Waterworks Káraný 

Let's take a tour to Káraný, a very special place, producing drinking water of excellent quality.

Drinking Water Treatment Plant in Káraný is located at the confluence of the Jizera River and the Labe River around 25 km from Prague.  It was commissioned in 1914 when it became the first Water Treatment Plant providing Prague with innocuous drinking water. Prague is the capital and largest city in the Czech Republic. It is situated on the Vltava River and there are about 1.3 million inhabitants. Its metropolitan area is estimated to have a population of 2.7 million. As of now, there are three main sources of drinking water for the city: Waterworks Káraný, Želivka, and Podolí.

WHEN AND HOW IT ALL STARTED?  

 At the end of 19th and beginning of 20th century, people living in the city of Prague suffered from low drinking water quality. That is why in 1889, the Act on the Establishment and Operation of a Waterworks and Water Supply for Prague No. 48 (16 August 1899) was approved. Consequently, the project assignment of joint water supply of the cities of Prague, Karlín, Smíchov, Královské Vinohrady and Žižkov was published. In 1896, Adolf Thiem was approached by the Prague City Council to comment professionally on Česká Spořitelna's project and subsequently, he was entrusted with the supervision of the entire construction. After Thiem’s death in 1908, Emil Printz, his student who was a well-known hydrologist at the time, took over the construction management work. He introduced a number of improvements to the original high-quality project. Thanks to which, a flawless future operation of the waterworks was ensured. However, the man who saw the finalization of the construction works was Alois Opatrný, who also acted as the first director of the Waterworks. The project was completed in 1912 - the first water withdrawals from 220 wells were realized on the 18th October, 1912. The projected full extent operation started 1st January 1914 when the total pumping rate of 880 l/s was reached. At that time, 567 wells were in the operation.  Modernization of the waterworks took place in 1934, when steam engines were replaced by electric motors.  The increasing population growth and the industry development after the World War II. required capacity enhancement of existing resources. Thus, the construction of so-called artificial infiltration was started in 1968.

More historical photos can be found on official web pages of Káraný and also on the historical photos web page.  

 Figure on the left shows the health situation of Prague citizens between 1886 and 1936. The increased number of illnesses caused by low water quality used for drinking. Most of 1100 groundwater wells used for drinking was contaminated by insufficent sewage system. Safe drinking water was not available in sufficient amounts at that time. The effects of the newly constructed waterworks are clear. 

WHAT IS THE SITUATION NOW?

 For a long time, Káraný Plant was the most important source of drinking water for Prague. With increasing water consumption and number of inhabitants, additional plants were connected as well (Podolí in 1929 and Želivka in 1972). The waterworks in Káraný is a strategic source of drinking water not only for the city of Prague, but also for the central part of the Central Bohemia. The averaged capacity of the Waterworks is 1750 l /s.  Waterworks Káraný covers approx. 1/4 of the total need in Prague.



Water in Káraný is partly groundwater from sand-gravel strata and artesian wells and partly surface water from the Jizera River (obtained by natural and artificial infiltration). This is possible due to the hydrogeological conditions of the area. A shallow unconfined aquifer is situated in terraces of Quaternary fluvial sediments (sand and gravel) an is naturally recharged by infiltration of precipitation. The bedrock is formed by Quaternary (Lower Turon) marlstones of Bohemian Cretaceous basin. The marlstones act as aqutaird due to their low hydraulic conductivty. If fractured, they allow water inflow from deeper positioned aquifer(s).  Under natural conditions the groundwater would flow from the Quaternary aquifer into the Jizera River, but due to intensive groundwater extraction, the aquifer is recharged from the river  (enhanced natural bank infiltration).

HOW THE THREE SOURCES OF WATER IN KÁRANÝ ARE MANAGED? 

Natural infiltration through the sand-gravel strata filtrates the water naturally. It is pumped by a set of wells (8-12 m deep) spaced 20 to 40 m apart, and in operation since 1914. The naturally infiltrated water is collected together with the natural groundwater by a number of bore holes linked by a siphon at a 250 m distance from the river (already quality of drinking water). Water is transported by pumping stations and gravitational conduct pipelines into the main pumping station in Káraný. In total, 685 wells and 26 km of collection lines is able to deliver 900–1100 l/s. 

