Nové Mlýny is a system of three reservoirs on the Thaya below the Pálava hills in South Moravia; its design was approved in 1972, and the middle reservoir has been a nature reserve since 1994.
The Nové Mlýny waterworks is a system of three reservoirs in South Moravia. The middle reservoir lies at the confluence of the Thaya, the Jihlava and the Svratka, and the lower reservoir on the Thaya is the last and largest of the three.[2][3] According to the operator, the state enterprise Povodí Moravy, the confluence area had always been full of contrasts, since there was a shortage of water in dry periods and frequent floods caused considerable damage.[2]
Construction and purpose
The overall design of the system of three reservoirs was approved during 1972, and the first stage of construction began in 1974.[2] The middle reservoir was completed in 1980 and put into operation a year later.[2] The lower reservoir was completed in 1988 and put into operation a year after that.[3]
The waterworks serves several purposes. The middle reservoir is meant to supply irrigation water for agriculture and industry, reduce flood flows, allow the flooding of floodplain forests, support fish farming and help eliminate mosquito plagues.[2] The lower reservoir adds to these purposes the permanent guarantee of a minimum flow in the river below the reservoir, recreation and the generation of electricity.[3]
Middle reservoir
The dam of the middle reservoir is an earth-fill dam with a central sealing core, almost 1.4 km long and 6.7 m high. The slopes are reinforced with rock riprap. A first-class road connecting Strachotín and Dolní Věstonice runs along the dam crest, which is 13.2 m wide. The flow into the lower reservoir is handled by a spillway structure with six bays, each 23.3 m wide and closed by segment gates, with a capacity of 940 m³/s.[2]
Lower reservoir
The flooded area of the lower reservoir is almost 1,700 ha, and the volume of water at maximum level is almost 84 million m³. The dam is an earth-fill dam with a central sealing core, over 4.6 km long and 9.8 m high, with a crest width of 5 m. The slopes are reinforced with rock riprap. The spillway structure has three bays, each 15.0 m wide, closed by segment gates, with a capacity of 1,770 m³/s.[3] A series of side dikes was built around the whole waterworks to limit the area of the reservoirs. The land behind them is drained by ditches, and the water is pumped from them back into the reservoirs.[3] Adjoining the left side of the spillway structure in the dam is the hydropower plant building with the outlet works, whose bottom outlet has a profile of 1,200 mm. The power plant was built already during the construction of the lower reservoir and currently houses one generating set.[3]
Nature protection
The construction of the reservoir required the felling of a large part of a floodplain forest. Between 1996 and 2000, work began on artificial islands as part of a floodplain-type biocorridor, intended to enlarge the vegetated areas in the middle reservoir.[2] The middle reservoir was declared a nature reserve in 1994 and a bird area in the Natura 2000 network in 2005, in order to protect rare bird species.[2]
According to Povodí Moravy, the middle reservoir is a nesting site of the common tern, the red-crested pochard and the black-headed gull, with the largest regular occurrence in the Czech Republic, and the only regular nesting site of the Mediterranean gull, the yellow-legged gull and the common gull. It is also the largest regular wintering site of the smew, the bean goose, the white-fronted goose and the white-tailed eagle. The numbers of both northern goose species and of the white-tailed eagle reach European significance.[2] According to the operator, the dispute between water managers and ecologists over the existence and operation of the waterworks has lasted practically since its beginnings.[2]
Flood-control effect
During the flood of August 2002, a free volume of 35.5 million m³ was available before it arrived. The peak inflow into the reservoirs was about 400 m³/s and was reduced to 312 m³/s by the retention volume. During the flood of March and April 2006, the free volume was 42.3 million m³, the peak inflow about 740 m³/s, and it was reduced to 657 m³/s by the waterworks. According to Povodí Moravy, the operations at the waterworks contributed to flood protection on Slovak territory at the confluence of the Morava and the Danube, as well as to the protection of gas pipelines in Baumgarten an der March.[3]
The village of Mušov
According to the operator, the village of Mušov had a rich past and was one of the important Roman sites. What has survived of it is the church of St. Leonard on an island in the middle of the reservoir, protected by an embankment. The originally Romanesque building from the turn of the 12th and 13th centuries was rebuilt in the Gothic style in the 14th century; of the original structure, the southern wall of the nave with a Romanesque portal and windows remains.[2] A survey of the deconsecrated church uncovered wall paintings from the first half of the 16th century. The church is probably the oldest Romanesque ecclesiastical building in the Břeclav area. The surroundings of the middle reservoir are also an archaeological site, with finds mainly from the time of the Great Moravian Empire.[2]