In terms of production capacity, the most important way of obtaining drinking water is by natural (riverbank) filtration. Unless it is made of concrete, the channel of a river always leaks some of the flowing water into its banks and bed, and this then seeps down to supplement the groundwater reserves. This is the process by which water flows to 659 abstraction wells, which are located along a 30 km stretch of the Jizera at an average of 250 m from its banks. The river water purification process that occurs here in the gravel and sand layers of alluvial deposits is precisely what we simulate in water treatment plants by using sand filtration, but here it happens naturally.
This system for collecting infiltrated water from the Jizera is also used by other treatment plants, not just Káraný. The water from the wells is fed to the Káraný plant via a system of siphons and intake pipes, where the total length of the intake line is 16.25 km and it crosses the Jizera River four times along the way. This natural filtration system gives us drinking water at a rate of around 900–1,000 l/s.
Since the very beginning , the Káraný treatment plant’s technical equipment has been continuously upgraded, often requiring extensive building modifications. Originally it pumped water to Prague using steam pumps, but in 1932 these were replaced by an electrical-powered system. This meant the plant also needed two large coal houses and its own railway siding, which was actually a requirement for the building permit.
The 1930s also saw the construction of a second discharge line to supply Prague and a reinforced concrete bridge over the Jizera River, which solved the issue of transportation between the water treatment plant and its abstraction and discharge facilities. In 1965-1969, an artificial infiltration system was then built, with a capacity of 900 l/s, doubling the capacity of the Káraný plant, and in the 1970s a new iron removal plant for the artesian water was added to replace the outdated facilities. The plant’s third discharge line was constructed in 1993.
...the abstraction wells are not simply at a random distance from the Jizera River? 200 to 300 metres is in fact the distance required for naturally filtered water to be converted into groundwater.
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