Artificial infiltration employs the same principal as the natural infiltration. Raw water from the Jizera River is transported to the treatment plant, where it is filtered through the high-rate filters with sorted sand and then it is pumped into the infiltration reservoirs (pools) with natural sand bed. The water table is averagely located at a depth between 10 to 14 m below surface, enabling water storage and natural purification and mineral enrichment. Water is retained underground around 40 to 50 days. The mixture of infiltrated water and original groundwater (having a good-quality drinking water) is collected by large-diameter wells at a distance of 200 m from the infiltration reservoirs. Artificial infiltration has been in operation since 1968. The water production is 800 - 900 l/s. 

Artesian water is obtained from chalk sandstone confined aquifers from 7 wells which are 60 -80 m deep. Thick marlstone confining layer protects the water from surface contamination. Age of the water is estimated to be 16000 years. Water of excellent quality flows into the area in deep ground from the northern part of the geological structure "Bohemian Cretaceous". That is why only iron removal by oxidation and consequent filtration is applied as a sole treatment of this water, and the water quality corresponds to the requirements for infants. Artesian water has been collected since 1914. The water production is 60 - 80 l/s. A small part of this water is used for bottling and for sale as potable water in distribution containers. 

HOW IS THE WATER TRANSPORTED TO THE CITY OF PRAGUE? 
Transport of potable water into the City of Prague (three lines of tubes:  two lines of 1.1 and one 1.6 m in diameter)

NATURAL INFILTRATION

Water from the River Jizera is seeps through its bottom and bank into the surrounding Quaternary sand-gravel layers towards a number of collecting wells.

 From the other side (direction towards the river) and thus, to the wells flows water from the hydrological hinterland. During the seepage process, the water is gradually cleared and enriched with minerals, so practically the properties of groundwater are reached. The flow direction and gradient are given by a continuous water abstraction from the wells. The distance between the River Jizera and the sets of wells (200 -300 m) is an essential parameter setting the time after which the water is collected. Continuous operation under changing external conditions requires constant overview and control of individual operating points. Special measures must be taken if floods or poor water quality occurs. The siphon system ensures low operational costs for water delivery to the collection well from where the water is transported gravitationally (almost 30 km) to the main pumping station in Káraný. 

ARTIFICIAL INFILTRATION - SITE SPECIFIC SOLUTION FOR GROUNDWATER ENRICHMENT

To ensure a constant level for surface water abstraction, a movable weir with two fields with coarse and fine racks was built on the Jizera River. From there, the raw Jizera water flows gravitationally into the raw water pumping station, where mesh filters (openings 1/1 mm) are fitted. 

The pumping station then transports the raw water to the upper terrace to the water purification station. The treatment of the water is represented by mechanical filtration on sand quick-filters. The filtrate is actually an intermediate product, which is pumped into a system of 15 massive infiltration pools with a total area of ​​70 050 m2. At this place, the next stage of water treatment is taking place. The bottom of the infiltration pools is formed by natural layers of sand and gravel and works as a slow-filter. After a short period, when water is stored in the infiltration pool, a “biological membrane” is formed at its bottom. This membrane plays a major role in the elimination of biological life in the water. When water is underground, the hardness of the water increases and the water temperature is balanced. Two methods of groundwater collection are used for water collection: i) where the groundwater level reaches the lower terrace, the water is collected by drilled wells connected by a siphon, and ii) on the upper terrace, where the groundwater level is at such a depth that practically does not allow the use of the siphon, large-diameter wells with horizontal collectors are build. From the wells, the water is pumped to the gravity conduct line and flows through the collecting object to the main pumping station in Káraný, where it is mixed with the water from the natural infiltration. After basic chlorination, the water is released into the water supply lines of Prague and other 9 surrounding towns and villages.
The tapped water is a mixture of infiltrated water and original groundwater in a sandy-gravel terrace inflowing from the east towards the Jizera River. It is estimated that approx. 70% to 80% of total water yield consists of water from the artificial recharge. 

ARTESIAN WATER

The groundwater (artesian water, 16000 years old) in Káraný is a high-quality drinking water. Its only treatment is iron removal as the water is naturally rich on this element. fter the iron removal treatment, the artesian water in Káraný meets standards for water for infants.

