of substantial importance. Town of Idrija lies in hilly region surrounded by vast forests. So dams were made on rivers Belca and Idrijca for timber transport all the way to town of Idrija. Nearby reachable forests were cut early, or were on very steep terrain, so the most practical was to tansport timber on waterways from forests far away. Klavže were made to dam water lakes, timber was piled in the lake, later to be released and water was driven timber downstream in town Idrija on river rakes, where timber was caught and pulled out the water to be used. First Klavže were built in 16th century, but were too dependent on rainfall and high waters. Around year 1770 monumental Klavže were built out of brick, stone and mortar, mechanisms enabled that only pair of oxen were enough to lift or close the dam barriers, also in extreme weather conditions. The biggest Klavže were Master Mrak's Klavže, where river Idrijca formed 800 metre long lake that could drive some 10000 m3 of timber at the time, downstream to Idrija 20km away. It has been calculated that river Idrijca carried approximately 3,600.000 m3 of fuel wood and 300.000 m3 of pit wood and round timber. The transportation of timber via rivers ended in year 1926, after catastrophic floods that took away rakes in Lenštat in the center of Idrija. Being klavžar - dam operator was very responsible, but also highly valued position among people. Models of Klavže and Lenštat rakes made by Janko Trošt can be seen in Idrija Municipal Museum. Due to huge stone structures some people call Klavže also Slovenian pyramids.
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