Iron is a very common element in nature. It usually enriches water when flowing through the sediments and rocks and iron gets dissolved in it. Basically, there are two main forms of iron, ferrous iron (Fe2+) and ferric iron (Fe3+). In groundwater, iron is usually found in its reduced form as ferrous iron, which is dissolvable in water. When oxidized into its oxide form, iron precipitates as solid ferric iron with its typical yellow – brown – red color. Ferrous iron does not give any color to water, unless when exposed to air, then it creates the reddish-brown sediment. Iron is an element which is important to human health; however, its high doses are unfavorable (accidental overdosing from nutrient supplements pills can be lethal). Iron in groundwater as a source for drinking water is not associated with health risks when the drinking water with a high-content of iron is used for cooking, the cooked food will have an unappealing dark color. For water being sold in bottles, iron is also undesirable element as it might change the water appearance when sold under the lighting of the supermarkets. So unappealing color, unpleasant taste or staining, are the main problems associated with iron in drinking water. Taken from another point of view, we can observe iron-imposed problems in the drinking water distribution systems. Deposits of iron can restrict the flow of water in pipes. 
There are several methods how the iron can be removed from water. Iron precipitation by aeration (oxidation) and subsequent filtration is the most common method used all over the world, as well as the Káraný Waterworks. During the oxidation process, ferrous bicarbonate Fe(HCO3)2 is oxidized to form ferric hydroxide Fe(OH)3. The oxidation is highly dependent on pH, pH of 7.5 – 8 is best for iron oxidation. The iron-bearing solids are than removed by sand filters. The filters need to be washed regularly. 

Sand filters are formed as concrete tanks with an area of about 25 m2. Their intermediate bottom is equipped with filter heads with water-permeable holes smaller than grains of filter sand. On this intermediate bottom, there is a layer of sorted filter sand with a thickness of about 1.5 m. The iron and other suspensions are intercepted here. There is a real bottom approximately 80 cm below the intermediate bottom. The filtered water is transported for use and a small part is used for bottling and for sale as potable water in distribution containers. 

 WATERWORKS KÁRANÝ – SUMMARY IN NUMBERS 

HOW ARE THE WATER RESOURCES PROTECTED? 

The Central Water Management Authority with respect to conservation of quantity and quality of surface water and groundwater is the Water Protection Department of the Ministry of the Environment of the Czech Republic. Water protection, water use and water rights are covered by Act no. 254/2001 Coll., on Waters and Amendments to some acts (the Water Act).  The key principles of the water management policy are derived from the EU Water Framework Directive, other Water Management Directives and the renewed EU Sustainable Development Strategy.

Area affected by water collection in Káraný accommodates 11 villages and towns. These communities pose threats of decreased water quality, for instance, through the agrochemicals applied on neighbouring agricultural fields which has the potential of increasing the nitrate levels within the area. Water Resources Protection Zones were announced in 1986 and protect approximately 850 of pumping well sites and major parts of the catchment of the River Jizera. Protection Zones I and II protect an area of 9000 ha, out of which one third is used for agricultural purposes. The River Jizera catchment (2200 km2) is protected by Protection Zone III.  Protection Zone I is determined as a continuous area and serves to protect the immediate vicinity of the water source collection or sampling facility. Protection Zone II shall be defined outside the Protection Zone I and may not form a continuous area but, may also be determined as non-contiguous areas. The Protection Zone II serves to protect the water source in the territories determined by the water authority. Based on the Protection Zone type, the urban-, agricultural-, waste-water-, and waste- managements are defined for the particular locality. 

The protection zones of water resources related to Káraný are shown on the following figure. The picture on the left shows a general view on the area while the picture on the right shows a more detailed map with the locality close to Sojovice and artificial infiltration pools.  

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LIST OF CITED LITERATURE: 

• Authors own experience based on guided excursions
• Web page of Waterworks Káraný: https://www.vodarnakarany.cz/
• Skalický, M. Artificial recharge of the Káraný site as a tool for solving the lack of groundwater for water use (in Czech). In Proceedings of the “Groundwater in Water Treatment 2015”, Pardubice, Czech Republic, 1–2 April 2015
• Křivánek, O., Kněžek, M. (2001) Zdroje pitné vody v Káraném - Principy získávání vody v oblasti Káranské vodárny, Pražské vodovody a kanalizace, a.s. závod Káraný.
• Křivánek, O. (2000) 85 let vodárny v Káraném (1914-1999). Pražské vodovody a kanalizace, a.s., Káraný, 2. upravené vydání